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MG MGB GT V8 Factory Originals Technical - Hood Crown
|I have heard that the late model 75 to 80 MGB hood has more crown than the earlier models. Is this true? |
|Bill, that seems to be the consensus. I have a '74 v8 conversion and clearance is VERY tight with an Edelbrock carb/elec. choke setup ... I was talking to Glenn Towery last week who is fiddling around with a couple of things on the car and he confirmed that there was a difference of about 1/2" in crown between the rubber bumper cars and the CB cars. I gather that the replacement steel hoods available from Moss et al. do have the increased crown; however, the alu. hoods which are occasionally available might not have it.|
|I wonder: could it have something to do with the age of the aluminum hoods...does aluminum sag or settle? My production data doesn't show any differences in parts numbers for hoods nor can I find anything about them retooling for a new hood. Of course that doesn't mean they didn't, but in keeping with the financial thought process of the time "if it cost extra & isn't needed, it doesn't happen" why would they change hoods by 1/2" crown? Or, could it be that the higher crowned later steel ones--Taiwaneese or British are coming from imperfect molds?|
|Bill on my car, with 302, the early hood won't close but with the later hood closes with about 1/2" of clearance. Steve|
|We have the Factory MGB-GT V-8 to thank for the increased crown in the hood. It was done to facilitate the clearance for the V-8 installation, although they still had to provide two circular cutouts in the insulation pad to clear the carburetter dampers. The lack of a part number change would indicate that it was a running modification that came in at the advent of V-8 production in 1973, but some 4-cyl cars may still have had the flatter hoods after that time. I know that all rubber bumper cars have the increased crown.. |
|If I can measure anything to help you guys out with this, let me know. I have a '66 B with the original aluminum hood.|
|After reading this post for the first time, I went out and measured an alluminum hood (68) and a steel hood (78). I put a straight edge from side to side and measured the distance right behind the hood crossmember to see if there was a difference. And I came up with the same distance. So where is this 1/2" coming from? I could sure use it with my conversion.|
Stock Hotwire EFi plenum, and no hood buldge!
|I have seen three part numbers quoted for MGB bonnets/hoods - early 4-cylinder cars, early V8s and one commonised for both V8 and 4-cyl. If I remember correctly they are given in David Knowles' V8 book. A later car could easily have an earlier, retro-fitted, bonnet or vive-versa, except aluminium.|
|Wally..did the same measurements on a '67 w/aluminum & a '79 w/steel hood from underside at the brace & on top using a 4' level (both are original hoods, i know as i bought both cars new & have never replaced either hood!)....no difference in either hood...but, when i measured another of my '79's w/aftermarket Taiwaneese hood, found 3/4" difference....still believe it has to do with original hoods versus aftermarket hoods.|
|You guys got me curious, so I went out and measured. '66 roadster w/ original aluminum hood, measured across the center brace using a 4' level and I got 1.25" at the center from brace to level. The gap up the sides of the hood is the same all the way up so I don't think it's bent.|
|So if I go out and buy a repro hood, it would be steel and 1/2" deeper in the middle? But other than that it would look like the others? Where can I get one of these hoods?|
|Wally, I don't know where the extra 1/2" of crown comes from. But, if any of you guys have been to my web site, you know how many MG's I own. Right now there are 6 MGB's ranging from a '64 I just purchased to 2 '79's in my garage. All have their hoods open 'cause I just measured every one of them....except for 1 hood on a '79 that I know is a Taiwaneese repro hood, I can't find 1/4" difference in the crown on any of them. That's why my V8 conversion project car has an MGC hood!|
|I quote from p. 117 of David Knowles' book "MG V8 - 21 years on"|
under heading "Further notes on changes during production - chnges which took place but for whch no reliable information on change points exist"
1.4 Bonnet panel. This was commonised with the MGB panel, since the V8 bonnet required a greater curvature than the contemporary MGB bonnet at the time of the V8 launch.This was to allow clearance over the carburettors.Thus the old MGB bonnet (HZA4015) and the original V8 bonnet (HZA4197) were both replaced by HZA4014.
