I have always thought my upper valve trane was noisy on my 88 vett. I have about decided a bunch of the rattle is coming from my pre-cats. I can bang on them and the right one rattles no matter what. Too noisy to start the engine and tell. Does anyone have any experience with this?

 

Experience with what in particular? If you're precat is rattling, it definitely needs replaced. You're losing power from the restriction. As far as valvetrain noise, my '86 makes quite a racket. It did before the engine rebuild, and it still does after.

 

I say just get a new y-pipe without those restrictive pre-cats, and go with a high flow cat. As for the valve train noise, maybe its time to rebuild or replace the heads. :cheers:

 

If your knock sensor "hears" that rattle it can retard the timing. :chevy

 

Just a little experience from GA. If you hear those pre-cats rattling the next thing they are going to do is come apart and plug up your main cat. I made the last 100 miles one night at 65mph because that was all the air that would get through the engine!
I know a bunch of people are going to say different, but here is the cheap way to fix your problem. Take the rear y pipe off the main cat. Spray the nuts on the exhaust manifolds with liquid wrench or WD-40 and start scrounging around for a piece of 1/2 pipe about 4ft long. Pull off the front y pipe and cat. If you are lucky you can get the pipes apart. Some years have a bolt on flange on the front, others are slip on. The slip ons get crimped by the clamp and you have to cut them off, if it won't come off leave it alone. We aren't spending money on this job! Take that 1/2 pipe and bend it until you can get it around the corner of the top of the y pipe and beat the on the brick in the pre cats until you bust it up enough to dump it all out. You might even stuff the vacuum cleaner hose down there make sure you don't leave anything in to plug up the main cat.
Total cost - a couple of hours and a 6pk
With everything gutted Dyno Max rear y pipe and mufflers it don't sound wimpy!
From what I hear any good main cat will pass a smog check by itself, we don't have any smog checks down here yet so I won't swear to it.

JS

 

If you don't mind spending the money, the MAD front Y-pipe fit perfect and was an excellent quality part. See my other post with the subject "front y-pipe installed."

MAD sells pipes that are stainless steel as well as aluminum and in 2.25(stock size) and 2.5" diameter pipe.

Chris

 

okinawa86vette, Did the MAD pipe appear to be mandrel bent?

 

I had the same same problem last summer, but mine was VERY noisy, and it first started has a bit of noise and 1 or 2 days later, It was very laud. I first thought the valve train had something wrong. I was really worried about it since the engine is pretty much new since the rebuilt "only put 10 000 km since it was rebuilt 3 years ago"

I had it checked by a friend mechanic and he found out that it was just one of the precats.

He simply gutted both of the precats and welded them back shut.
The precats are mostly resonators then anti pollution so you can simply have this done by a shop for not much $$ and it wont affect emissions.

 

Thanks for all the great comments guys. I just rebuilt my engine and have checked the valve trane more times than neccessary. I gutted the main cat, but not the pre-cats. I will do that, and I bet it helps... Thanks Again... :thumbs:

 

Most shops in towns w/ emissions testing won't touch them except to replace with new cats.

And to answer the other question, the pipe wasn't crimp bent, but it didn't appear to be truly mandrel bent. Most of the parts where the pipe isn't quite true is to get around other components. Here's the link, it's got a pretty good picture. The pipe was perfectly formed and welded. The fit was perfect too, which is unusual for exhaust parts. It's noticeably larger than the stock pipe.

Here's the link.......
http://www.madvet.com/shop?frame=1.36.971

Chris


[Modified by okinawa86vette, 9:48 PM 1/9/2004]