I purchased a set of Kenne Bell headers for my ’85 back in the early 90’s. First pair was so off we could never make them fit. In true Kenne Bell fashion the replacement set took a couple months to arrive. After some hammer work and a local custom exhaust shop doing some cutting and welding the headers finally fit the car.
I will honestly tell you, by seat of the pants… the car did not respond as well. The turbo did not seem to spool up as quick and response/pickup seemed slower. I have no numbers to back up my feeling.
Kenne Bell was always a big fan of listing huge gains in advertising (hell, they would sell you a bag of ice and say you could pick up 2/10ths!) The advertised gains with their headers were about 4/10th’s.
Headers in my first mostly stock ’85 GN (modified Trans) Kenne Bell dual muffler exhaust, 150k miles and a questionable pedigree my best was 14.3 on 105 octane race fuel.
My current GN with 130k miles ran 13.4 back in the day with only headers, gutted cat, brand new built trans., similar dual muffler exhaust on 93 octane + a can of Octane Boost. I only made two passes, and lifted at some point during each pass. First time the new Trans shift points scarred me, second time I had a T-top come loose and started leaking air… it threw me until I found the source.
I only purchased the headers due to a cracked exhaust manifold. They cost around $900 new, not counting the shop time and labor to make them fit.
My original GN was rear-ended by a drunk driver and immediately went up in flames. I was able to buy the car back from insurance and salvage everything from the fire wall forward and the main exhaust split tube.
I don’t know how much the headers gave me. My current GN was purchased with a cracked exhaust manifold so the headers from the old car went on the new car right away (hence the above comment.)
I just think back to the feeling of the car being slower once I put the headers on.
Short story long… I’ve been working on this and new posts and responses have been made. Screw the headers! They should be a last on the list item. I agree: 86/87 computer conversion, cold-air intake with the LS1/LT1 MAF, MAF translator and proper chip, upgraded fuel pump, better injectors, electric fan…
Don’t waste your money on headers when you can buy a lot of parts for the same total!
Good luck!!! Don’t be afraid to ask the board for help! This board has saved my a** many times!