Keeping exhaust pulses separated through a Cat

[Angel And The Wolf]

I've always loved the sound of true duals. I once had the pleasure of driving a true Quad exhaust. I was told that was called a California Quad Exhaust. V8, Two cylinders into one, (four times) four separate pipes straight to the rear. The problem is no exhaust equalization, and less power. I think by cutting the end caps off a regular catalytic converter and replacing them with four smaller caps that each feed one separated quarter of the matrix, I can create four paths that keep the pulses somewhat isolated from the other six. Equalization can be done in the center cavity which the O2 sensor samples, while keeping the majority of the sound in it's proper one of four out pipes.

[Angel And The Wolf]

More expensive, but easier to do:

[cajunfj40]

Hello Angel And The Wolf,

Interesting idea. You might want to read up on the Harley V-Rod/VRSC with the then-new liquid cooled 60-degree DOHC engine. They did a lot of work on the exhaust system with a resonating cavity connecting the two pipes to try and get as close to the old 45-degree engine sound as they could.

Got any links for that California Quad Exhaust? I'm not turning up any "true 4-pipe" exhausts for anything but exotic V12 Ferrari and Pagini vehicles - and those are 3 into 1 primary with 4 secondaries, not what you're describing.

Ok, more searching dug up old Stahl 360 degree headers for a small-block-chevy. https://www.jalopyjournal.com/forum/...ock-up.415461/

Firing order on an SBC is 1-8-4-3-6-5-7-2, so if you puzzle out that bundle of snakes, you see that the cylinders are paired up so that each pair is firing 360 degrees apart, so it would sound like 4 British parallel 4-stroke twins with 360 degree cranks, or 4 large single-cylinder 2-strokes.

I'm not sure how much power you'd lose without balance tubes compared to OEM cast-iron manifolds, unless you're starting with pretty decent OEM ones, since the pulses are nicely separated in each merged pipe - flow balanced. Do your homework on correct primary diameters and lengths, etc. and you can probably meet or exceed OEM output, using 4 separate smaller catalytic converters. You'll need to pick two spots for your O2 sensors or figure out how to "average" a pair of O2 sensors into 1 output that the ECU will feel OK about. I'm assuming a new enough engine that there's an O2 sensor for each bank of your V8. (Secondary post-cat sensors not included.)

Your second idea with the 4 short pipes to the O2 sensor *might* work, but you could be putting too much delay in the mixture feedback loop. Depends on how well that setup flows across the sensor, and with balanced pulses there might not be much flow. I think the first idea would work better in terms of getting a good mixture read.

On a standard "dual" exhaust with 4 into 1 headers on a common cross-plane crankshaft V8 needs the balance pipe because of the uneven firing order on each bank, which messes up the scavenging and causes unbalanced flow out a dual exhaust. 180 degree headers would mimic a flat-plane crank - quite a scream if you've got a high-revver - and don't really need a balance pipe because they're already flow-balanced and scavenge like a pair of inline-4 engines. Those headers are aptly called "bundle of snakes" because of how difficult it is to get all the pipes to where they need to be.

Either way, you're welding up something custom or having a shop do it for you, so cut and try will probably be what you need to do. Use the old converter for the trials, or a cheap aftermarket job if you want clean steel to start with. Once you figure out what you want, get a good unit and set it up.

Have fun!

[Angel And The Wolf]

Originally Posted by cajunfj40

Got any links for that California Quad Exhaust? I'm not turning up any "true 4-pipe" exhausts for anything but exotic V12 Ferrari and Pagini vehicles - and those are 3 into 1 primary with 4 secondaries, not what you're describing.

I can't find anything, either. This was in 1966, and it might have been a one off, but it sure did sound good!

[Angel And The Wolf]

Originally Posted by cajunfj40

Ok, more searching dug up old Stahl 360 degree headers for a small-block-chevy. https://www.jalopyjournal.com/forum/...ock-up.415461/

Thank you! That is my aim, to run each two 360 degree apart exhausts (or, each cylinder of a four cylinder engine) into one pipe, and keep each separate from the other three pipes.

Seems the headers shown are quite long, and would help low end torque, but hinder mid to high end power.
Maybe moving the exhaust ports to the middle of the engine, (See Picture) would facilitate shorter 2 into 1's.

Yes, the factory cat with walls to divide the input and the exit into four sections, as in my first idea, seems to be the most doable, and the honeycombs should keep each input in it's own quarter, and the middle chamber would allow equalization and a common O2 sensing area, though, if each path could have it's own O2 sensor, computer adjustments could be made to pairs of cylinders,(single cylinders, on a Four.) rather than to the whole engine, when only one cylinder might be out of compliance.

[Angel And The Wolf]

Originally Posted by Angel And The Wolf

Maybe moving the exhaust ports to the middle of the engine, (See Picture) would facilitate shorter 2 into 1's.

OK, that might be a bit excessive. I wonder if the cross bank routesmighttravel OVER the engine. Let me play with that a bit with my Paint program.