Motor Choice for Superformance GT40 MK1

[Laurent Gauthier]

Hello all,

I am ordering an SPF GT40 Mk1 (posting the first check tomorrow morning actually!), and I am far from having decided what engine I will put in there. I want to avoid doing anything sacrilegious , hence my question.

First of all, I guess I should avoid an FE since I understand they were only put in Mk2s, not in Mk1s? So that leaves me with a Windsor 427. To save weight, I am thinking of an aluminum block -- but are there any downsides to that?
There's some good amount of choice out there for engine builders, Keith Craft, Roush, RDI. These 427s range from ~500hp to over 600hp. Can I put that much power (say 630hp) without too much risk for the ZF? And in terms of quality, are some of these engine builders much better than others?

Thanks a lot for your advice
(oh and I haven't decided on color either - that's another discussion!)

LOG

 

[Lynn Larsen]

LOG,

The only downside to the aluminum block, IMHO, is money, but if that isn't an issue go for it. For builders, either mentioned is good; either go with a national name (reputation concerns force quality) or a well known local (to you) builder whose rep you can check out 6 ways to Sunday. Hook it up to RBT or ZF built by one of the well known Pantera/ZF guys and you'll be golden. (Do read: RBT Where Are You? though! Bottom line is: If you want an RBT get in line ASAP!) You want to nail down the transaxle (read - gear ratios & final drive ratio), so that the builder can select the right cam. That's the way I'd go if money were no issue.

Also, the guys are recommending a carb (4 barrel) set up 'till car is sorted and then going with whatever induction ─ webers, stack injection, what-have-you ─ that floats your boat. I agree with this unless the engine builder you go with has a tried and true combination that is a truly repeatable solution.

Just my $0.02 worth,
Lynn

 

[Rich E.]

LOG,

Welcome. I'm pretty much a newbie aswell, put my downpayment for a GT back in october. I originally chose a MKI but changed to a MKII a couple weeks back so I'll try to convey my original ideas. I initially went with a Kiethcraft 347. They will build what you want and believe me with the right heads and cam you can do well into the 500 HP range. Spend the extra money for an alloy block. I think KC charges $2,200 for alloy. The weight savings is worth it IMO especially in a midengine chassis. Put a downpayment on a ZF through RBT the same day you put down money on the SPF. I have a feeling the wait will be long........for the tranny I mean.

If you're gonna do a MKI a small block is the right motor.
IMO buy enough HP for your experience level. Remember with an alloy block your car will be somewhere around 2200 lbs and thats LIGHT for a car with 500+ HP.

Just my .02
Rich.

 

[Rick Muck- Mark IV]

The new Ford Boss 302 (old type, not the "modular Boss") stroked to 331 with a good set of Aluminum heads will make more than enough power to keep it interesting. Keep in mind most guys with 40's are running more reliable power on the street now than they raced withj back in the day.

The alloy block is good if wieght is a concern and the cost is not an issue. I like the Boss block for the four bolt mains and the extra rigiditity that the Boss has from the screw in soft plugs and general meat in the bottom end.

either way, enjoy!
Rick

 

[Laurent Gauthier]

Thanks a lot for the advice. I have just called RBT, and will put in an order over the next few days. And as far as the engine, for the Mk1, I understand it's more of a high rev screamer than a big displacement/low end torque logic (as with the Mk2).
As for the HP/weight ratio, I'm just trying to get the maximum. I want a race car, not a sports car . (I have a 996 carrera already...). I'm fully aware that I'm likely not 'qualified' to drive the beast I am building, but, hey, I'll learn.
Thank you again.

I also noted there had been a similar discussion in the past in the engine section of the forum, see here: http://www.gt40s.com/forum/tech-engines-induction/19154-engine-superformance.html

LOG

 

[johng]

I am waiting the arrival of SPF Mk2's #74 & 75. Both will have the Roush 427SR. It gives up 25hp to the straight R spec, but from what I have been told Dennis Olthoff helped spec the cam on the motor to make it more streetable. I have driven the car with the SR, and love it! I decided not to go with the ally, as power to weight is still amazing without it! Just my 2 cents.

