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does lower c/r mean slower???

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Old Mar 19, 2008 | 01:26 PM
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Question does lower c/r mean slower???

i am going from a ls1 to a lq4.....stock internals....
now will going from 10.5.1 down to 9.5.1 lower hp and make the car slower.....if not
how come everyone says c/r should be higher.....i do plan on running a wet nos kit after break in and tune....is that a good idea or not
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Old Mar 19, 2008 | 01:34 PM
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stock ls1 cr is 10.2:1 and stock lq4 cr is 9.4:1. i think the lower compression ratio would be made up by the difference in cubic inches - in your comparison. obviously more compression is going to generate more hp (and tq), but if you are getting into the motor during this build, why not do something to bump the compression up?
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Old Mar 19, 2008 | 01:37 PM
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Thats a good FI ratio. I'd personally want it higher N/A & with nitrous. Nitrous loves compression also. I'm running right around 11.0:1 & I wouldn't go back ever unless I was goin boosted.
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Old Mar 19, 2008 | 01:42 PM
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Generally speaking, higher compression will produce higher horsepower. If your a light nitrous user or naturally aspirated, you should shoot for as close to 11.3:1 SCR as you can get.
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Old Mar 19, 2008 | 01:43 PM
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Originally Posted by 405HP_Z06
Generally speaking, higher compression will produce higher horsepower. If your a light nitrous user or naturally aspirated, you should shoot for as close to 8.6:1 DCR as you can get.
Fixed.
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Old Mar 19, 2008 | 01:46 PM
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Originally Posted by Drew04GTO
Fixed.
Only if you subscribe to the DCR myth, I don't.
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Old Mar 19, 2008 | 01:58 PM
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so high comp higher hp.....then will 9.5.1 take 10%----15% off what i could be making on top line numbers or like 10 20 hp........
i am at my whits end with engine.....dont have the 200.00 for .030 gaskets from cometic
stockers are 63.02 for the set
oh and the reason it;s too late to do it while im in the motor....is because the machine shop just assambeled and balanced the stock lq4 pistons in my build
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Old Mar 19, 2008 | 02:18 PM
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i think it's something like 7-8% increase/decrease in hp per point of compression. it's not like the car would go from mid 11s @ 9.5 cr to a 9 sec car @ 10.5...

it'll still make good power, just go with it and stop worrying.
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Old Mar 19, 2008 | 02:20 PM
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haha....thats what i needed to hear...

THANKS GUYS!!!!!
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Old Mar 19, 2008 | 02:39 PM
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Originally Posted by 405HP_Z06
Only if you subscribe to the DCR myth, I don't.
x2

That **** is so over hyped it is not even funny.
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Old Mar 19, 2008 | 02:58 PM
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Here's an excellent article by David Vizard on compression ratio. Vizard knows his stuff. He has a chart in the article that speaks to what your looking for. The power increase isn't a linear factor, but more a diminishing one the higher the compression.

http://www.popularhotrodding.com/tec...ech/index.html
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Old Mar 19, 2008 | 03:00 PM
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Originally Posted by BIG_MIKE2005
Nitrous loves compression also. I'm running right around 11.0:1 & I wouldn't go back ever unless I was goin boosted.

I agree. I'm at 11.5:1 but my engine was built for nitrous. Regardless your engine will do fine on spray, but keep in mind a thinner head gasket is better for nitrous. Less of a chance to blow the head gasket. That's why I also went with cometic .030. Yes they were $180.00 but it's a little bit of insurance that my engine won't have any issues, and of course ARP head studs.

Sell a kidney and buy some cometics! lol
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Old Mar 19, 2008 | 04:35 PM
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That's a really broad question, but like other said, generally the answer is yes lower compression is less power. (Assuming your CR is not so high that pinging is holding you back)

For example, if say you are running a blower and you cannot run as much advance with 10:1 vs. 9.1....you lower the CR, and you may make more power.
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Old Mar 19, 2008 | 08:40 PM
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I would not use that low of compression unless you are going with a turbo or supercharger.
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Old Mar 19, 2008 | 08:44 PM
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What heads are you running? You could have them milled to bump up the compression some. I have mine down to 59cc's
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Old Mar 19, 2008 | 09:02 PM
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One point of compressioin is good for a HP difference of about 2%. So going from 11:1 to 10:1 in a 400 hp motor will result in around 10 less HP.
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Old Mar 19, 2008 | 09:05 PM
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You should be fine man. Look at it this way, you can probably use 87 or 89 octane fuel. I'm at 12:1 and not looking back though...
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