I had another thought (eyes rolling - when is this guy gonna shut up) - some may ask, if dp is an issue, why not slow the air down by making big intake runners. Big intake runners = low velocity = low dp.

Well everything is a compromise. Engines, because they operate over a wide range of RPM's have different inlet air requirements. One thing I remember from my reading, is that an engine needs a certain velocity filling the cylinder at low speed to get good fuel/air mixing and swirl in the cylinder. It takes some intake velocity to produce torque in other words.

So, the ideal situation would be an infinitely variable runner length AND diameter - and make it out of unobtanium while you're at it.

I don't know how big an effect Helmholtz tuning has on engine output, but I believe it is significant as F1 engines typically have variable length intake runners (like a trombone) with the runner decreasing length as RPM's rise. Seems like one would not go to that much trouble unless they got a pretty pronounced effect from it.

 

[QUOTE]Originally posted by silvershadow
Ideal gases (like air at low temperature (atmospheric temperature)) expand when heated.

 

Also, I think it helps to catagorize things so we're comparing apples to apples i.e. Weapon R, PRM, Comptech, and stock vs comparing these to the AEM/Injen types.

 

I have seriously considered making a "trombone" intake pipe on many ocassions, but always get sidetracked with other more important projects (read, pay the bills). I'd still like to do it...it would be kind of fun...and the space is there in the engine bay without the stock box.

I'll have to seriously consider this as a playtime project this summer...

 

[QUOTE]Originally posted by MacGyver
I have seriously considered making a "trombone" intake pipe on many ocassions, but always get sidetracked with other more important projects (read, pay the bills).

 

A short ram intake would be good at high rpm where there is lots of velocity to promote mixing, and you only want to get a lot of air into the engine with as little head loss as possible. You would still need to duct cold air to it though.

Engines with variable intake runner length have short runners for high RPM and longer runners for low RPM.

Friction loss in the piping is 4fL/D (not including the velocity term multiplier). f is the friction factor and if memory serves me right (I'm not at work yet - so don't have my books in front of me) the largest friction factor is about 0.01. So if we assume that L is about 2 ft and d is about 3 inches (I don't know the exact numbers) you have 4*0.01*24/3 = 4*0.08 = .32, which (you'll have to take my word on this) is not large (it's not small either). However, the K factor, which is weighted just as heavily as the friction factor, for a bend is about 0.5, and for a butterfly valve fully open may be as high as 0.9 (again I don't have my books here at home - so I'll check the numbers when I get to my office and post the actual k factors)

 

[QUOTE]Originally posted by MacGyver
I have seriously considered making a "trombone" intake pipe on many ocassions, but always get sidetracked with other more important projects (read, pay the bills).

 

Now that we have kicked the dead horse of intake design to death, I'm going to talk about filters a little bit (I have to - it puts bread on my table)

There are several parameters which describe filter performance - efficiency, permeability, and dirt holding capacity.

With that said, I have seen two general types of filters used on S2000's - pleated paper filters (like OEM) and foam filters.

Pleated paper filters are called surface filters - the dust is captured on the surface of the filter itself.

Foam filters are depth filters because of the large pore size of the foam - In other words the particle penetrates the foam and eventually will be trapped by it as it travels through the filter media.

Air filters are categorized by pore size - and often are tested with what is called AC Fine test dust (used to be called Arizona road dust). For some reason, Arizona produces very fine dust.

Pore size in air filters typically runs from about 5 microns absolute up to about 40 microns absolute (maybe larger even). The interesting thing about air filters is that they will capture particles that are 1/3rd to 1/10th the pore size, so a 20 micron pore will capture particles, at very high removal efficiencies, down to about 2- 5 micron.

I don't know what pore size the filter manufacturers typically use, but I would suspect that removal efficiency is not an issue with any of the filters we would normally use.

The second parameter is permeability - and this is a function of the filter media, porosity, pore size, and general construction. The pressure drop through the media is related to velocity through the media (also called flux rate, air-to-cloth ratio, face velocity, capacity, etc.)

This is where some filters will excel, because their permeability will be greater than others. For example, K&N shows an air flow permeability test in some of their ads. The little ball in the rotometer goes all the way to the top on their filter but is in the middle on another filter.

One can make up for lack of permeability by adding surface area (a big filter rather than a small one) which reduces the velocity of air through the filter.

This is one area that concerns me about aftermarket filters - most of the ones I have seen are considerably smaller than the OEM filters - less surface area - so even if they are more permeable, they may have the same pressure drop as the OEM filter.

The third factor is dirt holding capacity - this is essentially an indicator of the increase in pressure drop through the filter per unit weight of dust the filter removes. In other words, dp/gram.

One of the managers at the same company I work at is a weekend racer. He had an aftermarket filter evaluated by our labs, and found that while it was greatly more permeable when clean (good), as it got dirty, the permeability dropped off dramatically (bad).

Since Honda has engineered the S2000 very close to the edge, I am making the assumption that they also engineered the intake system that way. So with what I know about filters, and intakes, I made the decision not to mod mine(except for adding a cold air scoop). I might in the future, but it would have to be proven to me that it adds horsepower and torque, and it doesn't drop off 2 weeks after the new filter is put in.

One other thing, the dp through the particle buildup on the surface of the filter can be as high as or greater than the dp through the media itself.

So with all that said - I run an OEM intake system and filter with a cold air scoop, and change the filter every fall even though the car may only get 3-5000 miles a year.

If you are running an aftermarket system, you might want to change/clean the filter often particularly if you are going to do a track day or an autocross (i.e., high RPM, high inlet air velocity)

 

Now my brain hurts and I still have to go to work and be smart

 

So the Comptech filer counts as a "Foam" filter... correct.