Dolfan

I was just under the car getting the exhaust off the manifold for my head removal project and I looked at the y-pipe to the main cat. I'm thinking that an easy thing to do is remove the y-pipe take it to a good muffler shop and have them just cut the pre-cats out and replace with pipe welded in place????????? This wy my O2 sensor stays right where it is and all bolts back in.

I don't want ot change the pipe size or anything, and I'm not going to headers just wanted to make minor changes including replacing the main cat with a high flow.

Does this sound like a good plan?

engle1147

If you remove it from the car it will be very hard on the muffler shop to weld the hollow/filler pipes in and have everything line back up correctly so it bolts back up to the car easily. I recommend welding it why it is still on the car or replacing the Y pipe with one that is already without pre cats.

CorvetteMike2024

100%

Dolfan

I figured a good shop would be able to put it into a "jig" of some sorts but I guess I'm asking a bit much. OK, thanks for the advice.

jeffp1167

just punch the precats out

Aggravated4life

Do that or,
If you dont mind to spend a little money,get this if you havent seen it.

http://www.mamotorworks.com/corvette-3-36-971.html

Ps,I had my exhaust welded and etc before and they never lasted.Had leaks,cracks,rust or etc with some shoddy workmanship and money wasted.Bought a replacement pipe like the one in the link.

Dolfan

If I were to go the route of "punching out" the pre-cats how would I go about that. What to use? pipe? How do you get around the bend of the down pipe portion from the manifold?

jeffp1167

heres what someone did to mine but I dont know who or when he did it.

anyways take sawzall or grinder after romoving the heat shield and open it up, then simply gut it and re-weld the piece back on and then put the heat shiel back on.

M.J.L.

I went with there true dual set up that connects directly to the manifolds though. No cats period.

I jabbed a tire tool thru them. Then stuck a shop vacum in them. Took it around the block, locked it in first gear, and the car took off like a bat outta hell. My skin peeled back to form a temporairly unmovable smile.

Signature will help explain...

TJM

No. spring for a new pipe $200.00 at Summit, Mid America, et al

TJM

floridamale

The ones on my 87 started rattling so I had them cut off and a pipe welded on but they were on the car at the time there were a couple of slight bends they had to do for proper alignment. If your Y pipe is still good have them welded if not replace the pipe. However if you live somewhere they have a visual inspection you will not pass.

Dolfan

I'm Atlanta and we do have visual inspection. But how is the average tech running one of these places going to know that this model originally had pre-cats and then the main cat???? I guess if I go with the new pipe even the visual inspection would show a cat and O2 sensor so only a Corvette enthusiast tech might know the difference.

For simplicity I think I'm going with a new pipe.

j-wireman

Some states have emission exemptions for cars with low annual mileage. In PA, any car driven less than 5,000 miles is exempt. You should check out GA's law.

I'm with the other guys. Replace the front Y with one without the pre-cats. PLUS, replace the main cat with a high-flow cat. Random Technologies makes the best one, I think. This is exactly what I am going to do (when I get the time and the money). Freer-flowing mufflers will be added later.
I was asked once, "Why have any cats on it at all?" Because, if I go over the 5,000 mile limit, I'd get tested. And FAIL.



Mike
'90 'vert

RLG

I read somewhere that the EPA approved the removal of the pre- cats. I also went with a true dual exhaust system with no Cats at all. If you have inspections I would go with the front y pipes with no pre - cats. The previous owner had cut the originals out and the welding job was bad. It leaked and dumped exhaust gas into the interior.

jsinga

You can beat the precats out with a piece of 1/2 steel pipe, ridgid conduit, not emt. Just bend it up until you get it down in there and start wacking away until you break up the bricks. you need to take the Y pipe out to do it. The y pipe and main cat will come out fairly easy on most since most have a bolt on flange on the back. Just spray the manifold bolts and let them sit a few minutes before you start.
cost 0$

Dolfan

Yep, I'm going with a new front Y-pipe and a new main cat. I think I saw the difference between random tech and Magnaflow is like $345/140. For this build I really can't justify $345 for a modest L98 through stock manifolds.

I think I'll go with a new Magnaflow paired with a 2 1/2 front Y and hope that let things breathe better than stock.

GREGGPENN

I think that's the best move. And, you'll notice the difference with the bigger front-Y (as I also did that 3 yrs back). Better breathing mufflers on the back would be good too. Don't be surprised when it gets a bit louder. Cats also muffle.

gp

coupeguy2001

or, you can buy a front Y pipe off of an 85. They didn't have precats!!! and they have enough patina that they look original. AND, there's no welding because they fit your car

jeffp1167

thats basically why I had to do mine like this I figure the early 84-85ish had no precats and could pass sniffer thest. mine is done like this because I heard them rattling and to pass visual is all

RS69

+1, this works and is very affordable..