Tinvek

IMO It's the power figure that matters more than the torque. A high rpm power figure can be geared down to produce as much torque as you like at the wheels. As long as you have the appropriate gearing to keep it in the power band, give me power any day
Torque' motors feel fast, powerful motors ARE fast

 

I'm not quite sure what you're saying with that Tinvec, other than the equation itself. I didn't get the point. As far as the temperature of the transmission goes, I would have thought that any detrimental effect of hotter components (if any) would be out weighed by the oil lubricating in a more efficient way at the higher temp, than it would if it were colder.

AndyF, I'm not sure it's that simple, just to gear a highly powered engine to produce muchos torque. Again, I have to relate to something I know about, which in this case is the Peugeot 405 Mi16 engine often thrown into 205's. Compared to the 8 valve unit, it's lacking considerably in low down torque, but power is high at 160bhp in the upper reaches of the rev range. I don't think that simply adjusting gearing to lower engine speeds will do any good at all. Simply because the engine does not work as efficiently at these speeds. You'd end up with no power, and no torque. Surely it's not as simple as the maths suggest with gearing, torque, power, and revs. Gas flow within the engine becomes more important, and if a cam is designed to work efficiently in a particular range of speeds, then that's the only place it'll work. Unless of course you get clever and time all your valves in a variable stylee, ie Honda.

Sort of drifting off topic, but all very interesting anyway. Not that it was my topic to start with lol! Sorry.

 

Right,

I think I'm being thick here - it's not an unusual occurance

The hp=torque*revs/5252.......

ok so

An a3 turbo has under 52hp (155*1750/5252) ?
An Escort cossie has 149 hp (224*3500/5252)
And a Scoob has 163 (214*4000/5252)

WTF am I doing wrong?

 

The equation is correct, but you're just using the peak torque figure. Take say the escort cossie as an example, they are quoted at 220 ish HP at 6000 RPM( might be wrong but it's near), so turning the equation around, the

Power = Torque x Speed / 5252 so Torque = Power x 5252 / Speed
So at 6000 Rpm it has ~192 lb/ft of torque. This would be a typical torque curve for an engine, ie peak at mid revs, aim to be relatively flat across a broad band.

Pug - The MI engine does not have much less torque than the 8V engine, it just feels like it does because it has much more top end. My 1.9 had 119BHP when stock, did 0 - 60 in 7.9 at trax. 1 Year later with MI conversion on same gearbox (1.9) it had 163 BHP and did 0 - 60 in 6.9 at Trax.

Using gearing you can compensate for a lack of torque, but not a lack of power. This is why F1 engines rev to 19K Rpm but produce relativelt little torque. The gearing acts as a torque mutliplier (but not a power multiplier).

As an example, if you have an engine that produces say 100BHP (need to keep the numbers simple!) at 5000 Rpm, and one that has 100 BHP at 10,000 Rpm. Both engines must make the carhit say 100 mph at peak revs. 100BHP at 5000 Rpm gives us ~105lbft torque. 100BHP at 10,000 revs gives us 52.5 lbft torque. So in theorey the torquier car will be quicker? Wrong! When you add the gearing into the equation, say the 100BHP at 5000 Rpm engine needs a 5:1 gear ratio to hit 100mph, the wheels will spin at 1000 Rpm, and give 525 lbft torque (ignoring losses). It follows that the 100HP engine will need a 10:1 gear ratio, so again the wheels spin at 1000 Rpm, and we get 525 lb/ft of torque, so both are the same!

Going back to the issue of tranny losses, it does seem strange that the figures vary so much. The figures are calculated from torque measured at the wheels. I have seen rolling road runs where the engine RPM was calculated too (based on the operator inputing a ratio to the computer), these only be as acurate as the figure put into the computer, as it is impossible to calculate BHP without having an accurate RPM figure.
The tyre contact patch seems like the best explanation I have seen, but there may be more to it, as possibly the gearbox efficiency varies depending on whether it is driving the rollers or being driven by the rollers?

