I am trying to find out how compression ratios determine safe boost levels. I have searched google a lot, and I understand a little more, but if anyone has any good resources please post a link. Thanks.

 

I'm no help, but personally just knowing that lower compression generally equates to the ability to blow more boost is good enough for me.

Why are you researching? Do you have a particular amount of boost in mind and are looking for the correspondent cr for that?

 

I am just very curious, and trying to learn more about internal combustion engine. Either way this sort of explains what is going on. http://www.sdsefi.com/techocta.htm

From what I've read higher HP is obtained by raising the compresion ratio in N/A cars which allows more air for a better combustion, but in turbo cars somehow the higher compresion ratio the lower the possible boost, at least on street gas. According to that article on C16 compression ratios no longer matter as much as on 92 octane, then it just matters how strong the engine is.

 

here is another link http://e30m3performance.com/myths/mo...comp_ratio.htm

 

Thanks Dave.

 

I guess it boils down to what effects any sort of forced induction has on the engine. For a turbo guy, it's common knowledge that a turbo IS a replacement for actual displacement.

A 2 liter engine that has been fully optimised wrt it's intake and exhaust (there are no obstacles, nor anything that creates undue turbulence) versus a 5 liter, fully optimised engine. When you put both on the dyno, the 5 liter will produce more hp and torque. When you add a turbo to the 2 liter, it's effectively raising the amount of air/fuel mixture that it can combust without raising it's displacement.

Pat's definition of displacement is how volume of X would be displaced if the cylinder, squish area, and dome were filled to capacity with Y.

You've physically done nothing to the combustion chamber to increase the capacity that it would hold, but you've introduced a substance which combusts much more efficiently, so less of that substance is required to get the original amount of power. Therefore, if you want more power, you would be able to now fill the combustion chamber to capacity with the new, more efficient substance (compressed air.)

ANYHOW, maybe the same sort of function occurs to the compression ratio. Since you're now dealing with a mixture with more power producing capability, the amount of pressure required to effectively ignite it would need to be lessened. I'd say that the same function, in varying degrees, would follow no matter what 'power adder' you used. Alcohol, nitrous oxide, nitromethane, water. Each of those effectively increases the efficiency of the charge to ignite, and so less comp ratio (and less timing, I'm beginning to gather) would be required/necessary for optimum power.

Make sense?

From my knowledge of explosives, heat and compression are what are needed to create an explosion. EVERYTHING is flamable and everything is explosive.

Great links, btw.

 

Makes sence, but since a turbo offers 30% to 40% power increase at 14.7 PSI since that is double density of normal air minus the inefficiency; while raising the compresion from 8:1 to 9:1 on a n/a car produces about 3% more HP. Why doesn't every car have forced induction, and low compression?

 

I'd imagine that there are SO many factors that manufacturers consider.

Variance between geographical locations for one. I remember when I first installed the UTEC and I started reading about everyone's problems when the whether got cold. I imagine that the R&D on a turbo'd car is probably a chore in setting up the stock maps.

 

i got a book on automotive design for you to look at when you get back.

 

this is what you want

on pump gas effective ratio must be more than 12.67 because the evo is 13.32

 

hey nate when you get back give me a call ill let you borrow maximum boost by corkey bell it has hella info on the subject

 

Maximum B. by Corky B. rocks the hizzy fo shizzy.