Volumetric Efficiency

[CaffeineTripp]

I've done quite a bit of Google searching, some number crunching (then again, I didn't even pass Geometry in high school), and I'm looking for either an easy calculator, or a website which contains the VE of the B series engines, specifically, the B6-ME SOHC.

[CaffeineTripp]

Maybe not even the VE of the engine, but I would need at least how many cubic feet of air it consumes in a minute at various RPMs. That'd be definitely helpful.
Contacted Mazda directly, but haven't received any word back.

[Ryan]

This number changes dynamically according to (basically) RPM versus Throttle position or MAP.

It also depends on a few other details.


You won't find a VE table unless someone somewhere has written a tune for a B6 with your EXACT setup.

Any cheap tunes are called Alpha-n, which is RPM versus TPS.

This tune is written for a SPECIFIC engine. even between motors, it won't be the same. The tune has exactly zero capability to change according to hardware changes (intake leak, exhaust leak, burnt valve, low compression, CAI, exhaust changes, etc)


You can crunch the numbers yourself though.

The manual will spec a manifold vacuum at idle. Using that number (the pressure inside the plenum) you can figure out how much air is filling the cylinders, and start there. You could assume atmospheric at wide open throttle and low RPM, and assume close to 100% VE. (assuming lower VE will net a more rich tune, which is safer than lean)

VE will trend upward with TPS and downward with RPM.

[CaffeineTripp]

This number changes dynamically according to (basically) RPM versus Throttle position or MAP.

It also depends on a few other details.


You won't find a VE table unless someone somewhere has written a tune for a B6 with your EXACT setup.

Any cheap tunes are called Alpha-n, which is RPM versus TPS.

This tune is written for a SPECIFIC engine. even between motors, it won't be the same. The tune has exactly zero capability to change according to hardware changes (intake leak, exhaust leak, burnt valve, low compression, CAI, exhaust changes, etc)


You can crunch the numbers yourself though.

The manual will spec a manifold vacuum at idle. Using that number (the pressure inside the plenum) you can figure out how much air is filling the cylinders, and start there. You could assume atmospheric at wide open throttle and low RPM, and assume close to 100% VE. (assuming lower VE will net a more rich tune, which is safer than lean)

VE will trend upward with TPS and downward with RPM.

I was definitely under the assumption of the VE to specific engines, more looking along the lines of a general idea of VE for the B6. I was thinking somewhere in the neighborhood for 80%-90%, which isn't too bad for a 16 valve, though SOHC, at 5000-6000 RPM at WOT. Then again, there are so many variations, as you stated, given atmospheric pressure, sensor output, and a slew of other variables that can't really be accounted for unless I bring the car to a shop and have them plug in a barrage of sensors.
Mainly, I'm wanting the VE to design an intake around that particular number to net the most amount of horsepower and torque at mid- to high RPM. Of course, I'm no engineer and am not that great with the math, but since there are quite a few calculators out there and some good tutorials, I think I might be able to get the hang of it.
A bit off the subject, but I'm leaning towards (and I know, designing an intake is a little pointless since there are some available out there and they don't give that much of an increase in horsepower, maybe 1-3 depending on RPM, but it's just the matter of designing one specific for this engine, and heck, someone may want to know in the future) 2.5" near the throttle body and enlarging to 3", with either various couplers or tapering by fabrication and welding, close to the MAF/air filter.
Reasoning for the larger pipe at the beginning and tapering to a smaller diameter is this; the 3" pipe would be excellent for upper RPM, where some of the power is lacking, however, at lower RPMs, where you'd need the get-up-and-go there wouldn't be enough velocity. With a 2.5" pipe, or smaller in general terms, would be great for low RPMs, but lack the volume for 5000+ RPM, essentially choking the engine. Yes, a lot of velocity, but not enough volume. Of course, air cannot be compressed without some sort of forced induction; turbocharger or supercharger, which would greatly increase the amount and velocity of the air going to the engine. And, since I'm no scientist either (nuts), I'm also assuming that with a larger pipe at the beginning, and tapering down, it would potentially increase the amount of volume initially, at least to a point, and then increase the velocity the closer it got to the reducer. Fluid dynamics is not a strong suit of mine, but I'm thinking that with the reduction in pipe size will act such as a funnel; increasing the velocity the smaller the pipe, hence why I want to know the rough estimate for the VE of the engine, to design the pipe size.
But I could be wrong.

[Ryan]

You're very much on the right track.

Plenum design is one of the hardest things you can do to an engine. How air behaves is 20% science and 80% magic. They've been working on modeling fluid flow for over a century, and still, Navier-Stokes equations can only fully solve some 70-odd real life problems, most of which are idealized and useless. there are other theories and equations, but still, anything turbulent is basically magic.

The things you want to look into are plenum volume for throttle response, runner length for resonance tuning, diffusion mechanisms for increasing plenum efficiency (basically don't make a channel wall diverge from the centre line more than 11º if you can help it) trumpeting for efficiency (a basic rounded pipe end is at least 25% more efficient than a square edge entrance), convergence for even cylinder feeding.... the list goes on. Then you take it all and apply them separately and the final product will behave hardly anything like you planned.

If you don't like math, this probably is going to be a 'that looks about right' project, which is totally fine!

If all you want is a basic flow number to roll with, you can back-calculate it from HP. 88HP at 5000 RPM translates to about 60 CFM. That, in theory, is the most you will see from the stock hardware. You need to breathe more to make more power, 70 CFM is around 100 HP.

Here's a neat article with well explained equations: http://www.epi-eng.com/piston_engine_te ... ciency.htm

[CaffeineTripp]

Probably be going along those lines with 'looks about right', which is too bad. I suppose for the time being we might just hop onto eBay and pick up a knock-off intake, MAF adapter, and cone filter and do it that way. Wait until the BP swap for the good and expensive parts, where it counts of course. No sense in spending $300 on a name brand intake.

Thanks for the help!

[wytbishop]

Intake design is one of those things where the best guys at it in the world understand the math and the physics, but they're the best at it because they have tried thousands of variations and know what works. Certain high level attributes can be predicted and designed but a lot of the finer points of intake design are still done with trial and error on a dyno.

Your best bet for measurable success is to take a design that you know is good, but maybe has one obvious flaw that you know can be improved and fix that. Unless you have the ability built many prototypes and do multiple dyno runs or a flow bench at your disposal it's going to be very difficult for you to know what affect the design concepts you are implimenting are actually having on the engine.