Just looked and saw RAMM got a 6% increase, much higher than the Vizard chart I posted predicted. I suspect he found some "bonus points" by building quench into it, too.

Well, RAMM?

Would a switch to aluminum heads allowed you to keep running the 38 degrees of timing and resulted in even more of a power jump?

Like the title implies I had the chance to test a 440 RB @ 9.4 static compression ratio and then again (due to an oil leak) @ 10.4 static compression.

This is a 446 I recently built for a customer using '915 heads and flat top Wiseco forged pistons. It ran all right during the initial dyno session but the rear main was leaking a little and that was not acceptable so I took it off the dyno and couldn't leave it alone.

When I was assembling the engine the pistons measured .055" in the hole. Also understand the customer really wanted to save these pistons so I cleaned them up and CNC machined them with a slight conical dish netting a little more volume. Basically I knew there was plenty of room to play with here so I decked the block exactly .045" per side which put it @ 10.4 comp. I had the chance to re-dyno with NO other changes. The power increase is somewhat expected but the timing requirements changed dramatically. Previous timing for max power was 35-36 total--Now 30-31 total is all that it likes. Interesting to say the least. So +30 HP +38 ft/lbs at the peaks was observed--the graph tells a much better story. J.Rob

That's all that I am saying. I increased through machine work-the compression ratio exactly 1 full point--these are the results. Make of them what you may. I offered my thoughts on why and how--I do not know for sure--I only know what I know and have observed. J.Rob

I for one thank-you for sharing info. keep up the good work.

What fuel where you using on both test? Any idea of how much the weather changes where? One of the local Mopar races did some testing on one of his pump gas street motors and had a issue with ignition timing on that motor, he says he verified the TDC on the motor and tried 34 or 36, CRS and it pinged noticably enough to stop the pull. We talked about the plug heat range, carb. jetting, timing light accuracy and jetting, the AFR where fat and the symtoms he was having. He ended up retarding the timing to 25 BTDC for the best results, which where substanstial I'm having troubles with my computer and ISP opening PDF files so I can't open and read the dyno sheets to help illustrate thhis results Test, test and test some more

That's all that I am saying. I increased through machine work-the compression ratio exactly 1 full point--these are the results. Make of them what you may. I offered my thoughts on why and how--I do not know for sure--I only know what I know and have observed. J.Rob

Sorry if my reply came off a little harsh, but your thread title leads one to believe that the HP gain could be attributed to a CR change alone, and my point was that that was not the case ( although stated poorly by me ). As stated in this thread, I think a quench change had partly to do with the improvement, and maybe piston top reshaping, etc. I to, appreciate all your hard work and sharing the results. Just wanna clarify to all that adding a point to your CR my not automatically have the same positive results as you did. Making multiple changes is my personnel nemesis, as I don't have easy access to a dyno - and 2 - 3 trips down the track once a month can give pretty limited info.

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The piston tops were reshaped for the initial build. I did not do anything different other than decking the block .045" This was the ONLY change. Pistons were in the same configuration both times. J.Rob

Good info... from the testing I did.. the lower the starting
compression the bigger the gain... as in going from 9.1 to 10.1..
its a deminising return thing

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Rod