How much horsepower difference would there be between a pump gas race mod and a high compression race mod???

 

from what I have read you get 3 to 4% power increase for every point you raise the compression. So 12 to 1 to 15.5 to 1 would equal 14%. I don't know how acurate this is I got it off a website for tuning 2 stroke outboard motors for boats.

I'm sure someone will com along and confirm this or correct it.

 

im not really sure, but a 12.5-1 compression piston on a pred adds 5-6 horses

 

Good question?? Maybe Rick might know. Humm humm.[img]i/expressions/face-icon-small-wink.gif[/img][img]i/expressions/face-icon-small-smile.gif[/img]

 

I would guess that it would be pretty close.[img]i/expressions/face-icon-small-wink.gif[/img]

 

wow so if i take my stock compression race mod to a 16-1 it should really scream.

 

For a little while.[img]i/expressions/face-icon-small-shocked.gif[/img]

 

well this raises a question for me do you factor in the percentage increae over the stock motor or over a modded motor? don;t know if that explains what I mean. so I will list two examples. If I remeber correct factory compression is 9 to 1(or 9.5 to 1). So going to 12 to 1, the limit of pump gas I would increase this 3 points. so I would get a 12% increase.

No do I factor that on my HP prior to mods or after?
38x 12%= 4.56 total power 42.56
42.56 plus.
10hp pipe
1hp reeds
1 hp clamp on/jetting
total 54.56hp.

factoring after mods.
38hp
10hp pipe
1hp reeds
1hp clamp on
50hp x 12% =6 total hp 56hp

Does the second one seem correct? thefirst number seems low and the second number seems high. Just kicking some things around in the old head. I know this is bench racing and there are too many variables to count but I don;t think I have 56hp.

 

whats a good compression ratio for a hpd race ported 400?

 

Anywhere from 12:1 to 15.5:1.