Don Terrill’s Speed-Talk

My friend has a blown(871) 496bbc,that burnt up pistons 1,3,2,4.

It runs two Holley 950's. I'm thinking something must have happened to the front carb,because the rest of the pistons look great.

What kind of temps does it take to do this kind of damage?

Is there anything else I should be looking for?

I'm not positive,but I believe it is running about 12psi boost and it was dyno'd at 950hp.

Anyhow he wants me to fix it,but I need to know the cause first.

If the carb checks out fine what else should I look for?

Any suggestions appreciated.

Thanks,
Steve

Sever detonation lifted the ring land at it's weakest point which is right where it failed. "Most" of the time it's caused by to much timing for the octane or effective compression ratio running. It also looks like you had oil migration into the combustion process which can also be a major contributor to detonation in a blown application. The detonation unseats or rattles the rings which make oil migration even worse so it goes from bad to worse in a hurry.

I would also suggest you not run the gas ported pistons on the replacement set if the blower is continued.

Blessings.......Ron.

Ron C. wrote:Sever detonation lifted the ring land at it's weakest point which is right where it failed. "Most" of the time it's caused by to much timing for the octane or effective compression ratio running. It also looks like you had oil migration into the combustion process which can also be a major contributor to detonation in a blown application. The detonation unseats or rattles the rings which make oil migration even worse so it goes from bad to worse in a hurry.

I would also suggest you not run the gas ported pistons on the replacement set if the blower is continued.

Blessings.......Ron.

Thanks Ron, I thought it could have been caused with what you said,but pistons 5,7,6,8 look to be fine?

I'll have a closer look at them once we have them out.

I'll ask what he was running for total timing and fuel. It could very well be detonation.

Motor came out of Texas and appears to have been well built,and it did run very well in 3800lb 55 chevy.

Thanks again

[quote="Rommel Racing]

Thanks Ron, I thought it could have been caused with what you said,but pistons 5,7,6,8 look to be fine?

[/quote]

Every engine when you push it to the point of destruction will have cylinders that fail in order. You especially become familiar with that particular order when your trying to develop an engine to make more power and live. Blown gas is very unforgiving and I can tell you I've torched a few pistons in my persuit of competitive power. In my particular case it's number 6 cylinder that torches a piston first. So I watch and tune to that particular cylinder when I'm on the edge.

Blessings........Ron.

how about too much fuel?, kinda like on a nitrous motor?

Nitrous motors can lift ring lands due to an over rich condition because of the increase in oxygen that will allow the fuel to burn down in the ring land.
Usually on a blown engine when you get that rich it will back fire the blower, which causes it's own problems.

These conclusions are based on my own experiences and my own accessment. There are other theories out there .

Blessings..........Ron.

Were the other pistons damaged near the Intake area.Detonation will usually occur around the coldest part in the cylinder, & thats what it looks like.

So is that upper portion of the cylinder discolored or is it just bad lighting?
Was it run with no coolant?

mmmitch588 wrote:Were the other pistons damaged near the Intake area.Detonation will usually occur around the coldest part in the cylinder, & thats what it looks like.

Yes,the damage is in the same spot on the other pistons,although #1 piston was just starting to go,again the others all look fine

Looks like you have got too much compression for the fuel you are running. Blown alcohol engines run 10.5 to 11.5 on alcohol, not 94 octane pump gas. Looks like you need better fuel to me.

Engguy wrote:So is that upper portion of the cylinder discolored or is it just bad lighting?
Was it run with no coolant?

No,the cylinders looked really good,I think you are seeing a reflection of the piston tops.

Yes,he was running coolant.

Abbottracingheads wrote:Looks like you have got too much compression for the fuel you are running. Blown alcohol engines run 10.5 to 11.5 on alcohol, not 94 octane pump gas. Looks like you need better fuel to me.

I never mentioned what his compression ratio was or the fuel he was using

Although you still could be right.

-3370lb stock suspension 67 Camaro
-10.5-1compression 540bbc.
- Best motor only 9.64/140.77mph
- Best with 22n 20f fogger shot 9.17/147.08mph
- Chevron 94 octane only


Is this not the engine or car we are talking about?... I think someone is confused.. mainly me

Wrong Spark plugs heat range will cause problems too.

richyrich wrote:-3370lb stock suspension 67 Camaro
-10.5-1compression 540bbc.
- Best motor only 9.64/140.77mph
- Best with 22n 20f fogger shot 9.17/147.08mph
- Chevron 94 octane only


Is this not the engine or car we are talking about?... I think someone is confused.. mainly me

No,that is my signature for the car in my avatar.

If you read from the beginning you will see that I am talking about a blown 496bbc that belongs to a friend.