Will 2 1/2 cat back hurt me?
 

My current setup is 1 3/4 long tubes, dr gas x-pipe, and race bullits w/ turndowns. I want to quiet it down some and put a full exhaust system back on so I can drive it on the street. I wanted to get the mac 3" cat back with the 3" tailpipes but it was 460.00. I was not ready to spend that on a couple of mufflers and pipes so I bought the dynomax ultraflo 2 1/2 system. How bad will It hurt me reducing it from 3" to 2 1/2 after the x-pipe? Also, will the 2 1/2 ultraflo catback flow as good as a 3" mac flowpath cat back?
Thanks,
Wade

Exhaust pipe sizing
 

A 2 1/2" exhaust system will handle up to over 400 HP. You're fine.

'Sound' is subjective. You decide.

2.5" is perfect for stock to mildly modified applications. After reading your sig, I would recommend 2.75". 3" would work fine, but you may lose some bottom end torque. You'll be fine, but you might want to reduce the length of the tailpipes.

Take care,
-Chris

That sucks:( If it slows me down allot I'll just put the cat back on my 93. If I have to I will go to a exhaust shop and get some 3" tail pipes bent. I will never pay 460.00 for the mac system.
Thanks guys

I have a better idea
Why don't you get some of those resonating fart cans and bolt them straight to your X-Pipe :D

Knowing how loud and crappy those sound bolted to a single 2" exhaust pipe, I wonder what it would be like bolting 2 of them straight to an un-mufflered V-8. Probably like one of the race lawnmowers instead of the weed whackers that the Honda's sound like :)

ok, sorry, i just felt like talking

I wouldn't sweat it Wade. The cat back is easy enough to remove so just pull it when you go to the strip and run open after the crossover (man that's gotta sound wicked!). Your car will make plenty of HP with a 2 1/2" system on the street and more than likely eat most street cars for breakfast ;)

What if you just changed mufflers? Anything you do is going to hurt you at the track because you have MAC mufflers right? Those are supposed to be the best flowing mufflers made. Either that or maybe try some custom piping with baffles in the tips, kinda like the Super Trap mufflers work so you could remove them at the track a lot easier. It would be easy to fabricate something like a silencer for a gun. I'll make a pic for you and make another reply.

Also, are you planning on going to US 41 this Saturday? I won't be able to make it so I'll catch you next time. If you go be gentle on her. Not like you have much left to break on it though huh? :D

I've attached a crude rendering of what I was talking about Wade. It would be no more than a can that would slip into your tail pipes with a series of washers welded into it. It would act like a silencer and as long as you kept the inside diameter of the washers around 2 1/2" it should be fine for the street.

Something like that would be simple enough to attach with a couple screws and removed for a day at the track.

Kevin, right now I am running 3" race bullits w/turndowns. I was thinking of the supertrap thing but I want a cool looking set of tailpipes and I don't like the look of them. I think the Ultra flow flows better then all the chamberd mufflers so that is why I went with them. I should get my parts today and I will have it bolted up this sunday I'll post the results.
Wade

Are you going to US 41 tomorrow Wade?

I have to work this saturday or I would.

Wade, you could put the ultraflo mufflers in place of the bullits and your car would be quieter at idle and low rpms, that is of course until you put your foot to the floor. IMO, the 2 1/2 would be fine for street driving, but at the track I would remove the cat back after a few passes and see what kind of difference it makes... Probably pick up some e.t./mph, only one way to find out.

As far as a muffler shop bending up some 3" tailpipes for you, unless they have a mandrel bender I don't think they could do it. It's a pretty tight radius around the axle and our benders will not get the job done without kinking the pipe real bad, it's a pain in the buttocks and by the time they get done you will have been better off to just buy a set of prefab'd tail pipes and have them install them for you. IMO keep in mind... they could also run 2 1/2 out of your ultraflos up over the axle and then weld on some 3'' extensions, another option.

Has the law been bothering you or something? Or do you simply want your ride to be quieter?

I would put the ultraflo kit on your '93 and keep a race system on your '79. Swap out those bullits (glasspacks) for a real muffler. The ultraflo muffler could be installed with 3" flo-tubes and turn-downs and would sound wicked! If you want to go cheaper on a muff, get the welded aluminized ultraflo (Race Magnum). And there is always the 2 and 3 chamber flowmaster.

Rule of thumb -- smaller pipes make more noise (high pitch) than bigger pipes do (low pitch, deep tone). That is what I have realized working in a muffler shop.

Just tryin to help... let me know what you think.

Later

"IMO, the 2 1/2 would be fine for street driving, but at the track I would remove the cat back after a few passes and see what kind of difference it makes... Probably pick up some e.t./mph, only one way to find out. "
Thats why I wanted to get the 3" system best of both worlds.

"IMO keep in mind... they could also run 2 1/2 out of your ultraflos up over the axle and then weld on some 3'' extensions, another option. "
That would look cool, but the reason I wanted 3" was for the performance.

"Has the law been bothering you or something? Or do you simply want your ride to be quieter?"
I am converting the car back over to a street car (kind of) and turndowns with no sound deadning is killer on the ears.

"Rule of thumb -- smaller pipes make more noise (high pitch) than bigger pipes do (low pitch, deep tone). That is what I have realized working in a muffler shop. "
Thats cool... I like a car that screams not rumble.

Thanks for the help. Do you know what a mac flowpath muffler flows? The ultraflo's are like 1300cfm. So I was thinking that the 2 1/2 ultraflow catback will be better then the 3" mac catback.

If you want your car to scream when you stomp on it, the ultraflo cat-back is the way to go. I ran that system on my car for a few years and had lots of compliments on the "unique" sound (most others run flowmasters). It's a good "street car" system.

I heard the Mac 3" system on a nearly stock GT (turns down at exit of course) with headers and off-road h-pipe and it had a real deep rumble to it...

As far as flow #'s I believe the ultraflo vs. Macflow in 2 1/2 config.; the ultraflo out does the macflow as far as an "apples to apples" test goes, but the 3" I would imagine out does 'em both (not sure, I'll get back to ya later tonight).

I remember you talking about a nitrous kit, the 3" system with your motor hp + nitrous shot would be a nice setup. It's hard to beat the ultraflo kit, I'd try it and if it's not what you expect you've got another stang to put the dynomax system on. It's a beautiful thing!!! Options, that is...

Good Luck with your decision Wade,

later