Alexppp

Ok I have a question as I've recently started to understand Transmission loss (only a little bit) Now how I understand it, is that a Scooby can put the power down from the start but will suffer at higher speeds due TL that's which i.e., an M3 (RWD) will pull away from higher speeds. Maybe I have the wrong end of the stick or I'm asking the wrong questions?? How is that something like an Audi RS4/6 (AWD) will pull away at higher speeds. Is it through larger engine size?? Difference engine set up? Higher BHP??

Many Thanks Guys

Alex

lestippp

I would say a simple case of more bhp to start with therefore the losses will still be there but a STi PPP with 23% loss is putting 230bhp on the road whereas a 414 bhp RS4 would be putting down almost 320 bhp with the same losses, so is almost 40% more powerful at the wheels as opposed to 37.5% more powerful at the flywheel
This could of course be rubbish as I am only applying my understanding of it and am not an expert

Remember if your car is black, like mine, it goes faster still

Alexppp

Yeah I know - it's faster you don't have to rub it in! there also cleaner when they've just been washed and waxed. I remeber when I had mine done in a shopping mall - Paid the full Wack for the polish and you still could tell the difference.

Cheers, I supposse that would make sence with as much as I know. So then I would ponder on, that if you had say....Type 25 or another scoob running at the same power it would be just as quick??? or faster - taing into account the Power/weight. Maybe i'm way out of my league with this one

Thanks Alex

RedScoob

Yeah, transmission losses are higher with AWD, simply because no mechanical device is 100% efficient. Luckily the efficiency lost isn't double what it would be with a RWD (or FWD), but both 2WD transmission types will be "faster" than a 4x4 with the same amount of power as soon as traction is no longer an issue.

Martin2005

The cars you mention are much heavier than a Scooby, thats why Scoobies are better off the mark. Power to wieght is much less of an issue at higher speeds, then it's all about absolute power and tourque and aerodynamics.

BTW a new T25 would murder an M3 and RS4 right up to the limiter

silent running

Along with transmission loss, you're throwing in a whole load of other factors. Acceleration is not only affected by trans loss, but also power/weight, gearing, aerodynamics, suspension setup to name but a few. So you simply can't drill down into trans loss to try and explain why one model of car pulls away from a completely different one at speed.

In general though, yes the 4wd advantage in getting off the line quickly is negated once you're rolling, as long as your 2wd drive rival has traction. Hence why you often hear incredulous UK Scoob owners who can't accept that a 180 bhp fwd hot hatch can easily keep with them once rolling.

Once you're up to high speed (e.g. over 100mph) it's all about outright power and weight ceases to be of any significance, as power starts to be needed to overcome air drag. In these circumstances, I'd guess that trans loss also becomes insignificant compared to the amount of power 'wasted' in overcoming air resistance. Even the most powerful supercars take longer to get from 100-150mph than they do from 0-100mph.

turbodan

I wouldnt worry about it too much, the difference between 4wd/rwd is very little in my opinion. Its very difficult to measure these losses making it difficult to be certain. Remember this, even with 2wd youre still dragging 2 wheels around. Ok with 4wd they are driven but the extra losses are bugger all in my opinion. Even if its say 5% extra thats only 15 over 300bhp, which is pretty negligable when you considered the extra traction.

Most rally slags have crap aerodynamics and the engines are set up to be punchy. They can hit 150+ of course its not their ideal application. Turbos always run out of puff at high revs which is where the power is for impressive top speeds. Its just the way they are designed.

Alexppp

Thanks,

Guys,
That explains alot as I thought there wold be more to it at high speeds but hadn't a clue what?

Thanks,

Alex

silent running

Another interesting thing to note is that the power requirement to achieve a certain top speed varies with the cube of that speed e.g. let's say you have a Subaru with 280 bhp that will do 150mph max. Ignoring other factors such as gearing, if you wanted it to do 160mph flat out, you'd need (160/150 cubed = 1.214) another 21.4% more power i.e. another 60bhp to achieve just 10mph.

Should be pretty obvious from that, that 0-60 tests are for the ladies in their shopping cars. 0-100 is the minimum acceleration test that a MAN should be bothering with LOL :-)

Tidgy

think rought terms swd is about 26% loss, 2wd is about 16% loss


although i understand some gearbox's can created less transmission loss, such as straight cut gearing.

anyone know what sort of percentage loss it reduces? is it 3-4% less loss or is it neglegable?