Most cars out of the factory today run lambda = 1 almost everywhere on the map. (I wouldn't recommend doing that with older engines making similar power. One of the things they had to do was to cool each cylinder individually to do that, especially around the exhaust ports. With a stone-age cooling system, you wouldn't want to run WOT at lambda = 1.)

There's an argument for tuning the engine to 0.85-0.90 lambda, namely that one can usually make more power that way,

There's an argument for tuning the engine to 0.80 lambda, namely keeping they cylinder head temperatures (especially the exhaust side) lower.

There's an argument for tuning the engine to lambda >= 1, which is low fuel consumption.

If the ignition of a knock-limited pump gas engine is tuned to, say, 0.8 lambda and then the fuel mixture goes to 0.9 or 1.0 lambda, the engine will likely knock.

In my opinion, pre-ignition is the fastest way to severely overheat the pistons. This regardless of where the pre-ignition started. If it's starting from burned exhaust valves, running richer would maybe help. If it starts from diluted oil from glowing in the combustion chamber, then running leaner would help. If it's starting from spark knock breaking plug insulation, then either higher octane fuel or less ignition advance would probably help.

 

WOW those photos are crazy......some serious destruction for sure.......

E85 or race gas is a must for these engines...... My old USA 4.5 with euro parts made a whopping 265whp-285 torque with its lowly 9-1 CR.....even less considering the Euro S cams....I ran 91 octane sunco from the track.....I did have some issues near torque peak at 34' timing....once I pulled timing at torque peak to 32' the car ran much stronger and I kept the timing up near redline to improve high rpm power..... I should have tried 100 octane... oh well....I didn't have an wideband then, so I didn't know what me AFR was, but the stand alone ECU allowed +/- 25% fuel by a **** on the dash...it didn't help.

Of course it blew up shortly after this....so who knows...maybe I should have left it at the flat 30' timing where it made 243whp-260torque......oh well such is racing, always chasing that few extra HP

 

I do not agree, MK's engine is proof of that.

He's running 11:1 static compression ratio with a mild street cam which will produce a higher dynamic compression ratio than with a race cam. He has run 100+ race weekends without an engine failure. Almost UNBELIEVABLE...

And ALL of it while running on 91 octane gas from the corner gas station.

Mark and Joe's engine's at 11 and 12:1 is not that high of a static compression ratio, especially for a race engine. Combine that with their big custom-grind race cams, and both engines will have a relatively low dynamic compression ratio, and I'm guessing, lower than MK with his street cams. Because of their relatively low dynamic compression ratios, the need to run a super-high octane fuel is minimized as evidenced by MK's 100+ race weekends.

As the current story goes, nearly all cylinders are affected which implies something happened globally to the engine.

Here are some global items:

1. Fuel
2. Tuning
3. Intake manifold integrity

1. MA has stated he drained the tank and refilled with a 50/50 race/pump fuel mixture. Given the low dynamic compression ratio of the engine, it is my opinion fuel was NOT an issue.

2. Tuning, this is a big one, and high on the list of probability since it literally controls everything. Without knowing how it was tuned, in the end it's just speculation. However, it is a big smoking gun, maybe even a smoking howitzer...

3. Intake manifold integrity. If the intake bodies had leaks, it would lean out the corresponding cylinder bank(s) leading to detonation.

Given those available choices and ranking them in order of greatest to lessor probability I choose:

2. Tuning - where did Joseph get it tuned?
3. Intake - it has leaked in the past.
1. Fuel - I just don't see this as a root problem per reasoning above.

One thing that confuses me though are the sparkplugs. Earlier in this thread, Greg showed a picture of a gnarly looking plug which reportedly came out of this engine. However, much later in this thread Greg reports that all the sparkplugs look good and can be reinstalled as-new. How can both be true unless I misread something?

 

Blaming this failure on the "tune" is borderline....well, let's just say "uninformed."

Keep in mind that this was not the first time this engine was run. Joseph had run it at several events, without any problems, using race fuel. The "tune" was not changed between Joseph running the car and Mark running the car. Magically, the engine knocks, breaks the pistons and crack rods.

Please tell me your scenario for the failure...

The spark plugs are not melted, the porcelain isn't cracked. The steel portion looks like it got bead blasted. There's a few little "*****" of aluminum stuck on the top electrodes.

Why do you think these same spark plugs wouldn't run again?

I think those two separate statements should be very informative....not confusing.

 

marks blew up and joes blew up, both in very short order. sometimes engines last a few hours and blow. they blow like this and it takes time for the damage to be done. sometimes it happens first time you push the throttle like the "Coke" car. So, the common denominator was a different tune vs the many many years that both cars ran fine with the same gas. Now, if the tune was the ONLY real factor that changed, why not examine it? its just a logical question. now, that said, if the tune was different and more on the edge, maybe it did require 110 octane. btw, are you saying it required leaded 110octane? or was 100 octane race gas ok? both marks and joes lastest about the same 2-3 hours before they blew. How did Mark's engine blow? what was the cause there? both blew, both catastrophically, and both lasted a few hours and both were on the new same tune program. if both needed 110 octane for whatever reason, then sure, that could be the cause. but as sway bar said, the dynamic compression vs mine was probably not much higher if at all and ive been using 91 octane for near 10 years and 120 hours (albeit with 150 less hp which is a big factor i agree)
One thing that stands out, is that if the pistons got that hot to make the bottoms black and super heated, and pre-ignition could have been the only cause.. what caused the pre-ignition?

