GT40s Engines

Ron Earp

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The more I think about it (I can't work on the car as the garage is junked with with wife stuff at the moment) the more I think the 342 stroker I have isn't the best motor for the 40.

It will make a lot of power and torque, I'd estimate 425 hp and 400 lb/ft torque (11:1, AFR heads, good cam) but it might not be the best suited.

How high can one build a 302 block to go? 7500RPM? Or a destroked 351? Looks like one of these motor making in excess of 450 real hp would be a lot of fun.

Any thoughts? How much would it cost to build a serious bulletproof SB that can rev to the moon?

I don't mind so much on maybe not starting with the best choice, because I hope to have a Cobra in a few years and the 342 would be excellent for an FIA car. And it can easily be taken out of the 40.

R
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Ron,

It's my understanding that you can squeeze out more than 500HP from a 302. One problem is reliability. The more you rev it the faster you'll be rebuilding it. The other problem is that any more than 500HP out of the 302 makes the block actually twist under the load. This can cause a lot of different problems if carried to the extreme.

For my money, I'm going with a stroked 351. Should be less engine strain which gives me more miles between rebuilds. The 351/427 at Coast puts out 515HP and over 500 Ft-lbs of torque. That'll be a good start for a street car.

Mark
 
I think it depends on how streetable you want it to be (and how reliable)... They ran 289's with 390 bhp @ 7000rpm in 1965, and the 302s ran with just over 400bhp in 1968, but those were not street cars. I don't know the answer to the 7500 RPM question (wish I did), but I'm sure there are heads & cams out there that can manage it. On the bottom end, you'd probably have to worry about the rod bolts and beefing up the main bearing caps - maybe start with a Boss 302, though there are aftermarket solutions as well.

Hopefully someone more knowledgeable on these matters can give a more definitive answer.

FWIW, I'm going with a real bonafide 289 in my car, and expect in the range of 325bhp for a reasonably reliable, streetable car (which will be no slouch at the track
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This is a general reply rather than a detailed one.

In Australia, our major racing category is Ford vs GM using road cars as a base model, and then modified to the moon. The Fords use the SB engine and is capped by the rules at 7,500 RMP. The engines put out up to 600 BHP and are used reliably at a number of endurance events, the best known being the Bathurst 1000 (km). These cars run flat out in this race for 8Hrs in very arduous conditions and at speed of 300+ km/hr (200mph).

These engines, incidentally, are offered as an option in the Australian built Ultimas.

Again, the comment made previously was, how do you intend to use this engine?

[ May 09, 2002: Message edited by: Chris L ]
 
Ron, Nothing will ever sound better than a 302 winding up into the stratoshpere with a full crossover exhaust... By the way,I know this will open up a can of worms, but the hot rod guys around here say that the standard 302 block should not be pushed much beyond 400 HP or so or they will eventually split along the freeze plug line, durability has proven to be an issue. Brian
 
I'd think that a 302 based 342 could be twisted plenty tight if you built it well with high quality (but expensive) parts. I would think billet steel or titanium 5.315" rods (to keep the piston pin out of the ring lands) and a light crank and pistons in a R302 block should take 7500 rpm regularly. Of course, the higher RPM's require a light valve train (more titanium)with high pressure (? triple) valve springs---which then require you to turn your engine over (or start it) frequently.

To me high RPM problems are three-fold: piston speed and momentum and money.

FWIW
Scott
 
well here is my take: A 342 is close to max stroke, i'd hesitate on that one. a medium stroked 351 would suit you better. Realisticly, the hp badwidth is @ 425-485hp in these cars. now if you want to be different a stroked 351c, say to 392, it will rev high, and make @450-550hp. just a little different thinking.
you can stroke a "W" to 396, 408, 418, 427, 434, and 454. you can stroke a "C" to 396 and 408. these are popular kits from flatlander.
 
I think a stock block that regularly sees revs in excess of 6,500 is living on borrowed time. In hot-rodding circles, the generally accepted limit of a stock 302 block is 500 hp. That is with a stud girdle folks. The things that kill these engines are (1) detonation (nat an issue generally in a normally aspirated engine) and (2) high rpm operation. If you can locate a Mexican block or a Boss 302 block you can squeeze a little more out of it, because of the extra webbing around the bearing caps. The "R" block or the new sportsman block is nice, but they're definitely heavier and they cost a lot more.

I think the best block to go with is one of the FRPP aluminum blocks...they weigh over 100 pounds less than the R302, they have 4-bolt mains, and they have steel sleeves that can easily be replaced. I also think the practical limit of rpm for a "streetable" car is between 7,000 and 7,500 rpm, above which even well designed hydraulic lifters will be useless.

Regards,
Mark
 
Why are you so keen on high revs?. We dyno all of our engines, and this shows the point at which both power and torque drop away and you are in fact producing lesspower after this point!. We then design an engine to produce its maximum power at a reasonable level (say 6000rpm )and then set the rev limiter to just above that figure. We use our engines hard, and with the exception of a few, no longer see the reason for such high revs.
 
