Rb30det Fuel Consumption

[sky30]

As the title says, im interested to know what fuel economy people are getting out of their RB30det engines, especially if your running larger than stock injectors. Also list what ECU your running.

Im getting 13.3 litrees per 100kms (some hi-way, and some town driving) using a microtech ECU and 550cc injectors, i think this is pretty poor, and would like to improve on it.

Post away peoples......

[paulr33]

injectors shouldnt affect fuel economy one bit, if your using 400cc or 1200cc injectors your fuel economy shouldnt be any differen. the tune and how you drive it will affect your economy. do you have any light load / cruise AFR's charts from any dyno runs (not max power runs)? these will reveal your cruise AFR's

does the microtec support 02 closed loop? if anything you should get some better economy vs the rb20/rb25 as you dont have to rev/load as much to travel at the same road speed. are u using the same diff gear ratios as the 32 gtst?

[sky30]

Bigger injectors cant be fine-tunned aswell as smaller injectors at Low opening periods ( say around 1 millisecond). I have found with the microtech that i need to run the larger (550cc) injectors slightly richer than necessary to get smooth running than i would with a stock 270cc injector.

[rob82]

injectors shouldnt affect fuel economy one bit, if your using 400cc or 1200cc injectors your fuel economy shouldnt be any differen. the tune and how you drive it will affect your economy. do you have any light load / cruise AFR's charts from any dyno runs (not max power runs)? these will reveal your cruise AFR's

does the microtec support 02 closed loop? if anything you should get some better economy vs the rb20/rb25 as you dont have to rev/load as much to travel at the same road speed. are u using the same diff gear ratios as the 32 gtst?

Do you really believe that bigger injectors wont affect consumption??

[paulr33]

if tuned correctly, why would it ?

i dont see why it would... perhaps im missing something obvious?

[rob82]

if tuned correctly, why would it ?

i dont see why it would... perhaps im missing something obvious?

Bigger injectors flow more fuel. There's no two ways about it.

[paulr33]

for sure they flow more fuel. but if you dial in stock injectors which are 370cc and on the fuel map at say cell 5x5 you have a certain fuel injection value dialed in, which turns out to be say 14.6 AFR out the exhaust.

now if you go and fit 550cc injectorsl the same fuel injection figure is dialled in, providig the injector settings are put in correctly shouldnt the same 14.6 AFR come out ?

[sky30]

1. OK say i run my 550cc injector at 1.0 m/s and it runs a AFR of 14.0:1(a bit rich), then say the next step down on the microtech is .93 m/s it then runs an AFR of 15.3:1 (too lean and wont run smooth).

2. Ok then say a stock 270cc injector at 1.0 m/s runs an AFR of 14.0:1, then at the next step down .93 m/s it runs an AFR of 14.7:1.

So as you can see the smaller the injectors the finer/better they can be tunned and the better economy you can get.

[paulr33]

perhaps the stepping is too large.. is that the ecu's fault?

how do other ecu's achieve the same goal?

is the powerfc the same in terms of its stepping

surely there are cars with 550cc or even 740cc getting near stockish economy

[paulr33]

just looking in datalogit now for rb25 i can see 3 decimal point precision for each injector correction and 3 decimal point precision for lag time.

you can't just dial in your own numbers on the microtech? it has to be taken from a moving scale set by the ecu?

[DennisRB30]

Large injectors don't work as well as small injectors l when injecting small amounts of fuel. IE in cruise and idle conditions, that is why you get worse economy with them. Its pretty simple really.

Edited May 15, 2006 by DennisRB30

[mr_rbman]

hey andrew, when she was on the road i was getting between 12.5/13.5L per 100 kms depending on how i drove etc. thats with GTR injectors and Power FC, i too wasn't that happy with it but my dad drives a late model magna and averages around 13L/100kms and he drives like a grandpa so that made me feel better!

[rob82]

for sure they flow more fuel. but if you dial in stock injectors which are 370cc and on the fuel map at say cell 5x5 you have a certain fuel injection value dialed in, which turns out to be say 14.6 AFR out the exhaust.

now if you go and fit 550cc injectorsl the same fuel injection figure is dialled in, providig the injector settings are put in correctly shouldnt the same 14.6 AFR come out ?

The bigger the injector the larger the lag time(time from when the electrical signal is sent to the time the injector opens). This means that under dynamic injection conditions (which in closed loop is all the time) the ECU or tuner has to take into consideration this problem. Alot of aftermarket ECU's out there dont recongnise this factor and mask this problem by using accelartion enrichments. I can tell you that just about every OEM ecu has provisions for calculating this delay. You've got to remember that steady state conditions usually only occur at idle. So practically all of your drive time from A to B is a dynamic condition.

