dale5050

I recently had a local shop install a 408 iron block in my car and dyno tune it. The car put down 394 rwhp on 8.5 to 1 compression. The problem that I am having is the following:

I am having an intermittent knocking sound coming from what seems to be the passenger side of the vehicle. Some times the car will run like a champ with no hesitation or miss, other times it will knock like a bitch through the entire rpm range specifically from what appears to be the passenger side of the motor. It makes an audible thump...thump...thump and is only noticable under load--at idle I can't get the car to make the knocking sound. I have TTS headers and a big cam along with ported heads and forged everything.

I auto tapped a run yesterday and the car was showing on the auto tap 14-16 degrees of KR--frankly I didn't even think you could have that much KR....hmmm. Anyway, if the car is knocking, why would it knock from one specific area of the car???

I looked under the car and can't seem to find any areas where the exhaust could be hitting the k member. By the way, I have saved the autotap file of a full run if anyone is good at interpreting data.

Thanks

Boostaholic

iTrader: (4)

If your getting audible knock at 8.5:1 I would be pulling the head myself and making sure everything is ok, espically if you have reusable head studs/bolts. Its the cost of a gasket to make sure everything is ok in there.

But first you should verify that nothing is f'ed up in your valvetrain, all your pushrods are tight and stuff, which is very easy to do.

technical

Are we talking about a banging sound, a "knock" or knock/pre-ignition?

If it's a banging sound...under load, the engine may torque more in the mounts and you might not be able to tell at idle. You can powerbrake it if you have an A4, and see if there is something banging. Look around the trans crossmember, I had some intermittent clearance issues that plagued me for a couple of days.

If it's pre-ignition...again the engine will need to be under load, but at 8.5:1 I doubt it.

If it's some kind of rod knock or something, that should be more consistent. eg. at startup, but dimishes as the engine warms.

dale5050

First of all, the car is an M6. Secondly, it almost sounds like pre ignition knock and it is coming from the passenger side of the car. One thing I remember the shop tech telling me is that they had to use slightly longer push rods for some reason with my set up....hmmm. Anyway, what is totally wierd is that sometimes the car will run good and sometimes I will start it and you can just feel that it is lacking power and has that knocking sound that I mention. What worries me is that if it were simply pre ignition knock, why would it always sound as if it is coming from one specific area of the engine compartment? Also, when the engine runs bad you can feel the car jerk sporadically like it is missing or something.

I apologize in advance for the broad terms that I am using to describe my problem, but I am frustrated that I spent soooo much money on this engine and it isn't running right. Besides, I need to find out what is wrong before I slap on the turbo!

technical

Almost sounds like your tuning. Since you say it actually runs bad when this happens, try getting it tuned first. This way you'll have piece of mind when bolting that turbo on. If the engine bogs and jerks bad enough you'll hear some noises, especially clutch and exhaust noises which can sound like they're coming from a specific location in the engine compartment.