My Gtst Fuel Consumption -- Need Advice

[Mitz]

Hey guys sorry about another fuel economy thread, but this one is specific to my car.

Im only getting around about 190kms per tank of 98 octane fuel (220 maybe till dry -- no highway kms, alot of short trips) and i was wondering if thats normal for what I have done to the engine.

Here is every modification done to the car

•CP Forged Pistons

•Eagle Rods

•Tomei Metal Head gasket

•Extensive Head Work

•N1 Oil Pump

•N1 Water Pump

•Nismo Thermostat

•HKS Step 1 Cams

•HKS Cam Wheel

•Z32 AFM

•HKS GTRS Turbo (set at 10psi low boost, 14psi mid boost and 18psi high boost)

•555cc Injectors

•Bosch Fuel Pump

•Split Fire Coils.

- Front Mount Intercooler

•Tein height adjustable coilovers

•Cusco Front Strut Brace

•DBA4000 slotted rotors front and rear

•DS2500 front brake pads, •RACEBRAKES rear brake pads

•GFB Stealth Fx blow off valve

•3inch split dump/front pipe into 3inch CATCO hi flow cat continues into 4inch through to 7inch cannon with 5inch tip

•Power FC & Hand Controller

•Apexi AVCR Boost Controller

•Apexi Turbo Timer

•Apexi pod filter

•C’s shortshift kit

•Excedy 5 Puk Ceramic clutch

I set my BOV to about 1/3 in the atmosphere but i doubt thats the main reason why it consumes that much fuel...

And I'd say Im a mix between crusiing and spirited driving.

Cheers

[pipster11]

tune related or leaking injectors maybe

get it into a good tuner

dunno how much power you are making but im pretty sure e85 users are getting better fuel economy than you are

[Mitz]

Its making 278rwkw, well unigroup were the last tuners to tune it, so i guess something happened between the last time it was tuned and now.

So I'll let them have a look at it.

Thanks for the quick reply mate !

[89CAL]

Do you know what the cruise AFR's are?

Can you set your BOV to 100% plumb back?

[Mitz]

Sorry mate but what do you mean by 'cruise AFRs' ?

And yes im pretty sure, as it makes no bov noise at all when set at minimum.

[paulr33]

depends on how hard you flog it

how are the afr's cruise for light load - air fuel ratio or it just a max power tune (most are)

does your 02 sensor work (most die after a few years)

is 02 feedback turned on

[pipster11]

unigroup are supposed to be really good i believe

something is definitely up, i'd go back to unigroup and ask them to look into it

was it always this bad?

[89CAL]

Sorry mate but what do you mean by 'cruise AFRs' ?

And yes im pretty sure, as it makes no bov noise at all when set at minimum.

Cruise AFR (Air Fuel Ratio) is the fuel ratio when you are cruising along at say 60km/h with minimum load on the engine. If the car runs rich at these points your fuel economy will be shocking (as this is where you will most likely be spending most of your time)

Got a dyno graph that shows the AFR's of the power run as well, if this is rich and your flogging it everywhere then this will have a pretty bad effect on economy, but seen as you wont be going for fuel economy while loading it up, i think the issue would more be cruise AFR's

[abr33]

I get about 500-600kms a tank on my 25. When driving sensibly on highway. When I drive it on track i can get around 200 per tank! On road driving a bit harder between 450-500. I dont run it under 1/4 usually though. I think, (dont quote me) my cruise afr's are around 17-18?? rings a bell anyway.

Im getting a bit more fuel added on cruise next time as it doesnt do plugs alot of good when doing big kms on highways etc.

[Mitz]

depends on how hard you flog it

how are the afr's cruise for light load - air fuel ratio or it just a max power tune (most are)

does your 02 sensor work (most die after a few years)

is 02 feedback turned on

Well im usually running low boost (10psi) and here or there ill run it on high boost for abit of spirited driving

I actually dont know, since I've bought this car pretty recently about 2 months ago and the previous owner got it tuned at unigroup before he sold it (have receipts).

unigroup are supposed to be really good i believe

something is definitely up, i'd go back to unigroup and ask them to look into it

was it always this bad?

