1971 2"-2.5" exhaust system
Thread Starter
Intermediate
Joined: May 2001
Posts: 38
Likes: 0
From: New York
1971 2"-2.5" exhaust system
I currently have the stock 2" on my 350/270hp. Would like to replace with the 2" >2.5". A couple sites list it as an LT1 system. Has anyone already done this? Was ther any noticable differences? What else is needed besides the pipes and mufflers?
Le Mans Master
Joined: Jan 2001
Posts: 6,743
Likes: 1,385
On my 68 I installed 2.5" ramhorns, 64-65 2.5" downpipes, and then the rest of the 2.5" system all the way back including the mufflers.
Give me a few and I'll find the link.
I bought from several different places for the best prices with parts and shipping.
Be right back.
Give me a few and I'll find the link.
I bought from several different places for the best prices with parts and shipping.
Be right back.
Le Mans Master
Joined: Jan 2001
Posts: 6,743
Likes: 1,385
Here you can see.
You need the center support and 2.5" clamps. See below and there's lots of information and part numbers and whatnot:
https://www.corvetteforum.com/forums...post1598185200
You need the center support and 2.5" clamps. See below and there's lots of information and part numbers and whatnot:
https://www.corvetteforum.com/forums...post1598185200
Last edited by carriljc; Jan 30, 2021 at 08:09 PM.
Race Director
Joined: Oct 2008
Posts: 19,234
Likes: 1,672
From: Long Island
I've been toying with the idea on my 71. Was just wondering if you felt or saw any increase in performance.
I figure the exhaust will need replacement this summer.
I was looking at speedway for the ram horns.
Did anyone look at the walker exhaust gasket / donut , looks flat on the bottom and tapered on the other side. for the drivers side.
Walker Exhaust 31398 Walker Exhaust Flange Gaskets | Summit Racing
I figure the exhaust will need replacement this summer.
I was looking at speedway for the ram horns.
Did anyone look at the walker exhaust gasket / donut , looks flat on the bottom and tapered on the other side. for the drivers side.
Walker Exhaust 31398 Walker Exhaust Flange Gaskets | Summit Racing
Last edited by BLUE1972; Jan 29, 2021 at 11:09 PM.
Old Pro Solo Guy
Joined: Dec 2017
Posts: 8,095
Likes: 4,449
From: Marlton NJ
Yes the stock LT1s still used the standard 2" opening rams horn manifolds. So the original header pipes were 2" opening and within 6 inches or so grew into a 2.5" pipe. I am not sure if there was a weld there or if the pipe was just re-sized. There were some 2.5" rams horns made sometime in the mid 60s on some of the C2 engines. IIRC those are being reproduced today. Hopefully the C2 header pipe would work for you. 64-65 maybe? 327/365 or 327/375 models?
Last edited by leigh1322; Jan 30, 2021 at 01:09 PM.
Le Mans Master
Joined: Jan 2001
Posts: 6,743
Likes: 1,385
You can use the 64-65 2.5" downpipe with 2.5" ramhorns. see my comment above and the link where I did it.
Yes the stock LT1s still used the standard 2" opening rams horn manifolds. So the original header pipes were 2" opening and within 6 inches or so grew into a 2.5" pipe. I am not sure if there was a weld there or if the pipe was just re-sized. There were some 2.5" rams horns made sometime in the mid 60s on some of the C2 engines. IIRC those are being reproduced today. Hopefully the C2 header pipe would work for you. 64-65 maybe? 327/365 or 327/375 models?
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
If you install 2.5" pipes on a stock 270hp SBC, you will notice ZERO difference. That engine doesn't need 2.5" pipes to breathe; its "lungs" are too small. Save your money.
Now, if you decide to install much better heads and cam, THEN you should up the exhaust size.
Now, if you decide to install much better heads and cam, THEN you should up the exhaust size.
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Pro
Joined: Aug 2000
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From: Vancouver B.C.
I recently installed a 2.5” Corvette Central complete exhaust system with Magnaflow mufflers on ram horns. Went from 2” system. I initially had clearance issues where the pipe goes through frame crossmember. Had to get a new tranny mount. My factory original mount was in there and had compressed over time causing the clearance issue. Just a heads up. I can’t comment on power definitively cause I changed heads and cam as well. It is much louder than I thought it would be with the Magnaflows and 2 1/2” pipes.
