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I am starting to figure out a plan for the rear exhaust on my 1973 LS3 conversion project. The goal is to have the best performance with the least amount of noise. I have the the LS3 manifolds and plan on using them, also plan on using the stock intake as well so I don't think I need any fancy headers for better flow. My plan is to get the 2½ rear (or intermediate, pipes - the ones that run back from the center crossmember) and 2½ inch mufflers, and will fabricate the pipe from the manifold back to the cross member. I have seen where people have fabricated brackets that attach to the rear side of the crossmember to replace the stock bracket that is bolted on as part of the transmission mount. My car was originally a 4 speed, putting in the TR6060, not sure that it being an original 4 speed car matters much. Having said that, what is the difference between the 2½ auto and 2½ manual rear exhaust pipes, if there is a difference is there an advantage to using one over the other?
So I didn't use anything from the 71 vert here's what I did.
From the headers I did 2.5" mandrel bend pipes. Mine was a 4L60E so you may a bit more clearance as you aim towards the stock? cross member.
My 40 years ago muffler guy would say don't attach any brackets until you get to the mufflers. Keeps any vibes away from exhaust
So I buy a bunch of mandrel bend tubes. 2.5" and route the exhaust kind of like the stock routing. Second mounting point after the mufflers was the rear axle housing. Then again using more mandrel bend tubes to 2.5' Dyno super turbo mufflers. Sounded great. Not too loud.
I really don't like the crimp tube exhaust bender stuff.
I don't have a lift so I spent a great amount of time on the creeper. Kind of relaxing after a long day at the office.
Good luck with your project.
So I didn't use anything from the 71 vert here's what I did.
From the headers I did 2.5" mandrel bend pipes. Mine was a 4L60E so you may a bit more clearance as you aim towards the stock? cross member.
My 40 years ago muffler guy would say don't attach any brackets until you get to the mufflers. Keeps any vibes away from exhaust
So I buy a bunch of mandrel bend tubes. 2.5" and route the exhaust kind of like the stock routing. Second mounting point after the mufflers was the rear axle housing. Then again using more mandrel bend tubes to 2.5' Dyno super turbo mufflers. Sounded great. Not too loud.
I really don't like the crimp tube exhaust bender stuff.
I don't have a lift so I spent a great amount of time on the creeper. Kind of relaxing after a long day at the office.
Good luck with your project.
Thanks. I think I will stick closer to my plan. I have the mufflers and rear pipes on their way and got some mandrel bend tubes locally to start mocking up the front pipes. I think with a 90° turn from the manifold and then a couple small bends in a straight piece I should be able to get it to meet up with the rear pipe. The car came with at set of 2" stock pipes and mufflers so I have been able to lay them out and get a feel for what I need to do to get them to match up. I am getting the mufflers/pipes from Corvette Central, which I am told are a good choice for performance and low noise.
So I didn't use anything from the 71 vert here's what I did.
From the headers I did 2.5" mandrel bend pipes. Mine was a 4L60E so you may a bit more clearance as you aim towards the stock? cross member.
My 40 years ago muffler guy would say don't attach any brackets until you get to the mufflers. Keeps any vibes away from exhaust
So I buy a bunch of mandrel bend tubes. 2.5" and route the exhaust kind of like the stock routing. Second mounting point after the mufflers was the rear axle housing. Then again using more mandrel bend tubes to 2.5' Dyno super turbo mufflers. Sounded great. Not too loud.
I really don't like the crimp tube exhaust bender stuff.
I don't have a lift so I spent a great amount of time on the creeper. Kind of relaxing after a long day at the office.
Good luck with your project.
I will post a link to my thread on my exhaust system. To many pictures. Now this I have to say there is probably no better built exhaust system for an LS swap. My car was the prototype for American Racing headers for an LS swapped early C3. I trailered my car to their shop and they spent about 3 weeks with the headers. They asked if I wanted the entire system built by them I said absolutely. So this is a very high dollar system and it goes from 3 inch and they necked it down to 2 1/2 as it goes through the crossmember so you can’t really tell. This system will hold about 750 HP according to AR. Overkill but it is damn nice.
No pics of mine but I did try to do 3" thru the stock cross member and it was just too tight. If I did it again I would mod the stock cross member for 3" to the mufflers. Then 2.5" to the mufflers. Mine was only a stock LS1 so 2.5" was fine.
