SS Autochrome Headers and Collectors

[shall36]

I've been reading a lot about the SS Autochrome headers and the missing torque issue. I installed mine and I'm happy with them, but of course, I could use some more torque down low. I pulled the December 2003 issue of Car Craft off of the shelf and re-read the article on header theory. They say that extending the length of the collectors will boost low-rpm torque. I looked at the setup in my '03 and it seems like the collectors could be extended by about 8 inches. The flange comming off of the cat pipes will have to be cut and relocated closer towards the cats and a new section of pipe with flanges at both ends would have to be fabricated.

Any thoughts or ideas on this one?

[KLS]

I don't think you'll have any luck due to the short primary tubes. Collector length and diameter matters a lot on race headers without exhaust pipes, and the length doesn't make nearly as much difference on street rigs with a full exhaust system.
http://www.burnsstainless.com/TechAr...ry/theory.html


Ken

[shall36]

Hmmmm....Checked out the link about the merge collectors. Not sure that the link specifically says that standard collectors aren't worth torque on a street car. Their (Burns Stainless) focus seems to be on using Merge Collectors to increase exhaust port scavenging. Conincidentally, Car Craft has an artlicle on it's site about merge collectors that's also worth a look. They compared HP and Torque numbers on a motor with standard collectors and with Merge Collectors and found a descent bump in HP and Torque. What's funny is that the Dec 2003 article, "Hot Air", specifically states that race car setups (drag race) won't benefit from collectors at all, but that working with collectors is a good idea for street engines (p. 64). It may be that collectors really only work on long tube and/or equal length headers. I do know that as the length of the collector is increased, the amount of torque below peak torque is increased. Note that peak torque is not increased, which is why drag race engines won't benefit from lengthening collectors; they run above peak torque almost the entire time.

As for going with the more expensive long tube headers, I'd be more inclined to do that once dyno numbers are published comparing the SS Autochrome headers to the S&S Long Tube headers demonstrating non-trivial gains in torque below say 3,000 rpm. (Side note: HP and Torque number comparison, especially when the likely differences are relatively small, should be based on data collected using the same dyno.) Not sure what the S&S Long Tubes costs, but the SS Autochromes cost me $150 and fabricating a pair of collectors and modifying the rest of the exhaust system to accomodate them might set me back another $100. Add to that easy installation, and the SS Autochrome setup is very appealing.

Of course, making gobs of torque with a 4-cam, small displacement motor isn't easy. We could have custom cams ground to enhance torque, but that would be cost prohibitive. Probably the most effective modification for more bottom end grunt would be to install a 4.55 rear gear. The S/C seems like a reasonable option, but it's not cheap, either. Other than that, we'll just have to wait for a stroker kit ;-).