raising compression

[busa dave]

OK I'm doing some winter upgrades to my gen 1. ported head, web 378/330 cams. i have the chance to pick up some JE pistons that would raise the compression about 1 point. How much of a gain could be expected from adding the higher compression pistons with the ported head and cams vs just doing the head and cams.

Thanks,
Dave

 

[mountainmotor]

The short of it is not as much total hp gain will be had compared to the benefit of increased power throughout the rpm range by compensating for the increased valve overlap with the extra compression.

It will run harder compared to exact same engine recipe without the compression. Better throttle response as well.

This is std bore correct ? If so, don't use a base gasket and seal with Yamabond. That will help the combustion process and give another small increase in compression by tightening the quench .

 

[busa dave]

yes, std. bore. I assume it would be ok to just do a quick hone of my cylinder bores as they all look good?

 

[mountainmotor]

Scuff a little with scotchbrite .

 

[ogre]

or just purchase a finishing hone. they're not expensive.

 

[8secBusa]

On my 07, I went from 11.5 to 13.1, ported the head, added cams, gained 26hp....Stock bore, pump gas.

 

[glenn71]

With those cams it gonna be tough because
Youll need around 13.5:1 for them to work
Over a widerange but youll struggle to
Get that comp in a stock bore without
Squeezing it tight and then youll be stuck
Running 106+ lobe centres for safe ptv. In summary
Its not going to make much power under
6000 but will scream up top.