Fuel Consumption

[Dose Pipe Sutututu]

Definitely do this:

- New O2, any money yours is fked and on cruise you're just toasting away fuel

- Clean AFM with Carby cleaner

- Check for vacuum leaks, good way is to use an air compressor and apply SOME pressure to the pressure side of turbo and listen for leaks, etc.

- If you got a powerFC, which I didn't see in your 1st post, disable the O2 sensor, and get someone to cruise tune the car so it hits stoich, 14.7 A/F on cruise

[mad082]

If I may add to this^

There's also a misconception that driving down a hill in neutral saves fuel because of the low idle RPM, when in most cases this will use more petrol than leaving the engine attached to a gear (idle control valve is not your friend!). Just because the engine is revving high does not mean it is getting alot of fuel - it is the throttle plate that controls this, not engine RPM. A vacuum gauge is good biometric feedback for monitoring your fuel economy...or you could could put a piece of wood behind your accelerator pedal

I warm my engine up before driving, but not to get it up to temp so I can thrash it. I just like the oil to have circulated for a little bit before my engine sees 1500RPM+, after which I use normal driving to get the rest of the drivetrain up to par.

i'm pretty sure that at higher rpm, when decelerating the injectors don't fire at all (or only fire the tiniest amount). when idling they have to fire to keep the engine turning over, but when decelerating they don't have to fire as the engine is already above idle and there is no load on the motor according to the TPS.

doubt it ..different turbos, different dump pipes and possibly connectors .. If you look here http://www.kudosmotorsports.com/catalog/ad...keywords=oxygen you'll notice even R33 S1 and S2 use different Nissan (OEM) sensors. R34 is different also but R33/R34 GTR ones appear to be the same.

yes but nissan often use different part numbers for things on cars that are used on some of their other cars and are exactly the same, and charge different prices for them.

Definitely do this:

- New O2, any money yours is fked and on cruise you're just toasting away fuel

- Clean AFM with Carby cleaner

- Check for vacuum leaks, good way is to use an air compressor and apply SOME pressure to the pressure side of turbo and listen for leaks, etc.

- If you got a powerFC, which I didn't see in your 1st post, disable the O2 sensor, and get someone to cruise tune the car so it hits stoich, 14.7 A/F on cruise

you could probably go even leaner on cruise than 14.7, like to 15. i know a tuner who runs his 355 stroker at a cruise afr of about 17:1 and my old remapped ecu in my 33 was tuned to mid 15's at cruise.

also there is a slight misconception that sometimes using a higher gear won't yield better fuel economy. such as using 5th at 60kmh. i had a consult cable hooked up in my pulsar (which has similar gear ratios to skylines, just a touch shorter) one day and thought i would give this a try. on a flat piece of road at 60kmh the fuel economy was 0.5L/100km better in 5th than 4th (6.4L/100km in 5th vs 6.9L/100km in 4th). now on an uphill it was a different story, but on a flat piece of road, down hill (slight down hill where the accelerator still needs to be pressed), or even the slightest incline 5th was more economical. this won't be the case for every car (such as falcons and commodores as 4th at 60kmh is much lower rpm than skylines and 4 cylinder cars). i was actually expecting it to be pretty much indentical for 4th and 5th.

[Dos]

will running a de-cat increase fuel consumption, i recently took mine off and im getting 23L to the 100, Never seen a car blow so much smoke haha although it did run rich to begin with. Im assuming it needs a retune with the de-cat?

[r33canada]

will running a de-cat increase fuel consumption, i recently took mine off and im getting 23L to the 100, Never seen a car blow so much smoke haha although it did run rich to begin with. Im assuming it needs a retune with the de-cat?

a cat shouldnt effect gas mileage and if anything, running without one would be less of a restriction in the exhaust and i would think that would improve mileage unless that slight bit of added back pressure changes everything.

unless im wrong... i just dont understand why it would effect it.

i get the same mileage with or without a cat. the only difference is a bit more exhaust smoke.

[Thelen]

a cat shouldnt effect gas mileage and if anything, running without one would be less of a restriction in the exhaust and i would think that would improve mileage unless that slight bit of added back pressure changes everything.

unless im wrong... i just dont understand why it would effect it.

i get the same mileage with or without a cat. the only difference is a bit more exhaust smoke.

+1, decat could only improve on a properly tuned car.

On my 95 ECR33 automatic (yea it was cheap though ) I was getting about 12-13. That was driving about 300km a week, 200ish on the highway, the rest without much stop/start or lights either. So that is pretty good, an being auto as well..

[The_AU_Viper]

My r34 GTT, 104,000km, basic mods. Exhuast, Intake, FMIC, bit of boost, nistune. 205rwkw.

