So again: Start with the transaxle. Assume your engine will make 500 ft/lbs of torque and go from there. I am sold on Porsche G50's 01,02,03, G50/50s and the G50/52. The 52 is the one to go for but the G50 01-03, IF they are properly built and with added internal modifications as well as the necessary strengthened side plate are fine. Gear ratios are an issue but G50s have numerous alternatives available. I think 5 speeds are enough if the final drive ratio and 5th gear keep the engine rev under about 2800@ 80MPH. This will give you north of 180MPH top speed depending on max revs and still be comfortable on the highway at cruise speeds.
Why Porsche? Because they will fit in a GT40 length-wise, are good for the amount of power you will want, Porsche made 10's of thousands of them and you can get parts easily from many sources. They are well known and widely used in mid-engine prototypes like GT40s. There are also several rebuilders that are reputable and have been in business for a long time to get help from. My advice is to buy a built box from one of them instead of buying an unknown quality used box and then asking to get it updated after the fact. Here's my source and I recommend them fully. (I have no financial interest).
Type: G50/00, G50/01, G50/02 Original equipment for: Porsche 911 Carrera 1987-1989 Description: H Pattern 5 speed manual transaxle with Borg Warner single cone synchromesh and synchronized reverse Limited Slip Differential: 40% LSD optional equipment Weight (approx): 146lbs Oil Capacity...
californiamotorsports.net
Now! LSD's.............. I LOVE the two Quaife TBD's in my cars. I have a G50 in my SLC and a R-21 Renault with the one-piece input shaft mod. Both have Quaife's in them. Any GT40 must have some sort of Limited slip IMHO. I like Quaifes the best.
Don't save money on the power train. This is the most difficult group of systems to try and change later. Buy uprated half shafts, stub shafts, wheel bearings etc, the first time.
Engine: 400 CI's is just about right. 400-500HP is plenty and an SBF 351 stroked to about 400CI will run on pump gas, use a hyd roller cam and be well mannered on the street while making more than enough to run on the track with ANY street tire. Add slicks and be a hero!
CARB verse FI............ Carb easy..........FI.............you better have a tuner who knows what he is doing.............search FI systems on this forum and ask around before you commit to FI. It works great when it's right and will make you crazy until it is.
Tires and wheels. Too much fo say for this response but I would go with 18 inch wheels TODAY if I had to make a choice TODAY. There just isn't much of a tire choice otherwise, and it's getting worse all the time.
Get the AC system right. You'll need it unless you live in Jolly ol England..............where you will NEED good rain tires. I'm kinda joking...........kinda.
Bodywork first or last? I go both way on this from time to time, You will more than likely do the mechanical systems and the body
simultaneously in reality. It all needs to get done and doing body work for weeks on end gets old............so do it the way that is most fun for you. Note: bodywork and paint prep is the place to save a LOT of money! Paint is another. My advice is to make the paint job suit the usage. Don't put a $20K paint job on a track car. Or for that matter on a streetcar that you are really gonna drive. I would study wraps and see if that would work for you unless you are building a show car. Track car? Wrap or cheapest single stage paintjob you can find. It's only gonna look good for a few outings anyway.
The main thing is to have fun!!!!!!!!!!