I quickly checked the archives and didn't find a thread on the subject. Anyways, has anyone determined the optimal size exhaust system for the 6.5? Does application have any bearing on sizing, for example, someone heavily modded and towing large loads will see more benefit from 3.5 than someone with basic power adders and moderate towing?


Some have posted in the past that it is best to match the port you are coming from, and may go to a larger diameter if you do not reduce that diameter later on (the actual quote said it would "not cause problems", not add power or something positive). Since the outlet port is 3 inches from the turbo, doesn't it make sense to maintain that diameter with the smoothest bends as possible? Or, does a larger diameter really flow better than 3 and adds like x% power over a mandrel 3 system?

i run a banks 3in to the muffler (no cat) and then 3.5 out the tailpipe to a 4 in tip. im happy, and cant see anything any bigger being much better without serious modification. its a 2door tahoe with a 3.42 rear. i have no problems making 70mph on the flats all the way from florida to NC. it has helped with towing alot. the turbo lag is non existant and like i said, i cant see anything bigger helping that much, but as youll see, im probably about to get slammed as being dead wrong

i run a banks 3in to the muffler (no cat) and then 3.5 out the tailpipe to a 4 in tip. im happy, and cant see anything any bigger being much better without serious modification. its a 2door tahoe with a 3.42 rear. i have no problems making 70mph on the flats all the way from florida to NC. it has helped with towing alot. the turbo lag is non existant and like i said, i cant see anything bigger helping that much, but as youll see, im probably about to get slammed as being dead wrong


From my years of hanging around GM Diesel Forums it seems that a 3 inch mandrel bend exhaust will do for someone who is running stock too modest power modifications. 3 1/2 inch seems to be what is best if you plan on really adding mods. JK has said in the past the he feels that 4 inch and up for the 6.5 is just for show and doesn't ad any go.

I run a 3" downpipe that goes to 3.5" just after the bend at the bottom and then just past the crossmember goes to 4" with a large magnaflow 4" muffler and 4" the rest of the way back. I am extremely pleased with mine. It sounds like a big block gasser at the tailpipe until you get on the throttle and here the turbo whining. I can see and feel a big difference in power. The throttle response is much quicker and now seems to run out of fuel and boost long before the engine feels dogged by the exhaust pressure, like it did before the change.


Also I got my entire exhaust including the muffler, hangers and shipping for only $340 from Jardine Manufacturing (Pinnacle). I priced out the downpipe, pipe, muffler and hangers to create my own and I would have only saved about $40-70 not including my time for welding and fabing it together.


It has been one of my best mods yet.

That's interesting, but i bet with a better turbo that changes.

my exhaust comes out at 3" then goes to 4" just before i dump the wastegate 1-5/8" tube into it. Just making sure I have enough area to cover the 3" exhaust wheel and the 1.625" wastegate diameter.

i would have went with 3.5 inch on my exhaust, but i got the 4 inch pretty cheap from a buddy. only paid 25 dollars for 10 foot.

Has anyone put a Duramax or powerstroke takeoff exhaust on a 6.5?


I have seen a lot of people post about it but never actually saw someone that did.

I used the polishable stainless 3.5" system from a crew cab PS Diesel simply because it is STAINLESS - no rust, ever, including large STAINLESS muffler.


Did I mention that it is STAINLESS, polishable, no rust - ever. Doesn't get that surface rust like the GM stainless pipe.


Been on the truck since Dec '99.


4" system may flow a little better on a hot rod, but the 3.5" is adequate for the ~2200rpm I hang at.


Only upgrade I'm not running is the marine hi-flow injectors 'cause the truck is not a hotrod, and timing will be set back to -1.5deg from -1.94 because of the low rpm range I run in.


That's my story, and I'm stickin' to it.....

If I found a better matched nonwastegate turbo, wouldn't optimal size increase a bit? at least to the point of justifying 5"-6"?

From what I've seen the GM 4 turbo is good for off the line and runs out of air in the high RPM's.


The GM 8 is just the opposite.


The quicker and smoother you get rid of the exhaust the cooler and better the truck will run. I put JK's 3.5" front to back with his down pipe and lost the "cat" with an open muffler. I picked up 3lbs. of boost and dropped 100* on the pyrometer temps.


This should be the first mod you make when upgrading for performance!

GMCTD,


I am not sure what material they used for exhaust systems in 94, but my 6.5 Blazer's system lasted about 3 years before falling off. Given that, wouldn't mind a nice 3.5 stainless system for my Suburban. Only problem id finding one. Exhaust systems don't last long here in N.E. Ohio and I really don't want to put another on my truck after this one.


