Rpm for CU2 Euro Lux Auto vs Euro Lux Manual at 100kph

[aaronng]

Thanks for your comment aaronng - but help me understand why the manual car uses less fuel when the engine is turning over faster at 2500rpm than compared to the auto at 2000rpm. To me, the manual engine is running faster at 2500rpm (thereby using more petrol) than the auto running at 2000rpm (thereby using less petrol). I am having trouble understanding this.

In the test under highway conditions where the manual runs at 2500rpm and the auto at 2000rpm, the auto gets better fuel consumption. However, the car is also tested in city conditions and here the manual has a much better result with fuel consumption compared to the auto because manuals are just more frugal with fuel when acceleration is required frequently (no torque convertor). When the results for both highway and city are totaled to give the combined result, the manual ends up with a lower fuel consumption.

[ahefara]

Thank you all for your contributions so far - they have been very constructive.

On both the vehicles I have described (CU2 Manual and Auto), they have the Michelin 235/45/18.

Theoretically, based on the formulae that SPQR has supplied and used, 2 x pi(235x0.5)+(18/2x25.4))/1,000 = 2.1754 metres

At 100km/h, this tyre undertakes 100 x 1,000/2.1754 = 45,968.6 revs per hour (r.p.h.).

45,968.6 r.p.h. / 60 = 766.14 revs per minute (r.p.m).

Multiplying the various gear ratios for the AT and MT gives theoretical engine r.p.m. at 100km/h:

AT: 766.14 x 0.57 x 4.44 = 1,939 r.p.m. at 100km/h

MT: 766.14 x 0.69 x 4.76 = 2,516 r.p.m at 100km/h.

However, as buddah51au has said, the circumference of the tyre changes with the car body's weight and the theoretical figures we calculated above would be slightly incorrect - his GPS figures are more likely to be reflective of what is reality.

So, now I can conclude that Honda's Euro with automatic transmission at 100kph does have less rpm compared to the Euro manual transmission.

This now raises a new question - with the Euro with manual transmission revving much higher than the Euro automatic transmission, surely the cabin noise within the manual Euro is higher than the automatic Euro?

It would be interesting to know the cabin noise results in Euro manual and Euro automatic vehicles - ie decibel readings within these vehicles at 100kph.

So, the question now for me, is the manual Euro a noisier car within the driving cabin than compared to the Auto Euro?

Or has Honda factored this in and inserted more insulation? Any comments?

[ROBERT]

CL9

I have a CL9 auto and live in the country. My SHORTEST drive from home is 10km on open roads, no trafic lights and only one junction. Apart from 4 of 6 weekly trips to Sydney on the F3 my most frequent drives are to Forster at around 17 km. also clear roads no lights. So I expect my OVERALL consumption would be better that that of a manual as probably 85% of ALL my driving is around 90kph.

At what speed does the thranmission lock kick in?

[aaronng]

So, now I can conclude that Honda's Euro with automatic transmission at 100kph does have less rpm compared to the Euro manual transmission.

We knew about this back in 2004 for the CL9. Info is in all the old threads. CU2 has the same thing with the auto having longer ratios than the manual, so the auto will have a lower RPM than the manual as well.

This now raises a new question - with the Euro with manual transmission revving much higher than the Euro automatic transmission, surely the cabin noise within the manual Euro is higher than the automatic Euro?

It would be interesting to know the cabin noise results in Euro manual and Euro automatic vehicles - ie decibel readings within these vehicles at 100kph.

So, the question now for me, is the manual Euro a noisier car within the driving cabin than compared to the Auto Euro?

Or has Honda factored this in and inserted more insulation? Any comments?

The difference between 1900rpm and 2500rpm is NOTHING compared to the road noise coming from the tyres! You won't notice any difference between a manual and auto. Plus when cruising at 100km/h and then having to accelerate gently away, the manual can do it in 6th gear at 2500rpm, while the auto will have to downshift to 4th, putting the RPM at the same or higher than the manual before being able to accelerate. So there difference that you think is there just isn't.

[buddah51au]

Engine noise is not a concern, I suspect there would be very little if any difference between 2000 & 2500 RPM. The main Noise problem you will have is tyre noise, especially if you spend a lot of time driving on course chip bitumen such as we have in rural QLD. On Hot mix roads there is very little tyre noise.

Gentle acceleration from 100kph in an auto doesn't normally cause it to shift back to 4th, it depends how quickly you need to accelerate. When overtaking i normally use the paddles to shift down 1 or 2 gears depending on how quickly I need to get passed whatever is in front of me.

[Type R Positive]

I think you guys are missing a huge factor. It is not the engine rpm's that are of particular concern, rather it's the engine load.
I use less fuel at 110km/h than at 100km/h, but use a fair bit more at 130km/h. Still, at these speeds, I use less fuel than driving around town. Less engine load = less fuel used. I focus my driving on being smooth, regardless of being sedate or giving it a hard time!

[ministig]

Based on the formulaes, does that mean AT has higher top speed? Who has tried? Lol.

I got a obdII reading thing, will post engine load figures at 100kph when I have a chance.

[aaronng]

Based on the formulaes, does that mean AT has higher top speed? Who has tried? Lol.

I got a obdII reading thing, will post engine load figures at 100kph when I have a chance.

The auto has a theoretically higher top speed but you won't reach that as both the auto and manual will be drag limited before you reach redline in top gear.

[buddah51au]

I know what the (indicated) top speed is of my base CU2 Auto, but I am not about to post it for obvious reasons. Obviously i don't know how far out the speedo is at that indicated speed.

[SPQR]

Thank you all for your contributions so far - they have been very constructive.

On both the vehicles I have described (CU2 Manual and Auto), they have the Michelin 235/45/18.

Theoretically, based on the formulae that SPQR has supplied and used, 2 x pi(235x0.5)+(18/2x25.4))/1,000 = 2.1754 metres

The tyre on the Luxury is 234/45R18 as you said so the formula is:

2 x pi(235x0.45)+(18/2x25.4))/1,000 = 2.1008 metres.

The physical/actual circumference of the tyre does not change with load but the radius does reduce with load and as the radius reduces the tyre's effective circumference reduces. This affects the true speed in that to travel at the true 100km/h the engine revs are higher. That's why buddah51au says the revs are 2,200 rpm at 100km/h.

As I said "There is no allowance for tyre growth at speed or actual real world tyre inflation or wear or torque converter slip if not locked at 100km/h." The theoretical speed calculated in not the real world speed. And so buddah51au is correct.

The theoretical speeds calculated from gearing is what is quoted in motoring magazines as a means of comparison that elliminates the many variables (wind speed, tyre inflation, tyre wear, torque converter slip, etc) between different cars.

As I live in the NT and at the time it was legal, my CL9 would top out at an indicated 229km/h. My MY97 WRX would top out at and indicated 239km/h.

[buddah51au]

SPQR, I know you have a CL9, but not sure if it is manual or Auto. As the CL9 is a lighter car than the CU2, I thought the CL9 would be quicker. You don't say if 229 was indicated or GPS recorded. I have only ever tried mine out once & I didn't have a GPS at that time, but think of a black Friday number above the figure you stated, a whisker under 5400RPM. In a wheels road test, they stated the top end was 226, so that sounds more realistic allowing for speedo error.

[tron07]

Does the autobox allow the car to be rev to redline, holding the gears?
Bassed on my experience with other cars overseas, manual tend to be able to achive a higher top speed due to the reason being able to hold the gears towards redline. Else you probably need tons of straight road doing speed excess of 200km to achive max top speed, and risk loosing your car and license trying...