I have a bone stock 91 vert. I want to upgrade the exhaust system and have about $1500 to spend. I'm pretty settled on the B&B exhaust and Magnaflow Cat.

My question concerns the front Y-Pipe and Pre-Cats. Should I go ahead and replace that also? And if I do, should I go without the Pre-Cats? If I do go without the Pre-Cats, will it mess with my emissions system and give me unwanted warning lights on my dash.

My overall goal is a SLIGHTLY louder and deeper exhaust note with a little more performance. I don't race it.

I noticed my Fiancee's 2004 Honda Accord is quicker than my Vette. That just doesn't seem right!

 

That's a lot to spend. I think you could get the full Melrose system with that. Headers, cat, true dual pipes, but you'd need mufflers. You can elim. the pre-cats with no troubles, unless you have to pass a visual emmissions test.

 

so.....cutting out the precats will make you fail an emmissions test????
Anybody in Texas able to confirm this?
I was wondering if no precats and a high flow main cat would pass down here (we do get the sniffer test)???

Wanting to do this type of thing....but.....want to keep it legal as I can.

 

You can remove the pre-cats and pass the sniffer, but not a visual inspection if they look for them and they are not there.

 

If you want to improve performance, and have that kind of budget, put
the money in headers. Look at the full Melrose system and dual cats. I believe it was designed for the Corsa mufflers. That is a much better use of $1500 IMO.(You might even catch that damn Honda).

 

Funny..NOT!

Seriously though, although I value your opinions, I'm not ready to go with headers. I just want advice on the Pre-Cats and whether or not I should keep them or do away with them.

 

Yeah, I did away with my pre-cats. I just had the muffler shop cut them off and sleeve the front y-pipe with 2.25" pipe. I kept the original O2 sensor and it's fine.
I also installed a Magnaflow hi-flow cat with the air hook up. Then I put on Magnaflow straight through dual outlet mufflers. I would guess I may have picked up 20 CHP. I sounds good but not loud until you go WOT. I only spent about $400, but my system isn't stainless. I want my car to look stock.

 

What do you mean by that? What are the pro's and con's of going stainless?

 

Fortunately, most of the people running these emisions places are just looking for one Cat and not three. At least that's how it's done in GA.

 

Your stock system is aluminized steel pipe. Stainless systems are shinier and are supposed to last longer. If you don't drive in salt etc. like here in the South, it doesn't really matter. (unless you are lying on the ground)! It is also MUCH more expensive.

 

Kitsap County doesn't have an emissions inspection requirement (sniffer or visual) so you could remove the pre-cats and not hurt anything. You can replace the main cat with a high-flow unit to help get gasses through and not hurt the air. But you might have a hard time finding a shop that will remove the pre cats and replace the existing main cat if it's in good condition.

For the rear Y-pipe, Walker makes a pipe with a balance tube to cut down on resonance. For mufflers, you can go without or use something like the Mid-America Muffler Eliminators that are simply a pair of small glasspacks on each side. I have the muffler elim's on my 87 with an otherwisw stock system and it has a nice sound but no interior resonance. WOT acceleraton does bring out the noise, but when you cruise, there is a nice deep sound but nothing obnoxious.

Corvette Central (a Forum vendor) has a bolt-in true dual exhaust system for L98 cars for about $250 and all you need to add is muffflers. They are bent to fit and should provide an increase in power. But this system does away with the cats entirely and IMHO, it's not a good deal for air quality. Bremerton is not bad right now, but it may not be long before counties around King, Pierce and Snohomish may see emissons testing.

The Corvette Central system would allow for some small universal cats, you just have to have them welded in and connect the AIR tube to one of them. Then add your choice of mufflers.

 

It would be no problem for a good exhaust shop to cut that system and install a pair of bullet hi-flow cats to pass the sniffer. Of course that would bump the total cost to over $500.

Our stock front Y is restrictive and so is the main cat if you bump power into the 300chp range, easy to do with a late L98.

A good cat only flows to about 450cfm, if that; that only supports 205 hp at the crank.

 

Not entirely true. There are two kinds of stainless commonly used. Can't remember the numbers for sure (e.g., 401 vs 304 or something like that). Don't feel like lookin it up right now.

Look for allen stainless and Corvette exhaust using a google. You'll find allen stainless. They make an oversized 2.5" (304?) stainless front "Y" without cats (maybe with cats too). Anyway it's not shiney, it's a heavier stainless that's common in front exhaust systems. It's brownish in color. Good stuff. I believe this version of stainless has even better high temp properties.... At any rate....

Stainless lasts longer than alum. You can also buy alum from them for less money. If you don't see the item listed, call. They still have it. The oversize diameter will help alot. It did on mine. Before installation, I wouldn't put mine in 6th (I have 3.33 hwy rearend) until 70mph. (At that speed, it was running 14k rpm. It was rediculously slow and lugged). Just by putting the larger pipe on, it doesn't lug until 60mph. MORE POWER!

It's what I recommend you put on the front. And, it's the company I recommend you buy from.

gp

FYI: Your front, stock Y pipe is 2.25". The factory header outlets are 2.5". This oversize exhaust is just what the Doc ordered!!!!!!!!! This will provide as much (or more) improvement as headers (WHEN YOU LOOK AT CHANGING THE EXHAUST PIECE-BY-PIECE). Headers cost about a grand for a good set. This upgrade is 1/5th that. You figure it out.

 

Gregg,
If I go with a bigger front Y-pipe will this mean I have to do something special to hook it up to a stock cat?

 

No. The part past the "Y" pipe is still 3" -- like stock. Keep in mind the exhaust pulses with the firing of each cylinder -- so having a joined 3" section isn't quite as bad as it sounds. Because the 2.5" inputs are filling the center section sequentially.

However, the higher the rpms, the closer it gets to a constant flow and the more dual pipes would improve your performance.

It is my opinion that the best improvement (over stock) is to use a 2.5" front Y pipe (with front cats), a high flow main cat, and performance (or no) rear mufflers. You'll still be legal in any state.

Of course, TRUE duals with an Xpipe, hi flow bullet cats, and headers are even better -- but that's not stock any more....

gp

Note: The Y pipe comes with an O2 bung and requires not computer changes. It does not throw codes. Also, if you're not familiar with exhaust systems, you should know that cats act like mufflers. They do provide considerable quieting power. Having GOOD replacement (hiflow) pre and main cats w/o any mufflers will give you the best performance, sound, and emissions of any setup. (Assuming you're concerned about emissions).

 

BTW, Gregg there are literally dozens of stainless alloys. All of the Catback systems I have seen are POLISHED stainless and are shinier than aluminized steel. Just to be "entirely" correct.

dtomar, you can buy 2.5" front y-pipes and I would suggest that IF you are going to replace the front y. On mine I didn't replace it because it was in good shape. If you replace it, I would suggest getting a new O2 sensor to install in the new pipe near the flange.

 

Guys, thanks for all your comments and opinions. iIm kind of surprised Corvette Ron didn't chime in with his thoughts though!

 

Sorry, I thought you were saying all stainless was "shiney"/polished. I wanted to make sure someone thought they were cheated if they bought a SS system and it wasn't of the polished variety. And, wanted to make sure the OP knew that 304 stainless wouldn't stand out as a custom job (to inspectors). I thought that was your point.

I would agree that replacing the O2 is a must. I've heard NOT to use Bosch (which I did). I forgot what's currently recommended.

gp