Ogolden1

Ok, I went to the muffler shop to get the raspy exhaust note problem solved. They recommended a Magnaflow resonator. So, it solved the rasp, but it now sounds as quite as stock , AND I've noticed a slight lose of low-mid range torque. It used the "light" the tires from the start, and do a 4 ft "scratch" when it shifted to 2nd (floored on asphalt).
But now, I bearly get a "bark" hitting 2nd!
Shit, I need some advice!!!
I did some research on performance exhausts, and it said that a car with 250 to 300 HP should have a 3" exhaust!...Our's is ONLY 2 inches from the cat to the axles. Then it even gets SMALLER at the "Y"!
I was wondering if I had 2 1/2" or 3" put on from the cat to the axle, if (1) it would eliminate the rasp and give me a more "sports car" sounding exhaust note! And (2) if I HAVE TO use a resonator - should I go back to the stock one, as it is only an 8" passage thru (as opposed to the 2 ft of the Magnaflow)

My goal is:
Maximum Flow
Maximum low-mid torque
Sporty note, but do too loud!

I know one of you guys used to build exhaust systems - YOUR INPUT IS GREATLY APPRECIATED!



[ 07-03-2001: Message edited by: Ogolden1 ]

mr tl

i think you should put the pre muffler back in, take out that resonator the shop put in and work from there

Ogolden1

The "pre-muffler" is actually the stock "resonator" -
And it's still going to sound "stock"! Plus, I think I should go to 2 1/2" or 3" tubing from the cat back to the axle... and maybe even to the dual mufflers!

I'd like to run without a resonator IF POSSIBLE, because it had MUCH MORE low-to-mid torque without it!

dlew308

Are you hooked on magnaflow? Why not go HKS or something else? I had the magnaflow on my previous car, it didn't stay on for long.
You may want to rethink 2.5-3" piping on a non-turbo'd car...

spiroh

I wouldnt do it. Put the stock res back on, and get the comptech exhaust. All I did was put a high flow cat, and I lost A LOT of low end torque.

Spiro

Ogolden1

... Well, I'm going to have to replace about half the "cat back" tubing, as that was the only place the put the Magnaflow resonator!
So, why not replace it with 2 1/2"???

I read a thread last week that Comptech said (at the openhouse) the 2" tube was junk for performance(?)

langjae

Are you sure increasing pipe diameter would help?? You can go to a custom piping place. Is Mugen Cat-back? I remember I had custom piping on my 3000gt and increased pipe diameter and lost a lot of low-end torque. Not sure if this is the solution...

jeremy

Ogolden1

I just researched some of the "cat-backs" for the Accord V-6, and the tube diameters are either 2 1/4", 2 1/2", or you can request 3" as an option!

C'mon ...I need more feed back from someone with knowledge in this field!!!!

HELP!!!

Ogolden1

No, I'm not hooked!
This is a hi-flow straight-thru polished SS racing type resonator (check their website)- same high quality as HKS! They had some stocked there on the shelf - that's why he used it!

BTW: Why should I rethink the 2 1/2" or 3" tubing ???

[ 07-03-2001: Message edited by: Ogolden1 ]

Jake

Ogolden1,

Have you thought about taking your seat of the pants impressions out of the equation and do some dyno runs. Often in cars (and in audio) I have noticed that I notice changes when I see the change made even though in a blind test I can tell no difference at all.

It may be possible that you are experiencing the same thing. You belive that the removing the resonator gives more torque and of course it does. If I were you, I would take the car to a dyno and do a back to back. Or just buy a good pre-designed cat back system that has dyno-proven results.

Just a tought.

Ogolden1

Jake - Great advise, but a major hassle!

Actually, the fact that it would "light up" the tires for about 12-15 ft off the line, (VSA off w/ AAA traction rated "gummy bears") and do a 4 ft "scratch" when it hit second BEFORE, and now it's half that at the start, and only "barks" into second, is ALL THE DYNO I NEED!!!
That car WAS running the FASTEST it ever HAS! ...Trust me! (I have a racing background!)

