1 3/4" vs. 2" Header Size
 

Just watched an Engine Masters video, https://www.youtube.com/results?sear...rs+header+test, (love these videos!) where they tested various primary tube size headers on a small block Chevy. They found that 1 7/8" headers vs. 1 3/4" made just slightly more power at the top end and lost some torque in the mid-range. Wondering if anyone has any dyno results of Watson (1 3/4") vs. Stainless Works (2") for our cars? Are OBX 2"? I'm guessing 2" helps the LT5 in the 6000-7000 rpm range but hurts down below.

Re: 1 3/4" vs. 2" Header Size
 

FYI, Watson also made 2" headers..

I also understand there are difference lengths, Watsons, Jeal and some Stainless Works are a longer header while I believe Stainless works and OBX sell a shorter header that allows cats to be installed without modifying the cat back

Re: 1 3/4" vs. 2" Header Size
 

SW sells both Long tube and Short tube, I have a set of long tube I got them over 10 years ago had them coated and they still look great. I also still run high flow cats as I like the tone better.

Re: 1 3/4" vs. 2" Header Size
 

My headers are a set of Watson 1 7/8” primaries. Thought about swapping to SW
2” but I don’t think any gain would be worth the pain.

Re: 1 3/4" vs. 2" Header Size
 

I remember reading some time back that the long tube was a bit better, but not sure about the difference in 1 7/8" vs 2"

Re: 1 3/4" vs. 2" Header Size
 

I would agree from what ive come to believe the smaller will pick up the low and midrange and the bigger the top end. Same holds true about primary length. Longer primaries pick up torque midrange while shorter will aid top end only. I was pretty upset that my SW headers were the short kind but when Burns told me about that I had a nice grin on my face. Im all about 6-7400 anyways:-D

Re: 1 3/4" vs. 2" Header Size
 

I had 2" Watsons and there was no point in the power curve that was less than with stock manifolds. Part throttle was better too. The LT5 is so under manifolded, it kind of defies convention (at least 2 valve per cylinder convention).

Re: 1 3/4" vs. 2" Header Size
 

LS7s use 1 7/8” primaries.

Re: 1 3/4" vs. 2" Header Size
 

One has to be able and willing to delve into some involved physics to make definitive predictions that might result from (1-7/8" vs. 2") primary cross sections: length, area, rpm, gas volume, resonance, etc., etc. And, because the cross sectional area difference is relatively small (less than 14% for the smaller tube), length will become more important than area alone in the final answer (in this case).

All things being equal, the smaller diameter primary will favor slightly lower RPM than the 2", until the inherent back pressure (of the smaller tubes) "pinches off" further gains to where the 2" tubes become superior.

Length being equal, side by side comparisons would ultimately be needed to distinguish the practical difference between them. But, from this frustrated physicist's perspective, I'm betting a very slight superiority in peak torque at around 5200 rpm for the smaller tubes (perhaps), but torque "under the curve" above the peak will favor the slightly bigger diameter tube. Sure would be interesting to see, huh?

Bench racing... Gotta love it!!:blahblah:

Re: 1 3/4" vs. 2" Header Size
 

Ok so now lets throw in the mix fully ported vs stock?

Re: 1 3/4" vs. 2" Header Size
 

Paul,

I think Marc may have documented no significant difference between 1 7/8 v the 2” primaries. If there was a difference it could be easily lost somewhere else.

Re: 1 3/4" vs. 2" Header Size
 

Smaller primaries would likely be the better choice for road course racing where more time is spent in lower and mid-range rpm's and larger would be the better choice for drag racing.

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Re: 1 3/4" vs. 2" Header Size
 

I have a book by David Vizard, I think the SBC on a budget. It links exhaust flow to the size of the primaries. Also there are "stepped headers" that have a bigger initial size then going down to a smaller, i.e., regular size tube that sounds like it's the cats meow. I bet you could find the article on line.

Re: 1 3/4" vs. 2" Header Size
 

Don’t “stepped headers” have the opposite, smaller initial tubes, then get bigger down line to the collector?
I have had Watsons with 2” downtubes since 1995, and they’re pretty good, (117mph trap speed on an otherwise stock engine.)


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Re: 1 3/4" vs. 2" Header Size
 

Uff-da! (as they say here in da Viking country).

Gotta love that sea level DA! ;)

Re: 1 3/4" vs. 2" Header Size
 

Yes, you are correct. Smaller to bigger.