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MG MGB Technical - Moss's Supercharger
| "Moss Motoring" has Jackson's new Eaton supercharger featured in the latest issue and it sounds impressive. I don't have my copy yet. It will be interesting to see how it pans out. A friend of mine had a very nicely done turbo'd 'B a few years back and had problems with detonation at 6-7 PSI of boost with 8.7:1 compression. The Moss blower runs a lot more than that. |
| David |
| "I don't have my copy yet" but Bob Thompson called to tell me about it. |
| David |
| I don't suppose they supply an extra-thick head gasket with the kit? Would help lower the compression ratio a little. Given that a lot of 'stock' Bs (with maintenance overbores) are 9:1 CR or higher, I would expect some problems if this blower is simply bolted on. Perhaps they have some trick up their sleeve... Taraa, -- Olly |
| Oliver Stephenson |
| >>>>I would expect some problems if this blower is simply bolted on<<<< Me too :-/ I hope they educate their customers at the time of sale! ~PHIL |
| Phil |
| I have my toyota blower that I am engineering to fit the B. I have a fully programmable electronic ignition system that I can recurve the advance with the keypad. I am running 98 octane ulp with max 30deg advance plus 10deg static. Don't know my cr or bore but have a std cam fitted. Current progress is to convert to serpentine belt. henry, 65cbrd, 18gb, nissan 5sp. |
| H O |
| I am in the infancy of my learning curve regarding superchargers. Would those of you out there that have some true experience with and understanding of superchargers educate me on the pros and cons of supercharging. Specifically what really needs to be done to a relatively stock engine prior to supercharging to handle the extra power. |
| Frank |
| Frank Like you i only starting to learn about superchargers recently - beofre i tried it on the B i thought i should read up about their general use first. With specific regard to the B engine, some people say there may be a problem with the bottom end, but providing the crank and bearings are in good nick, i reckon it would be fine... The biggest thing you have to check (and check again) is CR. Hans Pederson recommends a 8.0:1 CR, however speaking to him again a few times later, we are both of the opinion that an alloy head might allow the CR to raise to 8.5:1 because the alloy can handle higher running temps. - you have to remember that the supercharger will effectively raise the CR which is why you lower it, as opposed to a normally aspirated engine which you aim to achieve a higher CR to get more power. In a supercharged engine, the supercharger (compressor) raises the air coming into a cylinder above that of atmosphere. In a normally aspirated engine the air is at atmospheric pressure or thereabouts so the compression to get power has to be done by the mechanical action of the pistons... Simple theory: Consider; Normally aspirated engine. CR 10:1 Air comes into cylinder at 1 bar (I said it was simplified). Piston reaches TDC. Pressure in combustion chamber is 10 bar. Forced induction engine running at 2 bar. CR 10:1 Air comes into the cylinder at 2 bar. Piston reaches TDC. Pressure in combustion chamber is 20 bar. That's an increase of 18 bar, against 9bar for the NA engine. As you run higher boost, the temperature difference will get even higher as it is compressing the air that much further... In theory you don't need to do any more for a supercharged engine as you would when building a normally aspirated one. You wouldn't dream of rebuilding your engine without checking the bottom end, piston and bore conditions etc, right? So you would do these same things for a supercharger... HTH ~PHIL |
| Phil |
| Phil, Thanks for your reply...I would assume from your description that my 79 North American spec MGB (stock except for a Mike Brown port and polished head and a Euro-Spec dizzy) with its dished pistons would be an ideal candidate for a supercharger...assuming the CR numbers work out. It is my understandiing that the late model MGB's were lower compression than the earlier ones. I have read in the archives conflicting reports on the need for more heavy duty pistons than were standard...if the CR is lower is this still necessary? |
| Frank |
| Frank I reckon provided your pistons equal the correct CR they should cause too much probs - however, forged pistons offer intact strength over standard items, so companies like JE (who i am looking at) would be a worthwhile look-see at least. If you go to Doug Jackson's site www.mgbmga.com you will find how to calculate CR. It is important that it is calculated before you do any fitting otherwise from what i have heard you will end up with holed pistons... If you are using a standard head, then you need CR of around 8:1 - the fact that it is ported will not matter, infact will enhance slightly your performance AFAIK/can work out... If you ran a higher CR than 8:1 you would need to lower your boost, so it stands to reason to lower CR and raise boost - will need to dig out an ideal figure boost from my archives, but stick to 8.0:1 and i reckon you'll be fine i think... Dizzy will likely need to be remapped to match the performance increase... HTH further - btw, i dont have my supercharger engine running. I wanted to, but have run out of cash for such endevours for now, am hoping next year might bring me more fortune - bit annoyed that Moss beat me to it, but can;t win 'em all! I also need to start from a new block which of course raises the cost a bit. I still reckon that supercharging is a viable and realistic power increase for a B, and is a worthwhile alternative to v8 conversion which everyone else does anyway... The only alternative to a supercharger is fitting a rover k series engine i reckon, which is similar power/cost... Supercharger has a better ring to it though don't you think! ;-> Good luck...! ~PHIL |
