Is 3" exhaust needed?

[vcrpro3]

"The cut-out ideas are great for cars that'll see somemore track time .. but vcrpro3 hasn't expressed that desire. I say keep the 2-1/2" and be happy ... for now"

Probably 250hp will be the highest the car will ever go for and as stated, it will not ever be on the track--just for street and higher than usual open road cruising speed ability

[xrattiracer]

Sounds like a good plan then. My daily driver will be about 250 hp, and i plan on using full 2.5" system on it as well.

[scott_s]

A 3" cylinder (exhaust) is 48% bigger than 2.5" That is what tipped me to go 3" though it is now too loud that my wife will not drive in it. Which may help one decide what to do as well.

[90Acclaim]

Quote:

Originally Posted by scott_s A 3" cylinder (exhaust)....it is now too loud that my wife will not drive in it. Which may help one decide what to do as well.

3" all the way!

[Polygon]

I just had my 3" installed a little over a week ago on my stock TII. You can say what you want but I feel a NOTICABLE difference. After I got it installed I gave it a good run from a rolling start in first and when I shifted into second the clutch was slipping. I had driven it harder with the old exhaust and was NEVER able to make the clutch slip at all.

I know for a fact there is more power just because of the reduced back pressure. Also, this is with the stock down pipe because I have the wrong sized donut and have to wait for the right one to get here before I can get the 3" down pipe welded on.

Here is the thread I started about it, it has some pics and sound clip:

New exahust for the GTC (Sound).

[puppet]

Clint ... were you going from stock to 3" ?
vcrpro3 already has 2-1/2" all the way back.

[Polygon]

Oh, yeah, I missed that.

I went from a stock exhaust to a 3" mandrel.

[Ondonti]

There is gain to be made going from 2.5" to 3"

I hate it when people write long articles so they can feel justified in doing something subpar. When I do something subpar, I just do it knowing its not the best

[detobias]

Quote:

Originally Posted by Ondonti There is gain to be made going from 2.5" to 3"

of course there is a gain...

the question is: for a particular engine configuration and HP goal, does the extra expense, weight and hassle of a 3" create *enough of a gain* to justify itself ?

*my opinion*, after shoehorning a 3" into an L-body which was designed for a 1-7/8" and now clunks the axle into the pipe over moderate bumps, is:

unless you are planning something more aggressive than a stock-ish TII with <20 psi, then a 2.5" is adequate

if you plan (one of these): Super60, 2.5L/.63, T3/T4 turbo, 4V conversion, >20psi/FMIC, 2-piece+expensive headwork, etc. THEN a 3" SV, DP, and exhaust is certainly going to give you worthwhile ADDITIONAL gains over a 2.5"

if you are low budget and running a 2.5 SV & DP then don't bother with a 3"

the reason I installed a 3" is: I have a balanced, oversize valved, ported 2.5L which will go in there someday (with a FMIC and at least a .63 turbo)..

[Ondonti]

No problem fitting 3" in an AA body when installed properly with good stiff bushings. If you are just reusing the crap stock bushings, then you get what you installed.
You can also slide the gas tank over a little bit if you really are worried.

Last I checked he has a J body, not an L body...........

[phantomrt]

Check for how much exhaust backpressure you have. You can make a backpressure adapter using an old, shot oxygen sensor and hack it up so you can put a vacuum line on it and run it to a pressure guage. Unplug and remove the oxygen sensor, install the adapter, and go for a run. No backpressure? I can't see bigger exhaust helping anything.

This ghetto tool is great for diagnosing clogged catylitic converters. Also, to get the most out of your 3" exhaust, you need all 3" parts (including swingvalve)

[shelbyplaya]

somthing everyone is leaving out is what or even if this person will be running a cat (is so what kind?) and/or a muffler (if so what kind?) or will it be mandrel bent or crush bent?

i personaly have experince with a few differnt types of exhaust on TD's and to my enjoyment was that i found a 2.5" cat-back mandrel bent exhaust will do the trick. i also have a car that has a 2.5" SV into a 2.5" DP then opens up into a 3" crush bent with no cat or muffler.

the 3" sounds like crap and it NO good for street driving. the way i look at it is that the compleat 2.5" mandrel bent set up is good seeing as the exhaust has to pass though a crappy flowing SV into a much better flowing exhaust. sooo whats the point on going any bigger if if you only have a given size SV (not to say a 2.5" exhaust wont be usless on a 2.25" SV {i also have a car set up like that})

i guess when it all comes down to it, it's a matter of perferince. if your goal is only 250hp and you know you'r not gonna be pushing for any more, get a 2.5" exhaust, if you think some day you'r gonna try for more power, go with a 3" set up. and hell if you cant deside what to go with...... just go 2.75" i know a place where they sell that size by the dozen!

[xrattiracer]

theres math that does show that the length of the restriction makes a big difference in flow. so thats the difference between the short about it stays 2.5" at the swingvalve, or staying 2.5" for the entire length. if you thought the 3" sounded like crap, then do something about it. adding the right muffler will make it sound better, and the people you share the road with will thank you (because of less noise). and it will actually be legal to drive.
its not a matter of preference, there are real power differences, and significant ones in most cases.

[GLHNSLHT2]

I upgraded my exhaust in stages. Stage 1 was eliminating the cat and running a piece of 2.25" pipe (stock size) out the side. It helped a lot. But it was loud, sounded good though, but popped very loud on decel. Stage 2 was a JRB downpipe with 2.5" donut that instantly flared to 3" with a dynomax bullet out the side. There was an improvement once again (I could spin the tires rolling on it in 2nd gear now) The tone was deeper, not as overall loud. Stage 3 was going to a full 3" donut/downpipe and eliminating the Dynomax. Another significant gain was noted, as well as that deep tone still being there but being able to hear the turbo spooling. It's quiet at cruise and idle and just the right sound when you're on it. It's a bit loud if you're right up against a wall but then you just laugh cause the sound is awesome and the noise is only temporary. I should of done this stage 1st. Well worth it but all the stages had gains over the previous versions. My experience has proved to me that the 3" is quieter than the 2.25/2.5" was. If you have grandma car (new yorker etc.) and don't want huge performance gains or to spend lots on the exhaust, Get rid of the cat and upgrade the muffler at least. If not get the 3" It truly rocks.

[Polygon]

Quote:

Originally Posted by shelbyplaya the 3" sounds like crap and it NO good for street driving.

How so?

Everyone that has listened to mine says it sounds great. Also, how is it NO good for the street?