Help with custom pistons & compression ratio
Thread Starter
Joined: Jan 2002
Posts: 4,069
Likes: 74
From: Casselberry FL
Help with custom pistons & compression ratio Back in '04 I bought a used 1998 LS1 shortblock which contained Wiseco pistons. I just found out yesterday upon shortblock disassembly (turned a lifter) that since they don't have a number stamped on the piston head, they are not off-the-shelf pistons. They have valve reliefs and a funky small dome. I was told by the previous owner that they were ordered with the intent of nitrous use. We cannot find any numbers on the piston at all. I am picking up a used bare block to resolve the lifter bore damage.
I already have a new PatrickG cam and TSP heads which were ordered ***uming the pistons were normal 3.905" -2cc shelf pistons. These pistons did seem to be noisy. Are there quiet forged pistons?
The guy who installed the used motor, Whistler here, thinks they may be +6-+10cc, which would put me in the 12.4+ conmpression range.
What can I do to determine the piston volume so I can correct my DCR/SCR calculations? Would the piston ring grooves or type of rings be of concern?
Maybe I'd be better all around (well, not financially) to just order new pistons? If so, what specs? We have both 92 & 93 octane locally, and I was expecting to be in the low-mid 11's for compression.
Heads: TSP PRC 5.3L Stg 2.5, 2.02/1.575 valves
Chamber: 59cc
Gasket: Cometic .040
Cam: 227/235 .645/.650 110+2 LSK
Rods: Eagle 6.100", .927 wristpin
Thanks!
Jim
I already have a new PatrickG cam and TSP heads which were ordered ***uming the pistons were normal 3.905" -2cc shelf pistons. These pistons did seem to be noisy. Are there quiet forged pistons?
The guy who installed the used motor, Whistler here, thinks they may be +6-+10cc, which would put me in the 12.4+ conmpression range.
What can I do to determine the piston volume so I can correct my DCR/SCR calculations? Would the piston ring grooves or type of rings be of concern?
Maybe I'd be better all around (well, not financially) to just order new pistons? If so, what specs? We have both 92 & 93 octane locally, and I was expecting to be in the low-mid 11's for compression.
Heads: TSP PRC 5.3L Stg 2.5, 2.02/1.575 valves
Chamber: 59cc
Gasket: Cometic .040
Cam: 227/235 .645/.650 110+2 LSK
Rods: Eagle 6.100", .927 wristpin
Thanks!
Jim
Last edited by JimMueller; Jun 14, 2007 at 01:34 PM.
Thread Starter
Joined: Jan 2002
Posts: 4,069
Likes: 74
From: Casselberry FL
Results of finding off-the-shelf pistons for a 6.098" rod on a 3.905 bore/3.622 stroke:
JE Pistons: 194884 (-2cc, but .945 wristpin)
Diamond: Nothing
Wiseco: K366A05 (3.903 bore, -2.2cc), K398A07 (3.905 bore, -2.2cc) - writstpin info not listed
Mahle: Right wristpin or right rod length, but not both
Correct me if I'm wrong, but I either need a custom piston to work with these Eagle 6.1" rods, or I need new rods AND pistons, or I need to find a way to measure the piston volume on the current pistons and maybe I can re-use them if the volume is reasonable?
JE Pistons: 194884 (-2cc, but .945 wristpin)
Diamond: Nothing
Wiseco: K366A05 (3.903 bore, -2.2cc), K398A07 (3.905 bore, -2.2cc) - writstpin info not listed
Mahle: Right wristpin or right rod length, but not both
Correct me if I'm wrong, but I either need a custom piston to work with these Eagle 6.1" rods, or I need new rods AND pistons, or I need to find a way to measure the piston volume on the current pistons and maybe I can re-use them if the volume is reasonable?
Consult an engine builder in your area and they will be able to help you identify what you have. If all else fails and the dome is too much they can machine the dome off to work with your CC head you have.
TECH Regular
Joined: Feb 2006
Posts: 437
Likes: 2
From: Cleveland
Hey there, Brian from Wiseco here....maybe I can help. If you can give me the dome rise in thousandths, I should be able to get you a volume. We've got a LS1 dome and a LS6 dome that are a bit different, so a digital photo would help. let me know the name of the engine builder and maybe we can track it down through their account. email me at bnutter@wiseco.com
Thread Starter
Joined: Jan 2002
Posts: 4,069
Likes: 74
From: Casselberry FL
E-mail sent. For any others, the shop seems to recall it's an 8cc dome because the original owner wanted almost 12:1 compression and at that time there were limited stock pistons which would offer that.
I've found the Wiseco K398A07 (421g) for $505 without rings, Summit carries the matching 3905H ring set for $160. A custom Diamond 11502 (410g) with rings would be $805.88 direct from Diamond. So what am I getting from Diamond for the extra ~$150 other than saving 11g of mass? Is 11g significant?
I've found the Wiseco K398A07 (421g) for $505 without rings, Summit carries the matching 3905H ring set for $160. A custom Diamond 11502 (410g) with rings would be $805.88 direct from Diamond. So what am I getting from Diamond for the extra ~$150 other than saving 11g of mass? Is 11g significant?
Last edited by JimMueller; Jun 15, 2007 at 08:57 AM.
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Thread Starter
Joined: Jan 2002
Posts: 4,069
Likes: 74
From: Casselberry FL
I guess I've decided upon the Wiseco K398A07. The ring set they recommend is not file-fit and the gaps would be ~.23. Total Seal apparently has a bad reputation on this board for sealing. So which brand/model piston ring kit do I order?
Wiseco recommends .004 per inch on the top ring, and .0045-.005 on the second ring. So I'd want about .016 on the first ring and about .019 on the second ring. The rings are 1/16, 1/16, and 3/16, btw.
Wiseco recommends .004 per inch on the top ring, and .0045-.005 on the second ring. So I'd want about .016 on the first ring and about .019 on the second ring. The rings are 1/16, 1/16, and 3/16, btw.
Last edited by JimMueller; Jun 15, 2007 at 03:06 PM.
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Your Total Seal Rings should be just fine. I have been running them for over 10 years now without a single problem or failure. I think what problem's people have run into with them has alot to do with the surface finish left onto the cylinder wall. If it is left with too ruff of a surface finish onto it, it will rip the the moly face right off of the piston rings.
