MG-Cars.com
MG Midget and Sprite Technical Camshaft change for street BBS discussion at MG-Cars.net
MG-Cars.net
Welcome to our resource for MG Car Information.
Recommendations
Parts
MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.
|
|
MG Midget and Sprite Technical - Camshaft change for street
| Hi All, As I was in the middle of a LHD conversion , one thing led to another and I am now into porting head , new carb and Manifold ( HIF44), 123 ignition , etc... Looking at camshaft change , I heard there's a technique to do the work with the engine still in place . ( I don't want to go further and take the engine out) My questions are : 1. Anyone heard about this technique ? 2. Do you know the original specs of the marina engine ? ( same as midget?) 3. Is porting head worth it without touching cam? I just wanted to add that I don't need a rocket impossible to drive at low rev , just looking for a small increase of power and torque all the rev range. Any comments and suggestions are welcomed ! Serge |
| Mr. carlier |
| no, on a 1275 you have to remove the engine, as otherwise the cam followers (tappets) will drop down and you cannot fit the new cam. Uless you have a rollover frame and turn the whole car upside down ! |
| David (davidDOTsmithAT stonesDOTcom) |
| Vizard (IIRC) describes using magnets to hold the cam followers up to allow a cam to be inserted and removed. However, in practice this might be harder than it sounds: 1. You need to install new followers with new cam 2. You need to remove and insert the cam without the lobes scoring the soft metal in the shell bearing 3. You need to be certain the oil pump drive does not fall out and is properly re-engaged, or else you won't have any oil pressure (well, more importantly, oil flow). With all these considerations, it seems that DS advice stands. It may still be worth porting the head; why not give the cam a helping hand by using 1.5:1 rockers (opens the valves more quickly and more fully and in some ways is like a cam change). HTH A |
| Anthony Cutler |
| But, if he has already pulled the head, could he not use a magnet to remove each lifter, and a long bolt to remove the oil pump drive shaft, making it possible to do in situ? David "weighing MY options..." Lieb |
| David Lieb |
| BTW, not being facetious this time around, just curious, especially as I do need to get around to installing my new cam. David "master procrastinator" Lieb |
| David Lieb |
| Thank you David , Anthony yes it's this use of magnets that I was been told . But with the risk of ending bad I think I'll stick with my cam , maybe with 1.5 roller rockers as you adviced . |
| Mr. carlier |
| Serge- Changing to a hotter camshaft before doing the headwork is a mistake. If your headwork is performed by a practiced professional, you may not want to bother with the expense of a different camshaft, new tappets (always mandatory with a new camshaft), and redoing the advance curve of the distributor. Peter Burgess can modify your ports and combustion chamber to his Fast Road specification to give you about 30% more horsepower at the top end and 25% more torque at midrange, and that's with a stock camshaft! If, after driving, that isn't enough of a power increase for you, then a change of camshaft will have its potential fulfilled with the headwork having been done first. |
| Stephen Strange |
| I would always do a cam change with the engine out i just makes life easyer. Especialy with the timing of the cam. I do not agree with Stephen With a cam change or as an alternatie high lift rockers (or both) you get the best out of your head. And without a substantial increase of CR his power figures are a bit optimistic and with the verry good modern cam profiles (SW5 morespeed PH 2) you wil not have the disatvantages of hot cams of the past. |
| Onno Könemann |
| Onno- If enough fuel/air mixture is getting into the engine to produce the power increases that I refer to, then the compression ratio is substantialy increased. However, with the amount of overlap that the stock camshaft has, there is little advantage to an increase in compression ratio, other than a small increase in fuel economy. What constitutes getting "the best" out of any head is a matter of personal values. A good Fast Road head alone can deliver much the same performance as an unmodified head and a hotter camshaft, simply because it breathes better. A Piper 285 camshaft is about as hot as most would care to go on a street engine, and it will give, at best, a 14 HP increase, which is less than what a good Fast Road head alone can produce. I don't know of any high ratio rocker arms that, combined with a stock camshaft, will do as well as that with an unmodified head (been there, done that). Changing the camshaft before doing the headwork is putting the cart before the horse. Once the headwork is done, then a hotter camshaft can come into its own and produce the results that the designer intended. |
| Stephen Strange |
