I just read some interesting information in the April 2005 issue of Hot Rod magazine. The article is doing a dyno flog of a new LS2 engine. It touches on several aspects of the engine(cams, rockers, heads, exhaust ect). Among other things I found the exhaust testing very interesting. It seems by data acquired in this build up that stock Z06 exhaust manifolds aren't too shabby. Katech compared stock LS2 mainfolds that came with the engine to stock Z06 manifolds and their own header brand. The numbers were (1) Stock LS2 manifolds 422 peak h.p.(2) Stock Z06 manifolds 427 peak h.p. (3) Katech 1 3/4" headers 427 peak h.p. These tests were done with 13.0 in-Hg backpressure to simulate stock exhaust. Then they tested only the headers with 6.0 in-Hg to simulate a freeflowing aftermarket exhaust system. This resulted in 435 peak h.p. They did not test the other two exhaust manifolds at this backpressure(I wonder why?) Anyway, just shows me how good the G.M. design that everyone seems so bent on changing really is. -Bob

 

And maybe shows other folks that the brand of header tested doesn't quite measure up to the top header brands discussed here.

 

Doesn't show me nothin'! Common sense, and research shows that the only way to get these engines to make the kind of power alot of us look for is by installing longtube headers. That's why so many of us use them. Come on man, if you don't have headers, IMHO, I think you should put them on. And high-flow cats, and hi-po catbacks, and on and on and on! Don't you want to fit in? Just kiddin'! We'll still like ya if you don't want headers!

 

Car Craft did similar tests on an LS1 and came to the same conclusion. However, as soon as I put on my headers I noticed a huge difference and on the dyno they showed up as 25HP as well. Not sure why they are not find the same on the engine dyno, but all the stuff I have seen on several forums concludes that headers are a good addition.

 

Headers work! Biggest bang for the buck! DynaTech rules.

Chas.

 

It's not that I don't like headers. My Corvette is the only performance car I own that doesn't have tube headers. All three of my other "fun" cars have them. It's just that I get a lot of conflicting data on the value of not only headers but all of the "easy" bolt-ons for Corvettes. I experimented with my first Z06(2001). I tested several bolt-on pieces in the quest for the 20 h.p. difference between the 2001 and all of the other Z06's. After spending over a thousand bucks on Vararam, Stinger, smooth coupler/air foil,ect.ect and many hundereds more at the dyno I came up with 11 additional h.p. I toyed with the idea of headers but was talked out of it by the data I was reading about the actual effectiveness of that addition without aftermarket program tuning. I live in Socal and have already had a run-in with the BAR with an 80 Corvette that I extensively modified(headers, heads, cam, intake and good exhaust-cat removal). I got caught and had to replace all of the factory equipment to avoid a possible big fine/jail sentence. That was an experience that I don't want to re-live. Now, I don't do any mods that could potentially put me at risk for another bad experience. I wasn't trying to talk anyone out of the header mod or imply that such mods are a mistake. I only thought that I was sharing some interesting information from a source that seems to have everything to win by showing a larger gain from the mods they did(to sell more headers). As far as Katech not being as good as some other designs-I really can't comment on that but I do know that if headers are sized correctly and are reasonably close to being equal length there shouldn't be much performance difference. There isn't much "black magic' in header design. I know that I'm probably in for a whipping for my out-of-the-mainstream ideas. Let's hear it! -Bob

 

Strangely enough I was told something very similar by a DFW (Carrollton) tuner. It was further suggested that unless I wanted to upgrade heads and cam that my stock Z06 manifolds were quite good enough. And that if I wanted more gains (up to 15 was quoted) I would be better off swapping out the stock h-pipe for either an off-road or high-flow cat version.

 

I had about the same results as vettenuts with my QTP`s,
98 C5 A4, base line dyno @ 309.86hp 318.89 tq, borla cat back and twin flow intake.
Added QTP headers with random tech cats & x-pipe.
After results: 333.53hp 342.43tq
Increase: +23.67hp +23.54tq.
Also, broad tq curve across the graph, very noticeable seat of the pants improvement.
Bottom Line: A good set of headers "really wake up" the C5.

Cheers, Rick