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Discussion Starter #1
I have been struggling with this lately, my exhaust is extremely hot just cruising around like normal (street vehicle). I have a TGT probe just prior to the turbine flange. Idle is around 800-900F with around 30 degrees of timing. Light cruising at 75mph in OD at ~2400rpm is around 1550-1600 degrees. All pre-turbo pipes are doubled wrapped and the turbo has a blanket, but even when they were not wrapped temperatures were around 1450 degrees. Timing at cruise is 45 degrees. And fueling is pump 93 closed loop at stoich.

I know low timing will cause excessive heat, but 45 degrees seems like a lot of timing to have this issue. Setup is a 402" LS with BW s400 82/96 turbo with 5" dp. Cam is a 230/233 114+4. Has anyone had to run more than 45 degrees during cruise to keep EGTs reasonable? Having the turbine glowing under the blanket at light cruise is a little excessive IMO.

I have a temp gun and at idle the temps are close so I trust the sensor, plus its a pretty new. I saw something about installation depth being critical, I have it roughly to the center of the pipe, not sure if this is correct for the autometer gauge or not.

Hard to tell temps under boost, too many other things to look at, but I suspect around 1800 or so. I use pump 93 mixed with c16 at the track and I use 100% meth with 2 15gph nozzles above 5psi.
 

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"93 closed loop at stoich"

I think i found your problem.

Might want to pull the timing back a little and bring ithe fuel back down on the rich side of the curve to cool it down some.
 

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I have been struggling with this lately, my exhaust is extremely hot just cruising around like normal (street vehicle). I have a TGT probe just prior to the turbine flange. Idle is around 800-900F with around 30 degrees of timing. Light cruising at 75mph in OD at ~2400rpm is around 1550-1600 degrees. All pre-turbo pipes are doubled wrapped and the turbo has a blanket, but even when they were not wrapped temperatures were around 1450 degrees. Timing at cruise is 45 degrees. And fueling is pump 93 closed loop at stoich.

I know low timing will cause excessive heat, but 45 degrees seems like a lot of timing to have this issue. Setup is a 402" LS with BW s400 82/96 turbo with 5" dp. Cam is a 230/233 114+4. Has anyone had to run more than 45 degrees during cruise to keep EGTs reasonable? Having the turbine glowing under the blanket at light cruise is a little excessive IMO.

I have a temp gun and at idle the temps are close so I trust the sensor, plus its a pretty new. I saw something about installation depth being critical, I have it roughly to the center of the pipe, not sure if this is correct for the autometer gauge or not.

Hard to tell temps under boost, too many other things to look at, but I suspect around 1800 or so. I use pump 93 mixed with c16 at the track and I use 100% meth with 2 15gph nozzles above 5psi.

Big problem with EGT readings is probe location. Temps/ranges are not something that you can compare to other vehicles usually. You almost need to run yours to failure while logging to know your range/limit. From what I’ve seen your readings are high all around. Have you tried dropping timing to say 32 at cruise and watched the EGT? Or played with advancing/retarding the timing at idle to see if you can get lower EGT readings? Generally I’d say your cruise/idle EGT isn’t very important but yours seems really excessive. Did you degree in the cam?

Not the best comparison, I had my thermocouple on my leanest cylinders runner 1.5” after the exh port on the head. I was setup to run 14-15:1 AFR in OD when cruising. I’d see 1200ish at cruise with 41*. WOT I’d see 1600ish at 11.4ish AFR. 1750ish I’d push gaskets…melt pistons etc. That was on pump 91oct and meth inj at 25lbs/18* timing. Turbo 3.8 buick with a 218/218 baby cam. (iron head/block motor)
 

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Discussion Starter #4
Yes the cam is degreed in properly. Setup makes great power, just has a ton of heat in the exhaust. For the sake of argument, would delayed cam timing would display this type of issue?

I havent messed with adding/subtracting timing at different points yet (just got the setup back together), but will next time out. Thanks for your input!
 

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My opinion is that 14.7 is perfect to make heat and light off a catalytic converter. 14.7 is not perfect for a turbo car running pump gas on the street with no cat. Start adding some fuel and see what you get.
 

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Discussion Starter #7
I have it at stoich because I like using the factory 02s and closed loop, but I will try it richer in open loop, thanks.
 