I would assume that one could do pretty well using proven NASCAR technology and DETUNE the motor to what ever power level you want.

The motors are 358 CI make 750 HP and regularly turn 8700 - 9000 RPM for 500 miles. I am sure the parts are expensive, but if you want a track tested platform then this would be a viable option.

There is a good market of used NASCAR parts. I am not sure how you determine what is good vs. bad shape on these items, etc.
 
F Catt,

I'd be interested in your response to my understanding of the benefits of high revving engines.

It has always been my belief that a high revving engine will benefit from the use of lower gearing for a given road speed and therefor increased net torque to the rear wheels. This can be an advantage, even when taking into account the drop in flywheel torque at higher revs.

This benefit can be had by either altering the gear ratios (including final drive), or by simply shifting later.

Your thoughts?
 
HP=Torque*RPM

Engine A produces some peak torque at some RPM. Enigine B produces the same torque at double the RPM of engine A. Engine B will produce twice the HP of Engine A. If so desired you can gear engine B (operating at its torwue peak) so that the driveshaft speed is the same as engine A (operating at its torwue peak) and produce twice the torque.

For racing applications the main concern is HP over a reasonably useable RPM range. You can get torque at the rear wheels through gear multiplication as stated above.

Case in point is an F1 engine:
~800 hp at 18,000 RPM which equates to ~233 ft-lb of torque at 18,000 RPM.

Ford 5.0 L stock mustang engine:
225 hp at 4200 RPM, 300 ft-lb at 3000 RPM.

Even though the 5.0L has more torque in equal weight cars with appropriate gear ratio changes to take best advantage of each engines characteristics the F1 engine will far outperform the stock 5.0L.

Driveability on the street can be a totally different thing where a torquey engine can be a plus.
 
G

Guest

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One would think that with a 4 bolt main block like the ones from Ford (both iron and alloy) or the new cast iron block from Dart, a 302 could easily be capable of upwards of 10K. However, the Dart block and the Ford cast iron block both have Siamesed cylinder bores. The question is "does this make these blocks unsuitable for use in a street machine, especially from a cooling point of view?" Apparently, allow blocks have such good heat transfer, cooling is not a problem with them. But will sleeves hold up under high revs?

I feel that a boat load of torque is not necessary for a car that is as light as the GT40 and I would gladly trade some of that torque for RPM to suite my transaxle (Porsche/ZF G50 of course.) The plus is that it would sound better than regearing the transaxle
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The advantage of a 302's overly square bore
is that it's built to rev. Because of the
short throw, piston speeds are lower than
you would expect. With the right parts
(forged internals, girdle, beefier mains)
these engines can be built to rev up to
10K. Doing a long rod build, and offsetting
the wrist pin slightly, reduces piston speed
even further.

Of course, winding up a 302 to 8000 on city
streets is more difficult than it sounds,
but occasional jaunts to the track would
suit me fine
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Ian
 
I think intended purpose is a vital consideration..
The '40 is a very light car, and the power and weight characteristics of the motor will have very significant results on the usability and character of the car.
For any kind of half sensible street driving, low rev, light throttle drivability would be very important, as would be smog legality. This usually points towards a mildly tuned motor: where more power requires more cubes, or forced induction.
Engine weight may not be an issue in a road car..
For track days, matching the power band with reliability, AND the available gear ratios and diff ratios will mean that the power produced can be optimised.
Weight could easily be a big issue- saving 50 kg off the rear may make the car faster on a lap than a whole heap of extra power.
Designing peak power just short of the reliable maximum revs would be great at Boneville with a huge selection of gears..
but everywhere else, the average power through the gears is the key.
Perhaps a list of pros and cons for each possible engine, for a given use/power/cost is the only way to get to an optimum combination- with a thorough understanding of what reputable experts have to offer.
Just my 20c worth

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If you have over 425 hp in a 2300 lb car, I will tell you that there are very few times you will ever drive the car when you say to yur self, " I wish I had 50-100 more hp". Even in racing situations on the track, more HP does not always = faster lap times. How many out there are proficient enough to get 100% out of their cars? 90%? It's a lot more fun to put hours behind the wheel than hours working on the motor because something broke or it requires a lot of upkeep. The motor I have will make 440 HP and revs to 6200 and a friend of mine has one with that rev's to 7200. His motor cost 50% more than mine for that extra 1000 rpms (forged crank, girdle, Sportsman block, light valvetrain).
 
G

Guest

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I understand what Wayne is saying and for the "fun" factor, I will concede that, to an extent. Reving through 7K is fun for me as is coming back down through 7K (several times) coming into a corner!

As to less time in the shop, I don't think so: the problem Ron is forseeing is that this torquey engine is going to beat the crap out of his gearbox; AND, his clutch, tires, half-shafts, rear bearings, etc., etc. So, just opting for more low end torque, by no means, keeps you out of the shop! The other issue is just keeping that much HP hooked up! Some have the discipline to use a light touch on the right foot; far more just stomp it to the floor.