Race Director
Joined: Oct 2008
Posts: 19,234
Likes: 1,672
From: Long Island
Yes the stock LT1s still used the standard 2" opening rams horn manifolds. So the original header pipes were 2" opening and within 6 inches or so grew into a 2.5" pipe. I am not sure if there was a weld there or if the pipe was just re-sized. There were some 2.5" rams horns made sometime in the mid 60s on some of the C2 engines. IIRC those are being reproduced today. Hopefully the C2 header pipe would work for you. 64-65 maybe? 327/365 or 327/375 models?
64 - 65 327 / 365 had 2.5" - factory , same frame so they fit.
Just wondering if a 400 hp engine will benefit enough to make it worth wile
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
Here you can see.
You need the center support and 2.5" clamps. See below and there's lots of information and part numbers and whatnot:
https://www.corvetteforum.com/forums...post1598185200
You need the center support and 2.5" clamps. See below and there's lots of information and part numbers and whatnot:
https://www.corvetteforum.com/forums...post1598185200
Unless you are going long tube header...this is what I would do......and it is most definately worth power on the 350.......the 2" Rams Horn is a cork.....the 2.5" is much better but still not optimal.
On the factory stuff....the 2" outlet was small enough, then GM bent the front pipes with a heavy kink in them......terrible design. And as far as no gain? Take a look at any new 2.4/2.5l 4 cylinder nowadays......tell me what size the outlet is......part of the reason the 270hp made 270hp is the damn manifolds.....you can put long tube headers on this engine and gain 25hp........the 2.5" outlet is worth 15 by itself.....
Jebby
Last edited by Jebbysan; Feb 1, 2021 at 08:24 AM.
Burning Brakes
Joined: Oct 2020
Posts: 1,149
Likes: 265
From: The frozen wastes...
Unless you are going long tube header...this is what I would do......and it is most definately worth power on the 350.......the 2" Rams Horn is a cork.....the 2.5" is much better but still not optimal.
On the factory stuff....the 2" outlet was small enough, then GM bent the front pipes with a heavy kink in them......terrible design. And as far as no gain? Take a look at any new 2.4/2.5l 4 cylinder nowadays......tell me what size the outlet is......part of the reason the 270hp made 270hp is the damn manifolds.....you can put long tube headers on this engine and gain 25hp........the 2.5" outlet is worth 15 by itself.....
Jebby
On the factory stuff....the 2" outlet was small enough, then GM bent the front pipes with a heavy kink in them......terrible design. And as far as no gain? Take a look at any new 2.4/2.5l 4 cylinder nowadays......tell me what size the outlet is......part of the reason the 270hp made 270hp is the damn manifolds.....you can put long tube headers on this engine and gain 25hp........the 2.5" outlet is worth 15 by itself.....
Jebby
2" pipe, even mandrel bent, is enough to flow a stock 200HP V6. Maybe. 2.5" mandrel should be considered MINIMUM. Why are we even still having this conversation? Exhaust technology has come a LONG way in 40-50 years.
Old Fart Pilot
Joined: Apr 2010
Posts: 1,925
Likes: 995
From: Spokane, WA
After reading all this and considering WAY too many options, I just ordered forum vendor Corvette Central's 323710-MAG exhaust system for my '71 SB. It's aluminized steel, 2" @ manifold necking right up to 2-1/2" for the remainder of the system. I went with the seperate pipe pieces which then mate to Magnaflow mufflers rather than the welded system. My rationale was since this is what the LT-1 had, it should be better than the all 2" system that was originally on my car. My mildly upgraded rebuilt 350 should breath better and this still allows for future upgrades such as 2.5" ram horns and '65 2.5" down pipes connecting to the remainder of the CC 2.5" system. Who knows, might even get headers one future day, but for now I just wanted to get the parts ready for easily getting her back on the road. $427 (incldg 10% discount) + $60 flat rate shipping.
Last edited by nwav8tor; Feb 2, 2021 at 06:51 PM.
