Extremely thirsty supermodel - eco attempt!
 

I decided life is short, and used car prices have shot up in the last year...so I got this (probably the lowest mpg per occupant or per unit length/height on this forum lol):
https://ecomodder.com/forum/attachme...1&d=1617592102

Yes, 3600lbs, V8, 15mpg (drinks 91 octane). Right now I have a beater Infiniti G35 that gets around 24mpg on a good day, and it has an even less efficient engine (albeit quite a bit smaller) and similar weight and aero. If I can get a 26mpg tank, I will probably have set an Aston Martin owner record. Obviously, fuel cost is almost negligible compared to maintenance, but it would be nice if I could hit 500 miles a tank and reduce refueling.

I'm making this thread to document the eco-friendly mods that do happen to this car, which will be rather few in number. This car is mainly going to sit parked as automotive art and not burning through copious amounts of fuel.

All the planned mods that will maybe eventually happen are as follows:
-Partial grill block, pending fluid temperature measurements. The bar grill makes this extremely easy and aesthetically pleasing, just add tape to the back of the sets of bars. There's plenty of space behind the grille to do a bit of smooth ducting as well.

-Thinner fluids: The transmission fluid is already 70w-75 (OEM fill), but the engine has 10w-60 in it and the power steering has the original factory fill. The oil spec is A3/B4 which 0W-40 meets, but 5W-50 is factory approved and still an improvement. The PS fluid was updated in a service bulletin to CHF11S, the lowest viscosity fluid on the market, which I'll be doing. A P/S delete is not practical because of the way the belt is routed and also because the front of the car is extremely heavy, though some day I would love to figure out an underdrive pulley solution.

-Slightly taller tires when I need them in a few years, the 6th gear is fairly short.

-ECU Tune: At high rpm, the engine runs near 10:1 AFR :( On top of that, the EGR seems to be very underutilized at 4% maximum dilution, bumping this up and adding a few degrees timing should drop pumping losses by a lot, but figuring out how to flash this ECU may be a major challenge. If I can get the ECU reflashed to my preferences, I am optimistic that I can gain 5% more efficiency.

-Weight reduction:

• Lithium titanate battery, which will drop 40+lbs out of the car and use less power from the alternator to charge. This may or may not work, as the battery is located behind the seats so there's some voltage drop in the cables going to the starter, which combined with the low working voltage of LTO and the large engine may be an issue. I may opt to buy a LFP battery if the voltage is inadequate.
• When the time comes, lightweight flywheel, the AMR package should be around 10lbs lighter, and the rotational inertia is dramatically lower, which should be like removing >100lbs in 1st gear. Also, instead of the 25k mile original clutch life expectation, it'll instead outlast everything else on the car.
• When the time comes, Wilwood two piece brakes (-16lbs), since it's barely more money than OEM replacements. I am thinking about getting them chromium or tungsten carbide sprayed so I don't need to replace them ever again to save money.
• Airbox delete, -10lbs.
• Trunk compartment divider delete, -10lbs (already done).

Ideally, the seats could be replaced with the Recaros they sell over in Europe (no side airbags), but my interior is in fantastic condition especially after I spent the whole day filling in all the wear spots in the leather and those seats would cost half a lifetime's worth of fuel XD

Considering how a Recaro could improve the support while pushing this beauty to its limits on a track day, it may be worth :D

The Recaros would drop 60lbs which is really substantial, the issue is the shape doesn't really seem to fit the rest of the interior style, and losing the side airbags isn't great. I could go buy Recaro shells and then have an upholstery shop make leather covers for probably 3-4k all in vs. 11k for the OEM pieces (yea...). My acrylic paint touchup made the leather look almost just like new, and the foam in the seats is still mostly intact, so I'll probably never be able to justify replacing seats.

I drove it to get gas at Costco and then took a short fun spin around town...based on the needle movement, I'm pretty sure I went through over 1 gallon of gas in around 16 miles (still haven't figured out how to set the trip meter lol).

I was driving pretty efficiently and slowly but the oil temp hit 100C very quickly (measured with an IR thermometer pointed into the oil tank, as the car doesn't have a sensor :/), so that 10W-60 is creating some SERIOUS friction.