| Phil |
| The issue with supercharging (whether mechancial or exhaust driven turbine "turbocharging") is always detonation. Modern engines have sophisticated engine management systems which detect detonation and retard timing until it goes away, so that the engine is always run to the limit of detonation. This is why such engines benefit from higher octane gasoline - octane is a method of preventing detonation, permitting more advanced timing. The lower the compression ratio, the lower the likelihood of detonation as well. Phil is exactly right, if you have a higher compression head, then either lower your boost or change your pistons to a lower CR and keep a higher boost to get the same power. Temperature control through materials can help, too. The alloy head route permits faster combustion temperature disperal, another route would be aluminum pistons - most performance aluminum piston applications are of the forged variety, which would try to shed their heat faster - assuming that the heat can still be effectively transferrred through the rings. So - there's lots of arrows in the quiver - detonation detection and timing retardation, lower compression, lower boost, materials choices. I suppose a detonation-linked boost pop-off valve might be another approach as well. Some early turbos used water injection - but that's a total loss system, and one wouldn't want to run out of water halfway home in a long commmute. When the Moss kit comes out generally, it'll be interesting to see their strategy in handling this problem. |
| John Z |
| One very important thing to consider when building a blown engine (super or turbo) is the "squish distance" (also called "quench clearance"). This distance is the space between the flat surfaces of the head and the crown of the piston. The purpose for these quench/squish areas, is to "squish" the air/fuel mixture into the combustion chamber. This promotes turbulence within the chamber, and helps to increase the speed at which the flame front will propagate within it. The faster the combustion event can happen the better, as we can lessen our spark advance and net a gain in power, with more pressure happening after top dead center on the power stroke rather than before. When this distance becomes larger, the squishing action is lessened considerably. The flame front is not allowed to progress as rapidly, and there is more time for detonation to occur. Additionally, when the squish distance becomes too great, The squish area can even become a "nook" for mixture to reside in, effectively allowing a protected pocket in which secondary ignition can take place, which is the onset of detonation. If you're not familiar, detonation is a number one engine killer, so it's to be avoided at all costs. This begs the question, what should the squish distance be? It is generally agreed upon by most major manufactures and engine builders that this distance should be around .030-.040". Tighter than this and you risk the pistons contacting the head, with larger distances losing effectiveness incrementally. Thus, for any engine build, regardless of compression ratio, getting the squish area right is an important point if optimum performance and detonation resistance is to be had. Now I should add something relative to MGs in particular. The dished pistons inherent in all MGs with factory designed pistons, are not ideal when we consider the above. The squish type chamber designed originally for the B-series engine has significant "squish" area built in with it's heart or kidney shaped combustion chambers. When a flat-top piston is used with this combination, all of the available squish area will be effective. However, when a dished piston is used, a great majority of the squish area will no longer be functional, as the "interface" will no longer be present between the piston dish and cylinder head. When a flat-top piston is used with an otherwise standard chamber and given an .040" squish distance, the compression ratio becomes rather high (easily above 10:1). As already pointed out, this is not a good situation for a blown engine! The cure for this problem, is to have pistons made, which incorporate a dish only where the combustion chamber exists. This will retain a flat surface for positive squish action, yet lower the compression ratio accordingly. There will be a limit as to how low one can go with this piston configuration, but the retention of the squish area will allow a higher boost to be had over any combination which chooses to ignore the squish area. There are some other things needing consideration, one of which is mixture quality and distribution. If some cylinders are rich and other are lean, you could run into a situation where half the engine is running perfectly and the other half is on death's door. I have seen this first hand, and you must make sure all cylinders are running well, or you'll be re-building your engine soon. Also consider exhaust flow, you need to get the exhaust out of the head. With the