Over to David for perhaps a discussion on his sources and any factory specs or measurememtns that might be known......
|Sure would be nice to get a definitive answer...remember, they used whatever parts were laying around until they used them all up...so, if there was a difference in hoods, where did it begin? why isn't there a difference across the spectrum of cars built from '64 to '79 in one collection yet other cars show significant differences? don't believe one can just go our & buy any old hood & achieve more crown.|
Just to clarify: you are saying that the current HZA4014 has the increased curvature?
the implication from the book quote is that the THEN- current HZA4014 had the increased curvature, back in the mid-seventies. Whoever makes a part labelled HZA4014 now, there is no guarantee it is to the same dimensions.The only guarantee would be if someone can prove the late MGB bonnet (hood) press tool survived and is the same one in use at the BL Heritage factory (in Faringdon, Berkshire IIRC). Heritage did in fact save and re-use a lot of the old MG press tools but I believe some had to be re-made.
|I wonder if someone with one of the higher-curved bonnets could give it a measurement. E.g., laying a straightedge across the underside of the hood exactly halfway back, how much distance is there to the underside of the hood? |
It may be worth sourcing a new hood altogether, for I just am not getting there on the clearance issue. I don't imagine having my existing hood bulged (incidentally, would they have to weld in a bulge from another car, or could they just bang a bulge into the sheetmetal?) is a whole lot cheaper than just getting a different hood altogether, and the latter would certainly look more kosher.
|Trouble is, how do you know if you have one with the grearter curvature (i.e. is the Part No. on it anywhere), and where is that greater curvature supposed to be? I have a factory V8, but I know the bonnet has been replaced - but with what? If I squint along the join between the back of the bonnet and the front of the panel of the bottom of the screen on the V8, the bonnet has more of a downward angle than the screen panel. If I do the same on my roadster they seem to be level with each other. What does that mean? Did the angle of the screen panel change as well and do I have a non-V8 bonnet on the V8? Or am I just seeing assembly tolerances?|
|You guys have brought up an interesting question. It appears that the higher-crowned bonnet was supposed to have been commonized with the 4-cylinder cars sometime around 1974 or 1975, but it sounds like there are low-crowned bonnets on cars after that date.|
This may cause a problem down the line. I have had to replace the bonnet on my V-8 (since some schlock put some ugly louvers into my original). I obtained an original 1975 bonnet (off a 4-cyl roadster), but since the bonnet change has coincided with my ground-up restoration I have not had the new bonnet installed on the car with the engine in place. It will be interesting to see if I run into any clearance problems. I do not have the new bonnet available yet for measurement - it is still at the bodyshop. Maybe I'll go check the crown anyway.
Anybody know if the part number is stamped on the bonnets anywhere?
|Oh no. I can see a thread coming at least ten miles long regarding whether a purported Factory V8 is a real Factory V8 with a replaced bonnet!|
|Of course it's not ! well, not for Concours, anyway. PK, what's it worth to keep shtumm? ;-)|
Part numbers are not usually stamped on body panels - they used to come with a little metal tag with the part # on, held on by wire through a convenient bolt hole.
BTW earlier this evening I did some measuring on my as-far-as-I-know original factory car (it even has DPO-fitted louvres, but it's not PK's old one).
I put a straight edge across the centre stiffener, and came up with 1 3/8 inches. Did the same across in line with the carb dashpots and got 2 inches plus the depth of the sound deadening material.
PS - I have put an appeal in the MGF section for David Knowles to contribute, he is 'active' over there at the moment......
|Very confusing, The reason I ask the question about crowns is because a friend install a V8 Rover using the same mounts as another friend and had clearance problems. We found a difference of 3/4” between the two hoods. Both B’s are 77 vintage. |
Does anyone know of a fiberglass hood that possibly may have more crown than the original hood, either in the US or UK This could solve some of the problems on engine clearance.
Thanks for all of your inputs.
|Just measured my roadster (bonnet history unkown) and my 75 V8 (bonnet definitely been replaced) and they both have the same curvature as each other both at the back edge of the bonnet and in the middle. What does that prove? Haven't the faintest idea. But whilst three V8s were produced in 1972 production only began in earnest in 1973, and my 72-built roadster is a 73 model, so maybe it has the commonised bonnet anyway.|
Don't forget that V8 carbs are just a few inches from the back of the engine compartment and so that is where any extra clearance is required, not in the middle which is where many conversions need the clearance. Having said that Clive Wheatley states that the extra curvature is present for most of the length of the bonnet. Going back to the factory V8s, if there was extra curvature very close to rear edge of the bonnet, wouldn't it also require extra curvature in the panel at the base of the windscreen as well in order to line up across the width of the join?