The power steering was actually only barely warm. The original factory fill was a Texaco Cold Climate low viscosity fluid that's already thinner than most PS and ATFs on the market, but I'm putting in the updated even thinner fluid.

Avoiding idling should help a decent amount, though replacing the starter motor is extremely time consuming so cycling too much is probably not smart. This engine burns about 1.7 liters per hour (that's 0.44 gph) idling, which is fairly bad but relatively low for a V8 lol. I think for the custom tune I'm trying to figure out, dropping the idle from 750rpm to 680rpm like a more normal car would quench its thirst a touch.

You know you're an ecomodder when...

I guess the pleasure of seeing the results of your own work on the restoration of the upholstery may decrease any will to replace those seats :D

Okay not much mpg progress, been working hard at touching up the bigger paint chips on the front.

Did a little more research, apparently the PS was filled with normal ATF from the factory, so switching should actually drop the viscosity by almost 50%! AFAIK, this could actually be a measurable improvement if it can drop the PS pump power from e.g. 500W to 300W.

Still debating whether I want to go thinner than 5W-50 on the motor oil...With very few miles of gentle street driving, I feel like a 0W-40 would not shear below the minimum viscosity, and the factory used 0W-40 for break in. The viscosity drop would reduce friction probably 10%. However, NAPA has 5W-50 for dirt cheap so I might just go all 5W-50.

I've been contemplating the grill block more. It seems like the radiator fan is very eager to turn on (the engine is large after all), so it's probably best to be conservative and have something easily removable that only blocks a small portion, like a piece of tape (easiest), or a bit of foam behind the grill (more streamlined, slightly more work to attach).

https://i.imgur.com/DyxweiZ.jpg

Only blocked off a small portion of the grill, but half the oil cooler in the hopes that my oil gets hotter and thinner. Looking at some charts, it seems like 10W-60 at 120C is more like a 40 weight at 100C, with 60% of the viscosity.

Also I hooked up my OBDII scanner again and was pleased to see that with a hot engine the idle fuel flow is actually 1.6lph not 1.7lph. Still very high...

If you are happy owning it, like when sitting on the couch at home, then you are enjoying it while not burning fuel at all :)

(subscribed!)

10w60! :eek:

They have 0w-50 now, but maybe that's too expensive for your eco-project.

And you can swap that Infinity for a proper slow car like an old Prius now, just add a bumper sticker that says: "My other car is an Aston Martin"

I got the Infiniti because it was the cheapest Japanese, somewhat modern manual trans car I could find, with the intention of getting rid of it in a year (I only have a temporary need to drive a lot right now, I would normally drive well under 1000 miles a year). I almost bought an old BMW, but got scared off by stories about replacing water pumps every other year.

I'm not buying a Nissan product ever again...maybe I have a bad example, but all the plastic bits are crumbling apart (it's a 2004, not that old...), there are tons of things that seem to be intentionally designed to rattle from the factory, and apparently all the weird unhealthy noises from the drivetrain are completely normal.

At some point in the future, I plan to add an ultra-light sports car again for a more carefree and raw/fun driving experience. I took the Vantage on a twisty hill today, and the width of the car made me very uneasy on narrower roads.

AFAIK, 0w-50 only exists as racing oil, which is a no-no. Mobil1 0W-50 racing has very similar specs to Redline 0W-40, but Redline oil is crazy expensive. Mixing 0w-40 and 5w-50 would get something close for 40% the cost. Mobil1 5w-40 or 10w-40 would be similar but not quite as good, meeting ACEA A3/B3 with HTHS of 3.9 cSt.

Most of the Nissans of that same vintage I usually see are Frontiers and XTerras, and they're often in a good condition.

Road trip today! A lot of findings from watching the mpg gauge...mostly bad. It appears I went through approximately 16 gallons in 285 miles, though the first 4 I burned while trying to diagnose rattles and driving around town for fun, so today I got more like 20-21 mpg.

6th gear cruise control flat ground: 26mpg @ 50mph, 24mpg @ 60mph, 22mpg @70mph, a little under 20mpg @80mph. Wow, this is more awful than I expected.

