Who\'s good at working out MPG?

[bimbleuk]

justin you seriously getting 400 miles a tank!?

That\'s what the fuel gauge is indicating and my odo is accurate as I\'m using a programmable conversion box on the gerabox output and I\'ve verified it on GPS etc. I\'ve fiiled up to half with 32 litres previously so the gauge appears accurate to at least half anyway.

I\'m only driving the RX now as I cycle quite a bit anyway so was silly to have two cars (other is a 106 TD) on the road. That\'s mixed driving to work and out n about this weekend no motorway but some dual carriageway.

This is not uncommon from what I\'ve seen posted on another forum.

[turbotoaster]

400miles isnt that extreme, ive managed 450miles to a tank, but that was 99% motorway driving, its all about how you map your vacuum areas

[bimbleuk]

400miles isnt that extreme, ive managed 450miles to a tank, but that was 99% motorway driving, its all about how you map your vacuum areas

I certainly wouldn\'t claim it\'s like a diesel but it\'s at least reasonable enough to let me drive the car most days. Like any RX it will quite happily burn fuel as fast as you can fill it when using it how it was designed!

[carlbrainiac]

Surely mapping for fuel economy though takes away the whole point of the car I.e performance though doesn\'t it?

[bimbleuk]

Surely mapping for fuel economy though takes away the whole point of the car I.e performance though doesn\'t it?

I believe Turbotoaster has spent time mapping part throttle for lean mixures as you\'re not on the gas but merely cruising. Often cars are tuned on the rollers for full throttle power runs and part throttle load sights are neglected.

[carlbrainiac]

Sounds good. So why don\'t we all do this? Too exspensive?

[turbotoaster]

Sounds good. So why don\'t we all do this? Too exspensive?

its very time consuming to be fair.

and if your paying someone to do it, then it works out expensive.

i do all my vacuum tuning when i was on my way to work, or to the shops or on the motorway to give myself something to do.

i regular hit an average of 28mpg over a journey, i think blitz said hes had his over 30mpg when he was running low of fuel once

it does make a big difference in your mpg figures and i think the money i saved in fuel easily pays for the wideband kit i bought.

I mentioned this on another forum and said most tuners will tune the full throttle, idle and a little bit of part throttle....they wont tune perfectly every cell on the map as it takes forever.

I still believe this to be the case, but it created mayhem, a thread was made about me and i was accused of calling all tuners crap by it which i never said, and infact praised 2 tuners.

My rx7 was a daily driver so it was worth me doing......if i only used it once a month for a midnight blast then i wouldnt have bothered.

If anyone wants to get into basic rx7 tuning then it really isnt that hard, i was expecting it to be alot harder that it is, but up to yet its been a walk in the park and im running 20psi of boost on non-seq twins

[B.Martin]

Sounds like you\'ve done a good job to me, well impressed.

[Brett]

How come Grinder hasn\'t posted on an MPG based thread?

Someone summon the tight arse!

[carlbrainiac]

So how do you actually do the tuning? Especially on while on your way to work etc? lol. I dont understand. Do you permantly have a laptop connected to it to see what its doing as you drive and adjust accordingly till you get your desired result? In which case surely the software/kit is exspensive? If it was so simple I really struggle to see why more people havent done it. Could be a good tip for all thirsty cars not just Rx\'s

[turbotoaster]

a wideband kit is £140, as long as you have a power fc commander, thats really all you need.

well to make it very simple ill try to explain it.

say for example you travelling along at 60mph and your wideband says your AFR is 13.5

now you know that the higher the number the leaner the mixture is, so you set yourself a target afr of 14.5

now 14.5/13.5= 1.07 or 7% more fuel than you need.

you then adjust the fuel map by -7% at that point, then look at your wideband to see if it has done the desired effect.

obviously before everyone jumps on me im just trying to think of a way of simply saying it so i know the numbers arnt exact and you have to take in consideration the map points around the plot and blending the transition

most of my vacuum tuning was done on my commander as you dont have to worry about running to lean and popping your engine so you can spend time fiddling to get it spot on.

infact alot of my boost tuning(including up to 20psi) was done on the commander as i learnt to be able to get around the unit pretty fast in the end, you just have to have a good memory so you dont forget stuff while your flickign between screens.


I believe that i could teach someone to map there fuel tables on there own rx7 with a few hours of work, obviously ignition timing takes longer to teach.

[carlbrainiac]

Interesting but I have no idea what AFR is nor a FC commander. lol. Means nothing to me. You might as well be speaking another language. I guess I\'ll leave as is for now and if the fuel keep disappearing really starts getting me down then I may re consider. But being that I also have a Subaru means I can split my journeys between the two cars. And also being that I own a subaru Im kinda used to regular trips to the petrol station lol. I\'d start getting withdrawl symptoms if I didnt go to the petrol station for a while. Its like a second home to me now lol

[turbotoaster]

AFR = Air Fuel Ratio

13.5:1 means for every 13.5 litres of air the engine is getting 1 litre of fuel........its a basic ratio.

a common ecu for the rx7 is a apexi power fc, they come with a unit(looks like a gameboy) called a commander, it shows all the data that the ecu sees, like water temperature and revs.....you can use it to change 90% of what the ecu does(including changing fueling)

[Dehs]

Yeah, carl i seriously reccomend getting an Apexi Power FC ECU and Commander.  They are a large setback cash wise, but keep an eye on here, as you can regularly get 2nd hand ones for about 450 quid.  In fact there may still be a couple in the sale section kicking around.  I learn a little about the mapping process for setting the basemap on mine, took me about... 4 hours of researching to get the gist, but i wouldnt dare try it on my own yet xD, im just too scared of breaking my baby.

Heres the link to a basic knowledge and faq, with links to higher reading if you care to take it that far mate.  Its definately worth a read, and is really interesting (PS: if posting this link isn\'t allowed, im happy to remove)
http://www.rx7club.com/showthread.php?t=573647

Once i get mine to a stage where im interested in fuel economy, i may contact you for more info toaster, if thats ok?

[carlbrainiac]

Oh right cool. How much are those ECU\'s? And what other benefits does it give? And is it a job you can do yourself to install it? Or is it a specialist thing?