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511 detonation and valve clearance

925 views 2 replies 2 participants last post by  bowtie44s 
#1 ·
Here is what I'm working on. 9.8 mark IV block 4.310 bore, 4.375 stroke, 6.385 rods for a total of 511in³. Aluminum 118cc combustion chambers, -18cc dome pistons.

What I want to go with is Howard's 120325-10. Hydraulic roller 229°/235° @ .050. .589/.600. 110LSA

I am worried about two things. Here are my pistons.


They have a huge intake valve relief for the intake valves and nothing for the exhaust. Will I have to worry? The exhaust does have .011 more lift. I don't know of a way to check this before I order the cam.

I am also worried about detonation on pump gas. The static compression is 10.48:1. I realize elevation makes a huge difference. I am at 600'. Howard's emailed me the cam card. The intake closes at 67° ABDC. That will put my dynamic compression at 8.18:1. Do I need to worry about detonation here?

I'd like to advance the cam 4°. That puts my dynamic to 8.44:1. Is that in the danger zone with aluminum heads and 93 octane? Does advancing the cam help or hurt piston to valve clearance?
 
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#2 ·
Just two weeks ago built a 511 with similar Mahle pistons. Lunati 335 by .660 lift reground hydraulic roller and there was plenty of clearance on the exhaust side.

In my own projects. In the 488 cube, I have a Howards roller with .680" lift, 4 degrees retard. Plenty of valve clearance on Probe pistons. The other BBC is a bit over 500 cubes with a Lunati roller .680 x .715" lift also with 4 degrees retard. Clears 10-1 Keith Blacks.

Dyno sim. on both combinations showed a large power increase with the retard. :thumbup:
 
#3 ·
Thanks guys, you sure have put my mind at ease. Bobcrman, what kind of power were you making with those setups? I don't have any estimating software. I'm hoping for 500. I know I could get a bigger horsepower number with longer duration, but this IS going in a truck. I need to keep low end power. If it was going in a sub 4000lb car, I agree, I would want a lot more duration.
 
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