 

[Paul]

John,
I looked on the Roush website and couldn't find the 427SR. I found the 427 R (550/535). What is the difference between the two? Is it an iron block?

 

[johng]

Paul,
They do not have the SR on the website yet, but if you call them they can give you the info. I have left my sheet at work, but the HP is 525, I am unsure of the TQ but I think it is 515, and it is an iron block, but I think you can option it as a ally. Before I ordered my cars I visited Olthoff as I had business in Charlotte, that is where he mentioned the SR motor and his involvement in it's spec. I drove a MK2 with a SR in it at Dynamic in Ohio. In the past I have raced Forumla Ford, and owned a Ferrari 308. The MK2 with the SR is simply amazing! By going with the SR, and dropping the 25 hp, I might not get over the 200 mph mark, but I will be close enough and I would rather have a car that is a bit more streetable. If you are really concerned about hitting 205, than the ally might be an option, you will trade the weight for the HP and it will be close to a wash.

 

[johng]

BTW, Roush also has another motor that is not on their site. It is a 427IR, Beautiful fuel injected, 8 velocity stacks, closed loop system. 550 hp, the biggest down side is the $21,000 cost.

 

[Laurent Gauthier]

Hi, I talked to someone at Roush, and they also build that 427 w/ "weber" style Fuel injection, all alluminum, and quoted me 575hp. Now that's 25 grands for that engine.

 

[Mike Drew]

When doing the calculus to determine the optimal motor choice for your GT40, you have to be honest with yourself and ask what your intentions are for the car. While it is all fine and well to concentrate on Big Numbers (the horsepower and torque figures for monster stroker Windsors for example), realize that these big stroker motors have characteristics that some may perceive as a great disadvantage--particularly a fundamental inability to really rev.

The radically enlarged displacement delivers mountains of low- and mid-range grunt, but at the expense of rev-ability. There is a lot of reciprocating mass going around in there, and particularly with a 427-inch Windsor (and the 347 smallblock), the rod angles start to get really extreme. If you are primarily going to be driving your car on the street, and mostly want to absolutely blast away from the stoplights and are willing to short-shift the car (5500 is a safe redline with a 6000 rpm max), then you can probably be happy with a big stroker.

However, big strokers aren't normally very happy on a racetrack, where often it is more prudent to stretch the rpm a bit rather than upshift just before a braking zone. In particular, 347 strokers have proven to be rather short-lived in open-track conditions; the Nor-Cal Shelby Club has had numerous members scatter connecting rods and pistons all over the racetrack, as they found out the hard way that the 347's rev limit is substantially lower than anticipated.

A stock-displacement engine (289/302 smallblock or 351 Windsor) will undoubtedly sacrifice low- and mid-range torque compared to stroker equivilants. However, they can safely rev higher--much higher. Depending on how radical the build is, this can mean that you can achieve similar horsepower numbers--albeit at much higher revs. This is often quite handy, and depending on your gearing (not something you can easily change in a ZF!), a given track may demand the type of flexibility that only an 8000+ redline will deliver. Too, there is something inherently gratifying at literally screaming around at 7500 rpm--the sound alone will send chills down your spine.

Conveniently, there are excellent in-between compromises available. Of late, people have found that the intermediate strokers (331-inch smallblock, 392-inch or 408-inch Windsor) deliver the best of both worlds, with greater horsepower and torque than stock displacement, yet with the ability to rev substantially higher than a 'big' stroker.

I am in the process of having a 331-inch stroker built for my GT350 clone; I am conciously making sacrifices in peak performance in the name of reliability, thus am using an aggressive hydraulic, non-roller cam as opposed to a solid or solid roller cam. Thus my horsepower expectations are a bit lower, yet still respectable; I am anticipating something in the 425 hp-440 ft/lb neighborhood, with a 7000 rpm redline.

