1 3/4" vs. 2" Header Size

[Top Toy]

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.

[-=Jeff=-]

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

[We Gone]

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.

[XfireZ51]

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.

[We Gone]

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"

[5ABI VT]

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

[mike100]

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).

[XfireZ51]

LS7s use 1 7/8” primaries.

[Paul Workman]

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!!

[We Gone]

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