stock engine and ports, this is chore enough, but with a boosted engine, this problem compounds itself. The stock exhaust ports are extremely restrictive and need to be reworked substantially for improvements to be had. Otherwise exhaust residues will be left in the chamber, the results of this will not only be a reduction in power, but also the possibility of detonation onset by the slowed combustion events. Last but not least, don't forget that the stock distributor is probably completely wrong for any performance engine and no doubt for a blown one. With all that out of the way, remember foremost that a blown engine is not very different than a naturally aspirated one, the biggest difference is that it will be considerably more "picky" about tuning. If your tuning is spot on, then you'll have no problems and happy motoring, if it's not, it's probably going to ruin your engine, sooner or later. Sean |
| Sean Brown |
| Hi Haven't seen the Moss advertisement for the supercharger but it could be the same as the kit that is available from Australia ? ( good web site) If so it may be cheaper to go direct. |
| G Roberts |
| Sean Thats good stuff, cheers!! It has firmed up some of my own thoughts. As emphasis of tuning changes slightly from the inlet side of the engine to exhaust side would you agree it is also useful to change the cam profile to give a wider exhaust port opening? i have aqcuired about custom pistons (hence people like JE. They are pricey! However it is cheaper for us Brits to buy from the US at the moment... However how does one keep squish distance to 0.040" and still keep the CR down to around 8.5:1 without resorting to slightly dished pistons? One assumes its a sort of compromise situation..? Just wondering what the best top of piston profile would be - is it a case of just reducing the dish area (smaller diameter but deeper)? John Hadn't thought of aluminium pistons as well as the head - would any great difference in rings be needed do you think? I'm trying to remember the name of the rings i was using but i am at work and they are not - is it total seal? I think they are a US make anyway and from what i have heard very good... G Roberts Speaking to Hans (Australian Blower) it would cost us here about £2090 for the blower, carb and air filter, plus all the ancillaries to fit. Remapped distributors etc are all extra but because of exhange rates are all reasonable. A quick back of fag packet comparisons of costs when it was mentioned here a couple of weeks ago brings the cost in between £1500 - £2000 for the moss kit, but as i haven't seen the moss kit as yet, i would still be inclined to go in for the Hi-flow Australian version.... Mind you theres lots of mercedes out there with compressors on them, i'm sure some of them are too powerful for their drivers ;-> Therefore you could pick up a secondhand one for considerably less cost, i bet!! Regards ~PHIL |
| Phil |
| I have just started my own supercharger project and bought s/h toyota roots type blower for A$330. Forgetting labour I have bugeted A$1k all up. I have 2" su and will fabricate a custom manifold/chamber interface. Blow off valve will be made from a valve spring and some studs and metal with an opening of approx 2"diam. This is to protect the system from backfire. There is lots of good info available and with a lot of common sense, a good project. I try to keep boost to 1/2 atmosphere (7psi) then input and outpout temp won't be an issue. This will give me approx 40% increase in hp & torque and 60% increase in underbonnet looks dept. I use my B for occasional autokhana, touring car test & tunes as well as country cruising. My collection if info grows daily making me wiser. I am electronics eng by trade with home grown mechanical skills. The most immediate problem is converting the belt system to use a flat serpentine type so I am looking for mods to the front pully to suit this belt. . . . . . . henry |
| H O |
| I built a TR6 with Wade blower giving max 9psi. It feels like a friend's BGTV8 to drive with lots of low-rpm torque. Engine is bog standard except CR is 8.5 using thicker USA-spec head and squish effect degraded as Sean says accordingly. So it needs 95 octane fuel plus Millers VSP to add 2 extra points. And it needs boost retard at 6psi ( 2500rpm with wot). Commercial devices are available with electronic ignition, but I use a rotary solenoid to move the contact breaker 3mm anticlock to retard ignition whenever boost actuated manifold switch senses 6 psi. Brief desription and books to read ( Allard's is highly recommended startin point)at: http://triumphs.50megs.com/blower1.htm |
| Peter Cobbold |
| If anyone has any specific questions regarding the Moss Supercharger System, please feel free to post them either here or direct to the e-mail address above. I've got a reputation for honest answers, and will try to cover any questions. I've got about 15 hours of driving time on the Supercharged 1973 MGB and am in touch with the owner of our other development car a 1976 MGB. I'm knocked out by the change in the car, so if I appear too effusive it's not marketing it's old fashioned enthusiasm. I've owned MGBs since 1978 and am scraping the pennies together to put the blower on a project 1980 MGB. I'm really interested to see if it will fit on my '58 Magnette ZB all the best Kelvin |
| KJ Dodd |
