Fuel Consumption

[jarrod83]

You could reach a descent compromise, dont push the afrs or timing with a bit of care not to stomp your foot down from light cruise or to labour your engine up while going up hills, all should work well.

I only tuned the first 3 rows of 20 and lightly touched on the forth row, 5th n 6th is where i go to if i give it any more than light cruising

I only touched the rpm columns that the car sits in at 80 and a 100 in 5th gear and smoothed out the adjacent cells so there wasn't any large jumps

It only interpolates with adjacent cells, so anything more than maintaining constant speed it would easily move two or more cells away, you never cross through those cells rapidly after youve stomped your foot down, with a bit of care not to stomp your foot down within that small range you should be fine, i wouldnt see why mild overtaking would be a problem.

[JonnoHR31]

say at 3K rpm which is about where 110klm is on the highway

Best economy might be around 16:1 with light acceleration enrichment

Best off boost power might be around 14:1 with more enrichment then the above

Or it could be around 13:1 with a bit more timing then above

The Map area you cruise in isnt usually where you run on full load, (but can be) but it is in a zone where you go through

and near a lot in normal every day to day driving when you are going through other gears. Constant Rpm and Load is

only 1-2 load zones. Slight up hills are another 2, bigger hills are another 2. So you might only use say 6 load zones on

a PFC (for E.g) if your REALLY trying to be econimocal. The ECU interpolates so you need to compromise the zones around

it for a total of 18 load zones. For simplicity reasons I wont bother interpolating any more. So you now have this big hole in

your map and it runs leaner in the lower gears. Not so bad if you have extra capacity but annoying if you have stock capacity

and bigger turbo/s. This is one compromise.

Most aftermarket ECU's have 1 enrichemnt at 3k RPM. Running f**k all is good for economy, but if you come to a big long

hill, switch to 4th as you start to loose speed, still in the lean part of the map, switch back to 3rd and nail it just to get to a

different part of the map where its actually mapped for power. This is a compromise

Because your running f**k all fuel in these 18 load zones your forced to run Less timing. Less fuel is better for economy

but as your railing through gears in suburbia just to keep up with all the auto commo's etc you now wish you had more

fuel so you could run more timing and overall have more power. This is a compromise too.

On top end ecu's with a lot of time spent on the tune you can get a better compromise, even with a shit ecu like the pfc im using atm an

acceptable compromise can be made.

You can dam near double your mileage if you specifically tune for it. It involves really lean mixtures, realy shit timing and hardly any enrichment to

the point where you can feel the car surging for fuel when you go up a hill with an incline of more then 3*

you really couldnt be further from the truth in this case if you tried.

for starters running leaner does not mean you have to massively retard the timing under light load, 99% of the time you'll reach MBT well before you have any troubles with knock, i personally run around 16:1 afr's and 50 degrees of timing under light load cruising areas with great results. its very repsonsive, makes great torque and uses bugger all fuel.

on a pfc you have a 20x20 map, so you have 20 rpm points and 20 load points, unless your cruising at top speed (200+km/h), in which case your not gonna be worrying about economy, you'll never be in the same cells under cruise and WOT at any rpm. if your not accelerating fast enough at low revs, put your foot down further, if your foots on the floor, your in the part of the map tuned for max power under those conditions, no where near where you'd be under cruise.

having said that whats best for economy and whats best for power in the same cell is usually pretty similar anyway, you simply tune to your desired AFR (16:1 on light cruise, 14-15:1 under medium load then gradually down to 12:1 under full load) and run as much timing as you can without exceeding MBT or getting knock

[Simonster]

Sorry if this has been covered before, but when I did a search I got all the ones from the FI section and not just the RB30 section. Link it if you know of it.

When you went from an RB25 to an RB25/30 did your fuel consumption increase at all?

Interested in litres/100km, not your tank etc, and highway miles not around town.

I presently get 10.8/100km at 300rwkw out of my RB25 [not a thirty yet].

Thanks

I went from a 2.6 getting around 10-10.5km/L to the 2630 which is getting around 7km/L Still need to revisit a few things but am hopeful of getting close to 10km/L but 9 is probably more ike it. I use 260X9.1 cams

[sucram]

you really couldnt be further from the truth in this case if you tried.

for starters running leaner does not mean you have to massively retard the timing under light load, 99% of the time you'll reach MBT well before you have any troubles with knock, i personally run around 16:1 afr's and 50 degrees of timing under light load cruising areas with great results. its very repsonsive, makes great torque and uses bugger all fuel.

So this is your highway cruise afr or is this your arf around suburbia around 50-80kph?! Highway cruise speed at 110kph will also use the same load zones as when your in 3rd gear and squeeze the throttle on from 2800 RPM. Even if you stand on the pedal depending on turbo charateristic. Unless im seriously mistaken the PFC doesnt have a gear compensation to run it richer in lower gears! So if your running 16:1 afr and 50 deg at highway speeds, in the case of a 3rd gear roll on your now running somewhere around 18:1 AFR and 50 deg timing and it will det. Unless your running really low comp.

