dart headers
I can appreciate that,also its a pretty unique deal when your racing with limits like you are and as crackedback said step headers work in a very small window so if your in it they could be of some benefit.I would be skeptical though of any increase over low,low teens for h.p. and only in a small rpm range and they defintiely do not flow as well as a true 1 3/4 header.Step headers were a fad long before tti had them and their pitch was the torque of a 1 5/8 tube while still maintaing upper end h.p. but we all know there is no free lunch.I know of alot of small block cars running 1 5/8 and running very well,12s to 11s,now these are cars that have ported heads ect but run on 3.55s to 3.91s so they are street cars.Ive found alot of it is based on cubic inch and rpm range,there is at least one calculator I stumbled across on a circle track site that seemed to coincide with what Ive experienced.I wouldnt run a 1 3/4 on my 340 in its current form (approx 420-430 h.p w/6,300 shift points) since in my experience it wouldnt add any overall power and minimal if any afect on e.t.s,but this could also help explain why tti elected to do a step tube design simply to try to acheive a happy medium.At any rate its hard to beat a straight 1 5/8 or 1 3/4 since in the proper application either will make more overall power than a step tube design.
Thanks, but I still can't agree with some of your blanket statements:
* "and only in a small rpm range and they defintiely do not flow as well as a true 1 3/4 header"
* "At any rate its hard to beat a straight 1 5/8 or 1 3/4 since in the proper application either will make more overall power than a step tube design".
- The exhaust dyno comparisons show the step headers as better across the board over 1 5/8" and 1 3/4" headers on a very mild 360.
http://www.moparmusclemagazine.com/...0307_mopar_crate_engine_exhaust/photo_17.html Then there is the fact of a lot of higher rpm Mopar small block Stockers use them with good results. As mentioned earlier, besides TTI's, I've seen several examples of custom steps, some starting as small as 1 1/2" or actually port-matched. A 1-2,000 rpm difference in operating range between engine combos can't be considered a "small rpm range".
There are other factors that come into play. Jetting should be checked and adjusted any time there is an exhaust change to
optimize the combo, just as noted in the intake manifold discussion. I don't think that was done in the header comparison so we can't say for sure if TTI's would have been even better or worse. As an example, I added a 3" X-pipe with Dynomax Ultraflows and it ran at least as fast as before. Then with slightly leaner jetting, it picked up a bit more. But I agree with you that certain combos/applications would prefer smaller tubes for torque based on the rpm range they run in the most.
A specific header can be better than another in a
very specific application because there are bore, stroke, cam, rpm, weight, etc. differences that can change the diameter requirements, tube lengths, equal/unequal lengths for fitment, etc., even if the difference are small. There are plenty of good performing examples of straight and stepped headers. The debate is an old one and can go on forever. One interesting story is about a very fast 340 Mopar racer who spent $3,000 on a set of custom stainless headers. I don't know what he was running before (I'm sure it wasn't a $100.00 mail order special), but the new set didn't help any! Why it didn't run better could have been one or more of many reasons, not just because it was stepped.
But when racers who look for every .01 of ET do use stepped headers, I pay attention. Just don't make blanket comparison statements putting a particular type down. There are too many variable and examples either way. I'm just giving examples of combos that TTI's do work in and people can factor in their own variables and priorities, whether they are financial, performance or convenience.
