Hot Rods Compression / HP gains

If I bump the compression up on my 11.5 -1 630 hp sbc to 14.8 -1 ( and recam?) what kind of gain could be reasonable? 30-40 hp? I run aviation fuel and ( as yet to be tried) methanol which is accomplished with carby and plug swap and a lil timing change.

 

I’ve not a clue in the atmosphere you are at.
Care to share the details of your engine? Sure seems like a beast.

 

Too many unknown details and variables to even guess.

 

There's a lot of variables than just a "pat" answer.
ESPICIALLY...if you want to change cams!

If your "new" cam has more duration than your existing cam, you will loose "dynamic" compression, which can be seen as cylinder PSI. Then, upping the compression ratio is almost a must to keep the dynamic ratio up.

So NOW...you want to add methanol, or...some...combination of methanol and gas ! NOW, you've thrown a whole new combination together.

What I'd do if I were you...pick a cam manufacturer, call them, on the phone, and tell them EXACTLY...what your current combination is, exactly what you want to do and the goals that you want to see.

Be honest, upfront, and don't argue, most of all listen.

Mike

 

I think the compression will definitely give you *how much gain.

 

So your current combination makes 630 on AV gas correct?

My bet is you'll get your 30-40 just switching to methanol even though 11.5-1 is a little low to fully utilize alcohol. You won't run a 14.8 motor on AV gas IMO.

Other than that, depends on what you have to do to get that compression. I've seen some super high compression engines that didn't run that well because the piston domes really kind of wrecked the flame travel.

 

Thanks I was just bench racing. My current combo works great and I have methanol carb I am going to try. I was just curious how much I would pick up with more compression. It seems 2.5 % is typical. Not enough to worry about...

 

My 455 Pontiac picked up 4 tenths switching to methanol, same for dad's car when we tried it on his. Methanol takes all the overheating problems out of the equation so you can run the same in any weather, mine did.

 

You didn't say what CID your SBC is, 327? 430? Or more? Something in between? HP gain will depend on which carb and cam you add when you add the compression and change fuel type. Way too many variables to guess, but if the rest of the engine is able (heads & bottom end) and the right cam & methanol carb are used, I don't see why you couldn't get a 10% gain or more.

 

There is more to gain from the compression increase with the increase of the camshaft because you must have the compression ratio for the duration the two work together…