Admittedly rescaling will help but there is only so much you can do until you take load zones from other required parts of the map. Its not like most wire in ecu's that have a higher resolution if needed

on a pfc you have a 20x20 map, so you have 20 rpm points and 20 load points, unless your cruising at top speed (200+km/h), in which case your not gonna be worrying about economy, you'll never be in the same cells under cruise and WOT at any rpm. if your not accelerating fast enough at low revs, put your foot down further, if your foots on the floor, your in the part of the map tuned for max power under those conditions, no where near where you'd be under cruise.

Its possible, easily possible especially on larger turbo's. Load it up on a dyno from low RPM for a power run and you run easily run through some of the cruise zones. The turbo/s are trying to spool on low load and since you have more cruise/economy settings its showing less then favouable results (down on power). Punch in settings to bring the turbo on quicker and your economy suffers. Its one of the reasons why some people start at higher rpm/load- so the graph simply wont show how badly effected it can be. I agree that it doesnt effect your upper rpm load zones but in this situation it will effect your mid range power/torque on a graph. It can bear a massive difference to mid range if you have a small engine massive turbo type set up.

having said that whats best for economy and whats best for power in the same cell is usually pretty similar anyway,

Similar isnt the same as exact

you simply tune to your desired AFR (16:1 on light cruise, 14-15:1 under medium load then gradually down to 12:1 under full load) and run as much timing as you can without exceeding MBT or getting knock

Yeah but this will result in pretty "typical" economy. Not "exceptional" which is more along the lines of what I was talking about.

Dont get me wrong, I know what your trying to say and get where your coming from, but from what I gather the OP does a shit load of klms. Typical highway fuel consumption from an RB isnt that great. Compare it to a 2.5 or 3.0l BMW on the highway which can do as little as 5-7 L/100 and 7.5l/100. I gooled the 3.0l as I never driven one but when you do a stack of interstate travels it adds up when fuel is $1.60 ish per litre.

In the case of the OP, a multi purpose car he might be better off with a more advanced ECU, or a 2nd map just for highway use. In the case of using a power FC you could use a data logit to switch maps as needed.

Heck if I did that many klms I could probably justify a map soley for highway use. Rescale the map for 4k rpm, lowest peak boost needed for overtaking/big hills along with a less aggressive boost curve. Maybe even water/meth so you could run decent timing/egt's while running it still pretty lean for the times you do need to run it into boost. In this case normal unleaded might even be an option with water injection since the 3.0 offers additional torque. Its almost excessive for highway use hence you could dumb down the tune quite a lot in the interest of economy

[jarrod83]

What about the accel enrichment from jumping on the throttle? plus who stomps on he throttle in 3rd at 60kmph at 2800 RPM.. alright i suppose there is those that arent terribly bright.. but its alot smarter to drop back to second.. usually when im below 70 i drop to 2nd and above 75-80 i go to third.. usually try to get above 4000.. but i do have a gt35r, someone with a smaller turbo might run into problems we dont.

also i have some 4th gear log runs on another pc from 20kmph to 200.. i can show you it doesnt go anywhere near it..

[tridentt150v]

Apologies to all if I gave the wrong impression>>>

I don't do a shitload of highway kilometres - I never ever said half the stuff I'm told I did..........but when I go somewhere I travel. If you do 1500km in a weekend and you fill up every 500km, it makes a big difference to filling up every 300km. Both in cost and ability to make the next town or having to splash and dash all the time because the next town is just beyond your limit.

The above two issues are the difference between doing 1,000km in 10-12 hours or 15-18 hours. Happy or miserable, relaxed or worn out etc etc.

Well I do do a shitload, but mainly in my work vehicle. But I guess this has influenced my private/weekend driving a bit.

And I don't want a fuel miser, really just wanted to know what the fuel rate was and if it was affected much. I'm not trying to save heaps, don't want to sacrifice power, but I'm not going mega power either. I guess I just want a normal cruise machine - but a Skyline with some extra.

[JonnoHR31]

So this is your highway cruise afr or is this your arf around suburbia around 50-80kph?! Highway cruise speed at 110kph will also use the same load zones as when your in 3rd gear and squeeze the throttle on from 2800 RPM. Even if you stand on the pedal depending on turbo charateristic. Unless im seriously mistaken the PFC doesnt have a gear compensation to run it richer in lower gears! So if your running 16:1 afr and 50 deg at highway speeds, in the case of a 3rd gear roll on your now running somewhere around 18:1 AFR and 50 deg timing and it will det. Unless your running really low comp.

