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Experience w/ true duals w/ downpipes pre-rear wheels?

K

krakhedd

NAXJA Forum User
Location
Buffalo, NY
2000 Classic, 4.6L stroker, Stage 3 Bulletproof (?) cam from 505 Performance, Stage 2 head from 505, 505 roller rockers, Clifford headers.

I want to run true duals, but instead of running them all the way back & over the rear axle (which I feel has too little clearance for an exhaust on the driver's side), I want to run 2" pipe through high flow cats & mufflers, and end them with downpipes. The downpipes would be located so they exhaust under the rear doors (I have a 4dr). Basically, pointing down & away from the vehicle at 40-50 degree angles on all three axes, just inside the frame rails. Also probably have an X-pipe.

Has anybody ever tried a setup like this on anything from bone stock to full-bore performance? What were your results?

Thanks guys :)
 
I don't have a pic of the engine going in today from the left side of the engine so you can't see the header, but yes, the engine was dropped in, and the header was definitely on it!!
 
You'll see absolutely ZERO performance gain running "true duals" on an inline motor. (No such thing as true duals is what I'm getting at)

A motor with true duals, running and X-Pipe is so the two opposite sides of the motor can communicate with each other through the combustion stroke, giving you a smoother exhaust note, and evacuating exhaust gasses. Run it into a single pipe, and dump it before the axle if you'd like.
 
krakhedd said:
2000 Classic, 4.6L stroker, Stage 3 Bulletproof (?) cam from 505 Performance, Stage 2 head from 505, 505 roller rockers, Clifford headers.

I want to run true duals, but instead of running them all the way back & over the rear axle (which I feel has too little clearance for an exhaust on the driver's side), I want to run 2" pipe through high flow cats & mufflers, and end them with downpipes. The downpipes would be located so they exhaust under the rear doors (I have a 4dr). Basically, pointing down & away from the vehicle at 40-50 degree angles on all three axes, just inside the frame rails. Also probably have an X-pipe.

Has anybody ever tried a setup like this on anything from bone stock to full-bore performance? What were your results?

Thanks guys :)
Click to expand...

I would think a "true dual" setup, properly designed, would show about as much benefit as going with true duals on a V-block engine (vice a single with a Y-pipe.)

That said:
- "True duals" on an inline six are still to be divided at the engine. Division is typically a 'fore-and-aft' setup, split as 1-2-3 and 4-5-6.
- A crossover pipe may be as beneficial as it would be on a V6 or V8, although some experimentation would be needed (a crossover is typically done with a left-and-right exhaust setup, where each pipe runs down its side of the vehicle. If the pipes are too close together, the crossover benefit may be negated thereby.)
- Optimax pipe cross-sectional area will still apply, it will just be calculated using the smaller flow source (three cylinders' worth of displacement, vice all six.)
- If this is a road vehicle here, you're going to have to fight with the smog referee to get it approved - with dual cats, dual mufflers, and the like being mandatory. I don't know if the fight would be worth it. If it's an off-road vehicle, I'd just run it as headers with a straight pipe (the exit behind the seating area) and spark arrestors if you're interested in maximising flow throughput. You could run it as a 'dual' setup that way (although I'd probably run it as a single with a resonator before the exit) if you like, but I don't know how helpful that would be.

If you'd like to bounce ideas off of me, I can look a few things up and see if I can't get something helpful from the literature I have to hand. Let me know if I can do anything to help!
 
krakhedd said:
http://www.cliffordperformance.net/...de=CP&Product_Code=57-2300&Category_Code=J258

That's my header, you tell me!! :)
Click to expand...

That doesn't look like an "equal length" header to me, but it's got the right split for a dual setup.

By the by - you have the grind card for that cam? Can you send me a copy? Scanned would be fine - I'm just trying to amass cam data, and not everyone seems to be willing to part with it readily.

(As far as the "out here," I'd gotten your moniker crossed with someone here in town. I don't know how difficult NYS can be about emissions test, but I've heard horror stories about the East Coast...)
 
Just do it krakhedd and post pictures. You will be the one to provide info to others.
 
crazyjim said:
You'll see absolutely ZERO performance gain running "true duals" on an inline motor. (No such thing as true duals is what I'm getting at)

A motor with true duals, running and X-Pipe is so the two opposite sides of the motor can communicate with each other through the combustion stroke, giving you a smoother exhaust note, and evacuating exhaust gasses. Run it into a single pipe, and dump it before the axle if you'd like.
Click to expand...