Yeah exactly, same from what Ive heard aswell. I will ask them to have a look anyway Since i bought the car two months ago it has always been like this.

Cruise AFR (Air Fuel Ratio) is the fuel ratio when you are cruising along at say 60km/h with minimum load on the engine. If the car runs rich at these points your fuel economy will be shocking (as this is where you will most likely be spending most of your time)

Got a dyno graph that shows the AFR's of the power run as well, if this is rich and your flogging it everywhere then this will have a pretty bad effect on economy, but seen as you wont be going for fuel economy while loading it up, i think the issue would more be cruise AFR's

Oh ok well thats something I'll check with unigroup .. but i have a feeling it may be this, thanks for the explanation. Plus there is barely any turbo lag, so im always boosting, even when i take it easy.

Thanks for all the replys.

[discopotato03]

I would have thought 278 was high for a GTRs but anyway .

Nismo thermostat ? Possible cool running not helping .

3" into 4" exhaust , big pipes particularly if they increase down the system often allow reversions and cost low end torque , and consumption .

Personal bias but I dislike split dumps because the gates tube is often too small and reintroduces at stupid angles .

My experience with button clutches in road cars is the need to rev them to get them moving , consumption ?

Your call but you may have overkilled in a few areas .

Please tell me your static CR is not a lowly 8-8.5 to 1 , cheers A .

[wolverine]

^^ 278rwkw on 98ron on Unigroup dyno??

I would like to see a print out of that run.

Definitely an issue with the car returning that sort of economy. If O2 feedback is switched off with a Unigroup tune it still won't return that sort of economy. There is another issue IMO.

[lovelessnator]

I'm making just over 300rwkw an my highway k's are about 400 an in town on an off boost is about 220-250. I'm using premium 100

[Mitz]

^^ 278rwkw on 98ron on Unigroup dyno??

I would like to see a print out of that run.

Definitely an issue with the car returning that sort of economy. If O2 feedback is switched off with a Unigroup tune it still won't return that sort of economy. There is another issue IMO.

I have a big folder of reciepts from the previous owners, performance wise I'm going off a dyno dynamics dyno sheet which is the latest dyno sheet I can find. If I find the uni group one I'll post it up tomorrow. Why does that power figure sound surprising ?

Well hopefully it's not a big issue, the car seems to run 100% there's nothing unusual that happens when i drive.

[wolverine]

Post up all the dyno sheets.

[AngryRB]

lol..im getting 350 on each tank with a mix of highway and wot at 1.2bar Eflex

what temp does a nismo thermostat open at? does it get up to correct temperature?

Edited October 25, 2012 by SliverS2

[R31Nismoid]

If all your "short trips" are less than 5mins, then that's of little surprise given the car is on cold start the entire time.

Otherwise it's as simple as the tune or something related to that - is up the creek.

Or you just need to learn to drive more economically.

It can only be those really.

I doubt it's the coilovers or Ferodo brake pads causing the problem.

[89CAL]

I doubt it's the coilovers or Ferodo brake pads causing the problem.

You can never be to sure....... lol

[Moodles2]

You really shouldn't be playing with the BOV if it's got a tune. It's going to be a combination of things that is the cause for the bad fuel economy. A possibility that hasn't been mentioned is the coolant temp sensor, without a working one it will be stuck in cold enrichment and chew through fuel.

[abr33]

You really shouldn't be playing with the BOV if it's got a tune. It's going to be a combination of things that is the cause for the bad fuel economy. A possibility that hasn't been mentioned is the coolant temp sensor, without a working one it will be stuck in cold enrichment and chew through fuel.

What would playing with bov do for the tune at all?

Unless your running a afm obviously