| David - You cannot remove the 1275 lifters from the top, the holes are too small. And there isn't an oil pump drive shaft, it's a spider at the back of the cam. There is a distributor drive shaft, which you take out with a long bolt. Don't even bother to think about changing cams in the car! Serge - Do the head work, leave the cam alone for now. FRM |
| FR Millmore |
| While I agree that the head should always be the first place to start, cam changes still work even with a standard head - as do mild compression ratio increases. The key to releasing the postential from a cam change is to dump the original exhaust manifold for and LCB unit instead. Once you extend exhaust duration on the original manifold there is all manner of interference between exhausted gas and backflow into adjacent cylinders. The LCB provides enough separation to kill this problem. Someone over here once fitted a "3/4 race" camshaft and modified head to a Midget - but retained the std exhaust manifold. It was slower than the original engine and infamously got dragged off by a dog. For ever after, said Midget (despite having rectified the error) was known as the 3/4 race dog! We had an Austin 1300 once, and gave the engine a refresh in the rings & bearings dept. While it was apart, I tickled the cam, raised the compression to 9.6:1 and fitted an LCB. I had plans to do the head later but never got round to it, not least in part because it went so well as it then was - 3rd gear was an awesome passing gear between 60 and 70 mph. I think the key issue about cam changes and 1275 engines is that you (effectively) DO have to remove engine and strip (or invert) to do so, unless you have the trick magnetic gear. So: If the engine is out and you have plans to tweak it, change the cam then. On the other hand, if the engine is still in the car and you have plans to tweak it, save the cam for later and do the head first. (But if you don't mind spending the time, you could always remove engine just to do the cam.) And either way, fit an LCB while you are at it. |
| Paul Walbran |
| I reccomend retaining the twin carbs. It has far better performance this way. Second I reccomend the SW%-07 cam. But you do have to remove the engine from the car to do it. You will need to get a timing disk and time the cam when it comes. You dont need a vernier set of timing cogs, but you should replace the chain, and get yourself the appropriate offset cam key. |
| S.A. Jones |
| Seth, You might want to do a little more research through the archives. Many more people going from dual HS2 carbs to single 1.75" SU (HS6, HIF6, HIF44) than vice versa. No complaints from any of them. The more continuous flow and higher flow capacity tend to be beneficial and the variable venturi feature of the SU line minimizes the potential losses at the low end. David "waiting for a manifold..." Lieb |
| David Lieb |
| Being that your looking for a mild upgrade, Id do the cam like S.A. says But if your going to have the head off, Id say do a mild port job your self aa in visards book....get a die grinder from harbor frieght and some stones, 1st grind out the lumps of metal that the valves go into, 2nd grind off the casting ridge on the ceiling of the ports by the valve heads, 3rd use a sharp knife and cut off the over hang lip of the combustion chamber side of the head where the 2 valves meet at....take to a machine shop for no-lead inserts, freashen the valves and seats...Or do the mini cooper size upgrade with 214N stainless steel racing valves aka Rimflow if you have the cash If you want the more fancey stuff done other then that above on the head, then take the head and vizards bible to a machine shop and let them do the work of messing with the chamber shape Prop...the disk came with my Sw5 cam kit...Prop |
| Prop |
| David, I wish I had known you where wanting a manifold for a single carb. there was 2 on ebay several weeks ago that went for stupid money....under $30 as i recall, I almost bid on one just to have it in my spares box....Ill keep an eye open for you if you want. Prop |
| Prop |
| I have to agree with Paul about the Original Equipment manifolding. Let's face it, its all about helping the engine to breathe. Logic states that headwork and camshaft changes will achieve less if the engine is suffocated on intake and constipated on exhaust at the same time. The Original Equipment exhaust manifold is awful, and the Original Equipment intake manifold is worse. Maniflow makes the best ones, and they really unlock the engine's potential. These are what I installed on my engine before doing the headwork, and the results were worthwhile. |
| Stephen Strange |