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I understand the 'adding fuel to cool it down' theory, but is there any school of thought that says leaning it out (leaner than stoich) in that cruise/light load area would also reduce the temps?
Combustion temp curve seems to fall off pretty evenly either side of stoich, and in that light load/cruise and low/no boost area, is there any reason it wouldn't run leaner than stoich and cool off the temps, while using less fuel?
Would the leaner mixture combined with the increased timing in that area result in detonation even at low load?
Would a leaner/less timing cruise work as well as a richer/more timing cruise?
 

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It will work fine.

But you have to cross over PEAK, and thats where shit gets burned.

Why risk it? Can't afford the gas? O2 sensors add up at 1 a year maybe?


Cheap bastards do it in aviation. Mechanics love them because they torch valves/seats and melt other shit. EGT's react slow. Sure you think you were good, but some cylinders banged full hot a few times on the path to lean of peak (LOP) even though EGT's appeared good. That damage adds up to a premature engine rebuild.

Just stay on the fat side and keep it happy, or pull the power back (LOP kills hp, so pull it back to 60 percent of max like LOP does). Or fuck around on the lean side and post a bitch in a year when ya but a ring gap or torch a ring land/valve.
 

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I have it at stoich because I like using the factory 02s and closed loop, but I will try it richer in open loop, thanks.
Factory 02s have a very narrow range, when you burn it up what are saving in the long run
 

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Generally when your not under a heavy load you aren’t going to “burn up” a motor running it lean. People who think you need to cruise around “rich” so they don’t burn up their motors are just plain wrong. Going a little over or under stoich is a good idea, but I wouldn’t get carried away with adding a ton of fuel. I do agree there seems to be an underlying problem though as the OP’s temps are out of the norm. I’d try dropping timing and raising timing 5* and see what the temp’s do at cruise. Is this a really heavy vehicle?

Have you marked your balancer and verified true TDC? Verified your timing with a light? My LS ign timing was off quite a bit.

Retarded cam timing will also cause higher EGT’s.

On a side note my most recent gen4 crank was keyed 6* retarded. (2008 alum 5.3) I just threw in the cam dot to dot without checking it. When I put the wheel on it and saw 6ish* retarded Dot to Dot on an OEM timing set. Added 6.5* with an adjustable timing set and picked up 13mph.(same boost) I’m sure EGT’s were through the roof. May want to check your cranking compression too. Mine went from 155-160 to 200+.
 

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Discussion Starter #14
My comment about using the factory 02s wasnt about saving the sensors, it was just a feedback mechanism to make sure fueling stayed consistent. Running it richer isnt a problem since the tune is good. I could care less about the life of the sensors or using extra gas to keep it happy.

Combo is in a 5,000lb truck, so yea its a pretty heavy vehicle. I havent checked timing with anything, but this discussion is making me a bit paranoid about it and I am thinking about pulling the front cover off and checking the cam timing again to be sure and also getting a timing light. I set it correctly initially but had to change head gaskets at one point (to a different size). I dont see how that would affect cam timing though since I left the timing chain there.

Cranking compression is around 175 or so.
 

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Playing around peak part throttle may not hurt the engine, but the hot EGT may no do your turbine wheel any favors.
Nor will it do it any harm.

Turbos are designed to live in a hot environment, and whilst 1400degF is hot...nothing out of the ordinary.

I'll assume he doesnt do tens of thousands of miles at part throttle anyway ? nor at full throttle where EGT's and loads will be even higher.

The main query I'd have, largely because of the large variances I see on my pre-turbo EGT's....are actual reliability of any readings.

Ive two probes on one bank, beside each other. One for an in-car gauge, complete package by Greddy, the other a typical fast acting K-type thermocouple hooked up to my ecu for logging.

More often than not these two read different. At part throttle, full load etc.

Now which do I trust ? I see as high as around 2000degF at WOT under full load on the ecu. This is same with 7psi as 27psi, and no damage has yet occured.

Hell, it hasnt even burnt the black BBQ paint off the turbine housings ! LOL That paint is rated at around 1100degF

And that's even with some 1km runs a few days ago. In car gauge however doesnt seem to indicate much over 1800degF at most.

Cruise seems to vary at ecu from 1100-1300degF, in-car gauge seems more steady at 1100degF

This is pump fuel, similar 40deg timing, running at stioch. This will not do any harm at all.
 

