MadBrad

Been doing a little bit of reading here and there. One theory that I have come across couple sites that say the ideal diameter for an intake is when the intake has 25-35% more cross-sectional area than the TB's bore cross-sectional area. Assuming that the stock 2.2 ecotec throttle body is 58 mm the ideal diameter should range around 64.85mm (25%) - 66.13 mm (30%), or 2.55" - 2.60". The dia. of the AEM intake is about 2.75" and the Injen intake is 3". So to produce peak torque early in the power-band a 2.5-2.6 intake would be helpful. But I also have to understand the possible design of the AEM and Injen intakes is to produce power later in the higher rpm's. 2.4 throttle body is 65 mm (not sure, I can not find a reliable source for the size). So ideal range is 72.67 mm - 74.11 mm, or 2.86" - 2.92". So neglecting everything else. Would it be correct to say that the 2.2 would benefit better with the 2.4 throttle body if you have an aftermarket intake? I am still learning and reading some more on this. Feel free to theorize with me.

Thnx MadBrad.

MadBrad

bump

MadBrad

bump. bored

BLKLS

Umm... Just buy an intake lol.
The injen works great for me...
Not trying to be a jerk man, unless your gonna go mad detailed and use that scientific detail all the way threw a full motor build I wouldn't worry about it.

Lmao me too

MadBrad

It's cool, plus like my Injen. I am currently researching different IM designs. I plan on using my schools machine shop, SAE team, and simulation computers to design a custom IM for my current setup.

BLKLS

Sounds intense, lol want a stock one to model after?

Leafydialupking

iTrader: (1)

What school? You should know that there is real math and not ricer math behind choosing the diameter of intake piping. Just use your fluids equations and keep the intake velocity near to but below 200 mph, which is the magic number where you have good velocity but arent creating too much drag. Intake's flow vs velocity, you want both high but you cant get both high. Then once the intake tubing is the correct size, then you want to size the tb for throttle feel/resolution and flow.

Now intake manifold designs, equal length runners (not log), tuned for a thousand or so above your peak rpm goal, with your header tuned a thousand or so below. A wider split provides a wider powerband but less peak and vice versa. Then plenum... um its black magic, theres some formulas that give you a basic idea but finding the correct balance of wot flow and throttle response takes trial and error, I dont even think theres an accurate computer model of it.

What school, and were you at michigan this year?

MadBrad

I am a sophomore studying my BSME at The University of Texas at Arlington. I have not taken fluid dynamic systems yet.

Ricer math? I am not researching just car forums. And yes I understand that there is more to it then just that. Yes you could use fluid dynamics systems to simulate flow rates in a tube. Dry air is thought to behave like a compressible elastic fluid. And as far as I know there is no accurate computer models to find the correct balance flow and throttle. The best answer I can find about the black magic of the plenum design. Is to simulate it as an acoustic behaviour, or sound wave and it's frequencies. The plenum acts as resonance chamber. How the resonance chamber works is that it acts like an oscillating spring (i.e. imagine the plenum acts like the spring) with a block attached on the end of the spring (imagine the air wave in the IM runner to behave like the block) . As the block compresses the spring, the spring builds or stores up energy and when the spring uncoils, the block is given a push or energy as it travels away from the spring's compressed position Like our block and spring, the air resonates ( or compresses the spring) at a certain frequency (spring bouncing back and forth) inside the plenum and gains energy (pressure) . The air wave is then bounced back down the IM runner. The problem is trying to match the resonance wave as the intake valves open and close. The basic mechanism of intake manifold "tuning" or design is to provide high pressure at the intake valve so that the mass flow rate into the cylinder is boosted at a given engine speed or rpm.

Leafydialupking

iTrader: (1)

You're talking about holtzman resonance. That doesnt really apply to what I was talking about with plenum size, technically it effect plenum geometry. With plenum volume you get two things, bigger is better for throttle response and smaller is better for wide open throttle power. You basically have the plenum as a Reservoir of air and since you know that air doesnt move instantaneously you have a wait time between when the throttle opens and when the new pulse of air starts coming in from the air filter. This is where air intake length plays a part and why my blower setup has better throttle response than any of the blowers in cobalts. My air filter is right on the tb, so I have like no wait time for the first pulse to reach on opening the butterfly, but I have virtually no wave tuning effect from the intake tubing (honestly I really dont need them with the blower). You want to tune your intake tube for the desired torque/power peak, and imo make the plenum large enough so that the first wave can reach the throttle body just before the plenum would "empty" at some rpm that you think you'll be mashing the gas. Thats my thoughts on plenum size, but it normally ends up being larger than the displacement of the engine. Works great for an FSAE car since you're only dealing with a 600cc baby engine, BUT there you have the restrictor to think about.

MadBrad

With that in mind, what do you think a top down design vs. a side mounted throttle body on IM would do? Thinking top down design with equal runners.

Leafydialupking

iTrader: (1)

I would think I would want it top fed but have part of the plenum be an elbow to a side mounted tb. Its easier for packaging but it may not be the best for geometry (performance).

Blk08coupe

The term you are looking for is called Helmholtz Resonance.

Leafydialupking

iTrader: (1)

Yeah thats right I was on my phone and can never remember the exact word.