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[North Star]

I'm wondering about when people talk about an engine that has too much compression, pings with lower quality fuel, causes gasket leaks, and general PMS.

Is that solely due to running higher compression pistons, or is it because the total engine package has too high a CCP?

For example, if 10.5-1 pistons were run with the appropriate headwork, etc (ie- a GMR 113 build), which ended up with a lower CCP number than stock, there shouldn't be any of those issues, right?

I believe CCP stands for cold cranking compression, but I have no idea how having too much CCP affects the way the engine runs.

[prodrag1320]

compression has to be matched to your cams,short duration with high compression will result in detonation & overheating,like wise long duration cams with not enough compression will result in soft power.cams closing specs will also effect in corrected compression.when picking parts for a build,corrected compression should be considered over static compression

[HD Street Performance]

Compression is too high when the combination of parts is not right. The owner of the bike made a wrong choice somewhere.
There are not "good and better and best" parts, there are "good and better and best" combinations of parts. The guys that slap a lot of great parts on their own merit together can and usually end up with a fair to poor result. You will see me recommending parts such as the SE259e cams. Many on the net will discount anything made by or designed by Harley. I use the parts but I know what works with what and why. I also know what to avoid. The motor is an air pump remember. Too big of a hole slower flow. Too small of a hole fast flow and pumping losses. Both result in problems, lower VEs and less power and TQ. There is a proper CSA in the RPM range these motors will run. The valve size out of context is just as erroneous information. Everything must match to fill the cylinders and make power in the range the motor will spend most of its time. Find a shop to sell that not just parts and pieces and then rely on a menu approach to get from A to B

[grc]

Compression is too high when it causes detonation.  But you have to look not just at static compression, which is just a calculated number comparing the volume of the combustion chamber to the total swept volume of the cylinder plus the volume of the combustion chamber.  You need to look at the dynamic compression.  Some like to call that CCP, but the more correct term is dynamic compression.  And dynamic compression is affected by many things other than the static calculations.  For instance, fill that cylinder with more air and the effective compression rises.  Think supercharger for an extreme example.  Install a cam with a huge amount of overlap and the effective compression drops because some of the fresh charge of air and fuel escapes.  Install a cam with no overlap and effective compression increases.  That's what Harley did with the 255 cams in the 110.  There are many other variables as well.  As HD Street Performance mentioned, it is the combination of parts that determines the effective compression, not just the volume of the combustion chamber or the dome of the piston.  Quoting static compression ratio's in a spec sheet or when bragging to the guy next door about your hopped up motor is not terribly enlightening.

By the way, you do realize there are plenty of engines in all kinds of vehicles that run a much higher static compression ratio than Harley, and yet they run on 86 octane regular gas with no detonation.  That should be the first tipoff that there is a lot more involved than just static compression ratio.

Jerry

[North Star]

Thanks guys.

[ultraswede]

Some cams produce CCPs that are much higher than expected.
In my case that happened, the motor got PMS wich was cured with alcohol  , i.e. E85.

[98fxstc]

Some cams produce CCPs that are much higher than expected.

Curious about this
Supposed to be the case with some T Man cams ?
Big Boyz calculator comes pretty close with most cams for corrected compression and ccp
but there are some exceptions ?

[ultraswede]

Seems like the 255 is one (reported here), and in my case the 263E.

[HD Street Performance]

Plenty exceptions.
You rely on math based on .053 valve opening.  The seat to seat @.006 would reveal more.

[GMR-PERFORMANCE]

In a 124 with a 640 cam I like to see 200-210 so with that cam you are going to need 11.5-11.8  . Now that scares many but think about this a stock 103 today is going to pump right into the 200 CCP range

[firefighter156]

Compression is too high when the combination of parts is not right. The owner of the bike made a wrong choice somewhere.
There are not "good and better and best" parts, there are "good and better and best" combinations of parts. The guys that slap a lot of great parts on their own merit together can and usually end up with a fair to poor result. You will see me recommending parts such as the SE259e cams. Many on the net will discount anything made by or designed by Harley. I use the parts but I know what works with what and why. I also know what to avoid. The motor is an air pump remember. Too big of a hole slower flow. Too small of a hole fast flow and pumping losses. Both result in problems, lower VEs and less power and TQ. There is a proper CSA in the RPM range these motors will run. The valve size out of context is just as erroneous information. Everything must match to fill the cylinders and make power in the range the motor will spend most of its time. Find a shop to sell that not just parts and pieces and then rely on a menu approach to get from A to B

Well said Don.

[GMR-PERFORMANCE]

Plenty exceptions.
You rely on math based on .053 valve opening.  The seat to seat @.006 would reveal more.

no way so that means that two cam's that have  close event numbers are not the same 

[ultraswede]

The seat to seat @.006 would reveal more.

Where can this info be found?

[HD Street Performance]

It is not generally published for motorcycle cams