I got a pretty good idea. To be honest, I don't think it's really worth figuring out and bolting to a car, unless for fun to fill spare time. But this does seem like a good concept.

Basically, since smaller exhaust piping at higher rpm causes a lot of back pressure lowering the engines high end torque keeping the engine's low-end torque at an optimal level. So enlarging that exhaust pipe will cause the engine to produce greater high end torque at the cost of low end torque. All this is explained in another post on the board. Now for the idea:

So if one could install dual exhaust pipes on the car at stock or slightly smaller and make it strait through from the cat to the end of the left pipe at lower rpms, and when the engine reaches a certain rpm, trip a switch causing the second pipe on the right to open up giving the exhaust more air flow when it needs it. The only theoretical bottlenecks would be the smallest part before the gate to the second exhaust pipe, and the gate itself causing turbulence in the air as it exits the first pipe at lower rpm speeds. And of course the car's exhaust would probably sound like crap when you're just revving the engine.

Well, I think I got the idea across well. Again I don't know if it would even be worth a try, since the benefits of this kind of setup wouldn't give much. But it's always fun to think up things like that. You know this idea kind of sounds like the concept behind the whole V-tech thing. Change timming at different rpms and change ehxaust volume capacity at different rpms. Lol, maybe I should email this idea to Honda and watch it come out of their latest rice platform. But that would be a waste of time, more so than trying to adapt this idea to my car. I'm going to sleep now. Night all.

OMG!! someone that actually understands backpressure... I like you..
Seriously though I know exactally what your talking about. The real way you would wan't to do it is the same way Suzuki GSX-R 1000 crotch rockets are set up from the factory now. They actually have a computer controlled butterfly valve in the exaust (like in your throttlebody) that opens and closes to change backpressure for optimal performance at any givin rpm and load. Apperently it works great, but you can't put an aftermarget exaust on and still have it work. Another idea would be for someone to design an aftermarket Vtech type head for our cars, wich would give you the biggests gains your looking for (or at least dreaming about).

HKS made an aftermarket Vtec set up for the R-34 skyline. It was obscenely expensive and the only real advantage was a fatter low and mid power band. So that big turbo you slap on works over a larger RPM then simply peaking right at redline. Saw it on Best Motoring.

PSN ID: Phatchance249

Which car was it that utilized a variable exhaust on it again?
I have heard that the problem they had was the debree coming out of the exhaust would clog the mechanism and it needed constant adjustment and cleaning and was abandoned.

Don't know enough about this but what I figure is we have no problem with low end torque. My torque is what gives me an edge on racing cars with more HP, but up high I've lost to some V-TECS. I figure get a single cat back with a 2.5 inch exhaust. I've had the 2.25 and the more bolt ons I added, the more I felt I needed a bigger diameter exhaust, but not great up top. 5850 RPMS on my ECO isn't enough to give me the necessary pulling power against 8000 RPM SI's. I have a friend with a 2000 CIVIC SI with all the bolt ons I have, and I still have the edge, specially down low. He would pull on me a little at higher RPMS, but again my low end torque once shifted would get up. 2000 CIVIC SI stock has 160 HP, 111 lb torque. My ECO has 140 HP, and 150 torque as you all know. I bought the 4-2-1 header specifically to get low to mid range torque. Wasn't until I added a bigger TB, CAI and crank pulley that I felt more power after 4500-5000 RPM, but didn't give me more top end that I wanted. I figure changing my retainers to Titanium once I put cams on, would allow for slightly higher RPMS and with a bigger exhaust give me top end and have no back pressure.
Sorry if off the topic but can someone substantiate this? Thanks


"FRIENDS DON'T LET FRIENDS DRIVE STOCK"

The C6 corvettes have butterflies in the exhaust that are rpm controlled.

You could use a larger diameter exhaust pipe like a 3" back to two 2 1/4" pipes, where one side (or both) would have the rpm controlled valve/butterfly. And I'm only going to say it once:

It is not BACKPRESSURE that is giving you the extra low end. It's EXHAUST VELOCITY.


-

"Youth in Asia"...I don't see anything wrong with that.

mitsubushi and mazada both used a muffler by pass back in the 90's


and it is where muffler bearing are used , so its not just a farce any more

I had this idea a long time ago - but I thought it was too complex to implement practically - and of course the trouble of getting valves(I'd want one right on each header primary) to open and close quickly - based off of the RPM. It would have to stand high heat as well as the problem of it probably gunking up with carbon in no time until it no longer operates.

I decided a simple electronically actuated exhaust dump right on the downpipe was a simpler, more reliable bet - yet still pretty effective.

Now with a turbocharged engine - the exhaust size question/problem is out. Since most of the time you're flowing a ton, You want a bigger pipe and that's all there is to it. And an exhaust dump is definitely a good option here.

...I just did have an idea relative to yours - for those with automatics that is. If you installed another petal(where the clutch petal is on a manual) - you could actually rig that petal to open this valve(or valves) when you press on it. You'd pretty much just need a spring and a cable(not unlike your throttle or hood-latch cable) to connect between the valve and this extra petal. Of course you would need a tachometer installed as well - to see your RPMs to - do this effectively. Then you'd just need to practice getting it right during a 1/4 mile run/race.

But... I'm not so sure that you'd get enough gains off of this to justify the cost and time it would take to implement.



I've never heard of this "part throttle" before. Does it just bolt on?

