What equation expresses the relationship between compression ratio and torque?

Question

I have looked all over the place. I am wanting to reduce the compression chamber for torque gains if it is worth it. Please help.

Answer 1

The improvement in torque should be about equvalent to the improvement in BMEP which is the ratio of new CR divided by old CR - result taken to the 0.4 power

Example - if you had 10:1 and now have 10.1:1 (10.1/10.0) to 0.4 power is 1.00398
OR 100 ft lb -> to 100.398.

A lot of people think that raising CR is MUCH more effective than it actually is.

Gwynne quoted this eqation from "Design and Tuning of Competition Engines" by Phillip H. Smith

Answer 2

Compression Ratio Equation

Answer 3

In an idealized (not precisely realistic) model of an Otto cycle internal combustion engine, the efficiency of the engine is described by:

e = 1 - 1/r^(k-1)

where e = efficiency, r = compression ratio, and k = ratio of specific heats for the gas mixture (typically around 1.3).

Now we can use some scaling laws to find how torque varies with compression ratio:

Torque is proportional to power (at a given RPM), so
T ~ P
Power is proportional to efficiency
P ~ e
Therefore, torque is proportional to efficiency:

T ~ e
T ~ 1 - 1/r^(k-1)

Keep in mind this is only an approximation.

If we trust the model, we can predict that going from a compression ratio of 9 to a ratio of 11, the torque should go up by about 6%.

Answer 4

open this site. may be this may help u in any way:

http://books.google.com/books?id=p3ZHkkm4QU0C&pg=PA139&lpg=PA139&dq=compression+ratio+and+torque&source=web&ots=J57xZ2aErF&sig=z_DfX6i_74Wj-dyaVJwy3LGUA0A