| Some garbage talked about here, as usuual when power mods are spoken about. I sometimes wonder if some people have actually tested what they preach as bible!! A cam shaft on its own will do WONDERS to an engine. It does not matter about breathing as all a cam shaft does is up the rev range where the engine makes torque, therefore torque plus revs equals substantially more power. High compression on a standard engine will increase power and torque loads, this is without question. All that said both those scenarios will be better if a cylinder head is ported. Porting however is the worst of the 3, without the other 2 it is very limited irrespective of the views of those "flogging" their wares. The reason why people generally believe that a cylinder head porting gives such a high return is because ALL head modifiers will ALWAYS skim a good few thou of the surface of the head to give the engine a good bit of CR this they then claim as power and torque gained by porting! I onced raced in a championship where only CR and camshafts were free, ie no porting allowed, it surprised me how much power and extra torque could be made by these 2 simple mods. A few seasons in to the championship and porting became allowed, we only gained a few BHP as a result. But that is only my opinion that I have got from extensive testing others by the sound of it have got different results. Except ONNO, nice one mate. |
| Robert (Bob) Midget Turbo |
| Hmmm, Im in the "MORE the balanced approach camp" my self, I think when it comes to any performance upgrade, it has to be about balance...I know Im a broken record on this point but i dont belive a hot engine is a good investment if you dont have the brakes and suspension to back it up. that said I dont think a hot cam and CR is a good investment if the engine cant breath or take a dump, or go the other direction its not a good set up if the engine can breath easily while effortlessly exit toxins But possess no CR, big bores and camshaft ability agian it all comes down to balalnce... mild cam (kent 266) and basic CR means minor porting and K&N air filters and a rc40 exhauste and some silone wires on NGK plugs and no lead valves with a 3 angle seat grind Hot cam (kent 286 scatter cam) means 10.5 CR, with max bored out cly. to 1380, hevily moddified carbs, maniflow intakes and large bore exhaust with an aldon 123 dissy re-curved, 7 port westlake head, and a 1.5 roller rockers basically it makes no scence to buy a $1,000,000 ferrarie aand take it to K-mart and buy $39.95 tires for it, or have a car worth $200 and invest $1000 into the stereo system... BALNCE, Balance, balance. Prop...I could have been a Zen Master, if not for my huge heavey right foot. Prop |
| Prop |
| Some quite specific numbers their Prop, by the way did you find out how to time an A series engine last week? Anyway would you like to tell us, well me at least, where and how you have come to those Specific conclusions? Not sure fore example that this is true is it? ""with max bored out cly. to 1380"" I have an engine under my bench with 1400CC from an offset bore. |
| Robert (Bob) Midget Turbo |
| Finaly i am joined by some reason thanks bob :) And prop i would like to advize you to re read your posts before clicking submit "aldon 123 dissy re-curved" ;P You do to an engine what is needed but mostly what you can afford and do! This can sometimes lead to strange combo's of exotic parts with mundain items. witch can be verry mutch fun |
| Onno Könemann |
| 'Max bored out cly' ...I seem to recall that fitting 74.7mm Triumph pistons in a standard stroke 1300 A series gives 1425cc... Not a particularly reliable or desirable mod given the quality of the pistons however... Racing pistons are available in 74mm bore as Bob points out |
| J A Bilsland |
| Robert- You said "ALL head modifiers will ALWAYS skim a good few thou of the surface of the head to give the engine a good bit of CR". Tuners routinely skim a few thousandths of an inch off of the head in order to produce a flat sealing surface. After all, it simply wouldn't help one's professional reputation (or professional future) if a freshly-delivered-to-the-customer head blew head gaskets! Peter Burgess has heads sitting ready to sell off the shelf, and skimming to the point that compression jumps considerably could result in valve/piston/deck clearance issues, especially with high-lift camshafts and rocker arm ratios, so I think it unlikely that many head modifiers would be stupid enough take the gamble of radical skimming without knowing what else is done to the engine specification. It just wouldn't make sense. When it comes to the issue of increased compression ratios, by pointing to race engines your are introducing a red herring. I will not dispute that an engine with high enough compression to take advantage of running on higher caloric value 114 octane leaded racing fuel could produce significantly more power than a common street engine that has to run on lower caloric value unleaded 93 octane fuel. However, here in the USA such fuel is illegal to run on the street, and is usually unavailable to the general public. This is comparing apples and oranges. I'm not a racer, I build engines for street use. Most of us on this BBS are street drivers, not racers, so whenever I post here, that's the audience that I address. As for the issue of camshafts, you said that "It does not matter about breathing as all a cam shaft does is up the rev range where the engine makes torque". A longer duration lobe profile will indeed increase volumetric efficiency at higher engine speeds so that more power is produced, and that is the proof that breathing is what its all about. Certainly a racing camshaft will produce impressive results, but it will do much better still with a well-ported head. However, on a street engine, there is no streetable camshaft that I've ever heard of that will equal the increase in power output of a Peter Burgess Fast Road head. Here's what Peter says on his website about his Fast Road head for the B Series engine of the MGB (Which I have used on my MGB): "Bhp is increased from idle to a maximum at 5200 rpm with a standard camshaft. There is a gain of approximately 25% at 3000 rpm and a maximum increase of approximately 30% at 5200 rpm (with a standard camshaft and K&N filters). This specification of head works well with a standard camshaft and shows even more impressive gains with a Piper HR270 or Piper HR285 camshaft....