Pre vs Post Turbo Pyro - PeachParts Mercedes-Benz Forum

PanzerSD · #1 04-30-2007, 10:34 PM

I know that for the most accurate "clinical" readings, that the Pyrometer thermocouple should be mounted before the turbo.

I really don't feel like removing my exhaust manifold to drill tap and possibly crossthread a thermocouple, I'd rather weld the bung in my downpipe, What (if any) difference in tempurature readings is there between the two that makes PRE better than POST?

300SD81 · #2 04-30-2007, 10:35 PM

I think there is a significant drop in temp because of the drop in pressure after the turbo.

PanzerSD · #3 04-30-2007, 10:35 PM

Also, I have a HUGE trip thru the Rocky mountains (can.) planned in JULY. should I really be looking at my pyro more then than anywhere else?

PanzerSD · #4 04-30-2007, 10:37 PM

Quote:

Originally Posted by 300SD81

I think there is a significant drop in temp because of the drop in pressure after the turbo.

I've seen a few Kenworths and Cummins powered Eagles come thru my shop and all have thier pyros post turbo. Those guys are the ones that need an eye on the pyro alot...

deerefanatic · #5 04-30-2007, 10:38 PM

Go pre-turbo for 1 major reason....

Varying altitudes, driving aggression, etc can put different loads on the turbo, which will cause a fluctuating temperature drop... thus, you can never really know for sure what the pre-turbo temp really was with a post-turbo pyro....

Quinn8it · #6 04-30-2007, 10:55 PM

Im sure you are well aware of what is involved in placing the probe pre-turbo.... But i will just say, I did it and it was really not that bad! I had the pyrometer and was contemplating when I would do the install. My plan to drop my water injection nozzle in my EGR block plate went south the second I took the plate off. So I hastily pulled off the turbo to drill the intake.... I then realized that the metal would fall in the intake if I drilled it "in place" so I pulled it.... And with it the exhaust, (didnt want to pull it all again in a few weeks)! Tapping the hole was no problem. Picked up some new Gaskets at the dealer the next morning and it went back together in no time.

The point of this was the old "if I can do it anyone can..."

PanzerSD · #7 05-01-2007, 12:30 AM

Quote:

Originally Posted by deerefanatic

Go pre-turbo for 1 major reason....

Varying altitudes, driving aggression, etc can put different loads on the turbo, which will cause a fluctuating temperature drop... thus, you can never really know for sure what the pre-turbo temp really was with a post-turbo pyro....

Convincing point! Yeah, I think I'll go pre-turbo..and I won't even have to remove the exhaust manifold! I'll remove the turbo (because I want to dial in more boost anyway) so I'll just drill a hole with the turbo off, then any shavings I can remove with vacuum cleaner or magnet..

arew264 · #8 05-01-2007, 12:37 AM

LOL!
I know this is unrelated, but I looked at your title and thought this was about pyromaniac rehab

bgkast · #9 05-01-2007, 12:38 AM

I've pulled the turbo alone, and the turbo and manifold as a unit. It is easier just to pull the manifold too.

#10 05-01-2007, 01:00 AM

Quote:

Originally Posted by bgkast

I've pulled the turbo alone, and the turbo and manifold as a unit. It is easier just to pull the manifold too.

Except for those with the K26 turbo. It must come off first otherwise the wastegate will hit the fender and prevent the manifold from clearing the studs.

Preturbo is definitely the way to go. There are way too many variables that can alter temperature drop across the turbine.

I have heard a trick from two pro technicians. Hose clamp about 3 rags over the exhaust tip, start the engine, set it at a high idle (~1000rpm), slowly drill the manifold, and slowly tap the hole while backing out every 1/2 turn to clear the shavings. The idea is that the backpressure will blow out any shavings before they can drop inside.

PanzerSD · #11 05-01-2007, 03:44 AM

Quote:

Originally Posted by ForcedInduction

I have heard a trick from two pro technicians. Hose clamp about 3 rags over the exhaust tip, start the engine, set it at a high idle (~1000rpm), slowly drill the manifold, and slowly tap the hole while backing out every 1/2 turn to clear the shavings. The idea is that the backpressure will blow out any shavings before they can drop inside.

Don't think I like the idea of trying to SLOWLY tap a hot exhaust manifold with hotter exhaust blasting out from the flutes onto my hands. I think compressed air at the exhaust tip is a much safer (and fuel efficient) method. That is of course unless back pressure like that will wreck something.