Ford SB Stroker for Roaring Forties GT40

[Ron Earp]

Well, we're about done with my "new" old motor. I worked with a local Ford engine guy, Billy at a local shop called T-Hoff, to spec out a motor more suited for an Audi gear box. I finally came to the conclusion there was no real way around the gearbox problem in that the ring gears of these transaxles (except ZF, some Porsche) are numerically high and they "want" high revving motors. So, I thought I'd re-think my motor and provide something that can rev high.

Our target for this motor was an engine that could take 7700 RPM for track use and live to tell the tale. Here are the basic specs, there are a lot of things I don't have listed such as dizzy, windage tray, cam drive, rockers, ARP fasteners used throughout, etc.

*342" Sportsman block, no overbore, new block, relieved
*Forged Eagle stroker crank
*Billet crank girdle
*Forged H beam rods
*Ported AFR 185 Heads, 2.02" In 1.60" Ex, race three angle valve job - flow is amazing!
*Double coil race springs, 600lb open pressure, 260lb seat pressure
*Compression 11.3:1
*Solid roller cam specs - 0.676" In, 0.673" Ex, Duration at 0.050" lift 256 In, 262 Ex; Advertised duration 287 In, 295 EX

The target hp goal for this motor is around 530. Basically, this engine is identical to one that Billy used in an engine builders competition that was able to make 538 fwhp at 7400 RPM on 93 pump gas, and much less torque, which is a good thing. I think this will be a nicely suited motor to a GT40 character, high revving, high power, and will do well on road courses. Now, I just need a car to put it in......

Ron

 

[Bill D]

Ron-

The engine sounds killer. What type of induction are you using?

Also, have you given any thought to applying thermal coating to the piston tops, combustion chambers, and exhaust ports to help prevent detonation? Your compression is pretty high at 11.3:1.

Your engine will sound incredible through the crossover headers.

Bill D

 

[Ron Earp]

Hey Bill,

I forgot to mention, they are coated, I think Billy used SwainTech, but really it isn't needed if everything is kept under control. Don't let people tell you that you need coatings to run "high" compression (which isn't so high really, had a look at modern motor specs lately - 11:1 is very common) - you really need attention to detail on the timing and fuel and you'll be just fine. Any good carb tune can manage it, and certainly the high end ECUs people are using on this site and others can handle it readily.

You know me, I prefer NoTec over MoTec, so we'll use IDAs (hence my sell of the IDFs). The test motor that Billy built used a Demon carb to make the power it did - carbs are not dead at all and do quite well.

Ron

PS - Did you know your avatar is broken? Could be you see it in a cache but it is dead to everyone else I think.

 

[Bill D]

Thanks

I'll fix it. It's great to finally be a part of the GT40 family after so long on the outside looking in.

Bill D

 

[Ron Earp]

IS anyone running a mechanical pump on their SB Ford with a serpentine setup? I might put another thread out there on this in another section, undoubtedly someone is like me and feels less is more and would run webers with a mechnical pump to cut down on "crap" around the engine. Any details?

Ron

 

[Bill D]

Ron-

I talked with some Weber specialists and they said the pulsing of the mechanical pumps don't work well with Webers. They said the best pump is an electrical rotary vane made by Carter (P/N P4070). It provides 4-6 PSI and delivers 72 GPH. He said I could run two pumps simultaneously with check valves to ensure adequate supply at high RPM's.

I can give you their phone # if you would like to talk with their tech people.

Regards

Bill D
Los Angeles, CA

 

[Ron Earp]

Bill, there are dampers made that take care of this and those guys should know about them (Pierce, Inglase). Dampers are used on quite a few factory cars with Webers and mechnical pumps, plus, there are performance mechanical pumps available from FMS and others than have greatly reduced signature. Not saying you can't have problems, but I don't think it is something that should keep one from doing it since it is a recognized issue and there are solutions.

Ron

 

[Ron Earp]

Question to those that have tried webers and FI stacks - are 48mm webers going to handle the top end of this thing at 7500 RPM? I'm thinking no, but have no done the calculations. Jerry, Paul, any with track/engine experience that could chime in?

Ron

 

[Steve Toner]

[ QUOTE ]
are 48mm webers going to handle the top end of this thing at 7500 RPM?

[/ QUOTE ]

Ron,

There's a graph in the Carburetor Performance book by Forbes Aird and Malcolm Elston, showing main venturi diameter (in mm) vs. single cylinder displacement (in ci).

