Great .pdf discussing intake manifold design

[dsm-onster]

I just had to post this. It's great info. Especially for those of us in the market of SMIMs. You can take what you've learned from this and put it up against your desired results and see which intake mani will do best for you. Also for those who want to build their own intake manifold, you can "hit the nail on the head" w/ your design.

Induction Systems

It seams that this is geared toward N/A applications but the principles apply. Considering the mathematical model of the Helmholtz resonator, raising the air pressure is like increasing the runner diameter a bit. Increasing diameter decreases the mathematically ideal length for a particular rpm & Effective Valve Closed Duration. So one can get away w/ shorter runners for lower revs as opposed to an n/a setup of similar flow characteristics. Also, note that when plenum volume is discussedin the begining, it states that a larger plenum will generally be neccesary for high revs. But, it is stated later under "Helmholtz Theory" that a smaller plenum improves higher rpm performance. Doesn't this applies to n/a vehicles? When boosted, the intake manifold is not in vacuum and the opposite strategy should be employed I believe. ??? It's been a while since I've looked into the Helmholtz resonator strategy. . . I'll probably be spending the afternoon poking around for the answer.

 

[dsm-onster]

I think I've answered my own questions. The above .pdf states in the second paragraph:

As rpm goes up you need a larger plenum,
but a larger plenum will reduce throttle response and
low-end power. A plenum also reduces peak air
velocity through the carburetor (or throttle body).​

It seems that manufacturers employ the helmholtz resonator concept to increase throttle response, not just horsepower. So I was getting hung up on my own preference vs. the paper's articulation.

A properly sized plenum based on the helmholtz resonator model is ideal for response and flow. But as one goes higher and higher in the rev range, the plenum necessary to supply the air will conflict w/ the helmholtz effect.

So, in over simplification, a large plenum will allow the helmholtz effect to "ram" air into the intake runners during low revs. And during high revs, though the helmhotz effect is nulled, the proper volume plenum will be there to supply the engine. SMIMs shouldn't kill low end that much if properly designed. This is why s many have reported little to no loss in the low revs when swapping manifolds. . .

 

[DirtyBirdRacing]

Thats a very interesting read. But does the Helmholtz resonator theory still apply to our engines since we have an extremely long intake ram pipe length. Like doesnt the ram pipe length have to take into account everything from the filter to the plenum, such as the intake and intercooler pipes and such. The port and runner discussion was very informative. I think that intake plenums for our engines should be around 3 liters shouldnt they?

Bill

 

[DirtyBirdRacing]

A properly sized plenum based on the helmholtz resonator model is ideal for response and flow. But as one goes higher and higher in the rev range, the plenum neccesary to supply the air will conflict w/ the helmholtz effect. . .

Oh, so the helmholtz model is used to maximize throttle response and flow. But the higher in rpm's you go the more flow you need so the larger a plenum you need, so the more throttle response has to be jepordized I guess. Is that how that works?

Bill

 

[dsm-onster]

Thats a very interesting read. But does the Helmholtz resonator theory still apply to our engines since we have an extremely long intake ram pipe length. Like doesnt the ram pipe length have to take into account everything from the filter to the plenum, such as the intake and intercooler pipes and such.

since the turbo "grabs" the air from the intake pipe, I an inclined to ASSume that the aircharge sees the turbo as shortening the pipe. or atleast chopping the pipe at that point. So we have two intake rams to tune: one to the compressor inlet, and one to the plenum.

I think that intake plenums for our engines should be around 3 liters shouldnt they?

You know, I've heard this too. I'm attempting to understand why, though. I think if we can understand why then we can tweek the applications of the principles for our particular preference.

 

[dsm-onster]

Oh, so the helmholtz model is used to maximize throttle response and flow. But the higher in rpm's you go the more flow you need so the larger a plenum you need, so the more throttle response has to be jepordized I guess. Is that how that works?

Bill

I am supposing. . . as of now

Also, their discussion of displacement does not take in to account the volume displaced by a turbo/supercharger (this is an n/a article). So the plenum volume will be much larger for a 4-cylinder turbo than a 4-cylinder nonturbo.

A n/a 4g63 intake manifold is the same as a 1G turbo intake manifold in dimensions. . . That's something to think about.

 

[DSMunknown]

Thanks for sharing, Matt.

 

[DirtyBirdRacing]

Hi,

I did some research and came up with this.

To take into account forced induction, the only thing I could find was that you should take the temperature of the compressed air into consideration when using the pressure wave speed.

The intake plemnum should be larger then engine displacement, so I think the 3 liter intake plenum for ours eninges is good.

Also many people said that since on many engines boost changes so much that it is a "futile" attempt to mathematically design anything.

This came from http://www.eng-tips.com/ .

So perhaps if you are going for dragracing and top speed racing the math would be useful since you are going for max engine speed at all times. But for a road racing engine perhaps you should just do it by prototype testing, and develop the manifold that flows the best...

I would like to ask if anyone here has any knowledge or way to find information on the turbo era of f1 cars, becasue if anybuddy had it figured out it would be those guys, . Also I think that this is so complex that if any company had figuered it out it would not be common knowledge, if you know what i mean.

Bill