Ok, here's what my exhaust used to be:

--factory downpipe (3'', I think) with pyro 2'' behind turbo outlet
--3'' mandrel bent t-case roundabout, aluminized steel (old Bank$ stuff, I think)
--3''-3.5'' adapter and 3.5'' muffler eliminator straight pipe (cheap steel, this rotted off yesterday, hence this post)
--3.5'' mandrel bent over-the-axle/tailpipe, aluminized steel

With the full setup, I was running what I thought to be normal temps for my truck. Between 500 and 550 post cruising @70, just shy of 2k rpms. Lettin her eat from about 1700 in 5th would produce toasty temps within several seconds. Pulling a steep (12%) grade at 55-60, I usually went with 4th to keep the revs up, and that would yield about 700-750 post.

Sooo, my straight pipe rotted to the point where I had to remove it yesterday, which meant losing the tailpipe too. Let me first say that running the truck straight off the t-case pipe is downright ear-bleed loud! And, being 3'' pipe, it's tinny, ratty and cheap sounding, too So, if you reply to this post, please use CAPS so I can HEAR YOU!

Get to the point Greg, I know

While pulling some back country state roads this afternoon, I couldn't get the old girl hot. I was rolling into the throttle on a steep grade from 1800 in 5th and I pulled up to 75mph and only produced a lousy 650*---this on a pull that would normally hit 850 with ease! I thought about the probe being bad, so I didn't push any harder than I normally would, but I'm consistantly seeing temps 200-250 lower than yesterday with the full exhaust system. On a related note, I hear the compressor quite a bit louder at any load level than before, so does it seem likely that it's spooling/moving air quite a bit easier? I thought 3.5'' pipe would be big enough for the puny VE, but maybe not? ASSuming the probe is good, is it possible that a 3.5'' t-case back setup is too small? I'm tryin to scrape some pennies together for another pyro and place it in the manifold. I'm gonna keep the post just for comparison and conversation. So, what's everyone think---was the 3.5'' that restrictive or did I almost melt a piston today

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This could lead to some good discussion... I wanted to change my exhaust somehow and it would be at LEAST somewhat interesting. I mean, I'd like to run mine straight out the back(same route as stock instead of the tip curve) but when you think about it that just isn't gonna reduce a thing temp wise. Then I wanted stax but that could be a scary process, being should I use 4" or 5" pipe and the final outcome(clean setup or not)? And then there's the idea of running it straight out in front of the back wheel... but do I want a soot covered wheel?

Oh and btw, I ran mine without any exhaust pipe or muffler from the back of the cab back for about 2 days and to be honest I LOVED it. It was loud but when held wide open it sounded like a Skidder

 

Well, with less backpressure you have lower EGT's. You chopped off all the pipe behind your transfer case- that's what, half of the exhaust system? You got rid of a lot of backpressure, and that allows the gasses to expand much faster as the cool off, in your case expanding into the atmosphere rather than attempting to expand through 304 stainless steel. The bigger pipe the better, always. (Until we break into the "Oh no, backpressure is necessary" argument. ) I wonder how much reduction you can get if you were to just remove the downpipe too? (Throw on some ear plugs and do it, man! We need science project data!)

As you noticed, the effect of all this is lower EGT's. I think that a few feet of pipe being cut off should be good for a 100-post (150-200 pre?) degree reduction, sounds right to me.

But the cost is a lot of noise; too much for 98% of the population. You turbo isn't working any harder either; you can probably just here it better because the noise isn't cancelled out from the pipe reverberations. Like how a Scotty II with hole or a BHAF can also make the turbo louder.

Even without the pipe, 850 degrees post is right on the edge of "safe", right? Nothing to worry about?

Unless you got more boost, I think that everything is what I'd expect to happen. Or am I missing something strange?

PS: I think that 4-inch pipe is as big as can fit in a first generation without any frame or routing modification, correct? But a 6-inch velocity stack out of the hood with a piece of flex tubing extending road-warrior style out over the back of the cab- that'd be cool...

 

I wunder how many have taken a first gen, chopped the exhaust and routed it right out through the hood... ? 2 feet of pipe is all I'd want anyway. Well, that and a good set of ear plugs... Illegal or not, you'd still get EGT reduction there.

Someone should take the time and do a project and approximate how much your EGT's do increase for every foot of pipe you add to your exhaust system. I'm aware it could vary, BUT it would help ballpark alot of theories

 

Give serious thought to moving the pyro probe 'pre-turbo' at least that way you'll get fast accurate readings and you won't have to "do math" while yer driving.....

pb...

 

PB--as I said above, I'm gonna add a pyro here shortly for just that reason. I'm thinking the 12cm probably makes the difference between pre and post even more, so, since I put the 12cm on, I haven't sustained anything higher than 800 for more than a few seconds. My thoughts are that the post location is good for steady state loads like pulling a trailer, but that it may not react fast enough to the spikes in temps due to ummm, R&D full throttle application In any event, I see no choice but to speed up my stack building process now! I priced out all the stuff at my local Fleet Pride and, including 48''X5'' chrome turnouts, 4'' splitter etc should be around 200 bucks +or-. Not too bad and I get to buy local, which I like to do when I can. Thanks for the replies, fellas!
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Greg,

Did you check to see if there were any restrictions in the section of pipe that came off?

Assuming that it was all free, I wonder if the effect of the reduction in back-pressure is having as great an effect on pre-turbo EGT's as post turbo EGT's . . .

I used to keep a set of ear-protectors hanging from the light switch in my Jeep -- exhaust, who needs an exhaust?

It is too bad you didn't have the second pyro probe installed before the pipe came off -- it would have been interesting to see the effect pre & post turbo.

 

I'm thinking the post #'s are affected more by pipe length than the pre #'s. It's just a guess, but I'm gonna have a basis for comparison when I get a new pyro this week. Though I won't be able to compare with the tailpipe, I'm gonna try to get a video of both gauges as I run up though the gears WOT. The pipe all seemed clear, but the muffler eliminator pipe was badly rusted vs the aluminized steel...maybe that slowed things down? Presently, I've got a 3.5'' length that I made from the old tailpipe coming out in front of the rear tire. Temps have stayed the same as with the 'open' t-case pipe. I'm sure I'll put all my quandries to rest with a new probe and gauge...

Alec--did you get my e-mail? You've got some snail mail on the way! (finally...)
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