5% increased gas mileage

Pete_89T2 · 01-01-2012, 10:42 AM

Interesting thread... I'm currently running the stock ECU with the Rtek v2.x mod, and was toying with the idea of leaning out the off-boost/cruise part of the map a little bit to improve highway cruise MPGs. Basically looking to play with only those cells in the RPM range of 2000 - 3200, at MAPs deep in vacuum below 10 inHg (i.e., steady cruise, light load conditions). Unfortunately, I don't have anything to monitor AFRs or EGTs, so I'm a bit hesitant to screw with this. Is there any real danger here, presuming I do this intelligently, i.e., small adjustment increments followed by road testing to assess results?

My "baseline" highway MPG average to date is pretty good as-is. I got just shy of 25MPG (24.9), measured on my way back from DGRR/Mitty last year. That was over a 10 hour trip, average speeds between 70~75MPH. As for lights & A/C, lights were on for maybe the 1st 2 hours (dawn/early AM), and A/C was on for maybe the last 7 hours of the trip; it started getting hot by mid-morning. At that time, car was set up with 720cc injectors in all 4 holes, Supra TT fuel pump, BNR stage 1 turbo, Bonez DP into the stock main cat and Borla catback exhaust. Otherwise basically stock (stock S5 boost control, working air pump, emissions, stock fan).

Since then, I got her registered as a historic (no more sniff test), so I yanked the main cat & air pump/emissions gear and replaced it with the RB 2.5" DP and pre-silencer combo that bolts up to the Borla catback. Another trip to Dave at Speed1 is in order for some dyno tuning, since new the setup is now able to consistently hit 8psi boost with the stock boost control solenoid doing its thing. I was previously limited to about 6psi, due to the aging main cat.

RETed · 01-02-2012, 05:03 AM

Quote:

Originally Posted by Pete_89T2

Interesting thread... I'm currently running the stock ECU with the Rtek v2.x mod, and was toying with the idea of leaning out the off-boost/cruise part of the map a little bit to improve highway cruise MPGs. Basically looking to play with only those cells in the RPM range of 2000 - 3200, at MAPs deep in vacuum below 10 inHg (i.e., steady cruise, light load conditions). Unfortunately, I don't have anything to monitor AFRs or EGTs, so I'm a bit hesitant to screw with this. Is there any real danger here, presuming I do this intelligently, i.e., small adjustment increments followed by road testing to assess results?

No, you don't *need* to monitor AFR or EGT if you know what to look for...
It will help to have an EGT gauge though - you want everything to be burning at it's hottest temps - misfires will cause the EGT to drop.
No need for a wideband - I hate those things.
A narrow-band AFR gauge is "good enough" in my book, as it will tell you that you're at least LEAN and not RICH - it's cheap enough that it's no excuse not to have one, unless you already threw away your stock O2 sensor?

The idea is to lean the fuel out and advance as much as possible.
Realistically, you can usually only advance the timing up to 50 - 60 degrees of total advance.
Lean out the fuel up to the point where you can tolerate the "lean surge".

There is no danger in doing the above if you do go beyond the "ideal" range.
If you do lean it too much, the lean surge will get annoying - the car will buck noticably.
If you keep leaning past that point, the engine will stop firing.
It is a trick for emission to run ultra advance ignition timing to burn as much as the combustion as possible.
Just don't run more than 60-degrees, as this is the point where you start to fire into the other rotor - which is not that big of a deal since the prior rotor face is going into the exhaust cycle, but it's still not recommended.

This all should work if you're keeping to legal speeds.
This means that for most FC's, this should be under 3k - 3.5k RPM's.
Don't try to do this over 4kRPM's - we're talking about speeds approaching triple digits at this point for most FC's.
At this point, the engine is running fast enough to negate effects of early lean surge.
The engine is so smooth, you don't feel the typical lean surge, and the EGT's start to climb dangerously.
I guess a "disadvantage" of the rotary engine?

I've seen temps hitting 1050C and climbing...this is getting close to 2000F.
Sustained EGT's at this level will cause damage to the engine.

-Ted

Pete_89T2 · 01-02-2012, 04:55 PM

Thanks Ted, good info there. Still have my O2 sensor hooked up, and with the Palm hooked up, the Rtek Pocketlogger software can datalog the O2 signal, and just about everything else that the stock ECU uses as an input (i.e., MAP, TPS, water temp, intake air temp, RPMs, etc.). Sounds like this may be worth the effort.

t_g_farrell · 01-03-2012, 08:33 AM

Jamin get a honda

01-03-2012, 08:33 AM	#4
t_g_farrell Waffles - hmmm good Join Date: Aug 2008 Location: Huntersville, NC Posts: 757 Rep Power: 0	Jamin get a honda __________________ 1980 GS stockport, Fat Nikki, RB Dual Facetfuel pumps, Holley regulator, RB Street port exhaust, 2GDFIS, MR2 MK I electric fans, 2G strut bar, relayed fans, lights and fuel pump, LEDs Project Fat Nikki Budget 12A rebuild Video setup < $30.00

01-01-2012, 10:42 AM	#1
Pete_89T2 Lifetime Rotorhead Join Date: Apr 2010 Location: Elkton, MD Posts: 874 Rep Power: 16	Interesting thread... I'm currently running the stock ECU with the Rtek v2.x mod, and was toying with the idea of leaning out the off-boost/cruise part of the map a little bit to improve highway cruise MPGs. Basically looking to play with only those cells in the RPM range of 2000 - 3200, at MAPs deep in vacuum below 10 inHg (i.e., steady cruise, light load conditions). Unfortunately, I don't have anything to monitor AFRs or EGTs, so I'm a bit hesitant to screw with this. Is there any real danger here, presuming I do this intelligently, i.e., small adjustment increments followed by road testing to assess results? My "baseline" highway MPG average to date is pretty good as-is. I got just shy of 25MPG (24.9), measured on my way back from DGRR/Mitty last year. That was over a 10 hour trip, average speeds between 70~75MPH. As for lights & A/C, lights were on for maybe the 1st 2 hours (dawn/early AM), and A/C was on for maybe the last 7 hours of the trip; it started getting hot by mid-morning. At that time, car was set up with 720cc injectors in all 4 holes, Supra TT fuel pump, BNR stage 1 turbo, Bonez DP into the stock main cat and Borla catback exhaust. Otherwise basically stock (stock S5 boost control, working air pump, emissions, stock fan). Since then, I got her registered as a historic (no more sniff test), so I yanked the main cat & air pump/emissions gear and replaced it with the RB 2.5" DP and pre-silencer combo that bolts up to the Borla catback. Another trip to Dave at Speed1 is in order for some dyno tuning, since new the setup is now able to consistently hit 8psi boost with the stock boost control solenoid doing its thing. I was previously limited to about 6psi, due to the aging main cat.

01-02-2012, 04:55 PM	#3
Pete_89T2 Lifetime Rotorhead Join Date: Apr 2010 Location: Elkton, MD Posts: 874 Rep Power: 16	Thanks Ted, good info there. Still have my O2 sensor hooked up, and with the Palm hooked up, the Rtek Pocketlogger software can datalog the O2 signal, and just about everything else that the stock ECU uses as an input (i.e., MAP, TPS, water temp, intake air temp, RPMs, etc.). Sounds like this may be worth the effort.