Some new exhaust upgrade questions

[gavio]

I'm planning on redoing my exhaust on my NA 6.2 van and have some choices to make. I will be putting the exhaust all on one side of the van as I'm adding a tank under the body in the area where the driver's side exhaust pipe and muffler are now. So here's the deal.

I can have 2 1/2 inch head pipes running through a collector into a muffler and out a single 3 1/2 inch tail pipe, which had been my first thought. For some extra dough, I might be able make that a 4 inch tailpipe but there might not be clearance.

For less money (go figure), I can have 2 1/2 inch head pipes run into a dual in/out muffler connected to dual 3 inch tailpipes. This maximizes flow area of course.

There is a slight chance that the van will get a turbo someday (at present, this is a wish, not a plan) so if that were to happen, would it be OK for the single turbo downpipe to run through a splitter and into the above dual setup without causing undo disturbance?

Or if I'm even dreaming about a turbo should I make sure I go with a single pipe system?

I know these exhaust issues have been discussed many times here, but those threads are history now, so let's start over.

Thanks for any input, as always.

[Eric Deslauriers]

Gavio,

3" will flow better than 2 x 2.5" so I would go with that. You can go bigger, but I don't see anyone really doing it w/ 6.2s, 6.5s and don't think the value is there.

I just did 3" out the back w/ a Magnaflow and I'm quite pleased and I'm running a turbo.

YMMV, but not much I don't think. smile.gif

[gavio]

If I've been correctly following along, it seems that the naturally aspirated engines respond well to having the widest open exhaust possible since they don't have the turbo in there stirring things along. Dr. Lee went with dual 3 inch tailpipes for this reason.

I can get dual 3 inch pipes for less dough than a single 3 1/2 inch pipe so would be inclined to that, all other factors being equal.

Question is: if I later get a turbo (big IF) would I then be throwing my duals out and getting a single pipe anyway, or would it be fine to run the downpipe into a splitter and into the dual tailpipe system? In other words, is there some obscure reason that the turbo NEEDS a single exhaust all the way out the back?

[britannic]

Don't forget to add a balance pipe to join the two runs together - I couldn't find the posts that deal with the best position, so hopefully others will chime in with that info.

On the subject of retrofitting a turbo later:

No problem, the turbo only cares about backpressure and in fact if you and the law could tolerate it would be happy with only a short downpipe. Just be sure to install a non-restrictive collector later.

[gavio]

Since all the exhaust will be on one side of the van, the plan is to run it all through one muffler with dual inlets/outlets which should take care of the balance issue.

I'm hoping that with all that flow area I can use a reasonably quiet muffler and still have it pretty unrestricted.

Unfortunately, I just found out today that my suspension is eating about $400 more than I was expecting so the exhaust might not be quite as imminent as I'd hoped.

Ah well. . .

[mhagie]

Gavio,Here is ones own personal opinion which is just that one persons opinion.
In the present form your exhaust exits the manifold at 2" diameter, unless at this time you are willing to cough up the bucks to make a copy of Dr. Lee's adapters 2" to 2 1/2" 2" is all you get.
One could run 2" down untill pipe levels out then expand up to 3" bringing the other side over and joining at the size increase then run 3" all the way to rear using as large and free flowing muffler as possible. :D
I am using the banks exhaust along w/turbo on a 6.5, pipe size 3" which I believe is large enough unless one is building a modified 300HP monster motor, the size increase over 3" is not cost effective or justifiable.
The single in dual out 3" muffler would really look cool with the dual 3 inchers side by side but thats all it would be is looks, there would be no performace improvement. :(
The average muffler shop can handle up to 3" above that and it takes a specialty shop and they are scarce and costly. :(

[gavio]

Yeah, that's true about the cost - that's kind of how this started growing. My shop needs more money to do a single 3 1/2 inch pipe than two (count 'em, two) 3 inch pipes and I believe that is typical as you say.

I'm not building a monster motor, but do want this old engine to breathe as easy as possible. I also would like it to be reasonably quiet (if you can say that word in a sentence about a diesel ;) ) and I had been thinking that if I opened up the flow area it would compensate for having less than the most open (and hence loudest) muffler.

I was planning on upgrading the head pipes to 2 1/2 inch with manifold adapters although, of course, I haven't priced those yet, either :rolleyes:

Thanks for the opinions, guys, keep 'em coming.