Take a Guess!
04-08-2012, 07:46 PM
#28
Your cam is in wrong or your piston dish is larger than you think (or the engine is smaller than you think and the cam is in right.....that's a scary thought!!).
Borrow a leak down tester if you can....but at this point I would plan on pulling the engine or trying to degree or at least reconfirm the dot to dot install of the cam. You wouldn't be the first person to install it off a tooth.
A well set up combo has almost twice the cranking compression btw.....120 is suuuuper soft......like the "S" in your avatar soft.....LOL
(Sorry man....couldn't resist!)
At least you have an inkling to why your numbers are low....if your a glass half full kind of guy you can spin the info you have in a positive fashion. Knowing whats wrong is half the battle.....now you have to dig deeper to find out why.
Good luck.....try and keep a good attitude and know the car will be alot more fun to drive when you finally rectify the situation.
-Tony
Borrow a leak down tester if you can....but at this point I would plan on pulling the engine or trying to degree or at least reconfirm the dot to dot install of the cam. You wouldn't be the first person to install it off a tooth.
A well set up combo has almost twice the cranking compression btw.....120 is suuuuper soft......like the "S" in your avatar soft.....LOL
(Sorry man....couldn't resist!)
At least you have an inkling to why your numbers are low....if your a glass half full kind of guy you can spin the info you have in a positive fashion. Knowing whats wrong is half the battle.....now you have to dig deeper to find out why.
Good luck.....try and keep a good attitude and know the car will be alot more fun to drive when you finally rectify the situation.
-Tony
04-08-2012, 11:35 PM
#30
I do agree he needs lighter rockers (YT Ultralites or stock IMO), possibly better springs depending on whats on the AFR heads he has now, but finding the root cause of his low cranking CR should be priority one IMO. That shows there is a mechanical or fundamental flaw in his set-up.
Even if his shortblock was retarded low on static CR based on wrong pistons, too thick a head gasket, etc. etc., even a 9 to 1 compression 427 would make more torque at the lower RPM's than the dyno results he posted.
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OP....you need to roll up the sleeves, pull the heads and cc the chambers, verify what exact piston is in this engine and how far its out (or in) the hole so the exact compression ratio can be calculated. Then you can mill the heads accordingly (taking advantage of their removal) to bump your static CR and based on the piston deck height figure out the optimal thick head gasket as well for better quench. Then you need to definitely check the cam installed position because there is a decent chance thats potentially your problem.
While I was in there I would also recommend you verify you really have a 427 by measuring the bore of the cylinder and the stroke of the piston (measure how far down the hole the piston retracts at BDC).
IMO, at this point there is no magical piece of advice or a keystroke of the laptop thats going to fix your deal.....your going to have to get into the engine and see what's what if your truly motivated enough to improve its performance. I would like to be wrong....and there is always a chance that it is something simple, but I have a sneaking suspicion that's the case.
If you had another dyno local to you that you could make a couple of pulls on for $75 or so (to verify your original numbers were close) that would certainly be money well spent IMO so you know your not on a wild goose chase. What if you engine is really a bunch stronger on a different dyno and your cranking compression gauge is messed up? You never know....its worth verifying the engine needs more looking into before investing the time and money.
Good luck
-Tony
