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exhaust flow questions

exhaust flow questions

exhaust flow questions

Hello all,
  I'm building a project car for track / street use. It's an all motor aplication that has a high flow cat. I'm 41 so having a car thats loud doesn't appeal to me very much. BUT, at the same time I want performance. My ecu is tuned with Hondata so changing the exhaust when I go the roadcourse isn't an option. I need to find an exhuast that will give me the best of both worlds.
  I have been playing with the idea of putting a factory.....restrictive muffler on it and then adding yet another one to relieve back pressure from the factory exhaust and reduce the amount of exhaust note of having one none restrictive exhaust. Is it worth the added cost to add another muffler to it and will it yeild the result I want?

Thanks in advance,
Barney Demonbreun

RE: exhaust flow questions

If I understand you correctly, you want to have two mufflers installed in parallel? If so, the sound coming from the low restriction muffler will not be reduced significantly when compared to a single low restriction muffler only. If you want reasonable flow without the "boy racer" sound, get a lower restriction muffler like those used on muscle cars and hot rods. You could even go with the adjustable types with the removable discs (I forget the brand right now).


RE: exhaust flow questions

Well actually I was thinking of branching off of the exhaust main pipe at the back and having sort of a fake dual exhaust so the two restrictive exhaust could share the flow. Theoretically (in my mind) that would reduce the backpressure on the motor. Am I thinking correctly?  

RE: exhaust flow questions

Welcome to the forum, Barney.  You will find a wide variety of opinion on this subject.  For me (I'm 70 and a vintage racer), I like LOUD...but then I only do it on the track.
For a street/track car, the options are endless.  A nice high flow cat and something like a Flowmaster Hushpower II could be a winner.  Won't hurt hp too much and a moderate loss in midrange tq for most engines up to ~300hp for a single exhaust.  You could use a Supertrap (the disc thingy that ISZ refers to)but it's a real PITA for most street applications.  It IS, however, easily "tunable" by adding discs for track and removing them for street which makes them a good choice.  

I've used both for track applications over the years (SCCA mandates sound limits) in racing, but with the exception of Laguna Seca, no tracks in Socal require noise attenuation in vintage race cars.---Lucky me! smile


RE: exhaust flow questions

Sounds great! The only problem is that my car is an Acura integra. Its only running about 210 HP. But tuning the exhaust will change the air/fuel of my motor due to the fact my computer is tuned to a particular exhaust. So ill need to figure out a good exhaust for 85% street driving and 15% track driving without changing anything between track events.

RE: exhaust flow questions

You have me there.  Last course I took was in the early 80's for the EEC IV.  Even then I was able to keep mixture control up to par with a very much modded '83 T-Coupe (294hp @ ATRW).
Soooo.  Would I be really off base to assume that modern ECU could accept a wide range of mods (within reason)?

That's one reason I love my "vintage racing" Mini Cooper--- MSD/plug wires (no COP's)/Weber carb/open exhaust/etc.  "No worries, mate"!


RE: exhaust flow questions

Not at all off base.  But a tuned Ecu is much less able to adapt to change than a factory ecu. This is why I'm cautious to get an exhaust that will be suitable for track and street without leaning or richening my fuel mixture.
  I carry my kids around in this car and the exhaust is loud enough that we can't hardly carry on a conversation. Not to mention.....on getting old enough to not want my car so loud just cruising around town.

RE: exhaust flow questions

In the early 80's when my two youngest were teens, I rather preferred  the loud exhaust to their "noise"...LOL!

Be that as it may...When you try to combine street and track capabilities in ONE automobile...You most often get the best street characteristics (unwanted?) in your track setup...and...the very worst characteristics of the track version in your street car.

Perhaps I'm a little older, but I would not take a race car to the store....so you should think hard on the concept of using your "grocery getter" on the track.


RE: exhaust flow questions

I've been taking my track car to the grocery for 10 years. The set up I use is very easy to convert from street to track minus the exhaust. I'm just trying to find a cure for backpressure and decibels. The rest of the car is fine.

RE: exhaust flow questions

Still....May I convey an experience of mine, an effort at putting a much modified "street Mini Cooper" on the track?

Just food for thought.  Most forum members have already seen this so it's probably going to bore them to death...sorry for that.  None the less, what happened to my pretty little black '63 Mini could happen to you.  I knew better and that makes it even worse!!!



RE: exhaust flow questions

bore us to death?  nah... it still gets my pulse up to watch it. even brings back a few split-second images in my own memory.

RE: exhaust flow questions

If you had two entirely separate but parallel exhaust systems then the noise "in" each one would be half of the original, but at the tailpipes you'd have two sources of half the intensity. So the net noise would be the same.

The good news is that the back pressure would probably be reduced, theoretically to as little as 1/4 of the original back pressure.

So, you are on the right track, but the practical complexities are enormous.


Greg Locock

New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies  http://eng-tips.com/market.cfm?

RE: exhaust flow questions

Have you measured the pressure at one of the OS sensor bungs ahead of the cat, at full throttle and peak revs?

RE: exhaust flow questions

Here is a neat little change of pace.......Just saw it in the Sept. Hemmings.




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