I still believe that the proper testing hasn't been done with shorty headers.
And believe me, I've searched and searched for proper tests.
When you put long tubes in, you aren't just putting in headers, you're also removing
the big restriction of the pre-cats and cats and often putting in a catless pipe or a high-flo cat pipe.
In order to compare apples to apples, one would have to give the shorty headers the same benefit.
It is amazing that it seems the stock exhaust manifolds can handle at least 550 rwhp without starting to show
its hindering flow.
The best article in a long time which brings this to head is from BigBobsL on nloc.
He posted:
Locally, Andre (1BADTK, myself, and other HALO club members have been investigating and documenting the effects of exhaust back pressure on power. Changes have ranged from partial removal of cats to replacement of cats and stock exhaust manifolds. One of the things we discovered is that exhaust back pressure @ WOT is controlled by the cats: Stock= 10 psi, Bassani= 5 psi, and Magnaflow= 3 psi, regardless of the headers and mufflers installed.
Some speculated that reducing back pressure might reduce low r[m torque, others felt there was not a significant improvement with exhaust changes.
Steve's MyRedToy saw ~0.3 et (12.51 to 12.21, Hoosiers and better air later gave another 0.1) improvement when going from stock to Bassani cats. Steve already had Bassani headers and catback, but stock cats.
Reducing exhaust back pressure provided NO measured torque loss for me. Dyno'd today after long tube and cat installation. This is a BEFORE and AFTER Comparison with the BEFORE being after removing the second (rear) set of stock cats and lowering back pressure from 10 psi (stock) to 7 psi. The modified cats had been worth a 0.1 et improvement. The AFTER is with JDM/Kooks header and cat installation and a back pressure of 3 psi. I used a Dynomax 2 in-2 out muffler for both tests.
RESULT: 12-15 hp increase in peak hp at ~ 5000 rpm. While that does not sound like much, at 3800 (lowest measured rpm) torque was up 50-60 lb-ft and hp 40-50! This level of gain slowly tapered to the 12 -15 at 5000 rpm and stayed at that level or greater until 5700+. A lot of new area under the curve and very noticible at seat-of-pants. The same level of gain was seen with two different chip programs and and one program was run twice in both BEFORE and AFTER configurations to verify consistency of the numbers. Gains were likely higher at still lower rpm and more so had I started with a full set of stock cats.
We just completed a driveway install of Hedman short tubes and Bassani cats in front of Silver Bullet cat-back on Andre's truck and saw a big increase in sound and will do his AFTER dyno soon. Analysis of those tests will allow us to compare characteristics (magnitude and distribution of gains) of long vs short tubes. I am sure he will add his results to this string at that time.
Did I mention the incredible sound? We also discovered that the cats do more to determine sound level at idle and WOT that mufflers of headers, while the headers add a distinct cadence and pitch/growl.
End result: Very glad I made did the install. I had heard complaints of too little power gain before and that would be the case if you looked only at peak numbers, but the improvements at less than 5000 rpm is huge! Guess where our engines are at most of the time? New peak numbers: 430 SAE (corrected) hp and 527 lb-ft. More to come as soon as new cams arrive.
Will post graph overlays and track improvements later; racing this Sunday and planning/hoping for first eleven second run. Last run before headers was a 12.09 @ 111 mph. @ 4700# & 60F
Thanks again to Keith and Chris for help with my driveway install.
and followed up with:
The short answer is much of the performance improvement is in the cats or otherwise stated if adding headers, be sure to do the cats so you can see maximum gains. MyRedToy gained 0.3 sec when adding Bassani cats as last segment of a full bassani set-up. I think the long tube headers were responsible for a lot of the low end gain, but can not say until we see how the shorties perform. We have done some high flow cats on stock exhaust manifolds, but have no BEFORE and AFTTER dynos and they have not made it back to track yet. My 12.09 was with stock exhaust manifolds and pre-cats only. Had run 12.21 with both sets of factory cats. Best bet is to buy a fully built set of cat pipes with are $400-$500, if staying with factory manifolds or shorty headers. Long-tubes of course require different cat set up.
I have had three mufflers and found no performance advantage in any of them, only different and louder sound. I would like to try a stock cat-back with long tubes and high flow cats; save money and the quiter exhaust might keep me out of troble and be a bit more stealthy. I am sure it would also be much louder than stock, but still quiter than aftermarket mufflers.
As you know there are numerous sources for the mandrel bent Bassani or Magnaflow systems, both systems perform well. Any savings from buying the cats alone is lost in paying a muffler shop and the shop not having a mandrel bender.