C3 73

I have a '73 base model with auto transmission, the engine was swapped at some point in it's history for a '78 C-20 350, I think it has a little more aggressive cam, but it's choked by a eco Edlebrock carb and manifold that were designed for low end torque (suiting for a pickup truck). I intend to upgrade the intake system at some point in the near future.

However, the exhaust is in need of replacing now. Some PO installed glass-packs (in addition to Thrush mufflers) that terminate right under the differential, subtracting about an inch of ground clearance. That along with a broken exhaust bracket cause the glass-packs to drag any time I hit a bump, and they are dinged, dented, and have a couple of small holes already.

I am looking at a true dual, 2-1/2" exhaust system (probably from Corvette Central, they seem to have the most recommendations here) with ceramic coated 2-1/2" rams-horn manifolds, and Magnaflow mufflers. The problem I am having is trying to figure out which CC exhaust system will work. I am new to Corvettes and don't yet know all the model year differences. All the 2-1/2" systems for a '73 have a reducer from the manifold to the down pipes. Will another year that is full 2-1/2 work? Or should I get a muffler shop to remove the 2" section make the connection? Can someone recommend the model number from CC that will work?

I want to stay with dual exhaust system, but am considering catalytic converters, I can barely stand the exhaust stink as it is now. Does anyone know if its possible to add one to each down pipe, or somewhere else?

P.S. - I did go by and talk to a local shop who does a fair amount of classic cars and he recommended buying an Eckler's (or Corvette Central) system, as it would be very expensive and time-consuming for him to do a custom system.

JC 1975

An improperly tuned carburetor will kill a catalytic converter fast.

• Carburettor systems – A worn or defective carburettor can cause a catalytic converter to overheat. Problems such as improper float or air/fuel mix adjustments and worn metering rods can damage the catalytic converter. The choke system also needs to be operating properly so the right level of fuel enters the system. If too much fuel enters the system it will overheat and eventually fail.

https://www.catalyticconverters.com/...ic-converters/

You could always put a Holley Sniper type fuel injection on it and then cats…. However, you could still get a smell. I have a ‘13 Mustang GT that’s all stock (and no, I don’t drive it to cars and coffee) and on cold starts it can stink up the garage bad…

ddawson

Hey NorCal.

The cut off seems to be 68 to 72, then a different exhaust for a 73. For 73 I don't see a Magnaflow system. Not sure why the 73 is a different system.

You could use the Magnaflow full exhaust. https://www.summitracing.com/parts/m...ette/year/1973

On the CC systems my 427 Four speed system was a 2.5 to 2" at the mufflers. I have headers so I had a shop make me pipes from the header to the transmission cross member. Wasn't expensive for such a short run.

So my 2 cents NO cats. Get a new carbonator and set it up properly. Buy a wideband and have the bung welded in. This with a good vacuum gauge you can dial in the correct A/F. My C3 was so bad no one wanted to be behind me. After my cloths don't stink and my eyes doesn't water LOL.

Mdbirk

I bought a full 2 1/2 in exhaust system from Corvette central last year during a free shipping promotion. I highly recommend them. Took 45 mins to install.

carriljc

C3 73
Pretty sure this is what you want to do. This fit great on mine and it had not had a stock system since I bought 3+ decades ago. BUT really, I would recommend going to a pass-under tranny crossmember anyway..... Last year I ended up going to a pass-under.

Here. Go read this. You can install 2.5" ramhorns and use 2.5" 64-65 downpipes that do NOT neck down and then the rest of the 2.5" exhaust to the back.
My exhaust pipes were all labeled Corvette Central and they fit like a dream on my 50+ year old car that used to have headers and a fabricated exhaust system. You can see where I got the parts in the thread. Depending on shipping rates I would order from different places and it is mentioned in the thread.
It includes part numbers and all (for my 68) so you wanna make sure you get what you want for your year.
https://www.corvetteforum.com/forums...post1598185200

C3 73

Good points! Maybe I should hold off on the catalytic converters until I get the intake system squared away. Already contacted Lars about rebuilding a Quadrajet. Thanks for the link, good info.

C3 73

Hey Fellow Norcal!

