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KiwiTT
27-04-2005, 11:32 PM
At a recent meet, I mentioned that when I cruised at 100kmph/60mph, I was running at 2,200 rpm. Those running manuals were doing 3,000 rpm for the same speed. They kind of wished they had an overdrive

According to these ratios

1st Gear
3.333 3.789
2nd Gear
2.105 2.057
3rd Gear
1.407 1.421
4th Gear
1.031 1.000
5th Gear
0.761 0.731
Reverse
3.416 3.865
Last deceleration ratio
4.111 3.684

I would have thought the last deceleration ratio of 4.111 would have made the manual rev lower at a certain speed.

Can someone a little more technical than me please explain why the manual revs higher than my tiptronic at 100kmph

Kenneth
27-04-2005, 11:40 PM
The higher the ratio, the larger the difference between the 2 (we are saying 2 for simplicity) cogs.

The larger the difference, the faster the small cog has to turn in order to rotate the larger cog one turn. so, the bigger the ratio, the faster the little cog is turning.

if the little cog is the one attached to the engine, then the higher the ratio, the faster the engine will need to turn to make the wheels go at the same speed.

Benefit? acceleration. I was thinking about this at the meet... could this be a factor in the difference people are report in the ability of the car to accelerate quickly to 150 mph?

KiwiTT
27-04-2005, 11:45 PM
So 0.731/3.684 = 5.0 revolutions will have slower acceleration then 0.761/4.111 = 5.4 revolutions. i.e the manual needs to make more revolutions for a given speed.

BTW, I was considering dropping my gear from 5th to 4th when I was shadowing a Monaro, but ran out of road at 150k

tig202
27-04-2005, 11:49 PM
Dont forget the auto box has to generate pressure to work which saps engine power... which could relate in the different gear ratios :scholar:

Kenneth
27-04-2005, 11:55 PM
Good question...

Not nessicarily. All things being equal, yes. ie: same car, same engine power, same rpm both put the foot down.

If we were to both do a 5th gear roll-on from 80km/h, my car would likely pull away giving me an edge.

If we were racing, then we would shift at different times and it would probably not make a great deal of difference until we got very very fast. in which case, you might have the advantage of being able to hold 4th gear longer than I.

KiwiTT
28-04-2005, 12:02 AM
I think if we were racing, I would not use 5th at all. 2nd-3rd and sometime 4th would be for me. and these ratios appear to match the manuals, but the final drive ratio, would give me a little more speed at a given rpm, but you would have more acceleration, given you will be delivering more power, due to the higher rpm your have and probably more boost..

Kenneth
28-04-2005, 12:13 AM
Boost should not be affected by RPM... or at least not to that degree. if the wastegate is doing its job properly, the bost will get to its max pressure and not climb. I can make peak boost (8psi) at 2500rpm maybe a little more depending on when I start spooling up (ie at what rpm I WOT)

In the same gear, the maunal should accelerate easier than the auto, but of course as soon as someone shifts, its another ballgame.

In 4th I would be shifting at about 170-180 km/h. At 180 I have well and truly overrun the peak power (which is at 5,500rpm in stock trim) and approaching redline

to4garret
28-04-2005, 12:55 AM
hehehehe go the single turbo :D peak power for me has shifted to 6500rpm nearly 7000rpm :D mind you i do have a hole below 3000rpm now :(

bradc
30-04-2005, 12:54 PM
If you compare the actual road speeds of the gearbox's, you get this:

(assuming 205/55/16 tyres and 6000rpm engine speed)

manual:

50
80
120
163
221

auto:

49
91
132
188
257

Of course if you want to know what speed your engine will be running at with a given speed, just divide that speed into the speed you want. For example, lets say you want to drive at 110kph in 4th gear in your auto, you'd be at 3510rpm. Of course this will change depending on what size tyres you are running, and what your torque converter is doing.

I'd also say that due to those gear ratios, the manual would accelerate faster overall.

Kenneth
01-05-2005, 07:50 AM
Interesting and useful info, Thanks

bradc
01-05-2005, 08:30 AM
I just bought a 1999 Legnum VR4 today actually, it is a 5 speed Tiptronic, a large upgrade from my 1998 Legnum 1.8 GDI. I took it for a bit of a trash on the test drive and 1st gear simply flew by in no time at all! I wonder why they didn't make first gear a bit taller, say at 60-65 kph. An R34 GTR has 1st gear topping out at 72kph for example.

Kenneth
01-05-2005, 08:53 PM
I just bought a 1999 Legnum VR4 today actually, it is a 5 speed Tiptronic, a large upgrade from my 1998 Legnum 1.8 GDI. I took it for a bit of a trash on the test drive and 1st gear simply flew by in no time at all! I wonder why they didn't make first gear a bit taller, say at 60-65 kph. An R34 GTR has 1st gear topping out at 72kph for example.

Yeah, a longer first gear would have been a good idea. Unless I am starting from completly stopped, I just use second. I also drive around in 4th. Auckland has a lot of hills, but there are not many that I need to go to third for...

The low first would be ideal for towing I suspect, so maybe it is useful to keep it. A 6 speed box would definatly be a good thing.