Inliners International Forums General Discussion Truck Talk Alphabet Soup

In my line of work in Civil Engineering, I see a lot of acronyms that people use all of the time, but mean nothing to me because I don't know what they stand for. Usually State employees dealing with federal paperwork.

Yesterday one was used in my introduction thread here but then the entire post was removed.

What does VE stand for in the engine building, dyno testing realm?

Post up your alphabet soup acronyms and meanings for those of us that are new to the game.

Volumetric Efficiency? Please don't ask me to define it.

Welcome the Forums DD. I am a fan of the engineering forums site - and although the posts there can be a bit dense, they are worth the time invested to understand a concept. In this case a post from ENG-TIPS circa '04 is apropos while the quote it contains sums it up nicely:
"Breaking it down even further, it is: Ratio of the amount of air getting into the engine’s cylinders vs the amount that will fit. Basically, how efficient is an engine at filling its cylinders, that’s all."

Although correct, it's still a bit vague, as the charge itself is a compressible gas which expands to fill the container.

Indeed. Text book definition of VE glosses over a myriad of variables in play durning the intake stroke. But fill-rate versus swept volume remains a critical object of every tuner's affections. After all there is no replacement for displacement - and shame on the tuner for wasting any of the displacement at hand (by not filling it to the fullest possible extent).

To your point on the compressible nature of the intake charge - this discussion about realizing VE above 100% over at Physics Forums seems apropos. In this case a velocity stack is providing the compression of the intake charge which then proceeds to 'over-fill' the cylinder.

regards,
stock49

It was long held that "inertia fill", resulting from intake charge velocity after BDC, despite the fact that the piston is going the wrong way, will improve VE.
Vizard believes that this is more rare and less effective than supposed, and has little value compared to the same intake event beginning earlier (advanced).

Blair suggests using "charge mass" (weight of molecules) rather than volume to make the VE, CR and CCP effects more clear.

Acronyms drive me nuts, but it's a short drive.
One problem is if you are doing things in a few different fields the same set of letters means very different things. And secondly if you are learning new stuff you may not know what the words they stand for mean anyway. Several years ago when I was putting a MegaSquirt board together I was trying to learn the terms for the board it's self as well as throttle body Injection terms and also, as it ended up, several versions of Windows for the dedicated laptop. At this time I don't remember any of it and I'd have to start all over again. Oh wait I know what TBI is.

Good stuff! So in layman's terms, the more efficient the fuel/air mixture can be introduced into the combustion chamber, and then compressed before the spark is introduced, the better.

Gasket matching, porting, bigger intake valves, smaller combustion chambers, longer duration on cam lobe.

Basically allowing the air pump to flow as much air as possible in the most efficient manner? Does that explain VE in simple terms?

How is the air/fuel mixture effected by using 2 or 3 carbs on the intake of an inliner? I've been told the engines are more powerful and get better gas mileage when upping the carbs on the intake.

Any truth to that? And if so, does it relate to this fuel/gas mixture? (seems it must...)

Indeed, the era of a build and the inherent limitations of components matter. Where cylinder head design and valve size is limiting, velocity stacks and a longer rod ratio can improve VE via inertial fill. Given a better flowing head & larger intake valves an earlier valve event may be in order (but then we need to be concerned with overlap and potential exhaust gas reversion diluting the charge.)

I am not familiar with Blair's work in particular but I have read others who approach the discussion from the perspective of stoichiometry with a concomitant focus on the mass of fuel and air. Is there a specific Blair article you can recommend?

Indeed there are a lot of variables, but to panic's point let's not cloud the concept. VE is simply how much of the displaced cylinder volume is actually being put to work.

Let's look at two examples from 70 years ago. Check out the specs for the '49 Pontiac Chieftan 6. The engine displaces a little over 239 cubes. Now compare that to the specs for the '49 Chevrolet Special 6. The Chevy engine is over 22 cubic inches smaller. Yet both produced ~90HP at roughly the same RPM.

Why?

The 216 Chevy has a much higher VE then the 239 Pontiac.

Why?

Valve in Head versus Valve in Block:


The overhead valve configuration flows better. Given a flat-head design the Pontiac engineers had to employ more displacement in order to produce the target 90HP driving experience for their customers.

As a tuner one needs to take the displacement at hand and make the most of it.

The Pontiac is actually well developed, the valves are inclined toward the bore, there are 4 intake ports and 6 exhaust ports, the connecting rods are huge.