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Old May 14th, 2009, 05:17 AM   #1
kj kyle
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Default 5.0 heads. who wants 25hp for free?

Im most likely going to be getting a v8 YJ here soon. it has a mustang 5.0 L in it bored .30 over, explorer intake, b303 cam, ford racing valve springs, bbk 65 mm throttle body, 70mm MAF, 24lb injectors, ceramic coated ford racing headers, and gt40p heads @ 10.5:1. (stock rotating assembly)

my question is.. I dont want to run premium fuel all the time as this will be my daily driver, and I am willing to take a slight loss on power. so what is the CC on these heads, and what heads should i put on it to drop the CR down to an 87-89 octane level? I would rather not tear the motor apart to install dish pistons

I DO NOT OWN THIS JEEP YET. THIS IS ASSUMING ALL THINGS GO TO PLAN.

but, If someone has a set of heads that would put me at the right CR, I would be willing to trade. I did some light reading, and most say these heads are good for about 25hp. please dont pummel me with offers. I need information before i make any decisions.

I grew up on small block chevy's so Im not familiar with all this ford stuff so bear with me.
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Old May 14th, 2009, 08:11 AM   #2
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if my numbers in my head are correct, gt40p heads suck because the exhaust holes are side by side, and therefore you have to get special headers or manifolds.

If you wanna go on the cheap, just double up the head gaskets, and call it a day.

If you are goona change the heads, just put sone on from a 351w, but you'll have to get bushings for the bolts since the 351w heads use 1/2 bolts and the 302's use 7/16

That should do ya
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Old May 14th, 2009, 08:28 AM   #3
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is a double head gasket really going to drop almost a point of compression ratio?

is that even safe? Ive never heard it done before...
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Old May 14th, 2009, 08:56 AM   #4
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dont double head gaskets unless you want a leak. thats just retarted.

if you dont want to use a higher grade fuel then a stock set of 4v 351w heads will work fine.


i personally love horsepower so i would keep them and just pay a touch more for fuel. midgrade should be fine in that motor.
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Old May 14th, 2009, 11:02 AM   #5
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unfortunatly premium is more than "a touch more" where i come from.

so if i get a set of 351w heads can i keep my ceramic coated headers?
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Old May 14th, 2009, 12:02 PM   #6
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I dont know what my CR is but i have a GT40P getup the motor is actually a 2000 explorer and I will be running 87

Say the timing is bumped up to 14* for 92 could he simply back it down to 10* stock for that motor and be able to run 87 without any problems
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Old May 14th, 2009, 04:41 PM   #7
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gt40 headers wont work with regular 351 heads
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Old May 14th, 2009, 09:30 PM   #8
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I've seen the double head gasket thing done, and seen it on shows and read about it in magazines. Dunno about longevity, but they were able to make quite a few dyno pulls that way.
gt40 and gt40p heads are very diffirent.
351w heads have offset exhaust bolts, just like 302 heads. gt40p heads are side by side.
so yeah, you will probably need diffirent headers.
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Old May 14th, 2009, 11:22 PM   #9
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maybe ill just break down and buy a set of dish pistons...
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Old May 15th, 2009, 02:43 PM   #10
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The major difference in the GT 40 P heads are the bigger valves and revised spark plug angles. It has nothing to do with "side by side what ever BS he was feeding you" Your 351w heads will be the exact same flow as any 302 head after 1973(ish) production date and you will gain nothing. Your GT40p heads will run on 87 octane just fine. Standard valve sizes are 1.78 intake and 1.46 exhaust, your gt40p heads have a 1.84 intake and 1.46 exhaust. People have put regular headers on gt40p heads, but they need to dent them further to have room for the spark plug. A set of shorties that can be bolted to the gt40p heads are about 150 and I believe are made by MAC.

The gt40p heads are nice heads if you gasket match the ports, and smooth out the runners and combustion chamber. They are good to .500" lift on your intake and exhaust cycles with standard valve springs and rockers.


And your 10.5 : 1 compression ratio is still within tolerance to run regular unleaded fuel.

Last edited by Never_Evil; May 15th, 2009 at 02:50 PM.
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Old May 15th, 2009, 09:30 PM   #11
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this is what I was talking about.

Mabye mine are just diffirent.
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Old May 15th, 2009, 11:50 PM   #12
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The gt40p heads are based on the e7 design only opened up, your gaskets appear to belong to a Ford Yates* racing head . The first pic I found of the gt40p head, the exhaust is a symmetrically even spacing with all bolt holes in one line. The second pic is the Yates heads, highly sought after and well worth the money if you can get them if horsepower is what you want.


* Ford Yates racing heads are found on stock cars and will out flow even the Cleveland heads while using the larger valves. Capable of supporting 1000 horses naturally aspirated.
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Old May 16th, 2009, 12:38 PM   #13
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If that motor has a stock bottom end with a replacement 30 over piston and the GT40p heads there is no way it has more than 9.3-1 compression unless somebody milled a ton off those heads.And by a ton I mean so much that the intake would have fitment issues.

Stock 5.0 pistons have about a 12 or 16cc dish and the heads have a 60- 61cc chamber.
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Old May 16th, 2009, 06:40 PM   #14
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heads are not milled any. he said aftermarket .30 over pistons.. didnt say the CCs. he did say they were flat top with valve relief.
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Old May 24th, 2009, 08:04 PM   #15
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I'll trade you for a set of 351w heads off of a 94 f150
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Old May 25th, 2009, 11:32 AM   #16
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Kyle, If you do get this engine, keep it all together and don't swap heads. The worst you will have to do is reset the timing for the lower octane gas. The only reason to lower your CR would be to add a blower to it.

Here is your sign from GOD... BUY IT BUY IT KEEP IT KEEP IT RUN IT RUN IT!!!!!!!
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Old May 29th, 2009, 12:34 AM   #17
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I have a fresh .030 306 shortblock with small dis pistons. brand new I will trade ya. if it is a roller mine is a 71 hi - nickle block
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Old July 10th, 2009, 02:42 PM   #18
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Quote:
Originally Posted by junk90xj View Post
dont double head gaskets unless you want a leak. thats just retarted.

if you dont want to use a higher grade fuel then a stock set of 4v 351w heads will work fine.


i personally love horsepower so i would keep them and just pay a touch more for fuel. midgrade should be fine in that motor.
Thank you for stating that before I could. Doubling up a head gasket is beyond Autistic dont ever do that.....

Last edited by 2000_WJ; July 10th, 2009 at 02:48 PM.
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Old July 19th, 2009, 09:20 AM   #19
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get it yet I have a new remanned set of 302 heads extra...
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