nashman69g

iTrader: (3)

Does antone know what the volumetric efficiency of the 86-88's are?

I doubt anyone will know what it is, but what the hell I'm hoping too get lucky!

deadRX7Conv

It varies with RPM. And, rotaries are more VE than piston engines. I have never heard of anyone running it on a dyno for anything other than power. Good luck with your VE search.

RETed

Yep, it varies a LOT versus RPM.&nbsp 80% is not unheard of in terms of peak efficiency.


-Ted

'Vert in Vegas

Simple answer: NO.
I've never seen any published specs, but I am sure someone has some numbers.
Every thing on the engine affects VE.
Air filter, compression ratio, intake diameter, exhaust work, porting, etc.
You could put your engine on a flow meter for a rough answer.

BDC

Correct. 80% seems to be a good figure on the stock engine porting and such. I've heard as high as 100% before but it greatly depends on engine RPM as well as how the intake and exhaust ports flow (stock casting vs. ported, etc) as well as the port overlap and such.

B

NZConvertible

I did some engine dyno work on a Nissan SR20 (NA) where we measured and plotted VE vs. RPM, amongst many other things. The VE curve is what gives the shape of the torque curve; they match exactly, so peak VE is where you get peak torque. I think we got a peak of about 85% from memory.
If you have a closed airbox with an inlet duct, VE is easily measured. You measure the velocity of the air at the inlet and multiply that by the inlet area to get volume flow. You divide that by the calculated flow (volume x rpm) to get a percentage, which is VE. We measured it at 1000rpm intervals to plot the curve.
Rotaries don’t quite match piston engines for VE. Even thought there are no valves, the shape and size of the ports results in a lower VE. Thermal efficiency is also lower that a piston engine, but mechanical efficiency is much higher.

BLUE TII

iTrader: (9)

Rotaries don’t quite match piston engines for VE.

Aren't peripheral port race engines the exception to that though?

HWO

Bridgey's and PP's with good overlap will all get over 100% VE if they are set up correctly, i think RICE had some info about a Turbo'd PP, works out at around 123 or 132% VE, something horrendous anyway. I doubt there are many pistion engines getting numbers that high

NZConvertible

Remember, volumetric efficiency is measured airflow divided by the calculated airflow (swept volume x rpm). So calculating VE on a turbo engine is pretty pointless, because the airflow is dependant of boost level. The higher the boost, the higher the airflow (to a point), so the higher the VE that will be calculated.
Those figures seem about right for any mildly boosted engine, and a piston engine would achieve them with ease. If an engine with a VE of 85% when non-turbo is boosted to 0.5bar (1.5bar absolute), this would push VE to around 125-130% (1.5 x 0.85 = 1.28). If you up boost to 1.0bar, it'd be about 185%. So you can really only compare VE of non-turbo engines.

deadRX7Conv

Rotaries are more VE than piston engines. How do you explain 160hp from 1.3liters? That was in 1989. A couple years ago, the car magazines went nuts over the 160hpCivic SI(1.6liter), which had the latest technology, and a VE alot higher than my 160hp 5.0 Crown Victoria from the '80's.
Mazda is releasing a 240+hp(247,250-noone knows) Renesis rotary in a year or so; still the same 1.3 liters. It needs to push a lot of airflow for that much power. Thats more than the S5 turbo and almost as much as a 1993 twinturboRX which has more than 100% VE while under boost, right?
During engine dyno pulls, some of the domestic mags over the years listed VE and other factors. It takes a hell of a lot of engine tuning/building to produce good VE numbers on piston engines. The used to brag about the 1hp per cubic inch. We've had that for years and some. We also have a longer power band.

Read these articles and make your own call.
http://personal.riverusers.com/~yawpower/techindx.html
http://personal.riverusers.com/~yawpower/jundyn.html
http://cp_www.tripod.com/rotary/pg29.htm
http://cp_www.tripod.com/rotary/pg27.htm
http://members.rogers.com/sofronov/C...otary/13B.html

relvinnian

Actually this is wrong. The VE% is not calculated ON boost. The VE% is calculated in N/A format, and then the PR is applied to that to give total airflow. The only hard part of the calculation, is applying ambient variables, and the affects OF the turbocharging system on VE%. It's done via an engine or chassis dyno, with all ambient conditions data-logged, with boost curves, etc. The VE% is then calculated out based on boost curves and conditions.

You are perfectly right about VE% vs. TQ curve. That's why dyno plots for a combination are so important. I recently took Peter (rice racing), dyno graph and calculated the VE%. Came out to just over 100% @ tq peak. I will refine it even more once he sends me his data logs.

NZConvertible

You need to fill a few gaps in your rotary knowledge. The 1.3L figure is based on the standard definition of swept volume for a piston engine. That is the volume swept by one piston in one crank revolution times the number of cylinders. If you apply this to a 13B you get 654cc/rotor, a 1.3L engine. However a single rotor has twice as many intake strokes per revolution than a single piston (once per rev for a rotor versus one per two revs for a piston), so the theoretical maximum amount of air a “1.3L” rotary engine draws in is twice the amount drawn in by a 1.3L piston engine. So a 13B actually breathes like a 2.6L piston engine, making your 160hp figure look a lot more ordinary (61.2hp/L).
The rotary’s two main strengths are this ability to draw a lot more air in for it’s size (external dimensions) than a piston engine, plus due to the lack of valvetrain and much lower internal friction from fewer moving parts it has a much higher mechanical efficiency than a piston engine. The result of all this is that the rotary makes a lot of power for its size and weight.
The VE of a side intake port/peripheral exhaust port rotary engine has been proven to be lower than your average piston engine. However a motor with peripheral intake and exhaust ports has shown a much higher VE, hence the 300+hp figures from a PP 13B. With the Renesis engine, moving the exhaust ports to the side plates means all the ports can be much bigger, again resulting in much higher VE and hence power.

deadRX7Conv

Yeh, I know. But.........
Compare one crankshaft revolution of a 2.6 litre V6 to one e-shaft revolution of a rotary. Same volume, right?

