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| Re: to shim or not to shim |
Subject: Re: to shim or not to shim
by L18_B110 on 2005/5/6 8:34:54
not just for the first few minutes - until you have all the tuning sorted and no detonation problems. The first few minutes you just want to be sure you are getting oil pressure to the turbo and engine. Sitting there idling isn't going to be a concern if you have oil supply sorted. You might have trouble finding a mechanic willing to touch the thing, so you'll probably have to do it yourself. While tuning and road testing, if you hear any hint of detonation, back off immediately and go do some more head scratching. That can't be stressed enough! it doesn't take much detonation to kill an engine running forced induction, or at least do enough damage to cause piston/ring failure in the not too distant future. Less timing or more fuel will be the main things you'll be adjusting obviously. If you can get access to a portable sniffer unit they are invaluable, so you can keep an eye on your mixtures while road testing. Boost gauge is pretty much mandatory too so you have some idea what's going on when tuning.
If you really are going to only run 5 or 6lb boost you might get away without a head shim.
Our rough'n'ready A14 turbo engine was a standard A14 with .030" ACL head shim, locked dissy (ie no mech advance) set at 10degrees advance, which was not the greatest for off-boost driveability, but that wasn't a real objective of ours. That's the easiest way, but certainly not the best. Bit hard to describe how to limit the dissy's advance mechanism, but its not particularly hard to do. We also ran water injection and up to 12lb boost. It seemed that 4lb was the point where it started doing anything useful - under that and it may as well have been naturally aspirated. 5 or 6psi won't be a rocketship or anything, but you should get a useful power gain.
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