Hey folks I have read all my replys from the posting I made about the downpipe for the 6.5. I would like to thank everyone who gave all those good answers to all my questions. Bet you though I would never stop. Well you are right one last question before I order the 3in downpipe. After installing the downpipe everyone referred to a 3in or a 4in exhaust system the rest of the way out the back. Now then is this 3in or 4in exhaust system including the muffler if used ID or OD? Thanks once again Gordon.

I'm pretty sure, exhaust sizing is standardized, whether its ID or OD, if you order the same size pipe from 12 different muffler shops they will all be the same. That being said, I'm pretty sure thats the ID measurement.

Not to confuse matters but i thought all pipe is measured OD, different wall thickness for heavier pipe is on the inside reducing the ID.

Least thats the way it is in the oil patch!

After looking around at some exhaust MFG's websites, I agree with CR now, looks like its all measured OD.

Pipe is measured I.D. - that's why it is larger than the specified size, and why id is reduced for higher pressure. 1/4"npt requires 7/16" drill

Tubing - exhaust PIPE is tubing - is measued O.D.

Just out of curiosity, why the need to know anyway Gord? Does an 1/16" on 3" really make that much difference?

You know your are right how much difference can 1/16 of and inch make. Thanks Texas Diesel Guy. And thanks everyone else. After measureing between cab and cross member it sure would be tight to put a 4in in there. Thanks once again everyone that took the time to answer my questions, I think this is it for now. If I run into trouble installing the downpipe and exhaust I'll be back. Gordon.

it is tight buy it will fit in between the cab and cross member

As long as the down pipe is bigger than the turbine outlet the down pipe should be adequate for almost all applications.

I believe most everybody goes 3" downpipe for approx 2ft then 4" the rest of pipe.
My muffler is 5".
There isn't much clearance right below turbo, and with engine movement when you start it cold you don't want to bang pipe on frame or body.
It is anyway a huge improvement on stock downpipe and muffler.
I felt most improvement on mandrel bent crossover, you will also replace leaky donut gaskets.

My exhaust is all stock, except that I've replaced the cat and muffler with a straight pipe and I have a 3" Flowmaster downpipe.

I can't seem to get a vender to sell me a 3" exhaust system minus the downpipe and muffler/cat. "We only sell complete systems." What a crock.

I'm pretty sure I've seen cat back systems listed for the 6.5L

Ok, I'll admit that I haven't looked too hard yet. But the two places I've asked about it (one is an advertiser on this site) both gave me that "we only sell complete systems" response.

If they're making their own stuff, how hard could it be?

QM: PM me if you know where I might find such a cat back system.

EDIT>>> A cat back system would include a muffler. I don't want a muffler. All I really need is the slight bend where the exhaust goes over the frame crossmember and the tailpipe.

I just went to the local muffler shop and they installed it for less than I could have bought a system. like 130.00 or so.

If you go the local shop route, price it first. some shops work with you and some act like it's a big deal. Personally, I'd cut the 4 bolt flange off the downpipe, take it to the shop and have them expand the opening to accomodate the next joint and measure from the flange to where the axle bend starts on the 'burb and they should be able to pop it out in 10 minutes. Walk out is the cheapest way for the local shop to make it, otherwise you pay for all the things you can do, like take it off and put the new one on.

Walk out is the cheapest way for the local shop to make it, otherwise you pay for all the things you can do, like take it off and put the new one on.
Excellent idea. I'll have to kick that a round a little. Like I said in a PM to QM, I'll just take the exhaust off from the downpipe flange back and go for a ride. Then if I don't register an improvement on the seat-o-pants dyno, there's no sense in putting on a bigger exhaust.

And if the seat-o-pants dyno registers a "WHOO HOO!", I already got the exhaust out of the truck and can easily haul it to the muffler shop.

Wade,

I don't know if it's allowed here, but here's my exhaust:

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=7957629607&category=33630

Hey, I've been looking at the way that snorkel is placed or better yet how they built the fender and truck around it. A typical GM after thought. How are we going to get air to the turbo great engineers. Any suggestions on how to remove the whole air intake, or is it necessary? Is there an easier way to get air to the turbo without removing it? If add on how big an intake air hose or pipe to use, and where to place the filter? Thanks. Gordon.

Gordo update your sig in users CP so we know what flavor 6.5 you have, makes a difference to what we tell you.



Hey, I've been looking at the way that snorkel is placed or better yet how they built the fender and truck around it. A typical GM after thought. How are we going to get air to the turbo great engineers. Any suggestions on how to remove the whole air intake, or is it necessary? Is there an easier way to get air to the turbo without removing it? If add on how big an intake air hose or pipe to use, and where to place the filter? Thanks. Gordon.

What I have is a 93 2500 ext cab LB 4.l0 70000miles. Gordon.

Okay with a 93 that qualifes for snorkle how do I answer, 96+ don't have them go to www.kennedydiesel.com (http://www.kennedydiesel.com/) in his tech help section are details how to remove snorkle, in our own FAQs at sticky thread at top of 6.5 forum are other things you can do for more oomph from your 6.5. If you would if you have more snorkle questions please start another thread on that topic, changing topics in another post make it more difficult to use search engine to find info.