engine builders, inside... engine math help!
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From: Hinesville, GA USA
Car: '86 IROC-Z/'94 Z28
Engine: 350 LT1/382 LT1
Transmission: 4L60-E/T-56
Axle/Gears: 3.45/3.42 (soon 4.10)
engine builders, inside... engine math help!
OK. I'm planning on upgrading my crate motor while it's apart. At the same time, I'm considering upgrading from coated hyperutectics to lightweight forgings. My problem is I don't have the $$$ for a custom set of pistons, but I want to be able to run forgings. The shortblock has also been prepped and tanked, all that jazz. So here's my dimemma...
Stock deck block, 9.025"
3.8" forged crank
5.7" connecting rods, I also have forged 6.0" rods available
pistons are 0.029" in the hole at TDC
piston compression height is unknown. Even GM doesn't seem to know
I thought that maybe a 396 piston would work, but I'm not great at engine building math and I don't wanna guess. Can anyone help me out, if you know of any type of pistons that may work? If worst comes to worst, I'll just use the stock pistons and put my money into my 409.
Stock deck block, 9.025"
3.8" forged crank
5.7" connecting rods, I also have forged 6.0" rods available
pistons are 0.029" in the hole at TDC
piston compression height is unknown. Even GM doesn't seem to know
I thought that maybe a 396 piston would work, but I'm not great at engine building math and I don't wanna guess. Can anyone help me out, if you know of any type of pistons that may work? If worst comes to worst, I'll just use the stock pistons and put my money into my 409.
Thread Starter
Senior Member
iTrader: (2)
Joined: Feb 2001
Posts: 938
Likes: 1
From: Hinesville, GA USA
Car: '86 IROC-Z/'94 Z28
Engine: 350 LT1/382 LT1
Transmission: 4L60-E/T-56
Axle/Gears: 3.45/3.42 (soon 4.10)
the motor is externally balanced from what I can see. It has a counterweight on the damper and it came with the coated hyperutectics and studded 5.7" PM rods from GM. The crank is made by Cola. The size of the weight on the flexplate is the exact same as the one one a regular 1 pc. RMS 350, and I see alot more metal than normal has been removed out of the rearmost counterweight. This leads me to believe that the motor is balanced more in the damper and crank to make the use of a regular flexplate possible. This is a ZZ383 shortblock that SDPC sells. I was fortunate enough to get it for free 
Love having friends at a dealership...
I figured I could lengthen the rod without clearance issues, just not shorten it.
Love having friends at a dealership...I figured I could lengthen the rod without clearance issues, just not shorten it.
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Joined: Apr 2002
Posts: 232
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From: N. Illinois
if my math is correct you have a 1.396" compression height. anybody want to double check me. here is what I did:
9.025 (if this is actual, I'm not sure, can be inconsistent)
-0.029
=8.996 (actual height if deck height is correct)
8.996-1.9 (half of stroke)-5.7 (rod length)=1.396"
it is late and I may be off but unless I have my head up my ... then this should be it. it sounds like a custom make to me just because the stroke.
with 6.0 rods it would be 1.096" and that definately sounds like a custom job.
9.025 (if this is actual, I'm not sure, can be inconsistent)
-0.029
=8.996 (actual height if deck height is correct)
8.996-1.9 (half of stroke)-5.7 (rod length)=1.396"
it is late and I may be off but unless I have my head up my ... then this should be it. it sounds like a custom make to me just because the stroke.
with 6.0 rods it would be 1.096" and that definately sounds like a custom job.
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