Vorsprung durch Technik
A2OC Donor
Thats very nice and a unique looking A2 for sure. Your 6 speed conversion is something as a club we should try to replicate.
Longer FSI 5th gear
- Thread starter A2Steve
- Start date
PlasticMac
Member
No, I don't think so.
The longer 5th gear, in a 5 speed box is not a good idea, and I gave my reasons why.
The next post is about a six speed conversion, where the gear ratios of 1 - 5 were close to the original, with a longer 6th.
Two different things entirely. The long 6th would not, I think, cause problems with the standard maps.
The follow up post from the owner of such a car, bears that out.
Mac.
Jellybean
A2OC Donor
PlasticMac
Member
I've explained why, in my opinion, an alternative five speed box, with longer ratios would not suit an FSI with the original engine and cooling map.
Adding a sixth gear, with a longer ratio than the standard fifth gear would probably not go against the maps, and your car supports that.
Which bit do you think I've got wrong?
Mac.
Adding a sixth gear, with a longer ratio than the standard fifth gear would probably not go against the maps, and your car supports that.
Which bit do you think I've got wrong?
Mac.
PlasticMac
Member
@Jellybean What are the ratios in your six speed box?
Mac.
Mac.
Jellybean
A2OC Donor
I bought this car already with the 6 speed box. As far as I am aware gears 1 to 5 are standard and 6th was added, giving a higher ratio.
I guess somewhere on here there will be some write up about it from TonyA2, who had the conversion done.
@PlasticMac, your opinion was that a higher 5th would not suit the engine mapping. How is this any different to the 6th gear I have?
Sent from my SM-N960F using Tapatalk
I guess somewhere on here there will be some write up about it from TonyA2, who had the conversion done.
@PlasticMac, your opinion was that a higher 5th would not suit the engine mapping. How is this any different to the 6th gear I have?
Sent from my SM-N960F using Tapatalk
PlasticMac
Member
Because at higher engine, and road speeds, the engine is running well into Homogenous Mode, where engine torque is controlled only by the ignition angle and throttle opening angle, not by fuel supply, as it is at lower engine speeds, in Stratified Mode, and Homogenous Lean Burn Mode.
The gear ratios should match the mapping at lower revs, where fuel supply is the main controlling factor. That's why I'm not impressed by the longer 5 speed conversion, because all the ratios are different, not just 5th gear. But I can understand the logic of a long sixth gear, if the lower gears are close to the original ratios.
It's not something I would consider, because I can see a lot of work went into the FSI, to optimise performance, power, fuel consumption, and emissions. That would have included the gear ratios. So I'll take it that a standard car, the car Audi designed, is not going to be easily improved.
Mac.
PlasticMac
Member
This is why I’m not a fan of longer top gears on an FSI:
In Steve's post, at the top of this thread, the longer top gear reduces the revs at 80 mph by about 10%.
Surely that's an improvement, not least, a decrease in fuel consumption?
Maybe, maybe not. With that 10% reduction in engine speed, comes a similar 10% reduction in engine power/bhp. Remember, the FSI engine is normally aspirated, and power continues to increase up to about 5,500 rpm, (around 110 bhp). It's an engine that's designed to rev. Torque is broadly flat between 3.000 and 5,000 rpm.
To run at 80 mph for an extended period, at least in UK, would involve a few hills and dales.
I think the loss of 10% of engine power, (from around 72 to around 63 bhp), could result in the need for a bit more right foot, or a gear change, maybe both, going up the hills. (Much the same for 70 mph).
So fuel consumption on a run could actually rise, and the increased engine load, (pulling a higher gear at lower revs), could increase engine wear. The same is true at 70 mph, similar drop in power, (from around 62 to around 53 bhp). You need power to maintain a steady speed, as gradient varies.
Sadly, the opportunity to drive at high speed, for extended periods in UK, tends to be a bit rare in my experience, so it's all a bit academic.
Mac.
In Steve's post, at the top of this thread, the longer top gear reduces the revs at 80 mph by about 10%.
Surely that's an improvement, not least, a decrease in fuel consumption?
Maybe, maybe not. With that 10% reduction in engine speed, comes a similar 10% reduction in engine power/bhp. Remember, the FSI engine is normally aspirated, and power continues to increase up to about 5,500 rpm, (around 110 bhp). It's an engine that's designed to rev. Torque is broadly flat between 3.000 and 5,000 rpm.
To run at 80 mph for an extended period, at least in UK, would involve a few hills and dales.
I think the loss of 10% of engine power, (from around 72 to around 63 bhp), could result in the need for a bit more right foot, or a gear change, maybe both, going up the hills. (Much the same for 70 mph).
So fuel consumption on a run could actually rise, and the increased engine load, (pulling a higher gear at lower revs), could increase engine wear. The same is true at 70 mph, similar drop in power, (from around 62 to around 53 bhp). You need power to maintain a steady speed, as gradient varies.
Sadly, the opportunity to drive at high speed, for extended periods in UK, tends to be a bit rare in my experience, so it's all a bit academic.
Mac.
Vorsprung durch Technik
A2OC Donor
Regarding driving a factory A2 5th speed gearbox or any 6th speed gearbox who would stress an engine on low revs going up a steep hill, thats just incompetent driving. The same applies for the older 4 speed gearboxes we all used in the 70's and 80's until the 5th gear arrived. Having a genuine longer 6th gear over the standard 5th used intelligently, as the Audi manuals tell us and the pure physics of it, is going to save you fuel and make for a more relaxed drive.
PlasticMac
Member
A longer top gear means lower revs, and in the FSI's case, lower power. When more power is needed for a gradient, surely that requires more fuel, wether you change down, or foot down?
Mac.
PlasticMac
Member
The OEM top gear gives 80 mph at 3450 rpm, I think that is where it should be, at the lower end of the rev range that gives best power output, (3,500 - 4,500 rpm) and close to maximum torque. Almost as if Audi designed it for cruising at 80 mph in the standard top gear.
Mac.
Jellybean
A2OC Donor
But if you change down, which is logical, then fuel consumption will be no worse than a 5 speed car?
The 6th gear is ideal for cruising, giving lower engine rpm, better fuel consumption and lower noise levels.
I really cannot see why fuel consumption is important, in a car requiring premium fuel. If its that important get a diesel!
Sent from my SM-N960F using Tapatalk
PlasticMac
Member
@Jellybean
I agree with you 100%.
I'm happy with the mid forties mpg I get out of my, (standard gearbox), FSI, including on long fast runs.
Mac.