Well, I do not know, I have seen 1,1 VE numers regulary... nothing unusual but max VE I dont know exactly... most of the books sey more then 1.
P.S. Privat message to autor, I am making that spredsheet what I promist you for input data for my program... in the moment I am taking vacation 7 days in alps skying after that I will send you... wont be at ofice next days.
Don't know what max VE is theoretically possible but I have a dyno sheet in front of me with numbers that range from 110% to 120% VE. The sheet was run by Larry Meaux (MaxRaceSoftware) last year from stats that I derived on a Clayton for a race engine. NA, no supercharger, with Weber carbs. Acoustically tuned for 5000 to 7000rpm with a flat TQ curve from 5100 to 6900 and the 'bad wave' is 2000 to 4300 rpm. It is a 1300cc Weber carbed engine showing a VE of 120% and 132.1 hp @ 6725rpm. This is last years engine this years is up 3 points in CR to 13.37 . No problem with the out of tune range as in a race it never sees less than 5000 if I do my job.
Yes, of course over 100% VE is possible on a forced induction engine. It's possible on a Naturally aspirated engine. A well designed naturally aspirated road engine with machined ports and big plenums (maybe using port throttles to keep the throttled volume down) such as a BMW M-series engine ( do not confuse this with the strangled anaemic US spec M3 engine -I'm talking about the Euro spec one) can achieve close to 105 % VE .
You can expect a modestly boosted supercharged V8 that has refinement as one of its priorities to reach over 130 %VE (with respect to ambient).
I've seen figures that show the NEW supercharged Mini cooper reaches close to 150% VE!
A turbo charged engine, with good charge cooling ,may be higher, with close to 180% possible, in extremely well optimised (for performance) cases. The reason a turbo charged often gets higher horse power per litre over a supercharged engine is the lack of the incredible parasitic loss you get with a supercharger such as a rootes blower.
To answer the question, normal engines would see about 75-80% with the best legends proabably getting around 90% (unconfirmed)
Marquis, i think you are getting a bit carried away - you don't refer VE at boost back to ambient it is then meaningless
On a turbo engine the exhaust back pressure will be at least 1.5 times the intake boost. the remaining gases at the end of the exhaust stroke will thus be at pressure, preventing the induction of air until the piston has travelled down somewhat- further more, tuned length exhausts make bugger all difference on a turbo car.
Playing with pressure waves on a boosted car also has only a mild effect when you are already shoving boost down its neck - whats the gain from reflected waves? probably about 0.5 psi compared to the 7-10 psi of boost pressure?
A supercharged car doesn't suffer the above of course
I think you should think about the VE formula a bit bore before claiming 150% VE!!!
VE calculations depend on the density of air. The density, on a turbo engine, depends on where you're measuring. You can either use the density at atmospheric conditions and get really large VE numbers, or you can use the manifold density and get numbers that compare to an N/A engine. Either way is technically correct as long as you make it clear what you are referencing. As many have listed above, with ram and tuning effects over 100% numbers are possible any way you slice it.
"To answer the question, normal engines would see about 75-80% with the best legends proabably getting around 90% (unconfirmed)"
This post illicited a few laughes here- no offense.
I'm not quite sure what engines are being refered to here, perhaps 1950's engines? Side valves?
Unconfirmed- I should definately say.
No disrespect intended, But I have an array of engines I've helped develop out in the field, not to mension competitor engines and seen the figures I quoted on dyno test bed- Nope- not some ageing old chasis dynojet but an actual calibrated Schenk dynos to EEC 1585 and DIN 700020. So all the figures I quoted were either seen by me or read in SAE papers, or tested at out Resserch labs in Dearborn- You see I don't guess, I don't quote unconfirmed data- I post as I see and have seen from my experience- else I say nothing.
"Marquis, i think you are getting a bit carried away - you don't refer VE at boost back to ambient it is then meaningless"
I don't think I'm getting carried away at all. It concerns me little what conventions you choose to use, my friend, however, any OEM and/or manufacturer of boosted engines quote with reference to the ambient conditions post intake zip tube. I'm not quite sure what reference you're using, but if you're refering to using pressure in the plenum as a datum- that would only indicate the efficiency of the manifolding/ports post the actual compressor- THIS is totally meaningless and useless to a manufacturer. If this is indeed what you're refering to, it COULD explain partially why you're figures are so low but they're still far too low.
"On a turbo engine the exhaust back pressure will be at least 1.5 times the intake boost. the remaining gases at the end of the exhaust stroke will thus be at pressure, preventing the induction of air until the piston has travelled down somewhat- further more, tuned length exhausts make bugger all difference on a turbo car"
I think that is a generalisation at best. I've seen enough data - for example look at Heinz Heisler Advanced Engine Technology book, -figures 6.47 page 324 - it clearly shows boost pressure being higher the MEAN exaust backpressure. There will be exhaust pressure pulses that exceed mean boost pressure just as there are scavenging pressure troughs that are far lower.
