A buddy of mine just had his motor built. It's got a supercharger and 302 stroker kit. The car runs great until it hits 10 lbs of boost. It starts rattling like crazy when it hits 10 lbs of boost and the car falls on it's face. He can shift gears and it'll go to pulling like hell again until it hits 10 lbs. Any ideas of what could be causing this? It sounds kinda like valves rattling very badly when it makes the noise. I know it's probably something serious as it looses all of it's power when it starts doing this. I really want to avoid pulling the motor but I will if I have to. We know it's not deotonation and it's been to two different dynos to try and resolve the problem and both said it's something inside the motor doing it. Any ideas will be appreciated. Thanks

 

I'm looking for any and every idea of what could cause this and why, so don't be scared to tell me whatever you think it could possibly be. I want to know everything to look at. I've gone through 2v motors in the past and dealt with problems but not 3v and I've never tried to deal with a problem like this.

 

302 stroker is known to have valve slap. Sounds like that is your problem under higher boost.
If you have the PCM knock sensors enabled, The valve slap will be interprated as pre-detonation (pinging) and it will cut out timing advance and that will kill power.
So that is why people who research these mod motors recommend using a 298 inch stroker kit. You can keep the knock sensors enabled and there will be no piston slap from the over-stroked crank.
Does he have the knock sensors enabled or not?
Who built his engine? They should know about this stuff......

 

He doesn't know if the knock sensors are on or not. The engine was built by a handy man with a shop, it was his first 3v and his first stroker kit. He did not get the pistons fly cut. I got with the car owner and found out that the kit is a 301 stroker kit with a 3.75 stroke but he went with standard sized pistons instead of the .020 over pistons.

 

Well it's very possibly valve slap like Zkiller said. I don't think i'd go with a built stroker if I was going to add a blower.

What kind of blower is it? I don't know what spark blowout feels like, but I know it becomes a problem at 10psi and the spark plug gap is closed to .035 to help control it. Check the spark plug gap, it couldn't hurt.

 

It's a vortech blower with a 3.0 pulley. He's got the 8 rib kit and a S trim.

 

I would check the spark plugs. are they 1 range colder? With 10lbs of boost he probably is misfiring. It may be valve float too. He may need to get some better valve springs

 

Im going to ask something almost to obvious.....

What kind of upgrade did he do to the fuel system?

 

+1.. Could be going lean and causing detonation..

 

He's got a gt 40 fuel pump and a KB boost a pump. The car was on the dyno a couple of weeks ago. James from RWTD dynod it. It ran great on the dyno but still had some piston slap. He ran it to redline on a few passes with minimal slap from the motor. James also put the spark plugs in and they are one range colder. After a few passes the slap got louder so James quite. The car owner then drove the car which makes no noise if driven regular. He tried to race it a few times and every time the noise got louder and louder and the car lost more and more power at 10 lbs of boost. The few passes James run it to redline it hit 16 lbs of boost and made really good power. The noise just progressed as time went on and has gotten super loud now when he stomps it.