I realize that this is a bit of a loaded question but from your experience how much power will a motor lose from reducing the compression given that you have a suitable cam in both engines, given every thing else in the engine is the same.

Compression from 13.5 to one to 10.5 or 11.00 to one Race gas to premium pump gas..

Thanks

.I'm guessing it will depend upon the other matched components. ie a cam that works well w 13.5-1 may not work well w 10-1 . Contemplating the same type change, so Im curious to hear what the experts have to say as well.

Could lose up to 10% but not necessarily. Most engines are not optimized so if you had a "normal" bracket engine at 13.5 and then you switched to a pro built pump gas combo you might not lose any power at all. All depends on the details. I've run pump gas engines on the dyno that made more power than high compression bracket engines. That actually happens on a regular basis, especially if the bracket guy picked his own cam and/or ported his own heads.

The way to look at it is....... does the combo still “make sense” with the CR lowered 3 points?

Are the heads, intake, carb, headers still appropriately sized for the engine displacement at 10.5:1?

In other words, are they still the optimal pieces for the combo at the new CR?

If the answer is “no”, then expect to take a bigger hit in power than what just the loss of CR, and reduction in cam duration would yield.

The other side of the argument is...... how much can you afford to lose and still have the combo be “good enough”....... and does that seem like a reasonable outcome from the CR loss?

I feel as though high compression is a fairly effective way to help crutch up a less that optimum combo.

I have read in many different places that a point in compression is 2-3%. Once you get to a high compression, its a case of diminishing returns.
You said you were going to swap to a cam more suitable to the new compression.
My guess 30-40 horsepower just from compression.

I've seen testing done on a SB Mopar bracket motor that lost 30 HP by reducing the compression ratio from 12.5 to 10.6 or so so they could run pump swill with no other changes(timing or jetting)that made a 560 HP motor make 530 HP
They should have optimized the timing, jetting and spark plug heat range with the lower compression ratio on the engine dyno instead of doing it later at the track Those changes made it run faster than it had before, that racer is now a big advocate of low compression race motors

Is a 200 horsepower shot of nitrous oxide an option to make up for the reduced compression?

seems to me that 2 things are really important.. volumetric efficiency and burn rate. hi compression requires better fuel to control burn rate..ve changes with compression if you take the piston location into the deal. - a bump in compression will always mean some increase in power no matter what short of perfect ve. the overall goal is to improve volumetric efficiency . rite ?? i have seen a lot of 9 to 1 engines in class rule racing make big power. all things considered , an engine with 13 to 1 that has been worked out like the 9 to 1 will make even more power.... i am looking at the expansion ratio which gives a longer time to apply power during the power stroke as a reason for this.

Thank you for the replys.

My intension is to purchase a cam that Dwayne suggests for this combo.
I also have the option of surfacing the heads to get a little more compression. It will have a flat top piston in it regardless. The max compression I am looking for is mid to high 11.

I guess I have to get it together and see how it works.