Anybody know what the volumetric efficiency of a stock 3.4L is?

[nova]

I'm running some numbers for various engine modifications and need the volumetric efficiency. I can just guess but I'd rather have the real deal if I can find it.

[Patrick Javert]

No clue, but doing heads, intake, and exhaust will get you better efficiency on any car. Cam will help too.

[Backfire]

That should change through out the RPM range shouldn't it? The intake system and exhaust system will resonate at certain frequencies/RPMs to give the best efficency.

If you can find an accurate way to measure RPM, fuel flow (like L/sec) and your A/F ratio, I could calculate it for you, but that is probably asking too much!! [img]tongue.gif[/img]

[ May 07, 2002: Message edited by: Backfire ]</p>

[nova]

<blockquote>quote:</font><hr>Originally posted by Backfire:
That should change through out the RPM range shouldn't it? The intake system and exhaust system will resonate at certain frequencies/RPMs to give the best efficency.

If you can find an accurate way to measure RPM, fuel flow (like L/sec) and your A/F ratio, I could calculate it for you, but that is probably asking too much!! [img]tongue.gif[/img]

[ May 07, 2002: Message edited by: Backfire ]<hr></blockquote>

It probably does change with rev but I was looking for an average or something similar.

Later on fuel flow, A/F, and RPM wouldn't be that big a deal but right now it is.

Anyway I think I've found some equations that I can back the VE out of using flywheel HP, compression ratio, and a few other things. I have to try it though and so far I've been too lazy. :D

[ May 07, 2002: Message edited by: nova ]</p>

[Blue Jay]

Ok, I've done a little bit of reading, the Volumetric efficency changes a lot through the RPM band. It is a function of the Piston speed.

At idle the Volumetric Eff of a 4 stroke gasoline engine is anywhere from 85%-100%. As you go up in piston speed (RPM) it goes down. Once you are at 6000 RPM, it's range is 60%-75%

[ May 08, 2002: Message edited by: Blue Jay ]</p>

[Backfire]

Where are those numbers from? You can have the efficiency increase with RPM if the intake and exhaust are tuned that way.

There are pressure waves in the two systems. There are peaks and valleys,high pressure and low pressure. When a peak arrives at the intake valve just before it closes, you get a high pressure region near the valve which helps "force" more air into the cylinder before it closes. When a low pressure wave reaches the exhaust valve just before close, it helps draw a little more residual out of the cylinder before the valve closes.

I have seen volumetric efficency close to 100% at high RPMs when the systems are designed for that. If those numbers are for our cars specifically, that could be true. But if they are just general they won't be very accurate for a engine power sim.

[ May 09, 2002: Message edited by: Backfire ]

[ May 09, 2002: Message edited by: Backfire ]</p>

[Backfire]

Vol Eff = Mass of air inducted/Mass to fill displacement@ambient conditions

To get mass of air inducted you can use the fuel consumption and A/F ratio or MAF data if present. That will give you a mass/time measurement.

The mass to fill displacement is based on cylinder volume, number of cylinders and RPM. Multiply the total engine volume by RPM/2 since you only fill each cylinder once every two revolutions. That will give Volume/time. Multiply that by the density of air at ambient conditions to get Mass/time.

[ May 09, 2002: Message edited by: Backfire ]</p>

[Blue Jay]

I pulled the numbers out of a Mark's Standard Handbook for Mechanical Engineers, out of the section on Internal Combustion Engines.

[nova]

OK. I ran through the equations I have and by my estimate the average VE is around 70-75%. Thats a really rough estimate based on some equations that I don't actually know for a fact are valid.

Again if someone else can tell me I'm wrong please do because I don't really trust those numbers.

[Blue Jay]

I would say that those numbers sound pretty good to me. Obviously they are pretty rough. I can take a look at the equations that you used and let you know what I think of them if you like.