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Generally when your not under a heavy load you aren’t going to “burn up” a motor running it lean. People who think you need to cruise around “rich” so they don’t burn up their motors are just plain wrong. Going a little over or under stoich is a good idea, but I wouldn’t get carried away with adding a ton of fuel. I do agree there seems to be an underlying problem though as the OP’s temps are out of the norm. I’d try dropping timing and raising timing 5* and see what the temp’s do at cruise. Is this a really heavy vehicle?

Have you marked your balancer and verified true TDC? Verified your timing with a light? My LS ign timing was off quite a bit.

Retarded cam timing will also cause higher EGT’s.

On a side note my most recent gen4 crank was keyed 6* retarded. (2008 alum 5.3) I just threw in the cam dot to dot without checking it. When I put the wheel on it and saw 6ish* retarded Dot to Dot on an OEM timing set. Added 6.5* with an adjustable timing set and picked up 13mph.(same boost) I’m sure EGT’s were through the roof. May want to check your cranking compression too. Mine went from 155-160 to 200+.
THIS
 

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As others have stated, running 14.7 during cruise is fine, I even run 15.1 at light cruise. I have a ton of street miles and have never had any issues doing this.

Just recently I installed individual EGTs (approx 1" from header flange, tip extends about 1/4" into tube) and am still testing and collecting data to get a better handle on what to expect for peak power settings. However, I have been running an EGT sensor in the collector just prior to the turbo for 7 years so I know what to expect there.

Here's what I have seen at cruise. For me "cruise" (in OD) is 75mph, 2300rpm, -5 to -5.5 psi (vacuum), timing advance around 40-44 and mixture around 14.7-15.0. The individual EGTs are typically 1050-1100 and the EGT at the turbo inlet is 950-1000. Interestingly at full power under boost, the individual probe temps go to approx 1350 and the sensor at the turbo is around 1600. My headers are 316ss, not wrapped but both sides have a sheet metal cover to retain some of the heat.

For some reasons your EGTs are much higher than I would expect at cruise. You better figure out what the number really is at full boost, 1800 is a very high number for most combinations IMO.

I don't remember anyone mentioning this yet - Have you verified the accuracy of your timing pointer on the damper? I don't know your setup so I don't know your trigger pickup info or how you adjust timing but if it's adjustable and you are using the damper to check it, first you must always check the damper to make sure TDC (and all other marks) are correct.

Note - every engine combination will have different EGT numbers for similar operating conditions such as cruise, idle, full power, etc. As stated you have to use your EGT readings as a tool with a lot of other data to get a feel for what's right or wrong.
 

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Oh, I would also suggest taking a look at your plugs and see what they are telling you.
 

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Discussion Starter #19
I did some testing this weekend with fuel and timing. Adding fuel did not have any effect (went down to 0.9 lambda). Adding timing (up to +10 degrees) also did not have any effect. However it felt better with more timing so I think I need to relook at that part of the map anyway.

I really dont want to pull the head to install a piston stop for checking TDC and cam timing with the engine installed. Is using a stop through the spark plug port just as useful? Seems it would be as long as its consistent.

Also payed closer attention during boost and saw egts go from 1500F at 10psi on the 2 step to about 1650F at the end of an 1/8th mile at 20psi. The sensor seems relatively slow though, so I am not sure that is a good number.

Crank is a 4" callies dragonslayer and timing set is an adjustable roller master double set to +0 advance from the cam.
 

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I did some testing this weekend with fuel and timing. Adding fuel did not have any effect (went down to 0.9 lambda). Adding timing (up to +10 degrees) also did not have any effect. However it felt better with more timing so I think I need to relook at that part of the map anyway.

I really dont want to pull the head to install a piston stop for checking TDC and cam timing with the engine installed. Is using a stop through the spark plug port just as useful? Seems it would be as long as its consistent.

Also payed closer attention during boost and saw egts go from 1500F at 10psi on the 2 step to about 1650F at the end of an 1/8th mile at 20psi. The sensor seems relatively slow though, so I am not sure that is a good number.

Crank is a 4" callies dragonslayer and timing set is an adjustable roller master double set to +0 advance from the cam.
Plug style piston stop is pretty accurate from what I've seen. It will also give you a good estimate. Which is really all you need. Start low and let the plugs/mph tell you when to stop as far as adding timing is concerned. Since it's an aftermarket crank I doubt it's off by much if at all. Also if adding or subtracting 10* didn't change the EGT, I doubt timing is the issue.

I'd consider trying a new thermocouple.
 
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