New CR-V AWD mods

[serialk11r]

Context: I was shopping for a practical and relatively efficient family car for my parents and myself. Need AWD for ski trips, Caltrans make your life hard without it. Has to be "SUV", because the parents insist. Needs to be newer and have lane keep assist because I get extremely tired driving on longer trips.

After a lot of frustration looking for a used car, I discovered that you really can still buy Hondas, Toyotas, and Subarus at MSRP (less than a 3 year old used car ) if you are willing to wait a few months, and better yet they have subsidized financing!

I just ordered a 2022 CR-V AWD with 0 down 2.9% APR (thanks for eating inflation, Honda+Fed)

-1.5L turbo engine pushes a mighty 190hp on 91 octane fuel but a little outdated compared to Toyota, Mazda
-CVT, so car should not run rich unless it's floored and revving all the way out (will need to verify this)
-Relatively lightweight at a bit under 3600lbs, that's actually lighter than my Aston Martin
-32 mpg EPA highway suggests reasonably low drag despite the boxy shape
-Not a great AWD system, transmission is transverse FWD so the rear is driven through a spiral bevel gear reducing efficiency a little

Ecomodding ideas:
-Switch the rear o2 sensor for a few % lean bias since the car doesn't have high volume EGR (probably shouldn't flash the ECU, since it's under warranty)
-Strap a huge cardboard box (box cavity) to the back for long trips at higher speed
-Tire fairings?
-Extra thin diff oil in the rear, since it's rarely powered? No idea what viscosity Honda uses, but I know Redline MT-LV 70w-75 is thin, there's also LV ATFs. Maybe this can be blended with original Honda fluid? Maybe underfill by a small amount? These are admittedly crazy ideas...

Any more ideas?

[ECO-AKJ]

I wouldn't touch the fluids or sensors until it is out of warranty, dealers can void whatever warranty is affected by non oem part, that being said, that is me, just my two cents, otherwise, congrats on the new ride.

[serialk11r]

Originally Posted by ECO-AKJ

I wouldn't touch the fluids or sensors until it is out of warranty, dealers can void whatever warranty is affected by non oem part, that being said, that is me, just my two cents, otherwise, congrats on the new ride.

Yea it occurred to me that messing with the fluids is probably not a good idea especially under warranty. The diff fluid is something I'm just thinking about because an unpowered diff at highway speed is mainly going to be losing energy churning the oil, so I think it's worth asking why do they set the fill level where it is given the lubrication is passive?

I don't think I want to reflash the ECU since that might void the warranty, but swapping the rear oxygen sensor will cause the ECU to recalibrate the front wideband sensor when it does its catalyst efficiency monitoring. Since it's a physical change that can be easily reverted by going back to the original sensor (that the ECU would then adapt to without remembering), it would be undetectable for warranty purposes. A few % difference in fuel trim is completely normal and attributable to different fuel (high butane "winter" blend requires 4% more fuel flow for example).

The easiest thing to do as a start is add a bit of E85 to the fuel. With reformate at a record price, ethanol in California is basically a free octane boost. The turbo engine is very sensitive to octane rating so any time there is a hill the timing adjustment should boost efficiency by a few %.

I will have to get the car and see how they affix factory mud flaps to see if I can attach some fairings. Lowering springs would probably be more effective but that is a modification that doesn't make a whole lot of sense IMO.

I am very curious to see if my cardboard box idea works but I saw some other thread where someone put a huge cardboard tail on their SUV and could not measure any difference I'm thinking more like just taping 2 boxes together and spraying some paint on as waterproofing, then taping some foam to the car to protect the paint from any grit on the boxes that might rub.

[Drifter]

Congratulations on ordering a new Honda! I tried a few months ago and finally gave up - inventories were practically non existent and dealers around here wouldn't place an order for anything that wasn't already in transit to them (which all had mandatory $5,000 in dealer add-ons). Due to the ridiculous used car market, we ended up a mechanic's special 07 highlander hybrid (which I have still yet to put on the road). Definitely would have prefered a new HRV or CRV...

E85 has good octane, but less energy so I would expect total fuel efficiency to go down. For ecomods, I increasingly like the idea of a hitch mounted cargo box that is shaped like a partial tailcone. Using cardboard to create a template would be a good step 1 (or step 1-10 as your iterate into better shapes). If not that perhaps an extended kammback.

I would wait on fluids until the normal fluid change interval. Any gains would be minimal & would probably not offset the cost of the premature change...

I'm assuming you've already raised tire pressures? Can you add another brake pad spring to ensure no brake drag? If you plan to own the car long term, perhaps buy a lifetime alignment and make sure it is in spec (and maybe tip the mechanic to adjust it closer to the 0 toe end of the specified range).