Good concept, but looking at the big picture it wouldn't really be worth it. The RPM at which the smaller diameter pipe would be beneficial are RPMs that you engine will never see during a race.


'96 GSX
towed more often than driven

its an interesting idea, but it sounds like an aweful lot of work for the gains.

good call on the exhaust velocity comment brian. as i understand it though, after the collecter, the less restriction the better. i seem to recall SCC bolting a three inch dump pipe into the header of the their project civic and seeing gains across the board. i will be testing "bigger is better vs. exhaust velocity" on my head swap project this summer...



ZZZZZZZ

only one problem weight vs. gains for what you would achive it would be over shadowed by the extra weight



"boobs now with Riboflabin"

Yea, it's nothing more than an interesting idea. Like I said, those who have applied it were probably bored and just wanted to add more moving parts to their cars so that they can brag or something.But if you really think about it, there really is nothing special that is thought of to do for exhaust. Bolt on a hi-flow cat, bigger down pipe, bigger pipping fom the cat, hi-flow muffler, and replace your exhaust mani for your desired power band. Compared to intake, there's nothing too special other than freeing up back pressure though hi-flow/volume parts.Hell, What would be cool is if you can run dual S/C's given the room, run a roots for your intake and a centrifugal (spelling?) for your exhaust... Yes I said exhaust. hook it up like you would your intake S/C but instead reverse the flow so it's sucking exhaust out of the engine. And then of corse change the gearing in it so it's not sucking as hard as would an intake S/C. This way you're not robbing power from your engine at the pully to drive the exhaust S/C.

In theory, that should also work somewhat well, but again, do the gains make it all that practical?

Its NEVER been about backpressure, its about thermal velocity, the faster you get the gasses away from the engine the less it has to work, any backpressure will inhibit the movement of the engine.

This is why different exhaust pipe sizes have different effects on engines of the same displacement. With the stock eco exhaust, you have a hinderance to exhaust flow and a lot of backpressure which is BAD, when you open up the exhaust you lessen this and allow higher flow which is good, but if you go to large the gasses cool to much before they leave the exhaust, slow down and call resistance. This is more prevelant in an NA or supercharged exhuast than a TURBO charger setup.

A better Idea to try and achieve what you want Apex Active Silencer. Apex also sells exhausts that change in size from the front to the rear(tho not for our cars). Also something to consider. I was looking at the active tail silencer for my car because when I'm not autocrossing the exhaust can get really droning during long hills. I really don't think the cost of the system your thinking abou would be worth the gains especially if you total in R&D time and materials. We're talking about very little horsepower gain. On a vehicle with a larger rpm band like the GXR or an Rx-8 you would see more of a difference.

FWIW Apex also sells a butterfly valive that you can put inline with your exhaust, you could hook it up to a controller that would open and close it in realation to your RPM's, something which you can teach HPtuners to do on the output I believe, then its just a matter of making the controller open and close dependant on the level of signal it received.

02ECOTECIMPORTKILLER: Looks like your in the same boat as me as far as mods go. Time for you to get HP tuners and start tuning for hi-test gas.


-Chris

you guys and your hairbrained ideas...

here's my idea: modify your car to make it faster. port the head, change the cams, put on a real exhaust system, TUNE the air fuel...
not dual stage exhausts and fans on the intake (another post in this forum)

Quote:

02ECOTECIMPORTKILLER
Friday, May 25, 2007 12:08 AM

Don't know enough about this but what I figure is we have no problem with low end torque. My torque is what gives me an edge on racing cars with more HP, but up high I've lost to some V-TECS. I figure get a single cat back with a 2.5 inch exhaust. I've had the 2.25 and the more bolt ons I added, the more I felt I needed a bigger diameter exhaust, but not great up top. 5850 RPMS on my ECO isn't enough to give me the necessary pulling power against 8000 RPM SI's. I have a friend with a 2000 CIVIC SI with all the bolt ons I have, and I still have the edge, specially down low. He would pull on me a little at higher RPMS, but again my low end torque once shifted would get up. 2000 CIVIC SI stock has 160 HP, 111 lb torque. My ECO has 140 HP, and 150 torque as you all know. I bought the 4-2-1 header specifically to get low to mid range torque. Wasn't until I added a bigger TB, CAI and crank pulley that I felt more power after 4500-5000 RPM, but didn't give me more top end that I wanted. I figure changing my retainers to Titanium once I put cams on, would allow for slightly higher RPMS and with a bigger exhaust give me top end and have no back pressure.
Sorry if off the topic but can someone substantiate this? Thanks

why are you stopping at 5850rpm? redline is 6500. use it

you guys crack me up with this "low end torque". Low end is 3000 and below. how often are you guys at 3000rpm unless your cruising in 5th gear at 80mph?

I don't even launch at 3000rpm. Making power there is completely and utterly useless.. unless of course you enjoy punching the gas in the wrong gear. try downshifting.

midrange and top end is where its at. low end torque is good for pulling tree stumps, not for winning races. Unless you race to 20mph <shrugs>

to the OP, there's a reason modified cars don't have this junk on them.. it doesn't work, and if it does it isn't enough to justify the overcomplication of what is normally a simple system. All you have on your car is an intake. before going off the deep end with more rediculous ideas about how to make your car faster, try modifying it first.

and to finish up about the exhaust... I was told by many 'experts' that 3" is too big for all motor...


you'd be surprised how quick posting up my time slips and videos shut people up.