Robert has the most balance view point: study your wants and needs, then make YOUR choice. The beauty and curse is that there are so many choices! Ain't it grand!
 
G

Guest

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Robert, as to your comment about smog legality. From a governmental point of view, that is a load of hooey!

I am a good earth citizen and when I built my car, EFI 5.0L, I left everything on it that I could and only removed what wouldn't fit or hook up. Now this engine is very clean, but, by the book, inspectors wouldn't even put a sniffer on it because they don't see airpumps or an exhaust riser off of 1 of 8 headers- that's going to do a lot, right? And this doesn't even consider that I might have come up with a fantastic, creative way of reducing emisions.

Now, on the other hand, if I go out and buy a 1965 289 on which they did not give two hoots about emissions and put that in my car, everyone would be happy.

So tell me, where is the logic in that?

The reality is that the number of hobbiest, home built cars is so small that compared to production vehicles and other polluters, the affect we have is an absolute nit: not even rounding error. California, as wigged out as they are, has even passed a sane law with regards to hobbiest built cars. States which have been too lazy to take a realistic look at the emissions laws they adopted lock-stock-and-barrel from the Feds have criminalized a whole community of otherwise fine, upstanding, law abiding motor sports enthusiasts. (We all know how rational the legislation produced in Washington,D.C. is!)

My $0.25 worth.
 
G

Guest

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Guys,

I love the sound of high reving engines. The Cobra replica currently has a Coast 347 and only makes 6500 before hitting the rev limiter. Is built with a girdle, Victor Jr. heads, and much neat stuff. Driives 335 x 17 Dunlop 8000's on 12" rims behind a Tremmec. Lots of bottom end torque makes it easy to drive on the street. Has the proper boomy sound for a Cobra replica. Yanks 2200 lbs around like a rocket.

While I was in graduate school I hooked up and became friends with a local machine shop owner (masters in Automotive Engineering) who went on to build motor for Sharp Racing. He and I are Mopar fanatics.

On weekends over a couple of years we built a 440 in a Max wedge configuration for my Road Runner. It has a knife-edged chrome journaled hemi crank, blue printed six pack rods, forged pistons, 426 wedge stage III heads, dual quad plenum ram, and the stage III cast iron headers. Everything that could be done was done: Align-bored, decked, bored, heads CC'd and flowed, and the assemblies balanced progressively through the build. I went nuts polishing the thing ... the rockers are ground, polished and match weighed. Even the oil return surfaces on the head are polished instead of epoxied.

The monster made tons of torque and HP ... driving a close ratio 4 speed through a 10.5" racing clutch inside a scatter shield. After lots of suspension work, it would eat Turbo Carrera's regularly in the corners no less on the straights. Used to kill the local 500KR from a 60 mph punch on the interstate. He hated it ;> )

The sound was awesome ... particularly when it started to flow well above 6 grand.

This engine regularly hit 8k+ ... and lasted 35k miles between requilds. Engine still exists, awaiting a rebuild at 105k miles and a new home in a 'Cuda for my youngest son.

High reving engines do lose torque and that makes them "interesting" and hard on clutches on the street. They have to be bullet proof to live long ... and that is only accomplished with cubic dollars and very, very good machining practices and extraordinary attention to detail.

The limiting factor on GT40s (it seems to me) is the transaxle. These things will be torque limited. High perfomance clutches are EXPENSIVE for these as well.

So ... you can have what you want if you have the monies to invest ... but the price for a beast that spins high and lives well on the street will be high in dollars at the outset and not be cheap to maintain. But remember that too much engine will eat some other aspect of the car ... probaby the transaxle or clutch. A high revver represent some challenges in use on the street ... Gawd it will sound GREAT!
 
I've been following this thread with some interest. As one who builds many high hp engines, here are some things to concider.
1st is are you building a drag race engine or road race engine. These are 2 totally different combinations and require to difference ways of thinking.
A drag race engine only turn high revs for 8-12 seconds at a time. You can rev a stroker small block 8000 for this period of time. If you try to do this with a road race stroker you will blow the hell out of it at 8000 revs, no matter how good the parts are that you use. The side loads on the piston and crank with ether break the skirts on the pistons, or more commonly snap the rod in half right in the middle. You can help relieve these side loads by using a very long rod. I have used up to a 5.7 rod in a 347. It does put the pin into the 2nd ring galley but it will rev higher.
A road race engine works best if it a high hp low torque engine. We build streetable 306's that are 500+hp on pump gas and will rev all day to 7500. We have destroked a windser that will rev over 9500 and puts out over 725hp. Both of these combinations are very reliable. A 302 built with the right parts will develope over 700hp at 9000 revs and do it time after time.
The stroker is a better street engine. It has a lot more torque than the 306 for street driving. The issue is that a 2200 lb car doesn't need that kind of torque to go very fast. The seat of the pants feel is cool but in road racing it is a much harder car to drive fast or well.
It really comes down to how you want to use your car. On the street the stroker is a fun little engine. Of you want to race, the car will be faster and easier to drive with a 306.
 
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