bump for some new info. shortly after this thread i got an S5 vert, which was getting like 15mpg, the previous S4 was 19ish. same driving circuit. 17-18mpg is fine, but 15mpg sucks!

i did some testing on the freeway, which was inconclusive. it turns out that when you put 1.2xx gallons in the tank, that the extra xx makes a HUGE difference in the MPG number, and the pump doesn't consistently fill the tank to that degree of precision.

so the first test was cruise control set @100kmh, 49 miles, 1.848gallons = 26.5mpg, which is great. the second test was 90kmh, 49 miles (same loop), 1.58 gallons = 31.2 mpg

the third test i didn't record but it was 90kmh, and 40mpg! 5mpg improvement for a 10 kph decrease in speed is hard to believe, but a 15mpg improvement is just indicative of an error somewhere....

doing any other different speeds also would be impossible, 100kmh is faster than most of the traffic already....

anyways what that testing did was split up my MPG into freeway and city. 26mpg is fine on the freeway, but in town it was about 12mpg!

so i went thru the car a little. i replaced the slow thermostat. for no difference.

the one thing that seems to have made a difference is i unclogged the thermowax (again) and i adjusted it so that its not so aggressive, instead of the 20 minutes @2000rpm, it spends 2-3 minutes @1500 rpm. my last car had a bad thermowax, so i know it only needs it for 30-60 seconds...

i've put more miles on this tank than most of the others, and it still shows half, so i think the thermowax made a big improvement!

 

40mpg....rotary...glad you called BS and saved us the trouble lol.

26 mpg highway is great for a stock car (especially a vert). A number of things could be causing the 12mpg city though. Wasting fuel on startup/warmup is a good place to start, I'm sure that will help. I've never owned an n/a but I could have sworn that my mpg's got better when I freed up the intake and exhaust (everything else being stock).


I have gotten I fairly consistent 16-17mpg city and 18mpg highway (avg 80mph) since my last update. I took out another 3% accross the map and it doesn't seem to make a big difference. I know I can pull some fuel up top as AFR's are in the low 10's past 10psi, however I doubt this has anything to do with my low mpg's.

I'm wondering if there is a problem w/ closed loop not coming on? perhaps the ecu doesn't like the siumulated narrowband signal from my WB O2 sensor? (although I'm not sure how it would know the difference). While cruising on the highway AFR bounces between 15.xx - 17.xx so it would appear to be working, but my mileage suggests otherwise.

My other theory is that the lower secondary staging point of the rtek is the reason highway mpg's are down (currently mine is set at 3310). I think the main reason the stock staging rpm was set north of 3700 was for milage/emissions purpouses. Before my next fillup I plan to bump the staging rpm back up to 3500 or so and before my next road trip perhaps bump it to 3800 and see what happens.

 

based on an idea i got from a buddy, I recently experimented with keeping the secondary throttle plates closed, and measured about 5% gain in mpg (~2 mpg). I just reinstalled the 3rd set of butterfly valves (normally removed for the TB mod), and wired them closed. I may rig them to a solenoid controlled by an "ECON" button in the cabin

 

haha, yes, i've done 40mpg in an Rx7, AND achieved time travel too! although its the poor mans version, the clock in the gym is slow, so you can arrive before you left, time travel....

i remember i tried to hook my LM1 up to the stock ecu once, and the stock ecu wasn't fooled for a second. if you're wondering if it works hook up an LED to the diagnostic port, i believe the instructions are earlier in the thread. i have done it to diagnose a bad O2 and it does work.

i have experience with the staging thing too, the trip to sevenstock is 400miles each way, one year my friend brought the 20B B2600 truck, its a stock ECU 20B fully sequential turbos and everything in an 87 B2600 truck. its such a sleeper that he did a burn out with 20B noise, in front of all the Rx7 people and nobody noticed...

anyways that thing is over the staging rpm @70mph, and it gets like 10mpg. my 20B FC with haltech got 19.... so you can set the staging RPM where ever you want, but if your cruise RPM is over that, its in open loop and going to get horrible mileage.

hmm neat, i wonder if you could hook it up like the FD, where the second set of valves is ECU controlled with a solenoid?

 

Interesting thread. I'd never go too far in the search for more MPG in an RX-7, but a little challenge is always fun. I don't daily drive my RX-7 anymore, so much of this I probably wouldn't attempt, but it makes for a good read.

On my old N/A, I would usually see 20-22 MPG, combination highway/city. The best I ever got was 25.5 MPG on a trip from Tampa to Jacksonville for a meet. My TII would usully see around 18-20 MPG.

 

you can use the early vac delay s4 TB,, or the s5 auto TB, also with vac delays

doesnt take much imagination to hook up a circuit with a changeover relay , a couple of switches and a pair of nest solenoids to control the delay operation

when the relay is in one state,, it can use the vent solenoids to trap a vacuum in the hose against the can,, keeping the secondary throttles disabled

when the relay is in the other state it will fail open the original solenoid to the open vac source
and the other upstream solenoid can seal the line and vent the can to atmo,, so it works as normal


deleting the one way valve and modding this circuit for a third mode with a switch to isolate the second solenoid from the relays
will amount to using the vac delay cans to operate the secondary delays as on load demand
( secondarys will not operate until boost builds )