Cadillac CTS-V - header question

Does the diameter of the tubes matter much in terms of horsepower/torque gains? I watched someone struggle today mounting Kooks 1 7/8 longtubes in an 05 V with brand new LS6 longblock crate motor. Tubes are actually touching in several spots, including steering shaft. These headers are wrapped in fiberglass tape BTW. I'm thinking headers for my 06, but would it be wiser to buy the smaller diameter model-is it 1 3/4, I think?

Aren't you doing a blower? If so it's 1 7/8 all the way. I have 1 7/8 and mine dont hit anywhere at all so his motor mounts might be way past gone. I think 1 7/8 is the general consensus now as there hasnt been any proof that they hurt hinder low end performance.

Generally speaking, smaller primaries are better for lower-mid range torque and larger is better for mid to upper rpm gains. The length and sequencing (e.g. tri-Y vs. 4 into 1, etc.) make a difference, as well and then there's equal length primaries. I haven't seen any for the LS-series engines (but also haven't looked; Hedman makes them for others), but they also have stepped headers, where the primary starts off smaller, then increases; they even had some where it had like a smaller tube in a larger tube and had supposedly help with anti-reversion or something like that (been years since I read about them)...not sure how popular or well those work on something like an LS though. Finally, if you can get something that matches the exhaust port of the head (some are 'O', some are 'D'), that would help too...

So, really it depends on your goals...I would think 1 3/4" or 1 7/8" could work on even a stock engine and when you step up the cam, the larger for sure. However, there is a lot to consider more so than just the primary sizing, but seems Kooks are pretty good in that respect and it's not like we have much choice. You can go too big too, of course, but the ones offered for the LS seem decent...Just avoid the shorties, as you're not going to gain much there; modern exhaust manifolds are pretty decent (i'm not 100% familiar with what the CTS-V manifolds look like, but the GTO ones were decent), but typically long tube headers can get modest gains, with a tune...

The only real exception is if you were to have turbo(s), where a cast iron manifold typically works better for the heat retention to the turbine wheel, but ideally you'd want the compressor (turbo) close anyhow..

My 1 7/8's rub on the steering linkage and have with both stock and CS motor mounts.
http://i26.photobucket.com/albums/c146/DavidWomack/rubbingsteeringshaft.jpg

Ouch...Can you dent the primary slightly?

Is the steering shaft solid or hollow, do you know? Could turn it down slightly at that area, if it's solid, but I wouldn't go overboard! :D

My 1 7/8's rub on the steering linkage and have with both stock and CS motor mounts.
http://i26.photobucket.com/albums/c146/DavidWomack/rubbingsteeringshaft.jpg

No kiddin? Any problems with that contact area? We noticed it on Matt's build over the weekend, but his builder seemed to feel the car had been in an accident, wacked in the front, and this may have caused the problem. How long have you run with the header touching the steering shaft? Matt also has brand new motor mounts, so I know that's not the issue. He has his Kooks wrapped in the fiberglass tape, also. I think that adds a bit of diameter to the tube. I was just thinkin maybe I should get the smaller diameter headers in order to avoid all of this stuff. Opinions?
leo

Ive been this way for several months, few thousand miles now. The steering wheel "sticks" when turning the car and there is a TON of vibes. I was just under the car and there appears to be nothing but cosmetic damage to the steering shaft and some annoyance on my part.

Mine did they same thing. Nothing a good whack with block of wood and hammer didn't fix.

When in doubt, beat it out.

1 3/4"

http://i1227.photobucket.com/albums/ee438/CI-V-IL/DSCF2732.jpg

http://i1227.photobucket.com/albums/ee438/CI-V-IL/DSCF2726.jpg

I guess I got lucky because im on stock motor mounts and 1 7/8 and mine dont give me any problems at all.

I've seen pics of 1 7/8" not hitting and my 1 3/4" TPiS headers hit. I think its just the headers and the car build variations.

When in doubt, beat it out.

I just decided! Goin' with OBX or Pacesetters so when I whack 'em I won't hold back as much as Kooks or American!! But seriously, think I'll use the smaller diameter just to be on the safe side. What about wrapping? Where are you guys with that philosophy? And I guess it's a good idea to use a higher grade spark plug wire to avoid melting.
leo

Rather than wrapping them, I'd get them ceramic coated, inside and out (if you plan on going turbo, then don't do the inside) at a place like swaintech (http://www.swaintech.com/)...I'd go pacesetters before the chinese ripoffs, personally though, if you're on a budget; just save up and get the real deal, IMO.

My 1 7/8's rub on the steering linkage and have with both stock and CS motor mounts.
http://i26.photobucket.com/albums/c146/DavidWomack/rubbingsteeringshaft.jpg

Geez Dave, looks IDENTICAL to Matt's situation. He has brand new motor mounts, yellow color, forget the brand. Their theory is the car was in a fairly rough front-ender, so there is underlying damage at some point. He's using Kooks 1 7/8 LTs with tape, so the rubbing is highly apparent. Funny, I posted this query on both forums and responses have been just about 50/50 concerning the rubbing issue. Steering shaft definetely #1 spot, though. I'm thinking picking up the smaller tubes might be a better idea, doesn't seem to cost much in performance departement.
leo

Rather than wrapping them, I'd get them ceramic coated, inside and out (if you plan on going turbo, then don't do the inside) at a place like swaintech (http://www.swaintech.com/)...I'd go pacesetters before the chinese ripoffs, personally though, if you're on a budget; just save up and get the real deal, IMO.

Pacesetters and OBX really not that much price difference. Friend is a welder,says "don't worry, I'll fix those OBX up just fine!" No turbo, just MP 112. Sometimes I wonder if you need the headers at all, for all the trouble they are to fit in there.