Well, i can't say what it's worth in HP, but my increase from 11.25 to 12.50 was worth 4 tenths and 4 mph. I will be honest and say i also ported the intake plenum and added an electric water pump as well, so not apples to apples, but the hp gain is much more than some may think. I try not to leave anything on the table anymore with my street/strip set up.

I'd guess 550ish. You could do better. The most mismatched part is the cam. That cam should be in a motorhome, not a street Hemi. I'd swap in something with 10 - 15 more degrees duration, and let'er rip!

I agree. I have that cam in my fathers 400 small block chevy. Works great and can be driven any where, but your leaving a lot on the table with that cam with a 511 cube street motor.

I agree, at least with the not being apples to apples part. Four MPH from a single point of compression is more that a little hard to believe.

Wallace Calculators gives a 600HP engine less than 5 additional horsepower when going from 11.25 to 12.5. Just one example, and not for a Hemi. But probably much closer to reality than the horsepower it takes to get another 4MPH. Which Wallace says would take about 17 more horsepower for each MPH.

http://www.wallaceracing.com/hp-cr-chg.php
http://www.wallaceracing.com/hp-mph-increase.php

Yep and thats what everyone else thought as well. I did the calculators and they were not showing much increase either, but i have the time slips to prove it. My 511 loved it and i think it might like some more.

You can’t attribute that whole gain to just the ratio.

You mention porting work and the addition of an electric water pump.

Glad it went faster though.

Yes, but the ratio was the biggest part of the gain. IMO that gain was worth 2 tenths. Well worth bumping compression up. Street car or race car, i leave nothing on the table, its there, use it.

That kind of gain isn't happening just by bumping compression up a hair over a point.
I suspect your gain was more because everything you had was too “ big” for the compression you had( in other words an under performing combo) and the bump in compression helped make the combo “ fit” better. In other words run more like its supposed to.
The shop doing my new engine, was taking to them about gains. Going from10 to 1 to 12.5 compression. 360 to 418 cubic inches. Cleaned up heads to mildly ported heads, dual plane to single plane. Same cam( too big on 360) to “ about right” on 418.
We are hoping for about an 80 horse gain from all of that. Seems pretty reasonable.
When you see the kind of gains you saw with that compression bump, it's more fixing an issue you had, than it is a +-3% gain from a little more than a point in compression would net 4 tenths and 4 mph.
Otherwise everybody on here would be milling heads a little and or changing to thinner head gaskets tomorrow to reap such gains

Not sure you remember at the time i was talking about bumping it up, most on here said it wouldn't gain much if anything. I can agree with that. I was talking to Wilsons one day and they told me any time the air slows down in the intake port, the fuel can fall out of suspension. Compression can speed things up on both intake and exhaust. My theory was at the time that my MW victors had lazy ports and more compression might be the fix and i believe it was. Helped the border line cam as well. so, maybe 1 point compression wont help everyone in every situation, but from this point i will always have at least 12.0:1 compression in every motor i build and just run good gas. They just seem to be happier with more compression.