I now avg 17.5 mpg(city).My best hwy was a little over 27 with my stock wheels,but it dropped off to 25.4 when i switched to18s.I will be doing a roadtrip soon and will report the hwy mpg data.

 

Damn! I need to re-tune my PFC to be way leaner at cruise...

 

What other mods do you have? Do you install anything at the same time as the twinpower? And what were you seeing mpg wise before?

 

I installed a hiflo cat and the tp within 24 hrs of each other.My mods, greddy smic,downpipe,intake,m2 ecu,rb catback,hiflo cat,hks tp,synthetic oil everywhereI think i was getting 16.8(city) before the hiflo cat and tp.I am sure abut the hwy mileage.The hwy mileage was on i95 from sc to fla on cruise all the way.

 

27 mpg??? Did you start on the top of Mt Everest & coast all the way down?

The best the the EPA could do was 25 mpg. Those guys must never go above idle & take 10 minutes just to get up to 55mph!

Open the flood gates. Just like Top Speed, vacuum @ idle & H.P. posts. Nothing but a bunch of fish stories. This would only be relevant if we all drove box stock cars.

 

With M2 ecu, regardless of the ignition you have you will only get lower MPG, not higher period.
If you are seeing different MPG because of wheel size then you have the wrong size tires.

 

damn.... let us know about the highway mileage

 

well,its a pretty simple thing(est mpg) 1st fill up gas till nozzle clicks off,2nd set od to 0,3rd drive car,in my case 310 miles to my mothers house. 4th fill up gas tank till nozzle clicks off,5th divide miles driven by x amount of gas used.I have done this a couple of times.Once with the ac on,and with it off.It is a flat straight trip on i95.i was going 70mph when possible.Maybe fds get better mpgs with a downpipe,intake cb etc.My current fd does get better mileage than my last one.its best hwy was 23.9. I also posted that my vac is between 20-21 at 850 rpms,with a defi boost gauge.All the naysayers also saying that it cant be true,something must be wrong ,etc.I guess that there is so much BS going here sometimes that people dont believe the truth when they read it.

 

you must of haved alot of ignition breakup. I bet it starts up faster and idles smoother better than it did b4


wouldnt that affect the actual mph than what the gauges show as well?

 

yes,with the hiflow cat and tp the car is faster,smoother. another forum member has added a tp ,and says that his car is running at more neg boost at 60 mph.It feels like you dont have to use as much throttle to maintain speed. the different tire sizes stock vrs 18s did vary my mpgs.

 

u ***.... i am getting 11.4 mpg!!

 

you guys getting low mpgs must be hitting boost all the time ,and downshifting a lot.synthetic oil and lube will help in getting better mpgs too. we get 1mpg more in are elantra with synthetic also.

 

I get about 25-28 mpg on highway. I used my PFC and wideband to make a 65mpg cruise band at 14.9 AFR.

Chris

 

Ahh the M2 doesn't tune the car rich under vacuum when your cruising. There's no reason it shouldn't get good highway mileage. Also a larger diameter wheel puts more of the weight closer to the outer diameter which will increase the rotational forces. Even if the wheel is lighter than stock. That's why cars with larger diameter wheels lose hp. There are guys on the forum who have admitted feeling more hp when switching back to the stock 16" wheels.

Here's another example. Go to the park and find a merry go round. Have someone sit as close to the center of the MGR and start spinning it. Then have that same person sit towards the outside of the MGR. You will quickly notice how much harder it will be to spin it. The overall weight never changed, just the position of it.

By the way my stock Fd with stock ignition got 26 mpg on the highway while on my trip to sevenstock last year. And that's with A/C on. Only mod is poor mans intake mod and downpipe. I feel bad for the Rx8 guys.

 

what i heard synthetic isnt good for rx7's something about it not burning right. what synthetic brand and kind are u useing? ex:castrol 10w30

 

Synthetic brands from years ago were formulated different from the brands of today. Any of todays synthetics with a low ash content will be fine in a rotary.

 

Just when I thought I was doing good... I went from 12mpg to 18mpg by doing a little leaning out of my cruising cells. Must be nice to get 25mpg...

 

Complete combustion and less overlap are your friend. Hell guys with ceramic coated rotors are reporting better fuel mileage. It seems that the coating is allowing the fuel/air mixture to burn more fully therefore giving the improvements.

 

which brand of syn should i use? and the thickness?

 

On the highway I get 23-24 mpg with the cruise on in the winter. In theory at least you should yield better mileage with the mods you have. The PFC runs leaner than the stock ECU, exhaust and intake mods would help as well. A light weight flywheel would help along with any other weight saving mods. The Problem is that the EPA test cars at 55 mph not 70mph. The FD is going to get better mileage at those lower speeds.

The larger wheels is much more complex and assume that the rear tires have the same outside diameter thus retaining the stock gear ratio the stock rims I would think would be light and more conducive to fuel economy. The stock rims weigh only 15.4 pounds and have a width of 225mm and the OEM tire are super light as well. I personally haven’t seen any 18” rims that weigh less than the stock rime but I’m sure for the right amount of money they could be had. My guess would be even with the extra weight of the rim the total package would be less at the same tread width because of tire weight. Pointless because we know that tire width will increase and the total package will increase. The tread would jump to 255-265 or more and that’s the real issue that creates a lot of drag and friction because of contact with the road.

 

Wow, are you guys reading what he is saying?

It was an all highway, no compromise drive. Not just "Some highway" with spirited driving through towns and to work etc.

He drove on I95 from SC to FL. A straight cruise, going 60-70mph for a full tank, will yeild the HIGHEST and BEST gas mileage for any car. This number will more than likely never be seen, even if you do mostly highway, in a "normal" 300 miles of off and on/shorter trips etc.

My FD got 25-27mpg on it's 260 mile drive home to my place when I got it. Since then, I only see 16-18mpg mixed city/highway and tons of spirited runs.

 

Mobil one or royal purple are two of the best brands of synthetic available. You should be fine with 10w-30. If you live someplace ungodly hot or track the car, you may want to go with royal purple 20w-50 or Mobil 1 15w-50. I live in Illinois and use Mobil 10w-30.

 

i live in cali so i assume 10w-30 should be okie. thank larz, imma start running syn now
Timmy

 

Wheel weight doesn't really affect mpg. Wheel DIAMETER changes gearing which for the most part just affects the odometer reading. If you use your odo reading to check for mileage (which is the way you are supposed to calculate mpg) then the miles traveled will be incorrect and your mpg will be incorrect.

"Improving" mileage is a relative statement, what did the car get before? Doing the math on some people's claims (personal life examples) shows some people claiming a 20-40% increase in mileage from simple changes. If it were that easy the factory would do it!

 

My first hwy mpg calculation was with stock wheels.If the stock od is correct,the mpgs were correct also.I would imagine that just installing a dp and catback would help increase mpgs,Free flowing exhausts help piston engines too.I like to share positive info about my fds .I read so much neg stuff here some times it overshadows the good things about fds and rx7s in general.Now if you want to hear me bitch about cars ,i can go on and on about the piece of junk low mile c5 that i sold!