Admittedly rescaling will help but there is only so much you can do until you take load zones from other required parts of the map. Its not like most wire in ecu's that have a higher resolution if needed

Its possible, easily possible especially on larger turbo's. Load it up on a dyno from low RPM for a power run and you run easily run through some of the cruise zones. The turbo/s are trying to spool on low load and since you have more cruise/economy settings its showing less then favouable results (down on power). Punch in settings to bring the turbo on quicker and your economy suffers. Its one of the reasons why some people start at higher rpm/load- so the graph simply wont show how badly effected it can be. I agree that it doesnt effect your upper rpm load zones but in this situation it will effect your mid range power/torque on a graph. It can bear a massive difference to mid range if you have a small engine massive turbo type set up.

Similar isnt the same as exact

Yeah but this will result in pretty "typical" economy. Not "exceptional" which is more along the lines of what I was talking about.

Dont get me wrong, I know what your trying to say and get where your coming from, but from what I gather the OP does a shit load of klms. Typical highway fuel consumption from an RB isnt that great. Compare it to a 2.5 or 3.0l BMW on the highway which can do as little as 5-7 L/100 and 7.5l/100. I gooled the 3.0l as I never driven one but when you do a stack of interstate travels it adds up when fuel is $1.60 ish per litre.

In the case of the OP, a multi purpose car he might be better off with a more advanced ECU, or a 2nd map just for highway use. In the case of using a power FC you could use a data logit to switch maps as needed.

Heck if I did that many klms I could probably justify a map soley for highway use. Rescale the map for 4k rpm, lowest peak boost needed for overtaking/big hills along with a less aggressive boost curve. Maybe even water/meth so you could run decent timing/egt's while running it still pretty lean for the times you do need to run it into boost. In this case normal unleaded might even be an option with water injection since the 3.0 offers additional torque. Its almost excessive for highway use hence you could dumb down the tune quite a lot in the interest of economy

wrong wrong and more wrong. with a power fc, unless you've set some crazy load points (like full throttle is p5 and the rest dont get used) you will never ever ever be in the same cells at WOT as you would cruising around on the highway, not under any circumstances. i have a largish turbo on my car that doesnt make full boost until around 3800 in higher gears but even if i stomp it at idle it jumps straight into p9 or p10 and goes from there (gradually down to p17/18 under full load), the highest cruising load you would ever use would be around p6-7, but even that would be at 2500+rpm, at which stage the full load run is down around p11/12, miles away from the cruising part of the map.

also if your running in a particular cell the AFR's will never vary by that much (half a point max) and the timing doesnt change at all, so no idea what you mean by the 18:1 and det?

[sucram]

p5-7 is all of my cruise points on no6. It will reach up to p10 on hills, overtaking etc.

All the cells interpolate around those zones too

Are you running a good high speed wide band? Could also be the way its mapped. If I run a map more to build boost quicker there is less of a difference but its still about 1 point.

Its not so noticable if your just running through the gears but is clear as day if your say going through a series of S bends especially up hill and only in those load zones.

[JonnoHR31]

all cells always interpolate, but only with the ones immediately next to them, which makes everything smooth and linear.

the only time cells will show a varying AFR in the log files is when you go through them with a change in throttle in that cell or in fuel cut. fuel cut obviously gives you really lean readings and everytime you sink the throttle the ecu adds extra fuel ontop of that in the map for a split second, this also messes with AFR readings, but it is in no way a tuning flaw and you dont need 2 seperate maps for economy and power, 1 map can give you the best of both.

[MBS206]

p5-7 is all of my cruise points on no6. It will reach up to p10 on hills, overtaking etc.

All the cells interpolate around those zones too

Are you running a good high speed wide band? Could also be the way its mapped. If I run a map more to build boost quicker there is less of a difference but its still about 1 point.

Its not so noticable if your just running through the gears but is clear as day if your say going through a series of S bends especially up hill and only in those load zones.

If you're cruising, at the same load points as with the boot in... You have an issue don't you...

Because you know cruising is part throttle, low air flow (And there's an air flow meter at the intake) and flogging it is WOT meaning lots of air.

The load is determined by air intake... If you're using the same load point for both, something is f**ked...

[sucram]

im guessing jonno is running a pfc with datalogit and using "average" setting that averages out afr which is why he is seeing only half a point. Try a log in 2nd gear using the min setting, then the max setting (going through your 5th gear cruise load zones). Repeat with a log in 5th on min and another on Max and compare logs. The difference should be around 2 points. If you want to get anal about it, do it on the same day, same stretch of road etc.

Im not arguing that you cant find an acceptable compromise, but remap it so its not as lean in 2nd gear and run through those load points again and tell me how much stronger the engine is ;-) Problem is when your in 5th you'll be running a bit richer then an "economy" afr. So a compromise has to be made

MBS im running map based which is a little different to afm off boost but, pretty much the same once you see a bit of boost. Once on boost, load is

load, doesnt really make much difference how the ecu calculates it.

