Rough HP Gain?

[econo racer]

If my 11-1 Compression SBC 400 makes 500 HP at 6200 RPM, About how much gain would I pickup going to 12 1/2-1 compression with all things equal? I run the edel rpm intake and switched to edel super victor and lost 2 tenths in the 1/8th mile. I put the rpm back on. I know this is sorta a vague question just trying to get some idea. I run E85 fuel. 850 Hp carb.

[Monza355]

What’s the rest of the combo ? Interesting the rpm intake ran that much faster !

[mt-engines]

Did MPH change?

[CGT]

Only 1 way to know, but my guess would be 7-10 average. Theyre could be some situations where it could be more, or less. How the extra compression is obtained is the big one.

On a 23° 400 sbc, 11:1 is easy flat top territory, 12.5:1 is usually small .125ish tall dome territory(usually not to obtrusive on most heads)...so thats what my guess is based on. If the compression was gained from a large chunk flat milling job, I'd go with the compression gain costing you power or washing out..

If the bump was from closing up some less than optimum piston to head clearance along with some well thought out angle milling, could be more. Definitely some variables there.

[ClassAct]

If my 11-1 Compression SBC 400 makes 500 HP at 6200 RPM, About how much gain would I pickup going to 12 1/2-1 compression with all things equal? I run the edel rpm intake and switched to edel super victor and lost 2 tenths in the 1/8th mile. I put the rpm back on. I know this is sorta a vague question just trying to get some idea. I run E85 fuel. 850 Hp carb.

Maybe the SV wasn't the correct intake. But I'd ditch that dual plane intake and maybe find a Victor or Strip Dominator.

[cjperformance]

If my 11-1 Compression SBC 400 makes 500 HP at 6200 RPM, About how much gain would I pickup going to 12 1/2-1 compression with all things equal? I run the edel rpm intake and switched to edel super victor and lost 2 tenths in the 1/8th mile. I put the rpm back on. I know this is sorta a vague question just trying to get some idea. I run E85 fuel. 850 Hp carb.

Maybe the SV wasn't the correct intake. But I'd ditch that dual plane intake and maybe find a Victor or Strip Dominator.

Agreed and im wondering on the convertor stall rpm he's running?

[CGT]

I'm thinking I might be misunderstanding the op's question Is this a compression or manifold query or both?

[cjperformance]

I'm thinking I might be misunderstanding the op's question Is this a compression or manifold query or both?

Compression! But a bit of off track banter never hurt

[CGT]

I'm thinking I might be misunderstanding the op's question Is this a compression or manifold query or both?

Compression! But a bit of off track banter never hurt

I was second guessing my interpretation...thinking maybe compression and manifold was changed at the same time. Be interesting to see what others say. Interesting subject.....The dual plane-single plane thing is interesting as well.

[Lizardracing]

My math says about 6% but you’ll have to change the cam and fuel curves to match.
I’m guessing that why you lost ET but a look at the 60’ and MPH would tell you.
You should have added a 1” spacer to the 2925.

[dannobee]

https://www.hotrod.com/articles/0311em-power-squeeze/

Way back when, the rule of thumb was "2% per point." When nascar made us drop ours from pretty much unlimited to 9:1, that rule of thumb was pretty close. As you get higher, there's diminishing returns, so going from 12:1 to 16:1 wasn't as big as we thought it would be.

[MadBill]

I was recently doing some simulations with Dynomation software on a 368" ~ 700 HP SBF. 13.5:1 vs. 12.5 was 15 peak HP, plus 2.1%.

[econo racer]

Yrs. ago I tried the intake swap. Power glide 5400 converter 411 gears 28 inch tire. about 3500 lbs. Lost 1/10 60 ft. 2 mph. I'm sorry I threw the intake thing in. I built a 400 short block about 15 yrs. ago. It still on the stand lubed up. The piston part # L2311F says 13.4 to 1 comp with 64 cc. I just realized the rings are 1/16 so that also might free up a little hp. Man the dome is huge. I thought it was only 12-1.Wrong

[ClassAct]

My math says about 6% but you’ll have to change the cam and fuel curves to match.
I’m guessing that why you lost ET but a look at the 60’ and MPH would tell you.
You should have added a 1” spacer to the 2925.

This nails it. I wouldn't change the CR that far and not change the cam. I'd be interested to see what MJ has to say about that. As in a CR change and whether or not to change the cam.

[econo racer]

I have a super sucker spacer I have not tried yet. When I had the super Victor on I thought about putting a turbo 350 in it. #3500 lbs. is heavy