Brice-RX8

I am kinda curious about gas mileage and tracking the car. I have heard that people that take their cars to a track (like VIR, not drag strip) get around 8-10mpg, since they are sustaining high rpm's for 30 minutes or more at a time.

My question or thought is what would a piston engine say S2000 get if it could hypothetically sustain the same kind of 8-10k rpm's for the same amount of time? Would it be that much better than a rotary?

It seems that the rotary takes a lot of **** for having bad mileage but what would a piston engine make if it turned the same rpm's as a rotary. Just seems that the rotary is not that far off for how high it is turning.

KYLiquid

its not just about RPM, it about how much fuel your buring.

Lets say you have the RX8 Rotary Engine and the S2000 Piston Engine both at 8k rpm..... they are gonna use differnt ammounts of fuel. It has to due with injector size, duty cycle, fuel pressure....ect.

Also even 2 of the same car or same engine will get differnt numbers cuase one might be a little bit more lean or more rich than the other.

Id say a safe bet would be to get around HALF the mpg you get durring normal driving in _____ car.

So if you get 20mpg now, bet on getting around 10mpg.

Brice-RX8

But I am more interested in say a comparison. I know that engines are all different, but is the rotary that much worse than a compariable piston engine at the same rpm? Make sense, the S2000 was the only car that came to mind that could actually do similar rpm's and not blow up.

I get what you are saying though, but was trying to think about it on a different level.

ZoomZoomH

iTrader: (1)

AFAIK, S2000's at track speed also gets aroun 8-10mpg, as well as other lower-revving (but larger displacement) cars like Mazda6's with the v6 engine.

when driven under track condition, similar powered cars will get similar gas mileage :o

ZoomZoomH

iTrader: (1)

btw last time i was at VIR with my 8, i averaged 11mpg per day at the track

maybe i should press the gas pedal a bit harder :o

Brice-RX8

so in other words the rotary really isn't that much worst than any compariable sports car, especially turning that many rpm's. I just didn't know if our cars get 8-10mpg at the track and for example an S2000 would get 18-20mpg.

BTW, I want to get up to VIR and track my car sometime, I bet it would be a blast! What type of speeds do you see in the straights?

Thanks.

GerryL

The RX8's inherent fuel disadvantage is a result of thermal inefficiency. Anyway you slice it (or rotate it) a larger proportion of the combustion energy released in a rotary will leave as heat as opposed to mechanical energy. This is because of the relatively much large surface area of the combustion chamber (it is moving and sweeps considerable surface) than that in a piston engine. All of that extra surface wall that is contacted during the combustion process provides more opportunity for heat to escape. There is no way around this issue. Whatever is lost through the wall will be that much less available to turn the driveshaft and make MPG. No matter what the RPM, the laws of physics still apply. There are certainly other mitigating factors in the equation that might help at higher rpm but the inherent thermal inefficiency will never be negated.

Brice-RX8

I know this concept GerryL, not really what I was thinking or originally asking, but thanks anway.

ZoomZoomH

iTrader: (1)

at track speed, it isn't much more about how thermaldynamically efficient the engine is, than about how fast you can dump fuel into the engine to make power, and we all know how rotaries are extremely good at dumping excessive amounts of fuel into the engine :D

there's a saying going around that, basically, rotary engines are designed as a RACING engine first (highly reliable in racing conditions due to very few moving parts), street engine second :D

there are no car at the track that I know of that actually gets street-driving level gas mileage, it just simply doesn't happen

oh yeah front straight at VIR i was going about a good healthy 125mph before i had to brake for turn 2, probably could've accelerated further and braked deeper into the turn, but i was playing it safe :o

Brice-RX8

sweet thanks for the info Zoom

Yea not worried about economy while running WOT, just curious

BlueRenesis82

20 min session=quarter tank of gas

nhk

my pal M3 8mpg on track,
my rx8 11 mpg on track,
my roomate type-r 13 mpg on track.
when the vtec kick in, type-r A/F run very rich (A/F close to 12 (6.5krpm), 11 (8k rpm))

SDB

I am not sure that I understand your theory but my last car, a 94 Mustang Cobra, averaged 18 mpg in normal driving and I got 10 mpg at the track.

My RX-8 gets 19 mpg in similar normal driving and it gets 7 mpg at the track. The 8 gets slightly better lap times than the Cobra but naturally it is reving much higher. The Cobra had a stock engine and modified suspension and the 8 is stock.

124Spider

For reference in this interesting discussion, I get 8mpg in my stock 2004 S2000 (stock except for RA-1 tires, and brake pads and fluid), when I'm driving hard at the track (Pacific Raceways near Seattle). If it's raining, I get at least twice that (showing, I think, that backing off a bit yields a large increase in fuel mileage), and on normal highway driving, I get a little over 30mpg. I get 23-25mpg in mixed, commuting driving.

I think that fuel mileage on the track would depend heavily on the track, and how it fits the car. The S2000 has little enough torque/power that I'm almost always either flat out (most of the time), braking hard, or maintenance throttle (around sweepers). I suspect that an RX-8 would be driven similarly at the tracks I've been at (I can't drive our RX-8 at the track; I don't fit in it with a helmet on )

Razz1

Yes, please do.

Razz1

It should be a little more. Push the pedal.