If two motors have the same effective compression ratios, regardless of induction type, should they make the same power?

 

Do these two motors have any different specs?

 

Well say one is turbo and the other is all motor.

Examples:

Static compression: 9.6:1
Boost: 6 PSI
Effective compression: 13.5:1

Static compression: 13.5:1
Boost: 0
Effective compression: 13.5:1

So the effective compression of the motors is the same, but I would imagine the boosted motor would make more power. Why is that?

 

Unless the n/a motor operates at 100% volumetric efficiency, effective/dynamic compression will be quite a bit less than static compression. Also, unless running a HUGE cam, 13.5:1 compression on pump gas ain't happening.

Even if both motors sport similar displacement, there are FAR too many variables to consider: cylinder head flow, cam profiles, boost, a/f ratio, timing maps, operating RPM range, etc. Compression ratio alone does not dictate power output.

To answer the original question as simply as possible, the forced induction motor simply moves more air, hence greater power production.

 

yeah, many people dont understand the difference with running that high compression with a Type R cam vs. a Toda Spec C cam ...

pretty much the answer is volumetric efficiency and O2 content.

Greg




[Modified by vtec4gs, 4:14 PM 12/6/2001]

 

To add, compression ratio, as the name states, is a ratio of cylinder volume at TDC divided by cylinder volume at BDC. Regarding the two motors in question, although they both feature the same compression ratio, there a whole lot more air in the forced induction motor at BDC compared to the n/a motor.