I will have a T5 with a 2.95 1st gear and 3.73 rear end. This car will be a street racer only, driven on street tires.

Would you go with a 347 or 331 with this set up for the street and please tell me why you would choose one or the other...thanks!

By the way, the cam will be very mild with high flowing heads.

 

figure out how much torque each of the engines can produce and then how much torque your T5 can handle. might want to be careful on that

 

Build a 347, and get a better transmission. I wouldn't trust a T5 behind my built 302, and I wouldn't trust it as far as I could throw it behind any 331/347 I'd build.

The T5 can live if you drive easy on it, they do well in road racing where the shifting is nice and easy, but hard shifting or sudden torque application in low gear will destroy them quickly.

You could also look into gear upgrades for the T5, but that's about as pricey as buying something like a TKO by the time you get the shafts, gears, synchros etc etc etc.

 

aye. the T5 is holding up well behind my 302. However that gearbox decided for me that I'll never use any power adder or stroke on this car.

and to the 331/347 question I'd say if you do it do it properly and go for 347. same weight more cubes, how can that be wrong?

 

It's either pushing the internal geometry harder, or will require less commonly available parts. There's only so much you can do when the deck height is only 8.2".

For a drag-race oriented motor that you maybe won't leave alone more than a few thousand miles before tearing into it again looking for still more power, you might as well go with a 347. But for an engine built to go the distance I'd pick the 331 every time.


While it's true that street tires will act sort of like a fuse (protecting anything fragile in the powertrain by spinning more easily), even that's only partly true. A bad case of wheelhop that happens enough times will still give you a fragged T5 even on crap-for-grip all-seasons.


Norm

 

I prefer the 331, and that's what I decided on when I built mine. The 331, particularly one that uses longer (5.4") rods, has a superior rod/stroke ratio, providing less side stress to the pistons, rings, and cylinder walls. Yes, the 347 will build more torque, but that extra 16 cubes really isn't all that noticeable on the street. A 331 also requires less clearancing work to fit it in the block. A 347 will require notches cut in the cylinder skirts and sometimes even in the oil pan mating surface, iirc. A 331 only requires slight notching in the skirts, and only if you're using cap screw rod bolts.

My 331 pulls hard from 3k all the way to 6200. I have zero complaints.

 

I forgot to add that the T5 will be beefed up to handle 330 lbs pounds of torque.

 

That only means that it's good enough to withstand that much steady engine torque, which is not the governing load case I see you encountering.

The impact factor associated with the sudden loading from a harsh upshift, clutch side-step/burnout/launch, or wheel hop can instantaneously cause double that much torque to appear across the tranny. It may or may not frag immediately, but it will eventually fail in fatigue when these things have happened to it enough times. Fatigue is an accumulated effect; the microscopic damage that occurs each time does not "heal" even though the part might not look any different afterward compared to before. Over the years, I've done a little fatigue analysis in my day job. Different objects, but the effect is pretty much the same.

Like was already mentioned, it'll live under road-race and endurance racing sorts of hard driving a LOT longer than it will under dragstrip or street race conditions.

Your street race options really boil down to a TKO. Or maybe a TR3550, if you can still find one of those (its rating was somewhere midway between the T5 and the orginal TKO; the one in my EFI 355 Malibu was rated at 400).


Ultimately, of course, it's still your call. I can only advise.


Norm

 

you back on the road? :-)

 

I would give Jim a call at http://www.fordstrokers.com/fordstro...or-longblocks/ and ask him what he recommends...If you are just going to run a street tire it probably won't matter much as either combo will blow the tires off when you stand on it(assuming your not running some sort of drag radial)...There has been tons of bad info on the 347 combo's burning oil and wearing out quickly or being down on power due to bad rod ratios...I would go with the 347 if you want the most power out of it but either can make more power than your trans or tires will be able to handle..