are you running to lean ?
does the headers glow cheery red ?
what intake you running ?
if your melting the top ring , this will cause the blow by of oil .
are the pistons hypertectic's
and have you checked the cam lobes for wear on the intake lobes of number 5 and 6 .

 

What about crankcase ventilation?? How is your engine vented?? Alot of oil into the mixture really messes up the fuel/air ratio. I'd probably make sure that thing isn't building up a bunch of crankcase pressure or you aren't dumping that oil laden crankcase pressure into the intake somewhere.......sounds like you already addressed the usual areas of concern so now you have to start looking at the odd stuff.

I'm assuming ring end gaps and all that basic stuff is ok.

 

intake is a edelbrock performer 2101 dual plane with a 1" adapter for a 2 barrel.The exh. has never gotten "red" and water temp stays between 190*and 205* at least until the piston comes apart,then the w/temp rises alittle.The crankcase is vented thru 2- 3" breathers filters on the top of the left valve cover. The cam and lifters are out of the block and look like new......ring gap set at .020..pistons are forged TRWs

 

wow, sounds like you have the bases covered.

The engine isn't all that radical to be causing too much of a problem, sounds like a normal claimer motor.

Years ago we ran a 360 sprinter that had a tendency to fill the right valve cover with oil after about 10 laps, we had to restrict the oil a bit more and open up the drainback holes. That was a solid lifter motor with alloy race heads, but with your iron heads and hydraulic lifters that shouldn't be happening.

This boils down to high combustion chamber temperatures and I suspect a lean condition more than anything. The piston crown "rolling" the edge and melting at the ring land isn't too characteristic of detonation. I've seen a few of the new GEN III engines hurt just like this when power adders or a bunch of boost is installed....just too much heat.

You originally suspected a vacuum leak and I think that might still be it......if you are convinced you are getting enough fuel. Gotta be a lean condition.

 

Right after it burns a piston did you remove the carb? if so did you see oil all over the plenum? this indicates a classic intake leak. Have your intake checked by a machine shop for warpness. I once had a edelbrock performer so badly warped even after they removed .020 it was still off so I threw it away. If that checks out okay I too agree it`s going extreme lean.
When I had a bad intake leak I could remove the intake with the carb still on it and watch the oil drip out of the runners, if your intake does this, it`s got a leak.

 

I'd look at an intake leak also. Has the block been decked and / or the heads milled?

I had an engine that I couldn't get the intake to seal though the gaskets "looked" like they had been compressed. All of the surfaces checked for flatness so it had me stumped. I set the manifold on the engine with no gaskets and I'll be darned, there it was, plain as day. The top was touching but the bottom had a good .060" gap. The manifold would come tight on the top but barely compress the gasket on bottom causing a leak along the entire bottom edge. The heads had been angle milled at some point in their life.

I see that you changed the heads and intake so it would have to be the block, which is unlikely but you never know, stuff happens. Mock it up "dry" and see how it looks. It's a long shot but it won't cost anything!

 

This wiki article was written for this exact scenario.....
http://www.crankshaftcoalition.com/wiki/Manifold/Head_vacuum_leak,_internal

 

pistons

What brand and type of material are the pistons???

Can you post a picture or 2 of the broken pistons??

What is the top ring gap??

Keith

 

Along with Keiths question what part number intake gasket are you using and are you using gaskets on the end rails or RTV?

 

Are you using a power valve in the carb?What rating is it? 4412 carbs are known to pull enough vacuum at the end of the straightaway to close the power valve causing a lean condition right at the wrong time due to the small carb size.

 

All i know of the pistons is that they are 10:1 forged trw 2 relief flat tops
The ring gaps for the top and second rings are both .020
the gaskets are the stock port fel-pro blue that come with the perma-torque blue engine gasket set
power valve is a 5 and at this point the jets are 75s
I never use the end seals,always use rtv

these pistons went in the holes spotless clean and shiny,as you see them here,they have about 45 laps or 15 miles on them.

 

Think about this.

Cylinders 5 & 6 are on the same 'crank' rod journal.

Has this 'crank' been 'stroked'?

This 'crank' rod journal, could have been ground "offset" higher compaired to the others.

 

Stock crank and rods..

 

We build a ton of circle track engines and we don't see that problem and after looking at your pistons I would have to say its detonation from to much timing.

1 Is your balancer degreed ?

2 Is there a 36 degree mark on on your balancer?

3 I seen a guy have this problem and after seeing him use a dial back we found the light was off 7 degrees, We always use the one wire light from Flaming River and run the engine up to full adavancement and bring the 36 degree mark up to the pointer.

(note 36 degrees is what we have seen on the dyno on our engines with this similar set up and was only using it as a base number)

Those aren't Hyper pistons are they???

Useally to much timing makes the exhaust runn cooler and late timing or to much fuel will make the exhaust run hotter.

If you want PM me your number and I will try to work through this with you.
Carl

 

pistons

IMO, the piston failure is from detonation.

Now we need to find out what is causing it.

As a side note, are the valve cover bolts always coming loose???


1st place i would look is at that HEI.

Tell us all you can about it.Have you ever checked the rotor phasing on it???

2nd an just as important is getting the intake gaskets sealed.

Do you know how much the block and heads have been cut???

 

Agreed it looks like detonation, I beleive your power valve could be a factor it is very possible for the small carb to pull more than 5 inches vac at the end of the straight closing the valve. What I did with the 2bbl engines was get an idle reading and went 1 inch under it seemed to work well.

 

I do agree with CNC BLOCKS NE and k-star that my biggest problem is the timing and possably the dist. itself,will try and find some one to set it up,and also figure out how to seal the bottom of intake..
Thanks everyone for all of your help,will keep you updated

Ray

p.s. valve cover bolts never loosen up.

 

pistons

What do the underside of the piston tops look like?? Are they burnt???


Those HEI distributors can be out of phase and cause the spark to jump to the wrong pole on the cap when firing.

Who ever you get to check the distributor have them check it for a problem called Hysteresis. They will know what that is.


Keith

 

I spent quite a bit of time with Ray on the phone Sat. nite and I would have to say the dial back lite was the culprit because after about 3000 RPM the timing lite was spuratic and was showing the timing marks bouncing around 10 degrees each way.

On those engines that run 6500 you have to know what the timing is at 6500 or so to make sure nothing is changes at the high end of the RPM.

Here is a couple of good links to look over.

http://www.chevytalk.org/fusionbb/showtopic.php?tid/173877/

http://www.dragracingonline.com/technical/vii_10-lights-1.html