Well, after the motor went "soft" and began overheating, he did insist on making one more 1/4 mile pass ... and that cooked the piston ... I suppose it was his fault as well.

LWM

 

What's a dowel pin?? Never heard of it before.

 

This would be the pin on the end of the cam that drives the optispark...

 

I got it back running with a new piston, ring, bearing, surfacing the head .002", and doing a valve job on #1 only.

I checked fuel pressure at WOT and found that it is climbing to ~53 psi and staying there, which means the fuel pump is doing its job.

I also had the #1 injector flow tested today. A 42 lb/hr injector is supposed to flow 440 cc/min. Mine did 460 cc/min, so the injector isn't the problem either.

I'll probably go to the grave not knowing what caused #1 to melt and break. :-(

Mike

 

Mike, you might want to retune for a richer A/F ratio. The colder weather is denser and possibly leaned out the mixture even more that night and just so happened that just one piston let go. I would shoot for mid to low 11's A/F. For longevity, this seems to be the best ratio on blown applications. Just a thought!

 

Dave, I've basically come to a conclusion based on the following:

-The Superfueler tends to make the rear cylinders run richer. The fuel is heavier than the air, so it tends to go staight to the rear cylinders rather than making the turn for the front cylinders. Also, NA LT1's run the front cylinders a little leaner base-case because the front cylinders are the shortest path for the air to take.

-The A/F ratio was 12.5/1 at full throttle, which is tad lean for a supercharger, as you mentioned.

-The night that it blew was colder than normal making it run even leaner, as you mentioned.

These all may have combined to cause #1 to lean out too far. The problem is that I have ALL injectors running 100% duty cycle. I'm thinking about installing an Acceleronic's impedence converter and some 75 or 85 lb/hr injectors.

Don't y'all deal in racetronix? Cut me a deal on some injectors?

Anybody want to buy a Carroll Superfueler (RKrause seems to have really good luck with his with 730+ rwhp) with 55 lb/hr injectors and a 58 mm throttle plate? How about some 42 lb/hr SVO injectors?

Mike

 

Is the piston ring gap perhaps a smidge too tight? If so, you can butt the ring ends together and rip big chunks of the ring land above the top ring off and send them flying into the combustion chamber causing all sorts of metal carnage. This can happen even with NO detonation (the flecks of aluminum could have been deposited on the plug AS it shredded itself- not from detonation BEFORE destruction).

Ring gaps for a blown application are typically .005-.007 wider than a N/A application, everything else held constat. Piston manufacturer is the RIGHT place to ask about ring gap for a particular application- NOT the ring manufacturer.

A picture of the destroyed piston would be helpful in determining if this was a contributing factor.

 

Mike,
Lonnie Pavtis is now a Racetronix dealer. I am sure he can cut you a good deal. Here is his info:

Here is his info:
Website: www.westol.com/lpavtis
Email: lpavtis@westol.com


Thx,
Claude

 

I doubt it since I gapped the rings at .024 - .026 top and .018 - .020 second ring.

I've broken pistons in the past due to this problem, so I gap them all wide now.

Mike

 

12.5 and maxed out injectors sounds like it might have leaned out detonated, maybe you saw more boost with winter weather.

I've heard of one LS1 friend having one combustion chamber that was too small and it caused his motor to lose that piston.

But you need more injector for your setup anyway I would think.

I have a YS, 348ci, and got 83's but I could have gotten by with 72's but I have room to grow with the 83's.

 

I hate to make a simple assumption, but what if it was just a defective piston?

 

That has definitely crossed my mind. There are cracks extending both directions from the broken section.

I think it wasn't a defective piston because there was melted bits of aluminum on the valves and spark plug.

Or maybe that was just shrapnel that wasn't actually melted.

Maybe you're right . . .

At any rate, I've ordered the impedence converter box (thanks, LJ) and some 84 lb/hr injectors.

Mike

 

Can you post come pics when you get it out, I love to see carnage. I would try to send the piston back with pics of the others still in the block and see if they will do anything for ya. Its worth a shot, then again it would make a good paper weight.