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Ok on my new BBC 540 i am putting the 335cc afr cnc ported alum heads. I plan to run 7 to 9lbs of intercooled boost from my procharger. I want to run 93 oct. will 9 to 1 be to much comp. For that much boost? afr said you can run 1 full point higher with there alum heads without detonation because of the fact that they get rid of heat so much faster. Any thoughts. Should i lower comp? Any help would be great.
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8.5:1 is what I would use if I knew for sure that I will never have the boost any more than that. After you do it, you are stuck with it.
My favorite is 7.5:1 You can always back off on boost. You cannot back off on compression. Plus you can throw a little spray in with it.
Oh yea, That M3 is SC and the current bidder is serious. I spoke with him about it.
502procharger:
I plan to run 7 to 9lbs of intercooled boost from my procharger. I want to run 93 oct. will 9 to 1 be to much comp. For that much boost? I guess it just depends on whether or not you want to shoot a piston through your pan. OK, so I'm exagerating a bit. I wouldn't run much over 8:1, even with aluminum heads on a blower motor making any kind of boost, but I tend to lean towards the conservative side of things as I don't like pulling motors and rebuilding them all the time.
jordy, you still on?
Nope.
Sorry we're closed.
what if i run 8.5 to 1. my problem is if i ever decide to take the procharger off i want it to still run well. i ran 7 lbs with 30deg timming in a stock 502 all summer with no issue. i think it has 8.75 to 1 comp. think that is still to much.
502procharger:
what if i run 8.5 to 1. my problem is if i ever decide to take the procharger off i want it to still run well. i ran 7 lbs with 30deg timming in a stock 502 all summer with no issue. i think it has 8.75 to 1 comp. think that is still to much. The question is, do you want to build a blower motor or not? You can't really half ass it and make a multipurpose short block. Like Info said earlier (and I am not hangin on his nuts) you can always do 7.5 and turn the boost up as far as you want. And also, once you have a blower you will never go back to NA.....
The problem as I sit here thinking about it, is not so much with the compression on the top end, where the aluminum heads help, but rather on the bottom end that takes the brunt of the force. Sure you can shave points off of what you need octane wise by running the aluminum heads, but that doesn't change the cylinder pressure or load that the rods, crank, mains and all bearings involved are dealing with.
Hell, the motor in my boat before I rebuilt it was a backup motor for Steele Marines K-boat. Come to find out when I tore it apart, it was set up at 7.5:1 and I ran it N/A for a season and a half and it ran great.
I'm sure you could get away with 8.5:1 but I'd want to be damn sure I knew what you were running on the bottom and that it would be up to the task.
Any of you blower guru's can step in and correct me if I'm wrong, but that's the way I've come to understand it.
I would say that you can run 7lbs with 34 total timing at an air fuel of 11.8-11.9:1. If you want 9, then I would say 30 total and 11.5:1 and it still will probably want to detonate a bit more. I"m assuming this is with there larger intercooler, would not do 9 without it. I would be closer to 8.25:1 and run 9-10 with 32-34 all the time. You will lose some low rpm torque with the lower compression though, but will gain back power with the more air and fuel.
Thanks,
Dustin
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