Why do some people lower the compression on a boosted car?
11-26-2002, 12:21 PM
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Why do some people lower the compression on a boosted car?
I've noticed this with quite a few boosted cars. Why lower the compression from, say 10.1:1 to 9:1?
newbie to the turbo thing, please forgive me.....
newbie to the turbo thing, please forgive me.....
11-26-2002, 12:25 PM
#2
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Re: Why do some people lower the compression on a boosted car? (ds9)
lower compression is safer on the motor compared to running higher compression...sorry for the short answer gotta run to work 
11-26-2002, 02:03 PM
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Re: Why do some people lower the compression on a boosted car? (ds9)
ok..here's the deal on high compression and boosted cars:
High compression engines produce more power, but they also produce more heat...so essentially you will need a good consistent air/fuel combination to avoid detonation.
Detonation is usally caused by excessive heat in the combustion chamber that cause the a/f mixure toignite prematurely (usually during the compression cycle)..severe damage to the piston and or rods and maybe even the crank can result.
In boosted cars, the turbine is sending compressed air into the cylinders. This alone can raise the air temperature causing the engine to detonate. So as a safety measure lowererin the compression a point reduces the chaces of detonation and raises the threshold for boost. Having said that, if you have access to good fuel (95+ octanes - which is harder to detonate a relatively lower temperatures), you can theoretically boost a very high compression engine with good tuning.
High compression engines produce more power, but they also produce more heat...so essentially you will need a good consistent air/fuel combination to avoid detonation.
Detonation is usally caused by excessive heat in the combustion chamber that cause the a/f mixure toignite prematurely (usually during the compression cycle)..severe damage to the piston and or rods and maybe even the crank can result.
In boosted cars, the turbine is sending compressed air into the cylinders. This alone can raise the air temperature causing the engine to detonate. So as a safety measure lowererin the compression a point reduces the chaces of detonation and raises the threshold for boost. Having said that, if you have access to good fuel (95+ octanes - which is harder to detonate a relatively lower temperatures), you can theoretically boost a very high compression engine with good tuning.
11-26-2002, 03:33 PM
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Re: Why do some people lower the compression on a boosted car? (MiraiZ)
Also with lower compression you give your tuner a wider window for tuning. With a high c/r there is little room for mistake when tuning.
11-26-2002, 06:46 PM
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Re: Why do some people lower the compression on a boosted car? (ds9)
a nicely done fuel system, along with an ignition system and the correct amount of tuning.
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11-26-2002, 06:59 PM
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Re: Why do some people lower the compression on a boosted car? (ds9)
yes.. the j&s senses detonation and retards the timing in each cylinder accordingly. I would love to pick one up but they are expensive...it almost covers the cost of a standalone like hondata.
11-26-2002, 07:10 PM
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Re: Why do some people lower the compression on a boosted car? (BlueSi2k)
The J&S is expensive, but it is so worth it. IMO it is an essential piece for a boosted motor.
11-26-2002, 07:49 PM
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Re: Why do some people lower the compression on a boosted car? (ds9)
other than lowering the compression, what else can be done to help prevent detonation?
11-26-2002, 09:14 PM
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Re: Why do some people lower the compression on a boosted car? (sharkcohen)
i've used both version of the J&S and would NOT recommend either. Save the cash for a programmable ECU. The J&S often misses clearly audible knock even at max sensitivity. A big waste of cash in my book and thats from someone that got stung twice.
11-27-2002, 09:42 AM
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Re: Why do some people lower the compression on a boosted car? (philo)
i've used both version of the J&S and would NOT recommend either. Save the cash for a programmable ECU. The J&S often misses clearly audible knock even at max sensitivity. A big waste of cash in my book and thats from someone that got stung twice.
11-27-2002, 11:16 AM
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Re: Why do some people lower the compression on a boosted car? (ds9)
11-27-2002, 11:21 AM
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Re: Why do some people lower the compression on a boosted car? (philo)
Yeah, J&S is a reactive system. You need to proactively prevent detonation. Only good tuning and the use of suitable parts will prevent detonation.
11-27-2002, 11:34 AM
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Re: Why do some people lower the compression on a boosted car? (CheezeFrog)
Yeah, J&S is a reactive system. You need to proactively prevent detonation. Only good tuning and the use of suitable parts will prevent detonation.
11-27-2002, 01:55 PM
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Re: Why do some people lower the compression on a boosted car? (MiraiZ)
High compression engines produce more power, but they also produce more heat...so essentially you will need a good consistent air/fuel combination to avoid detonation.
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