(mild road and fast road type cams). While the head works extremely well with the standard twin SU's it will show worthwhile gains with twin 1 3/4" SU's, I would recommend the fast road HR285 type cam to compliment the increase in carburetion." If you seriously beleive that he is engaging in false advertising claims, I'm sure that you can easily have him prosecuted. Just be prepared to scientifically refute his dynometer results when he presents them before the court. |
| Stephen Strange |
| Hi Stephen don't wanrt to take too much point with you but I must clear up a couple of things that you seem to have misunderstood. Let me reword the first statement ""ALL head modifiers will ALWAYS skim a good few thou of the surface of the head to ensure that it is a quality flat surface this will also give the engine a good bit of CR increase"" Is that better for you? What is in doubt is what affect this simple task would have on engine performance alone, I believe (through R/R testing) it to be quite a bit, what has your testing confirmed? Secondly I believe a more agressive cam such as one from the kent range like a 266, 276, 286 etc will have a big effect on engine performance alone (again through testing on a R/R) what did your testing reveal? My choice of cam for road use would be between a 276 or a 286 similar to Peter's choice what would yours be? I also stated that porting a cylinder head will give a power increase, do you not agree with that? Why would I therefore want to take anyone to court? Not only is high octance fuel also illegal here in the UK it is also illegal in circuit racing so I don't get your point? The fuels used in both racing and road use is the same, so the CR will need to be the same. Sometimes people's opinions differ, that is the whole idea of a BBS, the only problem is for the questioner to try and decide who is full of crap and who is giving the best advice? Not sure I would want to be the person with little knowledge who would need to make that decision. |
| Robert (Bob) Midget Turbo |
| Robert- Well, I guess that your revised statement is an improvement over your original one which seemed to state that much, and perhaps most, of the increase in power output attained by head modifiers comes from compression increase. The BMC B Series engine used in the early MGBs was available in both high compression and low compression versions, both using the same camshaft, but different ignition advance curves. The high compression version produced about 95 BHP with its ratio of 8.8:1, while the low compression version produced about 90 BHP. That's a bit more than a 5% increase in power output. On the other hand, a Piper 270 camshaft should produce an increase of about 12 BHP, and a Piper 285 camshaft should produce an increase of about 18 BHP. That's a power increase of about 13% and 19%, respectively. Of course, other modifications will need to be made to attain these figures, such as free-flowing intake and exhaust systems, and appropriate compression ratios and ignition advance curves. This I can confirm through personal experience with these two street camshafts. This falls significantly far short of what I have attained with Peter Burgess' head work. Yes, you did state that porting a cylinder head will give a power increase, but you also previously stated that it will achieve less than a change of compression ratio and camshaft. Based on what I have stated above, I can only conclude that you have been using heads that were flowed back in the dark ages. You ask "Not only is high octance fuel also illegal here in the UK it is also illegal in circuit racing so I don't get your point?" My point was that the only way to bet a big boost in power output from an increase in compression ratio would be to increase compression to a level that would require such fuel. Since such fuel is unavailable to you, I can easily conclude that from your experience you must not have intended to imply that a significant boost in power output could come from an increase in compression ratio alone. Perhaps you were actually refering to the change in power output that results from a hotter camshaft that requires a higher Geometric Compression Ratio in order to compensate for the reduced Effective Compression Ratio that results from some of the fuel/air charge being lost out of the exhaust port during the extended period of overlap that