1986 coupe, bought four months ago, enjoying the heck out of it!
Had been sitting in a garage for over 8 years before I bought it.
Developed a loud roaring vibration with any acceleration, even mild.
Got under it, found two rusted out areas in the rear Y-pipe. In the more forward and worse rusted out hole, found what look like pieces of catalytic convertor (A chunk of almost like tiny rectangular honey-comb pattern of metal). Patched the holes for now. Much better. No signs I can see of anything loose/leaking exhaust upstream of the big center catalytic convertor.
Two other pieces of info:
I am NOT in California (I'm in Northern Illinois).
When the weather is nice, I'd like to use the Corvette as a daily driver.

So:
I am pretty sure I need a new catalytic convertor. Should I get a stock-type, or should I get a high-flow type? Can I do this in my driveway with the car up on jack stands?

And, I should just go ahead and get a new rear Y-pipe, does not look too difficult to replace in my driveway with the car up on jack stands.

Should I just replace the Y-pipe? Should I also replace the mufflers? I don't know if the mufflers are original or not, but they look OK from the outside.

If I replace the Y-pipe and mufflers, should I get a larger/higher flow set of pipes? Will this really increase any performance?

Thanks in advance for your help!

 

I have done this. I would recommend changing the Front Y-pipe with one WITHOUT pre-cats and a new Random Technology main cat. See how you like that before you do the rear.
Yes, it can be done while on jackstands.

 

A 2 1/2" mandrel-bent front Y with hi-flow cat really makes a difference in performance as out stock exhaust is very restrictive.

I like to soak the front Y bolts overnight with PB Blaster to help free them up for easier removal.

The choice of rear Y & mufflers depends on what sound &/or resonance you want.

 

Dude- got an 86 myself- 4+3, just did this- first - you going headers or no ? 20+ HP right there- i could feel the difference, but what a pain in the ***.

Next- single Magnaflow cat or the one that other guy said- you gotta keep that air pump pipe and all that stuff hooked up for emissions and the ECU.

If headers, go without cats of course-with or without air pump pipes, I went with, Y Pipe collected to the cat, then go back to one 3" pipe to a new Y Pipe to the mufflers- you MUST put a cross over pipe in to balance the sides- no pop, back pop, just good sounds.

If you keep stock manifolds and all the air stuff, go with a new Y Pipe, no cats, just straight to the one in teh middle, same stuff all the way back. www.corvettecentral.com has an exaust site on their headers, check it out- lots of pics

 

Quick, send me $175 and your address and I'll take care of your muffler decision.

 

Thanks for the help!
I don't want headers - this is going to be a daily driver in good weather, I think headers would be too loud.
I actually want a fairly quiet exhaust, with as little resonance/drone as possible.

Also - the catalytic convertor has a pipe coming off one side that goes to the front; I think this is some sort of O2 sensor. In any case, is the attachment between the pipe coming out of the convertor (about 5" long) and the rest of the pipe welded? The clamp around this is loose, but I still can't wiggle the two ends apart.

 

Headers don't make noise.
mufflers determine the noise level. Headers are just pipes like the originals except the tubes are slightly bigger and longer.

 

IMO if your wanting to make this a DD and don't like noise, go to Sears and get a complete stock exhaust system. If the rear Y-pipe is gone the mufflers will follow suit soon. The cat is gone and the front Y is next.

This car has been sitting for a while and there will be more repairs to come. Your going to need a factory service manual and hopefully your mechanically inclined. Most Chevy dealers are no longer equipped to handle troubleshooting the early C4's any more so finding a good Vette shop in your vicinity is recommended.

Lots of great info to be found here so do some searches, read others posts, and ask questions. Corvette's are great cars and the 86 is not exotic. So don't think you need to pay top dollar for every part or service.

Remember to wave!

 

Here's some advice. I have 15yrs in an 87 coupe with 230kmi.
If you can't fix it yourself sell it as soon as it warms up again. Because you likely can't afford and don't want to deal with people making a living fixing new plug and play cars.
Hunt down a FSM. Problems, search this forum!
Keep the battery charged or it will kill the alternator.
If you found CAT chunks in the rear y pipe listen for funny rattles at light throtle; the front CATs have loose bricks and will break up and plug what's left of the main CAT.
You can take those pipes off and bang out all the bricks put them back on and still pass smog by some accounts. It won't be quiet if you do it. The main CAT is a big muffler.
I put walker dyno max y pipe and mufflers on over 10yrs ago and they still look good, no rust. They were the bang for the buck IMO.
If it gets where you can't get the tires balanced the problem is likely halfshaft u-joints. Look at the ujoints, if you see any red around the crosses they are shot. Replace all of them with good parts. I've done them 2 times in my backyard. Plan for a day the first time. Way less than $100 for parts. Then write yourself a $500 check because most people who pay spend that much.
Does the AC work? Keep an eye on it. A4 compressors are made in china now. I still have an unopened orginal system. Every couple of years I charge it up and put a few oz of oil in it.
You know the early cars have really crappy brakes. But weekender daily driver just get good pads. Don't even think about turning 12" rotors. They'll be shaking again in a coupel of months. They're front upgrades you can do for less than $500 if you shop for used parts that will make a big difference. Oh, check the flex hoses too. If they are orginal they can cause some really wierd brake problems.
BFG Comp TA's are the only 16" American made tire. I have them now. Had Firestone SZ50 before and the TA's trak straighter down the road.
Wheel bearings are a big issue. If the car is all over the road where the trucks have rutted out the road the bearings might be loose. Tire shake test is not the way to check them. It will tell if you have worn suspension. The FSM tolerance is I think under .005" end play. Without antilock brakes you can find bearings from something besides a vette and spend a lot less money.
Leave the roof on unless the roads are smooth. It's a completely different car with the roof off.
Try and find out if the fuel pump has ever been changed. In 15yrs and 150k mi that's the only reason I have walked. It gave me 5 minutes warning on the FL Turnpike. The vette is one of the few cars the gas tank doesn't have to come out to change the fuel pump. The old hard rubber boot around the filler neck was the hardest part of changing it out. From start to finish took 30 minutes for the guy to change it. I watched, it was easy to change.
Be careful with anything plastic. It's 25yrs old and brittle.
Weatherstrip is expensive. Keep the car covered or inside and most of all drive it!

JS

 

some sage advice

With your 86, you don't have front cats, just the one in the center. It is either clamped or welded to the front y-pipe so if it needs changing, good luck getting it off. Its just easier to change both pieces.

Seriously, if you want this as a DD and you don't plan any performance mods, I suggest going to RockAuto and buying the stock front y-pipe with cat (WALKER Part # 15749), stock rear y-pipe (WALKER Part # 40404) and stock style mufflers (WALKER Part # 22396 & 22397). It will probably cost about $600 in parts and the car will be quiet.

You can swap out the exhaust in your driveway with the car on stands. I would suggest spraying the bolts on the manifolds with some PB Blaster to loosen them up, that will probably be the hardest part of the job. If you keep with the same brand, everything should fit and you won't have many problems.

 

Superb advice, more than I could have known to ask for.

Happy to tinker around in my garage, so far no other major problems.
Switched A/C to r134 already, cleaned out fan and ducts and around evaporator.
Replaced most of the weather-stripping.
Took out the fuel pump, the plastic well in the bottom of the tank is still there, cleaned the contacts on the fuel level sender unit, working great so far.
New struts for the hood and hatch in.
Changed all the fluids.

I think I will go with the Rock Auto/Walker set up, hope to still see a performance improvement getting the old pre-convertors (yes, I have 'em) and the disintegrating main convertor out of the way. Thank you all again!