 

So is 195bhp at the wheels any good for a standard car or not ?

 

323, with regards to the Mi, I was comparing it with a like for like 8v, as in one that produces 160bhp or similar. This is the state of tune that my 8v is in, and it not only is quicker than a standard 16v, but also feels alot quicker. It was the major deciding factor when going from the standard car to something quicker. I fancied torque over out and out power, and so I stuck with 8 valves.

I don't think I've really thought it through properly, but I didn't quite understand the point you were making about gearing. My head hurts, I'll try agian later

 

My physics is a bit rusty but I think you can use conservation of energy, kinetic energy and work laws to show

acceleration = power / (mass x velocity)

So to accelerate faster, increase power or reduce mass (we could also reduce velocity, but that would be no fun would it )

Power is the benchmark that most relates to acceleration!!! Although you do need appropriate gearing to make use of it...

Internal combustion engines generate power as a function of RPM so the torque figures can be used to show how effectively the engine is working over a wide rev range. Who wants to explain BMEP next then?

PS. Yes, 195bhp at the wheels is good, but never quote figures, someone else will always come along with a mate who has more

 

It's about time I dusted off those Pyhsics books... lol

 

My mate's got more than that

 

Ex Pug, the reason I put the MI in mine was because I bough a BX 16V for £150, and sold all the other bits off it for £100. Cheapest BHP I have ever had, and one weekend to do the swap. Realistically, the 1.6 'box or MI 'box suit the engine better, the 1.9 box is too long geared for the 16V box. Either 8V or 16V 160BHP 205 will be a handy little motor

A mate of mine had his car on the rollers not long back, and he was told by the operator that stockish scoobys usually show 135BHP at the wheels on HIS rollers, so I think 195 sounds pretty good. Almost impossible to compare 2 different rolling road though...

 

When you say stockish I guess you mean a 208/215bhp UK spec turbo which kind of fits as mine was "suppose" to have 276bhp standard.

 

Yeah, i'm sure he meant UK spec.

 

Ex Pug, just coming back to why the scooby is quicker than the pug, I did a bit more reading up to remind myself how all this works, I think the answer lies in the tractive effort produced by the two cars, as opposed to the power.

Tractive effort is the physical quntity that rolling roads measure, and the power is calculated from this, and also engine torques etc. To prove (or disprove!) my theorey, I need to know the gear and final drive ratios of both the pug and the scooby and the torque figures measured.

Tractive effort is the basically the force generated at the wheels, which is the engine torque multiplied by the total gear ratio. This is what makes the car move. A Gear box is a torque multiplier, so if we have an engine that has say 100lbft at 1000 Rpm, with a 1:1 gear ratio, it will make 100lb tractive effort. With a 5:1 gear ratio, it will make 500lb of tractive effort, assuming there are no losses (there are, just don't ask how much ).

From the equation that somone posted before,
BHP = torque x Rpm / 5252

So 100lbft at 1000 rpm gives ~19BHP
and 500lb ft at 200 Rpm (same figures after 5:1 gear ratio) gives ~19BHP.

The power is the same, BUT the tractive effort produced is much greater. So if we have the torque figures and gear ratios / final drives, we can work out tractive effort, and see if the scooby does have more than the pug, explaining why it's faster with similar power at the wheels. Almost certainly the scooby has a much wider band of torque, although from the graphs I had of my pug, the torque curve is very flat.

PS If you're bored of this thread, ignore it

So if we

 

Can't do it right now, but I will try and find out.

 

Just had mine mapped and dyno'd

results.

234bhp@ wheels
290bhp@ flywheel

 

Ok, so the final drive ratio on the 1.9 is 3.69:1

1st 2.92 (6.2 mpg/1000rpm)
2nd 1.85 (9.8)
3rd 1.36 (13.3)
4th 1.07 (16.9)
5th 0.86 (20.9)