 

Octane too low.

The majority of the damage is from knocking, not pre-ignition. Pre-ignition melts and blows holes. Knock cracks and breaks parts.

 

What about the heat marks under the pistons? can a lot of knocking create high temps? or is that reserved for pre-ignition? i was under the impression that high advance can do both, cause knocks and create high heat.

 

I think that knocking also causes heat.

However, if the problem was octane, I'd think that there would be both pre-ignition and knocking.



Last night, we worked on figuring out how much fuel was left in the cell, when Mark drained it and then added fuel.

Sitting here, there was about a gallon of fuel left in the cell and the pump wouldn't suck up a drop of it.

We took the top off the cell and completely drained it. We are going to put in exactly 5 gallons and see how much the pump will suck out. That will tell us how much fuel was "left" in the cell when Mark started adding his "brew".

My thought is that if the cell had a significant volume of 5 year old race fuel in it, that volume of fuel would significantly reduce the amount of octane in the added fuel.

BTW.......Unless race fuel has significantly changed since I last bought some, the stuff left in the cell doesn't smell like any race fuel I've ever purchased. This stuff looks and smells like the 91 octane I buy at the pump.

I'm going to have it tested.....and then we will know.

 

so, did you really recommend 110 octane for joes engine or when you were talking race gas, you were talking 100 unleaded? If so, we would be surprised if that old race gas 1 gallon, could drop the overall octane of a mix of 91 /110. was that even the mix? anyway... if it was close to 100 octane in the end, how could pre-ignition even start? Im really curious because as was said, my compression dynamically higher, but i know the amount of air and fuel is a lot more! when i eventually get more power, i dont want to make the mistake that happened here. is it octane is it tune, is it , something else?

 

If the engine was successfully tuned using race gas, that means its ignition maps were updated allowing the engine to operate at its full potential - on race gas.

If a lower octane fuel is subsequently used, those ignition maps will destroy the engine.

In the past I know that both Mark and Joe's race engines were running Road America with stock computers and why I responded as I did above. Now that we know Joseph had it tuned changes everything because again, if it were tuned for 100% race gas, then 100% race gas should be used 100% of the time.

As for the sparkplug comment. Are you really going to install those sparkplugs back into an engine? If you do, how are you supposed to accurately read what's going on in the engine afterwards since they were installed already contaminated?

 

Of course not. I just said that they could be used and would make spark.

 

race gas meaning, 100octane unleaded? or are we talking 110? marks mix of 91 and 110 should equal 100... or did he mix 100 with 91?
yes, spark plugs tell a lot of the story............mine were mis read because they were so old, so when i put a new set in the car and had a race weekend, the plug looked good and told an entirely different story.. i just ran them again for another weekend.. all WOT racing . Ill have to pull those plugs again to see what they say now

 

Mark, I left it vague on purpose.

How about this: whatever octane was used during tuning should be the absolute minimum used afterwards for the life of the installed tune.

And after the engine was tuned, communication about the minimum required octane should have taken place, to all invested parties down the line.

 

sounds reasonable.

 

Here's something new....removed the water pump.

Not pretty. The rebuilt 928 International supplied water pump has a severe case of impeller migration....and the steel impeller did a really masterful job of machining the crap out of the front of the block.....perhaps the worst one I've ever seen.



The portable lathe. I love aftermarket water pumps and water pumps with steel impellers. Job security at its best! Everyone needs to use these pieces!


The corresponding volute surface is machined at least .100". Although I have a tool to repair this, I think this block is worn too far for my tool and inserts to repair.

The obvious question....did this cause or be a part of the overheated cracked pistons and cracked rod?

A few things make me think that this is not the direct cause.

1. And perhaps the most important....Mark Anderson has been driving 928's for eons. And he has had them overheat...for eons. My guess is that he watches the water temperature gauge more than the oil pressure gauge. Mark also reported (his is "heresay"....I got zero first hand information about the failure) that the gauges were completely normal as he turned the engine off.

2. Overheated pistons generally "skuff" the skirts and the cylinders. The piston skirts and cylinders, in this engine look fantastic.

3. There is no sign of a compromised head gasket, warped head, or warped block, as is common with an overheated engine caused by a coolant problem.


Of course, could an engine with low octane and elevated water temperature be more prone to pre-ignition and knocking?

Certainly. For the impeller to migrate, it has to spin on the shaft....the two things are absolutely going to occur.

However, that would mean the driver failed to see the water temperature going up.....