SidewaysFC

im doing research on turbochargers on rotaries...anyone happen to know the volumetric effeciency?

also since the crankshaft makes 3 rev for every 1 rev of the rotor and the rotor has 3 sides that means air fills the chambers every rev of the crankshaft?...giving it a 1:1 ratio canceling out that part of the air flow rate equation

Project84

do a search on "volumetric efficiency" right here in the general rotary tech support section. I've seen it mentioned in here once or twice but I don't remember the numbers or the title of the thread.

The crankshaft does rotate 1080 degrees (3 rotations) for every 360 degrees (1 rotation) of the rotor. As far as the flow rate equation, I don't know for sure.

SidewaysFC

thank you

SidewaysFC

no need for further reply, i saw what happened in the other post...all out war

fstrnyou

i was interested in the same question. for turbo sizing of course. i didn't search but i'm assuming the war was based on the actual displacement of the rotary. haha, always comes down to that. funny thing is, it doesn't matter what they think the displacement is.

i don't really care what everyone else thinks the displacement is, all i want to know is what the VE is.

SidewaysFC

yeah i know...cant tell if 85% was decided or not...thats what i used anyway...but when checking for CFM and lbs/min of the enginem my math was messed up cause the numbers were way too low...it turned out that a t60 or something was the best when t04 is usually what everyone gets...oh well

fstrnyou

85% sounds way high.

this page says that piston engines have 50-60% VE while rotaries have around 70% VE.
http://cp_www.tripod.com/rotary/pg29.htm

i'm not quite sure if i'll believe what he says, but it's worth investigating.

fstrnyou

http://www.auto-ware.com/combust_bytes/eng_sci.htm

and this site says that piston engines are between 80% and 100%

fstrnyou

and another thing. a friend of mine is big into electronics and is planning on using a GM MAF to determine air flow numbers on his car. if we can get the GM MAF mounted onto my intake, we can log some flow numbers/rpm to see what the VE actually is.

well, i have a turbo motor so i won't actually be able to do it on mine. umm, i guess i'll have to figure out how to remove the turbo and run NA on a 4 port motor to get the VE of the motor itself. i don't know, we'll figure something out. measuring VE on a 6-port motor shouldn't be a problem at all.

SidewaysFC

another thing...all the numbers will vary with how well the manufacturer design the components of the motor, exhaust, intake, cams, etc

so technically, not all piston engine can be spoken for with those given numbers

what gets me thinking though is that how good the VE is on the M3 motor to get 333 hp out of a 6 cylinder...unless theres something way different about that motor than any other

rototiller1

If your on the boost, ve numbers dont mean a thing
n/a engines however, calculate carb size with ve.

fstrnyou

for a 6 cyl. to make 333hp, it's not VE that's to blame, it's a large cam and high revving. good flowing intakes and exhausts help as well.
yeah, VE is very important to calculate proper carb sizing.
without boosting, you can't be more than 100% VE. and most high end motors these days are in the 80-90% range. most old school iron head v-8's from the early 80's and before were in the 70% VE area.

SidewaysFC

ported engines have been known to boast a 100%+ VE...according to the link above

KevinK2

That is true for na piston and rotor engines, that are fully race prep'd.

Most turbo sizing methods, for street use, use a reduced VE value when estimating cfm needed, to account for operating with high backpressure from the turbo. This VE reflects how well boosted air is injested, and is in typically the 60-80% range.

Start with 1.3L per rev for the 13B at 100% ve. Ray Hall Turbos has a good calculator to start with. I have a deeper excel ss that I could send you.

SidewaysFC

that would be awesome...infiniturboii@aol.com

MikeC

You can use formulaes for piston motors on rotaries with a little modification. Assume the rotary is a 3.9 litre 6 cylinder motor that is spinning 1.5x less than it is. For example, if the rotary is doing 9000rpm assume you have a 3.9l six doing 6000rpm.

Kevin's assumption of 1.3L per rev also works for volumetric efficiency but the 3.9 litre comparison works over a much wider range of calculations. For example, how long does it take a single chamber to expand in a rotary at 9000rpm? Just work out how long it would take the 3.9l six to do it at 6000.

fstrnyou

why not just use 2.6L and not change the rpms??
a 13b at 9000rpms is the same as a 2.6L at 9000rpms. why the hell would you switch to 3.9L and 6000rpms?

SidewaysFC

cause it sounds smart

seriously though i have been told to use 2.6L as well fstrnyou

MikeC

It is more accurate in a greater number of cases. For the volumetric efficiency it doesn't really matter but for other calculations it works better. As an example the time it takes a piston in a 2.6l motor at 9000rpm to go from tdc to bdc is 0.00333, but in a rotary it is actually 0.005. If you used the 3.9L six at 6000 rpm it would have given the correct answer.

Basically the 3.9L 6 running at 2/3rds speed matches in many many ways that the 2.6L motor doesn't.

KevinK2

you can, with 2.6L 4 banger.

Mike is refering to the 50% longer expansion and compression cycles, per crank rev for the rotary. ie 270 deg vs 180 deg. Just keep it in mind if trying to sharpen pensil and tune custom intake or exhaust manifolds, for example.

If you understand the 50% longer events, no need to go thru the 3.9L 6 with .67 od 'equivilant boinger' that mike (and I) have posted about.

fstrnyou

not to start another displacement arguement, but, the only thing a 13b has in common with a 1.3L is torque output, which sucks. i only use 2.6L. but, we each have our own reasons.

MikeC

Torque output of the rotary is much higher than any 1.3 litre motor. The rx8 puts out 211Nm while most 1.3 litre cars range from 60 to 120Nm.