Engine/Transmission (1998.5 - 2002) I moved pyro from Post-turbo to Pre-turbo-- glad I did!

[Hohn]

Well well well. I finally gathered the cojones to drillo my manifold and move the pyro to the PRE turbo location. I tapped it on the 4-5-6 cylinder part of the manifold, and about 1/2" from the turbo flange. I have been told this is almost ideal.



I also didn't tap the hole all the way down. This is to prevent the tip of the probe from touching the manifold (bottoming out). When I pulled the probe out, the soot line ran almost all the way up, so I figured my probe was a little too far into the hole.



Anyway, onto the results. YIKES! The response is TOTALLY different. The pyro needle moves and moves fast now! Cruise EGT is only difference by about 200°F. BUT, transient EGT is VERY different. Yeah, I could almost never hit 800° post before. PRE, I can see 1400° if I stay into it!



So the "rule of thumb" of 200 degrees difference between locations is a myth. I have personally seen as high as SIX HUNDRED DEGREES of a difference.



I am convinced that the only way I would see high EGT in the POST-turbo location is if I stayed into it long enough to really hurt something. By then, the damage is done! What's the point of having a pyro if it doesn't give you warning?



I just used the grease-and-magnets method that everyone seems to use. It turned out just fine.



Don't be afraid like I was. Go PRE-turbo and do it right!



Justin

 

[KatDiesel]

Another believer... ... ... ... ... ..... Glad you moved it before it was too late.

 

[Bob Wagner]

when extra fuel is added, pre is the only way to be

 

[TxDieselKid]

Originally posted by Hohn

So the "rule of thumb" of 200 degrees difference between locations is a myth. I have personally seen as high as SIX HUNDRED DEGREES of a difference.

Just thought more people should see this part!

 

[y-knot]

There is no stead fast rule to go by, and anyone who thinks they are ok by monitoring the post turbo temps, are just kidding themselves. I monitor both, with the same exact probe and gage, a the difference varies. Normal running on the highway can go from 150-200 , to no difference. The sad part is when you really need to know what the EGT's are (pulling a long hill, with a load) that is were the two differ the most. You can and do see differences of 500-600 degrees. It also makes a big difference as to the set-up of the truck. When I switched to the 16 cm2 housing, my EGT's dropped quiet a bit, and now the difference is not as much between the pre and post temps. I think you might as well not install the probe if you are not monitoring the pre tubo temps, you are getting erroneous data and what good is it? The part about being scared to drill the manifold is bogus, there is nothing to it. Just grab a hand full, and drill it.

 

[Oil Burner]

Good job Hohn, I bet you wish you did this long ago. Pre-turbo is a must!

-Jason

 

[Cooker]

The 300 degree "rule" is crap. I'm glad someone else has some concrete evidence to prove this. Hopefully this will warn some of the guys that are running post to rethink their EGT's.

 

[RobbyRam]

Even towing, with my mods, I only see 700-800 max at WOT 'post', going up a hill, and most of the time I back it off so that I'm only 600 'post. ' Our company has a fleet of Volvo's with the 8. 3L diesel and the only gauge that is in the truck is a 'Post EGT' gauge. I think I'll just stick with what I have.

Bob in Sacramento

 

[Truckie]

Drill and tap the hot side its the only way to go.

You will be happy you moved it.

MIKE

 

[pskaar]

pre turbo is sweet

I installed mine pre turbo couple weeks ago. The guage is really responsive. It moves alot quicker than i would think. Don't know how hot it will get when pulling, time will tell. Truck will push 24 lbs. boost WOT empty. I have cycled the key three times and it will not show any codes, just the odometer reading.

Preston Skaar

 

[Dkevdog]

I ran my 96 with pre/post for years- and have always been an advocate that if you do ANY towing at all, you have to have it pre-turbo. That being said however, you must also take into consideration how long it actually takes to cool the turbo off after a workout. Just because you gauge (pre) has cooled down to 300, certainly doesn't mean that your turbo has caught its breath. I've seen the pre register 300*and the post slowly (I'm talking 7-10 minutes here) settle down from reading a 650*. Case in point, pre turbo isn't as good as post for reading shutdown temps.



Kev

 

[StephenDelany]

This drilling and tapping of the exhaust manifold isn't as scary as you think it is. I was near shakin' in my boots when I started the drill spinning but it went really smoothly. Unbolt the turbo from the manifold flange and drop it back 1/2 an inch so you can slide a piece of cardboard into the joint and you are guaranteed that no filings will be hitting your compressor blades. You don't need to remove or disconnect anything from the turbo housing to do this. The turbo nuts are really on there, though, so be ready for some skinned knuckles. Use a magnet probe too as there is quite a bit of filings that drop into the exit passage. Tap in stages to control the depth of the probe. Put a little anit-seize paste on the thermocouple threads. . screw her down and your done!

 

[dresslered]

Excellent point Kev. I'm glad that somebody remembered that pyros are not just for accelerating. During cool down, the turbo is actually acting as a heat source which the pre pyro cannot see.

 

[kboettcher]

I don't believe you have to disconnect the turbo to do this. Just use a nice little pilot drill(1/8") with lots of grease on it. Then the 5/16" again with lots of grease. then tap it with lots of grease. I paid real close attention to mine and I don't even think a filing made it in to the turbo. And if a few little shavings do make it in there they will be sucked out the turbo no problem. Most industial vacuums that are made for sucking metal filings do this the exact same way, pieces right through the blades. Granted the vacuums need the blower wheels replaced when they get worn out, but I don't think you will harm anything, one or two filings aren't goig to where out the turbo.

 

[Snow man]

Good post Hohn!! I have been saying the same thing you found for years now. Pre turbo is the only way to go,post turbo is only good for cool down.

 

[illflem]

And if a few little shavings do make it in there they will be sucked out the turbo no problem.

Not always true. After personally experiencing two turbos whose impellers were wedged stopped with a shaving between the housing and impeller wheel then later warped when the exhaust heat was concentrated on one spot I will never drill without moving the turbo again. The cardboard method works good, just start the engine for a minute before replacing the turbo to blow any chips out. Takes less time to remove four nuts than fishing around with a magnet plus you're positive all the chips are out.

But hey it's your turbo.

 

[Rman]

Hey if ya ruin the turbo it's a fine excuse to upgrade to a HX40 or 50, hell TWINS!!!

 

[y-knot]

Hey if you really all that worked up over drilling the pre-tubo hole, and don't want to remove turbo, or trust the magnet. Then just start the dang truck and let it run while you drill, you'll know when yon pook thru, just wear some saftey glass so nothing blows into your eyes. Just might be a littlt loud.

 

[Hohn]

I agree that the post-turbo location is better for monitoring turbo temperature for cooldown purposes.



But I almost never tow, so my turbo doesn't see long periods of high boost. Also, I use synthetic oil so the concern with turbo coking is almost nil...



If I were a heavy tower, I might go with BOTH a pre and post setup. But post alone is only a good idea, IMPO, if you run a completely stock truck and tow heavy (but within GVWR). ANY fueling upgrade at all means you have to have a pre at least, if not both.









Justin



Justin

 

[RustyJC]

Originally posted by Hohn

If you run a completely stock truck and tow heavy (but within GVWR). ANY fueling upgrade at all means you have to have a pre at least, if not both.

To Justin's point, towing our 13,500 lb 5th wheel and running 21,180 lbs GCW (21,500 GCWR), my stock HO would hit 1300 degF pre-turbo EGT pulling grades in the Texas Hill Country! Based on my experience, I'd feel like I was flying blind trying to tow heavy without being able to watch my pre-turbo EGT.



JM2CW



Rusty