Thinking of spending the Tax Return on a new exhaust system and I have a couple questions... :confused:

Due to the aweful state I live in I'm stuck with a 2-1-2 w/cat setup :sad: so no duals for me unless you guys know a shop in NJ that will do anyway...

Here's what I'm planning:
Dynomax cerama-coat headers
High flow cat (not sure of any... so if you have one to recommed please do)
Flowmaster delta flow 40's
3" mandrel bend pipes

How would this compare to a 2.5" dual setup? My car is stock now, so what kind of numbers/performance increase should I expect? Also your opinions on my planned setup would be great.

Thanks in advance!! :cheers:

~~Ev~~

 

bump

 

That setup will help you a lot, but duals would help even more.
Just go with an off the shelf cat, they're very very good. The high-perf cats aren't worth the cash, you only pick up a horsepower or two.
-Steve

 

If you come off the manifolds with 2.25" into one 3" pipe, through 3" convertor, split into two 2.25", to the mufflers. Wouldnt that be legal? Even so, I bet if you ask around you will find someone who will do true duals with dual convertors( if theres room). If they say no, tell them you'll pay cash, and that you dont need a reciept. Sooner or later you'll find someone.

 

mid america[www.madirect.com]sells dual exhaust for off road use for a 1974-1979

 

I agree that if you look around enough, you're bound to find someone that will put a true dual system on. I've kind of gotten the impression that removing the old cat is the thing that these guys can really get burned for doing. So if you do that yourself, it may be easier to find someone that will put duals with dual cats on.

As far as 2-1-2, that's how I went. I can't speak to performance numbers, but I can say that the new freer-flowing exhaust and the shift kit made a tremendous positive difference in how my car felt to me.

If you haven't done the numbers, the smallest cross sectional area is:
2-1-2, 2-1/2" = 4.9 sq-in
2-1-2, 3" = 7.1 sq-in
dual 2-1/2" = 9.8 sq-in
So, while it's not dual, 3" single is a big improvement over 2-1/2".

FWIW, I've had several sources tell me that a good, free-flowing, 2-1-2 system will be good up to 400 HP. I think it'd be a long time before I ever see 400 HP :eek:

Finally, here are some pics of the custom system I got: http://users.erols.com/jerryp58/corvette/exhaust3.jpg http://users.erols.com/jerryp58/corvette/exhaust4.jpg http://users.erols.com/jerryp58/corvette/exhaust2.jpg http://users.erols.com/jerryp58/corvette/exhaust1.jpg

I think the front Y-pipe is probably the best feature (a small flare from 2" off the manifold to 2-1/2" in single pipes that meet at a 3" Y -- I don't have the 90 degree connection like stock).
The 3" in and two 2-1/2" out cat is nice too.
I have MagnaFlows which are a good bit quieter than the Flowmasters (I think).
There's a little bit of resonance around 20 MPH and above 70 MPH.

It's not dual (and that bothers me), but I like it and I don't have to worry about where to go to get it inspected.

Hope this helps. Good Luck.

 

Thanks for the help. I've read on the forum about people who didn't like the mid america kit, plus I don't have the shop setup to do the work myself. I think I'll call around and see if I can find a shop to do the dual setup before settling on the 2-1-2.

 

I'd run a 3.5" cat and pipe if possible.

 

I never thought of going to a 3.5"

 

Metal_Wulf,
Do you actually have emissions inspections or is it just that nobody will do the work because it has a single cat? If you don't actually have inspections, then you could theoretically remove your exhaust, install the headers, and then tow it to a shop to have the rest of the exhaust fabricated. If asked the year, you could possibly say it's a 74 so that when they check their books, they see that it is dual all the way back. Just buy the tranny mount hanger from Corvette World and install it before you take it to the shop. You would also want to remove the converter heat shield. Both items are real simple, 10-15 minutes tops. Paying in cash, not needing a receipt, and having it done on a really slow day are also good kickers.

 

We have really harsh inspections here...one of the many reasons why I want to get out of NJ... but anyways... If I can find a decent shop that will look the other way i'll do the duals(which is what i'd really like to do).

 

I doubt you'll find a shop that will look the other way during the visual inspection, and even if you do, you have to worry about whether or not that shop will be around in the following years and if they'll always look the other way. If you're stuck with the 2-1-2, then you're only performance option is to go with a bigger cat. You could also get a "cat converter test pipe" built and install it after the inspection. You would just have to put the cat back on later. They are bolt on, which helps considerably. Quite a few ways around the visual, all require some amount of work. Moving to a state without inspections is another one. But, you are where you are, and you don't have much choice. Good luck, hope it all works out for you.

 

i'm not worried about inspection, i know a couple shops that will put a sticker on anything for $100... but those shops don't do exhausts...

 

If that is the case, then go with my previous suggestion of doing the headers yourself and saying it's a 74. If they ask why the exhaust is off, it's because you wanted to save money by installing the headers yourself but couldn't do the exhaust. I think the basic rule is this:

If they remove a cat, they have to put on one.
If the year of the car requires a cat, they have to put one on.
They are only supposed to put on what was on it from the factory (i.e. one cat off = one cat on. two cats off = two cats on)

If you tell them it's a 74 and they don't check the reg numbers, then they aren't the ones that will get in trouble. The best shops to do this sort of work are the hole in the wall shops on very slow days and paid in cash, not the big chains. However, almost no shop will remove a cat and not put one back on the car. Granted, you are taking your chances on quality at the hole in the wall shops, but sometimes beggars can't be choosers.

 

That's why I figured I'd save myself the trouble and just stick with the 2-1-2 and just get larger pipes and better cat, so it will still be legal and I can take it to a better place to get it done right.

I couldn't imagine driving my car with open headers...hehe... My friend had a '71 chevelle that he had just headers into glasspacks, and that was soooo loud...

 

yeah, I drove my vette to the shop with just the exhaust pipes and no mufflers. It was definitely loud. Luckily it was only about 10 miles away, but it was very loud. I had mine done at 9am on Christmas eve. He did decent work considering I was asking a lot of him by wanting the Flowmasters tucked up like stock. Pretty difficult since they are bigger. Took some ingenuity but with my ideas and his skills, we managed. :)

 

I never thought of going to a 3.5"

I don't think you can get 3-1/2" through the crossmember. Check out the third pic I have listed ( http://users.erols.com/jerryp58/corvette/exhaust2.jpg ), it's a really tight fit :eek:

The guy at the shop couldn't figure out a way to go two pipes into and out of one cat (isn't that the way the C4s and C5s are?). He said that he felt that would be within the letter of the "one cat" law, but he just didn't know where to put it. Maybe you or someone else could figure out a way to do it :confused:

 

Unless you're running a huge displacement engine at high RPM, I don;t think you need 3 or 3.5 inch pipes. Remember Zora only used 2.5 on L-88s.
For street use you want high exhaust velocity to scavenge the combustion chamber which means medium sized pipes.

 

well my car's stock except for a K&N filter...

when I can find the money to build up the 4-bolt 350 that's sitting in my garage into a monster then i'll really need a dual setup...

 

Just a note on the performance capability of 2-1-2 exhaust systems. If done right they can breath very well. My brother owns a modified Buick Turbo Regal with a 2-1-2 system with convertor. 3" center section and convertor I believe. Fully loaded with creature comforts and leather and the whole 9 yards. Anyway , with exhaust fully connected he can manage to get this 3600lb car into consistant mid 11 sec 1/4 mi's @ 115+mph. If that aint breathin, I dont know what is.