Hi i have an 81 with stock exaust except for muffers. i just got a set of headman headers: 1 5/8 in. pipe to 3" collectors, and was wondering if 3" pipes all the way out would be a good or bad idea. i want it to sound good, but more importantly i want to maximize performance. is there much of a difference from 2 3/4 to 3".
also has anyone installed headman headers, if so, have any trouble???
thanks

L82 or L48 I don't know enough to help, but I do know that the engine matters. For the guys that do know! :)

Scot

It will work fine. Thats the setup i had as of yesterday. I pulled everything to fab a X pattern , insted of just runing two pipes back. I like the X pattern better than a H pattern. Your air flow is unrestricted , and more balanced with the X. I have two flowmasters at the ends and i'm going to cut the cat converters off! p. s.....the bigger the pipe , the more sound ya get. What muffs are you using ? I do remember something about the 81's haveing a port on the manafold...something to do with computor or emissions. Mine's an 80 , and it didn't have that. I think they make header's just for 81's if you want to keep your emissions hardware up to date.

|UPDATED|10/29/2003 5:29:48 AM|/UPDATED|

I'm no expert by any means, but I believe that 3" pipes all the way back in a small block, unless it's putting out gobs of horsepower, isn't a good idea. I understand that any engine, for best performance, needs a certain amount of backpressure. 3" pipes may not give enough exhaust velocity to do so. Pipes that large are best for big blocks with a lot of hp, or supercharged.

I remember reading the the Pratt & Whitney designers of the R-2800 radial engine for World War II fighter planes were able to increase the engines horsepower by how they designed and routed the exhaust tubes. I imagine this can have the same influence on a car's engine, though at a lower level, since the R-2800 put out well over 2000 horsepower.

Fabricating 3" pipes may really up the costs. I would think having a "X" pipe would do better with 2.5" pipes. I know that type of setup has been proven in tests of various cars.

I've had exhaust work done on a bunch of vehicles and 3" pipes have been reserved for my trucks only. That diameter pipe is too much for just a street application. I figure if 3" was OK to run on a street driven Shark the aftermarket companies that manufacture full systems would use them, and not max out at 2.5" pipe. Another thing to think about is clearance...C3's don't have much room to begin with and 3" pipes would sit that much lower. The 2.5" pipes on my '70 scrape every so often and they are routed the same as the stock 2".


|UPDATED|10/29/2003 7:53:12 AM|/UPDATED|

thanks for all the input, i love being able to come to this place and ask a question knowing i will get a response.
i will talk it over with a budy of mine at the shop and probably go with 2 3/4.
thanks again

oh, by the way, i am going to do with magnaflow mufflers, i think someone asked about that.

i don't know everything, but on my 74 454, i know that 3 inch pipe was the way to go. I have another 50 plus hp from headers and 3 inch, and i have way more bottom end torque as well. My engine is stock except for an intake and the headers, and by all means it runs excellent, no problems with lack of backpressure. I'm glad i went with 3 inch.

I have an 80 with the L48. My car already has the catalytic converter eliminated, however the crossmember at the back of the transmission only has one "hump" for the exhaust to clear. I took the car to a shop that does custom bending and to do a true, straight back dual exhaust, you need the "double hump" crossmember. Here in lies the problem, up to 1979 the crossmembers were made with the double hump, however it appears that you cannot simply unbolt a single and bolt in a double as the doubles appear to be welded in from the factory. Anyone ever encounter this problem? Any ideas on a fix? Thanks for the additional help.

Scott

i would'nt go any bigger than 2 1/2" any bigger than that is for high horsepower small blocks like over 400 hp would have 3" pipes. If anything you would be loosing hp with 2 3/4" -3 heres a good reference table i found

Dual Exhaust

H.P.

200-300 2 1/4"
300-400 2 1/2"
375-450 3"
450-550 3 1/2"
550-650 3 1/2"
650-800 4"
800-1000 4 1/2"
1000 plus 5"

|UPDATED|11/26/2003 2:49:17 PM (AZT)|/UPDATED|