more melted pistons

[jim34]

Using egt gauge for now getting ready to install wideband, cruising down the highway my egt's were about 1400-1425 go into boost and temps drop right down to about 1300.
Engine- 2.5 with new mahle pistons, 782 head light porting,super 60 turbo, stage 5 fwd smec, large spearco intercooler, + 40 inj, 3 bar map, stock 2.5" downpipe into 2.5 mandrel bent exhaust-- changing to 3"downpipe into electric cutout--also 255 lph fuel pump, adjustable reg, 89 roller cam.

running 18 psi hit the gas for about 3-4 sec on the highway in third let off the gas and coasted back down to speed limit get back into the gas and nothing look back and son of a ***** this freakin car melted the pistons again
egt never went over 1300 ! tore it down and all the rings were hit, 2 pistons had cracked 2nd ring lands and # 3 had what looks like sombody took a plasma cutter and burned a hole right through it.

Ive got the car back together now in the same configuration but ive turned the boost down to 15 and retarded the timing to 10 degrees from the 14 i was running and the car feels stronger than before and i also changed the injector harness as it was falling apart. egt's have not changed at all.

Ive joined up at dcal and am going to start learning how to do my own computer as i dont believe in a one size fits all computer and ive done lots of tuning on my lt1 with lt1 edit so i do know a little about this stuff already.

why did the knock sensor not retard the timing enough to save the engine are the sensor known to go bad on these cars ? The egt's seem to be worthless at this point in my mind how can i be at 1300 and destroy my entire engine ?

[crazymadbastard]

I dunno, egts dont tell the whole story. From my reading, not from experience wideband is the only way to go. Egts could be either too lean or
too rich. go figure.

[speeduphoria]

wheres the egt prope placed?

[jim34]

its in the #4 about 1.5 inch from head

[SUPER60omni]

wow, when my probe was in my manifold it used to wrap all the way down to the bottom of my autometer guage, like 1700 or somthing and it never melted my JE's, but now I have it tapped into the downpipe right when it comes off the swingvalve. Now it reads correctly @ 1300-1450 deg.


Its funny, I see everyone putting their EGT probes in the mani, but the directions say it should be post turbo......meaning after the turbo. I bought a manifold with the hole already there so I used it and it sucked, so now I have it in the right spot.


If yours is in your manifold then 1300 is VERY conservative...........well not with mahle's, but its VERY safe. I would check pump voltage, timing and make sure the map is acctually a 3bar and its wired correctly and it works. I had the same problem as you when I used to run +20s with a map diode with my GLHS stage 2 cal. No matter what the boost was at it would kill pistons. Then I went 3bar and never had a detonation issue again.

[scott_s]

I would check the knock sensor. Perhaps think of a custom cal with the CEL mod, Rob's PDA program, or a scanner to monitor knock retard. That is what I did my second time around.

[Shadow24V]

although it has been noted that when detonation or preignition occurs there is a drop in EGT. (cant find the link right now) so a low EGT doesnt always mean things are 100% kosher

[jim34]

I just aquired a monitor 2000 to watch for knock, and i am installing an in car fuel pressure gauge and a dynojet wideband so I will figure somthing out. I didnt have as many problems when i was running cold start injectors that motor lasted for a year with 24 psi and i only killed it after i held it down a little too long on the highway

maybe egt's arent as good for turbo engines as n/a motors ?
I will definatly check knock sensor out completely

most instructions for the exhaust temp gauge i can find are for n/a engines and airplanes and they put the probe in the cyl head or right next to the cyl head

thanks everybody

[dvera]

I have the same problem.. I know I'm running rich due that I had a custom made ECU for my car (2.5lt turbo) the EGT probe is localted on the exhaust mainfold on the #4 as I was understood that it should be. Readings where hitting 1700F with 18 pounds of boost and not reaching even the 5000 RPM. I installed the LC-1 Innovate wideband to monitor the AFR. The suprise for me is that I was able to put 26 lbs of boost and the AFR is safe.. but the Autometer EGT is showing like 1800F or more ( is on the 6 o'clock position )... so I suspect also that the EGT probe should not be placed between the turbo and the mainfold.. so what do you guy suggest to locate it?

