CVT swap? (Into 2005 Civic, replacing 4-spd auto)

[hayden55]

Originally Posted by EcoCivic

That's pretty low, the Honda Stream trans I have now has me running at 3K RPM at 70 mph. I thought I wouldn't like this transmission's 4th gear compared to my stock 4 speed, but it's actually alright. The higher cruising RPM doesn't seem to have cost me any MPG, probably because I live in a somewhat hilly area and it climbs hills much more effortlessly at a little higher RPM. It also pulls noticeably better in the lower gears since gears 1-3 are shorter as well.

With the 5 speed I am planning on getting, 5th gear is a bit taller than my 4th gear. 3K RPM will be at 74 MPH. However, I don't think I will feel much of a decrease in climbing performance from cruising at 2800 vs 3K since the manual trans is significantly lighter and is more efficient since it has less moving parts and no internal oil pump.

Shouldn't matter if you just shift down to get up the occasional hill. Dropping the RPMs on cruising is where the big BSFC gain comes from. 3k rpm to 2k rpm is about 10 mpg on the D16.

[EcoCivic]

Originally Posted by hayden55

Shouldn't matter if you just shift down to get up the occasional hill. Dropping the RPMs on cruising is where the big BSFC gain comes from. 3k rpm to 2k rpm is about 10 mpg on the D16.

Wow that is a big gain! I doubt that I would see those kind of gains on my D17 though, like I said I didn't see any loss in MPG from swapping in this shorter geared transmission. Also, when cruising around town, I get higher MPG cruising in 3rd gear than 4th gear up until around 3K RPM. The conventional strategy of "cruise at as low of an RPM as you can without lugging the engine" doesn't seem to work for me, perhaps because I have a Crower Stage 1 camshaft. Although it runs well cruising on flat ground down to around 1500 RPM, doing so doesn't seem to be efficient on my setup.

The other issue with the HX trans is those are basically impossible to find here, an 01-05 Civic with a DX/LX/VP 5 speed is hard enough to find here. "Older" Honda's aren't particularly common here and the ones I see in junkyards are almost always autos. Actually I'm not sure that I have even seen a 7th gen Civic HX here

[hayden55]

Originally Posted by EcoCivic

Wow that is a big gain! I doubt that I would see those kind of gains on my D17 though, like I said I didn't see any loss in MPG from swapping in this shorter geared transmission. Also, when cruising around town, I get higher MPG cruising in 3rd gear than 4th gear up until around 3K RPM. The conventional strategy of "cruise at as low of an RPM as you can without lugging the engine" doesn't seem to work for me, perhaps because I have a Crower Stage 1 camshaft. Although it runs well cruising on flat ground down to around 1500 RPM, doing so doesn't seem to be efficient on my setup.

The other issue with the HX trans is those are basically impossible to find here, an 01-05 Civic with a DX/LX/VP 5 speed is hard enough to find here. "Older" Honda's aren't particularly common here and the ones I see in junkyards are almost always autos. Actually I'm not sure that I have even seen a 7th gen Civic HX here

Yeah that cam changes your VE. I always did 1750-2150 RPM to stay in the center island on the map (BSFC Map)

[EcoCivic]

Originally Posted by hayden55

Yeah that cam changes your VE. I always did 1750-2150 RPM to stay in the center island on the map (BSFC Map)

It doesn't seem to have changed it for the worse though as long as its shifted in a way that keeps cruising RPM above 2K or so. I installed that cam 5 years ago before I tracked my MPG as carefully as I do now, but I don't recall seeing any decrease. Even with this short gearing I averaged about 37 MPG last time I went on a road trip with a best tank of 39 MPG, which is pretty much what this car did stock but with much better performance. A couple of the people who installed this cam actually reported slight increases in MPG, but that would obviously depend on how the car is driven.

I have been tempted to reinstall the stock cam temporarily for testing because I am curious if I would still get more MPG at a higher cruising RPM with the stock cam or if that is caused by my Crower cam. I may do that eventually, changing the cam in this engine isn't at all difficult.

[hayden55]

Originally Posted by EcoCivic

It doesn't seem to have changed it for the worse though as long as its shifted in a way that keeps cruising RPM above 2K or so. I installed that cam 5 years ago before I tracked my MPG as carefully as I do now, but I don't recall seeing any decrease. Even with this short gearing I averaged about 37 MPG last time I went on a road trip with a best tank of 39 MPG, which is pretty much what this car did stock but with much better performance. A couple of the people who installed this cam actually reported slight increases in MPG, but that would obviously depend on how the car is driven.