PS: Caltrans chain control stations are kind of a joke. My buddy in a fwd camry on studded snow tires kept getting tired of being told he needed to put chains on while watching flat landers in bald tired brodozers being waved through so he went to a junkyard and got a AWD badge and stuck it on the trunk. His generation of Camry never came with AWD, but the types of people who would turn around someone on studded tires don't know that...

[serialk11r]

E85 has 75% the lower heating value of normal gasoline and 78% the higher heating value or so. Since the fuel is mostly vapor by the time it ignites, and the combustion chamber is a little cooler, you really are getting more like 77% and more like 80% if the ignition can be optimized. Last time I went to a Propel Fuels, the E85 was a bit over 4 and the 91 I filled the rest of my tank with was a little under 6 bucks, so the E85 was a better deal in terms of $/mile. I imagine it's gotten even better since.

I don't have the car, need to wait 2 months for delivery. The AWD badge story is pretty funny lol.

Good call on the alignment, though I would be shocked if these cars leave the factory with significant deviation from 0 toe. Car already comes with brake pad return springs.

I thought of the trailer hitch but I saw someone driving around with one and I realized it's quite a bulky thing to leave hanging off the rear, and any tail attached to it would block the hatch. Cardboard box strapped to the hatch feels more simple and removable, it can also fold and be stored in the back of the car.

[cRiPpLe_rOoStEr]

I wouldn't use any differential/gear oil of a specification lower than what is required. Well, had it been a part-time 4WD or if you could disable the AWD on demand, I'd rather adapt free-wheel hubs if I would be willing to take the risk and use a lower-grade gear oil...

When it comes to CVT, my only experience had been with my mother's Yaris, and by not driving the aggressive way she drives I managed to keep the engine at lower RPMs than she keeps it. Even when I was supposed to flat-out and didn't, the car was still responsive enough.

Originally Posted by Drifter

His generation of Camry never came with AWD

IIRC every generation of the Camry, at least since the '90s, had AWD at least in Japan, and I'm not sure about Australia. I have even seen some grey-import JDM Camrys with Paraguayan plates which might've been AWD too.

[serialk11r]

OK I laid a silhouette against the template and got some approximate measurements for a cardboard box cavity. I also ordered a 3m nylon strap on ebay for 3 dollars (hopefully that and some leftover paint and tape will be all that's needed). The box would collapse vertically for easy stowage inside the car.

I would probably cut a piece of the strap and tie + glue it to the bottom of the box so that the straps pass through the hatch seals and clip together inside the car. The top strap would be anchored towards the middle of the box so that the tension keeps the box unfolded. Since cardboard is pretty soft, the top and bottom will need some stiffening, maybe just some extra cardboard with the corrugation going the appropriate direction.

Bottom edge goes against top of bumper/tailgate, width is just enough to avoid blocking the reverse lights.

Top edge goes out almost to template, makes a 14 degree angle to the spoiler.

Sides make a 17 degree angle to the widest part of the car, which is suboptimal. Angling the sides of the box would make this better but that would make it harder to stow inside the car.

Bottom edge is 21 degrees from the bottom of the car, so probably completely useless as a "diffuser".

Gut feeling this is maybe worth 5% drag or so.

[serialk11r]

I figured out how the rear diff works. It has a fluid pump that's always turning, and a clutch pack connecting the driveshaft. A difference in speed causes the fluid to go somewhere and engage the clutch. Thus, the fluid is ATF-like, but it has to be compatible with the clutch. Since it has that fluid pump, the clutch may not work if the diff is underfilled by any significant amount or if a different fluid with wrong friction modifiers is used, and the fluid is already pretty thin once sheared from use. I guess scrap that dumb idea then.

[Joggernot]

I have a 2018 CRV FWD. The engine data was found in an SAE paper (info attached). Hope this is useful for your driving pleasure. Search for the number of the paper. It is too large to post or email.

[serialk11r]

Yea I've seen that, here's a direct link: https://www.epa.gov/sites/default/fi...18-01-0319.pdf

They raised the boost in later years but as far as I can tell it's basically the same engine. Like the other Honda offerings, it's a little down on efficiency because they never really updated the basic design to optimize for high volume cooled EGR like Mazda/Toyota did, thus the relatively poor 37% peak BTE.

The good thing is that since it's only 1.5L, the average mechanical efficiency will be very good while pulling bigger/heavier cars. Paired with the CVT, tests have shown a very fast 0-60 so my assumption is on the lowest gear ratio the engine will give maximum torque (and run rich) if you give it a lot of throttle, but it'll back off at higher speed and medium throttle to use less boost.

With full ECU control, it should be easy to lean out the low-medium load fuel map and add a little timing to gain a few % efficiency, but not gonna do that in the warranty period. I just realized a custom rear O2 emulator can be used to spoof the catalyst monitor and resulting fuel trim correction by reading the amperage from the front sensor, but it's a lot more involved than a narrowband emulator.