Pulse and glide got me to 26mpg averaging about 75mph. The one good thing about the short 6th gear is it climbs hills pretty efficiently, I managed to get 19mpg climbing the Sierra Nevadas @ 75mph (going slower doesn't help all that much, you just end up idling more and losing efficiency on the pulses). 3600lbs and reasonably low drag makes the glides very long.

I was wondering why the fuel level gauge was dropping so rapidly when I hit some slower traffic...I noticed later on that THERE IS NO DFCO in gears 1-4 (it does DFCO in 6th gear, but I didn't check 5th). That's also why shifting seems so sluggish, it loses revs slowly since it's still injecting fuel.

So basically, I really need to get this ECU tune sorted out.

My neighbor had one of these.
I would just stand there staring each time he had the garage door open and I could see the car.
( My apartment rents garages )
He had the DB-9, a late 90's 911, and a 1984 Mercedes.
Oddly enough, his favorite was the Benz, because he grew up in it.
His dad was wealthly, and this guy lived in my aparments.
Didn't really work either.
Just tinkered with his cars.
TOTALLY out of place.
It was amusing when I would see him drive up in the Aston with some lady.
I could just imagine what the women must have thought.
" Wait - you live HERE ?? " " C-YA ! "

I remember him saying how annoyed he was when he would have people call the car an Austin Martin ( I live in Austin, Texas lol. )

BTW, I'd love to see more pictures of your car !

As long as a place is not criminality-ridden, I wouldn't be uncomfortable to live in a similar way if I had the money. But I'm sure I would prefer a house or a country estate over an apartment, as it would be supposed to not cause much trouble with neighbors complaining over noise or smell of gasoline and oil leaks at a shared parking lot.

Working more on the ECU, still not finding much info at all on this ECU, but I believe I found the VVT table and it seems like there is WAY too much valve overlap at low load, which may be why the gas mileage is so atrocious at low speed.

For some reason, all these years I've been a car enthusiast I never bought a legit OBD2 scanner that is fast enough to actually datalog, so I just ordered one off Amazon (Veepeak, still a relatively cheap one at 32 bucks, I watched some Youtube videos and it seems to log more datapoints than I can count in 1 second, which is good enough). I'll look at the logs and try to estimate how much internal EGR is going on so I can reduce the cam overlap if needed.

Unfortunately, the Jaguar VVT actuator seems to have a very limited range of 37 degrees (could be more, but eyeballing a picture of the physical mechanism agrees), and messing with the VVT position too much could throw off the spark timing since I don't know if there is VVT based spark timing compensation. Of course, if the spark timing logs show pretty sensible numbers, then I would be in the clear, so hopefully that's what ends up happening.

However, if the logs do suggest extremely poor combustion efficiency from big cams and lots of valve overlap, then I won't be trying to utilize much more external EGR and thus don't need to worry about spark compensation for EGR.

Figuring out DFCO is probably the next priority, but the lack of DFCO can be mitigated by braking in neutral with a lower idle speed (not great, but better than guzzling fuel in gear with foot completely off the pedal :/).

I'm still optimistic I can get a 26mpg cruise, high 20s pulse and glide, and something like 16+mpg "city".

What is it?

2006 AM V8 Vantage :)

Gonna continue using this thread to keep notes on my tuning efforts. Unfortunately, I still have not been able to figure out the DFCO parameters, which is costing me some fuel.

Idle: I think it'll idle okay at 680 instead of 750, dropping my hot idle gph from 0.42 ish to 0.37 ish. I haven't been able to find the idle speed control table though.

VVT: I made some really rough estimates, assuming around 30% iEGR dilution at idle based on observing that a small change in vacuum produced a big change in load, comparing hot vs. cold idle. I think I can bring down the iEGR amount in the low load, low speed cells to improve combustion stability for mpg, and then feed more EGR in at higher speed with later intake valve closure to reduce overall vacuum by around 0.5-1psi, by targeting ~20% total EGR (compared to 100% undiluted cold air, this has around 60% oxygen concentration, a good improvement!).

I think I can push that retarded cam position to medium load as well AND feed more external EGR in, giving me higher pulse efficiency for P&G.

