Zeus

I'm in the middle of designing and building a sheetmetal intake manifold, and I have the basics done already (flanges drawn up, port sizes/locations, etc). What I'm looking to do now it determine the optimum runner length, and plenum volume for my application.

Is there a cheap way to do this other than purchasing Dynomation or trial and error on the dyno? I have a limited ability to do CFD (computational fluid dynamics) with Solidworks, but I doubt it's going to be powerful enough to tell me something useful.

I'm not looking for every last drop of HP/TQ here, I just don't want to design a turd for an intake manifold.

rjgto

Where do you want your power to peak at?

SStrokerAce

iTrader: (2)

The 10,000 dollar question...

Yeah there is a cheap way to do it... LEARN THE MATH BEHIND IT.

"Scientific Design of Exhaust & Intake Systems" by Smith & Morrison

Would be the place to start.

Bret

Zeus

But if I had $10,000 to spend I wouldn't be asking for money saving advice now would I?

Keith

Search for "ram tuning" on google. You'll find a lot of info about runner crosssectional area and length.


The plenum, if I remember correctly, you want about 1.5 times the engine displacement for a 346 making about 520 flywheel(1.5 hp per ci).

Or about 520 ci of plenum volume.

Zeus

I hav the rev-limiter set at 6700 right now and shift at 6500.

Probably at around 6000RPM.

ConnClark

Google for "Helmholtz resonator" or "Helmholtz resonance"

then bone up on solving differential equations.

http://www.phys.unsw.edu.au/~jw/Helmholtz.html

SStrokerAce

iTrader: (2)

Yeah there is a intake already for that it's called the stock one.... you really cant do any better for that low of a RPM band.

bret

MadBill

The first thing I would recommend is some soul-searching re the desired RPM range. For example if you wanted "maximum torque from 1,500 to 6,000 RPM", your choices are: 1. Stock. 2. Variable geometry. 3. A belt-drive manifold (aka supercharger)
If you can narrow it down to maybe a 1,500 RPM spread, recognizing that gains in one area means losses in another, then you can begin working with the various formulas to get in the ballpark. For example, the formulae given by Curtis Leaverton, creator of Dynomation, are: Second pulse runner length = 108,000/RPM; 3rd = 97,000/RPM; 4th = 74,000/RPM; 5th = 54,000/RPM. As you can see, a given length can tune at several RPMs, but will of course "anti-tune" in between. The lower number pulses give a stronger tune. Plenum size gets a lot of different answers; you could do worse than approximating the sizes used by Hogan, Wilson, etc. for similar applications. Also, taper angle affects both power and effective tuned length (a 4° taper, 13" long runner tunes about like a 10" zero taper.) Bell has similar formulae, as do others; in fact one of the problems is deciding which to use. As the saying goes: "The man with a watch knows the time. The man with two is never quite sure."

Zeus

Just to make things clear to everyone, this isn't for performance reasons. I'm in a CAD class right now (Mechanical Engineering student) and this is my end of year project. The fact that I also want to put it on the car is just a "because I have it and can" type deal.

Zeus

I'm actually taking Diff EQ right now, I never thought I'd actually use it for anything cool.

rjgto

What is the port length of your intake runner in the head?

Zeus

~4.5"

SStrokerAce

iTrader: (2)

It's not that short thru the centerline of the port BTW, it's over 5"

Zeus

By inverse logic, does this mean that a reverse taped runner would behave as though it's longer (i.e. a 10" 4° inverse taper acts like a 13")?

rjgto

No, because we are interested in flow in predominantly one direction. On a naturally aspirated engine i wouldn't go more than 1.5 degrees taper, 4 degrees is quite excessive, it may work but i have no experiance with that much taper. And yes you need to know the port length through the CENTER of the port, you can do this easy at home, get some string or thread and lay the string on the floor from the valve seat the the valve contacts to the entry on the intake manifod face and measure the length. Then lay the string on the roof and measure, add both lengths than divide by two and that's the port length through the center of the port.