Thought this N93476 would be perfect. The picture on Amazon says it's 26 1/2" fully compressed, I needed somewhere around 29 1/2". However, the description was wrong and it turned out being 261/2" fully extended. After going back and forth with CRS, I came to the conclusion that they're just a re-seller for some Chinese driveshaft manufacturer. I couldn't seem to get a quick answer, and my emails were only immediately responded to at 9:00 pm EST. I checked with the Cardone seller...same thing, they didn't seem to know what they were selling. I thought about going down to the local AutoZone who sells CRS or Advance who sells Cardone but since every question you ask there seems to be met with "what's the year make and model" and no-one seems to know how to use a parts book anymore, I decided otherwise.
Thought this N93476 would be perfect. The picture on Amazon says it's 26 1/2" fully compressed, I needed somewhere around 29 1/2". However, the description was wrong and it turned out being 261/2" fully extended. After going back and forth with CRS, I came to the conclusion that they're just a re-seller for some Chinese driveshaft manufacturer. I couldn't seem to get a quick answer, and my emails were only immediately responded to at 9:00 pm EST. I checked with the Cardone seller...same thing, they didn't seem to know what they were selling. I thought about going down to the local AutoZone who sells CRS or Advance who sells Cardone but since every question you ask there seems to be met with "what's the year make and model" and no-one seems to know how to use a parts book anymore, I decided otherwise.
Thanks for the information, I was hoping you would find the 'magic bullet' and I would use that as well. Currently the plan is to take the shafts that came with the engine and the original drive shaft and see if the local driveshaft place can make something that will work for me.
Well I'm still working at it. I'm trying to avoid having to go to the local machine shop and have one made up. It has to have a slip joint in it I'm pretty sure, so I'll probably order couple other drive shafts see if those fit if I find one I'll let you know
I made some progress on the exhaust this evening, the mufflers, tips and rear pipes arrived from Corvette Central and I got the LS3 flanges a couple days ago. I think this should clear everything under the car, I was able to use my '69 and '75 as references along with the original 2" front pipe that came with the car. I bought a box full of 2.5" bends from NAPA and was able to piece this together. I have about a 2" extension coming out of the flange, going into a 90, then into a 45 that goes into a nice offset piece they have. Will try to finish up the driver's side over the weekend.
My exhaust guy was unwilling to weld up my system unless I brought the chassis in with the body temporarily in place. Are you the welder, Scott? Looks like you've already committed yourself!
About your fuel pump, what's your plan for vibration isolation, if I may ask. Just that rubber sleeve?
My exhaust guy was unwilling to weld up my system unless I brought the chassis in with the body temporarily in place. Are you the welder, Scott? Looks like you've already committed yourself!
About your fuel pump, what's your plan for vibration isolation, if I may ask. Just that rubber sleeve?
I am the welder and everything else as well! The body is hanging in the garage where I can easily measure and I have 2 other C3s for reference, so I think I am at least close, if not I will try again.
Just planning on the rubber sleeve for the pump, is there anything else I should consider?
Just planning on the rubber sleeve for the pump, is there anything else I should consider?
I've got my car up on a lift right now. I'll take a look at what access looks like from where yours is. Mine is on the back crossmember. Not great but I can get at it if need be.
Update for you. Not a great picture, but here's what I see of your mount location with everything in place. I would recommend you make it easy to drop that muffler.
I put everything on the rear crossmember. I've got a sleeve like yours and another rubber isolator between that bracket and the frame. One the motor starts I don't hear anything.
I'm carbureted. I wonder if you've considered the in-tank configurations.
I've got my car up on a lift right now. I'll take a look at what access looks like from where yours is. Mine is on the back crossmember. Not great but I can get at it if need be.
Update for you. Not a great picture, but here's what I see of your mount location with everything in place. I would recommend you make it easy to drop that muffler.
I put everything on the rear crossmember. I've got a sleeve like yours and another rubber isolator between that bracket and the frame. One the motor starts I don't hear anything.
I'm carbureted. I wonder if you've considered the in-tank configurations.
Thanks for the pictures. I contemplated the in-tank options but I saw that other people had made this work so I went with this option. I do not have the one piece welded rear pipe/muffler setup, so if I take off 2 u-bolts I can drop the muffler to get at the pump.
I have the front pipes fabricated, where is the best place to locate the bungs for the O2 sensors? It seem like putting them right below the manifold point forward would be the best option, any thoughts on that?
01-18-2019, 08:44 PM
1973 LS3 Swap - Rear Exhaust Considerations