Either debit the rotary with the '1.3L times 2' volume correction factor, or credit the piston 4-stroke for being able to fill only 3 bores in that 1 revolution---but don't do both.
The 4 cycle piston boys are already giving themselves the 'times 2 credit' when calculating their VE.
Either credit them or debit us, but not both.

So, both piston and rotary engines can have a VE of 50% or lots more depending on the manufacturer tuning, year.....
The dyn link in my previous post shows a 12a with a VE of 85% at certain RPMs. This matches the VE of the previously mentioned SR20. Before you scream that the 12a was ported, remember the SR20 is using FI/twincam engine VS. the 12a older technology(noVDI/4-6p here).

I also was thinking of engines from the '80s. 61hp/L was rare back then. 140hp from a 2.8 GM V6 or 140hp from a 3.0 Ford V6 was average then(can't recall any 2.6 V6's). Comparing a 1989 13b to an average engine today is unfair. We will have to wait for the Renesis.
So, certain rotaries won't match certain pistons engines for VE and vice versa.

Funny thing is that the original question was for the 86-88 NA?? And, other than guesses, no real answer.

NZConvertible

Yes, but not the same volume of air is drawn in! Reread my post. Turn a 2.6L piston engine over 10 revolutions and it will only have 5 intake strokes, so (ignoring VE for a sec) it will inhale 2.6 x 5 = 13L of air. Turn a 13B over 10 revolutions and it will have 10 intake strokes, so it will inhale 1.3 x 10 = 13L of air. The same amount! It’s the same reason why 2-strokes make so much power for their size; they do everything twice as often, just like a rotary.
Putting it simply (and assuming identical VE), at the same engine speed a 2.6L piston engine and a 1.3L rotary engine flow the same amount of air, and airflow = power.

RETed

I don't want to repeat myself in here - it's a bit involved.
https://www.rx7club.com/forum/showth...threadid=63079

-Ted

RICE RACING

NZconvertible, not many piston engine can match the ve% of rotaries in any form !

Where they tend to out do Most rotaries is in BSFC, as far as outright air flow goes ( for the output shaft revs )though rotaries are the king ! And there are no race engines (piston) that can match the VE of a peripheral ported rotary across a wide rpm range, some can match the peak figure but only in a narrow range. NOTE: Engines that run the same RPM's

Wether the engine is forced induction or N/A is not relevant as you are talking the VE of the engine, not it's attachments.

Some PP's are measuring over 130% VE, stock ports around 85 to 88% and some street ports around 100%

NZConvertible

All the info I’ve seen indicates that a side intake port/peripheral exhaust port rotary engine can’t match the VE of a modern multi-valve piston engine. Heavily ported engines may be a different story, and the PP’s impressive VE is well known. Not entirely true. VE is hugely affected by bolt-ons, that’s part of the reason why you see a power improvement from free flowing exhausts and intakes. These improve VE. But you can’t compare the VE of a turbo’d engines because it depends on boost level. That seems way too high to me. I’ve heard figures of just over 100%. Can you explain in engineering terms why this would happen?

BLUE TII

iTrader: (9)

Well, I'm no Rice Racing or an engineer, but this is what I've seen reading some airplane engineering pages of scientific tests. These guys are so **** they have documented the affect of waxing their planes for better aerodynamics and when calculating optimal exhaust size work out the affects of smaller tubing/end tubing providing "jet" thrust for the aircraft!

1. Ram air- higher speed of aeroplane and propeller draft should exagerate the effect, but interestingly still not a big boost in VE from what I've seen- w/ direct intake path of P-port maybe there is more affect.

2.Dynamic affect intake- sizeable documented gains. Doesn't really seem apply to most the P-port applications I've seen; though Mazda race engines use a continuously varying length "tuned induction" intake.

3.Intake/exhaust overlap- This has been shown to really increase VE and I believe a p-port has quite a bit! From what I understand a very efficient scavenging exhaust combined w/ overlap will really help power as it starts drawing intake into the engine much sooner due to the low pressure area present in the engine from the exhaust scavenging. The very large direct ports of a P-port should make the most of this. The downsides of this is worse MPG as a bit of intake charge is wasted out the exhaust due to the port cross flow and lots of intake reversion when not in scavenging rpms.

-edit- But, you probably knew all that and were looking for specific %s- right. Oh well.

RICE RACING

To answer some of your points, VE of an engine turbo or not, when I talk about it is as a system, that means the exhaust manifold, Intake manifold, turbine housing etc etc.... The function of the boost pressure is an entity on its own, as defined in any good formula. So discounting the boost pressure it is possible to detirmine the "true" VE of a forced induction engine, as all that is changing is the condition of the "aspirated" air going into the unit.

To explain what happens in a well ported rotary or any engine with a good deal of overlap is that in certain conditions, there comes a point where the interaction of gases flow and pressure wave events results in "dynamic" charging of the induction cycle...the harnesing of this principle cause much more than 100% filling of the volume. Peripheral porting principle allows this to happen over a wide speed range, the same can be used in side Intake ported engines if the overlap is increased and tuned exhaust headers are used.

I have many charts dating back to the 60's showing charging efficiencies of around 115 to 120% @ engine speeds around 2000 to 5000 rpm for engines running the peripheral port system ( and street style bolt on's ), This capacity can be tuned to any speed range up to around 9000rpm and is the reason why for racing there is no better porting style, for n/a or turbo engines.