There is no formula for optimal intake manifold volume only guidelines of which i used the higher end

About the velocity stacks anywhere above 1-1.5" off the floor and below half is ok. There are 2 reasons in my design that require them to be mid plenum, the first is the diameter of the bell; the larger the better and placing them mid plenum means i can go larger while still maintaining a large enough gap between the plenum wall and the OD of the bell. The other reason is the runner length, the length of the runner in the plenum is still part of the calculation and i needed that length, the plenum cannot go any further from the head (it would hit the fire wall) and if the runners were any shorter i would never see my 2nd harmonic (the strongest of the 3).... the whole "3/4" off the ground for fast moving air" is just bad information

 

i agree with the idea of putting the trumpets further into the plenum. has anyone ever seen the inside of a plenum on the champ car cosworth engines? they almost hit the roof of the plenum they are in so far. making 800 hp from a 2.65L V8 at only 6psi running upwards of 13000rpm, i can't help but think they might be on the right track so to speak. of course there are a lot of other things that make the engine efficient, but i'm sure this is part of the equation.

 

Have you got any pics of the champ car intakes?

Lee

 

This is what I was talking about. It is a bit off of his style of intake manifold but I like the overall design and the idea behind it. http://forums.evolutionm.net/s...96546

 

I'll definitely pass on the huge pressure drop just for even air distribution.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by weiRtech &raquo;</TD></TR><TR><TD CLASS="quote">by "variable volume" do you mean tapered? i want the long answer!</TD></TR></TABLE>

You can do as some MotoGP and F1 cars do and have variable intake runner. The new Yamaha R1 has it stock. The velocity stacks have stepper motor that increases or decreases the length of the stack or tube to have the "variable volume" that is ideal for throttle repsonse and power.

 

Thats not done for the same reason... variable length trumpets like you are talking about are used to keep the intake runner "in tune" through the RPM band, with a fixed runner length you only have beneficial pulses at specific rpms, if you can keep the runner changing length in a accordance with rpm you can use that pulse throughout your entire power band. If you wanted good throttle response and high end power you would need a variable volume plenum not runner.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Justin Olson &raquo;</TD></TR><TR><TD CLASS="quote">Why are the velocity stacks protruding so much into the plenum? Seem a bit like overkill to me. The air that flows behind the stacks will have trouble getting into the runners.

Justin</TD></TR></TABLE>

you want to do that. allows more air to enter the runner.

i've been doing a bunch of research lately.

i've been told a couple times that 4 cylinders = 1~1.5% volume. cylinder is easyer to make flow evenley. when you get into a wedge, its hard to get 2 & 3 to flow evenly without a couple trys at plenum design.

good little tid bit from my buddy sam for finding optimal runner length for desired rpm:

90/runner length (to the valve) = desired rpm.

 

You would want closer to 1.5-2 times engine displacement (mine is actually over 2). There are many equations for optimal runner length, personally i like hemholtz i do not believe i have ever seen your equation nor can i figure out what units to put into it to get a reasonable answer

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Ben-NSI &raquo;</TD></TR><TR><TD CLASS="quote">You would want closer to 1.5-2 times engine displacement (mine is actually over 2). There are many equations for optimal runner length, personally i like hemholtz i do not believe i have ever seen your equation nor can i figure out what units to put into it to get a reasonable answer</TD></TR></TABLE>

its an equation that my buddy came up with and works pretty good. units are in inches.

sorry, posted under co-workers screen name.

 

according to your buddy's equation my manifold is designed for a peak gain at 6.9rpms

there are a few things missing from that equation including:

runner area
engine displacement
compression ratio

there are complex equations that take far more than that into account but thinking that a random number (90) divided by length could equal your tuned RPM is pretty ridiculous...