joshuaho96

So clearly then fuel consumption does matter? Or it doesn't? I'm unclear here. Just because a high performance vehicle has a high energy per mile requirement doesn't mean that it's pointless to try and optimize the efficiency with which fuel is converted to KE.

I too disable DFCO and run a lambda 0.7 target globally for all my tunes because fuel consumption doesn't matter.

If you want the answer to the question of when to change gear the map helps though.

Your 14.7 AFR gas target is stoichiometric. That's pretty normal and where the TWC operates best. You can run leaner like 16 or 17:1 AFR gas for cruise but as a general rule the efficiency benefit is not going to magically turn a throttled PFI gas engine into a diesel engine in that regard. I don't know RBs well enough to say whether they can efficiently cruise lean, some engines really need to stay near stoichiometric, some particularly bad engines like the L26 4.9L actually had to run rich to avoid stalling and did an "interesting" trick where it would operate at stoich and run like complete crap until you turned on the AC or heater at which point it would enrich the mixture. Even a turbo RB26 can wait until ~3-5 psi to start enrichening, it's a 8.5:1 CR naturally aspirated engine until the turbos really wake up and the ITBs really screw with intake runner pressures so it's really easy to hit 0 psi. Helps a bit with the spool as well to keep EGTs as high as you dare. I don't blame you for staying conservative beyond that though, RBs are ridiculously expensive to build and kind of fragile. Generally speaking the problem with staying at too low an RPM is that the engine is just not tuned to breathe well at those RPMs, either because of valve timing or intake runner tuning or exhaust runner tuning or some other fluid dynamics problem I don't understand. If injection timing is not adjusted to avoid the low lift portion of the intake cam opening you can also experience higher covariance of IMEP from stuff like pre-ignition. So the best strategy is to increase the RPM to the sweet spot, whatever it is, and stay right around 100 kPa MAP to maximize efficiency. NA engines tend to have less dynamic range and you tend to want to be closer to ~70-80 kPa MAP instead. It's not a perfect comparison but we can compare the 2.0L Skyactiv-G to the 2.5L Skyactiv turbo engine: If you squint and compare between these two engine maps actually at 180 Nm of torque at 2500 RPM the Skyactiv turbo engine is more efficient, not less. If you drop down to 140 Nm of torque the 2L NA has a ~4% advantage in BSFC. As you go down you can tell the turbo engine is less efficient due to the extra displacement, but that just means you need to apply some more load, either in the form of accelerating harder, gearing, or increased speed. Or your car is just too light. So as a general rule I think if you drive a turbo engine correctly and use the lower compression ratio to run right around atmospheric while accelerating and keep the load high the efficiency hit is not terrible, and when you compare to a bigger displacement NA engine the efficiency will be better at low loads, but if you have a lot of boost enrichment like these early turbo engines then pretty much any kind of scenario where the turbo engine has to run boost + boost enrichment and the NA engine can stay out of high load enrichment is an easy win for the NA engine. If you toss tricks like E85 or water injection in though you could keep the same amount of torque and reduce enrichment for better efficiency. Same goes for GDI which allows for quite lean AFRs even at WOT.

Depending on the engine the map might look different but you can see that full throttle 1500 RPM to have the same power as you would at 2500 RPM you need to basically be right around full load. Your BSFC is going to be in the high 280 g/kWh range if you keep the engine at 1500 RPM. If you instead let the car sit at the 2500 RPM or whatever RPM it wants to really be at you can instead be in the 240 g/kWh sweet spot for thermal efficiency. So the conclusion for turbo engines like this one is basically try and stay right at the edge of boost if you're accelerating. If you're cruising you want to maximize load by using your gearing, but you don't want to overdo it either. The US EPA has a lot of very nice public data on some engines where they took the time to run through the dyno with a fuel flow meter to derive BSFC and thermal efficiency: https://www.epa.gov/vehicle-and-fuel-emissions-testing/combining-data-complete-engine-alpha-maps Maybe you guys have less traffic but around here you're almost entirely limited by traffic and lights unless you get out of the city and into the back roads. Trying to drive efficiently helps to make things a little less boring.

Very carefully? Jokes aside the point is that lugging the engine at 1500 RPM and WOT to cruise is going to actually be quite inefficient even if the pumping loss is minimized. It's better to cruise at 2500 RPM with less throttle. The exact numbers are going to vary by engine but the principle is the same.

It's simple, it's the condition where you are accelerating with the throttle.

For efficiency shift based on the peak efficiency RPM, shift just past the peak efficiency point while maximizing load without encountering high load enrichment so you sweep through the efficiency sweet spot. Looking at the gearing of the GTRs it looks like you want to be shifting at 3000 RPM so you drop down to ~2000 RPM when accelerating. Hold the engine right around 50-60% throttle if this is an NA engine or right at atmospheric pressure for turbo engines for best results. For cruising pick the highest gear that doesn't have you exceeding the accelerating throttle condition. As for the best speed to cruise at, something high enough that you aren't running below 2000 RPM and something low enough that you don't exceed 3000 RPM.

Give it some more time, the US economy is currently in the process of unraveling so people are going to be unloading things they can't afford anymore.

If it felt even the slightest bit wet/slick it's oil. Otherwise that's probably soot from running rich. I would also confirm against the plugs. Running rich will turn the plugs black but it should be a dry deposit, not a wet one.

Rub the exhaust tip with your finger. If it's oily you're burning oil, not running rich.

dE2000 of 0.3 would be incredibly good across all light sources. Generally speaking just staying under dE of 1 is good enough.

