I'm sure everyone here who has modded their car's exhaust has noticed they've lost a little bit of low end power. Well I've done some research as to why that happens and think I have a decent understanding of how the system works.

I was thinking of a way to make the exhaust piping smaller for the low end and bigger for the high end so there would be a nice balance between low and high end power. What I've come up with is putting throttle bodies in the exhaust and having the butterfly's position vary in relation to rpms. An example would include, having the butterfly open 1/4 way in the low rpms, 1/2 in the mid range, and fully open in the top range rpms ofcourse a lot of testing would be done to find the sweet spot for respective rpms.

We have a guinnea pig car that we will be using and have already designed how the device would work and be operated so that is not the issue. Before we start with this project tho I just wanted opinions if the theory is sound and if it should work in principle. Just wanted to confirm that a somewhat closed butterfly should equate to smaller exhaust piping and thus restore low end power to a resonable extent.

Thanks in advance for any input on the idea guys.

 

in theory it could work, just seems like a lot of money to throw into a minimal gain. when you go to forced induction then back pressure is not as important. Yes still need some, just not as much. also you got to think that it is not just the sizing of the pipe that makes back pressure, but the type, amount, and angle of the bends.
although it might be worth while for people with ITB's and serious N/A cars.

 

LOL! Someone that has thought the same thing as I did. I did a ton of research on this same thing and found the solution to our problems.



You can find these things all over ebay for under 200 bones, and some have conrollers, some have *****, some have the tube assembly on them and some don't.. Get one that fits your idea the best and the real trick is going to be having the ECU control the butterfly!! There's also a few vids floating around out there on youtube I think that show these in action. Search ebay for "Exhaust Cutout"

I was thinking that you could rig up a potentiometer somehow to the gas pedal, so that the farther you pressed it, the more it would open the butterfly, but that wont be as good as having the ECU itself control it. But other than that, you basically still have your stock exhaust AND another pipe that dumps straight out of your side fender. (of course the 4 ft. flame that will come out at high rpms would be a bit... Dangerous? or cool. I can't remember which one it is right now)

 

Thats an interesting product for sure but I think its a little counterproductive actually to our problem. For stock exhaust I can see how that might be a good investment so you can free up the system in the higher revs.

For our purposes tho we already have a larger aftermarket exhaust and it flows well in the high revs. Its the lower revs that pose a problem since the piping is too large for the smaller gas flow so you would need something to restrict it rather than open it up further. My idea is like the product above but instead of a Y shape it would just be a single pipe that fits directly into the exhaust.

 

I thought the exact same thing about variable size exhaust for my ITB setup. That is when I started researching into how the Individual throttle body system works on bikes. I found that GSXR 1k's use an Exhaust control system or Exhaust Tuning valve. It's a titanium butterfly placed at the collector of the header and controlled by the ECU. It works in conjunction with the secondary butterflies in the throttle body to help keep the optimum air velocity going through the engine for all rpms.



Here are the headers that I am currently tinkering around with to create a system to work with my ITB's. You can see the throttle type sprocket and return spring on the side of the collector. That is how to control the butterfly inside.

<FONT COLOR="red">To answer your question: Yes your project will work and not just in theory.</FONT> It already works on bikes why not a car eh! It will have to be opened gradually for optimum effect and that will take some major tuning to get it to work properly as you mentioned above. That is where I am at in my project right now. Building a variable voltage controll unit for the rpm ranges.

Let us know how you make out with your project

Cheers and good luck


Modified by GhostAccord at 12:39 AM 7/29/2007

 

Wow I had no idea they already had this system on bikes. It seems you've already made a lot of progress on the idea, thanks for all the information. I hope you have sucess with your project and we can make something that works

 

yeah I figured it would work, but I still wounder if it will make that much of a difference in smoothing out the power band. once either of y'all figure it out please post pre and post dyno pulls.

 

bikes even have variable plenum/ intake runners that can change properties along with that exhaust valve to make sure they have enough torque on the bottom end of the power band to be street able, the optimized for 15K+ topend. Those bikes are very advanced, there ecu's are also pretty powerful.

 

http://www.automotiveforums.co...13199

This article is relevant to the topic at hand, and may clarify what you may be seeking, this also contains corrections to terms that really do not make much sense in a scientific manner, like "backpressure".

This is a very good article and may be a bit techy for some.