| Phil, The idea is to "mirror" the chamber in the cylinder head. Though I would not recommend the piston side be cut as deeply as the cylinder head side! If you look at the PDF: http://www.jepistons.com/pdf/2002-je4-13.pdf and scroll down to page 5-12, you will see an "inverted dome" piston for a small-block Chevy. These are very similar to the pistons currently being used by nearly all NASCAR teams. By using a very shallow chamber in the head and using an "inverted dome" piston, they gain airflow around the valve (less chamber shrouding), yet still stay within the rules regarding compression ratios. The obvious advantage to an "inverted dome" piston over one machined in a lathe, is the retention of the squish area! In order to machine a piston like this, it must be set up in a milling machine and cut accordingly. In this case, JE ships them this way, but the same thing could be done after the sale providing the piston has the necessary material in the crown. As an interesting note, the Triumph/MG 1500cc engine has pistons with very similar characteristics! I just got my British Motoring today and read the article, I will say the kit looks to be very well developed right out of the box, and the only 'problems' I foresee, are more likely to be the result of end-user over-exuberance. Maybe time will tell... Sean |
| Sean Brown |
| Phil - I'm quickly reaching the limits of what I know about the subject - people like Sean and other pros would be able to help on many of the fronts. But one of the contributory factors for detonation is heat - the higher the more like it'll occur. Since the combustion chamber is formed by the head and the piston, if an aluminum head transfers away more heat (everything else being equal), would there be an oppotunity on the bottom side, with the piston? Pistons do have heating issues - on many diesels and high performance cars pistons are cooled by crankcase oil being squirted onto their undersides as a cooling strategy. Other than that, any other heat from the piston is actually carried to the cylinder wall through the rings - and while the aliminum piston will have the OPPORTUNITY to transfer more heat, it has to get through the piston ring bottle neck. And as rings are there primarily as sealing devices, and only secondarily to help with piston cooling, you certainly don't want to throw out good strong durable rings (likely to be cast iron) just to make the piston cool faster. It might be a good idea to consult with soeone knowledglabe in solving these problems to see what the options might be to help out in the situation. And me - I'm going to see what this "bolt-on" costs. I think my GT "needs" this upgrade. |
| John Z |
| Sean My eyes glazed over when you started talking about 'having pistons made'. I'm wondering now if the supercharger is a practical option for a non-engine builder with limited tuning skills like myself. What do pistions like that run? Where would you get them? And, more importantly, how critical would they be for a longlasting blown engine? Or will we find that that is an oxymoron? If you were to build up a B engine, from a strock core to take use the Moss blower for street use what steps and components would you recommend? Also Kelvin had recommed CR form 8:1 to 8.8:1. With an iron head, your thoughts? How strongly do you recommend the aluminum head for this applicaton Thanks Steve. |
| STEVE |
| I've been running a blower on an Olds 215 in my MGB for a couple months now. With ~8.5 CR and 12 psi boost I have yet to hear any indication of ping and it is very strong. It is an Eaton M-90. This series of blower was designed for fuel injection applications which means it is compressing dry air. I'm not sure what difference running a carb makes but there must be something. At any rate, I think it's a great move by Moss. Incidentally, on your pop off valve using a valve spring may be a bit much. Mine is calibrated to 14 psi which is plenty. If it sneezes you want it to vent all the pressure immediately. That means a large valve opening wide at a pressure just a little above your maximum boost. Valve springs are likely to be a little less than ideal for this application. A spring that does not increase pressure much as it is compressed is a better choice. Jim |
| Jim Blackwood |
| Steve, In talking with Kelvin yesterday, he related the experiences they've had so far with otherwise stock engines of both compression ratios and standard pistons. Apparently it's not a problem, and remember there was no trick machining or custom pistons involved with the bottom ends of their prototype test mules. My comments really stemmed from an earlier post suggesting the use of an "extra thick" head gasket. It is my opinion that the use of such a devise, while certainly lowering the compression ratio, would also decrease the squish effectiveness and possibly even increase the tendency for detonation. So providing you use their kit and adhere to their recommendations, you won't (based on what I heard) have any issues. However, you need to understand that you can't go slapping something like this on a tired engine or it will exaggerate the flaws. In building a new engine, I would certainly prefer the custom pistons. However, were that not an option, I would probably use the lower compression, stock versions, but still deck the block as necessary to arrive at the correct squish distance. Custom pistons can be made by JE or Wiseco. You'd have to call them, but about $125 each with pins and rings was what I was quoted last time. I can't say how much of a "safety factor" the alloy head would bring, so I'm not sure it's an absolute necessity by any means. If Moss has proven the product with the iron heads, I don't see any need to rush out and throw money at perceived necessities. Sean |