Fuel consumption has alot to do with closed loop control. The way it works is by taking an 02 sensor reading and sutracting fuel until its a little lean of stoichiometric and then adding fuel until its a little rich of stoichiometric and then subtracting fuel and so forth. If the injector has a delay in fueling the response will become alot slower and the injector will start to overshoot the bounds of a stoichiometric AFR. So while closed loop is fine on smaller injectors larger injectors may not prove to be more efficient fuel wise.

The precision of the ECU is also a huge factor like sky30 has said the smallest increment in change of injector pulse width makes it either to lean or a little too rich. If you want better economy go to a better ECU.

[Mr. iNFMS]

Martin Donnan says your wrong about bigger injectors not making a difference.. Have a read in the last fast fours..

He pretty much says the spray is harder to control.. therefore more fuel is used..

[WetGTR]

With regrads to large injectors using more fuel for economy, this is correct as atomisation is not as good as smaller injectors.

The smaller injector atomise better, even more so at light loads.

Injector manufactures have developed single,twin and four pittle injectors to help the spray pattern and atomise the fuel better. This also helps direct the spray towards the rear of both valves in a four valve per cylinder engine.

I have tried this myself and have changed the same injector brand and size from a single pittle injector to a twin pittle version and the twin pittle version ran richer then the single pittle version. This has to do with the above comments mentioned.

[Cubes]

My last tank where I was quite stuck up it returned 11.6L/100.

Thats pretty much the highest I will see and its due to driving to uni, the hills around uni always see it hard up on boost, generally in a low gear between 2-3000rpm. I love the low reving fast accelerating sound.

If I drive it nice and hardly ever bring it up on boost it will touch 450-470km's per 50l.

I don't do any open road driving, its all local to uni and back.

Its so so tempting to bring it up on boost and feel that shove in the back with a slight twitch of the foot when accelerating out of every corner/roundabout traffic lights. This is what sucks the fuel.

I drive it normal unless there's a reason to bring it up on boost.

With my old rb20det injectors when the motor went in they would return around the 11L/100km's. They soon went to the complete sh*t with hard starts, flat spots and eventually the car would randomly stall at traffic lights when the car was cold.

Fuel consumption at this point was around 13.5L/100km's no matter how light I drove it.

I dropped a new genuine o2 sensor in to it and replaced injectors with flow tested R34 gtr items. They flowed up as 480cc on std rail pressure.

Over the std rb25det base map my whole light load area's are running 3-5degree's more ignition.

I have leaned it out ever so slighty everwhere under light/medium load over how shaun set it up which was for response/performance. i.e 13:1 up until 0psi where it goes straight to 11.8-12:1.

My leaning out didn't do much I saw ~10-20km's per tank. May have just been my easier driving as I was watching myself a little more.

[jas/slo32]

my skyline uses 22 litres of fuel per 100km of driving

1600cc injectors on minimum setting rb26/30 with a microtech

[Cubes]

lol.. and 1068rwhp to boot.

[discopotato03]

Cubes I would have thought 13:1 was a smidge rich for light load AFR , I'm sure RB's could easily deal with more like 14 - 14.5:1 and maybe even a little more light load advance - depending on what your running .

11.8 to 12:1 particularly at around atmospheric manifold pressure I think is way too rich and you may find more torque with less fuel and how ever much advance it can take without detonation .

The tuners I used to talk to said they would not go beyond about 12.8:1 AFR because they believed the extra fuel didn't achieve anything worthwhile . Some suggested filthy rich mixtures can promote detonation so said don't do it . My own experience is that really rich mixtures only served to lighten the wallet . Often my best gains were from being right on top of the ignition timing and running conservative mixtures ie between 14.7 and 12.5:1 . I know that aeons ago it used to be said that putting a little extra fuel through an engine just to cool it was a good idea but the mass of the fuel in the inlet charge at around 1/14 will have very limited cooling ability .

I believe that small throttle openings pull down the effective CR enough so that reasonably lean mixtures can be used with a fair bit of advance to light the fire early and get some heat and pressure into the cylinders at that all important 20 or so degrees after top dead centre . It sounds logical to me that this is the way to get the most economical use of the fuel and air for part throttle torque .

Its also been suggested to me that taller rear gears will make for less revs at the same road speed so with a little more throttle opening you may lift the dynamic compression enough to make a difference in torque so a little better economy - for an RB30 in a GTST with std gearing ?

Just my thoughts - open to other views .

Cheers A .

[Bl4cK32]

Im currently around 10 to 11 lts per 100kms. Running rx7 550'c on a slightly modded rb25 pfc base map (10 if i baby it, 11 or more if i give it some..)

Shaun has had it running better though...but we had a play with the datalogit and changed a few things....

When i fix my coil problem soon, i'll throw some 3.6 or 3.9 diff gearing in and Shaun said he's gunna tune it up for me