attends hotter camshafts. In any case, my experience as an engine builder confirms that changing the camshaft before doing the headwork is putting the cart before the horse. The performance increase that comes from a well-done head alone will exceed that of a camshaft change on a streetable engine. Add a good camshaft to it, and the potential of the camshaft's designer will be fulfilled. Because the engine can breathe as it never could before, the powerband will be extended higher and farther. No more of that frustrating "and after that point the engine seemed to run into a wall" that comes from an engine that can't breathe. In conclusion: Mr, Carlier, have the head worked by a real professional first. You'll be glad that you did. Especially if you later decide that you want even more power and go for a hotter camshaft. Click on this: http://www.mgcars.org.uk/peterburgess/ Peter can answer your questions, and he stands behind both his claims and his work. |
| Stephen Strange |
| I know all of the people you refer to and I will keep my opinions until results from tests on RR suggest otherwise. It seems our sticking point is that the higher CR that I have tested have resulted in far more power gains on British Rolling roads than the gains you have measured on American rolling roads. I can not answer that question except to say that a CR (measured by the british technique) of 8.8 to 1 is not exactly a high CR Here I generally advocate a CR of about 11 to 1 (again measured by the british system) and a 286 cam plus fuel of 95 octane (octane as measured by British standards) if you do not use CR at these rates then an increase of only 5% is understandable. |
| Robert (Bob) Midget Turbo |
| Robert- I am unaware of a British or an American system of measuring compression ratio, only of Geometric and Effective compression ratios. I am also sure that all rolling roads use the same mathematical system of measuring torque and horsepower. However, I suspect that you were not serious, but merely intending to communicate an air of being smug, facetious, and condescending when you said that. I suspect that the differences in our available fuels are why this discussion has gone the way that it has. I'm not sure how octane ratings are done in the UK. Over on this side of the pond, we colonials use the (Ron+Mon) / 2 formula. A Compression ratio of 11:1 with an Original Equipment camshaft is impossible on our pump gasolene. The engine would detonate while idling! Of course, I suppose that we could mix pure Toluene with our lower caloric value unleaded 93 Octane inferior stuff (20% Toluene + 80% 93 Octane Gasoline = 97.4 Octane, 30% Toluene + 70% 93 Octane Gasoline = 99.6 Octane). However, it wouldn't be practical to drive around carrying a 5 gallon container of the stuff in the boot on trips. You lucky guys over there can still get the higher-caloric value leaded fuel (with superior octane levels, no less)on a limited basis, so you're free to roam all over the country with engines that can give a higher power output with no more than simple compression ratio modifications. Over here we have to go to greater lengths with our engines ($$$$$). |
| Stephen Strange |
| Thanks to all of you who contributed to this thread , sharing your experiences I'm feeling myself a bit less idiot now ,but more of that I know the way to go. |
| Mr. carlier |
| Stephen Smug? never simply trying to help our friend Mr Carlier get the best value for his money. For your benefit I believe the American way of measuring CR is different to that of the UK, but I am not 100% certain of that fact. However you surprise me with your assessment of CR and your fuel I believe your 93 octane fuel has the same anti knock abilities as our 97/98 in that case you should easily expect a normal engine to run happily with a CR of 11/1 on your 93 fuel May I ask you a personal question? have you ever actually experimented with CR or are you just surmising or going on the say so of someone else? Just imagine for one moment that what I am saying is correct. Wouldn't it be better to spend a few dollars on uping the CR rather than 500 dollars getting the same power benefit from a fully modified head? Naturally a combination of the 2 would be even better but we all work to budgets. If I had to choose between fitting a 286 cam or a modified head I would definately pick the cam. When funds allow simply do all 3! If of course I am wrong well skiming the cylinderhead is not an enormous expense is it. |
| Robert (Bob) Midget Turbo |
| Tarquin. I was right after all. |
| Nick |