| Sean Brown |
| Why didn't the mg and other racing teams of the late 50s and early 60s fit superchargers to LeMans, Sebring etc. cars? I don't understand this supercharger trend. There's gotta be a catch, or they'd be everywhere. Do they require gas that's rated higher than 93 octane. Do they get 1/2 the mpg? Nosiree, I don't like em...I don't like em one bit! They didn't race them in the old days,(except for speed record runs), they smack of rice burners and they're not what MGs are about. That's why, in the real world, with speed limits, children and dogs playing about, I remember the addage - "It's more fun to drive a slow car fast, than it is to drive a fast car slow". The thing I like about my A is being able to take it through the paces. My 1970-1/2 Camaro and 68 442 were doing 70mph in second gear. To really put them through their paces, I had to go waaay too fast, but luckily I was a young punky kid back then, but now I don't need that ego boost. Sorry to be a whiner! I'm already getting ready for the flaming I'm going to get....so I'll just sign off anonymously nyah! |
| Fred Horstmeyer |
| What is an MG about then Fred?? ;-> catch with the bblower as far as i can see is only cost... Trouble is IMHO of the moss kit and bolting it on a standard engine is that you will gain around 60% increase in hp - this is a good figure but its an awfully expensive way of doing it, when you could produce a normally aspirated engine with 140 ish horsepower (therefore near 50%) for less than the cost of the supercharger alone. Then if you factor goodies like alloy head, custom pistons etc - it becomes picey. Therefore i thought if i am gonna do it (which i am) i might as well do it properly from the start, build a good solid engine that is *designed* to take the supercharger from scratch. I am hoping for 100% increase in power. I'll let you know if i ever get it... Sean, you are right an you would not need to go to an alloy head - these bring about their own probs in use, such as running 100% coolant due to corrosion probs - but to gain more boost they are useful. For me i would be buying a new head which from someone like peter burgess are nigh on similar costs compared to an iron cast, so i figure no hardship at this stage.... the same goes for custom pistons, but bear in mind Dave Munroe did not fit forged pistons and also did not double check his CR. One rebuild later, he has forged pistons - nuff said i think! your point here >>>So providing you use their kit and adhere to their recommendations, you won't (based on what I heard) have any issues. However, you need to understand that you can't go slapping something like this on a tired engine or it will exaggerate the flaws. <<< i made on the other supercharger thread around at present and i think Moss owe it to their customers to produce some sort of history to supercharging and what is *happening* in their engines when they fit this equipment, as obviously there are not many people out there that have tried it. I have been researching this myself for the best part of ayear now, and this is the first proper discussion we have had on this forum in that time. Yes, people have mentioned it, but no one has discussed it, and i am very glad we now are getting some useful comments being posted on this subject, including the Moss guys, with real experience and of course Jim with his mother of all v8's! I have one ting left to say to Fred - live a little! We can't all be driving the same cars now can we?? Did you disagree with MG putting the v8 in the car to make the BGT V8? With the likes of bentley fitting blowers in the 30's and mercedes fitting them to their entire range here now in the 'nought-ies' i hardly think it "smacks of rice burners", there is a heritage of this technology and one that MG has a share in too! :-> Regards ~PHIL |
| Phil |
| Phil, don't forget the rolls royce p51 engine. I don't even think about the mgbgtv8. As a matter of fact, of all the MGB types, it's probably the least useful as an MGA parts car! And I DO live a little. Why just yesterday I rolled through a stop sign! But seriously - I still would like to know why the works cars didn,t use them. |
| Fred Horstmeyer |
| It's easy enough to burn off the kiddies in their tarted up hatches, made to look fancy with stock engines, with a stock or mildly tuned (read: standard cam) B. True you have to work your engine, shifting at 5250 and not 3000, but it can be done and is damn good fun too. A sideways lap of a roundabout with smoke pouring from the arches also does wonders for your faith in the original motor. However, the more enthusiastically prepared 'ricers' are very, very seriously quick machines. Certainly, I might not like some of their styling, handling and implementation choices, but when you take the time to look you will notice that the engineering that underlies it all is simply superb. These engines are putting out some serious torque and power, and weigh hardly anything. Even with no modification from factory setup and a cack-handed driver, any car they're in is going to MOVE! Add to that a few mods (which might actually make them less powerful, but even then...) and the car is likely to be a dot on the horizon very soon after we see it. On another side we have the opposition that it is wrong to try to make our cars into something they are not and that serious modifications spoil the experience. So we have a lot to contend with. Can it be done with the type of technology that we regularly work with? Can we produce something that will be able to play in the modern vehicular playground, whilst remaining true to the spirit of all that is MG? The answer is yes. Watch This Space. -- Olly |
