Summit Pro LS Piston and Rod Kits compression math wrong? - It was right I was wrong.
#1
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I plan on purchasing summits Pro LS Piston and Rod kit. I was researching and mathing out my compression ratios. It appears to me that Summits advertised compression rations are off.
https://www.summitracing.com/parts/sum-pr36l9037 - Pro LS 4340 Piston and Rod Kit, 347 Cid., 3.903 bore, 3.622 stroke, 6.125 rod, 7cc dish,
Summit site - 9.7:1 @ 65cc - I get 10.35:1
Summit site - 9.4:1 @ 68cc - I get 10.00:1
I am missing something?
https://www.summitracing.com/parts/sum-pr36l9037 - Pro LS 4340 Piston and Rod Kit, 347 Cid., 3.903 bore, 3.622 stroke, 6.125 rod, 7cc dish,
Summit site - 9.7:1 @ 65cc - I get 10.35:1
Summit site - 9.4:1 @ 68cc - I get 10.00:1
I am missing something?
Last edited by matt1289; 03-28-2020 at 08:47 AM.
#2
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You didn't figure the dish. I just used Summit's compression calculator, and while my numbers were not exact to these, figuring w/wo the dish came close
#3
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The better CR calculators ask the bore dia of the head gasket. The head gasket bore isn’t necessarily the same as the cyl bore.
The other thing not always specified by the piston manufacturer is deck height. Stock pistons protrude approx .007”.
I’m using Wiseco turbo pistons and verified they are 0 deck.
I took the time to CC the heads and valve reliefs, measure the deck height and run the numbers on my L33 5.3.
Ended up at 9.3:1. Wiseco said 9.75:1.
The other thing not always specified by the piston manufacturer is deck height. Stock pistons protrude approx .007”.
I’m using Wiseco turbo pistons and verified they are 0 deck.
I took the time to CC the heads and valve reliefs, measure the deck height and run the numbers on my L33 5.3.
Ended up at 9.3:1. Wiseco said 9.75:1.
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DualQuadDave (01-07-2024)
#4
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I did account for that. I am using the excel compression calculator here - https://ls1tech.com/forums/generatio...alculator.html
#5
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I did account for that. I am using the excel compression calculator here - https://ls1tech.com/forums/generatio...alculator.html
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I plan on purchasing summits Pro LS Piston and Rod kit. I was researching and mathing out my compression ratios. It appears to me that Summits advertised compression rations are off.
https://www.summitracing.com/parts/sum-pr36l9037 - Pro LS 4340 Piston and Rod Kit, 347 Cid., 3.903 bore, 3.622 stroke, 6.125 rod, 7cc dish,
Summit site - 9.7:1 @ 65cc - I get 10.35:1
Summit site - 9.4:1 @ 68cc - I get 10.00:1
I am missing something?
https://www.summitracing.com/parts/sum-pr36l9037 - Pro LS 4340 Piston and Rod Kit, 347 Cid., 3.903 bore, 3.622 stroke, 6.125 rod, 7cc dish,
Summit site - 9.7:1 @ 65cc - I get 10.35:1
Summit site - 9.4:1 @ 68cc - I get 10.00:1
I am missing something?
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#10
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Looks like to me using the compress spread sheet they are using 6.098 rod lengths vs the rod length that comes with the Summit Pro LS rod and piston package of 6.125. So they are in fact advertised incorrect.
I don't really know how much 0.6 difference matters but I do plan to run a Procharger. With my heads using that piston and rod kit I will be at 10.23:1. I think that will be fine for 7-8 lbs of boost on E85.
I don't really know how much 0.6 difference matters but I do plan to run a Procharger. With my heads using that piston and rod kit I will be at 10.23:1. I think that will be fine for 7-8 lbs of boost on E85.
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All Pro LS pistons are advertised with .045 Piston to head clearance factored in. The pistons are targed to be .005 in the hole at 9.240. The reason we went .005 down is we've found some iron blocks as low as 9.230 from the factory -which could get some people in trouble in the ran a taller piston. We also have customers that deck blocks or run .040 gaskets etc., so we are cautious on height.
#13
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Then set the head gasket thickness at .040", which should get you the same .045" quench that Summit uses. Your number will be a little higher, mostly because the spreadsheet is hot garbage and doesn't consider the head gasket bore in it's calculations. The calculations use the cylinder bore diameter, but the head gasket bore will be a litttle larger than the bore itself so there is extra volume not being accounted for and therefore contributes to a higher number.
IMO, delete the spreadsheet from your computer. Use an online calculator, like the one from Wallace Racing, and forget that spreadsheet even exists.
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DualQuadDave (01-07-2024)
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One thing about calculating with the gasket o.d. is a 4.100 gasket at .045 thick on a 4.000 bore amounts to .028 cc. It is something, but there are other factors as simple as the thermostat temperature and plug heat range that can get us in the weeds real quick.
#16
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Thread digging here....
i'm building a 6.2 stroker & had the same issue of the compression calculators not coming up with the Summit advertised Compression Ratio.
What I found is that nearly no one accounts for the first compression ring land height. I was coming up with anything from 13.5 - 13:1 CR until I found the calculator on Diamond Piston's website. When I entered the same exact info in addition to the top ring height, the resulting CR was the same as Summit's advertised.
i'm building a 6.2 stroker & had the same issue of the compression calculators not coming up with the Summit advertised Compression Ratio.
What I found is that nearly no one accounts for the first compression ring land height. I was coming up with anything from 13.5 - 13:1 CR until I found the calculator on Diamond Piston's website. When I entered the same exact info in addition to the top ring height, the resulting CR was the same as Summit's advertised.
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DualQuadDave (01-07-2024)
#17
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Thread digging here....
i'm building a 6.2 stroker & had the same issue of the compression calculators not coming up with the Summit advertised Compression Ratio.
What I found is that nearly no one accounts for the first compression ring land height. I was coming up with anything from 13.5 - 13:1 CR until I found the calculator on Diamond Piston's website. When I entered the same exact info in addition to the top ring height, the resulting CR was the same as Summit's advertised.
i'm building a 6.2 stroker & had the same issue of the compression calculators not coming up with the Summit advertised Compression Ratio.
What I found is that nearly no one accounts for the first compression ring land height. I was coming up with anything from 13.5 - 13:1 CR until I found the calculator on Diamond Piston's website. When I entered the same exact info in addition to the top ring height, the resulting CR was the same as Summit's advertised.
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Old Buzzard (01-09-2024)
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Smokey was DA MAN!!!
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Che70velle (01-07-2024)