Getting combined 11-12L/100km

9L/100km when all highway, 14L/100km thrashing it around. I average 500+ km/tank

Im very very happy with the fuel consumption

[sriver killer]

i'm still getting 460- 480 kms to the bottom quarter mark on the fuel gauge,

which from memory is about 38 ish L

i picked up heaps extra kms going back to standard wheels. picked up an extra 60 kms per tank going from 245 50 (?) 18's on the rear to 225 50 16's

[Galois]

damn. so the r18 235/35's front and 264/30's on back are pretty horrific for fuel haha

[BoostedBarge]

I get somewhere between 12-14L/100km in my Stagea 260RS (RB26DETT with Vipec ECU). Mainly city driving with a couple of kays of 100 zone each day. I still think I can tune cruising a bit more to get her a bit leaner.

I was reading this interesting article on Autospeed. They say that running the engine at low revs with large throttle is the best for fuel efficiency. So when accelerating use plenty of throttle, but change gears at low revs. I've been trying this in the Stagea and on my last tank I got around 12L/100km which is as good as it gets in the Stag, but I'd need to do more testing to be sure. Interesting read all the same...

Part 1: http://www.autospeed.com.au/cms/A_111510/article.html

Part 2: http://www.autospeed.com.au/cms/A_111511/article.html

[Marcus89]

My r34 GTT, 104,000km, basic mods. Exhuast, Intake, FMIC, bit of boost, nistune. 205rwkw.

Getting combined 11-12L/100km

9L/100km when all highway, 14L/100km thrashing it around. I average 500+ km/tank

Im very very happy with the fuel consumption

That's awesome as what you have is exactly what i am aiming for with mods now i know what to look forward too although i doubt my fuel economy will get much better than 13/14L/100km as i do a lot of short distance travels where it is in cold start

[Marcus89]

I get somewhere between 12-14L/100km in my Stagea 260RS (RB26DETT with Vipec ECU). Mainly city driving with a couple of kays of 100 zone each day. I still think I can tune cruising a bit more to get her a bit leaner.

I was reading this interesting article on Autospeed. They say that running the engine at low revs with large throttle is the best for fuel efficiency. So when accelerating use plenty of throttle, but change gears at low revs. I've been trying this in the Stagea and on my last tank I got around 12L/100km which is as good as it gets in the Stag, but I'd need to do more testing to be sure. Interesting read all the same...

Part 1: http://www.autospeed.com.au/cms/A_111510/article.html

Part 2: http://www.autospeed.com.au/cms/A_111511/article.html

Wow i find that interesting i always thought more throttle in a higher gear was worst for economy as the car is struggling more ect. might have to give it a go although wouldn't it be more likely to hit boost and use more fuel then?

[perzn_34]

my r34 gtt has a hks gtrs.. atmo ssqv bov... full exhust(stock dump) and i get abour 320k with 50L .. is that bad?? im a bit broke .. full time student style:(

[SiR_RB]

im loving my fuel economy ! it got aftermarket front pipes, hi flow cat and cat bak zorst, M's pod filters and profec b running 13psi, alwaysmanage to get between 440 - 480kms per tank, city driving ! with a hit here and there...

my mates got an r33 gtst series 2, he got terribal fuel economy, were talking 280 - 300kms per tank, we changed his 02 sensor, cleaned his afm, did a pressure test...now his getting close to 400kms...prob more if he changes his driving style lol

[Thelen]

Wow i find that interesting i always thought more throttle in a higher gear was worst for economy as the car is struggling more ect. might have to give it a go although wouldn't it be more likely to hit boost and use more fuel then?

The most efficient a car runs is when the torque/fuel usage is at its best. That means lower RPM (regardless of throttle being open or shut), will have less fuel usage than higher RPM. Making boost isn't a problem, it just means more air is being pushed through and more fuel. Comparing two gears, say up a hill, 5k RPM and 5psi of boost will use more fuel than 2krpm and 10psi. Sure 10psi will be using more fuel than 0 psi, perhaps 30% more, but 5k vs 2kRPM is 150% increase, so do the maths...

There will be some middle ground, where the fuel usage is going to be similar between two gears, the only way to know would be a fuel usage meter. Boost meter isn't enough, because it doesn't say anything about the actual air flow, only the increase given by the turbo

That autospeed article is very misleading, they are measuring fuel usage/HP, but that is bogus. They need to show the total usage for the thottle/RPM. The reason being, obviously more HP is going to use less and less fuel per firing (efficiency of engine motion), but the total fuel per second will be more. Anyway, a tuner should be able to give you the story from the maps they make.

