Thread: gt40 vs gt40p
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Old 10-09-2008, 04:21 AM   #9 (permalink)
Unit 5302
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Join Date: May 1999
Posts: 5,246
Default Re: gt40 vs gt40p

Originally Posted by goodyear1984 View Post
lets get one thing straight the stock bottomend will hold 6500 all day long the flywheel (manual) would only break at 6500 it it had stress cracks.cooling system mines stockother than a electric fan,transmission(t5) no problems mine lasted half the summer with over 500hp goin tru it,Dont under estimate a 302 they take a beating.its simple dont waste much money on gt40 heads.go with 165 afr a rpm preformer intake and a decent cam.then a 100 on a fuel pump and 200 a set of 24lb injectors.u aint gonn flow enough air tru a set of untouched gt40 heads to make 320 hp.with the gt40 and a intake ud be luckey toget 265hp.if thats what ur looking for thengoit if u wanna make over 300 then save ur money and get some aluminum heads intake cam.u will pick up power just on the cr gain
You're rolling the dice a little with your engine, and you may be getting great results, but I wouldn't feel safe taking a stock bottom end that high without at least upgrading the bearings. You might get away with it, but not everybody will. The 5.0 is stronger than it's given credit for, but that doesn't mean everybody has a 5.0 that's balanced as well as yours or in tip top shape at 80k miles.

Unmodified (not ported, no oversized valves) GT-40P heads were enough to push Jeff Chambers to 120mph, and they will not be a bottleneck up to about 325hp. After 325hp, they'll either need to be ported or aftermarket aluminum heads will be needed. That said, 325hp on a fox body Mustang is more than enough to get your traps into the 110mph+ range. If you hook up, you should be in the low 12s with a streetable combination, N/A, without revving beyond 6000rpm, and with a very strong torque curve.

The AFR 165s won't really restrict power production until the 400hp range (or higher with a high lift cam). That said, a N/A 302 will rarely see that kind of power production. Most street combinations will sit in the 360hp or lower area, even with pretty aggressive combinations (about 300rwhp). The AFR heads are great heads. They've been designed for high port velocity without sacrificing high end flow. That said, their peak hp advantages are limited on a mildly-moderately modified engine, and they will still not match the torque curve and mid range performance of the GT-40Ps. They would also be $800 more expensive than prepped and reconditioned GT-40Ps with bigger valves and an upgraded valvetrain.
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