Quench and compression on.98 ls1
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Quench and compression on.98 ls1 I'm trying to figure out quench for my 98 is block. I have 243 heads milled .006, before I got them, so that should be around 63.5 c.c. Chambers. I had the block milled about .003 just to make sure my head gaskets seal good. From what I read the 98 aluminum blocks are..006 to .010 it the home stock so I'm guessing once assembled I'll be .009 to .013 it the hole. How much would that number change once warmed up? I'd like to run the .051 gaskets to keep compression around 11.2. With those gaskets I'd be at about .043 to .040 quench cold but what about warm. And does compression lower as the deck grows? Also I have the weiseco pro tru piston with 4cc dome as that was all o I couI'd find forged for the 3.903 bore. Could I have the combustion chambers opened up a cc or have the dome cut down? I thought about doing .060 gaskets but then my quench would be around .050 and I thought that may be too much.Just looking for the best quench and compression for pump gas. This is going in a.96 impala every day driver. Thanks in advance.
Last edited by Wyteboii86; Apr 5, 2018 at 05:24 AM.
Your calculations are about right. But until you actually put it together and measure everything, they'll just be calculations that are about right.
If you need to, you could either open the chamber or shave the piston, either one will work. There are some that believe keeping the combustion up in head will be more efficient. So reshaping the chamber would be better. Others believe it doesn't matter. So pick your poison.
In either case, you have to choose whatever will give you the most consistent results. You need to do the exact same thing 8 times. Changing chamber design could change swirl and efficiency. And if you change the pistons, you'll need to rebalance everything. Again, pick your poison.
If you need to, you could either open the chamber or shave the piston, either one will work. There are some that believe keeping the combustion up in head will be more efficient. So reshaping the chamber would be better. Others believe it doesn't matter. So pick your poison.
In either case, you have to choose whatever will give you the most consistent results. You need to do the exact same thing 8 times. Changing chamber design could change swirl and efficiency. And if you change the pistons, you'll need to rebalance everything. Again, pick your poison.
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Thanks. Both makes sense. Yeah deff all just estimates for now. I'm not going to get any gaskets until I actually measure the deck clearance. Is there a solid number for how much the deck clearance changes when warned up on the aluminum blocks. And say it goes from .013 out the hole to .006 when warm... Would I calculate my target compression and quench based on the out warm .006?
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I just feel like I fucked myself by getting the block skimmed. If the pistons were originally .007 to .010 it the hole. Then got about .003 cut off plus new pistons are gonna stick out or another .007 I'm at damn near .017 to .020 it the hole. So with a .060 head gasket that's around .040-.043 quench but still 10.5 compression which is probably too much. Maybe I'm over thinking it lol.
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Squish Distance Hi WBoy, I like to use a .030"-.032" squish distance.
This is based on my Forged Rod, Forged Crankshaft, .0022" Main/.0032" Rod bearing clearance.
The Piston is a RaceTech, AutoTech grade with low wall clearance. (little rock)
MAX RPM limited by ECU of 7200. (common MAX 6500)
The engine balance is NOT "0" but close to 2% OVER.
The Pin Wall is .180"
The piston weight is UNDER 420
Your case is NOT well stated, your ARE NOT PROVIDING the REQUIRED information.
The SHOP who did the "deck" provided a MEASUREMENT ?
YOUR Piston C/D is 1.335", good to know.
What is the Rod Length ?
What is your piston Alloy/wall clearance ?
PLEASE supply the requested information.
MEASURE the Brown Hair on your head, the distance difference you speak about is ONLY a few hairs!
YOUR good tech about AL crankcase expansion IS CORRECT, just REMEMBER to bring the engine up to operation temperature BEFORE you "rev out".
MOST here could then give the correct ADVICE for a SAFE Squish Distance.
Lance
This is based on my Forged Rod, Forged Crankshaft, .0022" Main/.0032" Rod bearing clearance.
The Piston is a RaceTech, AutoTech grade with low wall clearance. (little rock)
MAX RPM limited by ECU of 7200. (common MAX 6500)
The engine balance is NOT "0" but close to 2% OVER.
The Pin Wall is .180"
The piston weight is UNDER 420
Your case is NOT well stated, your ARE NOT PROVIDING the REQUIRED information.