| Oliver Stephenson |
| Now Fred, are you quite sure a blower was never fitted to a works car? Those Eaton blowers have been used on just about every British car built at one time or another it seems, I can't imagine MG being left out completely. And somehow I missed the ricer connection. Have they gone to blowers? I thought they were all agog over turbos. Of course I haven't really kept up... Jim |
| Jim Blackwood |
| Fred From a very good book on supercharging and turbocharging (which of course are similar processes) by Allan Allard - whose father was very prolific in the development of supercharging of course, it states that supercharging came about as a means of gaining more power from aero engines. Think Merlins, spitfires and P-51's. The gas turbine jet engine effectively killed off this technology of course due to greater gains being had. I quote this however... "In europe,the use of supercharged automobile engines during the 1947-53 period was confined to the grand prix racing scene and some experimental specialist conversions such as the vane-type blowers fitted to record breaking mgs, in particular the MG XPAG engine, in which Goldie Gardner broke the class G record, achieving over 200mph with the 1,500cc shorrock supercharged engine. Incidently this engine produced over 300BHP which was similar to the best supercharged Grand Prix engine then in use." And this... "After the second world war, when racing was resumed in 1947, Formula One Grand Prix racing came into existence with engine capacities of 4.5 litres unsupercharged and 1.5litres supercharged. Initially the supercharged engines remain supreme, but in 1950-1 the 4.5 litre unsupercharged ferrari engine became dominant and thus began the decline of supercharged engine. In 1952, the adoption of a 2.0litre unsupercharged class and a reduction in 500cc for superharged engines, together with the general use of normal fuel pump, saw an end to the supercharged engine." So according to this book they were widely used in motorsport, but local trends in the sport faded them out. 1975 was the next time a super/turbocharged car became aparent in formual 1 i think. Turbocharging came about in the 50's and 60's on larger commercial engines, howeever automobile manufacturers appeared to prefer larger engine capcity (there was trouble in understanding the matching of turbochargers to engine capacities and performance, so they were at first seen as somewhat of a black art). The latest drive for cleaner emmissions has lead to an increase of smaller capacity turbocharged engines because of their decreassed emmission levels of course! Turbochargers are now fitted to most cars and i think this because they are technicaly driveless (being exhaust driven) so parts are less and low pressure turbo-ing is a cheap way of getting a unit to perform better. It is widely regarded that a turbocharged will give a 'smack in your back' driving experience, but a supercharged engine will be the most driveable engine... I reckon if the formula 1 teams hadn't shunned the engines under strict guidelines then we might have seen more of them in teh 70's. Watch this space though as it were, because with i have a feeling more manufacturers are contemplating blowers. Mercedes is one, MINI cooper S being another, Jaguar of course are using them on some their engines. People are realising that modest power can be had with smaller engines. A supercharger will increase power, torque and fuel consumption when set up correctly, so with modern emmission rules as they you can well see manufacturers replacing cubes, with blowers! :-> BTW,i apolgise for my slightly flippant comment about living, but i think you have a wrong view on supercharging in general. There is fascinating history there if you are receptive to it. Regards ~PHIL |
| Phil |
| Sean- I was under the impression that a 12 thou squish was ideal. How many head gaskets do I need to get back to 30? |
| vem myers |
| Vick, One should do the trick. Stock from the factory, the pistons were .012 down the hole with the thickness of the gasket added making something like a .056" squish distance. I should note that any time you over-bore the cylinder, the piston company will lower the compression height of the piston to offset the rise in compression based on the increased swept volume of the now larger cylinder. So with a .040" overbore, one may have to deck the block in the neighborhood of .040" or more to get the pistons up flush again. Obviously this raises the compression ratio, but it also retains maximum squish effectiveness. One needs to look at this sort of thing from all angles and not make assumptions based on one measurement alone. Sean |
| Sean Brown |
