Exhaust manifold designs

[jetrcr]

Thanks for all the info on exhaust pipes, very interesting stuff. One question I have that I cannot seem to find any answers on are exhaust manifold designs. I race in a class that allows for 1200cc engines but you must run a single exhaust expansion chamber. For me this means I need to run a three into one manifold. I realize this is a real performance killer but those are the rules. I am currently using the stock cast aluminum manifold and have a hand made steel dry pipe that seems to work ok. I had a guy who builds pipes for snowmobiles build the pipe using test pipes and a dyno (with his years of experience doing in doing this). I have since made copies of this pipe that seem to to well but I want to do more. I am a Product Design Engineer, I own my own engine dyno, I have all the tools necessary to fabricate my own pipes, all I need is some direction.

If I keep my current 3:1 exhaust manifold how do I compensate for its design?

Does anyone know of any design software for these types of manifolds and pipes?

Thanks!
Jim

[Admin]

I would like to have your ECcalc Excel file once you're entered all the data into it. Then I might be able to make suggestions for changes to the design.

[Sidewindermike]

Greetings Jim,
I am currently working with a 2 into 1 expansion chamber system also limited by our class rules. I have found that the shortest manifold works best. That is the distance to the merge of the 2 cylinders. The return wave strength is reduced when the pulse enters the manifold and splits in two. Longer manifolds make less power. I have recently installed pressure analysis equipment which allows me to look at the pulses in the pipe and the pressures in the combustion chamber.
Regards Mike

[jetrcr]

Thanks for the info Mike, this is what I suspect. When the guy building the pipe initially started he built his own manifold and it didn't really work all that well. He ended up using the stock Yamaha 3 into 1 manifold even though the #2 cylinder had a shorter overall distance.

I've started to fill out what I can into the Excel file but it is difficult to compare the header pipe with the manifold I am using. For whatever reason it has been really difficult for me to find anything written about these types of manifolds.

Thanks again!
Jim

[Admin]

Due to the complexity of return waves interfering with the other cylinders this may be just something you need to go just by trial-and-error.

[revengable]

If you get beyond the equal length puzzle. There are 3 sets of waves 120 degrees apart. I ran my 7k pipe through ecalc at 21k. My fatty peaked at 8.8 boost at 6500. 5 to 6 boost from 9500 to 13000. Then an increasingly negative effect from 14500 to 21000 where it was peaked at 0.7. I am working with an 835 cc triple.

The factory Japanese manifolds are a tri-Y style to get equal distance. Mine is a trident with a longer radius on the middle branch.(all bend 90 degrees at the block)
Kudos to Michael.

Thanks for listening,

Terry

[revengable]

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Please disregard my last post.....TA

On the subject of triples. Assuming equal length legs and 120 degree even firing order.There is a strong plugging pulse coming from an opening port as the previous port begins to close. Not a reflection but a positive wave the same one that goes down the header to the diffuser. This can be tuned by length/volume for torque before the frequencies of expansion chamber. Like a LeMans start calls for or a bogged turn on a buoy. My port timing is 178 staggered 120 is a lot of overlap. I have a rotax chamber I can fit on my boats but in all fairness its failure was probably do to my stinger sizing. With Mikes data acq and a dyno my drivers could place high enough to get inspected.

I measured that pipe and entered it to ecalc. It was pretty mild I thought.

Thanks again,

Terry

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