Offshoreonly.com - Compression change

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ROADHOG

03-27-2005 12:21 PM

Compression change

When changing compression from 8.75 to 9.5 of 9.75 what should a person see in the difference of HP? Base motor is 500EFI. Is there a rule of thumb as to how much HP gain per .25 increments?

excursion

03-27-2005 05:03 PM

Re: Compression change

I just did that too my motors over the winter and took them to 9.75 comp. , everyone said I should have with the other mods done, cam, porting, carb.....should be around 580-590hp.

mcollinstn

03-27-2005 07:33 PM

Re: Compression change

usually a longer duration cam accompanies a hike in compression ratio.
Some combinations could actually lose power with a hike, if you were running close tooptimal cylinder pressures already.

Bad to the bone

03-27-2005 08:16 PM

Re: Compression change

Hot Rodding did a article awhile back that started at 8to1 up to 12to1 averaged about 4-5%increse per increase. Of couse
cam, heads and other factions will come in to play.

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