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I posted last summer on this and went through all kinds of hell trying to figure out whats going on. I checked ignition and fuel, up and down, inside out. I think I found the problem. Is it possible the valves are hitting the pistons? Its a 71 351C 4V cc heads and TRW 030 over pistons. The Valves are stainless manleys. The cam is Lunati # 41113. Intake .576 lift 310 dur exhaust .574 lift 320 dur. I think it maks about 10.7 compression but Im not sure on that. I hav not pulled the heads yet but hope to in the next 2 or 3 weeks. If the valves and pistons are hitting, how much do I need to cut the reliefs in the pistons or can I purchase pistons with reliefs already cut? Any ideas out there?

<font size=-1>[ This Message was edited by: ddShelby on 2/3/02 11:17am ]</font>
 

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First off, did you have the heads or block milled when you built it? That could be a big factor if the valves are hitting the pistons. I am no expert, but if the valves are hitting the pistons, wouldn't the valves bend or something break and the negine would not run at all? if the valves were hitting, then why would it matter what it was running at. wouldn't not run good at any speed? I hope some more knowledgable guys here can help me out.
Hope this helps some.
Matt
 

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If the valves are hitting the pistons, you would definately hear it, and your engine wouldn't be running very well from all the damage caused by it. Is your valves adjusted properly? Do you have the correct springs? Maybe you're getting valve float at higher rpms?
 

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You will NOT necessarily hear the valves hitting the pistons. IF they were hitting, chances are they would be bent out of the way by now.

I bent all 8 exhaust valves at the strip once... back before the car had a rev limiter. I was powershifting into 3rd at 6500rpm and the friction surface came off the clutch. The car was WFO @ 6500, then the clutch was depressed (still wide open), tranny put into 3rd (still wide open), then the clutch released.... only to find nothing there. After realizing what happened, I backed out of the throttle.... but not until the tach was at about a bazillion rpm!


I was trying to get the car into the 12's back then, and had a best of 13.10 that day. After fixing the clutch that night, I went back the next cold morning at 8:00 only to run a 13.25! It should have been in the 12's!!!!


Turns out, After checking the cranking compression and seeing it was down around 10-15psi on every cylinder, the car had eight -slightly- bent exhaust valves that needed replaced. A MSD 6AL (relatively new and out of my budget at the time) was purchased shortly there after.


Anyway... enough of that story. Point is, bent valves aren't always that obvious. If they were bent to the point that the car was running rough, the compression on those cylinders would be WAY down. Plus, I would think the bent valves would be most noticable at low rpm where the gases have more time to escape the cylinder through them. Do a compression check to verify the condition of the cylinders. If it checks out, you're going to have to go over the rest of the car a little more carefully.

Good Luck!
 

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Unless the heads have been cut ALOT, and the block been decked alot, I dotn se h ow that cam would cause the valves to hit. I am running the old trw domed pistons in my motor, my heads have been shaved .050, and my valves dont hit. And thats using a .628/.625 lift solid cam with more duration than the one you have. I would bet your springs are soft and its floating the valves and thats why it doesnt run well over 3500.

I would be more inclined to look somewhere else for a problem.
 

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Discussion Starter #6
Took me nothing short of forever to figure this one out but alas. I got it. The MSD billit distributor has mech advance and the little plastic friction buttons in the distributor had passed on to a higher life. As it turns out the distributor was making no advance as rpm went up. Hence the car would run poorly after 2000 to 2500 rpm. I took out the distributor and fixed the advance mechanism and now the car runs like an animal. Its nice to get rubber in 3rd gear again !
 
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