I am in the process of planning to replace the headers and rusted/welded exhaust system.

The car is a 70 roadster with 350/350 4 speed. This means that it had a 2" exhaust system from GM. How much of a difference in performance is there between the 2" and 2 1/2" (LT1) system. I will not be running the car hard. Will he difference be felt in the seat of the pants?

How big a difference in the sound of the exhaust will there be?

Thanks!

I’m not sure about 1970 but in 1974 the exhaust manifold is 2” but the pipes, mufflers, etc. were all 2.5”. If yours is similar it sounds like a previous owner had the system replaced by a muffler shop that did not know Vettes. To be absolutely correct you should probably be replacing the pipes with 2.5”.

BTW - nice looking car

|UPDATED|2/17/2004 9:58:24 AM (AZT)|/UPDATED|

if indeed factory was 2 inch, and you replace it with 2.5 inch, you will notice a difference. With the hp you have i would think that it would certainly be reasonable to go with the 2.5 inch. I went with 3 on my 454 over the stock 2.5 and it made quite a difference. Hope this helps.

The last true 2.5" exhaust for a small block was in 65 (I mean C2/C3). Even the LT1 350s with 2.5" exhaust had 2" at the manifolds and quickly jumped up to 2.5". My guess is that for a basically stock car you will notice little difference. I have C4 TPI manifolds on mine which have a true 2.5" outlet. The bigger the pipe, the more trouble you will have with rattles where it goes through the transmission crossmember.

Spike74 said: I’m not sure about 1970 but in 1974 the exhaust manifold is 2” but the pipes, mufflers, etc. were all 2.5”. If yours is similar it sounds like a previous owner had the system replaced by a muffler shop that did not know Vettes. To be absolutely correct you should probably be replacing the pipes with 2.5”.

My '70 350/300 had the orignial pipes on it until I replaced the entire system and they were 2" from manifold to muffler. I upgraded to 2.5" chambered exhaust and feel (and hear of course) a big difference overall.

I am keeping the car pretty original.

Do the chambered pipes sound just like the side pipes?

I have to admit that side pipe sound is the bomb!

How quite were the stock 2" pipes?

The sound would be the same, but side pipes would seem louder because they're on the side of the car. I wanted to get a chambered system for my '80 but they only make a kit to fit up to '79.

"The Toy" is a 350ci/300hp and originally had 2.0" all the way (manifolds, pipes, & mufflers) when I bought it. When I replaced the pipes and mufflers a couple of years ago I went with a stock 2.5" setup from Corvette Central (I think).

I stayed with the 2.0" manifolds so got the pipes that have the 2.0" manifold connection but then fill out to 2.5" right away. I didn't realize until after hanging the mufflers that they had a 2.5" inlet but a 2.0" outlet. That seemed odd to me until I didn't see ANY exhaust bezels larger than 2.0" in any of the parts catalogs I had at the time.

I don't have any specific ratings numbers from before or after the new pipes went on, but it does seem to pull a little stronger than before. I do get compliments on the soft rumble at idle and I like the (not-so loud) roar when the secondaries open up...!!!
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Jim O.

"The Toy" - Save the Wave...!!!

Well I am leaning towards the 2 1/2" based on the great feedback.

Regarding the exhaust tips. What did the factory do? Did the LT1 have a 2 1/2" muffler inlet and 2" outlet?

I found out I have the original exhaust tips on my car but they WELDED them on and they fit inside the outlet of the existing 2 1/2" outlet mufflers.

I am going to be doing a lot of very careful grinding to save the tips. They are in excellent condition except for the welding. The chrome is almost perfect!

Thanks and keep the advice coming!

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=42610&item=2460931360


This is the same system (different auction) that I just got for my '79,, 2 1/2" w/no cats. The guys name is Gordon, very helpful, even offered to take the muffler "cans" back if I wanted louder (empty) ones. System was $357 to my door INCLUDING the trans-mounted front hanger for the dual pipes. It looks great laying next to the Vette, now I just gotta hook it up.
Bill A.