The reason Turbo charged petrol engines don't have tuned lengths is because quite often the over ridding concern is getting the Turbo lag down and- these days emissions (catalyst light off).
There are big Detroit Diesel or Navi Star engines with tuned lengths on the exhaust side- not to mension steady state engines, where lag is less of an issue ( no throttle),
Somehow I wouldn't dismiss all of Detroit Diesel or Navi Stars work, based on your "bugger all difference comment".
Oh, and if it's formulas you really want:
I use
9.566 (a constant) x Air flow in Kg/hr x ((273.1 + ambient intake temp-celcius)/(Engine capacity in litres x Engine speed x (Barometric pressure /1000))
Perhaps it's forced induction lawn mowers you're refering to - in which case I may be wrong regarding my comments on the level of VE You assert- however, in the future please don't be so blatantly dismissive about what I have seen because it's beyond the realm of your experience. Thank you
so you dont believe tuned length exh. manifold runners work well on a petrol engine? Why is this? We have found decent gains with both methanol and petrol racing engines.
The question was---"What is the highest VE...on a FORCED induction engine?", emphasis mine!
On a mechanical supercharged engine the benifits of exhaust tuning becomes iffy because of the high inlet pressure and at overlap the 'tuning' effect of a neg pulse becomes somewhat redundant (to a point). On a turbosupercharged engine the 'tuning' effect pretty much stops at the turbine.
I won't argue with folks that claim benifit from 'tuning' exhaust systems on a turbo because that's their right. Believe what you will. I know what works for me. BTDT!
Racing was/is expensive and I chose to spend mine on better cumbustion effeciency or a couple inches more boost. I race a vintage mini now and it takes all I can do just to keep it together. LOL
Rod, we run our supercharged Jags with quite short cam durations timed with no overlap at all,with perhaps a little via the ramps-else we find fresh charge is just pushed through to the exhaust.
Now i'm not saying this is neccesarily the case with Turbo charged engines, I don't know, I know Porsche Turbos run with some overlap I believe.
Marquis,
You seem a little offended at my quest to keep things sane - I am sorry for your offence. You are correct the 80% VE I was referring to was from plenum - thus at pressure, and neglecting throttle plates. So yes, one could subtract another 1% off or so for these effects. My point was that you don't compare 180%VE when talking turbo cars to the 120% or so NA engines can make and make an assumption about technology when the NA technology is very advanced "oh yes of course 180% is possible" - this is akin to bending statistics to suit your purpose - quite clearly the original qestion was referring to the dynamics of the head and combustion process, which is not an air compressor question.
- I thought we had established in the previous responses that we all know NA engines can achieve+100% VE and I chose not to explore that further so was your point a cheap jibe???
i wouldn't assume that as detroit diesel once made tuned length exhaust runners that it actually helped - but I am not beating my chest saying that it doesn't either - just be realistic about the gains
One comment on the issue of backpressure compared to intake pressure: It will NOT always be higher! When I was interning at Garrett, I was working on the issue of getting EGR to work on a new Detroit Diesel engine, and the hardest part of it all was that there were a great many operating points where the exhaust pressure was lower than intake, so exhaust gasses would not flow into the intake naturally. Unfortunately, I didn't get to do any aftermarket or performance gasoline stuff, so I can't comment on any of the other questions. However, I think relating VE to plenum pressure does have some value. When matching turbos, you can use the N/A VE values, "multiplied" by expected boost pressure, to estimate airflow so as to match the turbo maps. Seeing this, I would think that you could also go backwards, "dividing" out the increased density from boost to get N/A level VE numbers. Thus, VE numbers referenced to plenum pressure can be used if you want to compare your engine to another N/A engine at WOT.
Put another way: Sure, referenced to atmosphere you may be tickled pink to see VE's of 130%, but when you reference to the plenum and get numbers of 65%, this could be a huge hint that the cam you were using before you added the turbo is completely wrong with it!!
NOTE: All these numbers are completely "ballpark", I didn't do the above "test" myself, but I could see where it would have benefit.
"Put another way: Sure, referenced to atmosphere you may be tickled pink to see VE's of 130%, but when you reference to the plenum and get numbers of 65%, this could be a huge hint that the cam you were using before you added the turbo is completely wrong with it!!"
When developing boosted, OEMs don't use VE figures relative to ambient to be "tickled pink" or as some kind of ego trip relative to NA engine.
The reason for it's use is quite simple to anyone who develops engines for a living and it comes into it's own when doing zip tube/air box development work. If using figures relative to the plenum you will not be able to quantify any of the effects on performace arising from changes in losses upstream of the plenum such as in the intake spout, air box, zip tube etc etc. No development work will be able to be done on sizing the throttle.
Measuring VE relative to plenum would only allow you to evaluate changes to ports, cams, perhaps instake runners. Only a fraction of the picture to someone who needs to get more performance from a boosted engine