I didn't see a Magnaflow system on Corvette Central either, I found the different part numbers for the various pieces and would buy the mufflers separately. Hopefully someone else can give a clue about the various model year differences and which parts can be used on different model years.
You threw my for a loop when you mentioned carbonator, went searching for that then realized autocorrect probably turned carburetor into carbonator! LOL
Yes, my clothes stink for days and my eyes and throat burn. It's amazing people complain about all the advances in technology that prevent that from happening and yet still produce 1,000 hp engines!

onaqwst

https://highfloperformance.com/colle...ffler-system-1

I did a system similar to this... trying to find the vendor. I didn't have the X pipe in my kit.
lowered 1977

C3 73

That's what I've heard about CC. Did you have access to a lift when you installed your system? Did the 1968 models come with 2-1/2" exhaust pipes? If not,, what year downpipe did you order for yours?

Mdbirk

No lift. Click on the link below, that's the exhaust you'll need.

Mdbirk

https://www.corvettecentral.com/c3-6...f%3fcount%3d44

Mdbirk

Sorry this is the one you need

https://www.corvettecentral.com/c3-6...f%3fcount%3d44

carriljc

C3 73
Don't buy a straight kit. Since you're going to install 2.5" RamHorns get the 64-65 2.5 downpipes (they don't neck-down to 2" like the regular ones for your year). See the post #5 above -- it has part numbers and whatnot.

you can see here what I'm talking about....but start at the beginning for the whole story. https://www.corvetteforum.com/forums...post1598259107

C3 73

Unfortunately, both the systems you provided the links to are the ones that have the 2" manifold connectors that then expand to 2-1/2". I want to find the full 2-1/2" down pipes that will work with a '73 auto to connect to 2-1/2" ramshorns. Any ideas on which ones I'm searching for? Thanks for trying and for the help!

Jebbysan

Just remember that the Magnaflow exhaust for these has a 2" outlet of the muffler to accommodate stock tips......the inside of the muffler is 2.5" though so the tip can be cut off and a new 2.5" welded on and the tips modified.........a member here Chris Hewitt I believe did this to his slightly modified L-71 427 car with very good results......
After doing all the work to get 2.5" out the back you do not want it corked up like that....it is a restriction....although a guy a Corvette Central told me 10 years ago some BS about the exhaust being cooler back there and it didn't matter........I wonder how these tidbits of info get started?

Jebby

drwet

I highly recommend the Corvette Central system. It has all the little tweaks and bends for maximum ground clearance. Not sure how you get a full 2" system or if it is even possible. My '79 has their full dual system (I believe it is Part # 323737 but it's been under there a long time) but I have done some modifications to it over the years. The right pipe was moved over to clear the 700R4 when I had that trans in there. The system is connected to Hooker Super Comp headers so that eliminated the 2" part of the system, and high flow catalytic convertors fit very nicely behind the crossmember. I also have a balance pipe just behind the crossmember and in front of the cats to mellow out the sound. That is also highly recommended. The stock mufflers are plenty loud enough for me. I can't imagine going to the Magnaflows.
I don't recommend a custom system. I have never seen one that I thought was half as good as the Corvette Central setup.
As an added bonus, the Corvette Central system came with a lifetime warranty when I bought it, although I don't see any mention of that on their website now. I actually made a claim on that warranty a few years back when my mufflers rusted out. I didn't even know about the warranty until I looked up the replacements. I still had the original invoice in my file, so I sent the old mufflers back fully expecting to get some excuse from them, especially considering they had been on the car for about 20 years. But they were as good as their word, and sent me a new set of mufflers. So now Corvette Central is my first choice in parts.

C3 73

Thanks for all the advice drwet (and everyone else at that!) I think I will have to ask the local muffler shop I talked to if he can replace the 2" section with a 2-1/2.

Am I reading it right that you have 2 cats on your car? What size are they? How much ground clearance do you have? Would like to put some on mine at some point, the exhaust smell is killing me! As someone pointed out before, I have to get the intake system figured out and running lean enough first.

carriljc

C3 73
LOOK
here are the 2.5" downpipes that you can bolt directly onto 2.5" ramhorns. there is no need to modify anything.

drwet

Yes I have two cats. They are universal fit 2 1/2" units from Rock Auto. They have lots in various sizes. I just cut a section out of each side and welded them in. Not sure how big the ones I have are but they tuck up pretty good. They aren't the lowest thing under the car.

drwet

I have the car in the air to do a couple of maintenance items. Here are some photos of my exhaust. I won't apologize for the oil and dirt. I drive this thing.