ExVtec

I've read on multiple accounts that s2000 motors have been known to exceed 100% Volumetric efficiency. I was reading in Wiki --> http://en.wikipedia.org/wiki/Volumetric_efficiency and it states that motors can exceed 100% in VE.

I don't understand how this is possible. Maybe I'm not thinking outside the box, but if 100% is maximum, then how can you flow better than your max?

Anyone care to enlighten me please?

Thanks

coneheadsracing

Volumetric efficiencies above 100% can be reached by using forced induction such as supercharging or turbocharging. With proper tuning, volumetric efficiencies above 100% can also be reached by naturally-aspirated engines. The limit for naturally-aspirated engines is about 115%, these engines are typically of a DOHC layout with four valves per cylinder.

shifty35

Volumetric efficiency is generally a ratio of air mass trapped inside the cylinder when the valves close, to the volume of the cylinder under standard atmospheric conditions.

In an FI motor, the whole cylinder is pressurized, so naturally the VE rises above 100%.

In a naturally aspirated motor, well designed intake systems, exhausts, and cam profiles can cause a "natural supercharging" effect. The air flowing into the cylinder has enough velocity / momentum that it continues to cram its way in, resulting in a slightly higher than atmospheric pressure, and > 100% VE.

Alfa Turbo

I have heard tell the current F1 engines produce VE's equaling that of 4 psi of boost. Pretty kewl.

HiProfile

You're probably read about sizing the intake & exhaust parts for RPM. Special headers will aid in sucking exhaust out, while sucking intake air into the cylinder during the overlap period. Then you have the pressure pulses from the suddenly moving and stopping air in the intake manifold - if these come at the right time, with enough force, they will push more air into the cylinder like stampeding cows off a cliff.

The odd thing about forced induction (turbo & SC) is how the pressurized manifold can help this even more, in addition to simply pushing air in via higher pressure. Denser air will trasmit the air pulses even faster, and the higher exhaust pressure in the 'small' cylinder can sometimes lead to better-than-NA scavenging if the turbine/manifold flow enough.

theoldone.com has a 137% VE F20C on their front page. F1 for that matter has had rediculously-overpowered engines in the past, and continue to make even more power AFTER they banned turbochargers.

ExVtec

Interesting...

I read the wiki info after posting this question, and it makes since, but how can a person measure VE of a motor?

supaslowdx

there is a formula wise one

VE=(3456xcfm)/(cidxrpm)

Old skool sir Adam

supaslowdx

Also if you think about a standard air tank you would have at home. Obviously you can get more air volume out of it to run tools etc than it would actually hold at 14.7. If you think about how much air comes out of a regular impact then look at say a 30 gallon tank it owuldnt take long to deplete that volume at 14.7 but with copmressed you can have multiples of the standard volume.

I think thats a pretty good graphic for your mind

Also that 100% is measured at 14.7

RC000E

When I saw that picture it just disgusted me that the forums are gone. Back in the day, the Ask Too forum would've been a gaunlet of knowledge and information over that build, and various others past.

The Honda world lost a big source of knowledge input with that forum. Honda-Tech haters won that one and damn near ran the man into the ground. Years later and I'm still pissed off.

S2Integra

even so, in my studies in higer education, to reach anything at 100% efficientcy is termed ideal, ideal is used as examples where nothing performes ideally in reality. There is still probably some way to improve Volumetric Efficiency in the combustion chamber. Reshaping ports, valves, or valve seats, the list goes on. Basically we want air to flow in the chamber with no resistance, that is physically impossible so we try to make ways to get as close as we can. Superchargers(turbos) just increase the overall compression of the ambient air outside engine.
I haven't reviewed how they determine the percentages, so I will not discredit your information. What I am trying to say is that there will alway be ways to improve horsepower efficiency.

S2Integra

Nice, thanks for the formula, but why 3456, is it a random coefficient or is it some proffesor's theory?

supaslowdx

Im not 100% sure where it is derived from; it is used in most engine calculations that deal with flow though. So im guessing it is just a random coefficient.

For instance when you want to know the required cfm for any given engine:

CIDxRPM/3456=CFM Required

So a 350 sbc that turns 6500 rpm needs a 650ish cfm carb to perform at maximum efficiency. So then for whatever the VE happens to be you just scale the final by that percentage. If the motor only has a 75% VE then it requires around a 500cfm carb.