Rep Power: 118

I'm sure I'm going to get a lot of hate for asking about this, but here goes anyways. I have a few questions about swapping a CVT transmission into my Civic. I have been one of those few people who has always thought that CVT's are pretty cool, at least the concept, and I am wondering about swapping one into my car.

I have already done some research and I found that I can use my existing sub frame, trans mounts, and CV axles. In other words, a CVT trans would bolt right in just like the auto. So the only things I would need to change would be the engine wiring harness, PCM, and possibly shifter and cable, none of which would be a huge deal.

So my questions are:
1. How reliable is the CVT that is used in the 7th gen Civic HX? I have found reports of failures, but I have also found a lot of reports of failures of the regular auto, which worked great for me until 243K miles. So I am not sure how bad they actually are or how many failures are caused by abuse or lack of maintenance, but I am concerned that it might not hold up, especially behind my engine since it makes significantly more power than the D17A6 engine that it was meant to go with.

2. Would a CVT accelerate faster? I presume it would since it would hold the RPM at redline at full throttle for maximum power rather than the power dropping off after it upshifts. Also, there would not be time taken to shift, so there would be an improvement there too.

3. How much would gas mileage improve? I presume I might see an improvement of a couple MPG, but I'm not sure.

Thank you very much in advance to everyone who responds respectfully

 
Rep Power: 228

No idea swap it and let us know. 😁

 
Rep Power: 118

Gas Mileage is going to depend on the CVT keeping the engine at its peak torque output.

For that to work best, the controller needs to be perfectly matched to the engine, which in your case it won’t so I would not expect better gas mileage over the Hondamatic.

 
Rep Power: 118

That makes sense, thanks for the input! To be clear, the CVT's controller will be (somewhat) well matched to my engine's torque curve because I plan to use one from a Civic Ferio 1.7 with the same D17A engine that I have if I do this swap. Only difference would be that my engine is modded.

Please correct me if I'm wrong, but depending on the transmission's mechanical efficiency, I still think that there's a chance of slightly improved MPG because:

1. As I understand it, Honda CVT's don't have a torque converter. Please correct me if I'm wrong. But since if it doesn't have a torque converter throwing power away while accelerating, I think I may see a slight gain there. This wouldn't affect cruising efficiency though since the torque converter would be locked while cruising anyways.

2. Again, since the CVT trans apparently has no torque converter, my understanding is that it basically shifts to neutral while idling in gear, reducing load on the engine. Less fuel is consumed when idling in N than D on an automatic transmission. But I actually shift to neutral while idling in traffic anyways, so it wouldn't benefit me other than being more convenient.

3. The CVT's highest gear is a lot taller than my 4th gear, so a CVT would significantly lower my cruising RPM to around ~2100 RPM at 60 MPH. However, from my understanding, a CVT is least efficient when running at its highest and lowest gear ratios, so that may cut into or negate any gains from running at a lower RPM if the transmission is less efficient while cruising.

The EPA estimated highway MPG for a 2005 Honda Civic HX is 3-4 MPG lower with a CVT vs with a 5 speed manual, depending on whether you look at original or revised MPG figures. The 5 speed has a slightly taller 5th gear than the CVT's highest range, which may account for some difference in highway MPG. However, I believe that the lower mechanical efficiency of the CVT compared to the 5 speed manual makes up a large part of that difference, but again, please correct me if you suspect that I may be wrong.

 
Rep Power: 0

Well? Did you do it?

 
Rep Power: 118

I did not. I decided to not put any more money into trying to get more power out of this engine, I decided to put that money towards a K24 swap instead. The cost of installing a CVT or manual trans would be a significant chunk of a K swap.

 
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Ah.

Always nice to close out a thread with what happened.

 
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*looks around*

10: PRINT You do not want a cvt.
20:goto10

 
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Yeah I have heard that the CVTs are problematic. That was another factor in my decision to leave the SLXA 4 speed auto in until I K swap it, at which point I will get a manual transmission.

 
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So I hear.

I inherited one recently that has 151K on it, hence my interest.

I like it a lot, but the CVT worries me.

 
Rep Power: 118

If the fluid is old change it. Also, Honda CVTs from around this time use a start clutch to get going instead of a torque converter, so avoid crawling at very low speeds more than necessary because the clutch can't engage fully while creeping and therefore slips and causes wear in the same way that slipping the clutch on a manual transmission does. It's not quite as damaging since the start clutch is a wet clutch and is therefore cooled by the transmission's oil, but slipping clutches is still something that should be avoided when possible regardless of the type of clutch if maximum longevity is the goal.

 
Rep Power: 125

If you like the car, I'd sell it and get one without the CVT. You can get some low-mileage examples for a fair price.

Like previously mentioned, it's a clutch instead of a torque converter. Depending on how it's been driven, it may be toward the end of its life by now.

 
Rep Power: 118

I wonder why Honda decided to use a clutch instead of a torque converter. Seems like a torque converter would have been better all the way around since it would allow for crawling and starting/stopping without wearing a clutch while still allowing for efficient acceleration and cruising by locking the clutch up. Perhaps weight was a consideration, but these CVTs have a torque damper instead of a converter to reduce NVH and that thing looks like it would be quite heavy as well, I don't think a torque converter would be a whole lot lighter than the damper and start clutch and it would function reliably almost indefinitely. I'm guessing the reason ultimately came down to cost.

 
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I appreciate the info - thanks!

The fluid was changed several thousand miles ago by the PO when it was surging going up a long grade. Seemed to solve it.

Maybe they used the start clutch instead of a torque converter because of the Hybrid shutting off at stops then restarting? I don't know.

 
Rep Power: 518

I'd bet "feel" as in driver perception, more than cost.
Old version CVT used a start clutch. You KNOW it's not a normal automatic trans as soon as you start moving. And it feels like pulling a rubber band when you mash the loud pedal.
You know it just feels weird, especially if you aren't used to it, right? That hurt sales.
Hell we've had CVTs for more than 2 decades and sooo many people still come at me with first timer drama thinking it's broken because it's not acting like whatever they were used to.

New version cvt has a real torque converter complete with TCC. Plus the CVT drive belt system, which was a freekin torque converter in the first place LOL
They FEEL nice and smooth like most drivers expect from a traditional automatic, and now they even program the things to mimic gear changes so most drivers can see/feel/hear engine RPM drop and it feels much more like an automatic upshifting gears instead of pulling on a rubber band hoping it won't snap and put an eye out.

 
Rep Power: 118

Those are great points, last week I drove a friend of a friend's 2000 Civic HX with a CVT and I don't really like the feel of it, the way hitting the gas makes the RPMs go up feels like its slipping to me. I guess that's something the driver gets used to over time though. I like a direct feel, which is one reason why I wired in a switch to manually control my TCC, I can lock it whenever I want and it responds directly like a manual transmission.

I understand why manufacturers simulate shifts, but in my opinion shifting a CVT in steps kinda defeats the purpose of having it in the first place. As an enthusiast, my opinion is that the one way shifting a CVT in steps could be cool is if the driver could manually shift the transmission and program the desired ratios of each "gear", effectively enabling the driver to regear the transmission without ever leaving their seat. If the driver could store different gear profiles that would be cool too. There is no technical reason why this couldn't be done since all that would need to change is the programming, but I highly doubt that we will ever see this as a factory option in any production car. Maybe some aftermarket tuning company will figure out a way to do this though

 
Rep Power: 518

Kinda similar---econ/normal is a typical driver pushbutton now, plus some have a sport mode on various newer models,
You still only get what they give you though.

You want way more than a typical new car buyer should ever be allowed lol