Also, not to change the subject, but I thought -1.94 was the best all-around timing setting. From your statement, I appears that the effect is not linear across the rpm band. On my 94, setting the timing to -1.94 (and gear drive) really made a difference, especially above 2500 rpms. The power was smooth and the engine felt happy operating in that range. So, lowering the timing to -1.5 would lower that sweet spot? I really have not seen a lot of information out there on timing and its relationship to performance (besides ronniejoes testimonial with dyno numbers indicating a timing change does in fact produce a linear change). Perhaps someone out there with a dyno will do a study on timing.

I think increased size would be a requirement if overall system had a number of 90deg bends - any change of direction in flow is restrictive to flow.


Smooth bends and straight runs do not require the over 4" large piping.


5-6" looks good, and the ladies cannot get you out of their minds, but sometimes the extra real estate required is the cause of some requirement for the extra size.


'Course, I still want my twin stainless 4" stacks, with them little flappers on the top............ http://dieselplace.com/forum/smileys/Wink.gif

where you at in ne ohio, super tuscan? my girlfriend lives in randolph.


you could probably find a complete stainless steel system or have one made. im guessing it will cost twice as much, probably close to $700.


gmctd: becareful with stacks and rain flappers. i saw a stroker once that could barely move enough air to move them.

I live here in Cleveland. There is a local ss shop, but they don't bend anything larger than 3 inch.

ST - I'm experimenting with timing on my particular configuration, but it will probably never see a dyno. Fuel mileage will tell the tale.


If yours runs well at -1.94, don't mess with it, as your truck is not heavy as mine, doesn't have as much powertrain to spin.


Check out the 3.5" system on the PS trucks, '90-99 or so, see if any can be re-configured for your truck. All the body styles have the system - one should be close to what you need.


QM - I'm just pushing what is practical - if you want 6", go for it.


I just stated that it won't show any gain - doesn't mean that it will detract.


3.5" is practical - the twin 4" stacks is for the ladieshttp://www.dieselplace.com/forum/smileys/Wink.gif

What about for a non turbo 6.5L?? Roughly dual 3"??? what do you guys think?

Should be plenty. Have you seen the headers for nonturbo models?


Kansas diesel I think

Is there a web site? what about just running dual 3" off the manifolds? with no cats?


is dual 3" to big?? perfect? to small??(this is all with no cats)
Edited by: Elky

just called the exhaust shop, and this said that the manifolds are 2 1/4" (is that correct?)so its pointless going any bigger than that, and they want to put on "silver knight" mufflers.

GMCTD,


The Blazer has long been dead.


BTW, I want to make sure I understand what you are referring to. WTH is PS?

www.salinapowersports.com/midkansasdiesel.htm (http://www.salinapowersports.com/midkansasdiesel.htm)


These guys headers have 3" collectors.


The mufflershop might have to start 21/4" but I would take it to 3" after that, no reason it can't expand.





ST, PS=powerstrokeEdited by: quantum mechanic

would expanding from 2 1/4" to 3" actually do any good tho? because the bottleneck would be a the 2 1/4". and is the correct with the manifold size being 2 1/4"? and what mufflers would you recommend?





I didn't see any phone # for kansas diesel



Edited by: Elky

No mufflers needed. 2 1/4" is correct and expanding the diameter will allow your hot exhaust gas to flow better, even out of the restrictive manifolds.


get to the salina motor sport page, same website.Edited by: quantum mechanic

So I should tell the exhaust shop that I will run 2 1/4" right off the manifolds, then goto 3" as soon as they can straight back, with NO mufflers??


How loud will this be, and why no mufflers?

Diesels aren't loud like a gas engine, and here, at least, there's no law requiring them.


the shorter the distance the exhaust has to travel before diameter increase the better IMHO. 3" should have a nice sound.


I started my 93 not long ago without down pipe or crossover on and I was surprised how quiet it was compared to when all the exhaust is going to the turbo. It's not too loud.

Diesels don't require mufflers??? only gas motors there do???


so 3" is what i want, what about 2.5 or 2.75.


I just called mid kansas diesel and they want $450 plus frieght American, so thats like 800 bucks here! So I'm definitly not getting headers.

You can go any size you want, as long as your increasing from 2 1/4" up you'll be ok.


Gass engines seem explosively loud, at least my SB dodge does, with headers and bigger exhausts, diesels make a low rumble and not much more if you run just the manifolds.Edited by: quantum mechanic

what about your muffler laws?


why are diesels muffler exempt, and not gassers?

