Exhaust...

[dtruax]

So ive been looking to uprgrade my exhaust for awhile now, and right now im looking at these options:

-cherry bomb vortex
-flowmaster super 40 (or50)

im want a agressive sound, but not too loud, and i do NOT want it to sound rice at all, i cant stand that! any suggestions or personal opinions??
thanks in advance

[etlsport]

So ive been looking to uprgrade my exhaust for awhile now, and right now im looking at these options:

-cherry bomb vortex
-flowmaster super 40 (or50)

im want a agressive sound, but not too loud, and i do NOT want it to sound rice at all, i cant stand that! any suggestions or personal opinions??
thanks in advance

ive heard multiple people say that their flowmaster 40 series actually decreased their torque

[tomdietrying]

"ive heard multiple people say that their flowmaster 40 series actually decreased their torque"

I don't know about what etlsport is talking about, but I really like my Flowmaster.

Peace.
Tom
012009

[twistedsymphony]

searching through the threads here I've heard a number of people mention that by going to a more free flowing exhaust they saw a drop in MPG and a slight drop in performance as well.

I don't know that anyone has ever actually dynoed an exhaust setup and compared it to stock, short of maybe a couple people with superchargers, but they have completely different exhaust requirements anyway.

[VehiGAZ]

I replaced my OEM muffler with a Super-50 Flowmaster and 2.5" piping from the cats back. This was done after I supercharged.

I will swear up and down that my off-the-line performance improved noticeably with the new exhaust setup. The dyno graphs listed with the supercharger kit that Tone used to have on his site confirmed the performance enhancement of a 2.5" exhaust setup (PowerVault in that case) with a supercharger.

Since the supercharger does not affect low-rpm off-the-line performance at all, I would imagine that this upgrade would benefit a non-S/C'd VX just as well.

That said, it is brutally loud inside and out with the Flowmaster. It has a great gurgle at idle, but the rest of the time it's obnoxious - the stereo doesn't go loud enough to drown it out. I am waiting to hear if the Cherry Bomb muffler someone was going to try out was any better.

[twistedsymphony]

Basic Exhaust Design 101...

With a turbo charger 99% of the time a less restrictive exhaust = better
a turbos performance improves, the larger the pressure differences the better the turbo works... removing your ehaust completely after the turbo would give you the largest gains (though obviously it's a bad thing to dump all that hot air in the engine bay, and listen to all that noise)

With a Normally Aspirated vehicle this is not the case... there is actually an optimal diameter for the exhaust. Obviously if you restrict the exhaust too much it will cause pressure working against the motor. However since the motor works in "pulses" the dead air between those pulses can also work against you.

Tuning the diameter of the exhaust to tune the dead space between the pulses, while at the same time not restricting the flow will actually create momentum in the exhaust system... this creates a slight vacuum which has the effect of pulling the exhaust fumes along. This is call the "scavenging effect"

Obviously a certain size is only good for a certain RPM range, since when you change the RPMs you change the spacing between the pulses. Because of this you tune the size based on your goals, tuning the diameter for the lower RPM ranges will produce better low end torque and better fuel economy but you'll be too restrictive on the high end and reduce your high RPM power, tuning the exhaust for the higher peek HP rpm range will improve your peak power but you may actually lose some low end torque as well as MPG in the lower RPM ranges (ie: anything but hard acceleration). Most modern factory exhausts are tuned for the low RPM ranges already which is why on some cars owners experience a drop in RPM, and a drop in low end torque even thought they see a boost in peek power with a larger exhaust.

With a Super Charger you have a scenario that is half like that of a Turbo and half like that of a NA car... the intake is pressurized like that of a turbo, but there is no turbo restricting the exhaust, meaning that the benefits of the scavenging effect can still be realized...

the difference here is that the exhaust is coming from a pressurized state in the cylinder to atmospheric pressure in the exhaust, so it's expanding as it's released and as a result needs a much larger diameter pipe across the whole RPM range... in most cases the exhaust would need to be so large to create scavenging even at low RPM that in general with a super charger bigger is better.

In General
These rules are different from vehicle to vehicle and really the only way to know what's going on is to test various system and see how it effects fuel consumption and power output through the RPM range... even still these things can't reliably be determined from just one or two pulls on a dyno with some monitoring equipment since the ECU "learns" and adjust and it can be difficult to tell if the effect your seeing is the result of the ECU over compensating for new equipment (that would pass over time as it "learns") or if it's actually a result of the new equipment...

