Plenum Setup For Itb's

[xmoht]

From what I have read so far, taking advantage of resonance effects to naturally increase the pressure within the intake manifold/plenum is workable on a single throttle body.

 

I have seen a few setups where people employ a plenum over the top of ITBs in what I can only assume is an attempt to take advantage of this pressure increase. From the more technical sites I have seen they base their calculations on intake manifold after it has passed the throttle body. So with ITBs a particularly fancy intake manifold design would take advantage of the pressure increase, but the plenum would be largely useless (with the exception of air filtering / noise).

 

Is the increase in air pressure within the plenum going to be significant enough to contribute to power if it is only adding pressure to the throttle body rather than the valves? (As in an ITB setup with plenum covering them)

 

Is the increase in pressure from a combined plenum / intake manifold design going to be more significant than the advantage of using ITBs?

 

I have had brief conversations with a few very wise members, but I thought I would get this out there and hopefully find a few more answers (read: opinions).

[snot35]

I'll have a crack at this. Please note I'm not a professional in the field or an engineer, just an enthusiast. From my understanding, the pressure waves are created whenever there is any great change in volume or an obstruction to reflect off of. If you have ITB's and then a plenum then you will probably get a minor reflection from the throttle plates, and then a larger one from the volume change of the plenum. This reflection probably wouldn't be as big as if it were a single plate on the plenum, as there is nothing to disperse the reflection. However, if you're building a motor for torque then more than one reflection may actually be desirable if you get it right. It's akin to having two runners that you switch between. I believe Ford and Porsche have used this system, among others.

 

To completely not answer the question, how long is a piece of string? It all depends on runner length, diameter, plenum design as well as how much cold air your plumbing in. Probably the bigger question is what are your resources, and your design goals?

Edited June 26, 2010 by snot35

[altezzaclub]

Probably the bigger question is what are your resources, and your design goals?

 

Yes, how can you measure success?

 

If you're going to find an extra 3 or 5bhp it would pay to have a dyno in your garage at home. You would be looking at a lot of dyno runs and other factors like the weather may overwhelm the change you get.

 

The only other ways I can think of would be an oxygen meter to see if the extra air made it leaner, or pressure meters along the intake system to see if you could measure a pressure wave change.

 

Have a chat to Billzilla, this is right up his alley!

[xmoht]

Thanks for the replies. I'm just looking to getting the most out of a naturally aspirated 5K as possible and hoping to do it in something of a budget.

 

Unfortunately a dyno in the backyard is going to put my financial situation into the red a little too much, so I'm relying on getting it mostly right the first time. Probably sounds naive but as it's based on physics I can calculate a pretty close guess to how it's going to need to be.

 

Yes I know, "most power possible" is pretty ambiguous. I want to get a decent amount of power out of a mid range power band and of course having a decent looking dyno sheet to pin on my fridge wouldn't be too bad either. As far as extremely specific "this is how much torque I want in this rev range and this is the top speed I'm going to get" I am far from working out as I'm still in my infancy of learning about engines.

 

What's the easiest way to contact Billzilla? Through that performance forum he uses or does he have an email on his webpage?

[LittleRedSpirit]

Yes it will help the resonant pulsing. Its volume will determine how effective it is. It is primarily something people do to make there itbs legal and quieter. It can have the added bonus of improved air filtration through the use of a proper panel filter. Open pods and velocity stacks are for homos really. Old technology.

 

The most powerful stock rwd silvertop I have ever heard of mad 100kw atw, and it had a modified factory plenum chamber on it.

 

I may point out that Anthony Kellam told me this so its most likely 100% bullshit and then some.

[xmoht]

Yes it will help the resonant pulsing. Its volume will determine how effective it is. It is primarily something people do to make there itbs legal and quieter. It can have the added bonus of improved air filtration through the use of a proper panel filter. Open pods and velocity stacks are for homos really. Old technology.

 

Yes I heard that with ITBs you get resonance tuning through efficient velocity stacks, but I like to get off the bitumen every now and then so I need a remotely decent air filtering system.

 

Thanks for the directness of your answer LittleRedSpirit.

[philbey]

Open pods and velocity stacks are for homos really. Old technology.

 

haha gold.

 

xmoht, I got your pm about Helmholtz resonance and I've been mulling over it for a couple of days. That's all about tuning runner length so that the pressure wave at the right moment increases locally at the valve as it opens etc.

 

Avoid getting too scientific about it: There's plenty of straightforward equations to size intake runners. Sure you want to make the most of this motor, but your plenum will NOT get big gains that cams and carbs will.

 

I would say you'd be lucky if the difference between an average one and an excellent one netted you more than 5 horse power.

 

As for the plenum, again there are rules of thumb about sizing them. You want the area of the plenum (cross sectional in direction of flow) to be greater than the combined area of your runners etc your biggest issue will be pressure drop; use trumpets inside the plenum, avoid sharp hard corners and edges etc.

 

If you are game, download a copy of Fluent, model your manifold and learn CFD!

[xmoht]

As for the plenum, again there are rules of thumb about sizing them. You want the area of the plenum (cross sectional in direction of flow) to be greater than the combined area of your runners etc your biggest issue will be pressure drop; use trumpets inside the plenum, avoid sharp hard corners and edges etc.

 

If you are game, download a copy of Fluent, model your manifold and learn CFD!

Tried to get my hands on Fluent, nothing about getting it from their website or the people who are supposedly local suppliers. I guess it's one of those things that are meant for Universities and businesses to buy. Couldn't even find a reliable looking torrent.

 

Will I still want my plenum to be greater in size than the combined area of my runners, even in a quad throttle body setup though? Will the pressure that has built up in the plenum be mostly transferred in to the runners?

 

From what I can gather the pressure will be mostly retained before it goes to the runners, where it will again be subject to an increase in pressure. That all sounds far too positive and good to be true though, what's the catch?

[ke70dave]

see if you can get your hands on an SAE paper on resonance

 

http://www.sae.org/servlets/productDetail;...CD=2002-01-3318

 

something like this.

[Felix]

If you want to get the most out of your 5k, put it in a ke1x. You'd need to make 25-30% more power and torque in a ke70 to match the performance of a milder motor in a ke1x. ie. spend 2x the money or more for the same performance.

Edited June 28, 2010 by Felix