TheCorvetteKid

Hey everyone,

My car has the small pre-cats in the front 'Y' pipe and I know that some Corvettes didn't have these. If I replace my pre-cat front 'Y' pipe with the non-cat equivalent, will it seriously raise my emissions levels? I don't plan on removing my center cat (the car has to be emisions tested every two years).

Thanks in advance.

DON M

Walker/DynoMax sells a catless Y-pipe and converter that meets 49 state emissions requirements as a package. It is only 2 1/4" and punch bent.
I have a 2 1/2" mandrel bent SS Y-pipe and a high flow converter and it passes IM-240 dyno emissions here in VA. Actually it is illegal but no one knows the difference here. I figured that I could use the Walker as an example and BS my way past an inspector. I didn't have to resort to skulldugery as the subject never came up and the car burns clean.
It is worth a few HP on the butt dyno and it sounds healthier too.
Good luck.

65Z01

I have no pre-cats, a hi-flow Random Tech car, hi-flow cat back and run a 160 deg stat with fan sw.

Last year my '88 easily passed the OH dyno E-test.

I would suggest you replace your stock cat with a Random Technology 3-stage cat.

oldace84

That 2 year smog inspection sure comes around to fast.......
Been there done that.....just not worth messing with the smog parts anymore....so I just work around them....
tony
:flag :flag :eek: :flag :flag

96LT1

Most places that do the emissions aren't aware of which cars have pre-cats and which ones don't. Normally they will just look for the main cat and say 'yeah'. As long as it passes the sniffer test on the dyno they could care less.

The last time I had mine checked, they saw the long tube headers and asked "Is all the original smog equipment still on the vehicle?" :yesnod:

vader86

As long as you keep the Main cat, and its in good condition, you should pass.

I would replace with a Random Tech though.

pwrful c4

I had an 88 with the precats removed and passed emissons fine. :steering:

The Dingo

You should pass a sniffer test. I understand the precats were put there by GM to help with the cold start portion of federal emissions tests. That being the case, once your car is up to temp you should be okay.

Fastguy

:withstupid:
MA has the very strict dyno test and mine passed fine.

racerx

The smog tech geeks here in calif look for the pre-cats on the 86 & up vettes. If they are missing, it fails the visual part of the test. Some are more observant than others.

h rocks

Dead on Red 90. All he has to do is make sure the car's good and warm when it gets tested. (this of course presumes they don't have a visual inspection, but I do believe that in Canada is where GM had originated the "export" Y pipe.)

Wypster

I have an '89 and have the pre-cats removed and Magnaflow SS exhaust .... the car passed the tests (just barely) last Oct. ... just have to make sure the car is tuned up and the injectors are not leaking.

I go through the same emissions tests as you do. The only problem I had was with the injectors leaking. I fixed those and the car passed without a problem.

CorvetteZ51Racer

IF you fail any part of the emissions test as a result of the removal of the precats, it will be the NOx part. The precats are designed to handle the NOx and nothing else, whereas the main cat is designed to handle the HC part. The way you can tell is that you need additional oxygen (on the OEM style cats) to clean up the HC portion, and only the main cat has the AIR tube. The location of the precats (right past the manifolds) is indicative of a NOx cat, as they will heat up VERY quickly that close to the exhaust manifold, and you need a LOT of heat to break apart NOx molecules.

As a little sidenote, if your in-cylinder temperature never break 1500 F, you will not have any NOx emissions, as NOx molecules simply cannot form below 1500 F. This is why an engine that is running VERY rich will have nearly no measureable NOx emissions.

TheCorvetteKid

Hi everyone,

Thanks for all the responses. I appreciate it. I may just do this swap!

Oh, one more thing - did anybody notice any performance gain after doing this change?

Thanks again.

TIMSPEED

:yesnod: DEFINATELY did! It made it sound a WHOLE lot meaner than before. When I had TOTALLY stock exhaust (and actually a TOTALLY stock car, other than Ignition and K&N Filter) I passed California Emissions with NO NOX AT ALL!! So I figure take out the precats and I'll still be ok. :D As far as visual, when I smogged my vette, he didn't even look for the MAIN cat. He simply said "When a car passes that clean everything fine." LoL, works for me!

CorvetteZ51Racer

Well, I went from stock exhaust straight to Lingenfelter long tubes, but I gained 43 rwtq and 32 rwhp on the chassis dyno from the exhaust alone.

Rick86

Unless your smog certificate says Federal Emissions only :yesnod: I have a 49 state car (My '86 Vette) that I registered here in CA and they didn't give me any hassle about the catless Y pipe.