The SHOP who did the "deck" provided a MEASUREMENT ?
YOUR Piston C/D is 1.335", good to know.
What is the Rod Length ?
What is your piston Alloy/wall clearance ?
PLEASE supply the requested information.
MEASURE the Brown Hair on your head, the distance difference you speak about is ONLY a few hairs!
YOUR good tech about AL crankcase expansion IS CORRECT, just REMEMBER to bring the engine up to operation temperature BEFORE you "rev out".
MOST here could then give the correct ADVICE for a SAFE Squish Distance.
Lance
Thread Starter
Teching In
Joined: Apr 2018
Posts: 37
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Hi WBoy, I like to use a .030"-.032" squish distance.
This is based on my Forged Rod, Forged Crankshaft, .0022" Main/.0032" Rod bearing clearance.
The Piston is a RaceTech, AutoTech grade with low wall clearance. (little rock)
MAX RPM limited by ECU of 7200. (common MAX 6500)
The engine balance is NOT "0" but close to 2% OVER.
The Pin Wall is .180"
The piston weight is UNDER 420
Your case is NOT well stated, your ARE NOT PROVIDING the REQUIRED information.
The SHOP who did the "deck" provided a MEASUREMENT ?
YOUR Piston C/D is 1.335", good to know.
What is the Rod Length ?
What is your piston Alloy/wall clearance ?
PLEASE supply the requested information.
MEASURE the Brown Hair on your head, the distance difference you speak about is ONLY a few hairs!
YOUR good tech about AL crankcase expansion IS CORRECT, just REMEMBER to bring the engine up to operation temperature BEFORE you "rev out".
MOST here could then give the correct ADVICE for a SAFE Squish Distance.
Lance
This is based on my Forged Rod, Forged Crankshaft, .0022" Main/.0032" Rod bearing clearance.
The Piston is a RaceTech, AutoTech grade with low wall clearance. (little rock)
MAX RPM limited by ECU of 7200. (common MAX 6500)
The engine balance is NOT "0" but close to 2% OVER.
The Pin Wall is .180"
The piston weight is UNDER 420
Your case is NOT well stated, your ARE NOT PROVIDING the REQUIRED information.
The SHOP who did the "deck" provided a MEASUREMENT ?
YOUR Piston C/D is 1.335", good to know.
What is the Rod Length ?
What is your piston Alloy/wall clearance ?
PLEASE supply the requested information.
MEASURE the Brown Hair on your head, the distance difference you speak about is ONLY a few hairs!
YOUR good tech about AL crankcase expansion IS CORRECT, just REMEMBER to bring the engine up to operation temperature BEFORE you "rev out".
MOST here could then give the correct ADVICE for a SAFE Squish Distance.
Lance
Deck Measurement Method Hi WBoy, the QUALITY machine shop WILL provide a Deck Height measurement when the block is machined.
The is easy to read, just place a straight edge in the main housing bore, measure from the deck to that edge, Harbor Fright 12" Caliper I use, the ADD 1/2 the Housing Bore Diameter.
OK, a cast piston has no Rock, at the least very little.
Does this piston use an offset piston bore position ?
I WOULD NOT reduce the piston dome.
I would use a .051" HG to increase Squish, good for knock resistance.
YOUR D/D requirement SHOULD use a WIDE L/C camshaft.
THUS lets "talk" cams as a "wide" cam LOVES compression.
Lance
The is easy to read, just place a straight edge in the main housing bore, measure from the deck to that edge, Harbor Fright 12" Caliper I use, the ADD 1/2 the Housing Bore Diameter.
OK, a cast piston has no Rock, at the least very little.
Does this piston use an offset piston bore position ?
I WOULD NOT reduce the piston dome.
I would use a .051" HG to increase Squish, good for knock resistance.
YOUR D/D requirement SHOULD use a WIDE L/C camshaft.
THUS lets "talk" cams as a "wide" cam LOVES compression.
Lance
TECH Senior Member
Joined: Feb 2009
Posts: 5,445
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assemble the short block and measure everything ,these LS engines seem to like static compression .there many Ls head gaskets available to adjust your static compression . you can control dynamic compression with the right cam event timing .figure out which way is more affordable for you project .