Okay, so how deadly of a combination is too little timing and too rich or an a/f on the top end for a fully built motor. Say the engine was running around 11.5 a/f's all the way through and the rpm range and you were running 30 or so lbs of boost with a turbo that flowed 80+lbs a min. Is it possible to have so much timing retarded that the EGT's get so hot they melt pistons, or 2?

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Modified by josh green at 6:10 AM 12/4/2006

 

is it possible to run to LITTLE timing that can cause destruction? is that what you are asking?

IMO yes, sometimes to LITTLE timing is as bad as TOO MUCH.

Retarded timing causes EGTs to go up which can melt things , such as pistons. why do you ask?

 

11.5 a/f ratio is good and safe. But what fuel are you running? Also, depends on what the engine has--- compression ratio, port/polish, valve angling, cam gears, cams, etc.
But w/ specifics, we can probably give you a very close timing recommendation. I always start out w/ 20 degrees for car/engine applications that I do not know enough about.
Absubtle
CO

 

I dont think those numbers are that important, but anyway. GE sleeved ls block, 84mm cp pistons, 10:1 compression, P&P by a guy we know and trust, stock cam gears, gsr cams. 1600cc injectors, a1000 pump.

 

Retarding the timing too much may melt exhaust valves and damage turbos, but doubtful it would melt pistons.

Retarding the timing starts the burn process later, which means by the time the full combustion event takes place, it is already on its way out of the chamber thru the valves and into the exhaust manifold.

This will read as High EGTs on a guage mounted in the manifold, but that doesnt mean your cylinders are actually getting that hot.

 

so what could cause the pistons to melt if it wasnt a mechanical problem. I highly doubt that it was the injectors, I mean 2 brand new injectors failing isnt likely, fuel pump works great, its brand new. I suppose that it could be from lack of fuel in the sumped tank. Never let the gauge go below 1/4 tank.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by josh green &raquo;</TD></TR><TR><TD CLASS="quote">so what could cause the pistons to melt if it wasnt a mechanical problem. I highly doubt that it was the injectors, I mean 2 brand new injectors failing isnt likely, fuel pump works great, its brand new. I suppose that it could be from lack of fuel in the sumped tank. Never let the gauge go below 1/4 tank.</TD></TR></TABLE>
too much timing?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by josh green &raquo;</TD></TR><TR><TD CLASS="quote">so what could cause the pistons to melt if it wasnt a mechanical problem. </TD></TR></TABLE>

bad gas?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by xenocron &raquo;</TD></TR><TR><TD CLASS="quote">bad gas?</TD></TR></TABLE>that gets my vote, if the octane was too low, and the gas wasn't the best....i suppose it could cause that. either that or the wideband wasn't right

 

what injectors and what was your fuel pressure?? i have had some rc750cc injectors lock up above 60psi fuel pressure, rc specs the 750cc saturated injectors to 75psi....

post some pics of the piston.. if there is too little timing it will make the exh valves glow and get the head really hot which will cause pre-ignition which will melt the piston.. but its gota be that way for a long time to get that hot.

 

I think you probably hit it on the head jdogg, I think he was using some 110 or some 112 VP, the timing wasnt far out, I was thinking that there wasnt enough and that something got hot and caused detonation. Sorry I dont have pictures, but I am pretty sure it was the tune. The tuner hasnt really tuned big power cars before and I guess doesnt have the feel for it. He is super conservative and I was thinking that 17-18 degrees up top with 11.5 a/f's could have caused it to burn really slow and generate heat in the cylinders. The gas also was brand new, he had put it in the night before the race, it was pure, no 93 mix.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JDogg &raquo;</TD></TR><TR><TD CLASS="quote">if there is too little timing it will make the exh valves glow and get the head really hot which will cause pre-ignition which will melt the piston.. but its gota be that way for a long time to get that hot.</TD></TR></TABLE>

So what can we do to measure how hot the parts inside the combustion chamber are to prevent such a situation? what egt would you say is the maximum to tell if the exhaust values (or something else) are soaking heat?

is there a way or is it all guesswork?

 

experience, read the plugs... detonation has to occur over a long period of time to melt things...

