Displacement on demand

[j9fd3s]

Originally Posted by NoDOHC

I really should have done a better job of explaining my goals for this plan, I want my cake and I want to eat it too. I want a 250+ Hp rotary that will still give 35 or even 40 mpg.

Ted and i both know a guy who built a bridgeported Rx3, that did 230rwhp, and would get high 20's mpg on the freeway. with a carb! and an exhaust quiet enough that it was streetable. 10 more MPG would be tough though...

actually #2 thing i've noticed is that my other car, a 1958 Tr3, gets 35mpg. other british cars of the era, XK120, MGB, etc actually get decent mileage too, especially compared to "new" cars and they do this with carburated, tractor motors.

how? well the Tr2/3's are 2000lbs, with a 2L 4 cylinder. my S4 Fc weighs in @2880. that's a HUGE difference. and in 1952 the Tr2 was faster in the 1/4 mile than anything you could buy from an American car company, so its slow now, but it wasn't at the time.

oh and #3 back to the mazda rotary. we make the 1000mile round trip to sevenstock every year, and its almost the only drive i get that's almost 100% freeway, and having taken every car from a stock 79, to a 20B FC, to an FD, i've noticed that the FD and the SA both had an rpm range where they got better mileage. the SA gets the best mileage (23-25) in the 3500-4000rpm band. which in 4th puts you right around 65, and in 5th is like 80. driving @3000rpms, actually gets WORSE mileage, although not by a lot, and going over 4k, it gets bad quickly.

the FD also did the same thing. the FD pops out of closed loop @3200rpm, and best mileage is at 3199rpms, which is around 80mph. on that trip my stock FD got 23mpg, my friends ported car got 25. 23mpg + 22 gallon tank = you have to pee really bad.

the 3 rotor FC was plagued with ecu troubles, so it got tuned on the back of a trailer for 45 minutes and returned 19.9mpg, which is totally acceptable

i haven't checked the P port yet, i haven't put enough gas or miles on it to tell.

anyways, i hope it shows that i'm on board with better mileage too!
mike

[RETed]

Originally Posted by j9fd3s

oh and #3 back to the mazda rotary. we make the 1000mile round trip to sevenstock every year, and its almost the only drive i get that's almost 100% freeway, and having taken every car from a stock 79, to a 20B FC, to an FD, i've noticed that the FD and the SA both had an rpm range where they got better mileage. the SA gets the best mileage (23-25) in the 3500-4000rpm band. which in 4th puts you right around 65, and in 5th is like 80. driving @3000rpms, actually gets WORSE mileage, although not by a lot, and going over 4k, it gets bad quickly.

Another data point...

Several Sac to Vegas and back trips netted me 400 miles between gas fill-up's.
1987 Turbo II on a (reprogrammed) stock ECU
16.6 gallon full capacity fuel tank, but filling up at 14 gallons each time.
That makes it 28.5 miles per gallon.
Key is to drive run under the secondary injector crossover point at 3,800RPM, which is about 75mph - 80mph on my car.


-Ted

[FerociousP]

Originally Posted by RETed

Another data point...

Several Sac to Vegas and back trips netted me 400 miles between gas fill-up's.
1987 Turbo II on a (reprogrammed) stock ECU
16.6 gallon full capacity fuel tank, but filling up at 14 gallons each time.
That makes it 28.5 miles per gallon.
Key is to drive run under the secondary injector crossover point at 3,800RPM, which is about 75mph - 80mph on my car.


-Ted

I also noticed that with a Rtek ecu on my way to DGRR this year.... I would be around 15.0 afr until the secondaries kicked in, and then it dropped to 12.1 afr. I was alone so I couldn't tune the Rtek, but this is something that people with stock ecus are just stuck with

I got 23ish mpg while hovering around that point with probably spending most of my time about that

[j9fd3s]

Originally Posted by RETed

Another data point...

Several Sac to Vegas and back trips netted me 400 miles between gas fill-up's.
1987 Turbo II on a (reprogrammed) stock ECU
16.6 gallon full capacity fuel tank, but filling up at 14 gallons each time.
That makes it 28.5 miles per gallon.
Key is to drive run under the secondary injector crossover point at 3,800RPM, which is about 75mph - 80mph on my car.


-Ted

yes, it seems modded t2's get excellent mileage, because it runs 14.7:1 out of boost, and its easy to stay out of boost...

-mike