| Robert- I've built several A and B Series engines with different combinations of compression ratios and camshafts. Using an Original Equipment camshaft and an unmodified cast iron head, if you go over 9.6:1 and use straight 93 octane US Market-legal gasolene, you may get preignition when running hard or pulling steep mountain grades at full throttle, even with a painfully worked out ignition curve. At 11:1 you would be looking at holed pistons and fried valves in no time at all. With an aluminum alloy head you can go up to 10.5:1, granted correct fuel metering and the right ignition curve. We can thank our own EPA for this sad situation. Of course, now that our President wants all gasolene to contain at least 10% ethanol, which has a significantly lower caloric value, we can look forward to an even further reduction of power output as well. Many octane-enhancing additives have also been banned over the years. Fortunately, we can still purchase Toluene at any paint store, which sells it for cleaning brushes that have been used for applying oil-based paint (Until the EPA bans that as well). On a side note, just to give you an idea of just how much the EPA interferes, you really can't find a decent lacquer anymore. When I painted my MGB with cellulose lacquer back in 2001, it was unavailable here in the USA, so I had to personally go overseas and slip it through customs at the airport using airport transfers sevenoaks. Why? Because the EPA hates solvents. A painter at a local body repair shop said that he wouldn't dare use the stuff because if he got caught, the EPA would permanently shut him down, and then hit him with a huge fine. He is required to keep records of every paint that he uses, each and every time that he uses it, and how much he used on each occasion. Needless to say, I went to school and learned how to paint. I painted all five of my MGs myself, plus I've done a few for friends (my co-conspirators). However, I've now gone over to a using a nice, legal, polyuerethane, even though it is notably harder to get a glassy finish with. Thank you, EPA. To get back to the original subject, I cannot believe that there is any gasolene that will give a 30% increase in power output in a normally aspirated engine simply by means of a sole increase in the compression ratio from 8.8:1 to 11:1 (an increase of 2.2:1), even with the appropriate ignition andvance curve and even if preignition could be avoided. In the B Series engine of the MGB, an increase of .8:1 nets only a slightly over 5% increase in power output. Without a change of camshaft that would get a larger fuel/air charge into the engine, it would mean, in effect, a 30% higher caloric value for the fuel. Why would an oil company spend the extra money to refine it to that point and produce it in volume for all of the gas stations in the market when the customers would have to modify their engines in order to get the advantage of it? None of this makes any sense. I'd have to be present at the dyno session and see it happen in order to believe it. |
| Stephen Strange |
| OK - done a few calcs on combustion efficiency and compression to have some (theoretical) figures for how much more torque (theoretical!) for stepwise increase in CR. Here are the figures I cam up with (I'd be happy for anyone to replicate the calcs I've done in a hurry, BTW): Eff Compr Efficiency % increase 4 42.60% 5 47.50% 11.50% 6 51.20% 7.79% 7 54.10% 5.66% 8 56.50% 4.44% 9 58.50% 3.54% 10 60.20% 2.91% 11 61.70% 2.49% 12 63.00% 2.11% So a 9:1 engine is 58% efficient in this context. If I increase CR to 10:1, I get an extra ~3% increase in efficiency/grunt. Inceasing to 11:1 gives me a further ~2.5%. I think these figures are consistent with earlier comments. BUT... if you have a high overlap cam, at low rpm you're not trapping much gas, and so your effective CR might be 5:1. In which case, skimming the head such that you would achieve 6:1 in these circumstances means you have 8% more grunt. So (as we know) this says: 1. increasing the CR gives a small (and decreasing) increase in torque (but you can regard this as 'cheap' power or economy and is a 'bolt-on' mod) 2. that high CRs especially suit wide-overlap cams in that (along with other benefits seen at high rpm) they help improve the lack of torque at low rpm (due to poor trapping and low effective compression in this mode). [BTW - overall engine efficiency in the real world with heat/frictional losses comes in around 25%.] So (as others have comcluded): if you want more power, increase the CR; better still, if the engine's out, fit a different cam; best of all, do both. HTH and apologies for long post. A |
| Anthony Cutler |
| Stephen if you believe anything over 9.6/1 will cause massive detonation and holed pistons then you had best have a word with Prop, his new engine will blow apart immediately when he gets it started, ""are you listening Prop?" Where did I mention a 30% increase in power??? I am sure I did not and it will not give that kind of increase! To get that kind of increase one would need a high CR plus a 286 cam to get anywhere near it. If Peter Burgess say that he has found that by simply porting a cylinder head he gets a 30% increase in power from a B Series engine who am I to argue. Getting 30% more fuel and air into an engine is no easy matter but again I have not tried that on a B series engine so I would probably go with Peter. However I suspect that it is not only through porting the cylinder head but also from optimising and increasing the CR of the engine in which case how much is equal to each mod? Only the person who has done BOTH tests can say I think it best if we leave it there and you do your thing and I will do mine But please tell Prop that his engine is doomed, can't wait! |
