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Old 06-19-2021, 05:21 AM   #41 (permalink)
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It's running stoichiometric and pumping losses have been reduced...the problem is the airflow required to maintain speed has gone up. The discrepancy is pretty small, 0.27 vs 0.29 load, which may have more to do with air temp than anything else.

The thing is, the engine's efficiency should NOT be this sensitive to adding 2% more EGR, so I want to say it has to be the ambient temperature and fluid temperature, but it is difficult to explain how the fuel economy dropped after adding EGR. Even if you are adding EGR past the point of diminishing returns and not adding timing, the fuel economy loss from 2% more EGR would be closer to 2% than 5 or 10%.

The correct thing to do of course is flash my old map back and test the car on the same stretch of road at night when air temperature is stable, but I still think something is wrong.

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Old 06-19-2021, 09:47 PM   #42 (permalink)
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Okay, I think I found this curious bit of the spark table around 2000rpm where the factory seems to have mysteriously pulled several degrees of ignition timing, and I discovered that Aston Martin was too lazy to calibrate IAT and EGR spark compensation, just zeroing the tables out.

If this is what I think it is, I think I am seeing 20 degrees at 0.3 load, and 24 degrees at 0.4 load, which ... makes zero sense to me. You cannot limp the car home at 0.3 load, it would barely move.

It's possible I am over 10 degrees off MBT ignition timing right now, which could easily cost 10% efficiency, whereas before I was only off by maybe 4-5 degrees. I think there is something going on where the car is using a super conservative knock adjustment table that is pulling low load timing where it really doesn't need to, and the 91 octane California fuel is making it lose part load fuel economy. Moving the intake cam increase MBT spark advance even more, and now I'm off by enough to make it lose significant mpg.
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Old 06-24-2021, 07:10 PM   #43 (permalink)
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I added around 9 degrees of timing in the cruise area, but unfortunately I am not able to get any numbers because I think my lithium ion battery is making the ECU unhappy and cruise control refuses to turn on. I'm going to try putting some ultracapacitors in parallel because I think it has something to do with the BMS cutoff feature causing a momentary drop in voltage.

That said, I took it on the freeway on the section of road where I was getting about 24mpg before, and I held my foot as best as I could so that the display stuck around 25.0mpg...AND THE CAR ACCELERATED! So I think I'm definitely above stock mpg now, which is awesome.

My travel plans look like I'm saying goodbye to the car for half a year, but next time hopefully I get the electrical issues sorted and can share proper results.

Theoretically speaking, if the only thing I've changed is manifold vacuum, I should have gained approximately 3% more mpg, but I am estimating that the stock ignition timing probably was costing like 6% in fuel consumption, so I would not be surprised if I am now getting 26mpg at 60mph on flat land with 10w-60 oil, and when I finally get around to changing the oil to 10w-40 I expect to see 27mpg or more. Not bad for a car that started at <24mpg!

I also feel pretty comfortable saying I've managed to cut idle fuel consumption to around 0.41gph at sea level (the idle isn't steady but it bounces in between 0.37 and 0.44gph), whereas before I was seeing 0.44gph at 5000ft elevation, so I probably have dropped it more than 10%.
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Old 11-23-2021, 12:11 AM   #44 (permalink)
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Reunited with the car for the first time in a few months.

Fixed my electrical issues by adding a supercapacitor in parallel. It weighs only 150 grams or so. Now I can use cruise control again, and I got 25.5mpg on a slight uphill grade on a colder day than when I tested in the summer! (up from 23.5 with no oil cooler block off tape, factory tune) Unfortunately, the mpg is pretty bad before the oil warms up. I haven't gotten a chance to change the oil to thinner oil. I think later cars had a better ECU tune but I probably still picked up something like 0.5mpg with my laborious VVT/EGR fiddling.

Sadly, today I went to fuel up the car, and I had to add almost 8 gallons! I think I only drove maybe 70-80 miles since the last fill up, so not good Just letting this V8 idle guzzles down the fuel very quickly.

Ordered a custom fully floating brake rotor kit which I aim to install before the summer. I'm hoping this will help the car coast a little better, because the coast down is poor (though it may be my tires are underinflated, as I just remember it coasting much further last time I drove it). It'll also remove about 16lbs of unsprung mass and prevent any potential rotor warping issues if I take the car to a track.

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Old 11-23-2021, 01:07 AM   #45 (permalink)
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Now is the time to send them out for cryonic tempering.



It should double the part cost and extend the service life 3 or 4x.
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Old 02-02-2022, 11:41 AM   #46 (permalink)
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Well this is pretty incredible, the oil viscosity made even more of a difference than I expected.

I was going to do an oil change but the process is quite involved (have to remove two metal mesh filters and clean them, adding about 9 extra bolts and 2 O-rings to your typical oil change process, and that's after the 17 bolts on the underbody panel!), and with under 2000 miles on the oil with a stellar used oil analysis, I decided to just pump out 2 quarts of 10W-60 and replace it with 0W-16 for 9 bucks, then I topped it off with a few more ounces of 5W-20. 10W-60 has the consistency of snot so it stuck to the tubing on my fluid pump and made a huge mess everywhere that took a lot of time to clean, so I might have been better off just changing all the oil, but oh well.

