Scooterotica

so thats why everyone who does long distances /euros/ bsm/ etc, want a low revving , high geared motor. with torque. or have you got a load of JL4"s you cant shift for xmas?

shocky wrote:the only problem i can see with a lower revving high torque engine would be heat dissapation power creates heat and revs(higher speed flywheel/fan) helps air flow

That's interesting Steve but wouldn't higher revs mean more heat due to more detonations per minute and additional friction for a given speed

goldeneye wrote:so thats why everyone who does long distances /euros/ bsm/ etc, want a low revving , high geared motor. with torque. or have you got a load of JL4"s you cant shift for xmas?

No mate, we dont sell spares..... Although as it happens, i do have a JL4 on my TS1 race scoot, and it actually produces more torque than most scoots that come through our dyno......the school of thought that JL4 has no torque is a myth....it depends what you've done with the rest of the engine!

But i digress, I think what Sean is actually driving at, is that people often say 'i want a torque monster' but dont actually understand what torque is a result of........

I think your line about 'long distances /euros/ bsm/ etc, want a low revving , high geared motor' is correct, in that, that is what a lot of people say/want........but usually only because riding a lower revving machine to a rally can be less work and more comfortable than something higher revving......not because its got MORE torque though...... And because actually lower powered machines tend to stress other componenets less, resulting in fewer breakdowns......which is what we all want on rallies etc. So that is to do with the needs and comfort of the rider, but not the formula for 'monster' and 'stump pulling' torque as people (mis) quote.

Usually, a lot (but not all - some good graphs on this post) of these scooter that people think they have built for torque are done so at the expense of overall power....and dont always have the extra torque the user requires.....they simly have the power peak lobbed off !! Seans point is, is that it is possible to tune for both torque AND bhp if you tune correctly..........

Usually you either see an under-powered 250cc piston port with a small carb and box pipe as someones 'typical' torque build....or a peaky (and usually mis-geared) 225cc reedvalve tune with monster carb and rediculous port timings as someones 'bhp' tune........one extreme to the other.....but the best tune is to have low down torque AND top end power......balance, good porting, matching components etc.

At least i think that was his point......

If not....ignore me, im rambling!!!

I love these conundrum

Torque and power are related. The power an engine produces at a known rpm depends on the amount of torque produced at that rpm.

Though ive said that torque and power are related, more torque doesn't always result in more power. The rpm factor is important here.

Basically power = force X velocity & force = mass X acceleration
so power = mass X acceleration X velocity & velocity = distance/time

so substituting,

power = mass X acceleration X distance / time

but mass X acceleration X distance = work and since torque is the same as work,

power = torque/time

Torque represents the work done and power represents the rate at which work is done.

we can rewrite the above as,

power = torque X rpm

rpm basically stands for 1/time since it effectively it stands for rotations (a dimensionless quantity) divided by time.

So since power is the rate of work, it can be increase due to two factors. either by increase in work, or the increase in rate.

basically you can produce high power by doing a small work at a heavy rate, as well as by doing a heavy work at a small rate.

Lets take 2 different engines for example.
Engine A: is a 200cc engine producing or 14.7 lbft of torque at 2500 rpm.

Engine B : is a 100cc engine producing or 7.3 lbft of torque at 5000 rpm.

But see what happens when we calculate the power at the rpm where peak torque is produced.

engine A : bhp = torque * rpm / 5252 = 14.7 * 2500 / 5252 = 6.9 bhp.

engine B : bhp = torque * rpm / 5252 = 7.3 * 5000 / 5252 = 6.9 bhp.

As you can see, engine B which is just 100cc produces the same amount of power as that of the bigger 200cc engine, inspite of having half the torque.

Smiffy

when using bhp and Lb ft's, The figures for both will be the same at 5252 rpm and then cross over

always cracks me up when you see a graph with the crtoss over point elsewhere in the rpm range

the flexibility of an engine is the rpm spread between peak torque and peak bhp (and really is what people mean when they refer to a torquey engine imo)

davidblythe wrote:always cracks me up when you see a graph with the cross over point elsewhere in the rpm range

Ours cross at 5252......and i like it that way........but when you see graphs that dont, its only because they are using different scales for bhp & tq.

On such graphs, if you check the ft-lb reading at 5252 and the bhp reading at 5252......they will both match.

so where do we get these engines from?

goldeneye wrote:so where do we get these engines from?

MB Buddy, check out the graph in the LTH thread.............. hmmm nice !

davidblythe wrote:when using bhp and Lb ft's, The figures for both will be the same at 5252 rpm and then cross over

Not on my Skoda, it doesn't rev that high.
Turbo'ing must be the future. My VR6 Corrado produces 207 lbs ft torque at over 6,000 rpm with very similar bhp figures. My turbo'd Skoda produces 255 lbs ft torque at 2,000 rpm but only 155 bhp at around 4,000 rpm.
Can anyone turbo my Rapido 250?

i think a lot of people including me have had road race set ups in their younger days which suited the hooligan in us back then but as time went on (and some of us got used to the ease of big bikes?) the more revs/bhp became iratic and gutless feeling so some...again me included craved the any gear any time feel if a grunty motor.

remember as well that 90% of tuners have no idea what their customers want and are too fixated with with their own points of view or results on the track so getting what you want is hard work sometimes.

most riders say "i want it to do 70 all day every day" there is no mention of it having to get to 70 in 4 seconds. then on the road most riders ride at the speed of a p2 at 65mph apart from the odd blatt.

the other obsession for torque is the fact that we are mainly 15 stone + blokes that do long distances on heavily laden scooters often two up. I dont do ride outs or posing round town, its either fully laden or in the garage. i suffer anxiety riding a scooter, i always have. its just due to the lack of ability to hold top gear like any other vehicle on the road.

so my personal need for torque is to satisfy that need. if I have lost the peak off of my power curve then thats a reasonable sacrifice, so far i have found that I have preferred scooters that have shown a pretty flat curve. the best ts1 i have ridden was a 200cc taffspeed in a series 2. not mine but i had a hand in putting it together and it lifted the front wheel in first and second with a bit of assistance from undamped forks.

big cc and box pipes make lambrettas more powerfull but still as lambrettas, there is a place for them and my next motor will be one. its because i like lambrettas.....i can only ride a fudged up wanna be mx engine in a lammy frame so much. ring ding ding. gets on your tits a bit. 250cc box pipe with that nice donk donk donk sound and standard looks

and david blyth needs to sell me the drz and get himself a wr450 and then we will both be happy.