Calling all v6ers who have gone from 2.5" to 3" exhaust...

[camarocrzy]

I went 2.5" and i am very happy with it.

[HBHRacing]

I'm just happy that People are starting to think for themselves. Thats the important part. There will always be a few that hang onto the popular vote and simply go with 3 inch because others tell them it's best. But hopefully now you all understand that there are other choices out there.

[Perry]

Hey Farva....What's that restaurant that you like?

[FireFighter]

I had a flowmaster 2.5" cat back and later changed to a 3" flowmaster with a 3" carsound cat and also a cut out. I gained about 1.3 in mph everytime with the cutout closed. With it opened, it sounded fast but, it wasn't lol. 3" all the way.

[99camaro-3.8]

^^^how can u say 3" is so much better when the only gains u have are with the 3" exhaust and a cat. did u have the cat with the 2.5"? if not than u cant really justify that the 3" is so much better

[bird200]

I have the 80 series from flowmaster and it has been working out good. It looks excellent, satisfied with the sound, however when its really warm and the fans running sometimes theres an extremely high pitch buzz that might have been an install error

[Fbody3400]

I have a 2.5 inch. Sounds good, and it really helped out down low. I like the feeling of my 3.4 better than my buddies 3.8. It just feels like i get throwing back in the seat more down low. I guess its all of that 200 lb. ft. coming in at 2400rpms [img]graemlins/naughty.gif[/img]

[HBHRacing]

Firefighter helped prove part of my point especialy about RPM tuning. He must have had the cut out in a location that was not helpfull to his power band...

However his comparison is flawed. Too many things were changed to learn anything from it. If he had used the high flow cat on the 2.5 system and installed the cutout in the correct location for RPM that he wanted the power in he would have done so much better. Especialy since the flowmasters are known for not giving very good CFM numbers.

99camaro made this point well.

[Turbo V6 Camaro]

Originally posted by HBHRacing:
Firefighter helped prove part of my point especialy about RPM tuning. He must have had the cut out in a location that was not helpfull to his power band...

However his comparison is flawed. Too many things were changed to learn anything from it. If he had used the high flow cat on the 2.5 system and installed the cutout in the correct location for RPM that he wanted the power in he would have done so much better. Especialy since the flowmasters are known for not giving very good CFM numbers.

99camaro made this point well.

well on turbo car the back pressure is about ~2X the boost...... so right now its open down pipe the car "feels" to pull alot harder off the line (before boost lol) then it did with the full cat-back 2.5 crap bend flowfaster....

so my question is, is there something to be gained by hooking up a exuast....... ?/?

[HBHRacing]

Like I said turbos are not really my thing. your not harmed by needing to overcome the resistence of teh pressure in the system. however I still belive that you need to consider RPM tuning since I belive that there is still a reversion wave once the wave exits to atmosphere. But I will see if I can confirm this.

[slow6]

HBH, wheres a good place for the cutout?
or hows it gonna perform when its near or far from tha catalytic?

i wish we could adjust the output like an electronic. cause i dont want a full 3" open always.

[dmw319]

so what is better for a supercharged system, 2.5 or 3? and why..

[99v6cam]

Originally posted by dmw319:
so what is better for a supercharged system, 2.5 or 3? and why..

definatly 3" because there is more air coming in the engine because of the supercharger so there will be more coming out and it needs room to flow.

[FireFighter]

Originally posted by 99camaro-3.8:
^^^how can u say 3" is so much better when the only gains u have are with the 3" exhaust and a cat. did u have the cat with the 2.5"? if not than u cant really justify that the 3" is so much better

Ok... big deal, I went from a 2.5" catback to a 3" catback WITH a High flow cat, I doubt the cat made much of a difference, It Just made the whole system 3"s.

[HBHRacing]

Originally posted by FireFighter:
</font><blockquote>quote:</font><hr />Originally posted by 99camaro-3.8:
^^^how can u say 3" is so much better when the only gains u have are with the 3" exhaust and a cat. did u have the cat with the 2.5"? if not than u cant really justify that the 3" is so much better

Ok... big deal, I went from a 2.5" catback to a 3" catback WITH a High flow cat, I doubt the cat made much of a difference, It Just made the whole system 3"s. </font>[/QUOTE]Wanna bet??? It made a very large difference. Like I said, if you had went with a high flow cat and a "better" 2.5 inch cat back you would have been better off..


For the rest of you guys.

Boosted motors have A LOT more pressure in the motor then NA motors do. This means that they don't have to fight the resistence in the exhaust. this means that larger exhaust will NOT hurt you like it would an NA motor. So for this case (depending on boost) 3 inch would work well.


Cut out theory. The very basic formula for cutout placment is this.
If you have a restrictive cat put it in front of the cat. If not then put it betweenthe cat and the muffler. however I HIGHLY recomend no cat or a high flow and then placing the cut out between the cat and muffler.

When you place it betwen the cat and muffler the general idea would be to put it 30 inches from the Y pipe or 60 inches from the exhaust ports. This will put your tuned lenghth so that power will be best somewere between 4000-6000 RPM. The only way to narrow that down would be moving it inch by inch on a dyno or at the track. But 30 inches (which will be near the rear end) will get you close.

Your other option is to install it directly after the cat and then add a long length of pipe to the open end of the cut out. Then you can duno or make track runs, cut and inch off the pipe and run again untill you get your best result. Then you know where to permenently mount the cat.


Great questions guys [img]smile.gif[/img]