Randy 71

Vetters,
Question. I am looking to replace my exhaust soon. It has 2" manifolds. Can I put 2.5" pipes on it?

The reason I ask, after looking at some VETTE catalogs, some offer 2.5" pipes with either 2" or 2.5" manifolds. Is this correct? Would this be a 2" connection at the manifold then some kind of Increaser to 2.5" the rest of the way back?

If these is correct. How much difference is there between the 2" and the 2.5" manifold using 2.5" pipes?

While I am here. Mufflers, I like the deep tone on acelleration but when crusing I want to be able to carry on a conversation. FLOW MASTERS (series?), MAGNA FLOW ?????

Thanks in advance
Randy

PatsLs1vette

randy im not positive but the flange is alot bigger on the 2 1/2 inc h pipes so youll need the bigger manifolds...that sucks cause i just threw a set away i had sitting under the bench. :( i would have given them to you.

tsw71

The LT-1(2-1/2") exhaust will bolt right up to your manifolds. The LT-1 also uses 2" manifolds , but the exhaust pipes go up to 2-1/2" about 3" down from the manifolds. I installed these a while back before I made the switch to headers and the difference in sound is well worth the money. The only thing I am unsure of is if the larger pipes will work with TH400 cars, but manual tranny cars will be fine. As long as you do have a 4 speed car, then no mods will be needed to make the switch. I bought my kit(pipes and mufflers) from ZIP and all were mandrel bent. The fit was not the greatest, so shop around before you decide where to get them.

79MakoL82

I don't know if yours is a small block, but I think all the rams horn manifolds on C3's were 2". I believe you can get a 2 1/2" rams horn manifold from a C2 though. I recall reading a post from someone who was doing this and I believe it required new brackets or some modifications. But I think the dual exhausts for small block c3's all go from 2" to 2 1/2" to hook up to the 2" manifold.

Randy 71

I have a hook-up at BIG AL's muffler shop. Said, if I bring the mufflers I want on the car with me, he will custom bend the rest of the exhaust system for $100. Sounds good to me. $100 for the custom bend and around $150 for the mufflers. $250 for all sounds pretty good, doesn't it? Now thats for 2 inch. I figure maybe an extra $25 for 2.5 inch.

Randy

tsw71

Sounds like a pretty good deal to me. I changed mine over to the 2-1/2 for performace purposes, but the new exhaust sound alone made me very happy. You will be happy with the bigger pipes. What mufflers are you going to put on? I went with the stock type for the authentic sound. The mufflers were about $50-60 ea for the aluminized ones.

Zip Corvettes

G.M. stopped making the the 2.5 manifold in 65'. After that all manifolds were 2" and cars that had 2.5" had a 2" adapter welded into the pipe.

Randy 71

Sounds like a job for the muffler shop. I would think they could handle it. I definitly want 2.5 pipes.


Randy

Mr.Gearhead

Many aftermarket 2 1/2" pipes are fitted for stock 2" manifolds. I would recommend having a GOOD muffler shop hand shape the pipes. The aftermarket never seems to fit well. I had soooooo many problems with my exhaust from Mid America, that I took them off and had custom pipes (2 1/2") installed with Dynomax mufflers...GRRRRRRRRRRRR! :D

mulchie

I put the 2.0" to 2.5" system on my LT-1. It will also work with the TH. Make sure you get the off-road system (one less baffle in muffler)-it sounds much better.

PRNDL

Mr. Gearhead - Very good point! I had a fit problem with the pipes I bought from Zip.... but guess what? The manufacturer had me take some very careful measurements and he made me a new front drivers side pipe that fit!! A set of pipes alone costs $180 from Zip. Aftermarket mufflers (like Flowmasters) will require some elbows as well. If you can get a muffler shop to make you a custom set for anywhere near that it is probably a better option. This sage advice comes from the guy who did all the work himself and has installed $400 worth of exhaust system parts and has another $950 of unused exhaust system parts in the basement!!!!

MJ

Joe Lucia

Prior to 1962, all small block manifolds were 2" outlet size. In 1962, for Corvettes only, GM began using 2-1/2" outlet manifolds for 300 hp (manual trans only) 340 hp and 360 hp engines. This practice continued for 1963-65 300 hp (manual trans), 340 hp, 350 hp, 360 hp, 365 hp, and 375 hp engines. Beginning in 1966, ALL small blocks used 2" outlet manifolds. However, 2-1/2" exhaust systems were still used on many small blocks by providing a reduction fitting, welded or swaged, near the manifold.

Most of the 2-1/2" outlet exhaust manifolds are still available from GM. These include:

GM #3797901 (cast 3797901)------LH, side alternator bracket

GM #3814970 (cast 3797902)-----RH, side alternator bracket

GM #3846563 (cast 3846563)-----LH, forward alternator bracket

The 2-1/2" outlet manifold with NO alternator brackets has been discontinued for over 30 years, but is available in reproduction.

The 2-1/2" outlet manifolds can be used on any Corvette small block, including being retrofitted to those of model years 66+. However, NONE of the 2-1/2" manifolds have provisions for A.I.R. fittings. So, if your engine requires A.I.R., you can't use the 2-1/2 outlet manifolds.