 

Cold EGT's can mean detonation is happening too. That's why all the heat is stuck in the combustion chamber and no heat is coming out to the EGT gauge.

 

i have never seen cold egt's from detonation... in my experience cold egts are from too much fuel.

 

what spark plugs were you using? What do they look like now?

It's obvious it was extremely hot in there....But 17~18 degrees timing wouldn't cause it.. It could be many things that went wrong... but if i had to guess i would think it was pre-ignition. Hard to say though with out looking at the parts..

Besides pistons what else was melted?

 

basicallt the car survived a bunch of DYNO pulls at 27-30psi. first time it saw the track, one full 27psi pull down the 1/4 mile an it melted everything.

2 pistons melted, one of the GODZILLA sleeves is destroyed.

i wasnt there, this is all what i have hEARD. to me it sounds like it got WAY TO HOT, now my question is what causes it to get this hot?

he runs 9 heat range plugs, C112 octane gas, 9:1 compression, GT40

 

I can't speak from experience on this one (good I guess ) but speaking with people on the dyno and reading it the temperature will drop. Say under normal you are runing 1300 degrees and then suddenly run 1100 or lower, with adding fuel. This can be an indicator of det. Just food for thought

 

I don't think it can be cylinder specific ie: pre-ignition, injector going out, or things like this. I think it might be a general case, maybe the Dizzy moved, maybe the fuel pump went out. Do you have the timing and fuel maps?

 

id say either bad gas or something in the fuel system went wrong. what injectors and fuel pressure?

 

pics?

 

http://www.efi101.com/forum/vi...rt=20

"This thread is also about tuning, so I created a " blind " test at Dugans when
tuning a race engine, Friday last.

A SBC 600HP engine with a 12:1 comp ratio, race gas. The torque peak at
5000 RPM with 565 ft.lbs. (420 cid ). The engine now tuned and running well.
EMS was the ECU-882C. The " start of injection " was adjusted at 50 ft.lbs
until the greatest torque of 58 ft.lbs was found at the same throttle angle.

The spark plugs were changed, new, then the timing was SET BACK by
eight degrees retard. The PW at WOT was changed from 12ms to 16 ms,
the dyno RPM was set to 5000. The throttle was then opened, EGT's went
from 1200 degrees (base run) to over 1400 degrees (test run). The AFR
"wide band" changed, 12.5 (base run) to a 11-10.5 (test run) was noted.
The engine had a slight miss-fire, torque was about 100 ft.lbs lower.

The engine was stopped, the sparkplugs removed AND inspected.
First, they had the appearance of a "long race" plug.
There was " fuz " on the ground strap and body.
The color was gray. Aluminium " ***** " though very small (10 microns ) were seen.
The pistons were MELTING.

Those present agreed that it was NOT good to run an engine under these
settings. The engine would be DAMAGED."

Just something I saw on another forum that proves too little timing/too much fuel can cause problems.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by VtecKiDD &raquo;</TD></TR><TR><TD CLASS="quote">basicallt the car survived a bunch of DYNO pulls at 27-30psi. first time it saw the track, one full 27psi pull down the 1/4 mile an it melted everything.

2 pistons melted, one of the GODZILLA sleeves is destroyed.

i wasnt there, this is all what i have hEARD. to me it sounds like it got WAY TO HOT, now my question is what causes it to get this hot?

he runs 9 heat range plugs, C112 octane gas, 9:1 compression, GT40</TD></TR></TABLE>

it was not the first time down the track. it was about the 9th time that day, everything was running perfect all day long as far as the engine. The car never reached max boost for the "tune"

its golden eagle HD sleeves, their latest ones, not their older godzilla sleeves.

10:1 compression not 9:1.

3 and 4 CP melted, #4 was melted the worst and crumbling. #3, had to take a second look to notice it was melted but the exhaust side skirt melted thru to the insside of the piston.

fuel pressure at idle, 50 psi. Precision 1600 injectors

 

To melt a motor that bad in a pass, it has to be something more drastic than alittle too much timing.

Has to be Injector\Fuel Pump Related...Or possibly Overheating.

Definately Fuel related tho.

 

what bore CP pistons?