Clive said that he has had problems with clearance on a number of conversions of customers cars, and he now machines the intake plenum to sit just a little bit lower. He has had cars where the bonnet is almost flat - usually non-OE Taiwanese, it turns out, and in one case actually distorted the bonnet the first time he closed the bonnet with the engine in. In a couple of cases they reduced the height of the dashpot covers to get the clearance as the owner didn't want to fit a different bonnet.
|Bill...Re: fibreglass hoods....check Nick Smallwood's site <http://www.mgbv8.co.uk>...he has a fiberglass RV8 hood on his car...it has more clearance & still fits the lines w/o a big bulge...I talked w/him & he gave me the info on how to contact the manufacturer.|
....unfortunately, everything that WAS stored in my computer now ISN'T!!! That's part of the new e-mail address...
|I used an old ally bonnet(was Iris blue with red oxide undercoat. I used a jig built from a friends factory V8 when he had his engine out and genuine factory engine mounts/EH body mounts. I copied the OE engine inlet manifolds and shortened the SU dashpots.With the engine fitted and the bonnet shut you could just feel the dashpots if you pressed lightly on the bonnet above the carbs.I carefully marked the bonnet out and took it to the guy who made my valence-he hand beat two teardrops into the ally skin-not standard I know but it sorts the problem out and I think that they look quite good....|
|John has an excellent idea. I would like to add that the crown could also be increase to clear the Holley carb and air cleaner, this would be a job for a specialist in that area.|
I think is time to find someone who can make a mold and make a glass hood with more crown for conversion purposes. I live close to three mayor boat builders and several fiberglass shops. I will investigate the possibilities and cost.
|You say 'not standard' but in fact that is exactly what the prototypes had - they were known as 'Sabrina' bonnets, although I think the lady in question probably didn't appreciate that comparison as much as the large rubber overiders ...|
|Paul, the lady in question did not appreciated because...The large crown? Just some humor :-)|
|"not standard I know but it sorts the problem out and I think that they look quite good...."|
Yes they do.
|On this related clearance matter, is there a source for Costello style bonnets in steel or fibreglass?|
|Bill - the 'bulges' were rather small!|
|Paul, thank you for clarifying the size of the "bulges"|
Could they be called French bulges :-)
I saw a picture of the Hood/bonnet mention with the bulges and yes they look rather good, TR style. I also saw a picture of the Costello V8 big bulge on the hood/bonnet. I experimented last night with some welding rod and tape to simulate a larger crown. What I found is that the crown could be increase up to one inch without really changing the hood/bonnet appearance.
The increase starts from the rear about 4/6 inches and gradually increasing and ending without any changes in dimensions at front of hood/bonnet.
Only changing the center where the air cleaner would be on a V8 with a Holley. A bulge does not look good in this application. On a Twin SU two bulges does look, very attractive in the automotive sense.
I would like to put two bulges on my B just for looks!
|I wonder if the best answer isn't just to put an RV8 bonnet on there. The bulge on those is so incredibly well done and it is well-placed for Holley/Edelbrock carb setups. The only way I have found to surmount the clearance issue is to put a low-low rider air cleaner on there (Edelbrock carb, elec. choke) with just a 2" filter. That's just not enough air ... it tells you that right in the Edelbrock setup leaflet. |
The RV8 hood should, I would think, allow either an air cleaner with less drop or more filter, either of which would help a great deal.
AFAIK, RV8 hoods cost 250 pounds less VAT, which ain't bad at all, but the bad part is that get them here from England intact -- which according to Brown & Gammons would involve crating them -- the shipping is about that much again. If there is an interest, several of us mid-Atlantic folks could go in together and get a shipment of them in the same crate, which would save a lot of dough. E.g., they would ship them to the big port in Elizabeth NJ or something and we'd pick them up.
