General cam timing question.
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From: Cedar Falls, IA
General cam timing question.
Both of the last two cams purchased from CompCams came with a note that said they were ground 4° advanced from the factory. I'm assuming they do this because the later truck motors had the 4° retard built into the timing chains for emission reasons.
Ok, with this in mind and with the thought of keeping DCR to a reasonable level with Aussie heads, when rebuilding a motor such as this should we install the cams 4° retarded thus creating a "straight up" condition with these newer cams?
I ask because I'm thinking of doing this to lower my DCR because of detonation in the 351M I've built. It's either that or put the factory heads back on and sell a brand new set of Aussie's...
John
Ok, with this in mind and with the thought of keeping DCR to a reasonable level with Aussie heads, when rebuilding a motor such as this should we install the cams 4° retarded thus creating a "straight up" condition with these newer cams?
I ask because I'm thinking of doing this to lower my DCR because of detonation in the 351M I've built. It's either that or put the factory heads back on and sell a brand new set of Aussie's...
John
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Senior User
Joined: May 2003
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From: Cedar Falls, IA
Compression?
That's a good question. It's a 351M block, .060 over and has been zero-decked. Standard Aussie heads on top. What that works out to for compression I don't know. Without decking it should have been about 10.12:1. I'm guessing 10.5 or so but I don't know how much got added when it was zero decked. (anyone know how to figure this?)
Factory deck is 10.297 and the machining sheet says it was brought down to 10.250 so that means they took .047 off the top. I put in .060 replacement dished pistons back in that I believe were 10cc dishes.
So here I am with too much compression (DCR) for 93 octane. I'm guessing I'm going to go back to the factory open-chamber heads to relieve some of the pressure.
John
Factory deck is 10.297 and the machining sheet says it was brought down to 10.250 so that means they took .047 off the top. I put in .060 replacement dished pistons back in that I believe were 10cc dishes.
So here I am with too much compression (DCR) for 93 octane. I'm guessing I'm going to go back to the factory open-chamber heads to relieve some of the pressure.
John