Two different critters, I guess. but let me be clear. diesels come with muffler same as gas engines but once their modified you can't get an inspection in a gasoline burning vehicle without a muffler and no one says a thing about the diesels, nothing.Edited by: quantum mechanic

so if the law says i have to run a muffler, can brand or kind should i run?


do you think I would have any problems from the police if i didn't run mufflers on the truck, and only straight pipes?

it depends how loud you can be without your sherriff bustin you. i have had some really loud gas trucks.


big question though. is your truck non-turbo? makes a big difference. i have three friends at school, one with a 6.2 non-turbo, 6.9 non-turbo, and 7.3 non-turbo. i think they are all runnin true duals around 3" with 90 degree bends out the back. let me tell you, these trucks are friggin LOUD!!!!. they cackle like its there job, without even gettin on it.


i dont bother buying mufflers. they can be quite expensive. and i like loud things. my county doesnt have emission laws yet so i can get away without a cat.


ive never seen a turbo diesel get pulled over because it was too loud.

I can't say, I'm not familiar with Canadian law, but I would doubt it.


muffler brands I leave for people using them to answer.

ive never bought one so i couldn't tell ya what is a good muffler.

yeah its a 6.5L Non Turbo.


I don't have to worry about the cat, they don't do emission testing here either. I guess what i can do is: Try running the exhaust with no mufflers and if it is to loud put on mufflers?? Will a exhaust shop put on exhaust with no mufflers?






Edited by: Elky

get the straight pipes and if you need mufflers, you can always go in and put two in just by cutting out a section of pipe and welding a muffler in there. it takes a special shop to do it. when i got my straight pipes put on my old gas trucks, the guy said that he didnt do it so that i couldnt come back and sue him if i got in trouble. i went to several places and they said they wouldnt do it though.


if you have to go with mufflers, flowmaster comes to mind.

the bigger the pipe, the less cackle you will have.

SOoooooooo many people run flowmasters, I would like to have a slightly different sound than everybody else with there dual exhaust.

That's a good question. Some places don't want to remove the CAT either. That's why I put mine on myself.

Well they will take off the cat here, thats not an issue. Soo I guess call up a shop and see who will intall dual 2 1/4" going to 3" with no mufflers.

No pipes and no turbo ought to be fairly loud, probably will get the neighbors in a snit, turbo does a good job of knocking back sound.

would it not really be the same as a gas engine?


so No mufflers on a gas engine will be louder than no mufflers on a diesel(non turbo) engine?
Edited by: Elky

a non-turbo diesel with no mufflers can very well be louder than a gas engine with no mufflers. they can be VERY LOUD!!!!!!





if you run the pipes straight out the back instead of with 90 degrees out the sides, it will lessen the cackle.

so there is no way I would get away without running mufflers.

if you go with 3" pipe and straight out the back, you might be able to keep it quieter, and if you keep your foot out of it, it should be ok.


what does everybody else think?

I guess the only bend would be to go over the rear axles, then I would go straight back under the bumper?
Edited by: Elky

It's your call Elky. How urban is your area? I live in the country.


How loud are other trucks around your area? Here, they're loud more often than not.

I live in the city. There are a few real loud trucks here too.


I think what I will be doing is getting the exhaust put on without mufflers, then see how loud it really is, and if it is too loud then I will throw on some mufflers.

Elky why don't you start scrounging boneyards for a turbo set up, these things need a turbo to really get the power out of them


, In the meantime at least run some inexpensive glass packs something/anything to make the rumble a little bearable us Diesel guys already get a bad rap, waking the dead straight piped doesn't win us any friends, JC Whitney sells inexpensive do it yourself stuff, for a low buck approach until you come up with enough stuff to go turbo, their flex stainless tube works well for a temp or semi permanent set up.


I used it to fab my cat bypass and 1st IC plumbing, would not hold 15psi without weeping oil, about 3 psi rated, get their wrap around stainless muffler/tube clamps that way you can reuse tube for later without crushing it.Edited by: Turbine Doc

I have an extra turbo side exhaust, cost a $100.

a 6.5 w/o mufflers will get your attention from mile or so away. Flowmaster makes a diesel muffler that Doesn't sound anything like a gasser flow. But put the straight pipes on and if you don't like order a mufflers for it, thats what I did on my 6.2 sububan, I had a cross-over pipe put on to. quieten down the crackle some. Edited by: bowtie