Message

Sent: Saturday, December 20, = 2003 9:06=20 PM

Subject: [FlyRotary] Dumb = intake=20 question

Greetings,

OK, I have my = dunce cap=20 on, since I ignored the previous intake lectures. =

Say you = have TB that=20 has two butterflies, and each butterfly feeds one rotor (primary and=20 secondary). There is no connection between the=20 two rotors. Is the length of the intake runner = important for=20 full throttle operations?

I assume it = is, and=20 recall that racing manifolds can have a short, almost = non-existent=20 runner. I believe Ed used one of these originally, and = got=20 less than exceptional performance. If I recall correctly, it was = decided=20 that it would have been fine at racing RPM, but not 5500 or so, where = he=20 wanted to run.

Assuming it's = important,=20 is there a rule of thumb for the length of the runner for a particular = rpm=20 range? I'm wondering if I can keep my TB in the (turbo free) = left cheek,=20 and get enough runner length to optimize operation at=20 about 7500 rpm. Probably a silly idea, but my only other = option is=20 still trying to sneak it under the cowl to the right=20 cheek.

Thanks,

Rusty (I can = already hear=20 Ed screaming <g>)

Sigh! = If you would=20 only come to class, Rusty {:>)

Here is what = it appears=20 like. Since you are using an Open TB with two throats and no = connection=20 between the two rotor, the answer is still YES. For good=20 performance you do need to pay attention to your manifold = length. In=20 fact, at higher RPMs the appropriate length is even more=20 crucial.

But, since = they are not=20 interconnected, can not use the DIE equation. However, Here is = what the=20 calculations come out to using just a pipe from intake port out to = your=20 throttle body. I assume from your comment that you don't have a = lot of=20 length to deal with. I further assumed you do want to get some = help from=20 Intake "tuning".

The only way = I could see=20 to keep your runner length down and still get some benefit from pulse = tunning=20 was to calculate an intake length based on a pulse being = generated by the=20 closing of an intake port (the "A" pulse if you had paid attention in = class=20 {:>)) and arriving at the next opening of that same port. = That is not=20 the best possible arrival time, but longer timing - say to the closing = of the=20 port to overcome reversion makes the length infeasible. =20

So based on = that - it=20 looks like your length from port to butterfly inlet of TB ranges from = 13.1"=20 for 6500 RPM to 11.5 RPM for 7500 RPM. This provides time for = the pulse=20 to be generated by the closing of the port and to arrive after that = port opens=20 again after bouncing back from the throttle body once. So from = that=20 Length you would need to subtract your block to port distance of 2.5" = and the=20 length of your throttle body.

Ordinarily, I = would say=20 that the prop load (with a 2.17:1 PSRU would likely keep you from = reaching the=20 rpm range where this tuning would become effective. But, perhaps = with a=20 2.85 ratio, its within reach.

Hope this=20 helps

Ed=20 Anderson