FDao

Ogolden1,

My knowledge of exhaust piping applies to my days of 4 cylinder tuning, but in general, on a NA application, going to a wider diameter piping will increase gas velocity flow, thus decreasing back pressure and improving HP at the cost of low end torque. Going too wide will hurt both HP and torque due to decreasing flow velocity. In our case, I believe to achieve both reasonable top end and good low-mid range torque, we may have to go with a 2.25" piping rather than 2.5 or 3". Your research in piping is quite interesting in that you said for 250-300 HP we should use 3" piping. Is this for Forced Induction car? When I was experimenting with piping diameter, I found that, on a 4 cylinder engine, the best compromise for the street was a 2.25" piping. 2.5" produced better top end, but poor low-mid range torque. 3" was even worse to the point of minimal top end gain with significant low end loss...except on forced induction car.

Your thoughts.

[ 07-03-2001: Message edited by: FDao ]

Ogolden1

Check this out: scroll down to "Pipe Sizing"


Exhaust Theory

Pipe Sizing
We've seen quiet a few "experienced" racers tell people that a bigger exhaust is a better exhaust. Hahaha… NOT.

As discussed earlier, exhaust gas is hot. And we'd like to keep it hot throughout the exhaust system. Why? The answer is simple. Cold air is dense air, and dense air is heavy air. We don't want our engine to be pushing a heavy mass of exhaust gas out of the tailpipe. An extremely large exhaust pipe will cause a slow exhaust flow, which will in turn give the gas plenty of time to cool off en route. Overlarge piping will also allow our exhaust pulses to achieve a higher level of entropy, which will take all of our header tuning and throw it out the window, as pulses will not have the same tendency to line up as they would in a smaller pipe. Coating the entire exhaust system with an insulative material, such as header wrap or a ceramic thermal barrier coating reduces this effect somewhat, but unless you have lots of cash burning a hole in your pocket, is probably not worth the expense on a street driven car.

Unfortunately, we know of no accurate way to calculate optimal exhaust pipe diameter. This is mainly due to the random nature of an exhaust system -- things like bends or kinks in the piping, temperature fluctuations, differences in muffler design, and the lot, make selecting a pipe diameter little more than a guessing game. For engines making 250 to 350 horsepower, the generally accepted pipe diameter is 3 to 3 ½ inches. Over that amount, you'd be best off going to 4 inches. If you have an engine making over 400 to 500 horsepower, you'd better be happy capping off the fun with a 4 inch exhaust. Ah, the drawbacks of horsepower. The best alternative here would probably be to just run open
exhaust!

Other Rules
A lot of the time, you'll hear someone talking about how much hotter the exhaust system on a turbo car gets than a naturally aspirated car. Well, if you are catching my drift so far, you'll know that this is a bunch of BS. The temperature of exhaust gas is controlled by air/fuel mixture, spark, and cam timing. Not the turbo hanging off the exhaust manifold.

When designing an exhaust system, turbocharged engines follow the same rules as naturally aspirated engines. About the only difference is that the turbo engine will require quite a bit less silencing.

Another thing to keep in mind is that, even though it would be really super cool to get a 4 inch, mandrel bent exhaust system installed under your car, keep in mind that all of that beautiful art work won't do you a bit of good if the piping is so big that it gets punctured as you drag it over a speed bump! A good example of this is the 3 inch, cat back system sold by Thermal Research and Development for the Talon/Laser/Eclipse cars. The piping is too big to follow the stock routing exactly, and instead of going up over the rear suspension control arms, it hangs down below the mechanicals, right there in reach of large rocks! So when designing your Ultimate Exhaust System, do be careful!

Also, check this out:
Exhaust Tube Sizes

[ 07-03-2001: Message edited by: Ogolden1 ]

Ogolden1

I just came up with an idea! ...

How about if I have them make a "Helmholtz resonator" to replace the Magnaflow resonator!