0.5psi at cruising speed is a respectable ~600 watts, 1psi is around ~1200 watts (compare to the ~15-22 kW it takes to go down the freeway), and improved combustion stability hopefully has a noticeable effect. If I can get 50mph cruise from 26 to 29mpg, the numbers would start to look a little more like a normal car, and if I can crack 30mpg at 45mph, that would be amazing. Otherwise, I'll continue to P&G diligently.

I just came to a realization that oil might make a much bigger difference than I thought...

FMEP of a piston engine at 2000-3000rpm is something like 0.5-1 bar depending on load (0.5 is probably an underestimate). For this V8 at 2500rpm, 0.5 bar is a whopping 1250/60*0.5*4.3 = 4.5kW = 6hp!!!

Using the Ecomodder calculator, my car needs around 20hp to do 65mph. Well, the problem is pretty obvious now right?

It's even worse at 40mph, where we only need around 8hp, but friction is consuming 4hp.

If I can cut 10% of friction, I'm already up 3% in fuel economy. It seems switching away from 10W-60 should easily accomplish that. Any 0W-40 will meet ACEA A3/B3 (3.5cP HTHS is one of the main criteria), but given the factory only okayed 5W-50, let's take a look at some HTHS values:
Mobil1 0W-40: 3.6 cP
Mobil1 0W-50 Racing: 3.8 cP
Mobil1 5W-40: 3.9 cP
Mobil1 High Mileage 10W-40: 3.9 cP
Redline 0W-40: 4.0 cP
Castrol Edge 5W-50: 4.1 cP
Redline 5W-40: 4.4 cP
Mobil1 5W-50: 4.4 cP
Mobil1 15W-50: 4.5 cP
Redline 5W-50: 5.0 cP
Castrol 10W-60 (OE fill): 5.2 cP

I wasn't expecting the bottom shelf pricing Mobil1 10w-40 to have such a high HTHS! It's full synthetic, has high TBN, ACEA A3/B3 certification, API SP, and the 10W part isn't a problem since I'm not driving at -20. It's basically a slightly thin 50. If I spend double the money, I can get Redline 0W-40 which is a little bit better, but since this car won't be driven much, it would be a waste to just dump that Redline oil after 1000-2000 miles, so I got 10 quarts of the Mobil1 for 50 bucks total from Walmart, and one extra quart of Mobil1 5W-50 as a top off oil.

Word has it Shell Rotella T6 is actually "better", but the slightly higher phosphorus content isn't good for cats so I decided to pass on that. Unfortunately, the air oil separator on this car doesn't have a good reputation.

Given the oil viscosity is going to be reduced by 40%, I expect BIG mpg gains :D

If you're feeling adventurous, you can always go even thinner, and send a sample off to Blackstone for analysis (metal content). I determined 0w20 has very marginally higher wear than 0w30 in my car - which I don't feel is worth it, since the 0w30 is *nearly* as thin when cold, and most of my fuel economy losses happen at low temperature.

I would only dare to do that with a Redline 30 weight (since they're A3/B3/B4), and if the oil cooler thermostat could be switched out to slightly lower temp. The thermostat is mechanical and opens at 102C.

If I knew for sure I wasn't going to exceed 4000rpm for the whole oil change, then a common 5w-30 might work. You do get diminishing returns, since the thinner oil could make it run under boundary lubrication conditions, and this engine has wide clearances which is why 10w-60 was speced.

Look on the website bobistheoilguy.com. There is a member AEHaas, who has several exotic cars. Ferraris mostly. He runs 0w-20 in them. I would recommend you try Redline 10w-30. Yes it's expensive but you'll only need to change it once every 2 years maybe.

If you can write a custom tune, you should lean it way out. Forget 14:1, try 18. I would imagine the robust V8 can handle lean burn as the large metal volume and overbuilt cooling system can handle the heat.

Thanks for the comment, I am aware of all this.

The issue with running a light oil is that unlike the BMW S65 and S85 engines which had tight bearing clearances and failures on 10W-60 oil, Vantage owners all run 10W-60 with basically no engine failures, suggesting the oil is pretty well matched to the engine.

