This is topic Noob question, inspired by glenn in forum Tech Talk at Northern California Ford Owners  .


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Posted by 87 Saleen (Member # 1549) on :
 
Yea well I was reading Glenn's thread and asked myself, why is low compression better then high compression with running a super charger? Does this also apply to any form of boost, like nitrous? I though nitrous liked higher compression?
 

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Posted by 91 5.0 (Member # 1527) on :
 
Too much air in the combustion chamber, along with the elevated intake temperatures, due to the blower, can cause pre-ignition.
 

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Posted by Primer GR40 (Member # 476) on :
 
Superchargers get the air hot with lots of boost. Too much heat and compression will lead to pre-ignition. Nitrous cools, it doesnt heat anything up, besides a little more fuel you burn. This is just a guess.
 

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Posted by 93PONY (Member # 60) on :
 
HEAT

That's why low compression with boost is desirable. You can only run so much total compression (compression ratio * (boost in AU + 1)) before pre-ignition with a given octane occurs (the higher the octane, the higher temp/slower it burns). This is because whenever you compresses a gas, you heat it up. Heat up the air/fuel mixture too much & it will ignite.

N2O works very well with high compression for a couple of reasons. One, is that it is sprayed out at -120F degrees. This cools the intake air charge quite well. Also, with nitrous you're not compressing the air before it reaches the pistons.
 

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Posted by 87 Saleen (Member # 1549) on :
 
Shaun, you are a beatiful person .
 

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Posted by mustanggt5091 (Member # 444) on :
 
Couldnt have said it better myself shaun
 

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Posted by 91 5.0 (Member # 1527) on :
 
So when nitrous is injected, it comes out at 120F? Explain that to me. I'd think it would be a lot cooler since it was going from very high pressure, ~1000psi, to atmospheric pressure. When a something goes from high pressure to low pressure, it gets colder. Same concept as your A/C system.
 

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Posted by JohnB (Member # 969) on :
 
Ahhh, 91...that's NEGATIVE 120 degrees..
 

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Posted by 91 5.0 (Member # 1527) on :
 

quote:

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Originally posted by JohnB:
Ahhh, 91...that's NEGATIVE 120 degrees..

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Now that makes sense. I was wonderin about that. Shaun is a smart guy, so I was wondering what was goin on. I re-read it and saw the (-) sign this time. Thanks for pointing that out John.

[ September 25, 2003, 10:51 AM: Message edited by: 91 5.0 ]
 

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