Good info, Larry.

I was surprised at how small the (non-plate) Cup 4-2-1 headers were. For 800 or so hp in the high 8's I expect a 4 >1 would have larger primaries. Packaging is always a problem on a Cup car, and sometimes optimum primary length won't fit, even with 4-2-1s. They could be 1-2 inches off, which seems huge for those guys. Maybe they optimize each cylinder valve timing and for the intake and exhaust length they are able to get into the car. That, along with individual cylinder timing curves, doesn't seem that far fetched.

The benefit of Iconel is that you can use thinner wall tubing than with 304 or 316 stainless, so header weight is less. Inconel can be about .035 thick vs. .050 or so for SS and still last. That's a 30% lighter header! Before F1 engines went to one engine for the weekend, there were reports of "qualifying" headers made of .015 (0.4 mm) thick Inconel! Race headers were more like .030 (or 0.8mm). I pity the poor guy who had to fabricate those 'throwaway' qualifying headers. Inconel is not fun to fabricate or machine.

From what I gathered, no, they don't mandrel bend the 2-3/8 or larger primary F1 tight radius, .030 wall tubes. They press-form (draw) half of a torus, which looks like a bundt cake pan. Welding two of these together gives a 360 degree torus (hollow bagel which looks like a small torque converter) which can be cut to any degree of bend. Amazingly short bend radii are possible with completely smooth surfaces and very thin walls. I sorta doubt Cup headers go that far, but they might.

 

OldSStroker

boy you sure can do a lot with a NASCAR money budget/Sponsorship

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They press-form (draw) half of a torus, which looks like a bundt cake pan. Welding two of these together gives a 360 degree torus (hollow bagel which looks like a small torque converter)
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yes, awesome talent and equipment !!

 

After doing some reading in that book, he came to the conclusion that instead of the pressure wave going all the way down the pipe, it could "turn the corner" and part of the wave go back up the pipe leading to a closed valve. Now this can be of benifit bcuz you will then have 2 pressure waves in one pipe and could create a wider range of negative pressure in the exhaust pipe to help scavaging. But, he came to the conclusion that in the long run there is more negative effect then positive. When he goes into detail of building a pratical exhaust, he even says that it is better to go with a 4-1 then 4-2-1. The problem with a good 4-2-1 header in a street car is there isn't enough room for one. He suggest that if you do use a 4-2-1 header you should have no less then 18" from the bottom of the Y to the collector. I forget how much he said for the first part.

 

Page 101-102. Unduly short primaries can lead to this. Jack Burns discussed convergence angles also with 10-20 degrees being critical. If you have 20 inch or more primaries, that angle is doable. With 10 inchers it probably isn't. 19,000 rpm F1 engines use 5>1 (generally) stepped priamries of quite short length, which you might expect given the tuning rpm. 5-2-1's with 2-3/8 primaries 10 inches long would be a problem, I'm quite sure.

Remember Smith's work was in the 20's -50's, first published in 1962. Inspite of the objections you point out, high-end winners are using the 4-2-1, probably because it is so tunable to the engine and even a specific track. Unfortunately, there is a lot of cut-and-try still required, which costs cubic money ($^3).

I contend that a street full muffler system could be designed and built for the 450 rwhp area for say an LS1 H/C package that would be better than the 4>1 out-of -the-box headers used now. How much better? 5% is 20+ hp. I think that's doable for maybe $25/horsie more than the box header systems. That equates to a 120 hp H/C increase costing 3 large. Really, a broader torque curve would probably be more beneficial than 20 peak hp. That's where 4-2-1 is good.

Just my $.02. You opinion may vary.

 

I understand his work was done a while ago, but even he says, that at that time, there had been no evidence of the theroy. What he did say is that if you had to run a 4-2-1, the last 2 pipes should not be joined until much farther from the previous joint, most perferably in the collector. The problem he had, I beleive, is that the second pressure wave was causing a early rise in pressure near the connecting cylinder and defeating the scavaging effect on that cylinder. He seemed to get better results with the 4-1 system.

Putting together a good 4-1 system could help that LS1 engine even more. One of the problems with the out of box LS1 headers are too short. You could probably help match that intake better with a 4-1 header with a primary length closer to 40", but there isn't enough room for something that long in a 4th gen. I know the BBs in the Engine Masters were closer to these lengths, I didn't see what the SBs did, but I would assume that the pipe length would be similar, just smaller dia. primaries.

 

How is it "not possible" to have a longer primary? Just move the "y" joint back farther, along with the primaries. You'd have to remove part of the reinforcing, but that's doable.

 

I didn't say that it was not possible, just not feasible in the room you have to work with.

 

I have a set of CIA Tri-Y's on my 95 Imp SS/ with 396. There is proof that the 1-5/8 tri-y's out flow and out perform the 1-3/4 quad-1. They are not as long as jet hots, but I like them.


I cant find the site, But i have seen it and it is out there.

 

Balanger headers for ls1s are 1 3/4 and are 4-2-1