|Took me a while to join the party, but here I am. The story of the hood crown on the V8 is pretty much an apochryphal one, for as I said yonks ago in the book, there was no official mention of the fact. Clearances were certainly tight even then, for the underbonnet felt of the factory MGB GT V8 even has two neat circles cut out of it just above the rear mounted SU dashpots (I even did a V8 Register Workshop Note on it!). Don't forget that by the time that the V8 came out, MG (as a consequence of bellyaching from Pressed Steel) had finally lost the aluminium alloy bonnet in favour of a cheaper steel part. Of course I've never gone out with straight edges and tapes to verify if the story was true - just taken it on trust. As for Sabrina? Well, Sabrina was a well-endowed lady who had attributes that our American cousins might remember from their own pin-up Dagmar - she that inspired the name for the '50s Cadillac tipped over-riders. Sabrina lent her name to the heavy bumper over-riders on the 1974 MG midget and MGB, and her only tenuous connection with the V8 was the fact that on the factory built prototype - which had the standard pent-roof Rover V8 SU installation - two blisters were needed in the bonnet, and Geoff Allen at the MG factory said that the car looked as though Sabrina had been shut under the bonnet ...|
|Well...we're back where we started: a hood's a hood's a hood...NOT!!! Still, nobody can confirm there was ever a crown difference in OEM hoods...there might be a difference between aftermarket & OEM taken from different bucks, but who's to know? I just don't beleive the factory would put a lot of money into getting a half inch clearance under the hood..they didn't have that type of R&D philosophy...plus, V8's were never designed to take over as the primary vehicle, so: why would they go to all the trouble unless it made sense for the full range of models & markets?|
|All is not lost - we still don't have any facts - apart from my measurements on a factory V8 and Sean Squires' single measurement on a '66 aluminium one..|
It seems logical that any extra bow put in originally will have been towards the rear edge, IE exactly where the SU carb dashpots are. It also strikes me most of you guys need the clearance further forward, because you use Holleys and such. We could do with lots of actual figures from different hoods, all measured in two places, I suggest the centre stiffener and also in line with the SU dashpots. I'll measure this distance from the rear edge tonight, to give a precise location. Then with your help we can start gathering data.......
|Tony - firstly the factory made hundreds if not thousands of detail (and not so detail) changes to accomodate changes of all sorts of types. They commonised the chassis rails, engine mounts and inner wings, for heavens sake, compared to that the bonnet was trivial. Secondly it is more expensive to produce and get to the right place at the right time two different bonnets than it is one, particularly when the differences are marginal. I may be mis-reading you, but "they didn't have that type of R&D philosophy" sounds like an insult.|
|Paul...didn't mean it as an insult & apologize if it sounded such...what I meant was that, on the limited budget with which they worked, changes had to benefit the entire model line-up....my opinion of the hood situation--& its just that: my opinion--is that if the change was cost beneficial to the company & complete vehicle line: it was made; if not, they would do something less expensive like cut holes in the insulation, etc. for the limited V8 run. I have 9 MG's in my permanent collection (as of Sunday when I brought a '66 home) plus 12 (not including 2 Midgets & a Magnette) in my MG Graveyard...I've been measuring hoods since this interesting thread started...I can't find a "hill of beans" difference in any of the hoods except one Taiwaneese hood & I can't depend on the quality of their dimensions.|
|Tony - it really wouldn't surprise me if the whole story was a mistake - poor quality copies excepted. As has been said, any increase in curvature would have been within a few inches of the rear edge, which *must* have an impact on its alignment with the panel at the base of the screen. Unless this panel were also changed at the same time I can't see any change being made in the bonnet, part numbers not withstanding.|
|Paul...believe that's the case--an old rumor that's just lived on & on & on...yes, there were different parts numbers for the hoods over the '62-'80 run of the car..however, if you look at when the parts numbers changed, they were in conjunction with either the change from aluminum to steel or a different type of or location changed of the hood prop rods. The rubber seals between the hood and body were also changed & that might have necessitated a new hood part number...but a new hood? I stand by my first post...A HOOD's A HOOD'S A HOOD!!! (or, A BONNET'S A BONNET'S A BONNET!!!)|
|Just to throw some more fuel on the fire - don't forget that when the bonnet changed from alloy to steel, there inevitably were some changes (that was sometime in 1970, before the V8 was but a gleam in Terry Mitchell's eye) and it might be that some new tooling was involved. |
Pressed Steel hated the alloy bonnet from the beginning, but they may have used their considerable ingenuity to allow the same tools to be used for the later steel bonnet skin, just adjusting the tool pressure.
