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View Full Version : Anybody ever heard of this mod?


Sublime Drive
02-03-2006, 04:34 PM
My friend was telling me about this mod that they used to do to cars. Basically, you get a lever that when you pull it opens up your exhaust so that it bypasses the cat and muffler. That way, the exhaust freely flows right out of your engine for more speed and noise. Pull the lever back up and the exhaust flows like normal. It seems like a fun little mod to do to your car, but I haven't heard of it being done before. I don't think it would cause any problems for the engine, do you guys think this is feasable?

Malibubimmer
02-03-2006, 04:43 PM
My friend was telling me about this mod that they used to do to cars. Basically, you get a lever that when you pull it opens up your exhaust so that it bypasses the cat and muffler. That way, the exhaust freely flows right out of your engine for more speed and noise. Pull the lever back up and the exhaust flows like normal. It seems like a fun little mod to do to your car, but I haven't heard of it being done before. I don't think it would cause any problems for the engine, do you guys think this is feasable?
Wouldn't be feasible because of the catalytic converters all modern cars have, and it also wouldn't be feasible because of the noise laws. But, reducing back pressure is often a way to increase horsepower in forced induction engines.

NTB
02-03-2006, 06:33 PM
Marine has a application for this.

http://www.corsaperf.com/mcompare.htm

Fast Bob
02-03-2006, 06:41 PM
They were known as "exhaust cut-outs", usually cable-operated, and as they aged, were prone to exhaust leaks. A friend had them on his `63 Impala SS (w/dual-quad 409), when it was time to go through inspection, DMV made him weld them shut. These would not be practical on today`s cars.

Regards,
Bob

woody underwood
02-03-2006, 07:50 PM
My friend was telling me about this mod that they used to do to cars. Basically, you get a lever that when you pull it opens up your exhaust so that it bypasses the cat and muffler. That way, the exhaust freely flows right out of your engine for more speed and noise. Pull the lever back up and the exhaust flows like normal. It seems like a fun little mod to do to your car, but I haven't heard of it being done before. I don't think it would cause any problems for the engine, do you guys think this is feasable?
Had this on my 53 and 57 Chevys...we called them "lake pipes". Basically just welded a pipe with cap on it into the exhaust ahead of the muffler, took the cap off and made noise. I doubt if it really helped performance that much because we'd punched a lot of holes in the muffler anyway.

BahnBaum
02-03-2006, 08:04 PM
I have that on my boat engines. Rather than a lever, it's actuated by a switch on the dash.

Alex

BmW745On19's
02-03-2006, 08:43 PM
Yeah I've heard of that. Sounds like a good idea for an every day car, maybe make the ebrake into a lever for the mod?

If you were to do this to a crusin car, M5, M3, M6, I'd just take the stock exaust totally off and put straight pipes in, that way it makes lots of noise, and you get a nice little hp increase.:thumbup:

Tangent
02-03-2006, 09:43 PM
You can find ones that use cable-operated bypass doors, ones that are electric servo operated, or ones that are just Ys that have a cap you can bolt in place.

Sublime Drive
02-04-2006, 12:01 AM
I guess this mod isn't too practical for new cars, but on say an old turbo charged volvo, it might be a way to add some fun to an old car. So do you guys have any idea how one would go about doing it?

hawk2100n
02-04-2006, 09:52 AM
Ever watch the Power Bolck on Spike TV, the show Trucks had a project 69 chevy pickup(Project Copperhead) that was restored, and then given a 720 horse 572ci Big Block, with 350 shot of nitrous. This truck had over 1000 WHP, and they added some electric servo exhaust cutouts. I think that if you were to do something like this on an old car, you would be better off just putting straight pipes on it, and save your self the hassle of rigging up something like this. This would make a turbo volvo sound really Cheap Ricer-ish, and you DON'T want to do that either.

Fast Bob
02-04-2006, 10:54 AM
I guess this mod isn't too practical for new cars, but on say an old turbo charged volvo, it might be a way to add some fun to an old car. So do you guys have any idea how one would go about doing it?
This would be *totally* ass-backward....it`s the exhaust`s backpressure that makes a turbo spin faster....

Regards,
Bob

Clarke
02-04-2006, 02:55 PM
This would be *totally* ass-backward....it`s the exhaust`s backpressure that makes a turbo spin faster....

