Question: 1981 Dual exhaust

[andypriest]

Hi all, Sorry if this is a question that has been done to death before but I am new to the forum. I want to replace my stock exhaust with a dual system from corvette central.
If I leave the air pump etc in place can I just disconnect and cap the air line to the existing cat when i remove it? If I later wanted to install 2 hi flow cats in the dual system
would I need to connect an air line to them? If so could the existing air line just be split and run to both cats? Apologies if this is a dumb question.
Thanks for any help.
Andy

 

[melsy]

Back in the day I had a an auto '81 and installed duals on it without the Cat. Made absolutely no difference in performance or gas mileage that I could feel. But, I was also still running the computer controlled carb. Hope this helps.

 

[andypriest]

Back in the day I had a an auto '81 and installed duals on it without the Cat. Made absolutely no difference in performance or gas mileage that I could feel. But, I was also still running the computer controlled carb. Hope this helps.

Thanks Melsy. There seems to be a mixed response on wether or not they make any improvement. Some say yes and some say no. However my old system needs replacing and I like the sound of this system.
Andy

 

[Wajulia]

I cant help you here because I have not changed mine yet. Let us all know if you think there is any difference. I am thinking of just going with a new high flow cat on the single exhaust. Assures that the cat is breathing well, which I doubt now with my original 30 year old cat.

 

[andypriest]

Fitted

Finished fitting dual exhaust today. Had to fabricate mounts but no big deal. Not much louder than original but does seem to have more power. Maybe because I removed original cat that was more than likely clogged or maybe is breathing a lot better. Won't know about any possible milage improvements for a while yet.

 

[berry1133@bellsouth.net]

I did the same with mine a couple weeks back. One of the previous owners had replaced the single cat with dual cats. When I took them off, I found that the were both all broken up inside. I couldn't see any daylight when looking through and the guts were just falling out of the cats. Needless to say, I fell in love with my car all over again. Performance has improved tremendously. And, my tach gauge was very jumpy after 2000 rpm's. Now it's steady as ever and at about 80 mph, I'm at only 3000 rpm's. She's purring like a kitten now. And my new magnaflo's really sound good.

 

[terry82]

I cant help you here because I have not changed mine yet. Let us all know if you think there is any difference. I am thinking of just going with a new high flow cat on the single exhaust. Assures that the cat is breathing well, which I doubt now with my original 30 year old cat.

take off your old cat and open it up with a long rod .take out all the bad stuff and put it back on.it will cost nothing, then decide if you want buy a new cat.if your cat is original it is plugged up .they were not good even when new.putting on a new dual exhaust will give some improvment but a open cat will help a lot.

 

[Evolution1980]

Finished fitting dual exhaust today. Had to fabricate mounts but no big deal. Not much louder than original but does seem to have more power. Maybe because I removed original cat that was more than likely clogged or maybe is breathing a lot better. Won't know about any possible milage improvements for a while yet.

Welcome to the , Andy!

I'm not overly familiar with the airpump setup on the 81's and if has any direct tie-ins with the E4ME carb on your car. (I'm assuming you have the OEM stock carb.) Did you end up with cat(s) on your new setup or did you skip them altogether? What about your air pump? Did you just plug the hose?
And when you say "dual exhaust", do you mean that you still maintained the OEM front & rear y-pipe setup?

 

[andypriest]

Welcome to the , Andy!

I'm not overly familiar with the airpump setup on the 81's and if has any direct tie-ins with the E4ME carb on your car. (I'm assuming you have the OEM stock carb.) Did you end up with cat(s) on your new setup or did you skip them altogether? What about your air pump? Did you just plug the hose?
And when you say "dual exhaust", do you mean that you still maintained the OEM front & rear y-pipe setup?

Yes stock carby and distributor. New set up is two pipes straight back to magnaflow mufflers with no cats. At the moment I just removed the air line from the pump to the old cat and have taken the air pump belt off. I'll remove the rest later.
Set up does feel more responsive and sounds better but no very loud. I'll do some sound level checks this weekend.

 

[Evolution1980]

Yes stock carby and distributor. New set up is two pipes straight back to magnaflow mufflers with no cats.
Set up does feel more responsive and sounds better but no very loud. I'll do some sound level checks this weekend.

So you're running pipes directly from your exhaust manifolds straight back to each side? That should open things up a bit for you. However, if you are running the stock exhaust manifolds, they are very restrictive. Replacing those with some headers will give you that sound and performance bump you're expecting / looking for. If most of the engine is stock, stick with headers that have smaller primary tubes.

 

[andypriest]

So you're running pipes directly from your exhaust manifolds straight back to each side? That should open things up a bit for you. However, if you are running the stock exhaust manifolds, they are very restrictive. Replacing those with some headers will give you that sound and performance bump you're expecting / looking for. If most of the engine is stock, stick with headers that have smaller primary tubes.

Yes still running stock manifolds. I was under the impression that the stock manifolds were quite efficient on the '81. May look at headers in a while but I'll live with this system for now and see how it goes.
Andy

 

[terry82]

i have seen the inside of the factory headers.they are small .they also have a small tube in there for the emissions.what i want to do is buy mcjacks headers .they are easy bolt on .no restrictions ,better made and i think larger .problem they are not cheap .if money is a problem [my problem]take the old headers off take out the tubes clean up the inside [then maybe ceramic coat]that should help some .

 

[Evolution1980]

i have seen the inside of the factory headers.they are small .they also have a small tube in there for the emissions.what i want to do is buy mcjacks headers .they are easy bolt on .no restrictions ,better made and i think larger .problem they are not cheap .if money is a problem [my problem]take the old headers off take out the tubes clean up the inside [then maybe ceramic coat]that should help some .

I've had good luck with Hedman and Hooker headers. I have Hooker's in my car right now. (always tricky to say that without smiling).
I recommend getting your parts treated by Jet-Hot. (Might be a little more costly for Andy in AU.)
They will ceramic coat your parts and give them a lifetime warranty. For a while, they were selling Hooker headers for a our cars already treated with their top of the line coating (looked like chrome, but better durability). And they were selling them cheaper than what regular coated Hooker headers were selling from from other retail outlets like Summit Racing. (Example)
If you don't need fancy looking headers for your '81, then these should work fine. However, I speak from experience when I say that the non-ceramic coated (re: standard flat black) headers get really ugly after one or two years. It goes from a flat black to speckled brown rusty lookin' things.

 

[Tom Bryant]

The '81 manifolds are 1 1/2" stainless tubes with a 2" outlet. The '82s are 2 1/2 outlet; not sure of the tube size.

Picture 2 shows a stock flange (rt) with it's excess of weld restricting flow. These 81s are much worse than the ones on my wifes '81. The flange on the left is the other side after I removed the AIR tubes and the excess weld. There is still plenty of weld holding the tubes to the flange. I also found a lot of cracks in the weld where the tubes collect. This was probably the worse ones I have seen. Must have been the guy's first day on the job.

Picture 1 is on the engine after the welding and with Eastwood Stainless Exhaust Coating applied. It cures with heat.

Pictures 2 and 3 show the finished manifolds on my '69 stepside. It's a 355 with cam and ported iron heads. These manifolds should be quite addequate given the rpm range of the engine and the full dual exhaust that is pretty much straight through with a 2 1/4 " X pipe and 2 1/2" mufflers and tail pipes.