Oh, and last reason, because there 100% throttle line looks like it will always be below the 25% throttle. And that plain doesn't make sense. Doing 100KM/hr in 2nd gear will use more fuel than 100KM/h in 5th, not to mention destroying the engine, while their graph would indicate about half the usage.

Edited April 19, 2010 by Thelen

[BoostedBarge]

Very good points there Thelen. If I'm driving for efficiency, I'll generally shift just before it comes on boost (not as much fun). I think their idea of L/HP makes some sense. Lets say you want to accelerate at rate x. This requires y hp. You can make that hp by either low revs and high throttle or high revs, low throttle. So as they say, you use less L/HP with low revs/high throttle because the engine is not pulling against a partially closed throttle. I believe this is part of the reason Diesels are so efficient... they have no throttle.

The ECU will have some throttle enrichment every time the throttle is opened. I dunno if this is gonna totally blow the whole idea out of the water. Interesting concept though all the same..

[JonnoHR31]

its more to do with the engine needing much more power just to keep itself turning before putting any power to the wheels at higher rpm.

[benro2]

The reason why the engine uses more fuel at higher rpms is increased friction. Simple as that.

With more throttle, the ignition timing is retarded. This is also affected by your revs. Generally you will run more timing with more revs, but this is offset partially by throttle opening.

[Thelen]

Yes, that is right, but keep in mind, RPM/throttle really doesn't actually matter at all. The point is to keep the engine in its highest efficiency range.

The amount of air entering is NOT the boost, so power wise, 2k RPM and 15psi might be roughly the same power as 7k RPM and a vacuum/small/no boost. Per stroke the 2k RPM has to make 3.5x as much power which may not be efficient. I'm not entirely sure of exactly what all the figures etc are, but you get the idea.

What you really need is just find some straight flat 5km stretch, and then go back and forwards a couple of times. Start from lowest possible throttle, up to full bore. Then via some fuel usage tool thingy, you can see what was the best.

[The_AU_Viper]

my r34 gtt has a hks gtrs.. atmo ssqv bov... full exhust(stock dump) and i get abour 320k with 50L .. is that bad?? im a bit broke .. full time student style:(

Thats 15.6l/100km. Pretty darn bad really. Must hurt at the pump.

Im still rocking about 11-12l/100km with 205rwkw, combined highway/hard driving

[benro2]

Yes, that is right, but keep in mind, RPM/throttle really doesn't actually matter at all. The point is to keep the engine in its highest efficiency range.

The amount of air entering is NOT the boost, so power wise, 2k RPM and 15psi might be roughly the same power as 7k RPM and a vacuum/small/no boost. Per stroke the 2k RPM has to make 3.5x as much power which may not be efficient. I'm not entirely sure of exactly what all the figures etc are, but you get the idea.

Yes, you are correct in saying that keeping the engine in its highest efficiency range is the key to good fuel consumption, but generally the more revs, the more fuel. This is why they have cars with 8 speed autos these days - so they can still run really low ratios for good acceleration, still keep the gaps between gears small so they shift smoothly, and can run really high ratios for highway cruising. I remember reading about the new BMW 7 Series being geared so that it was running at something like 1500rpm @ 170km/h!!

Generally, with turbocharged cars, you're better off running more boost in a lower gear than less boost in a higher gear. However, at pretty much any legal speed on the flat, you're never going to need to be in boost to just maintain speed anyway, so just select the highest gear available! If you hit a hill, assuming your clutch can take it, leave it in the highest gear possible and let the boost do the work.

Also, I don't know the technicalities of it all, but turbos are there to get essentially "free" energy out of the exhaust and to aid the engine in overcoming the pumping losses associated with intake piping and a throttle. In other words, you've hit your hill @ 110km/h and you stay in top gear. You start piling on boost so that at 10 psi you're able to get up the hill, vs. 5 psi in 4th vs. 0 psi in 3rd (all made up numbers ), all at say 30% throttle. In 5th, you're getting "free" energy out of the exhaust to spin the turbo which is then forced into the engine to make more power. In 4th you're only making use of half of the potential "free" energy, plus you've now got increased friction from the extra revs, so you use more fuel. In 3rd you've got a lot more fricition again plus you're not making any use of the free exhaust energy, so this will use the most fuel, and so on. Yes, there is also the issue of the increasingly enriched mixture at higher boost levels and less timing at the lower revs, but I think you will find that this still uses a fair bit less than going down a gear with less boost.

I have one of the Consult port things which gives instantaneous fuel economy and going down a gear uses a LOT more fuel. It's actually quite amazing the difference that just 1-2000rpm makes!

So basically, I think you will find that it will be the opposite of what you said in terms of efficiency - using less revs and more boost = better fuel economy.

Edited April 25, 2010 by benro2