[phantomrt]

The instructions for my EGT guage also said SPECIFICALLY NOT to install the probe upstream of a turbocharger. Well, I did it anyway and it works great there. I can get temps up to about 1550 or so if I drive it just right. I wanted to monitor temperatures of the exhaust near the valves and I don't really care what it is once it is past the turbocharger.

An exhaust gas temperature reading by itself doesn't mean didly squat no matter where the probe is placed. You can be running really rich and get a reading of 1200 up by the cylinder head and 1500 south of the turbo. You can be running lean and get 1700 up by the head and 1300 south of the turbo. Ignition system, compression ratio, camshaft profile, spark advance, ambient temperature, etc can alter these readings. An air/fuel guage running off of the stock oxygen sensor can't tell the difference between a 13.0:1 air/fuel ratio and a 14:1 ratio, so you really do need a wideband for accurate monitoring of stuff.

I say there was some detonation going on as noted by the cracked pistons. Base ignition timing doesn't mean much. ON a stock computer, at high RPMs, you can get as much as 40 degrees of ignition advance. Retard the distributor 2 degrees, and you'd get 38 degrees of ignition advance when in fact you probably needed 35 degrees max... not that I know these numbers are accurate in any way, but its the concept of it that matters. SO yea, every different setup ideally needs its own computer calibration.

[dvera]

That is the reason why I installed the LC-1 from Innovate because as I put more and more gas the EGT was no showing any effects. What was my surprise than when I put the wideband everything was OK but if I looked to the EGT I was running "hot" or "lean"

So as I understood maybe I can get my pistons melted or blown motor passing the 1600F-1700F.. but I went even higher... the LC-1 was showing good AFR...

My question is.. know that I have de LC-1 running where should I put the EGT probe.. Im going to conect to the LMA-3 to get an accurate reading? Or should I dispose the EGT and base my calibration on the LC-1?

[jim34]

has anyone ever noticed there pistons damaged in the same spot a little left of center in the back of the engine ? reason i ask is ive burned and cracked a lot of pistons over the last 5 years or so (becuase im a poor/cheap bastard) and the damage is always in the same general area.

it looks like the wide band is the way to go but it would be nice to figure out how to use egt and wide band together for tuning

[phantomrt]

Well, I'm not positive that I am right or wrong, but what is the ultimate purpose of an EGT guage? The answer is: To see how hot your exhaust is. Why do we want to know that? As we now know, it is definitely not a good way of checking air/fuel mixtures. So, what good is it at all? My answer to that is: to ensure that the temperatures are not high enough to start burning exhaust valves. So, if this is the case, why mount the probe way downstream of the turbo? We don't care what the temperature is there. We want to know what temps the valves are seeing.

Another use for it would be that since we're always making changes in our tuning department, if a modification changes EGT's, it is another source of data to analyse to determine how the change has affected the engine.

Now, ideally, an EGT probe in the manifold AND downstream of the turbo could give some great insight of what is going on. If the air/fuel mixture is rich, you typically see lower temperatures at the manifold and higher after the turbo because all those unburned hydrocarbons actually continue to burn as it goes through the exhaust. Lean is typically the opposite.

I, too have made substancial air/fuel mixture changes and it resulted in minimal EGT change.

[dvera]

Quote:

Originally Posted by phantomrt I, too have made substancial air/fuel mixture changes and it resulted in minimal EGT change.

So if we have the EGT on the exahust mainfold to measure what is made for what will be the temperature to be looking at before melting pistons and valves?

[speeduphoria]

Quote:

Originally Posted by dvera So if we have the EGT on the exahust mainfold to measure what is made for what will be the temperature to be looking at before melting pistons and valves?

1500*F is safe, some go to 1600 or 1450 it depends