Certainly it is unlikely that 10w-30 oil at 100-105C would be an issue for street driving, but dropping 3 grades feels too aggressive on an engine that would cost 20k to rebuild, and it's possible that the thinner oil film will have diminishing returns for efficiency.

I would be shocked if I made it to 2000 miles in any year on the car, so it really doesn't make sense to buy Redline oil for 70 dollars more when my OCI is going to be like 2000 miles. The shelf life of oil is shorter than the time it would take to accumulate 7500 miles. M1 is very very cheap at 4 bucks a quart and the base stocks have fairly good VI.

As far as tuning goes, the issue is this platform isn't common and well supported the way Subarus or BMWs are. Even on a popular platform, lean burn can be very difficult to implement due to the ECU restricting open loop AFR to rich only.

There is a guy who did figure out pretty much all the workings of the ECU and ran lean burn (in open loop), but he spent many years and tens of thousands on his car. The easier way to do lean burn is to replace the O2 sensors with wideband sensors and bias the closed loop AFR, but it requires considerable custom ignition timing adjustments if you want the most out of it, and you need to spoof the post-cat sensors as well, so it'll take 2 wideband emulators + sensors + 2 sensor simulators and quite a lot of money and/or time on a custom tune.

My limited modifications are vastly easier since the OEM already built in all the timing compensation and it's just a matter of accessing a few tables. I will never break even on this mod, but for a little bit more effort over an off the shelf tune I can get my car a few % more efficient than 99% of the others.

I imagine you could get a fair bit of mileage with running as little lean as 1.04-1.07 lambda, even without adjustments to ignition timing.

Heat isn't an issue at low load (which it would be during cruise), and temperature actually starts to drop off past ~1.04-1.05.

It's a sophisticated British design, not even supposed to be as dumbproof as a small-block Chevy.

Yes, but the gains are bigger if you can go leaner. Lean burn is like high volume cooled EGR but with faster flame velocity. To get the best effect, you can bias everything lean and run open loop idle richer, or run open loop lean while cruising. Running open loop in commonly used operating conditions has its own drawbacks, and not forcing open loop limits the gains. Biasing the sensors means a few hundred bucks in narrowband emulators, a bunch of custom wiring, and a lot of custom tuning to reset the ignition timing.

For a car that doesn't have emissions restrictions and for which you have complete control over the ECU's programming, you definitely want to run very lean, maybe with warmed intake air or a hint of EGR to help with ignition.

This engine isn't short on EGR thanks to the MASSIVE cams, so pumping losses aren't actually that big of a deal. The intake vacuum is pretty modest near minimum load (i.e. pressing on the pedal enough to actually move the car), around 0.6 bar.

@cRiPpLe_rOoStEr I wouldn't call it particularly sophisticated, it's very similar to a Ford V8 in design. This car adds a 2 scavenge pump dry sump system, DLC coated shimless bucket lifters and a forged crank. Everything else is pretty ordinary, and thankfully it seems to all hold together unlike Porsches of the same vintage.

The coolant temperature goes up FAST, though it's a 1.5 bar system so it can run a little hotter than most cars I've seen. I do have some concerns that the radiator is near its limit and my grille tape might not be a good idea. Of course, this isn't relevant to the discussion as lean burn decreases peak combustion temperature and only increases EGT at high load and high speed where the slower combustion speed is a problem.

Alright so I don't think I can use lean burn, because that would require always staying in open loop or swapping all the sensors to narrowband emulators, which I'm not comfortable doing. Leaving it at stoich also means I don't need to spend tons of time tweaking ignition tables.

So the final changelist is going to be:
-Retard intake cam position at low load
-Lean out open loop fueling (it's stupidly rich, like a turbo car)
-Reduce closed loop delay
-Reduce DFCO delay
-Enable DFCO in low gears
-Reduce idle speed from 750rpm to 700rpm
-Add more EGR where appropriate

My oil change seems like it's going to be delayed, as the 2 post lift I wanted to borrow isn't available. I wanted to do the first oil change myself to witness the condition of the various bits underneath the engine, and I'll probably pay a shop to do the next one as removing the gazillion bolts is kind of annoying.