I have been tempted to reinstall the stock cam temporarily for testing because I am curious if I would still get more MPG at a higher cruising RPM with the stock cam or if that is caused by my Crower cam. I may do that eventually, changing the cam in this engine isn't at all difficult.

For the most part it won't be a big $$$ mod anyways. 15k miles a year for the average consumer, 45% highway, 40mpg = 169gal, 50mpg = 135 gal
Diff = -34gal @$2.20 for me = $75/yr saved

[Ecky]

Do you have the ability to track instantaneous MPG?

Changing the final gearing in my K24 Insight is worth 12-15mpg peak on the highway. The new final drive spins the engine at approximately 2,300rpm @ 70mph, whereas the old one was~3,300rpm.

[EcoCivic]

Originally Posted by Ecky

Do you have the ability to track instantaneous MPG?

Changing the final gearing in my K24 Insight is worth 12-15mpg peak on the highway. The new final drive spins the engine at approximately 2,300rpm @ 70mph, whereas the old one was~3,300rpm.

I do, I have a Scangauge. The problem is at least on my car, it is actually pretty hard to track because the MPG is always changing significantly, even under what seems to be constant conditions like just cruising down the highway with a constant throttle position. I think some of that may be because there are basically no flat roads here for more than a few seconds and there are so many potholes that when I do get a few seconds of "flat" road I am always having to steer to avoid potholes. This makes seeing even relatively significant differences such as AC on vs off surprisingly difficult as normal variance is much more than the difference from most of the things I would be testing.

[hayden55]

I'm guessing your on the east side of memphis?

[CVTCivic]

I think it's the best decision to go with a 5 speed MT. I think it's more fuel efficient than any automatic transmission and you'll safe a lot of money on maintenance costs (many automatic transmissions need oil/fluid ever other year).

Nissan had some problems with their CVTs from Jatco, but that was a long time ago. I don't know how it's these days. I'm reading a lot through some Honda forums and the CVTs of these days seem very durable and reliable. When there is failure, it's mostly due to neglect and abuse (racing and brake-boosting, not the stuff we Hypermilers use to do a lot). It's important to change the CVT fluid, but that's also important on any other automatic transmission as well.

For anyone who is curious, here you can see how the CVT of a Civic keeps the RMPs.

Normal acceleration in a city situation:
https://youtu.be/fIkoOWz3yVA

Slow highway speed coasting:
https://youtu.be/oJM7JqxiNFU

[EcoCivic]

Originally Posted by CVTCivic

I think it's the best decision to go with a 5 speed MT. I think it's more fuel efficient than any automatic transmission and you'll safe a lot of money on maintenance costs (many automatic transmissions need oil/fluid ever other year).

Nissan had some problems with their CVTs from Jatco, but that was a long time ago. I don't know how it's these days. I'm reading a lot through some Honda forums and the CVTs of these days seem very durable and reliable. When there is failure, it's mostly due to neglect and abuse (racing and brake-boosting, not the stuff we Hypermilers use to do a lot). It's important to change the CVT fluid, but that's also important on any other automatic transmission as well.

For anyone who is curious, here you can see how the CVT of a Civic keeps the RMPs.

Normal acceleration in a city situation:
https://youtu.be/fIkoOWz3yVA

Slow highway speed coasting:
https://youtu.be/oJM7JqxiNFU

Yup I wondered how the CVT would hold up in my application since sometimes I have a heavy foot. Also, to make things worse, my engine is significantly stronger than the Civic HX D17A6 engine that transmission is paired with here in America. It comes paired with a D17A (basically a D17A2) in Japan in the Civic Ferio but I have a D17A and it's making about 20-30 HP over stock, so I'm not sure how well that would hold up.

These 7th gen Civic 5 speeds seem to be pretty reliable from what I can find. There are people making 2-3X the stock power level or sometimes more and they seem to tolerate it no problem, so I don't think I will have any problems with it.

Another question- Assuming cruising with a locked torque converter and identical gearing, how much more efficient is a manual transmission than a conventional auto? I would think a manual would be measurably more efficient since it has no internal pump and presumably less losses through the gears, but how much more efficient?

I think the parasitic losses of an auto are significant even with a locked torque converter judging by how much it heats the fluid up even just idling in park or cruising. When I had no trans cooler at all my trans fluid would easily get up to 180 degrees just from cruising at 70-80 with the converter locked, which indicates that there are pretty significant losses through that transmission. The things you learn when you have a bunch of gauges