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05-20-2009, 10:34 PM
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#1
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I, Vettezuki
Join Date: Feb 2006
Posts: 14,754
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Max Compression Ratio for NA LSx Motors on E85?
So, if they make E85 more readily available in CA, I'm tempted to make my lil' ole 346 a forged 383, bump the cam one size up and crank up the CR as far as I dare.
E85 seems to vary in Octane rating between 100-105. It also has wonderful cooling effects being 85% alcohol and all.
So, who can calculate a highest safe potential CR. I was thinking at least 13:1, but maybe 14:1. 
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05-21-2009, 09:30 AM
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#2
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Fast & Filthy
Join Date: Jun 2008
Posts: 3,840
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Quote:
Originally Posted by Vettezuki
So, if they make E85 more readily available in CA, I'm tempted to make my lil' ole 346 a forged 383, bump the cam one size up and crank up the CR as far as I dare.
E85 seems to vary in Octane rating between 100-105. It also has wonderful cooling effects being 85% alcohol and all.
So, who can calculate a highest safe potential CR. I was thinking at least 13:1, but maybe 14:1. |
You won't be able to predict the exact compression ratio that you can use. There are a lot of other things to consider such as cam specs, combustion chamber design, timing, etc. I can tell you that with 100 octane race fuel I’m able to run 12.25:1 compression on the Chevelle with 40° total timing with a cam that has a .623 lift, 242° @ .050 on a 110° lobe separation with an aluminum head without detonation. I also know that I’m right at the edge from detonating because I’ve tried mixing pump gas and race fuel for less octane and the car detonated. If I were to run E85 I think I could get away with a little more compression (12.5:1 or so) with a 112 lobe separation and still not detonate. However, I do think I would be right at the edge but that’s just my opinion I do not know for sure.
I'm not sure what design the heads you have are but I've heard that the LS6 combustion chamber design is great so you might be able to get away with 13:1 if your heads have the same design. |
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05-21-2009, 11:10 AM
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#3
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I, Vettezuki
Join Date: Feb 2006
Posts: 14,754
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Is there any reason port injection vs. carburation would make a difference?
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05-21-2009, 11:50 AM
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#4
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Fast & Filthy
Join Date: Jun 2008
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Quote:
Originally Posted by Vettezuki
Is there any reason port injection vs. carburation would make a difference?
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I don't think it would make a difference as long as both were properly tuned. |
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05-21-2009, 12:43 PM
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#5
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I, Vettezuki
Join Date: Feb 2006
Posts: 14,754
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What's the most CR those Cometic gaskets can drop? Maybe something like targeting 13.5:1 as a start place, then dropping if necessary would be a good strategy.
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05-21-2009, 03:09 PM
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#6
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Fast & Filthy
Join Date: Jun 2008
Posts: 3,840
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I ran these on Comp Cams Camquest dyno program. I used the same setting and just changed the compression from 12:1 to 13:1. The difference was about 15 more hp and 10 more tq. The average differences were only about 4hp and 4 tq. I'm not sure it would be worth adding the extra compression unless you were going to be installing a huge cam and porting the crap out of the intake and heads. Here's the links to the graphs.
12:1
13:1 |
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05-21-2009, 04:08 PM
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#7
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I, Vettezuki
Join Date: Feb 2006
Posts: 14,754
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Quote:
Originally Posted by 94cobra69ss396
I ran these on Comp Cams Camquest dyno program. I used the same setting and just changed the compression from 12:1 to 13:1. The difference was about 15 more hp and 10 more tq. The average differences were only about 4hp and 4 tq. I'm not sure it would be worth adding the extra compression unless you were going to be installing a huge cam and porting the crap out of the intake and heads. Here's the links to the graphs.
12:1
13:1 |
Does it allow you to select E85 for fuel and dial-in various ignition curves? But I get the point. Somehow I would have expected the toruqe/hp to be more different between 12:1 and 13:1 all other things being equal, though it was just a hunch.
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05-21-2009, 04:14 PM
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#8
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Fast & Filthy
Join Date: Jun 2008
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Quote:
Originally Posted by Vettezuki
Does it allow you to select E85 for fuel and dial-in various ignition curves? But I get the point. Somehow I would have expected the toruqe/hp to be more different between 12:1 and 13:1 all other things being equal, though it was just a hunch.
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It doesn't. There is such a thing as having too much compression. |
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05-21-2009, 04:24 PM
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#9
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I, Vettezuki
Join Date: Feb 2006
Posts: 14,754
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Quote:
Originally Posted by 94cobra69ss396
It doesn't. There is such a thing as having too much compression.
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Please to explain. I know some of the NA drag boys move over from Gas (110 - 117) to pure alcohol at around 14:1, before the take it up any higher.
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05-21-2009, 04:39 PM
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#10
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Fast & Filthy
Join Date: Jun 2008
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Quote:
Originally Posted by Vettezuki
Please to explain. I know some of the NA drag boys move over from Gas (110 - 117) to pure alcohol at around 14:1, before the take it up any higher.
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Just like head selection, cam selection, etc you need to balance the compression with the rest of the components. Say you have a stock 350 with a stock cam, heads and exhaust manifolds it doesn't make any since to run 12:1 compression. It will probably run better on 9-9.5:1 and wouldn't need race fuel to keep from detonating. |
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