 

I would tune the system in on a dyno kinda like tuning a VTEC crossover point, like this:

Dyno graph full open, 3/4, 1/2, 1/4....then overlaying the graphs to find out what RPM the 1/2 open makes more power than the 1/4 open, etc. Should be rather easy to figure it out this way, and give you enough data to optimize the system. Might want to try 1/8 inervals or whatnot, but this is the basic idea

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by quicksilver &raquo;</TD></TR><TR><TD CLASS="quote">bikes even have variable plenum/ intake runners that can change properties.......... Those bikes are very advanced, there ecu's are also pretty powerful. </TD></TR></TABLE>

Yes sir, That's what I was talking about with the secondary throttle body butterflies. I also just picked up one of those powerful 32bit CDI ECM's. Hopefully I'll be able to wire it up to control my setup. The voltage references are going to be a pain to document. So far it seems that most of the Suzuki sensors run in the 0 - 4.5v, 5v range just like Honda's do............ fingers crossed.

 

Apexi makes one as well.

 

Wow the Apexi is $500 for a valve and a manual control. That is a waste of money in my eyes. You could take an electric cutoff, remove the three bolts and fit it in between two flanges. Voi la just like the Apexi @ half price.

 

Why not use a manual one; and use a throttle cable tapped in on the throttle body just how it works on an automatic transmision?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by cooper. &raquo;</TD></TR><TR><TD CLASS="quote">Why not use a manual one; and use a throttle cable tapped in on the throttle body just how it works on an automatic transmision? </TD></TR></TABLE>

That would work and it takes electrical failure out of the equation by making it fully mechanical. The cable would have to be adjustable just like the throttle cable is so you could fine tune it.

 

Have someone make a custom throttle body rotor where its adjustable.

 

none!!!

you dont want any at all .. the best would be a vaccuume on the exhaust side ... the problem you are having is due to the basic airflow law of faster moving air has less pressure (how an airplain flys).. if you have a small dia.pipe on your exhaust the air will travel faster out of it and have less pressure than if you had a big pipe with the same amount of air going through it with slower speeds and more pressure... think of it like a paper towel roll (small tube) with marbles in it , you can only add 10 per min. 9 black and 1 red one. you will get to a point where you can watch and find out how long it takes for a red one to come out the top. if you then switch over to a oatmeal box( the round ones with the quaker dude on them) and cut it to the same length as the towel roll.. now do the same 10 per min. with 9 black and 1 red keeping track of how long it takes for the red ones to pop out the other end .. you will notice that the red ones dont come out at the same rate and it is harder to push them through because you are lifting and moving a whole oatmeal box full of marbles( lets just say 500) instead of a tube of them(100?)..

but the exact opposite is true if you push 10 per min. and the tube is like a straw.. you will have a hard time pushing them ..

point is you have to size the pipe to the exhaust output of the motor ..

I am not even going to get into thermal expansion/contraction and ultrasonic waves that are also involved another huge part of exhaust systems

 

Your right back pressure is not wanted. I think the use of the word back pressure was used in error in this thread. It should have read "How to Manage Optimum Exhaust Flow or Consistant Exhaust Scavenging, The How To". The topic of this thread was all about how to keep the 9 black and 1 red marbles flowing at a consistant rate through all RPMs.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by xzodiackiller &raquo;</TD></TR><TR><TD CLASS="quote">point is you have to size the pipe to the exhaust output of the motor ..</TD></TR></TABLE>

What is the optimum size then? If you have to pick one size it will peak at a certain RPM/flow rate. Then at all the rest of the RPM ranges the flow will be like going through either a straw or an oatmeal box as you stated

This threads theaory for a naturaly asperated car is a varaible exhaust valve. for example...In a N/A ITB set up you will have at idle (750-850 RPM's) 10 marbles flowing through a toilet paper roll size pipe (= variable exhaust valve 1/4 open). Then when you give'er a bit of juice and your up to between 3500-5500 rpm flowing 1000 marbles, your going to need that oatmeal box sized exhaust (= variable exhaust valve 1/2 open). Then at full throttel your going to need a 3" sewer pipe flowing 2500 marbles (= variable exhaust valve fully open). Therefore one diameter pipe is not the optimum marble flow for a N/A vehicles exhaust system.

Cheers


Modified by GhostAccord at 2:02 PM 8/3/2007

 

yes this can be done using a cutout like shown above but the diff. in pipe size is not as great as you would think between the smallest you will need and the biggest.. so you have to make a compromise between a pipe sized for low rpm part throdle and high rpm wot ..
what size motor are you running ,what is the rpm range most used.. and what kind of gains do you expect.. on a bike 1or2 hp is huge . on a car you will not even notice

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by xzodiackillerx &raquo;</TD></TR><TR><TD CLASS="quote"> but the diff. in pipe size is not as great as you would think between the smallest you will need and the biggest.. so you have to make a compromise between a pipe sized for low rpm part throdle and high rpm wot ..</TD></TR></TABLE>

Why would you have to compromise? That is what we are talking about with using an ecu controlled variable exhasut valve. To give you that 20mm +/- in pipe size. If that's all we need to keep the tourque in the lower RPM that's what we're looking for. This variable intake and exhaust isn't new technology, Ferrari uses it in there F50.