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Old 09-03-2005, 02:43 PM   #1
Scooby Newbie
Member#: 64528
Join Date: Jun 2004
Default CR, Nitrous and Turbos

Why is it that High CR NA cars can handle 75hp nitrous shots
whereas they cant handle any boost

Nitrous is a form of adding oxygen

Is it because Nitrous cools the air and prevents detonation, which then allows it to tolerate high CR ?
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Old 09-04-2005, 12:34 AM   #2
Scooby Specialist
Member#: 2112
Join Date: Aug 2000
Chapter/Region: South East
2000 Impreza 2.5RS


Well...I've considered nitrous lately just for giggles (pun intended). FWIR and FWIW, nitrous is a chemical supercharger. The trick to making it work is more fuel. It doesn't work all by itself. Some engines built for higher doses of N20 actually have lower compression. It's kinda like using high compression and low boost vs. low compression and high boost. Any way you can build cylinder pressures is going to be fast. An 11:1 motor can actually handle boost with the right fuel, just not a ton of it. "Which is better" is always up for debate, despite the fact that they all still work one way or another.
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Old 09-04-2005, 07:45 AM   #3
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Join Date: Sep 2004
Chapter/Region: NESIC
Location: Sutton
2005 Legacy GT
Satin Pearl White


I actually use nitrous and love it. What its doing is cooling the incoming air charge. Cooler air is more dense than hot air. A car with slightly higher compression can only handle a 75 shot of nitrous with added fuel. The reason this can be done is because in any given cylinder, when the piston drops for the intake stroke, it creates a low pressure. Now cooler, more dense air fills the low pressure cylinder. In a NA car when this happens, you will only fill that cylinder to 14.7psi or what ever atmospheric pressure is in your area. Now in the compression stroke, the piston is compressing the dense air charge which contains more oxygen. Thats why extra fuel is needed. In return on the ignition stroke more power is made. Nitrous in no way helps prevent from detonation. It still creates high temps within the cylinder which can ignite the air charge. Now as for a turbo, say you are boosting 10lbs, on the intake stroke, air is compressed into the cylinder adding to the 14.7psi atmospheric pressure making it 24.7psi. When air is compressed it heats up, that is why a intercooler is used. Now when the valve closes you have a high pressure in the cylinder which is then compressed by the piston. As HamFist stated, you can have a high compression engine and low boost. Or you can have a low compression engine and high boost. You will get similar amounts of power but the power bands will be in a different rpm range.
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Old 09-04-2005, 03:51 PM   #4
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Hamfist, how much boost can 11:1 take with correct fueling

Last edited by G.Subramaniam; 09-04-2005 at 03:52 PM. Reason: error correction
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