| I once considered supercharging my car also until I saw the $2000 price tag! I am now running a turbo set-up with absolutely no detonation problems but my block is warped to begin with because it always seeped water out between cyl 2 and 3 other than this, my motor runs strong and reliable on 8 pounds of boost with a stock bore, stock cam, and a head that has been milled so many times it's CR is probably way higher than stock. to see my car check out my website, I am still adding pics however but the project is otherwise complete and running well. http://home.hawaii.rr.com/mosborne/ a turbo set up will cost half the price of a blower set up if you do everything yourself, and I know what you're thinking... turbo = lag lag is pretty much obsolite now if you match the turbo size with the motor size you will get boost almost instantly, and boost can be controlled by a knob on the dash instead of changing pulleys. |
| Mark Osborne |
| Dont listen to the doubters- a supercharged engine is a vast improvement over a high-revving, gas-flowed, over-bored, unreliable, rapid-wearing racing engine. The major contributory factor for supercharging disapearing from the tuning scene was the 40% cubic capacity penalty that was ( and still is ) applied to blown engines by the post-war UK racing fraternity. Supercharging was seen as too easy and too cheap to implement ( ie less profit for racing shops). Instead we see racing engines with a fortune spent - several times that of a blwer installation- on internal modifications to allow then to rev faster. That 40%penalty really drives home how effective a blown engine can be. For a road car there is no better way of getting low-down torque ( and hence acceleration), a vastly smoother power delivery compared with a high-overlap cam, and only a modest fuel consumption penalty ( around 5-10%). A standard engine in good conditon is all that's needed- no fancy cam, no gas flowing. A blower kit can be entirely bolt-on. Forget forged pistons- detonation will melt them just as easily as stock pistons. If you're in UK go to a VSCC race meeting and see what blowers can achieve. |
| Peter Cobbold |
| Detonation doesn't melt pistons. It breaks the ring lands and knocks the corners off the piston crown, and then subsequent combustion events blow fire down the side of the piston and burn it to pieces. Running high boost without chargecooling/intercooling will let you melt pistons if your inlet temps get high enough, but you have to be really going some. While a blower kit may 'bolt on' to some low compression engines, I don't think it would produce much power increase on high comp engines due to the risk of detonation. I can already get enough air into my engine to make it knock, I don't need forced induction to help. I don't have a point :o) -- Olly |
| Oliver Stephenson |
| I hate to be too picky, but the article on the MGB supercharger in British Motoring states that.... "Designing supercharger systems isn't an easy task. First you must understand the idiosyncrasies of the engine you are supercharging. An MGB challenge is its siamese center intake ports in the cylinder head. (the center two cylinders are fed by the same passage in the cylinder head)". Ouch. I bet whoever at Moss wrote that(and the editor) is red-face right about now. |
| David |
| I on't know why my arned d key sometimes sticks. |
| David |
| Maybe they've found a way to get oodles of horsepower by running the engine backwards? :o) -- Olly |
| Oliver Stephenson |
| Oliver, Yes I agree that's the sequence of events. But it takes a mere second or so from detonation causing ring problems to melting a piston crown in a blown engine. I also agree that fitting a blower to a high CR head is not feasible unless you use methanol. And that's where real power lies.... David, I suspect that the supercharged engine will actually have a better mixture distribution and will reduce the undesirable effects of those horrible siamesed ports. There's a saying that " where you have boost you dont need flow". The supercharger could result in much smoother engine with much greater ability to rev, better than achieved with attempting to gas flow those ports. Peter |
| Peter Cobbold |
| David: I don't know about the writer and editor, but I proofed the piece and didn't catch the mistake.>>the center two cylinders are fed by the same passage in the cylinder head<<. Maybe I should have gotten more sleep that night? Actually that's the top secret of how the power is so smooth. The kit includes a boring bar to drill through the back side of the head and redirect flow from the two intake ports to alternate cylinders : ) Peter: I think you hit the nail on the head. My biggest surprise was how smoothly the blown engine ran. Normally aspirated (with correctly adjusted twin HIF carbs) the car felt like it was getting flogged to death above 75 mph. (4 speed, non-OD) With the blower it felt comfortable cruising at 90, although there was a mildly annoying intake howl over 4500 rpm. All through the rev range the engine was smoother and felt stronger even under no boost conditions. I think the rotors wanging about do a lot to keep the mixture atomized. Kelvin. |
| KJ Dodd |
| Kelvin, Yes yes!! The blower transforms the car doesn't it? My TR6 ( with a vintage blower older than the car) easily pulls a gear higher than normal when cruising, pulls away cleanly from 600rpm tickover, and just storms up hills. And it still needs a few modifications to optimise the performance.... You should have winner there. Peter |
| Peter Cobbold |
