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09-10-2002, 02:18 PM
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| Raising the Compression Ration of 330ci.... Has anyone tried raising the conpression ratio on their 330ci??? like to 13:1???
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09-11-2002, 09:42 AM
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| 13:1 is the comp ratio of the m3 gtr m3...
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09-11-2002, 10:17 AM
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| You wouldn't be able to run pump gas. If you want to talk theoretically, thats fine. Assuming you got the SW and it was done right, it would kick ass. Before my ///M days, I had an 89 Prelude. I had done a ton of work to this car (cams, intake, bored-tb), but when I got the head milled from 8.5:1 to an 11:1, it was like a new car. The increased compression gave the 4bngr real kick. If I make the decision not to go FI, then I will think about raising the M to 11:1. This and some other goodies would put me over 330HP. In reality, listen to J Vitolo...not on a street car. |
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09-11-2002, 12:51 PM
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| Yeah, 11:1 is about as high as you can go for safe long-term street use. I'm running 11:1 on my 3.2 S50 and it doesn't detonate at all.. you could run slightly higher with hotter cams, but like 11.3, not 13!!! 330hp takes more than a FEW goodies!  |
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09-11-2002, 02:59 PM
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| i was talking to my friends auncle who works on tuning cars and he said he's got his own shop but he's planning to retire soon but he said w/ my 330ci thoreticlly i can get 13:1 compression ration but i'd have to replace a lot of things in my engine...and it should run about 410bhp
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09-12-2002, 03:47 AM
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| Sorry pal, uh we build BMW race/street motors, and 13:1 is sky-high.. if it was a track motor that was rebuilt regularly running 110 octane then you could probaby do it. 11:1 is the limit on the street really.. |
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09-12-2002, 04:46 AM
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| sounds interesting... so how do you raise your compression ratio? anyone mind explaining what exactly the compression ratio IS? 
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09-12-2002, 05:12 AM
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| Compression Ratio is the amount the mixture in the combustion chamber is compressed(11:1 means the mixture is compressed 11x the initial psi). The more it is compressed, the stronger the explosion when the plugs fire. Think of a spring. The harder you push it down, the harder it will jump up. The ratio can be affected by changing the thickness of the head gasket, milling the head, or different pistons. FI engines like a low CR so that the boost can be increased. You might hear about people putting a thicker head gasket in when they add an SC or Turbo. This increases the size of the chamber and lowers compression. The performance of NA motors can be increase by raising the CR. In the case of my Prelude, I had the head milled while I was getting other head work done. This shrinks the chamber and forces the explosion to happen in a smaller space. BAM! The piston goes down faster...more 'umph' By playing with the CR, you are changing the dynamics of the motor and will stress parts which may not be designed to handle it (ie rings, etc). This can cause problems. This is also why 13:1 would require constant rebuilds. The internals (esp gaskets) would be way too stressed. This is one of those things you do to a car after you have done the other mods (or when you are building a motor). Last edited by Keda : 09-12-2002 at 05:19 AM. |
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09-12-2002, 09:58 AM
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| so the gasket is not strong enough...what can u make it out of so it will be strong enough to last a longgg time w/ out rebiulding??? because when i buy my M3 in few year im thinking getting the KS supercharger which gives m3 i6 525HP or doing a custom bi-turbo system....
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