Optimal compression ratio for an LT1
01-15-2004, 11:32 AM
#1
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Optimal compression ratio for an LT1
I have a completely stock bottom end and I was curious what is the highest yet safest compression ratio you can run on 93-94 octane fuel in an lt1? I am getting the trick flow heads and milling them down to accomplish the raised compression, would you advise against this? The gasket will be .039"
The heads are a 61cc combustion chamber (not 64cc like their site and summit advertises)
These are the specs on the AFR heads so i would assume it wouldnt be much different
Angle Mill .008” per cc
Flat Mill .006” per cc
To attain getting 54cc I would have to mill the heads aprox .060" and with that much I will probably have to machine the intake anyways so why not go with a little higher c/r?
BTW: the heads have a 3/4" deck
The heads are a 61cc combustion chamber (not 64cc like their site and summit advertises)
These are the specs on the AFR heads so i would assume it wouldnt be much different
Angle Mill .008” per cc
Flat Mill .006” per cc
To attain getting 54cc I would have to mill the heads aprox .060" and with that much I will probably have to machine the intake anyways so why not go with a little higher c/r?
BTW: the heads have a 3/4" deck
01-15-2004, 12:14 PM
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Stock LT1s run 10.5:1 and LT4s run 10.8:1. You could try 11:1 since you're porting the heads and have exhaust it should cut down on tendency to detonate. But I wouldn't go over that. My engine has done just fine on 87 before so you should be able to raise the bar a little without any probs...
If you're planning on boost or juice in the future I would head in the other direction, though, and drop it some...
Keep in mind that raising the compression will make everything a little more sensitive- if you have a bad sensor somewhere it will make it more likely to detonate than stock...
Good luck. I'm sure you'll be able to tell what your engine likes and whether or not you've crossed the line...
If you're planning on boost or juice in the future I would head in the other direction, though, and drop it some...
Keep in mind that raising the compression will make everything a little more sensitive- if you have a bad sensor somewhere it will make it more likely to detonate than stock...
Good luck. I'm sure you'll be able to tell what your engine likes and whether or not you've crossed the line...
01-15-2004, 01:34 PM
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I am going to use the 230/236 cam on a 112 lsa, a .039" head gasket with a 4.125 bore, the advertised intake duration on the cam at .006" is 282. How close am I able to get to the recommended maximum of 8.5 DCR without detonating on 93? Assuming good timing as well.
Originally posted by rskrause
Depends on the cam you plan to use. What are your cam specs?
Rich Krause
Depends on the cam you plan to use. What are your cam specs?
Rich Krause
01-15-2004, 01:47 PM
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I have 11.86:1 compression on the stock bottom end. No knock retard at all with 92 octane. My heads were milled down to 50.5cc chambers and I use Felpro .039" heads gaskets. I use a GM847 camshaft.
01-15-2004, 02:08 PM
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Good to know, it seems like 12:1 is the furthest most people dare to go, with similar setups.
Originally posted by Grease
I have 11.86:1 compression on the stock bottom end. No knock retard at all with 92 octane. My heads were milled down to 50.5cc chambers and I use Felpro .039" heads gaskets. I use a GM847 camshaft.
I have 11.86:1 compression on the stock bottom end. No knock retard at all with 92 octane. My heads were milled down to 50.5cc chambers and I use Felpro .039" heads gaskets. I use a GM847 camshaft.
Last edited by Rodrigues; 01-15-2004 at 02:12 PM.
01-15-2004, 02:19 PM
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I am going to use the 230/236 cam on a 112 lsa, a .039" head gasket with a 4.125 bore.
To a poind the bigger cam you use the more compression your motor will take as the increased overlap bleeds off compression.
01-15-2004, 02:22 PM
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Originally posted by RE AND CHERYL
You might want to check, I don't think you can bore an LT1 block that far.
To a poind the bigger cam you use the more compression your motor will take as the increased overlap bleeds off compression.
You might want to check, I don't think you can bore an LT1 block that far.
To a poind the bigger cam you use the more compression your motor will take as the increased overlap bleeds off compression.
01-15-2004, 02:23 PM
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Originally posted by Grease
I have 11.86:1 compression on the stock bottom end. No knock retard at all with 92 octane. My heads were milled down to 50.5cc chambers and I use Felpro .039" heads gaskets. I use a GM847 camshaft.
I have 11.86:1 compression on the stock bottom end. No knock retard at all with 92 octane. My heads were milled down to 50.5cc chambers and I use Felpro .039" heads gaskets. I use a GM847 camshaft.
01-15-2004, 02:40 PM
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Read a bit closer 
"a .039" head gasket, WITH a 4.125 bore"
Relating to the subject of mis-reading posts Jon Adis sent me this
Aoccdrnig to a rscheearch at Cmabrigde Uinervtisy, it
deosn't mttaer in waht oredr the ltteers in a wrod
are, the olny iprmoetnt tihng is taht the frist and
lsat ltteer be at the rghit pclae. The rset can be a
total mses and you can sitll raed it wouthit porbelm.
Tihs is bcuseae the huamn mnid deos not raed ervey
lteter by istlef, but the wrod as a wlohe
"a .039" head gasket, WITH a 4.125 bore"
Originally posted by RE AND CHERYL
You might want to check, I don't think you can bore an LT1 block that far.
To a poind the bigger cam you use the more compression your motor will take as the increased overlap bleeds off compression.
You might want to check, I don't think you can bore an LT1 block that far.
To a poind the bigger cam you use the more compression your motor will take as the increased overlap bleeds off compression.
Aoccdrnig to a rscheearch at Cmabrigde Uinervtisy, it
deosn't mttaer in waht oredr the ltteers in a wrod
are, the olny iprmoetnt tihng is taht the frist and
lsat ltteer be at the rghit pclae. The rset can be a
total mses and you can sitll raed it wouthit porbelm.
Tihs is bcuseae the huamn mnid deos not raed ervey
lteter by istlef, but the wrod as a wlohe
I got an email with that in it about 9months ago. Cool stuff.
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