Quote:
Originally Posted by MoreGAS
Bummer R
Looks and sounds like it was detonating. You changed the heads but didn't recalculate compression it seems(CC the new heads and piston)?
Do the math , if the head reconditioner took off .010 or .020" , you may have lost several CC's of head volume, that will make quite a difference in compression. Also your math on the ignition timing: 22.7 plus 1 is 30 , can you clarify? As a rule of thumb, when we twin plug an engine like this , we generally need 5-6 degrees less ignition advance, vs a single plug to get to max tqe, pk hp. . So generally speaking, a race engine like that single plug may achieve max tqe and Hp at roughly 30-31 degrees, so 25 degrees of advance twin plug we commonly see. This is where Porsche Motorsport would set the factory RSR 3.8 sprint & original 3.8 Std engines we have seen, run and tuned . Of course there are exceptions and not all engines built the same run identically, but your advance of 30-31 would be way way too much advance.
You can check those damaged, and your other pistons and check the top ring land gap between top ring and the piston land with a feeler gauge and see if all pounded out, .004" is the limit tested with a new ring., but with your existing rings you'll get an idea of condition. New, this should be at or just under .002". You rod bearings also are likely pounded out with the detonation.
You also can send your pump out to whomever you use the service and calibrate it and check each cylinder flow is correct and even. On the last OG 3.0 RSR engine we rebuilt Gus at Pacific gave us our new injectors back(we supplied new streeter injectors) with each cylinder position noted to be more even.
Ideally, you need to be checking lambdas each side on a new engine(we log these ALL the time if EFI) , and use some form of high quality audio knock detection when optimizing your ignition timing at initial set up. I know it isn't always convenient but finding a Dyno and savvy operator with necessary equipment will save a bunch of time and money in the end. If you cannot do this be very conservative and stick within known realms.
Kevin
GAS Motorsport
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As stated in my original post, the engine is twin plug and 12 to 1 compression. The XDi ignition timing is configured as initial, 3000 and 8000. 22* plus 7* plus 1* equalling 30*. AFR are high 11s-low 12s. This engine has been in action for 3-4 years and on this refresh it got a diff set of heads and pistons to match so the compression stayed the same. On paper, the heads should have added power, but enough to blow up the motor? Don't know and that is my conundrum, what caused it? I will rebuild it, drop the timing to 28*, keep the compression at 12-1, test with a timing light, probably get a knock and head temp sensor. Again thanks for all of the response. Bob