Cast GT 40 Heads and intake

derrick2119 · Jul 15, 2009

Can anyone tell me how much difference these make over the stock 94 GT top end?
Thanks Derrick

final5-0 · Jul 15, 2009

derrick2119 said:
Can anyone tell me how much difference these make over the stock 94 GT top end?
Thanks Derrick

I guess you could use this rule of thumb

The difference would be about the same as a GT & Cobra
since you would have the major parts of the Cobra

Yes ... you'd not have the rockers and such
but
The difference would not be all that much as I see it

Grady

blksn955.o · Jul 16, 2009

final5-0 said:
I guess you could use this rule of thumb

The difference would be about the same as a GT & Cobra
since you would have the major parts of the Cobra

Yes ... you'd not have the rockers and such
but
The difference would not be all that much as I see it

Grady

nail

hammer

head

derrick2119 · Jul 16, 2009

Any info?

what about performance wise i got all forged internals e-cam in a 306 block.....heard the GT40P heads flowed better but what kinda increase would a set of ported GT40P heads in power or should i just go with aluminum heads? its my first build....and likely to be a street/strip car

blksn955.o · Jul 16, 2009

there are those who have gotten 300wrhp with unported gt40's with the right cam.

Going with avg. numbers with a combo listed above I would say 265-285rwhp range with unported heads and that cam.

FWIW with bad lifters that had me basically making 5 more hp from 4k to 5k rpm with power dropping off at 5k and 28* timing I put down 258 rwhp and 280 ftbls on a 99* day with very high humidity. Now with that lifter issue resolved I am realistically looking for 275-300wrhp (at least I will be totally happy with those numbers) and I do not think I am being un realistic in that thinking from what I put down prior.

nmcgrawj · Jul 17, 2009

got the intake if u want it cheap....

final5-0 · Jul 17, 2009

Here are a few iron head based combos for you to look at

This is just some info I found on the net and I have no way of
knowing how each dyno pull was calibrated which means ...

Those done with a STD cal would produce higher results
than those with a SAE cal

Never the Less ... You can get some idea about things

Grady

revhead347 · Jul 17, 2009

If you just look at the flow data, ported cast GT40 heads flow only a fart better than ported E7 heads. I don't see it worth the effort to put these heads on without doing major machine work to them.

Kurt

sl03gt · Jul 17, 2009

Untouched, not a ton. You wouldn't really notice a difference until after 3500 rpm due to the larger valves and intake configuration. To make them flow like a set of aftermarkets you would have to put $500+ into them and have the lower ported. Edelbrock makes a set of heads now that sell for under $1000 that will outflow the gt40's. If you do go this route I would get the gt40's cleaned up, milled to 58 cc, back cut the valves, valve job of course, and blend the bowls. This would bump the compression which would improve torque and flow good at higher rpm.

final5-0 · Jul 18, 2009

sl03gt said:
Untouched, not a ton. You wouldn't really notice a difference until after 3500 rpm due to the larger valves and intake configuration. To make them flow like a set of aftermarkets you would have to put $500+ into them and have the lower ported. Edelbrock makes a set of heads now that sell for under $1000 that will outflow the gt40's. If you do go this route I would get the gt40's cleaned up, milled to 58 cc, back cut the valves, valve job of course, and blend the bowls. This would bump the compression which would improve torque and flow good at higher rpm.

See ... that is how it usually works out with the old OEM iron heads

By the time you go and do all that and lay out the cash

Just get some Aluminum heads with later technology and less weight

Grady

sl03gt · Jul 19, 2009

final5-0 said:
See ... that is how it usually works out with the old OEM iron heads

By the time you go and do all that and lay out the cash

Just get some Aluminum heads with later technology and less weight

Grady

Agreed, I'm sure there are quite a few people on hear,maybe not in the 94-95 but the 86-93 forums, that would tell you the same thing. $1000 into a set of gt-40's and the car ran great. Put on a set of Twisted Wedge heads and was adifferent car. There was a guy I used to know who had a 95 cobra. After all the bolt on's (gear, ignition, chip, pulleys, etc...) he had the car dyno'd at 270 rwhp area. Torque was in the 280 lb ft area. The car was fast in my book. Than after he got bored and made some money street racing he got some old school twisted wedge heads and put $500 into them also had the stock cobra gasket matched. On the rollers the car put down in the 320 rwhp area. Which is a pretty good gain, but more impressive was the fat torque curve that cam with it. The car made over 320 lb ft of torue at 3500 rpm! With the 3:73 gear tis thing was an animal. On drag radials the car went in the hih 12's in street trim. When the LS1 came out the car got an F cam and 150 hp shot of juice. A little rant but the point being, buy a set of aluminum heads, it will be well worth it. It will cost at least $1000 to make someGT40's flow any where near after market heads. They hav more overall flow giving a fatter torque curve.

revhead347 · Jul 20, 2009

final5-0 said:
See ... that is how it usually works out with the old OEM iron heads

By the time you go and do all that and lay out the cash

Just get some Aluminum heads with later technology and less weight

Grady

I have to be honest, I generally don't use out of the box heads anyway. Even if I buy a nice set of aftermarket aluminum heads, I'm not going to put them on a car until they have had some machine work done to them. You'd be amazed how much out of the box heads pick up with just a valve job. So, from my point of view, the machine work is the same cost anyway.

Kurt

Dino Dino Bambino · Jul 20, 2009

derrick2119 said:
Can anyone tell me how much difference these make over the stock 94 GT top end?
Thanks Derrick

Not enough IMO unless you're on a very tight budget. A 5.0 that's maxed out with basic bolt-ons (CAI, MAF, TB, pulleys, LT's, midpipe, catbacks) will put down about 235rwhp with the stock H/C/I while the same engine but with GT40 heads/intake will put down about 270. With GT40P heads you could reach 280.
You could get 260 just by porting the stock heads/intake but since there are so many better aftermarket aluminium heads and intakes out there, why bother? Save your pennies and get the AFR 165's or the Trick Flow TW heads instead, and match them up with either an Edelbrock Performer RPM II or Holley Systemax II intake plus a streetable performance cam.

derrick2119 · Jul 21, 2009

thanks decided to save up for a trick flow top end and go with a 347 stroker kit for the bottom

revhead347 · Jul 22, 2009

derrick2119 said:
thanks decided to save up for a trick flow top end and go with a 347 stroker kit for the bottom

Sounds like a solid plan.

Kurt

Cast GT 40 Heads and intake

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