347 Setup Opinions

[Street89GT]

Hi Guys,
I currently have a 302 115k miles, GT40P Heads, GT40 Intake, 70 mm TB, Ford Racing Headers, High Flow Cats, Flowmasters. Rest is Stock. The Heads have had about $600 of machine work into them upgrades include, Upgraded Springs, Retainers, Seals, Ported Bowls/Exhaust Roofs. The heads have been port matched to the lower intake that has $150 in port work done to it.

The heads only have about 500 miles on them since the machine work. The engine is starting to burn a lot of oil and I want to rebuild it.

Here's my question, what kind of performance can I expect if I rebuild the motor and stroke it to 347, using the same heads/intake, and get a custom ground cam?

I am happy with the performance of the car as it stands, but since its being rebuilt thought it might be a good time to stroke it to 347. Has anyone done a setup similar to this?

 

[90lxcoupe]

If your going to use all those parts on a 347 it will make a ton of torque but wont produce great power numbers. If you are happy with the way the car is now, then the 347 will still be an improvment but nowhere near its potential

 

[mwood]

Agreed, torque but far from potential. I genrally say custom cam as the cam will determin how well the motor runs, but I also think you will likley desire a hci upgrade in the future. The thing I can't say is that upgrading to a 347 and using your existing cam will work. You would be changing alot about the piston (stroke, compression, ...) but the same cam would work? Doesn't sound right.

PS, this will hurt, but you could spend $1000 in those heads and they won't be as good as aftermarket heads. You will spend twice as much piece mealing this than you will spend doing it once and doing it right.

PPS, I say do a stock rebuild on the lower for now and save your cash to do a real motor build when you decide you are ready.

 

[90lxcoupe]

PPS, I say do a stock rebuild on the lower for now and save your cash to do a real motor build when you decide you are ready.

If you go that route, just buy a JY short block

 

[Street89GT]

Thanks for the replies. Mwood, I wouldn't be reusing my current cam(stock HO), I'd get a new custom grind. Regarding rebuilding the lower end to stock specs, doesn't it make more sense to do the 347 now and just switch the top end if I'm not happy with the power output?

 

[mwood]

Thanks for the replies. Mwood, I wouldn't be reusing my current cam(stock HO), I'd get a new custom grind. Regarding rebuilding the lower end to stock specs, doesn't it make more sense to do the 347 now and just switch the top end if I'm not happy with the power output?

I was just assuming you'd need a custom cam and possibly tune for make it run nice. I was just thinking cheep rebuild for now till you can do it right and spend it once. What you propose would work, but you might be disapointed in the amount of money you spend for what you get out of it.

 

[NIKwoaC]

A 347 with GT40 top end parts isn't necessarily going to make any more torque than a 347 with better flowing parts on it, it'll just get into (and out of) it's peak torque sooner in the RPM range.

Check out this 347, uses stock heads, cam and intake. Made 270ft-lbs at the tires, and horsepower in the middle 180s. Done making any sort of power by 4000 rpm.

Official Dyno Pull Thread

Obviously a 347 with some worked over GT40 parts and a custom cam is going to do a lot better, but it won't be ideal in any way, shape, or form.

BUT, I don't see why you couldn't put together a 347 bottom end, and just run the top end parts that you already have until you have the money to buy better top end parts. All it means for you is a little extra work and buying another set of gaskets.

 

[Street89GT]

Any idea what kind of numbers the setup I'm proposing would put up? I would of course make all the necessary mods such as injectors, maf, etc.