Volumetric efficiency

[lemming303]

So what is a typical VE for a performance motor? I downloaded an app for my iphone called "carbulator" and one of the fields is VE. I understand what it is (I think) but I don't know what a good number is. How hard is it to get a 100?

[72bluNblu]

Difficult. Typical ratings are usually between 80 and 100, but my understanding is that most street engines usually fall between 90 and 95 in good tune and condition. 

[73EStroker]

Chuck Senatore (Mopar Engine Authority) says that we should use 0.85 when calculating for carburetor size. I believe 1.00 is for those high end dragster motors running blowers etc.

[Marquis_Rex]

According to the Chrysler engineering report I have from the 1960s- the 426 DOdge Hemi achieved a peak VE of 90%.
An RB wedge I would estimate as lower than that- say 85%.On the other hand- if you're using good flowing cylinder heads like modern Edelbrock RPMs or xtremes , an Indy may be, that flows close to 300 CFM at peak lift (original 426 hemi flowed about 270 CFM) rather than the 230 or so of the 906 cyl heads, assume 90% +

A modern engine, such as some of the engines I have been involved in the design of:
Jaguar AJV8 = 95-97%

Aston Martin V8 Vantage= 98%

Jaguar AJV6 3 litre= 101%

BMW S54 M3= 106%

Jaguar AJV8 supercharged= 140-150 %

[Chryco Psycho]

I have heard that the race engines with a large cam can go past 100% at higher rpm without supercharging as long as the exhaust is scavenging efficiently

[quagmire]

 

A lot of modern engines are capable of 100% or more in naturally aspirated form.  Multi valve heads, direct injection, high compression, and variable cam timing all contribute to this.  I know the new 5.0L is capable of 110% VE at peak torque, and it's NA.  The Hemi and LS series engines are also pretty darned efficient.  Gotta love modern technology!

[moper]

The average NA street engine will top out around 90%. A modern performance build using the right parts and the best equipment can push NA street engines to 100% or more. A more racey engine will exceed 105% at peak power and I've seen as high as 112% on them. Boosted engines exceed 100% all the time...

[lemming303]

Very interesting. I love this site, I am always learning stuff on here.

Marquis, that BMW motor, is on the newer M3? Not the I6?

[Supercuda]

Volumetric efficiency is always highest at peak torque, and will reach or exceed 100% on an engine with good intake and exhaust manifolding. Natually-aspirated engines with no fancy engineering tricks (VVT, direct injection, variable-tuned length intake manifolding) will routinely top out at 85%. The ram engines from the late '50s and early '60s were capable of 95%-110% VE at peak torque. Supercharged engines will always exceed 100% VE,as the air charge to the engine is routinely bigger than the engine is supposed to be able to process naturally.

[Marquis_Rex]

Very interesting. I love this site, I am always learning stuff on here.

Marquis, that BMW motor, is on the newer M3? Not the I6?

Hi Lemming, the S54 is the old outgoing I6-which in European trim made 343 bhp and in US trim made about 333 Bhp. It has a much higher BMEP or brake mean effective pressure (torque per litre) than the newer V8 and therefore a higher Volumetric efficiency.
Compared to even firing inline sixes or even V6s, Cross plane crank V8s (like old American V8s, MOST contemporary V8s-except some Ferraris and Lotuses) have a harder time at achieving high VEs when they push for high Bhp/litre due to close adjacent firing cylinders charge robbing. I learned this from my performance development activities on the V8 in the Aston Martin Vantage.

[lemming303]

What exactly do you mean by "charge robbing"? And also "even firing I6's or v6's? This is a rather interesting thread; I had no idea it would get this detailed! 

[Marquis_Rex]

What exactly do you mean by "charge robbing"? And also "even firing I6's or v6's? This is a rather interesting thread; I had no idea it would get this detailed! 

If you look at the firing order of something like a Jaguar AJV8 or the V8 in the new Aston Martin V8 or even the engines mounted in the latest Land Rovers (designed and supplied by Jaguar) it is:

1-5-4-2-6-3-7-8

This assumes cylinder numbering as follows:

O5           O1
O6           O2
O7           O3
O8           O4


 [each "O" represents the spatial positioning of the cylinder and the adacent number represents the cylinder number- driver sits behind the schematic]

This is the numbering convention I'm used to and I know Chrysler use a different one. The Jaguar V8 firing order is actually the same as the Chrysler V8 and the Lexus V8 if they all use the same cylinder numbering convention. You will see cylinders 7 and 8 (the rear two of the  left bank) fire close to one another and are only seperated by 90 degrees- this is what can lead to those cylinder fighting for either fresh intake charge (depending on the inlet manifold design, or the exhaust pulses interfering with one another (depending on the exhaust manifolding design). This situation is excerbated when you use big overlap camshafts. This is why Classic American muscle cars make that lopey thumpy idle noise when you use big overlap- where as inline sixes which have equal interval firing aren't quite as suceptible. These are things that can be done to minimise it if you really care- but some of us like the classic american 'lopeyness'....

[lemming303]

I see. Very cool. Thanks for the info man! I really do love this site and the people on it!

[Supercuda]

And this is why flat crankshafts have been tried in V-8 engines over the years; the flat crank helps separate firing events into something more like two 4-cylinder engines. Racers will try anything for more power. It all comes down to trying to minimize pumping losses and other problems associated with vee engines and their construction.

[moper]

If you try to visualize the air/fuel mix as a single stream of water flowing in the carb and out each runner of the intake.. The flow is pretty even and smooth if the volumes are close for the plenum size and each port. But in a running engine, you need to add very fast cycling valves at the end of each port. Every time one port valve closes, the pressures inside the engine are affected because the mass of the water coming in has to stop in one port and in another it has already stopped and has to get moving again. Plus pressure waves are moving around in there and they also carry certain levels of effects on the system as a whole. When the pressures change in the intake, things that hurt power happen. Things like fuel seperatesing and pressure waves interfere with each other. This is what (I think) he means by "charge robbing". It's also why tunnel ram intakes for carbs and long individual runners (dry for efi) make for smoother, flatter power curves.