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Thread: Higher compression with blower

  1. #1
    Speedin' Ian
    What is the draw back of running slightly higher compression with a blower. For instance lets say you had a blown BB with 8:1 running a blower 20% over, how would that differ from a blown BB with 9:1 running 10% over? The reason I ask is I was doing some quick math and I think our new 540 is going to have about 9:1 compression, based on the pistons and heads we are running (SRP -9 dome and Brodix BB2's). We plan running gas, will this cause a problem? Keep in mind this is a dragboat that will get very little use, with no prolonged cruising (how far can you go on 5 gallons of C16)

  2. #2
    9:1 is low enough and 10% over shouldn't be bad either. Dont let it go lean and watch your timing. I've heard thats a recipe for a hole in the pistons with gas. There is a chart around that gives the 'real' compression ratio based on your built in compression plus whatever the boost is. I dont remember where to find on the net though. Maybe someone else will know.

  3. #3
    9 is ok with race gas. Lot of blown gas racers did that a long time ago. Timing 34. Personally I think C-12 is good enough.

  4. #4

  5. #5
    I have built and owned several blown gas engines over the past ten years or so. Infact my 85 Chevy Dooley has a 174 B&M blower on top. I picked up 4 mpg on the highway towing a 38', 12,000 pound trailer!!!! . One thing to consider is a marine blower engine see's less heat.So higher compression is not as critical. "MOST OF THE TIME" Im running 9:0.1 and even with a "timing control box" from MSD I have to run atleast mid grade. But my Deaver hydro with a 144 B&M will run cheap chit all day. And with 9:8.1 compression. The truck makes 8 lbs by 4400 rpm and the small block makes 8 lbs by 6200 rpm. I guess what I need to say is cylinder temp plays a major role in comp. and boost limits.
    Mike :hammerhea

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