anti-reversion cones in crossover exhaust

[glenn654]

Hey Guys,
I just read in my new copy of Kent Pasers' book Speed with Economy that he modified a crossover exhaust with mis-matching ports w/ anti-reversion cones installed and claimed his FF was reduced by 1 ghp in cruise. Does anyone make and sell these systems? Does anyone else have any experience with one of these? Could such an improvement be this easy and effective?
At todays' cost of fuel an exhaust like would pay for itself very fast.
I really want to know if this is too good to be true.

Glenn654

[Mike S]

This was popular in the hot rod arena 30 or so years back.

Basicly what I remember of it was the cones stopped reverse exhaust flow, due to long cam overlap, at low rpm ranges, where header schavengering hadn't yet started.

At the rpm of an a/c engine this might be helpful, however the cam timing is so mild that I doubt that there can be much benifit, unless the wxhaust system has some major problems in the first place.

My .02$

Mike

[gmcjetpilot]

Originally Posted by glenn654

Hey Guys,
I just read in my new copy of Kent Pasers' book Speed with Economy that he modified a crossover exhaust with mis-matching ports w/ anti-reversion cones installed and claimed his FF was reduced by 1 ghp in cruise. Glenn654

I like that book and think the world of Kents work. He has some good concept and an overall gold mine of thought provoking ideas, but I would not particularly do them. The cool thing about this book and his work is he went out and welded it up and tried it. It may not work for me or apply, but it shows you how to conceive an idea execute it. What else can you do to the exhaust?

In regards to the anti-reversion cone I agree with Mike. I have a custom "tuned" 4-into-1 exhaust. Even if the anti-reversion cone worked or gave some benifit, the "tuned" 4-into-1 is way better than his base line exhaust he used, in my opinion. We have better exhaust technology in the last few years. Hey my first homebuilt homemade "Y" pipe with 1 & 3 and 2 & 4 tied together. About the worst thing you can do on a 4-banger Lyc, but hey I didn't know. It worked pretty well and was simple. Also the Cafe Foundation work and testing gave some insight. Like the cone deal the "header" has been areound for a long time on cars. I can't explain the 1-gph improvement, but may have something to do with the pipes he had?

The other issue with the CONE is messing around with the flared Pipe to Head flange. It's hard enough to work on the Pipes and nuts in that area as is. It may have benifit but have no way of qualifying it without doing it. Hey I could be wrong and it may work wonderfully.

Some of his estimates he states in his book, like the drag of an external antenna I take exception and think are optimistic. My estimate for VOR, Com and Transponder drag combined is about 1 mph at 200 mph. Just a Comm antenna alone is only about 0.30 mph. He estimated 5 mph? Not sure how he got that, but he did improve the speed of his plane significantly over a 10 year period. No mod was too large or too small. To be fair he made a lot of mods over time and many at the same time. Also a mod made early in the evolution adds more benifit than a later mod when the plane is going much faster. It's big difference in going from 160 to 161 mph than going 200 to 201 mph, drag reduction wise.