SBC Dual Exhaust Advice & Pix?

Tinker · 12-06-06, 07:16 PM

Have to change the exhaust on my '84 with the 5.7 Vortec & 4L60E. Currently it's a single 3" pipe exiting on the driver's side in front of the (extended) shackle. Emissions Nazis (they're just doing their job) say I need 2 cats, so that makes it hard to do with the way the Y is now, so I'm guessing it will end up being duals. I've read that a crossover pipe increases HP - any thoughts? I kinda like the sound without it.

I like the idea of it exiting on the side (as opposed to the stock location), but I want to go to a Dakar suspension with the standard OME greasable shackles & I'm afraid 2-1/2" pipes wouldn't fit in front of the shackles & might get crushed on compression. What about after the shackles - will I crush them on steep departures?

Any pix of clean, clever setups would be appreciated!

2badfjs · 12-06-06, 10:49 PM

why not run two small cats inline like the 80's?

Tinker · 12-07-06, 05:14 AM

Has to be the same configuration as the donor vehicle: per side from the manifold O2 sensor/cat/O2 sensor. Nothing after that matters (no emissions equipment) so I could run straight pipes as far as the EPA is concerned.

hobiesbestfriend · 12-07-06, 08:17 AM

If going to dual, you need the crossover pipe or an X-pipe to help with the scavenging effect of the exhaust. It has to do with the firing order, and the pulses of exhaust pulling the next one along keeping it running smoothly. Could you just have everything same as stock up to the cats and then just route two pipes back into one? my 2 pesos

Corbet · 12-07-06, 12:37 PM

I'm a little confused as to what the emissions dept is requiring you to have. Did the donor vehicle have 2 in-line cats after a Y? 2 cats before a Y, or a duel exhaust with separate cats? Are they placing any requirements on where your exhaust dumps out?

philos1 · 12-07-06, 02:29 PM

Corbet, 2 pre cats w/ 02 sensors, then 2 cats w/ 02 sensors, then it Y's (IIRC) and he can do whatever he wants... i'd say go back into a single 3" after the cats????

Tinker, look at the BTB site, they have a slick looking install on a 40 that has both cats right next to each other and slightly offset so that they take up minimal room. that's what i'll probably be doing on mine this spring...

Tinker · 12-07-06, 02:50 PM

Hobie - yes I could, but I don't think it would fit the way it's plumbed now. The Y is in front of the trans, & there wouldn't be enough room for a cat unless they were vertical below the new ramshorn headers, immediately after the 1st 2 sensors. It could end in a single exhaust, but I'm concerned about placing a 3" pipe anwhere sensible (not in front of the rear shackle, anyway).

Corbet - again, per side from the manifold:O2 sensor/cat/O2 sensor. In other words, 2 sensors, 2 cats, 2 sensors. It doesn't matter to the EPA what comes after the last sensor(s) - that's not emissions equipment. Do you have cats on yours?

Cruisergreg · 12-07-06, 09:51 PM

Quote:

Originally Posted by Tinker

but I'm concerned about placing a 3" pipe anwhere sensible (not in front of the rear shackle, anyway).

I've got a 3" pipe running through the rear spring (before the shackle) and it works fine. You just need to angle it slightly toward the rear as it exits the line with the frame. I have a 4" Alcan lift and anti-inversion shackles. HTH.

Tinker · 12-08-06, 05:12 AM

Greg -
I'll be going to the 2-1/2" lift OME medium in the rear with greasable shackles (probably anti-inversion). What I didn't mention is that I have a Dynomax Ultraflo & a 3" pipe that exits just before the left rear shackle. It's annoyingly loud after about 15 min on the highway.

I know a good exhaust shop can set me up with mufflers that will rumble at idle, growl on acceleration, but purr at cruising RPMs.

Turtle60 · 12-08-06, 07:57 AM

Tinker,

I assume that this setup is particular to the vortec and not the TBI. Is that correct? Original equipment for the engine being swapped in? Or for the vehicle?

I am putting in a '92 tbi motor from a single cat, 1 o2 sensor vehicle and am curious. What are you running now? I wonder if your old setup would work for me...

Corbet · 12-08-06, 11:00 AM

I do not have cats but I probably have space for them if I wanted to. My 3" dumps straight down directly behind the rear axle. I think I've got some pics on my home PC. I'll post or take new ones later. I'm also running a 50 series Flowmaster. It has the sound traits your looking for. Modest noise unless you put your foot into it.

Tinker · 12-08-06, 12:25 PM

Turtle -
The configuration I described is specifically for the 98 5.7 Vortec. My current exhaust system might work for you, but it would depend on the exact placement of your engine. I believe it's all welded past the flanges on the headers, so it will have to be cut apart to take it off, anyway. The block-hugger headers are going away, too.

The truck is at my shop right off X184 in Castle Rock if you want to see it some time.

jefferson-mo · 12-08-06, 01:04 PM

This set-up is for OBD-II setups only.............the rear O2s are actually called 'cat-monitors'........they can tell if the cats are working or not......so yeah it has to be 2 seperate and side-by-side cats and 4 sensors....

here's what I did on my car:

http://www.hotrod.com/featuredvehicl..._lx/index.html

)scroll down to the last pic)

it wasn't OBD-II but I had to run a single exhaust 'cause of the external fuel pump and offset fuel tank.............

Flowmaster makes that cool Y-pipe that goes from 2 2-1/2" pipes to a single 3"

worked well in that situation and with the big muffler and mandrel bent 3" tailpipe I don't think I lost much HP if any..............

On a Land Cruiser there isn't room to spread out the exhaust like this but if the cats are laid on their side and welded together it could come out pretty compact..

Oh Yeah don'y buy cheap Hi Flo cats 'cause they suck and fall apart in no time(ask me how I know)

Magnaflows are pretty good..............

Tinker · 12-08-06, 06:16 PM

Thanks, Jeffmo - nice setup!

But I really need to see FJ60 setups with dual exhausts, preferrably with an auto (since I have one).

Turtle60 · 12-11-06, 07:47 AM

Still no pics? Darn - I've been watching this to see how it turns out. Is it that most conversions have been done in no smog law states? Tinker - have you asked some of the shops that do conversions if they have pics of their setups? TLC claims they do conversions.

Does your current setup have AIR injection in the headers?

Tinker · 12-11-06, 12:05 PM

Turtle -
I have an excellent example of an illegal, single-exhaust setup from a "good" shop (not TLC by any means, but that's another story).

I'll have pix when I'm done, but I'd hoped to see some clever dual setups with high-flow cats & X-pipes. BooHoo