Truth is I don't know for sure, and you'll forgive me I trust if I don't investigate further just now - but if I have occasion soon to talk to the men from Swindon (as opposed to the men from Abingdon!) I'll try to remember to ask.
|If anyone is interested in forming a group of orders for RV8 hoods and have them shipped onto Port Elizabeth,count me in.I live about 35-40 minutes from Elizabeth and would be able to pick them up.Let me know,I really am interested in an RV8 hood for my next project,so I want one.|
|I believe you'll find that the shroud top panel on the RV8 body is different from the shroud top panel of the regular B body...believe the RV8 hood with a definitely different crown meets the panel differently; thus, believe BH reformed that panel to fit the RV8 hood &, therefore, the RV8 hood won't fit the old B shroud top panel...When I looked into importing all the RV8 body panels from England to mount on an MGB, there was a different shroud top panel for the RV8 included in the kit....anyone have experience fitting the RV8 hood to an MGB?|
|Tony, that doesn't seem right to me ... there's a picture of an RV8 bonnet in _How to Convert Your MGB to V8 Power_ that, while it's kind of a small picture, seems to indicate that the bump goes away well before the aft part of the hood. Additionally, after reading the above thread, I had the # for Hopkinson so I called them regarding this and they told me the RV8 hood would indeed fit on any MGB and confirmed that the bulge was in the right place for 4-bbl carb setups. It's something like 230 quid for the hood and then more than that much again for the shipping. |
But the shipping isn't much more for ten than for one! I live half an hour from Elizabeth and I'll happily borrow a pickup truck and go grab some hoods for you guys if we can get an order together. As noted in another thread, hood clearance is a battle that I seem to be losing at the moment. The very first thing I did when I got my new GTV8 was, after nerding around with the carb for a second, I didn't tighten the air cleaner lid down all the way ... I closed the hood and promptly made a dent in it. (At least now I know exactly where the air cleaner sits, though.)
|Hey, has anyone tried scoring an RV8 bonnet (Rover part ZKX5425) at a U.S. Land Rover dealer? Just a thought, a faint glimmer of hope ...|
The local Land Rover dealer's parts department had no information on the RV8, I checked before the sale of Land Rover to Ford. The parts manager asked me who made the RV8. I thought it was strange that they didn't have any parts books for anything other than the current Land Rover offerings. If you go to a GMC truck dealer you will usually find part numbers for any car in the GM line.
|For anyone that is interested in reducing the height of their Rover fuel injection system. I have detailed two methods on my website.|
|About RV8 parts, e-mail Moss London directly. It cuts out the "middle man" and saves time and money. I ordered a remote oil pump base for the Rover V8 (Like the RV8 had) and recieved it from London in three days! I am still waiting on an RV8 fuel tank and waterpump. Could you believe that the waterpump was almost half what they wanted at a local parts store! That includes the shipping! |
The guy I go through is Russell Scott. You can e-mail him at firstname.lastname@example.org Maybe tell him I sent you :)
Hope this helps. It helped me alot!
|I think you guys have the right answer. My investigations (with Roger P's help and moral support) centred on replacing the original SUs with the LUCAS 14 CUX system. |
The original (sorry 1992 relacement) bonnet just cleared SU dashpots. (There wasn't more than 2mm in it but the felt did not have the cutaway sections ).
The factory car did/does not have a shroud around the radiator(Tony) and the factory radiator (top-up bunger) was very very close to the bonnet also.
The factory engine bay was hot and I reasoned that increased air around the top of the engine was at least as important as the aesthetics of the RV8 bulge. My target was also 25% economy so I was nervous that cutting back on the plenum and air stacks would sacrifice efficiency.
The EFI was fitted, the bonnet duly painted and clearances checked. There was still only 2 mm between the planum chamber and bonnet. Gloom !
Anyway - starboard engine mounting fitted the right way up and the two original spacers removed there is now plenty of space. The RV8 bulge IMHO is eyecatchingly unobtrusive (so much better than the Costello mod. The bonnet could be about 5mm wider but the car does 25% more MPG - CO emmission is 0.95% and the consensus is that the conversion is a success.
