Is it worthwhile changing headers after cam?

[evil_ss]

Hi All,
I'm getting a cam and 4.11 gears installed tomorrow, but its got me thinking about its support system, the exhaust.
I currently have pacemaker 4-1 1 3/4 headers with magnaflow cats (fitted 2007). Will I see a worthwhile gain in HP and torque of I change to the Sureflow 4-1 1 7/8's with 5" body 100 cpi cats?
I also have a problem with the current headers hanging quite low.
$1490 headers and cats
$450 black ceramic coat
$??? To fit to existing exhaust and touch up tune
Your thoughts would be appreciated.

[macca_779]

You won't see worthwhile gains mate 1 3/4 is fine

[white lie]

Yep, that 2K would be better going towards a pair of heads.

[Wonky]

Depends how annoying the current ones hanging low are. I had 1 3/4" 4-1 Pacies on my SSV sedan on SSLs and went to 1 7/8" 4-1 Pacies on SSSLs on the ute and actually scraped less! The only difference is on the sedan the cats were KPM ones and the ute had Ballistics but they look pretty much the same. However, the newer KPM 3" system was much better tucked up than the one on the sedan which possibly allowed the cats to sit up higher. I still scrape occasionally and have to take speed bumps slowly but bottom line is it may not be due to the extractors per se but there may be improvements to be gained by checking the whole system.

I doubt you'll see more than a poofteenth of difference in power, so not worth it at all from that point of view.

[evil_ss]

The scraping in definitely annoying but not life ending. I was secretly hoping the advancement in headers and cats over the last 6 years would give me a bigger power gain, the ceramic coating to reduce heat soak. It seems the general consensus is that it won't make bugger all difference

[Wonky]

I suspect sfa has really changed in extractor/cat basics over those relatively few years. Depending on the specs of your current cats you'll possibly pick up some on going to the 5" body Ballistics but from what I've heard you'll possibly counterbalance some of that at least in going back from the 4-1 Pacies to the shorter Sureflo extractors.

[evil_ss]

I suspect sfa has really changed in extractor/cat basics over those relatively few years. Depending on the specs of your current cats you'll possibly pick up some on going to the 5" body Ballistics but from what I've heard you'll possibly counterbalance some of that at least in going back from the 4-1 Pacies to the shorter Sureflo extractors.

That was one thing I was wondering about, as the Sureflow almost looked like short tubes.

[QldKev]

As above, I would use the money on something else unless the height is a huge issue; but don't do it for the power. Unless the tuner is using that Chinese horse button to give you a lot better final reading. That's that button that makes horses smaller so you get more horses for the same power.

[vassis]

I had genie headers in brendale qld make a set of vt-vz 1 7/8 headers on my car they where making the design through there fancy computer and ended up running out of 1 7/8 pipe so they made a set of 1 3/4 headers that i had on for about 4 or so weeks. Prior to that i had triy pacemakers and stock opened up cats. They set me up with 1 3/4 and there 200 cell cats. I noticed a decrease of throttle response under 2500 rpm but and increase of both torque and horsepower in the midrange and top end and gave it breathing space to rev to 6500 (6grand was the comfort zone for the triy). Once i went back changing to the 1 7/8 headers only it got worse down low upto about 3000 rpm was pretty gutless compared to the triys but as soon as 3 grand would hit it had never felt that torquey ever and now revs to 7 grand easy. It seriously needed that extra size up but it may be because of the L92 head that my car uses. Through this whole process the tune wasnt changed until after the current exhaust setup was on and after that alot of the bottom end torque didnt come back until the cart was retuned. I recently pulled a tad more timing from the bottom end and feels a lot better again
In my opinion the 4.11s are too short unless u are building it for full throttle and the gains may be little but i did find the 1 7/8 headers fit best with such low gearing especialy now that you need to rev it harder because of the road speed your going to loose per gear having the short ratios.
The 1 7/8 genie headers also have better ground clearance than even the pacemaker triys too and they join roughly in the same spot so you wont have to change ur exhaust to suit it should bolt straight up
Edit; you didnt specify what engine ur running but unless you have big heads like L92 ones from the l98 or l76 engines you probably wouldnt benifit from the larger headers

[Wonky]

you didnt specify what engine ur running but unless you have big heads like L92 ones from the l98 or l76 engines you probably wouldnt benifit from the larger headers

http://www.ls1.com.au/forum/showthre...6-2006-evil-ss

[vassis]

In that case dont worry about changing anything other than what ur getting.
The heavy VE probably needs the 4.11s and its probably not worth spending the money again to get that slightly larger header
What spec cam btw?

[Dillzio]

If you already have decent headers on it I don't think you'll see a worthwhile improvement putting on headers that are slightly bigger.

You also need to remember that the only time you will benefit from such a free flowing exhaust is when you're near max rpm (which usually only lasts a couple of seconds), and from what I've heard you need a bit of exhaust back pressure for the engine to perform well at lower rpm (which is where it normally is when you're driving).

The bigger exhaust might get you a few extra kw at max rpm on the dyno, but it may cost you a bit of power and responsiveness at lower rpm. If you really want to max out the dyno numbers the bigger headers might be worthwhile, but if you want speed and driveability I'd leave it as it is

These cars are expensive enough as it is, unless you're a millionaire it doesn't make much sense to pay for another set of high performance headers for a few extra kw that are only going to be noticed on the dyno. Also, if you have a problem at the moment with the headers hanging too low, going bigger ones isn't going to help matters.

[evil_ss]

In that case dont worry about changing anything other than what ur getting.
The heavy VE probably needs the 4.11s and its probably not worth spending the money again to get that slightly larger header
What spec cam btw?

Thanks for the input mate.
Can unknown at this stage, I have left that to Ed to decide. I'll ask tomorrow when I pick up the car

[evil_ss]

Cam:
Our grind is 231deg at .050'' on the intake and 243deg on the exhaust Lift
is 600''

[vassis]

thats a pretty large cam

have you picked it up yet and what did she make?