We could use a 3 1/2" or 4" diameter tube, reduced down at the ends, so they can slip right over the 2" standard tubing that's already there, creating a "Helmholtz resonator"! ...I think that I'd still have my pre-resonator performance, with the throaty sound, and keep the low-end torque! ...Maybe it will solve my problem! ...What do you think?

Resonators
On your typical cat-back exhaust system, you'll see a couple of bulges in the piping that are apparently mini-mufflers out to help the big muffler that hangs out back. These are called Helmholtz Resonators and are very similar to glasspacks. The main difference is that firstly, there is no sound-absorbing fiberglass or steel wool in a Resonator. And secondly, their main method of silencing is the reflective principle, not absorption. An easy way to tell the difference between a glasspack and a true Helmholtz Resonator is to "ping" one with your finger. A glasspack will make a dull thud, and a true Resonator will make a clear "ping!" sound.



check out this Helmholtz resonator on the middle straight pipe

[ 07-03-2001: Message edited by: Ogolden1 ]

FDao

Ogolden1,

Interesting thoughts on the Helmholtz resonators. I actually had this done on my Lude Si and the sound was quite nice. No raspy noise.

I did take a look at your Piping articles. I am wondering if these are HP to the wheels and not the crank. Even if it's to the crank, it did not mentioned to me if it'll provide broad torque or just peak HP.

Your idea of a 3.5-4" resonator reducing down to the stock 2" piping is a possibility in providing a nice sound with some low-mid range torque due to back pressure; however, HP may not improve much. Also, the thought of 2" piping expanding into a 4" resonator may slow down gas velocity significantly as to cause turbulence and cooling down of the gas, thus less eficient in evacuation and perhaps causing your engine to not perform at its peak. Perhaps you can try a 2.5-3" resonator tapering down to the 2" piping.

Your thoughts.

BNut

CompTech stated that their research showed MINIMAL gains from a cat-back exhaust and that the additional cost would not be justified. I can promise you that Mike B has said those exact same words over a dozen times in response to why comptech only has an axle-back exhaust.

Larger piping should only increase your high RPM power at the expense of low end power in a NA car. This is almost as widely accepted as gravity.

blazerbob1

Non N/A cars need smaller diameter piping for low-mid power. For F/I you increase pipe size for power. These facts are well documented with dynos to back it up. So if you want low-mid power change back to what you had. If you want top end power go to larger diameter piping. Good luck with your decision.

EricL

When I got rid of the rasp on my Bimmer, I did construct a Helmholtz resonator -- (just a 2" pipe that I drilled a ton of holes in and put a 3.5"-4" can over it (I fabricated the parts and welded them). It was about 1 foot long. It wasn't even packed. It killed the rasp, and there was no detectable power loss.

However, I was putting the "can" on the end of the pipe, and you're putting the "can" on the mid-section of the pipe.

If the "resonator" that the muffler guys put on is not "free-flowing" then there is no reason that you could not get that.

It is wonderful to experiment with stuff... However, I never did find an "exact" solution to "exhausts". I had 3 different headers on the car and about 10 different exhaust systems that came and went.. Finally, through a number of “trials” I arrived at something with excellent sound, good performance, and good reliability (It sure took me a while&#8230

EricL

More info for your exhaust studies...
http://home.att.net/~t.vago/faq-exhaust.html


Excpert on the resonator vs. glass pack vs. straight pipe:


What does the resonator do?


A resonator is the component in the exhaust system that muffles out the high-pitched components of exhaust noise, such as valve noise. It does this by using reflection to allow those high-pitched components to "resonate" away. The factory resonator does a good job at reducing this noise, but since it uses a small core, it also presents a restriction.

An alternative to the stock resonator is to place a glass-pack muffler (such as the example shown above) in place of the stock resonator. The glass-pack muffler uses a more conventional absorbtion technique to get rid of the noise. Another alternative to using the resonator is to place a straight run of exhaust pipe in place of the resonator. Both alternatives will give a noticable performance increase over stock. Of note is the fact that, while performance may be marginally better with the straight pipe over using a glass-pack, the resultant exhaust noise will be much louder with the pipe.



[ 07-03-2001: Message edited by: EricL ]