I would LOVE to put taller tires on the back, but I have brand new Michelins on here :/

So when I got the car paint corrected and ceramic coated, they took off the tape I put over the oil cooler...and I lost almost 2mpg? I didn't do an ABA test, but cruise control 6th gear 60mph with the taped off oil cooler used to be 23.8mpg ish, now it's only 22mpg. Didn't get around to oil change, but I did flush my power steering fluid with Pentosin. Probably a 0.5% gain at best, but this makes me hopeful about thinner oil. I'll need to measure oil temps again, but dropping the oil to a 40 weight will hopefully get me above the taped off cooler and 10w-60.

The nut behind the wheel is of course still easily adjustable: I was pulse and gliding very diligently for 100 miles of freeway and managed to exceed 24mpg during that time, but some slower streets quickly burned through a quarter of the tank while not covering much ground. This definitely has to be an Aston Martin record lol (well, maybe not, the 7 and 8 speed transmission equipped cars probably do better thanks to having a tall cruising gear).

Haven't had all that much time to mess with cars lately but I have made some progress on tuning the ECU, and I got my used oil analysis back. On the short trips I've taken the car out, it's been getting around 14mpg :/ :mad: :(

Despite the oil having 2000 miles on it and 10W-60 being notorious for shearing very quickly, my Castrol 10w-60 is still at 20.8 cSt at 100C! I'm going to start taping off the bottom portion of the oil cooler to block off more of it until I can get around to an oil change. I haven't been able to borrow a car lift, which I really want because the number of bolts and screws to remove on the bottom of the car is kind of silly. I think with only a small portion of the oil cooler exposed to fresh air, it'll hopefully increase oil temps to around 115C which will drop the viscosity considerably.

The ECU now runs much less rich in open loop, it goes into closed loop sooner, and I managed to get DFCO working, though it cuts out around 1800rpm in lower gears even though I want it to stay until 950rpm. I'm trying to figure that out, and also see if I managed to successfully lower the idle speed for engine on pulse and glide. Then hopefully increasing EGR and reducing some valve overlap will get me another 1 mpg on the freeway.

Ugh, this Ford ECU is proving very irritating to work with. Does anyone have a Mustang GT (circa 2005-2010, EEC 6) that they have experience tuning?

The DFCO is pretty stubborn, it seems like no matter what I change, it will go to 1100rpm in 6th gear and about 1700rpm in all other gears. 1700rpm in 2nd gear is about 17mph so I can't actually engine brake to stop signs very effectively as a result.

I've been able to lower the idle to 672rpm (from 750, though it seems to target 736 not 750) which seems to save a little bit of fuel while maintaining 13.6V at the alternator (plenty) and great throttle response off idle, no bogging whatsoever. Air conditioner and fans can be turned on with no bogging either. I retarded the intake cam a little at idle which seems to make it a little bit smoother, but that might just be placebo effect.

With a full battery and warm oil, I think it now idles at about 0.40gph at sea level, hopefully less on a hot day, and hopefully less after I replace the oil with thinner oil.

The car wasn't happy with my VVT changes and the ECU would shut off the engine if I pressed the acc pedal, so I'm trying some different values to see if it helps.

Sure is purdy. :)

Okay wow, I managed to retard the intake cam successfully and also think I know how the DFCO works (I believe it's using idle speed as a starting point), this is a pleasant surprise. I decided to avoid modifying any non-integer value thinking there might be some checksum or some kind of other black magic being done with those values, and voila the ECU seemed happy. Going to try pushing my luck and change the cam position a little more. I have DFCO all the way to 1100rpm now, though it sometimes doesn't turn on when I downshift into 1st.

I think I am going back up a little on idle speed to 688rpm because the engine sputtered a few times with a 672rpm target idle after blipping the throttle. There's about a 1/5 chance that the engine tries to catch the idle and it dips below 590rpm, at which point it kind of coughs and sputters. On my old Scion FR-S, I had a pretty bad slow idle that I decided I would live with to save fuel, but this car being expensive to fix makes me nervous if it's doing stuff like that. As long as it's over 600rpm the engine runs very smooth, which is surprising given the huge cams.

Next step is adding some external EGR, and then getting the oil changed. When the engine is idling, I see an extra 0.1gph usage if the oil is cold!