This is really what you're paying for when you buy a name brand exhaust... presumably they've already done the math, and the testing to figure out the right combination to fit whatever it is they're selling the exhaust to improve.



"scavenging" is what people are TRYING to talk about when they talk about back-pressure... Really this is something that should be "tuned" in the headers, where the individual cylinder tubes come together is where the diameter needs to be sized to induce scavenging.... beyond that point you can and should relieve any "back pressure" since the pulses should be normalized by that point. Some cars even have a valve to adjust this on the fly making the engine perform better across the whole RPM range, there are a few newer production vehicles that include this feature but it's actually illegal to install one aftermarket in the US (why, I don't know)

If the OE designed the headers well, upgrading to a larger exhaust will improve things, if the OE designed the headers poorly, or relied on the restrictions present downstream in the exhaust to produce the scavenging effect then upgrading to a larger exhaust might actually hurt your performance.

[etlsport]

"ive heard multiple people say that their flowmaster 40 series actually decreased their torque"

I don't know about what etlsport is talking about, but I really like my Flowmaster.

Peace.
Tom
012009

I dont have first hand experience with it, vcross007 called me up a couple months ago and was telling me about it.. i remember reading someone else who said the same thing on the forum.. but can't find it now

[etlsport]

found it.. heres what i was referring to

http://www.vehicross.info/forums/showthread.php?t=13584

[VehiGAZ]

Eric - Maybe a 2.25" Flowmaster is bad but a 2.5" Flowmaster is good?

Twister - thanks for the explanation. While it might be all dead-on accurate, it doesn't help us too much, huh? At least we know whay we see apparently contradictory results.

I might go for that CB Vortex if it's any quieter.

[etlsport]

Eric - Maybe a 2.25" Flowmaster is bad but a 2.5" Flowmaster is good?

Twister - thanks for the explanation. While it might be all dead-on accurate, it doesn't help us too much, huh? At least we know whay we see apparently contradictory results.

I might go for that CB Vortex if it's any quieter.

i dunno.. my 2.5" glasspack (pv2) helped a good amount though

[twistedsymphony]

Twister - thanks for the explanation. While it might be all dead-on accurate, it doesn't help us too much, huh? At least we know whay we see apparently contradictory results.

A better understand of things is always helpful

based on what I've heard from people I'm guessing that the headers on the VX are very free-flowing meaning that they're great for a supercharger but not so great for a VX without one...

I forget what they're called they make exhaust bits where you can add or remove plates to control the "back pressure" I'd say that you can put on any muffler/exhaust that you want but if you add one of these plates you can play around with the configuration until you have one that gives you the right amount of restriction for scavenging in your desired RPM range.

start with the least restrictive, check your gas mileage across 2 or 3 tanks, add a plate, check your gas mileage across 2 or 3 tanks, if it improves add another plate and keep doing that until you see the mileage go back down then back off a plate and you'll have your sound and performance too

when doing this be sure to keep tabs on when you use AC or ride with the windows open or with a roof rack on, since all of those can effect your mileage dramatically.

BTW I noticed we're in the same region... are there any New England VX meets? I saw a post from someone in Cape Cod recently too...

[Ldub]

[QUOTE=twistedsymphony;132873]A better understand of things is always helpful
I forget what they're called they make exhaust bits where you can add or remove plates to control the "back pressure" I'd say that you can put on any muffler/exhaust that you want but if you add one of these plates you can play around with the configuration until you have one that gives you the right amount of restriction for scavenging in your desired RPM range.

start with the least restrictive, check your gas mileage across 2 or 3 tanks, add a plate, check your gas mileage across 2 or 3 tanks, if it improves add another plate and keep doing that until you see the mileage go back down then back off a plate and you'll have your sound and performance too

when doing this be sure to keep tabs on when you use AC or ride with the windows open or with a roof rack on, since all of those can effect your mileage dramatically.[QUOTE]

I believe what you're talking about is the Supertrapp silencer system.

They make one that fits the stock 3" exhaust tip, if anyone is interested in experimenting, you can find them at www.summitracing.com

Been there, done that... didn't like the way it looked or sounded.

[twistedsymphony]

yeah that works too... I've never used one but I have a few friends who rage about them.

Alternatively you could also just throw on a restriction plate... unbolt a flange (ideally one right after the cat) and throw the plate between the two exhaust pieces and bolt it back up IIRC they make plates that also double as gaskets for just this purpose.

it will reduce the sound but it shouldn't effect the tone of the exhaust at all.