As with color choice, it is a very personal decision. But you owe it to yourself to rationally assess your anticipated use for the car and then procure an engine accordingly. There is no 'best' solution, for two people with radically different ambitions could have radically different satisfaction levels with a given engine. So choose carefully based upon what makes YOU happy.

 

[Laurent Gauthier]

Hi Mike,

I agree with your point, and I have actually been trying to figure out how to get an engine that would have a high rev limit, with max torque coming at a high level. The 427 fuel injected roush I mentioned earlier has a max RPM just at 6000.

RDI offers a 427 small block with a lot of HP, and a high rev limit (7200 rpm) RDI Engine Package (see package # 15). But I'd guess longevity is not the main asset for this engine.

I guess I'm going to start looking for a 351W, maybe bored a bit and stroked to less than 390, with a very aggresive cam. I hope to be able to get up to 550hp and very high revs. (all on pump gas).

 

[David Briggs]

What kind of racing are you condidering? Track days, Silver State or actual racing and what class would you be targeting? Are you planning on going 200 mph in the thing?
Just curious.
Dave

 

[Laurent Gauthier]

For now, track days, and as far as hitting 200 I dont know yet.

 

[Laurent Gauthier]

Dave, since you're a Roush engine distributor.... When I called Roush I did not get the impression they were willing to change their packages substantially to match what I was trying to achieve. Was my impression wrong? What would you suggest? I've been advised that putting a Roush in my car was a good thing to do, but at the same time I want an engine that makes me happy!!
Thanks a lot.

 

[David Briggs]

Roush builds engines that will stay together, they use combinations that they have worked out over hundreds of engines. They guarantee their motors and even though they are expensive they come out of the box complete and in the long run probably cost less than building it yourself.
They would probably build what you think you want but it would be very expensive and probably no guarantee.
If you put 500 plus horsepower in one of these it will probably be faster than you are for a long time!
I don't know what your level of driving ability is but for a track day car I would prefer a big lazy motor that makes lots of torque and power and is very driveable, that way you can concentrate on going fast and not be constantly searching for the power band of the cam.
Also, a big motor will live longer, that is what Ford did at Le Mans, it worked then and is still a good plan.
I have seen great track day cars with $50,000 engines that go like hell(8500 RPM, 750 hp?) but at the end of the day need a complete tear down and a new gear box, and I see these cars not go as fast as a lower dollar deal that just goes and goes.
IMHO
Dave

 

[Laurent Gauthier]

Dave, I understand your point, and it is very likely that given my driving experience a big lazy engine w lots of torque would be easier/better. Nevertheless, that is not necessarily what I am looking for.
But then are you confirming my impression that Roush would not do much tailoring? If that's the case then I'd rather deal with Keith Craft or RDI.
Laurent

 

[Russ Noble]

When doing the calculus to determine the optimal motor choice for your GT40, you have to be honest with yourself and ask what your intentions are for the car. While it is all fine and well to concentrate on Big Numbers (the horsepower and torque figures for monster stroker Windsors for example), realize that these big stroker motors have characteristics that some may perceive as a great disadvantage--particularly a fundamental inability to really rev.

The radically enlarged displacement delivers mountains of low- and mid-range grunt, but at the expense of rev-ability. There is a lot of reciprocating mass going around in there, and particularly with a 427-inch Windsor (and the 347 smallblock), the rod angles start to get really extreme. If you are primarily going to be driving your car on the street, and mostly want to absolutely blast away from the stoplights and are willing to short-shift the car (5500 is a safe redline with a 6000 rpm max), then you can probably be happy with a big stroker.