342 ci = 42.75/cylinder. This would need about a 46mm main venturi to run 7000 RPM (the highest it shows). So yeah, you're pushing it. Oh, they do caution that "Choosing a venturi size based on this will yield an engine adapted only for absolute flat-out top-end power" and suggest scaling down by 5-10%...

I think you're looking at a 4-barrel (or two) for this engine.

 

Build a 331 made 540HP,443TQ@6400,on IDA's with 42 choke,tested 45 no gain!!

 

[Steve Toner]

[ QUOTE ]
Build a 331 made 540HP,443TQ@6400,on IDA's with 42 choke,tested 45 no gain!!

[/ QUOTE ]

Based on the chart, 42 would be about right for that engine. The max RPMs make a huge difference. Extrapolating for Ron's 7,700 RPM, it gives a main venturi diameter of about 51mm. You can knock that down 5% and you still get 48+.

If this thing is going to get any street use, I think it's going to need a progressive carb (i.e. 4bbl). It may be able to turn 7700 RPM, but I doubt it will see that on the street,a nd driveability at lower RPMs (+ part throttle operation) could be an issue with a carb that is tuned for flat-out performance... Frankly, I think the engine is overkill, but it's probably not my place to make that call...

 

[colin artus]

You can go bigger than 48 with the IDA; see http://www.geneberg.com/58ida.htm . Anyway the 48mm size does not really represent the flow size of the carb, that is governed by the choke that is fitted .


Colin Artus

 

[Steve Toner]

Choke = Main Venturi

The 48IDA goes up to 45mm main venturi size. Therein lies the problem.

 

[Ron Earp]

Steve, you are right that the motor is probably too much, but I want to experiment a little and see what is possible. It isn't overkill as much as some (Dart,A4 block etc.) and really wasn't that expensive to put together. People have much more money in Roush engines and get less performance, they're paying for the name.

I'd like to see if we can get something like this to behave at all for street driving - highway/trips sort of thing. It'll be interesting to see. If we can't get it to behave at all, with webers or 4bbl, then we can easily bring it back down with a much milder cam.

This engine was put together a couple of years ago for my 40 and all I've simply done is gone back through it and changed a bunch of components. One thing I should have done at the beginning is zero balanced the motor, which I am doing now. It'll make life easier for swapping out flywheels if needed in the future.

The 48mm venturi size estimate I made was based on some comments I've heard from Jerry, Paul, and others. When they had a small stroker fitted with 44s and 48s (webers and FI stacks, referring to no choke being used in these applications so I don't know max size) all reported the engine being strangled on the top end and once switching to 52s and 58s it would breathe and make the power. I just can't remember the details they mentioned.

 

[Mike Dozier]

Ron

If your RF is going to be mostly a track car,
I assume you'd only run a water pump and alternator,
which is a piece of cake to do a serpentine setup.
My Cobra was serpentine with the street rod water pump
so no need to run any idler pulleys. Very simple setup.

MikeD

 

[Ron Earp]

Well, the car will have AC but that won't stop it from being used on the track a lot. Sure, it is an extra 70lbs of stuff, but that won't hurt anything at the weight and power we're working at. RF already has a nice serpentine setup designed that works very well with AC etc. But, that setup is made for a late model timing cover that has no fuel pump provisions.

Anyone fooled around with fuel pump type covers and serpentine setups, or is that what you are talking about that you have Mike?

Ron

 

[Mike Dozier]

Yep...my Cobra had the Carter mechanical pump...but no AC.
Will the Sandon compressor survive 7,700 rpm ?

MikeD

 

[mike_starling]

The 505 has a max sustained rpm of 6500. The 508 has a sustained rpm max of 6000. There is some overhead for short bursts but I do not remember what those numbers are. These values came from the Vintage Air catalog.

 

[Alex Hirsbrunner]

If I recall my discussion with the classicautoair.com tech support team (who supplied my Sanden compressor), there is no practical RPM limit while the compressor clutch is disengaged.

I am running a serpentine setup on my SBF with a mechanical fuel pump (but in my Capri, not my in-progress GT40). This was the factory configuration in 1979. I was not aware that there is a short (explorer type) timing cover that has a provision for a mech fuel pump. I believe the reason the timing cover is shorter is because the fuel pump eccentric is omitted from the front of the cam timing gear. I was under the impression that an RF needed the short setup to fit in the chassis.

Regards,

Al H.

 

[Ron Earp]

I think you are correct on the timing cover. RF does use that style timing cover, at least that is what was on my motor before I sold the kit and the serpentine setup worked very well. Might be I have to use an electric pump, and if so it isn't a huge deal, I just would like to use a mechnical pump for neatness.