Stock Exhaust Upgrades vs. New Entirely

[Stratosurfer]

All,
I'm convinced the cats on both vehicles are now plugged and destined for the dustbin of history. I am contemplating a Kennedy or Heath full system but really enjoy the nice stainless I have already. Can I solve the slow turbine response-highway passing/poor fuel economy (15.9 max under ideal highway cruising) problems by staying stock and:
1) Replacing crossover pipe with Kennedy's high flow
2) Replacing downpipe with Kennedy's mandrel bent (and ceramic paint internally)
3) -Displacing- cat con: it would not be found in the area
4) Either staying with stock muffler or having a nice stainless turbo muffler flanged in

All this vs. going all Kennedy or Heath.
I just like the stainless and my vehicles are kid haulers not rock crawlers and I need to keep the rig -relatively- family sounding. A slight bark on throttle response would make the old man and my teenage boys happy however!

I just don't want to go aluminized steel anything if unnecessary for my objectives. As a younger man I replaced many a system of all types of coated steel, high nickel stainless steel exhaust is a wonderful thing in terms of ridding one's life the headache of corrosion on a highly corrosion-prone component of our trucks.

Any feedback appreciated.

[Hubert]

Describe your nice stainless system you have now better. What size, muffler, and downpipe?

[93GMCSierra]

Mine has a stock, for the moment, exhaust but I recently cut out the muffler entirely, it sounds great not too loud an no real headache noise, I plan on larger exhaust in the soon to be immediate future though.

[Stratosurfer]

Mine has a stock, for the moment, exhaust but I recently cut out the muffler entirely, it sounds great not too loud an no real headache noise, I plan on larger exhaust in the soon to be immediate future though.

So you left in just the cat? I'm being told with our diesels these plug up rapidly.

[Billman]

I wouldn't replace the exhaust completely. For what you are after, gutting the cat, and replacing the downpipe/crossover will probably find your lost mileage.

I would leave the muffler in place also.

This is provided it is primarily used as a Family rig and don't tow too much.

[DaveNY]

Surfer, Hate to butt in on your bit but maybe someone knows if the replacement downpipes extend long enough to eliminate the cat?
Dave

[sturgeon-phish]

Most down pipes are to be mated to a larger pipe after the 3" to whatever transition.
Gutting the cat was my first step before a complete exhaust and the difference was huge. Cost "zero". A free flowing down pipe was going to be my second step, but I went to a complete exhaust because I tow.
IMHO best for the money, gut the cat, then add a down pipe if you believe you need more power cooling or what ever. You won't have a lot of money tied up in it and for your application it may be all you'll need. If you go for more mods in the future, a larger exhaust may be warranted to get rid of themore air you are pushing through the motor.
Jim

[93GMCSierra]

my stock exhaust does not include a cat, I dont know what year started the cats but 93 does not have it.
I would say if you need a cat to pass emissions or something gut it an call it good, or just cut it out.

[restoguy]

Let me throw this out there for your consideration. While changing the glow plugs on my 'new' '99 crew cab, I noticed that one plug was unusually hard to get to. Upon closer inspection I realized that the truck has an aftermarket down pipe!(bought it at auction so I don't have any history) Well that would explain why this truck has considerably more 'snort' than my '94. If I was keeping the 'old' one I would definately put a down pipe on it first thing, and probably a crossover too. Flowmaster has a kit with both pieces that looks pretty good. I don't own a truck with a full aftermarket system, but I know that the DP/CO kit is less expensive and for the way I used the '94 that would have been fine. This new one, however, is going to get a full stainless system in the near future.(about 5 min after the 18:1 engine goes in!)

[Kennedy]

I started by doing thedownpipe, then the cat gut, then the muffler delete, and eventually built what became the KD 3.5" exhaust. There is a VERY nice gain when upsizing the pipe. I have a dyno plot on my site showing the gain over a gutted cat/muffler bypass system:

http://www.kennedydiesel.com/photogal/pages/97-65-kd-exhaust.html

[RT]

Here is a question: Are you planning on doing the work yourself or paying a shop to make the modifications? If you are paying to have the stock system modified then you will likely spend more money than if you simply purchased a complete system and bolted it on yourself. The complete systems should just bolt in, no welding, cutting, etc. required. I did a BD 4" system 7 years ago and it is still going strong. If I had it to do again I would likely go with Kennedy. Just my 2cents. RT

[neckcrank]

Does the 6.5 pass emmissions after gutting the cat?
I have a 99 cutaway van w/ 4" catback, remote pmd from Kennedy.

[Robyn]

If you have to pass emissions testing you are doomed to keeping the cat in the system even if you just have to gut it.

My 95 has a Banks system and whoever (PO) installed it, replaced the cat with a length of 3-1/2 pipe and the difference is noticeable.

Flow is everything. Reduced backpressure allows the exhaust gasses to flow out faster and in doing so spools the turbo much faster too.

Just replacing the down pipe and removing the restrictions caused by the cat will help a bunch but the small stock pipe and restrictive muffler as well as tail pipe are still an issue.

To give an example My DaHooooley with the Banks system has very little noticeable wind at the tail pipe (High flow, low pressure)
My Stock 94 Burb will blow your pantleg off if you get close to it and its very hot too.

As far as the stainless Vs. aluminized goes, unless you live in salt country where your system is being attacked by copious quanities of salt laden water all winter I would not worry about it.
Diesels tend to be very easy on exhaust systems.
I recently sold an 84 diesel Blazer with its stock system still in place and it was in good shape with over 200K miles on it.

Many aftermarket companies offer stainless systems in kit form for the 6.5 so its a budgit choice.
I would go at least 3-1/2' and if the budgit will allow it 4" would be nice.
The down pipe will be limited to 3" I believe due to space
Seems I have seem a custom down pipe that had just a small area of 3" where it couples to the turbo then it transitioned to 3-1/2 for the remainder of it's run.

Hope this hekps some

Robyn

[sprice]

SSdieselsupply.com offers a complete 4" exhaust for $335. I put it on my truck and thought the huge stove pipe hanging out behind my tire would be noisy, but it was actually a deep throaty tone. It sounds great and it was easy to install. It has a 3" down that then turns into a 4". You can also buy the crossover which is a 2.25" for another $68. I have really noticed my truck breathing easier and running a lot cooler since I did this mod.
Shaun

[neckcrank]

I know the cat has to stay for inspection but will it pass the sniffer test after its gutted?

[Stratosurfer]

Does the 6.5 pass emmissions after gutting the cat?
I have a 99 cutaway van w/ 4" catback, remote pmd from Kennedy.

Folks,
Thanks for all the data, down here in -God's Country- (AKA: TEXAS!) neither of my rigs has to be gas analyzed. They are both exempt! I'm now in a rural area but lived in the smog saturated Houston Area playing under among the most strict smog rules: (dyno testing for emissions) when I had both of them inspected originally. I was told they are both exempt, there is no published data to smog either of mine with. I can't understand how any other jurisdiction can smog these vehicles, maybe those 1/2 ton and under had specifications listed for emissions, the 5/8's (Govt Tahoe) and .75 Burb both were exempt from the factory and as I understand it there is not published data to smog them with, so even if our government changes hands in the future (your still always safe in Texas!); I don't see how anything can change in this (smog) regard.
YEE HAA, or in other words, a straight pipe will suffice.

[kaylabryn]

Here in AZ they do an opacity test only, but they do check. They also have road side check periodically (I have only seen one) where they check with a mirror for a cat and dip the tank for red dye.