| Robert (Bob) Midget Turbo |
| just to check the first claim i have spent the last half hour searching the Peter Burgess website and have not found anny indication of power in % or BHP ! so stephen where do you get your info from? i personaly think peter is smarter than throwing with numbers and just let his good work speak fot it selfs Now my midget with 1380 block is curently running a compression of 12,5/1 and under heavy load (midget packed with camping stuf full throtle from mid range revs up a 25% hill) it did pink slightly on RON98 fuel having later adjusted the iginition verry slight amount back no more problem. i am how ever going back to a more sensible CR 10,5/1 or 11/1) because Ron 98 fuel is getting less available here in holland and i do a fair bit of driving and want to be able to throw in RON95 with out adding octane booster i will miss the power especialy the torque. who knows i might make a before and after dyno run.... |
| Onno Könemann |
| Robert- You said "High compression on a standard engine will increase power and torque loads.....Porting however is the worst of the 3". This is where you stated that headwork will not increase power output as much as increasing compression ratio. I stated that Peter Burgess has proven that headwork alone can increase power output by 30% with his Fast Road head. By your logic quoted above, an increase in compression ratio alone will exceed this improvement. That has been the crux of the arguement. My contention has been and is that you can get more improvement with headwork than you can with any other change. However, in addressing the issue of the 30% power increase gained from headwork alone, you have now reversed yourself in stating "To get that kind of increase one would need a high CR plus a 286 cam to get anywhere near it." Thank you. My order of tuning priorites are: 1st, free up the breathing of the exhaust and the intake system, in that order. 2nd, headwork. Done properly by an experienced professional such as Peter Burgess, this will give the greatest single improvement on a street engine. Best of all, you won't have to concern yourself with the reciprocating mass of your valvetrain and consequent lighter pushrods / stronger valve springs in order to prevent valve/piston clash, and faster wearing of your tappets that goes with a hotter camshaft. The first two steps can be done in a bolt-on manner with minimal effort and down-time, and the rest can wait until later if necessary. 3rd, hotter camshaft choice if the previous modifications aren't good enough for you. If you're smart, be prepared to spend on more than just a camshaft and a new set of tappets. 4th, only then can the optimum compression ratio be decided upon, dictated by the amount of fuel/air charge lost out of the exhaust valve during valve overlap. 5th, figure out the appropriate ignition timing curve to go with the new camshaft and compression ratio. As for Prop's new engine, I don't know the specifications. If he wants to discuss the issues involved, he need only post his Email address. |
| Stephen Strange |
| Onno- You should have looked further. Click on this: http://www.mgcars.org.uk/peterburgess/page8.html |
| Stephen Strange |
| Thank you Stephen i still think it is a verry bold statement to claim power increases like this. if this where the us it would be an invitation for lawsuits (i personaly know of a sucsesfull lawsuit according to claims of BHP not being completely right) |
| Onno Könemann |
| The point you have failed to realise throughout this conversation though Stephen is the fact that to achieve BHP gains Peter have increased the Compression Ratio. Argueing here today we can only guess at how much more fuel and air is entering the engine as a result of porting the head or how much BHP is being gained by more squeeze. As you can see from the calculations done by Ant this can add up to a good increase and a substantial percentage of the gains Peter has recorded from his ported head. Naturally a combination of 2 or 3 elements will always pay dividends. But BHP per penny works out better when you simply skim the head to increase CR then fit a cam then do the most expensive which is porting. I am sure Peter would even agree that porting is a time consuming expensive job compared to a simple skim!! By the way Prop has a new engine that he trying to start. Hopefully he will eventually start the engine and enjoy running it. It has 10.25/1 CR according to you this will detonate big style within an hour or 2 of hard running. lets see if that happens then either you or me can eat humble pie big style! I am sure we can both agree upon that. :-) |
| Robert (Bob) Midget Turbo |
