I've been thinking about this for the past few nights. But because i'm not a turbo wiz i couldn't come up with a answer.
Lets say that you have 2 motors that were EXACTLY the same... B18c1 that is.
Mildly built with all the normal goodies(rods, pistions, good fuel system)
both having a normal T3/T4
both tunned to perfection with Hondata at 8psi by same tunner

One having a low 9.1:1 CR
the other having 10.8:1 CR (yeah i know that high for a turbo car)

I know that the 11.1:5 will yeild more power throught the entire powerband BUT............... MY QUESTION is :

which one will spool up faster? Does CR have any affect to spool up time or lag? I know that with higher compression means you can't boost as much w/ out extensive tunning and higher fuel OCT.

which one would you want to have and why?

 

Yes, higher compression will make the turbo hit full boost faster. So take for instance the motor on 9:1 compression is going to start spool at 4000 the motor with the 10:1 compression will start spooling at 3500(Given that everything else is equal).

10.8 :1 CR isnt that high of a compression.

 

The short answer: Yes
The long answer: It depends.

Isn't that true of everything?

 

Holy **** MarkC is back on the board. Where ya been??? Guess you have a life hunh!!?!!!?? :D

Glad your back.

 

give me the long answer mang.. i got time and the willingness to learn more about FI. Teach me somthing new today. Help me out. The longer the answer the better and more complete comprehesion i will have about this subject.

(both motors are exactly the same. except for the compression Ratio)

 

By thermodynamics the higher compression engine is dictated by the volume at TDC/volume at BDC. So you get a ratio, and the higher the compression you get a greater numerical ratio. Using this and the 1st law of thermodynamics Q-W=m(u2-u1), the greater numerical volume from compression increases the work term (W). The mass cancels out since the system of an engine in the compression and power stroke are closed, and we get that Q is increasing. Q is heat, and heat is energy. The greater the energy that you put into the turbo (spent exhaust gas), the faster the turbo will spool up. Think of it as energy transfer.


[Modified by boosted hybrid, 11:31 AM 11/7/2002]

 

 

I had for awhile a 11:1 compression built b16a engine, that saw 9psi daily driven. There is a ton of posts in the archieves about this topic, as well as my comments on high compressoin engines. I have since went back to low compression (9:1) for my daily driver, but in the works is a 11.5:1 compression 2.0 liter gsr block fully built for turbo. Once you get a ride in a high compression turbocharged car, you'll understand the power delivery and powerband of the engine. Its almost seemless power, basically like a well tuned all motor engine. I would prefer a high compression engine for the street, but it takes dead on tuning, there is zero room for error. Also one bad tank of gas, and kiss the engine good bye. Your car will also run ALOT hotter b/c of the higher compression and boost, make sure you do everything to cool your engine, good fans, radiator, oil cooler, etc.

 

good info on that last reply. I will follow-up on it and use search under your user id name. if i can't find the post i will IM you. thanks for your insite.

anyone else... i'm sure once 7pm rolls around more people be signed on

 

ttt