Butterfly valve in exhaust for adjustable back pressure?

[inh]

I remember seeing a butterfly valve in my dad's exhaust one day on his 2003 or so Suzuki GSXR 1000, and while day-dreaming at work about things i want to do to my truck, i thought about putting one of those in.. Of course the one on the bike is computer controlled, and eventaully i could make one be computer controlled as well.. but for now, even a manual one would be fun to play with.. Just wondering what everyones input is.. And for those that don't know what i'm talking about:

"In essence, this new concept uses a butterfly valve (in the exhaust pipe) to change back pressure. This means that, depending on what gear you are in, how many RPMs your doing and even your throttle position, you will get more power where it often lacks - such as at low revs. Top-end and mid-range will also be bumped up slightly thanks to the butterfly valve." from http://www.webwombat.com.au/motoring/news_reports/mgsxr1000.htm

 

[jimbo74]

i could see use on a turbo engine or as a diesel uses a jake brake... but otehr than that....

 

[inh]

I was thinking of using it to allow the use of a high flow exhaust but still let you have nice amounts of low end torque

 

[jimbo74]

that idea is feasable, but in my opinion would be almost impossible for the regular consumer to use, you dont have the test capabilites or time really to do it, not to mention a controller for it...

 

[inh]

The controller could be made fairly easily, just needs to plug in to the OBDII port and get engine load/rpm/speed information. As for testing.. seat-of-the-pants calibration is good enough. If it makes a noticable difference its worth it.

 

[rookieshooter]

Try it and post results. With dyno reports before and after. If you can.

 

[Creager]

i could see it working... i just dont see how it would benifit you unless you have like ported heads and intake and whatnot. Or a heavy flow of an engine.

On a stock motor it would probably just make things weaker. Its when you have everything really opened up that you would need this.

I bet having :COUGH: your cats removed :COUGH: on an 4.0 OHV motor this would benefit... in getting your low end back.

worth a try...

 

[BeauJ]

There used to be a company named "WEEDS exhaust" that made what you are talking about in a kit. I saw a truck they did in an OLD issue of Truckin'. I looked for info on them a while back but I'm guessing they went out of business.

 

[Doug]

There are alot easier ways to regain low end torque, A properly ground cam would probably be your best bet. It seems like a lot of complication for a pretty simple solution. Besides if you do you mods right you shouldn't really have to worry about losing that much low end torque. Removing your cats wouldn't be the answer. First your vehicle is designed to run with them in place. I've heard people say they're fairly high flow so, restriction isn't much of an issue. Though thats all dubious with out fact to back it up. Also removing the cats and having little back pressure is what actually reduces low end torque. The only thing I've ever seen flapper valves in an exhaust is for faster warm up.

 

[danquin]

Looking at the camshaft is a good idea, but we are taking it in the wrong direction. The reason Yamaha started this back in 1989 was in order to use camshafts with extreme overlap on a motor that would have good low end power as well. The valve starts out more closed in the lower RPM/throttle settings, and progressively opens to full exhaust when the velocities have reached a point where the impulses will not re-enter the combustion chamber (which is very ineffecient for several reasons).

So now, take a look at this from another angle. If you could put a cam in there for killer top end, and still maintain enough midrange and low end torque to do what you want, would it be a worthwhile modification?

Yamaha has been doing it since 1989 on their 1000 cc motorcycles, and most of the manufacturers (japanese motorcycles have followed suit). And there are a couple of car folks worldwide that are expirimenting with it.

I'd study the Yamaha EXUP principles to get an idea where to start.

Hope this helps.

 

[inh]

danquin that is exactly what i am talking about and is the same principle that first got me interested in it based on what i saw on my dads gsxr. And for all those wondering, my cats will be staying. i live in california after all..

 

[rookieshooter]

If you want low end torque you need a cam that has that profile. I don't know about a bike that is probably a 2 stroke. But a 4 stroke motor will never need an extreme overlap cam for low end torque this is counter productive. That really neat sound of a muscle car with a extreme overlap cam is what gives it that distictive lope sound. That's when both the ex. and in. are off the their seats. Which is fine for the mid to upper range, catering more to the upper. This can really be seen when you put a degree wheel on the motor and some dial inticators on the lifters. With extreme overlap an engine wants to stumble at low rpm's which does not do a thing for the low end. At high rpm end it works like this. On the exhaust stroke the piston is coming up with the ex. valve open and you have this volume of air going out the exhaust tube at a high rate of speed. Now here is where the split overlap comes into play; just before the piston reaches TDC the intake starts to open and now there is a slight neg pressure in the chamber due to the momentum of the ex. gasses leaving the chamber. So now with the in. open, air rushes in befor the piston even starts to go down on the intake. Remember that the piston is connected to the rotating crank so the piston kinds of hangs there for a while allowing the air to come in. This is great for high end where the dynamics of the fast moving ex. gases comes into play.

 

[danquin]

All of the bikes mentioned are 4 strokes.

The purpose of the valve is to return low end torque that is lost from using a high rpm type camshaft (large overlap). Doing so makes it possible to have the high end performance of a large overlap camshaft, and still have the performance of what was traditionally thought of as a low end torque cam (which conversely do not make big horsepower at higher rpms).

Somehow I don't think the point is getting across... have to check and see if I have some dyno runs that make it more sensible.

Bottom line: for what they are designed for, they work well. If your sole concern is low end torque, then cam for it. If you want high end horsepower, and still want to maintain good low end torque... expiriment away. It has been done, and can be repeated.

 

[rookieshooter]

Thanks for explaining, makes sense now.

 

[inh]

Hmm i'll have to see if i can find a good overlap cam for my truck.. 96 OHV 4.0L... I'm open to suggestions

 

[danquin]

Thanks for explaining, makes sense now.

Cool! If you got it off my lame a## explaination, you understand motors. It took an engineer 2 hours, a whole bunch of paper, and a cutout mockup to get me to start to understand.... and I still don't completely get it. But I know it has to do with exhaust impulses trying to re-enter the combustion chamber at lower velocities (that part I remember because even after the motorcycles went by... he kept shouting it).

Yamaha has paired it with their five valve per cylinder head, for a pretty nice combo. I've got two of them... a 1991 (no longer has valve in place) and a 2004 with EXUP in place still.

http://members.tccoa.com/fzrdan/twoyamahas.jpg

Not enough time... and not enough toys

 

[rookieshooter]

It was my lame a## brain that did not comprhend. Now I see how you can get the best of both worlds, kinda like having your cake and eat it too. Yes it would have to do with the pressure pulses during the split overlap of the valves during the low end rpm's it would counter act the split over lap.

 

[danquin]

It was my lame a## brain that did not comprhend. Now I see how you can get the best of both worlds, kinda like having your cake and eat it too. Yes it would have to do with the pressure pulses during the split overlap of the valves during the low end rpm's it would counter act the split over lap.

Now see... you understand it better than me 'cause you are speaking like the engineer who tried to explain it to me

It really does work, but there seems to be a close balance or range that it works within. When I stepped up to race cams in my 1991 FZR, I couldn't get it to work well on top with the valve in place. But when I removed the valve and went 4-2-1 on the exhaust, I regained some of the midrange, and a WHOLE BUNCH of top end.

It's really amazing what you can learn from motorcycles. I mean... 170 crankshaft HP out of 1 liter? Good lord.... bring that logic to our motors and we could see 850 crank HP and 425 TQ out of a 5.0!

If only we could learn the fluid dynamics behind all of it.