| Obviously, when one puts a larger fuel/air charge into the same size cylinder, the result is a higher compression ratio. I'm sure that this contributes to the higher power output of Peter Burgess' Fast Road head. I have never argued otherwise. As for the idea of power vs money spent, I set a goal and then work to achieve it. The goal is always more power with as little sacrifice in durability and reliability as can be achieved. This approach is not cheap. To me, money is only significant in terms of how long it will take to get enough to achieve the goal. Cheap power is often short-lived and troublesome. Having a pension from my career in Law Enforcement, substantial investments that provide additional income, plus a new full-time career, in an era of economic hardship I am indeed fortunate in that I don't depend on supporting myself and my family by having a commercial shop where I eke out a living changing oil, replacing mufflers, shooting grease, and occasionally stooping to the cheap bodge of installing a skimmed head to increase compression or a hot camshaft while not advising a customer of the attendant problems that he may run into later on without spending yet more money to toughen and lighten the valvetrain, simply because he may be scared away by the prospect of the additional expense. I don't build for a profit, I build for the sheer joy of the challange. Instead, I increase compression ratio by boring and installing new pistons with the right dish volume and the optimum compression height. Not cheap, but definitely the best way to do it. To understand my approach you must understand that I am in the fortunate position of building only for myself and a select few enthusiasts who know that I can be depended on to build only to a standard. As an ex-Tool & Diemaker and part owner of a Tool & Diemaking shop, I have access to precision machining equipment that most engine builders can only fantasize about. There's an old saying: "If you ask how much it will cost, you can't afford it." For those who are too ignorant to know what's involved in doing it right and end up with problems and disappointment, they have my pity. For those who do know what's involved in doing it right and refuse to delay gratification until they can afford to do it right, well ........ As for the 10.25:1 Geometric Compression Ratio of Prop's new engine, it could work out OK if he has chosen to use a longer-duration camshaft that will allow some of the fuel/air charge to escape out through the open exhaust valve during overlap. That could reduce the Effective Compression Ratio to the point that he might get away with it. Under those circumstances, if he's using the Original Equipment intake manifold and aircleaners, he probably won't get enough of a fuel/air charge to endanger the engine too much (maybe). However, if he's using the Original Equipment camshaft with the right bolt-on breathing modifications, I cringe at the potential for preignition and detonation on our pump gasolene. If this happens, my mind will not be on the subject of who should eat Humble Pie, but rather on helping Prop to get it right the second time around. Like I said before, if he wants to post his Email, I'll be only too happy to review his specifications with him so that he can get it right the first time around. |
| Stephen Strange |
| Cheap bodge???? Nothing bodge about correct engineering my friend. I am very pleased that you have a good pension from being a copper, however many of us in the third world countries of Europe are a little bit more sensitive to wasting extremely HARD EARNED cash, than obviously your select group of enthusiasts. I wish them well and know whilst they may be paying well over the top for their improvements they will get quality. However I will continue to build for myself, using people like Peter Burgess and others with their substandard machine workshops to do all my machine work, whilst we all crave a better life and equipment we can only fantasize about. (What might that equipment be I wonder?). I am afraid I do not take lightly to being called a bodger You are entitled to your opinion on how to build an engine for maximum power and cost effectiveness, I and others are entitled to ours let us leave it at that! I am sure when Prop gets his engine going then it will not blow up due to CR being to high, it may however detonate due to being too far advanced but I am pleased you are comming around to the fact that you limit on CR is not quite right! |
| Robert (Bob) Midget Turbo |
| oh my god is this little argument still carrying on? |
| Tarquin |
| :-) Don't worry Tarq I think there is a new Whiltshire thread starting that may tax your intellect and leave us plebs to more mundane Spridgetty things. :)) |
| Robert (Bob) Midget Turbo |
| roflmao I haven't popped in much for a while but I can clearly see some things never change... |
| Bob T |
| BobT hows the car coming along? |
| bill sdgpm |
| Hi Bob T pleased to see? hear you back. I understand that you were one of the owners with the nerve to park a porker in the classic car show at St. Saturin this year?? It made me feel quite ill.... :) Nice one |
| Robert (Bob) Midget Turbo |
| tax my intellect! Lol. Bob you are spot on. It'll be like a ghost town round here soon. |
| Tarquin |
This thread was discussed between 14/11/2009 and 29/11/2009
MG Midget and Sprite Technical index
This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.