... but the engine bay remains hot - so when the front wings have to be changed - standby for phase two.
Those who do make the change will be pleased - the rest can maintain the delusion of originality just a little longer (but then you shouldn't have any V8 badges on either.
In any case - keep up the good work.
|Burst bubble ... I just checked the archives and one of the British mavens -- perhaps Roger Parker -- says that the RV8 bonnet is strictly for fuel-injected setups and won't help with the 4-bbl/14" air cleaner issue. But I now understand that there is a fiberglass fabricator in FL that sells a 'glass bonnet tailor-made for just this purpose. Will advise.|
|For MGeeeez sake lets just do a poll/comparision.|
Measure 24" from the rear edge of the bonnet,using a straight edge across the bonnet at that location measure to crown of curve. Mine is 2".
Note ,I picked 24" as that is the leading edge of my air filter,also the highest point under the bonnet.
Also, this is the second bonnet on my 1980,both fit the same.
|If you are looking for increased curvature in the factory bonnet you are wasting your time looking 24" from the rear edge. The whole point of this thread is speculation that the factory increased the curvature for all models when they produced the V8. But if there was any such increase in curvature it would have been about SIX inches from the rear edge because that is where the carbs are on a factory V8, not in the middle of the Vee. |
|I have a fibreglass RV8 bonnet, but the bulge is too far back to help with my Holley/Edelbrock setup with 2" cleaner. I will be going with the fuel injection and keep the carb as a backup.|
|& Nick...I believe you have the RV8 fibregalss hood don't you?|
I believe we are talking the same language, bonnet/hood they are one and the same.
I have lowered my fuel injection over 33mm now so I will probably do an exchange on my RV8 hood for an MGC one. This will keep the car closer to the MGC GT Sebring on which it is loosely based.
|Guys, This has been a wonderful string...but, we're back to square one w/Nick's input about his fibreglass RV8 hood/bonnet....There was no difference in the crowns of any of the MGB hoods/bonnets...the RV8 bonnet crown doesn't help w/US carb heights...so, I'm staying with my MGC hood..others of you will have to lower engine, change intake/carb, cut holes in insulation, graft on a scoop, go to MGC hood, etc...this is one of those that has no cookie cutter solution.|
|oh, Nick...does anyone make a fibreglass MGC hood? Is it worth it for me to pull a mold off mine?|
The Same place I gave you details on the MGR fibreglass hood, do an MGC item. Now that I am going back to metal on my Sebring wings I will probably go for alloy hood and valance if I can get them at the right price.
|'Scuse me for butting in, but didn't Nick say that now he has reduced his carb height he can use an MGC bonnet in place of an RV8 bonnet? I.e. doesn't that imply that an RV8 bonnet *does* give more clearance for US i.e. centrally located induction systems? It is the factory V8 bonnets - if they had greater curvature - that would not give increased clearance for centrally located induction systems.|
Sorry to confuse the issue.
With my Holley/Edelbrock setup the 2" x14” filter still touches outside of the MGR bulge towards the front. I have a chrome bumper xmember with the engine as low as I can get it.
I conclude from this that the MGR bonnet will only help the Holley/Edelbrock setup unless a smaller diameter, or more rearward positioned filter is used than the 2 x 14
My lowered fuel injection is now over ½ inch clear inside the bulge, therefore I may try an MGC hood to see if it will fit, as this is the style I really wanted.
I have not made any attempts to lower the carb setup, but it’s a thought.
|Nick awesome car and web page. Tony Great web site.|
HI! Everyone, finally my computer was fixed. On the subject of hood/bonnet clearance with a Holley carb. I think I may have a solution to that problem. I think that if a 14” or smaller air cleaner could be modified in the following manner.
Take the element off the air cleaner and enclosed it with alum or sheet metal with two/one opening for a hose. Guide the hose to the front of the radiator two a modern air cleaner. Camero style, square with a flat air element or a round type could also be use. This would increase the air volume with added psi of maybe 2 to 3 lbs. while in motion.
Also an alum box could be built to enclose the carb and a hose to the front. With the box a small orifice would have to be install on the bottom with a small air filter to avoid pressurizing on the carb. I would also add a K& N stub stack to further increase the airflow to the carb. I have used this set up with great results on other cars. (Non-MG’s cars) Cooler air means more hp. And better throttle response. This type of air box was used on the earlier Trans Am cars. And looks great.