However, big strokers aren't normally very happy on a racetrack, where often it is more prudent to stretch the rpm a bit rather than upshift just before a braking zone. In particular, 347 strokers have proven to be rather short-lived in open-track conditions; the Nor-Cal Shelby Club has had numerous members scatter connecting rods and pistons all over the racetrack, as they found out the hard way that the 347's rev limit is substantially lower than anticipated.

A stock-displacement engine (289/302 smallblock or 351 Windsor) will undoubtedly sacrifice low- and mid-range torque compared to stroker equivilants. However, they can safely rev higher--much higher. Depending on how radical the build is, this can mean that you can achieve similar horsepower numbers--albeit at much higher revs. This is often quite handy, and depending on your gearing (not something you can easily change in a ZF!), a given track may demand the type of flexibility that only an 8000+ redline will deliver. Too, there is something inherently gratifying at literally screaming around at 7500 rpm--the sound alone will send chills down your spine.

Conveniently, there are excellent in-between compromises available. Of late, people have found that the intermediate strokers (331-inch smallblock, 392-inch or 408-inch Windsor) deliver the best of both worlds, with greater horsepower and torque than stock displacement, yet with the ability to rev substantially higher than a 'big' stroker.

Sorry, I'm having trouble coming to grips with this statement. Surely a 408 and 427 will have the same rod angles? That is if you've gone the 'normal' way by using 4.125 bore. I think you can do it using a 4.25 stroke as well but from what I've read that stroke is usually reserved for building 454W and larger motors.

I can't see sufficient difference in piston weight between 4.030 and 4.125 to significantly justify the statement "There is a lot of reciprocating mass going around in there, and particularly with a 427-inch Windsor" as opposed to the suggested 408 being a better option.

Perhaps the reason some of the guys are scattering their big motors is incorrect assembly or choice of components which are not up to the ask?

Also if you're racing you've got to learn to change gears, even if it means grabbing the next gear for only a second or two. If you don't, you WILL, eventually, have a big off caused by spinning on your own oil! A given track may need the kind flexibility a big torque motor will deliver, particularly if you're talking about a ZF which has quite close ratios. The next gear up with a big motor may well be quicker than using the lower gear and revving the ring out of a smaller motor that's gone way over it's peak power output.

Just my personal thoughts.

Cheers

 

[Jac Mac]

Just to give you guys something to think about, The peak piston speed at 7000 RPM on a 4" stroke is about 83mph, on a 3" stroke it is around 62mph. Now at that RPM the piston is accelerating from 0 to those respective mph and back to 0 (( 233 times per second )).

Do you not think that the rings/pistons will have an easier job at the shorter stroke!

Jac Mac

 

[johng]

I am not pretending that I have raced anything as high end as a 200 mph GT40, I have raced FFord, Showroom Stock, and time trials in a 308GT4. Additionally I haved owned a 69 Cougar with a big 428Super Cobra Jet, I will be the first to admit it, that I did not race it, due to it's value. But driving the 427 SR was simply the one of the most rewarding cars I have driven. Keep in mind, I was on back Ohio roads, and I was not easy on it. I appreciated, not having to row the box all the time just to keep it in the power band, it had the tq, to pull out of all corners in most gears. Will it keep up with a 2006 18,000 rpm F1 car, not likely,,,will it uphold the heritage of the car it is designed for, certainly. I am building both my cars as a tribute to the past,,, yes I should be putting FE's with T44's in them. But I will also concede to the strength of a 4 bolt Dart motor, with modern technology. I would love to put in a T44, but if you think the price and wait are bad on a ZF,,,,well. Please understand I am not saying anything negative on either box, and some things are worth the wait. The reputation and reliabilty of Roush is what has me sold on their product. Please keep in mind however, that I have the luxury of building two cars for friends that trust me enough to buy what I tell them they need. It is VERY easy to make decisions with other peoples money! In the end everyone needs to make a decision based on how they will use the car! That is what is so nice about the SPF GT40, you can do it your way.!