Difference Between CVT and Manual at lower rpms

[Al]

My '18 Forester XT is comfortable accelerating at from 1500 rpm at say at any speed even as low as 15 mph. My manual Toyota is on the verge of "lugging" at the same RPMs and speeds. The Forester can run at say 1500 at 35 mph yet the toyota at that speed AND same RPM ...I won't even go there.

The interesting thing is that the XT has the FA20 and Toyota has the FA24 which is merely a bored out FA20. I really don't get it. at 42MPH and 1800 rpm it (Toyota) is really on the edge.

 

[Rand]

One has a turbo.. and a torque converter.. one does not.

 

[Al]

One has a turbo.. and a torque converter.. one does not.

Well the overall drive ratio is the same. One "lugs" at 1800 rpm (Toyota) the other doesn't (at the same speed). Turbo is not supplying power. I have a digital readout of Turbo output in the Forester.

 

[MRC01]

It would be interesting to see dyno plots of each engine side by side. My wife's '18 Forester is tuned for low end. When you rev it out it doesn't go much faster, it just makes more noise. Reminds me of a Harley I used to own. Seriously, maybe it is making more power at high RPM but it's getting lost in the CVT. Either way, that Subie was designed for utility, not fun.

But I don't see the point of comparison. Stick shifts are for fun, which means not lugging it around below 2000 RPM. My Mazda3's little 2.0 engine pulls smoothly down to about 1500 RPM, but what's the point? That little engine starts to get happy around 2500 RPM and when it's happy, I'm happy.

It's worth mention that lugging around at 1500 RPM may provide good fuel economy but it's not great for the engine when it's under load. The shift programming in automatics is usually optimized for fuel economy, not necessarily longevity or power.

 

[twX]

Well the overall drive ratio is the same. One "lugs" at 1800 rpm (Toyota) the other doesn't (at the same speed). Turbo is not supplying power. I have a digital readout of Turbo output in the Forester.

A turbo will still be doing work even when boost pressure is negative. When boost is just under 0 psi (i.e. the manifold is almost at atmospheric pressure), this would be full throttle for a naturally aspirated car, but a turbo car will achieve this manifold pressure at part-throttle. I just checked a data log from my FA20DIT, and the throttle position is only around 20-22% when boost is around -1 to 0 psi at 1800 rpm.

An NA engine would seem like it's working harder since you'd need to have the pedal to the floor to achieve what the turbo engine can do with a smaller pedal input. The tuning of the drive by wire throttle can affect this perception as well. The accelerator on my 2015 WRX is notoriously sensitive on the stock tune, and your FXT might be the same. The FA24 might have more linear throttle tuning.

Also, the FA24 in the GR86 is tuned to make peak power and torque at much higher rpm. Even with variable valve timing, an engine tuned this way will have more breathing difficulties at low rpm.

 

[KrisZ]

It's mainly the torque converter that does two things that help with this, a) it actually multiplies torque so at the same RPM the wheels will see more torque and b) it acts like a shock absorber, so the engine feels smooth at that RPM an load.

 

[supton]

Can you tell when your TC locks up? I'm pretty sure that by 15mph mine locks up, regardless of how fast I accelerate--and I think if I accelerate slowly, it might lock up by 10mph or sooner. And once it locks up, I think it stays locked... might be interesting to find out which wire to tap to figure that out (maybe it can be read on a scan tool or something).

Also: maybe if it detects something like lugging, it could alter ratio and get 10 rpm change, and I have to wonder, if we could hear that. It probably has a good map of power requested and current speed to what gear ratio to use (or rpm to achieve?), in the ECU that is.

 

[meep]

The TC should lock as soon as it can. In our CRV my guess is it locked around 5mph. The TC does serve as a nice, heavy, fluid-filled flywheel, however, which might play a part. Engine mounts matter. I’d also consider bore and stroke, and potentially even the range of spark advance the engine is capable of.

Even among manuals it likely varies. The 1.5T in the civic can pull nice and easy at 1300 rpm. The 5mt carbureted escort I drove years ago, no.

 

[KrisZ]

The TC doesn’t stay locked. It locks and unlocks constantly.

 

[barryh]

Shouldn't the dual mass flywheel be acting as a shock absorber for the manual car. Might it be worn out.

 

[Al]

Well, I believe the answer is the Compression Ratio the toyota is 12.5 and the Turbo is 10.6 Turbo is not used if you are at the low rpm and not accelerating much.