gt40 vs gt40p

[Coupe50h]

im sure the p's are nice, but i got my (non p's) off a 97 exploder, the heads went into a machine shop for refreshing, and .010 mill, i then bought them for 450$ i put them right back in the shop for some porting and 3 angle, then i put new springs on, if i would have had to pay for that port work, i could have already bought some gt-40x and been happier...but oh well
with the better springs i got 4-5 mph with the e-cam, explorer intake, and gt-40 heads, i think ported e7's can match these heads though.

I will say, if your going to just leave them stock, dont bother, but with porting they'll be good, i would rathe rhave ported e7's with some good springs, then some unported gt-40 irons...my .02

[goodyear1984]

gt40 heads are like a e7 with a band-aid.yea they flow a little better,have bigger valves.they dont flow enough on a 302 so dont bother with putting them on a 351.there are so many advantages of aluminum heads..if you sit and think about it u will spend 1300 for a set of good aluminum heads that are brand new...say u get a set of gt40 heads for 200.then to rebuild then springs 150,valve job 150,mill 100,seals 40,hot tank 50.there is around 700 bucks might be less or more depending on what needs to be done to them and the prices at your machine shop.now you have 700 into a set of production iron heads that flow a little better that stock and are good for a 302 nothing bigger.lets say in 2 years you decide you want to build a 331 or a 347 stroker if you have aluminum heads you can run more compresion on pump gas,they weigh half what a iron head does, they flow way better ,make more power.if you donthave the money now i would stick with the e7 and port them.i got 5 tenths inthe 1/4 mile when i ported a set.then when you have the money buy the aluminum.ive seen people make this mistake befor and are not happy that they barley notice a differance when they bolt on a set on gt40's.its a better bang for your buck to buy the right heads now and not have to buy a different set inthe future

[Unit 5302]

This appears to be an ancient topic, but since the recent comment was made, I feel a need to chime in on this debate once again.

Out of the box the GT-40P's flow better, burn fuel more efficiently, and have a smaller combustion chamber (higher compression), than the GT-40 Irons. The GT-40 Irons you'll usually find have a better valvetrain capable of taking cams with lifts somewhat higher than .500 whereas the GT-40P head stock valvetrain should not be used with cams having a lift over .500 unless you like valvespring bind (which you don't). There should be no debate still out there on which head is superior. The GT-40P is by far the better head, no ifs, ands or buts.

As to the aluminum aftermarket heads vs. a set of GT-40P heads, there is some debate. Bigger is not always better, and the GT-40P heads can make excellent power while not killing your performance below 4000rpm on a small block 302, unlike any aluminum head that's going to be really suited for a 331 or 347 stroker.

Building an engine is not like building a computer where the parts work independently.

If you put a set of big, high performance aftermarket aluminum heads onto a 302 without changing the intake and the cam, you're just going to get an unresponsive, torqueless gas guzzler because the port velocity is going to be terrible as the intake won't be able to flow to match. If you put a big intake on the engine keeping with the idea you're going to build the car bigger later, you're still going to have poor intake/head flow velocity because the cam isn't going to allow sufficient overlap, duration or lift to efficiently fill the cylinder. Okay, so what if you cam the little 302 to the moon. Gratz! You now have an engine that should have good port velocity... at 6500rpm, which you can't rev to with the stock rev limiter, and your flywheel, stock bottom end, fuel pump, transmission, fuel injectors, cooling system, and exhaust are incapable of safely supporting. If you manage to upgrade all of those components, you'll have one heck of a powerhouse 302, but for $10,000. Oh, and your fuel economy will suck, and you'll have to keep the engine above 4,000rpm to notice the extra performance. Your low end torque will be significantly worse so you had better be running at least 4.10 gears making 1st gear, and rush hour traffic a nightmare.

In summary, there is absolutely nothing wrong with GT-40P heads for the 302 owner that wants drivability, 320hp or under without forced induction, and the ability to stomp the mismatched 5.0 in the next lane.

[goodyear1984]

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

[Unit 5302]

Originally Posted by goodyear1984

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.

[goodyear1984]

ur getting to scientific.6500 is fine for a 302.i mean up grading the cooling system come on dude i have a 347 with over 11.3 to 1 and mine is stock with electric fans doesnt go over 170.if ur engine isnt balanced good enough to 6500 u had a problem at day 1 when it was built u dont need to up grade bearing there only gonna go if theres a balance problem at this power level.if any thing get a good fluidine balancer or a pp balancer.there are so many people that do it to the stock bottom ends its not even funny.i ran 11.8 with a stock bottom end shifting at 6200 for 4 summers and 30,000 miles and now its in a carbed 85 still gettin the crap beat out of it. my friend has a 92 roller bottom end witha 150 shot shifts at 6500.its been done ive done it ive seen it..but that here nor there were talking about heads.bottom line if u can get a set of gt40 heads for a few hunderd and they dont need any work then get them any more than that get aluminum.its just stupid to put money in iron heads.they dissapate heat better via u can run more compression without detanation

[Unit 5302]

Originally Posted by goodyear1984

ur getting to scientific.6500 is fine for a 302.i mean up grading the cooling system come on dude i have a 347 with over 11.3 to 1 and mine is stock with electric fans doesnt go over 170.if ur engine isnt balanced good enough to 6500 u had a problem at day 1 when it was built u dont need to up grade bearing there only gonna go if theres a balance problem at this power level.if any thing get a good fluidine balancer or a pp balancer.there are so many people that do it to the stock bottom ends its not even funny.i ran 11.8 with a stock bottom end shifting at 6200 for 4 summers and 30,000 miles and now its in a carbed 85 still gettin the crap beat out of it. my friend has a 92 roller bottom end witha 150 shot shifts at 6500.its been done ive done it ive seen it..but that here nor there were talking about heads.bottom line if u can get a set of gt40 heads for a few hunderd and they dont need any work then get them any more than that get aluminum.its just stupid to put money in iron heads.they dissapate heat better via u can run more compression without detanation

Haha, my advice wasn't really for you. A 347 is going to run into issues with the GT-40 Iron or GT-40P heads pretty quickly once you start adding a couple other parts so for you, the GT-40Ps don't make any sense.

You can still find the GT-40P heads reconditioned with upgraded springs/valves on Ebay for $500 or so a set.

That said, there is no doubt aluminium heads conduct and dissipate heat better than iron heads so you're right about being able to go higher compression on aluminum heads without detonation. With good gaskets, there shouldn't be any issues with expansion rate differences between the cast iron (cast steel) block and the aluminum heads, either. I can definitely agree 100% with you there.