This sounds like a GT-R with extra steps.

The HKS logo halves the turbo lag.

What's bizarre to me is that nobody at Nissan considered disabling the system as the car reaches the limits. The wheel sensors were all there, the lateral g sensor was there, the yaw sensor was there. Why didn't anyone write a bit more code to disable the system if any sensor value suggested the vehicle was at dynamic limits? I know the Porsche rear axle steer system has this logic present for exactly these reasons, to make the vehicle more predictable at the limit.

Is HICAS really that bad in the R33 and R34?

Definitely try GTRCanada/GTRUSA on Facebook, list with a 25-33% discount off new and someone will probably bite.

Yes, he has. But the topic is interesting beyond just helping him decide. -7s and -9s are a comparison that has been done to death. I think the GT3-SS is an interesting alternative for those that are willing to give up some of that high RPM compressor efficiency for better low RPM response. Ball bearing would help with response for that given turbo but no such option exists.

I don’t think it’s that simple. Journal bearings do have worse transient response from the oil viscosity drag but the oil film helps to dampen any imbalance in the rotating assembly. The oil flow also improves cooling and the thicker oil film also improves longevity. On the balance it looks like despite the cheapo journal bearings they’re more responsive if you can actually get the engine to flow enough at 2500 RPM. Based on the dyno charts out there a journal bearing R32 ceramic turbo can out-spool pretty much everything out there. It just doesn’t survive high boost or age. The R34 ball bearing turbo does spool faster but that tells me that it’s a second order effect on the boost curve of a turbo.

I'm not on that train. I would much prefer PRP's double VCAM if that ever makes it out of R&D, the intake only VVT even pulling the pistons for 50 degree cam advance doesn't make for a modern turbo engine response where it spools at 2000 RPM and pulls to redline. There's a significant bump again with dual VVT compared to intake-only VVT: https://www.enginelabs.com/news/spooling-up-tuning-dohc-variable-valve-timing-for-boost/ The GT3-SS is very likely just a recent single scroll turbo adapted to the RB26. Not new, but for those that want to keep the twin turbo setup instead of single it helps to modernize the engine.

This is true. When I looked it up a full kit for -9s with HKS actuators and various bits was within 400 USD of the GT3-SS. It’s definitely not a value for money choice and it’s only a matter of time IMO before someone figures out what turbo HKS rebranded this time and sells it for a solid 25% discount, maybe more. But frankly nothing about RB26s is good value for money.

-7s and -9s is a pretty simple answer. If you want more power get the -9s, they have a more efficient if narrower compressor map, especially at high boost. If you're ok with less in return for a touch better response get -7s. I agonized over this for a while but after seeing the prices for a full -9 kit vs GT3-SS I think I'm going with the GT3-SS.

VCAM should be pretty reliable, it's literally just the Subaru EJ25 AVCS bits with some fittings to get it on an RB intake cam. If your pistons have valve relief for high lift cams then they should work with 50 degree advance. Don't buy the hype from HKS, you can fit either your own cams to the VCAM system with some modification or regrind the cams to get the desired profile. If you want to save some coin in return for some labor you can buy the step 1 system, pop off the metal block that they use to keep it within 30 degrees of cam advance and regrind the cam to your desired spec. Or replace entirely. Here are some dyno charts for VCAM: Step 1 VCAM with -5s vs stock with catback, no VCAM: Blue is Garrett 3582 with step 2 VCAM, Orange is stock with catback: More dyno charts here: https://www.facebook.com/upgarage/photos/?tab=album&album_id=2754286177933791 As for whether you should pick VCAM or single, I would say both? But it's big money to do that. If you want to know what the benefit at the top-end will be, get an adjustable intake cam and fiddle with the timing and see what timing gets you the best top-end. That will be your peak power. Fiddle with it again for best low-end response. Do that for every RPM and load combination and you end up with what a VCAM can do for you.

You are correct that the GT-SS and GT2859R-9 are the same turbo, I never argued that. I'm just looking at the data that I can see and making assessments from there. As far as turbo spool goes the GT3-SS with VCAM step 2 looks like this vs stock: The -9s with the same VCAM step 2 looks like this compared to stock: This is from U.P. Garage in Washington. Maybe the guy has a vested interest in selling HKS turbos? What stands out to me is the GT3-SS is pushing 10 psi by 2500 RPM while the -9s/GT-SS are closer to 3000 RPM. The huge overboost from like 3000 RPM to almost redline is maybe overselling the capability of the turbo but clipping the boost to be 1.3 bar flat would just flatten the torque curve even more. He also had some other neat charts like this VCAM step 1 stock ceramic vs GT3-SS: This one shows to me that the stock turbos ultimately build boost the fastest, so if the power goals are maybe 250 kw then stock turbos are as good as it gets.

If you want the absolute fastest spooling bolt-on twins the best are still the stock ceramic turbos. With the ceramic turbine. The R34 ball bearing ceramics are the fastest spooling of the three gens. If you want more power and more durability the GT3-SS is the next step up. It spools faster than the -9s despite the journal bearings but you give up high-end power, an honest 300 awkw should be possible with good fuel and tune. If the engine flows enough at the midrange it will be a better option than -7s which trade a little bit of top end for not much faster spool. -9s are going to deliver more power than GT3-SS and if you don't have a VCAM step 2 or step 1 with 50 degree advance the RB26 just doesn't breathe enough for a really substantial difference in spool vs a GT3-SS. Beyond that just go single turbo. Honestly the only reason to stay with bolt-on twins is to avoid getting defected and to have a well-understood setup that tuners have done many times over the decades.