| Kelvin, I figured that you guys had a secret weapon. Our local MG club met last night. Wanna guess what the main topic of conversation was? One of our members has already ordered one of your kits and two others probaly will in the next month. I know how initial enthusiasm sometimes goes, but I believe that we'll see a lot of your superchargers in the coming months. You have certainly stirred up a lot of interest. |
| David |
| How does the reliability of a blown 4 (assuming you can work out compression issues, etc.) compare to a Rover V8? |
| Ted |
| Ted: That is going to be hard to compare. My feeling is that in stock form the MGB is a nice car, but a bit short on power. The supercharger kit is designed to improve that shortcoming. In normal driving, the blower is along for the ride, but is there when you want it for passing, hills and just having fun. A side benefit is that the engine just all around feels stronger and smoother, probably due to more equal cylinder filling. So even when you don't stomp on it, the car just feels better. The Rover V8 conversion is pretty intrusive, although now very well worked out. It has it's own problems with header cracking, component interference, cooling etc. combined with the inherent Rover V8 reliability issues of head gaskets, corrosion, main cap wander and cam wear. (please note before jumping down my throat, that I am giving worst case situations) I believe the Supercharger will appeal to the MGB owner who wants more power, but is not prepared for the expense and finality of a V8 conversion. For the ultimate in power/weight ratio and performance potential a V8 or V6 conversion is the way to go. I think the better comparison is between a 1950cc, big carb, high lift cam B engine and a fairly stock Supercharged one. The two are going to be about the same cost, and may give a similar improvement in low end grunt and high end potential but the Supercharged one is going to be much more tractable and get better mileage. Kelvin. |
| KJ Dodd |
| I think there will many owners who, like me, rebuilt a car to moreorless standard spec and put it to good use but who are now looking for more oomph. The beauty of a blower is that you dont need to pull the engine out, strip it down etc. Supercharging works best with a standard cam and most conventional tuning mods are not necessary. The widespread belief , which I often encounter, is that a supercharger makes a car less tractable. In reality the exact opposite applies. Once owners get a chance to drive a supercharged motor they wont even think of going the usual tuning route of high-overlap cam, gas-flowing, forged pistons and so forth. It just needs a few owners to believe in those of us who have seen the light and take the plunge! I have no commercial interest in Moss or in supercharging in general. So this is an unbiased opinion based on driving a blown TR6. When are Moss doing an Eaton kit for us? |
| Peter Cobbold |
| Peter brings up an interesting question....would it be better on a relatively stock late model MGB engine that was currently running fine to install the supercharger and rebuild the bottom end later or should the bottom end be redone prior to installing the blower? |
| Frank |
| If you do supercharge what other changes need to be made to the car? Brakes, transmission, drivetrain, etc? With a V8 conversion you need to do a lot more than just the engine. How does adding a supercharger compare? Unfortunately I am not in a position to consider either right now but this is a very interesting discussion! Simon |
| Simon Jansen |
| Frank, Simon, Its always a good idea to have an engine in good condition before any attempt by whatever means to get more power out of it. Having said that, you will find that the big torque increase from the blower will lead to you using less revs, helping reduce wear on the bottom end. Also the boost pressure reduces the positive to negative pressure swing seen by the piston on the exhaust/inlet change, again reducing loads on the big and little ends. Compared with conventional tuning when a reground and balanced crank is mandatory a blower is much kinder on the bottom end. But you will get more heat produced so a cooling sytem in good order is important, and an oil cooler would be useful. An engine swap is of a different magnitude of work- (engine mountings, gearbox and clutch swap, propshaft, exhaust- the list goes on and on). Fitting a blower is a much simpler task, especially if someone has already sorted the bits you need. I have not seen the Moss kit but I would expect it to include a manifold to bolt onto the twin carb one, a pulley for the crank shaft nose,a poly-V belt and tensioner, the blower ( from Eaton, off the shelf brand new), bits to retune one of the carbs ( needle and jet, piston spring) and various bits such as throttle cable, fuel hose etc) Bolting it together should be an easy weekend's work. The only engine work that might be needed would be to lower the cylinder head CR- I dont know whats standard outside UK, but you would not want more than 8.5 at a guess ( depends on fuel octane and max boost). Of course if you have a high-overlap cam you'd need to replace that with the standard one, or one with similar timing but higher lift. A blower is also a good pose!! All the money you've spent on tuning by conventional means is mostly hidden ecept for that pair of Webers, but a blower is very much evident as soon as you open the bonnet. So sell those Webers, find the SU you took off years ago and go for a supercharger! |
| Peter Cobbold |
This thread was discussed between 28/05/2003 and 04/06/2003
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