We already discussed that its possible to use common load zones when more power is required then an economy. Lets break it down slowly. Say your in 5th gear at about 2k rpm at around 65-70klm, light goes amber, put it in 3rd and nail it to get through before it goes red. Your at 3k rpm now, low load since your turbo/s are spooling, you might even be at a few psi boost. Your now in the exact same load zones as you would be if you were in 5th gear at highway speed limit. If your tuned for best reasonable economy for 5th at 110klm its lean what you have just done in 3rd. The engine still see's the same load but the only thing that has changed is the gear selected, well you just changed the mechanical leverage the engine has to deal with but the engine is still seeing the same engine load at one point and crosses through a part of the map (and its interpolated zones) that is tuned more for economy and runs leaner then optimum power. No big deal, its not gonna break since your only on low boost and its run through it quickly enough

Im not saying you CANT find a compromise, you can! I know where youre coming from, because in theory Load is Load, but its not that simple. If you look a little deeper into it things start to clear up. If you play around with it, and see for yourself you it will be easier to understand where im coming from.

Look at it from another point of view, a pfc has a 20x20 map for ALL gears and that is optimum!? Even though the gearbox allows mechanical leverage to differ

which allows the engine to process fuel at a different rate. 5 different rates to be precise (or 6) If you ever get the chance to look at some of the late model factory ECU's, some of them have a compensation for gears for fuel, ignition and even cam control. Some even have a 3D map for fuel enrichment, RPM Vs TPS so light throttle changes can be economical still but when nailed enough trim can be made for power. The flexibility allows a lot less compromise!

[JonnoHR31]

fact: going through the same cell under the same load (with same air temps and no changes in throttle etc) will result in the same AFR, regardless of gear (2nd and 5th will be the same).

fact: you will not be in the same cells at WOT in 3rd as you would be cruising along in 5th, regardless of rpm.

[Adriano]

Your point of gassing it in 3rd for the lights and 5th on the freeway doesnt account for the fact that when gassing it the accel pump enrichens the mixture. The difference in the logs you discuss are more likely caused by the notorious delay and inaccuracies caused by the Wideband-nistune setup, which is why you should use the average function, and its not accurate when you use it in the above example, as the base map AFR prediction doesnt allow for accel pump. Hence why when you do power logs on a dyno, you load the engine and/or turn off the accel pump before tuning power runs.

[tridentt150v]

As interesting as this discusion on mapping is...........can I get/are there any more fuel consumption figures out there??? Our is everyone sacrificing them for outright power??? I would have thought that a 400rwkw RB25/30 would get around 12/100km on a long trip. But still interested to find out - maybe I have to go to the VL forums?

[Adriano]

Its funny, a higher HP car can actually get better fuel efficiency, as it wont go into boost as easily being driven normally, I have a mitsu RVR which gets terriable economy as on the freeway, event he slightest prod of the pedal makes boost. As long as you dont put cams or lower the comp, the economy of the higher hp motor should be slightly better, as the larger exhaust housing will reduce pumping losses, however its all in the tune. FWIW i would say a functional VCT setup would probably make a good benefit to consumption.

[tridentt150v]

I just purchased an RB25 head with the VCT mod done on it, I would like to think I'm a mind reader, but I have trouble reading my own so i know that talent isn't in me

Long way from being ready yet though.......still have rods, pistons, oilpump, gaskets, seals, all things ARP etc etc etc to get yet, but havean RB30 and a head now so its a start. No rush though, my 25 is still going strong.

[R31Nismoid]

^ +1

I cannot see why it should be worse than 12L/100 if i can get around the 9-10L marker give/take in 2.6.

You should by rights be pretty close all things considered i reckon as a GTS-T will further aid due to the weight savings. You aren't lugging that extra 150kg.

Also something i didnt think of, i have the GTR win set to full angle "down", so over 500-700km having it "up" could even make a difference especially when i was @ 120-130km/h most of the way. I might up on the next trip

[Cubes]

Mine does 11/100 locally and around 9/100 on the open road. I'm sure with lower diff gears it would dip in to the 8's. 3000rpm at 100km/h with 4.3 diff gears can't be helping the open road economy.

Still the old RB26 PFC.

[Adriano]

What sort of power are you hoping to make. For a good street setup with good fuel economy, i would go about 9.2-9.4:1 c/r, stock r33 rb25 cams. Stock inlet manifold gt3076 1.06 on a stock manifold or a 3582 1.06 on something aftermarket. Just need to remember you wont be able to run big boost numbers, so you may wish to run a slightly bigger turbo than your power wishes.

Your only other issue as cubes said is the gearing, as freeway speeds is just revving too high to get great economy, But 8l/100km is still pretty good.