Regards,
Bob I don't think so! try the speed of the exhaust gasses passing through in relation to the housing and impeller scroll shape. Simply think of a water wheel,faster water flow equals faster water wheel revs. The turbo does furnish backpressure though.

Penforhire
02-04-2006, 05:18 PM
I had QTEC electric-valved Flowmaster cut-outs on my C5 Z06. It was technically smog legal because it was after both sets of cats. Had to fabricate some heat shields to avoid melting the rear transverse spring. Sure wasn't noise-legal though. When they were open (switch wired into passenger compartment) it sounded a LOT like a NASCAR machine. Totally bad-@ss. Under high-load conditions cabin resonance felt like a massage-chair. I could scare the paint off cars next to me.

However, I put it on a dyno and got very little gain (max +3-ish Ft-Lb, not noticeable on that motor) and eventually the valves rattled when closed. So I eventually uninstalled the whole deal.

Anyway, cut-outs are alive and well on modern cars. Plenty of C5 owners put on long-tube headers too (getting rid of the cats). Too much hassle in smog-conscious CA.

Malibubimmer
02-04-2006, 05:29 PM
I guess this mod isn't too practical for new cars, but on say an old turbo charged volvo, it might be a way to add some fun to an old car. So do you guys have any idea how one would go about doing it?
Borland makes exhaust systems. Check with them.

Tangent
02-05-2006, 09:10 PM
This would be *totally* ass-backward....it`s the exhaust`s backpressure that makes a turbo spin faster....

Regards,
Bob

With lower backpressure it'll take slightly longer to spool, but once it does you'll get more power.

Penforhire
02-06-2006, 08:21 AM
But you would certainly not put a cut-out ahead of a turbo. If you did the turbo would never spin up. Sounds perfect to put it directly after (you want low backpressure just after the turbo's drive impeller). Just having the turbo would damp a lot of the typical cut-out noise.

SmoothCruise
02-06-2006, 02:55 PM
My friend was telling me about this mod that they used to do to cars. Basically, you get a lever that when you pull it opens up your exhaust so that it bypasses the cat and muffler. That way, the exhaust freely flows right out of your engine for more speed and noise. Pull the lever back up and the exhaust flows like normal. It seems like a fun little mod to do to your car, but I haven't heard of it being done before. I don't think it would cause any problems for the engine, do you guys think this is feasable?


You might want to do a cooler mod found on the Z06, where after a certain rpm/backpressure, butterfly valves in the exhaust are opened up completely to increase noise and decrease backpressure.

SmoothCruise
02-06-2006, 02:58 PM
Wouldn't be feasible because of the catalytic converters all modern cars have,
[/QUOTE

Wouldn't be feasible, how? I think you mean it wouldn't be legal.


[QUOTE=Malibubimmer]
But, reducing back pressure is often a way to increase horsepower in forced induction engines.

Only after the turbines had a chance to spin on a turbo. But, it's a way to increase HP for either force inducted or normally aspirated engines.


Another cool mod is to extrude hone your exhaust and intake manifolds, although, there's some debate as to whether it's effective or not. I'd do my intake manifolds and not the exhaust.

Penforhire
02-06-2006, 03:28 PM
Then there's mandrel bending of the tubing. No debate there as to whether it is worth it or not, if your original tubing is not mandrel-bent you've got some restrictions. Also cutting off bolt-on flanges and using slip fittings to reduce weight.

Pinecone
02-06-2006, 05:23 PM
Actually on modern cars, doing a cutout before the cats will through a Check Engine or Service Engine Soon light. And may trigger limp home mode.

There are two sets of oxygen sensors, one set before and one set after the cats. If they aren't reading appropriattely for the cats to be inlin enad working properly, you will throw serious fault codes. And until those codes clear, you will not pass an emissions check in many states. This assumign the car doesn't go in to limp mode and drive like a burnt out POS.

Penforhire
02-07-2006, 08:19 AM
It is sort of an "arms race." You can use O2 sensor simulators to get around that.

Pinecone
02-08-2006, 12:59 PM
Yeah, but would you want to run O2 simulators for a cutout? Which you will only use a few times then forget it? :)

Tangent
02-08-2006, 02:57 PM
Yeah, but would you want to run O2 simulators for a cutout? Which you will only use a few times then forget it? :)

Why not? The post-cat sensors are only there to throw a code when the cats go bad...