The second day I cold started the car, I was astonished how the engine revved up like a normal car would...it used to slowly sputter to life. Clearly, the main oil pump was doing much less work.

The other day I was on the freeway and I put it in cruise control at 60mph. There's a very slight downhill grade on that stretch of road, less than 0.1% but enough to cause a difference in mpg, but the display was fluctuating between 27.2 and 28.8mpg when there was a car ahead of me, and it fluctuated between 26.6 and 28.2mpg with a completely clear road. Wow, that's a huge jump from 24!

I still need to verify this with more runs but the mpg is very clearly higher than before. I was driving into a 20mph headwind at 65mph yesterday and still getting 21.5mpg (used to be 22.5 with no headwind).

Using a viscosity blend calculator, 8 quarts of 21cSt oil and 2 quarts of 7cSt oil comes out to 16.5cSt (basically the same as Castrol 5W-50), so I actually have even more mpg left on the table if I go to a ACEA A3/B3/B4 40 weight oil.

Obviously, my car is a bit abnormal in that it has a very short 6th gear but this is kind of crazy to see. I would recommend anyone with a car that asks for 30 and above oil and a reasonable sump capacity to try Redline/300V and dropping a grade. The reduction in oil pump power consumption should be noticeable.

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Old 02-03-2022, 12:23 AM   #47 (permalink)
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Thought I would also mention my further ECU tuning exploration. I was hoping the idle would be a little better and fuel consumption would drop if I tweaked the VVT settings, but I changed what I think should retard the intake cam opening by 10 degrees and I can't really see much of a difference. What I notice is that perhaps surprisingly (or maybe this is normal for engines with a lot of cylinders, since they can tolerate misfiring and still run smoothly) the idle is perfectly fine with cold temperature and it'll idle at my requested 672rpm (down from 752) with target AFR of 1, but the fuel consumption will be very high until the coolant is hot regardless of what I do to the VVT.

Right now at high altitude and with thinner oil, I am seeing a 0.38 gph idle when the engine is fully warmed up, but at 180F it's more like 0.45, and at 150F it's 0.5. I guess the fuel just isn't mixing and combusting if the engine isn't hot. I think if I switch to 10W-40 as planned, the lowest it'll go to is maybe 0.39gph at sea level on a hot day where the cooling system is running over 200F. That's 0.09gph/L displacement, which is actually really impressive for a port injected engine with a lopey idle. I recall my Scion FR-S using 0.17gph for a 2L engine, but that had port + direct injection and dual VVT.

I added some more EGR and ignition timing advance but I don't think it's helping. The intake vacuum is not that high because there's so much cam overlap. Friction remains the primary enemy, and thinner oil and taller tires are the only things that will help.

On another note, I did get these beauties. They feel pretty light, but the springs on the floating mount feel really stiff as I can't get the rotor to move relative to the hat at all. I do need to remove the bolt to get a feel of how much force they actually apply, but the metal looks fairly thick so that's not great. Unfortunately, a full brake job involves buying new torque to yield bolts for the calipers while the original brakes still have a lot of life, so I am probably going to avoid installing these until I burn the originals up at a track day some day.
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Old 05-08-2022, 12:28 AM   #48 (permalink)
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Fill-up accounting time:

Unfortunately with fuel prices nowadays, I actually was not able to fill the nearly empty tank all the way at a Valero with a 100 dollar transaction limit! I added 17.2 gallons there and the needle was at the full mark. However when I last filled up, the needle didn't actually reach the full mark (the fill port is finicky and does this a lot), so I want to say I likely burned under 17 gallons, but we'll call it 17.

I had to go look at the State Farm app logs to see how far I actually drove and the number shocked me: I made it 462 miles!

462/17=27mpg

There is a catch: There's a 5000 foot descent in there which is like 40 free miles (and I took advantage of it by rolling down the hill in neutral).

Still, 25mpg on flat land is not bad! I did a bit of cruise control on a longer trip to reduce fatigue but 100 miles of that tank were very diligent P&G.

The nice thing is I actually still have more mpg left on the table: My engine oil can go down one more grade, my engine coolant temp was never hot so I could've blocked the grill more, and I was on winter fuel. More "normal" driving would probably end up at around 20 which is still way better than the 13mpg average displayed on the screen when I got the car.

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Old 05-08-2022, 02:00 AM   #49 (permalink)
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I like this thread, but I'll point out life is short, and my 2001 CBR600 gets 40 MPG and 0-60 in 1st gear.
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Old 05-08-2022, 09:32 AM   #50 (permalink)
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Originally Posted by redpoint5 View Post
I like this thread, but I'll point out life is short, and my 2001 CBR600 gets 40 MPG and 0-60 in 1st gear.
I will point out: you get wet in rain, cold in snow, and hot in the summer. Falling down is a PITA also. Btdt.

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