5/64 vs. 1.5mm Piston Rings & How much to shave GT40 heads for 10:1 compression ?

waid302

Member
Sep 25, 2012
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I want raise my compression from 9:1 to 10:1 in my 96 Explorer 5.0 with GT40 heads which is for street use only. I don't mind using premium fuel in my carburated 64 Falcon. I will be taking the block to the machine shop and have it bored 0.030 over and deck the block. I will also take the heads to the machine shop for new valve guides and a valve job. The machine shop should know how much material to remove to raise the compression to 10:1. I believe the GT40 heads are 65cc. In 1996, Ford switched over to thinner metric piston rings (for lower friction?) and for my Explorer Engine, I think I can use either the standard 5/64" or the 1.5mm piston ring pistons. All 302 up to 1995 used the 5/64" piston rings. The metric Explorer piston with 1.5mm piston ring has Compression Distance of 1.595. The standard piston with 5/64" piston ring has Compression Distance of 1.599.

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Speed-Pro Hypereutectic Piston and Ring Kits (5/64" x 5/64" x 3/16") $170:
Speed-Pro Piston and Ring Kits Z8KH273CP30 - SummitRacing.com

Speed-Pro Hypereutectic Pistons (1.50mm x 1.50mm x 4.00mm) $118:
Speed-Pro Hypereutectic Pistons ZH816CP30 - SummitRacing.com
+
Sealed Power Plasma-Moly Piston Ring Sets ZE458K30 $71:
Sealed Power Plasma-Moly Piston Ring Sets ZE458K30 - SummitRacing.com

TFS Cam: TFS-51403001 - Duration at 050 inch Lift: 221 int./225 exh. Valve Lift with Factory Rocker Arm Ratio: 0.499 int./0.510 exh.:
Trick Flow® Track Max® Hydraulic Roller Camshafts for Ford 5.0L TFS-51403001 - SummitRacing.com

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Can anyone please tell me how much material needs to be removed from the GT40 heads ?

Any issues with valve clearance using the Speed-Pro Hypereutectic Piston and Ring Kits Z8KH273CP30 with TFS Cam using 1.6 Rockers ?

Is it going to make any difference if I use the pistons with the 5/64" or the 1.5mm piston rings ?

The 5/64" version is cheaper since its available as Pistons and Rings set and was used on all 302 except 96+.

Thanks

Waid
 
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gearheadboy

Advanced Member
Jan 15, 2003
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It really doesn't matter in my opinion. Thinner rings are supposed to be better at higher RPM. I will tell you that hypereutectics scare me some. If they get hot and the rings seal real well they will pop the top off. Some guys choose not to run total seal rings with them and some don't even run a top ring at all. I'm no expert on them.
 

reldla1996

Member
May 4, 2011
356
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Dayton, Ohio
The hyper pistons expand less than forged pistons, so can fit tighter to the bores, which is good. On the down side, hyper pistons are less forgiving on lean mixtures, and not as strong. If you're planning a moderate street engine, say 300hp from a 302, the hyper pistons will work fine. If you plan to push the performance envelope, or plan on a s/c, the forged pistons are a better choice. The 1.5mm rings are roughly 30 percent thinner, and therefore have lower friction than the 5/64, which is why they switched to them in the newer engines. Your choice.
 

84Ttop

They make new pistons every day, so why worry?
Mod Dude
Jul 2, 2009
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IMO, there is no substitute for actually checking piston to valve clearance. No two blocks or heads for that matter have the same deck height it also depends on the thickness of the head gasket. Just because that combo had enough clearance in someone's motor, that doesn't mean that it will clear in yours. Do your self a favor and just simply check it.
 

gearheadboy

Advanced Member
Jan 15, 2003
1,439
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Greencastle Pa
IMO, there is no substitute for actually checking piston to valve clearance. No two blocks or heads for that matter have the same deck height it also depends on the thickness of the head gasket. Just because that combo had enough clearance in someone's motor, that doesn't mean that it will clear in yours. Do your self a favor and just simply check it.
Did you have your coffee this morning? I read it 2x and I can't see anything about piston to valve clearance. Or were you just stating a fact? LOL.
 

waid302

Member
Sep 25, 2012
66
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39
Once I go 0.030” over, do I need to have my rotating assembly re-balanced ?

Is it safe to assume that the rotating assembly with 1.5mm x 1.5mm x 4.0mm rings is "lighter" than the 5/64" ?

I would think it would balance out better with 1.5mm rings & pistons which is what my motor came with originally.

The old 302 pistons & rings kit is $170. For 96+ 302’s with 1.5mm rings, there is no kit and must purchase pistons and rings separate but he cost is only $20 more at $190.

My Mustang book lists the piston-to-bore clearance for a 1979-1987 to be 0.0018"-0.0026" and for 1988 on, the book lists 0.003" to 0.0038" (forged pistons ?). For the 96+ 303, the piston-to-bore clearance is tighter at 0.0012"-0.002".

Waid
 

waid302

Member
Sep 25, 2012
66
1
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39
Instead of going .030 over, I can go .020 over.

If I go .020 over, which head gasket do I use?

Thanks

Waid
 

gearheadboy

Advanced Member
Jan 15, 2003
1,439
184
74
45
Greencastle Pa
Once I go 0.030” over, do I need to have my rotating assembly re-balanced ?

Is it safe to assume that the rotating assembly with 1.5mm x 1.5mm x 4.0mm rings is "lighter" than the 5/64" ?

I would think it would balance out better with 1.5mm rings & pistons which is what my motor came with originally.

The old 302 pistons & rings kit is $170. For 96+ 302’s with 1.5mm rings, there is no kit and must purchase pistons and rings separate but he cost is only $20 more at $190.

My Mustang book lists the piston-to-bore clearance for a 1979-1987 to be 0.0018"-0.0026" and for 1988 on, the book lists 0.003" to 0.0038" (forged pistons ?). For the 96+ 303, the piston-to-bore clearance is tighter at 0.0012"-0.002".

Waid
Any time you change pistons you need to re-balance. The head gasket is the same.
 

waid302

Member
Sep 25, 2012
66
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I am going to get the 0.020 metric pistons.

I just checked Federal-Mogul's website and the weight is same for stock pistons, 0.020, 0.030, 0.040, 0.060 over pistons. All are listed at 731 grams!!!

Any good particular head gasket you guys recomend?

There is bunch of them on Summit.

Thanks


Waid