My 335i is an inline six with 'true duals'. One turbo per front/rear 3 cylinders, and divorced exhaust all the way back.

E46 M3 is the same way. Headers are 2 pieces and seperate exhaust pipes all the way to the rear. Not that it should be done on a Jeep, but BMW must know something you don't :)

Picture002.jpg


e46_m3_undercarriage-vi.jpg
 
@Jim - The X-pipe is actually to use the heat from the exhaust gas on one bank to "suck" (or, scavenge) the exhaust gasses from the other bank, thereby reducing the amount of energy used pushing the exhaust gas out of those cylinders ("back pressure" is a misnomer - back pressure hurts at all engine speeds, just that a good exhaust will minimize them at high revs while still providing ample scavenging effect at low revs). Point being, it has absolutely zero to do with "opposite banks" and such. Much more simple than that! :)

@5-90 - I've been on this forum for a long time, I used to live in CA and that's really the last time I was active - perhaps your memory isn't so bad after all? Oh, and that Clifford header dumps 1-3-5 into one collector, 2-4-6 into the other. I don't have the grind specs, I will try to chase it up. It all came to me as a kit though, except the crank, which I bought about five or six years ago.

@Gradon - I like how you think :) Stage 2 is ported, polished, 3-way valve job, larger valves (I do not know exact specs - I trusted Zach @ 505 to know what he's talking about, and to not screw me!) :)

Something else I thought of though (after I typed this up last night), what about immersion in water? That's no cheap engine, and I do NOT want to eff it up. Same logic though, using a Borla cat-back on my 1st & 2nd XJs, on a mostly stock engine, I could still get into water & the engine ran fine. Perhaps I'm paranoid about the engine working extra-hard to push not just the exhausted gas, but the water out, too?
 
krakhedd said:
@Jim - The X-pipe is actually to use the heat from the exhaust gas on one bank to "suck" (or, scavenge) the exhaust gasses from the other bank, thereby reducing the amount of energy used pushing the exhaust gas out of those cylinders ("back pressure" is a misnomer - back pressure hurts at all engine speeds, just that a good exhaust will minimize them at high revs while still providing ample scavenging effect at low revs). Point being, it has absolutely zero to do with "opposite banks" and such. Much more simple than that! :)

@5-90 - I've been on this forum for a long time, I used to live in CA and that's really the last time I was active - perhaps your memory isn't so bad after all? Oh, and that Clifford header dumps 1-3-5 into one collector, 2-4-6 into the other. I don't have the grind specs, I will try to chase it up. It all came to me as a kit though, except the crank, which I bought about five or six years ago.

@Gradon - I like how you think :) Stage 2 is ported, polished, 3-way valve job, larger valves (I do not know exact specs - I trusted Zach @ 505 to know what he's talking about, and to not screw me!) :)

Something else I thought of though (after I typed this up last night), what about immersion in water? That's no cheap engine, and I do NOT want to eff it up. Same logic though, using a Borla cat-back on my 1st & 2nd XJs, on a mostly stock engine, I could still get into water & the engine ran fine. Perhaps I'm paranoid about the engine working extra-hard to push not just the exhausted gas, but the water out, too?
Click to expand...

Could be. Were you over by Alum Rock Park?

Interesting that it's the odd/even split - most of the literature I've read treats the inline six as a pair of inline three-cylinder engines, ganged front-to-back. I wonder...

If you've got a flow card on the head, I'd appreciate that as well - again, just collecting data...
 
Well I went w/ more or less true duals. There's an X-pipe built into the muffler, which is offset toward the passenger side & dumps just in front if the rear axle. High-flow cats, the muffler place said they use them on SRT8s so they should flow just fine :) The whole exhaust is custom 2.25" stainless all the way back. Sounds absolutely bitchin', maybe a bit on the loud side but I'm getting used to my 283ci inline Jeep engine sounding like a wicked V8 :)
 
You say you want to dump the exhaust under the rear doors.... in some states that is illegal, especially if you live in a state with inspections. I know, at least in North Carolina, that if the exhaust dumps anywhere under the vehicle inline with the passenger compartment it is deemed a safety issue and will not pass inspection due to the increased chance of carbon monoxide intrusion into the passenger compartment. That too is why all XJ exhausts dump at the rear of the vehicle at the end of the passenger area. You may want to reseach this before spending too much money on a custom system.
 
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