Burning Brakes
Joined: Oct 2020
Posts: 1,149
Likes: 265
From: The frozen wastes...
After reading all this and considering WAY too many options, I just ordered forum vendor Corvette Central's 323710-MAG exhaust system for my '71 SB. It's aluminized steel, 2" @ manifold necking right up to 2-1/2" for the remainder of the system. I went with the seperate pipe pieces which then mate to Magnaflow mufflers rather than the welded system. My rationale was since this is what the LT-1 had, it should be better than the all 2" system that was originally on my car. My mildly upgraded rebuilt 350 should breath better and this still allows for future upgrades such as 2.5" ram horns and '65 2.5" down pipes connecting to the remainder of the CC 2.5" system. Who knows, might even get headers one future day, but for now I just wanted to get the parts ready for easily getting her back on the road. $427 (incldg 10% discount) + $60 flat rate shipping.
I'd upgrade to those 2.5" manifolds and headpipes before you even put it on. That Corvette company should not even be making those 2" drinking straws.
Old Fart Pilot
Joined: Apr 2010
Posts: 1,925
Likes: 995
From: Spokane, WA
You do realize that a system is only as big as its smallest section, right? Even a full 2 1/2" press-bent system is often less than 2" in some ov the bend areas. The engine/exhaust doesn't care how big the tips or the undercar pipes are, only the most restrictive points.
I'd upgrade to those 2.5" manifolds and headpipes before you even put it on. That Corvette company should not even be making those 2" drinking straws.
I'd upgrade to those 2.5" manifolds and headpipes before you even put it on. That Corvette company should not even be making those 2" drinking straws.
As for "that corvette company should not even be making those 2" drinking straws" comment, have you ever heard of people trying to keep their cars as original as possible? Not everbody is solely concerned about maximizing performance...
Paul
As for
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
So, I'm no expert and I don't know what your qualifications are, but I have to assume that the Chevrolet designers & engineers that worked on the LT-1 models had a reason for using the 2.5" pipes after the 2" manifold and I bet it wasn't to impede performance. Using your comment about the smallest section being the most restrictive, that may be somewhat true, but I still bet you that a 2.5" system with bends taking it down to a smaller diameter in places will flow better than a 2" syatem with bends reducing that system down even further.
As for "that corvette company should not even be making those 2" drinking straws" comment, have you ever heard of people trying to keep their cars as original as possible? Not everbody is solely concerned about maximizing performance...
Paul
As for
As for "that corvette company should not even be making those 2" drinking straws" comment, have you ever heard of people trying to keep their cars as original as possible? Not everbody is solely concerned about maximizing performance...
Paul
As for
2.5” outlet manifold on an LT-1 are worth 15-20 upstairs and a long tube header is worth 30 or better....this is through full exhaust at the tire....
It also just runs crisper with the exhaust uncorked....the LT-1 cam has a lot of overlap....the more overlap, the more crucial good exhaust is....
The 66’ in the Avatar has 2.5’s on it because it moved a lot of air.....it was worth it.
Jebby
Burning Brakes
Joined: Oct 2020
Posts: 1,149
Likes: 265
From: The frozen wastes...
They also had a reason for using complete garbage bias-ply tires and points ignition. Thats what was 'hot' and available (for reasonable cost) at the time. Doesn't mean its not useless garbage now. They didn't know any better, and as Jebby said, were likely trying to save money. How many (literal) miles ov that pipe did Chevrolet have to buy? 2" is a decent amount cheaper than 2.5". Besides... like the hot 427 cars with those horrible manifolds... they expected anyone wanting real performance to toss them for headers at the earliest convenience.
Advanced
Joined: Oct 2023
Posts: 71
Likes: 1
I recently installed a 2.5” Corvette Central complete exhaust system with Magnaflow mufflers on ram horns. Went from 2” system. I initially had clearance issues where the pipe goes through frame crossmember. Had to get a new tranny mount. My factory original mount was in there and had compressed over time causing the clearance issue. Just a heads up. I can’t comment on power definitively cause I changed heads and cam as well. It is much louder than I thought it would be with the Magnaflows and 2 1/2” pipes.