pump gas comp. ratio w carb
03-03-2012, 02:36 PM
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pump gas comp. ratio w carb What's the most compression you carbed ls1 guys are getting away with? I know w fuel injection there's ppl running as much as 12:1 or slightly higher is there anyone getting away w that with a carb setup?
03-05-2012, 09:52 AM
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Holy **** that's pretty stout. 28 deg total isn't very low for an ls motor either can you elaborate on your engine specs a bit more please?
03-05-2012, 11:48 AM
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Wow, 12.7 is about the highest ive ever heard of in a pump gas application. I have to give the OP credit, ive never thought about it before. Good question. Eric L
03-05-2012, 11:19 PM
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good info guys, and i guess i didn't specify, but it'd be nice if we could get engine specs along w your c/r i.e heads, cam, power adder, shortblock specs, displacement, timing, carb size, etc
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03-06-2012, 01:23 AM
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Who specd the cam? And im sure a round about duration and lift wouldnt hurt, lol. It seems from what im finding that the LS3 heads seem to like some extra duration on the exhaust to help fight the large offset between intake and exhaust flow. And in carbed applications they seem to like a fairly low (numerically) intake centerline. Eric L
03-06-2012, 05:11 AM
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http://www.youtube.com/watch?v=hFbSHvj8VQQ
03-06-2012, 06:18 AM
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Its really hard to say a specific comp ratio will work.
These are just some of the things that play a role:
-Weight of vehicle
-Gear ratios (tranz and diff)
-Fuel quality in your area
-Cam overlap
-DCR
-Quench
Bruce
These are just some of the things that play a role:
-Weight of vehicle
-Gear ratios (tranz and diff)
-Fuel quality in your area
-Cam overlap
-DCR
-Quench
Bruce
03-06-2012, 04:33 PM
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JMHO, In theory you want to run as much compression as your fuel will allow. More compression equals more power. But, for instance, if you live in a state that only sells oxygenated 91 octane, that would be your limiting factor. But, on the inverse, on the 6.0 im building for my car, im only going to have around 9.9 or 10-1 comp, so I have a cam that keeps cranking compression up there and dosent bleed off what little compression I have. Eric L
03-06-2012, 07:20 PM
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Protrac that is what I did got a cam spec'd for the ly6 for my build as its 9.67:1.. Comes out to about 8.4:1 DCR but its still 222/234 @0.050
I might goto a 0.040 gasket to up compression and get a better quench at the same time.
Bruce
I might goto a 0.040 gasket to up compression and get a better quench at the same time.
Bruce
03-06-2012, 11:57 PM
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03-07-2012, 12:16 AM
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Who specd the cam? And im sure a round about duration and lift wouldnt hurt, lol. It seems from what im finding that the LS3 heads seem to like some extra duration on the exhaust to help fight the large offset between intake and exhaust flow. And in carbed applications they seem to like a fairly low (numerically) intake centerline. Eric L
03-07-2012, 06:12 AM
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I understand all of these things, but thanks for your input sir! And i just wanted to see what other people are getting away with, not asking what specific ratio will work for me.... As for "dynamic compression", I believe it is entertaining at best. It doesn't calculate inertial "supercharging" that takes place when the piston is coming back up before the intake valve closes, or the scavenging effect that the exhaust gas exiting the cylinder has on the intake tract when the intake valve cracks open. These, along with other airflow theory related phenomena, cannot be calculated simply by using physical specifications. Therefore, I'm not convinced that DCR can be definitively useful, but to each his own!
I wonder if you could do a 13-14:1 engine using 93 octane and the water/methanol injection? I think it would work. Now we only need some sucker to step up and prove it
Bruce
03-08-2012, 10:41 AM
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Yea I've been wanting to do a high c/r e85 or 91/meth injection street motor for quite some time now. Was jus talkin to my buddy about it the other day. You could do like 14:1 on e, and if ur ever somewhere where E isn't available jus throw in some 91 and turn on the meth injection. I know it will work I might try it someday.