What do you expect from an external EGR on this engine? Are you considering a cooled or a warm EGR?

It has hot external EGR already built in, it just looks underutilized to me, mostly relying on cam overlap to get internal EGR. Cam retard = less internal EGR and also less volumetric efficiency, add external EGR adds back the charge dilution with less pumping loss, and also adds timing to make up for the lower dynamic compression ratio and charge density.

The valve isn't very big, but at low load it can supply much more EGR than it does right now.

Wow, I took it on the freeway to get some cheap Costco gasoline today and the dash indicated 25.5mpg@65mph in cruise control! That's a huge improvement over 23.0mpg stock. I had tape over the oil cooler in a slight different position so it blocks a little more of it off, but the oil definitely could not have been much above 100C because the freeway was a very short distance away and I immediately turned on cruise control to check the mpg gauge.

I think my intake cam retard must be responsible for most of it. I believe the cam should be something like 10-12 degrees retarded from its stock position, which should be in the vicinity of 5% reduction in volumetric efficiency, while internal EGR according to my simplistic modeling (residual exhaust gas + overlap * constant / rpm) should be down something on the order of 2%, so pumping losses are probably unchanged (EGR heats up the air) while combustion efficiency is up for one reason or another. It could be due to the fact that ignition timing appears unaffected by VVT, and now I have a faster burning mixture with the same ignition timing.

This kind of exceeded my expectations. 26mpg is probably within reach if I add a little more tape to the grille, 27mpg may be within reach with some external EGR, and 28mpg could be possible with thinner oil, which is honestly pretty respectable...a lot of V6 cars can't do much better.

I also realized that I could get mildly warm air if I do airbox and intake snorkel deletes (planned for when the air filters need replacement) and then tape off the entire bottom of the grille, as the engine would suck warmed air through the front bottom of the radiator from inside the engine bay. It would only be barely warm but it probably counts for something on a long trip and only needs a few strips of tape.

That's in the vicinity of 10%. A good inducement to want to do more. :thumbup:

Makes me wonder to which extent a warmer intake temperature could compensate for the lower EGR flow.

I took the car out with even more intake cam retard and saw a lower mpg number, and then I remembered that 101 on the Peninsula has a very very slight uphill grade to San Francisco (I usually get something like 2-5% more mpg going south vs north), so I did a bit of a longer test run in both directions. It seems I averaged about 26mpg going south and 24mpg going north, so I cannot definitively say if I've actually gained any mpg yet, as the higher air temperature today could easily have caused the difference, or differences in oil temp, etc.

However when I add in a few % more EGR, hopefully I get more mpg. I'm starting with 1.5-2% over stock, then I may add a little more if it looks like the EGR valve can support more flow. Assuming I have around 1.5 bar FMEP including throttle loss, I should see about a 1% increase in fuel economy from reduced pumping loss.

The biggest difference is definitely going to come from using lighter engine oil. I am still a little paranoid about dropping the viscosity too much, but I need to keep reminding myself that the factory recommended fill is Castrol which is comparatively thin (4.1cP for 5W50, 5.2cP for 10W60), and it's meant for a 10000 mile OCI. Using Mobil1 10w-40 at 3.9cP HTHS with an OCI of more like 4000 miles *should* be okay, if Castrol 5W-50 is fine.

Well this is a fail, I successfully got the EGR valve to open up more but I needed quite a bit more load to maintain 60mph today compared to yesterday. The problem with this car is that it cools the oil with ambient air, has short gearing and a massive gearbox made for V12 cars so the friction forces completely dominate.

I have no idea if my bad mpg today is because the fluids were a little colder, if the ECU isn't adding spark timing, or if I'm actually losing engine efficiency with my tweaks. I want to say I probably lost engine efficiency because the difference seems significant, but I really have no idea...

I think I need to add more EGR to see if the engine is actually advancing the spark timing, because if it's not then that would easily explain the loss in efficiency. For now I've only added around 2% more EGR which is kind of negligible, whereas if I get closer to 5% it should show up.

Maybe the engine is using more fuel to compensate for the higher temperature resulting in the increased EGR flow.