I may try the latter on the V6 project.
There is also and air cleaner that may work from B&M it has two small filters on each side. The center part that looks like is about 11/2 to 2” tall, the air filters are similar to a side draft Weber. The price is $197 a bit high but it looks good.
Just sharing some ideas with all of you.
I have seen a generic box on a supercharger site, which fully encloses any four barrel carb. It had a single large bore side inlet which was intended to be fed by a compressor, but could just as well take forced air from a position forward of the radiator.
I am working on a twin filter system for my twin plenum modification, which takes air from ahead of the radiator by routing through the inner wing. This would passed the radiator mounts on the outer wing/wheel side and feeds from holes cut in the inner wing sidewall where the horns usually mount.
Bill you are right this higher pressure air = better running and more power, I will post my results on my website when completed, but initial tests showed room was very limited with large tyres.
|Guys, with all due respect, I thought this ram air thing was an old wives' tale of the hotrodding fraternity. I mean, cool air is obviously what you want, no doubt about that part of your reasoning. But the added "boost" that'd be obtained by bringing it in forcefully is just not going to materialize. |
K&N does make a plenum for 4-bbl carbs that you can attach one (or two; I forget) hose(s) to. They caution you that it _won't get enough air into the carbs_ for HP engines.
I must disagree, take a look at all the latest motorcycles that use ram air systems. Ram air is just mild supercharging and fuel injection is self compensates for increasing in inlet pressure.
At the very worst is the system did not pick up any increased inlet pressure at speed it would benefit from lower intake temperatures in all conditions.
|Hi! Nick, Harry, the forced air does increase the hp. The new F body Trans Am and the Camero SS both have force air induction that is good for an extra 15+ hp. |
By further increasing the frontal size of the intake (bigger than the outlate, carb side) and creating a funnel effect will increase the velocity of the air thus creating a ram air effect, it does work! The only problem is that creates a lean condition on the carb due to the extra air. The fix is a small orifice with a small filter to exhaust the extra air that is not used. The pressure is linear; meaning that as speed increases the air velocity to the carb will do the same.
At normal speeds this is not a problem. Above 100 mph it becomes a tuners problem, of course it all depends on design. On FI is not a problem, Oxygen sensor takes care of the mixture.
|Bill...maybe you can answer a question for me: I'm trying to build a cold air box for one of my 4-cylinder '79's that has HIF-4's. There's no room for the stock air filters as I want to keep the stock brake booster...I'm thinking along 2 lines: (1) a "V-shaped" box that's 6"x6" at the front end by the front carb tapering to 3/4"x6" behind the rear carb (back by the brake booster) attached to the short stock HIF air horns...then, a 4" hose running out of the front of the box to in front of the radiator where a K&N cone filter will be located...with this option, I'm worried that the rear carb won't get as much air as the front one due to decreasing size of the air box; so, will your outlet idea help to draw air to the rear carb?|
(2) 90-degree plastic elbows over each HIF air horn fitted to a 3" plastic hose from each carb to a "Y" in front of the radiator where the K&N cone filter will be mounted..
....your thoughts please
one comment: The pressure is not linear. Pressure increases based on a geometric curve as speed increases. At 50 to 60 mph the main advantage is cool air, as you move to higher speeds the air pressure/ram effect grows exponentially and is signifigant at speeds above 100 mph. The draw by the engine in contrast is actually less than linear. for example if Engine speed increases from 3000 rpm to 6000 rpm from 75 to 120 mph. the engine is less efficient pumping air per revolution at 6000 than 3000. The increased air demand is perhaps 80 % while the increase in air pressure would be several hundred percent. Rams work good for race cars and look cool on street cars.
You're correct on pressure/velocity relationship being non-linear, but he RPM/velocity relationship really is linear.
|I stand corrected Barry. What I was trying to say is that air speed would increase as the car increase on speed.|
Thanks for keeping us straight Barry.
|I'd love to hear more about ram for efi. Probably not a limiting factor, but I can confirm, it makes a noticeble difference on carbuarated four stroke M/C's at speed. Am I getting goofy and do I need a laptop?|
I don't drag!
This thread was discussed between 01/08/2000 and 26/08/2000
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