Looks like I wont be joining you guys at njmp next weekend and looks like ill need some opinions on where to look. So this is the whole story last race of the year at limerock coming onto the front strait my car started clicking really bad I checked oil pressure and hit kill switch right away pressure was normal. Coasted into pits and towed it home. Following weekend took cam tower off saw had a broken inner valve spring on cyl 2 cant remember the valve though. So we replaced the spring with the head still on and started it and didn’t hear a noise.
Then during the offseason we had planed to make a new head for the upcoming year I had a few heads laying around and we grabbed one off the shelf and sent it to be decked. Head came back and we lapped in the valves installed new guides and new seals also installed a steam vent. About a month or so ago we slapped the new head on with a new gasket and started her up we heard a slight ticking or tapping sound intermittent and only when it was off idle. We swapped in another cam tower incase it was coming from there to no avail. Then we thought maybe the machinist took too much off the head so we put an extra thick head gasket on it from Porsche to raise it up incase it was just being touched by the piston (there were no blatant marks on the pistons or head that we could find). Thicker head gasket didn’t help either.
We gave up on that head and grabbed my old head from the previous year and slapped it on with normal gasket and went back to work with all the other work needed to be done to the car. At this time we were only running a new long tube headers we were upgrading to so when we started it we couldn’t hear the noise so we assumed all was well and disassembled the head we had built and tossed it out being too frustrated with it.
So last weekend we finished up the exhaust system and threw on our garage test and limerock muffler and low and behold the noise was there as intermittent as always. Out of frustration and exhaustion from working on this for so long and not finding any evidence at all in the cyl’s or head of anything my father sent it to redline and held it for about 10 seconds. Now the noise is more of a knock and a lot louder. We did notice some built up crank case pressure the dipstick popped out and the breather was flowing pretty steadily.
I’m writing this to ask if anyone has an idea of what the noise could be? I’m thinking its rod knock now but I really have no idea

I've heard/had a similar problem before. It probably is rod knock/spun rod bearing. They have probably overlapped each other a little and are just touching the valves.
Did you check that the valve did not get bent when you broke the valve spring?

yes we used compressed air to hold valve closed while we used the spring compressor had a perfect seal, if i spun a rod bearing does that mean the cranks toast i dont mind replacing the rod ive got tons of those but i lucked out and the parts car i bought that this motor came out of was at one time a pca track day car (could tell from the studs welded in for the bolt in cage) and lucked out crank was cross drilled and i really dont want to lose having that.

I will ask the MAN and get back to ya.

A quick way to get an idea if it's a rod bearing is to drain the oil through a screen or cloth to see if you have metal shavings in the oil. This does not guarantee anything but gives you an idea without tearing the motor down.

If a brg has spun, oil pressure should suffer. Compression test may also reveal some info. If brg is bad, piston won't travel as far affecting comp.

It takes a lot less time to pull the pan than the head. Wristpin can also cause a noise as can broken rings(which also may explain crankcase pressure).Also, rod brg noises usually occur under load unless it's so bad that it knocks all the time. Wristpin noises usually occur during the transition from non load to slight load.

This from the MAN.

thanks alot my plan of action is basicly to take the time and just pull the motor i feel much more comfortable working on the bottom end on an engine stand and it gives me access to check out all the other parts "eg. clutch, oil pickup pan baffeling" and make sure everything is in good shape. thanks alot guys for all the help ill make sure to let you all know when i get her on a stand in the next week or so.
ps. on a unrelated note i apparently am having a bad week with these 944s my 89 2.7 daily driver developed a steady oil leak somewhere near the exaust on the commute home so i have another headache on my hands. wish me luck i was too depressed to even look at it i just put an oil pan under and walked away haha

so finally got the motor out and opened up and looks like my motor decided it didnt like having a #2 rod bearing any more. it looks like the rod and the crank are dammaged. if the crank was bone stock id just replace the whole engine from a parts car but this bottom end has been done with from what i can tell cross drilling and id like to keep it. so does anyone have any advice on oversized rod bearings and where to get them. or is it a lost cause. i plan to get the crank out in the next few days and take it to the local napa machine shop to have them look at it but id like the opinion of people who know these motors. thanks John Brandenberger

Last I checked on oversized bearings, they were prohibitively expensive. On the order of $500. Only from Porsche. What does it take to put Chevy bearings in? New rods?

Oversized rod bearings is a bad idea....10 x more expensives then standard RB x how often u change the rod bearings.