Suprafest 08

[postfach]

Ahh i have a feeling my clutch isnt going to like the dyno tomorrow. boosting in 5th gear and the clutch slipped!

Or it was the rears lighting up, but doubt my lil car could do it in 5th on the mway with good tyres! In 4th with cheap tyres in the wet yes!

Oh well, i think i got the knock sensor settled down a little. Will see what happens.. time for new clutch i think

err - you should be doing it in 4th anyway - 5th isn't a straight through gear. And as such it'd load up the engine/clutch more making it more likely to slip.....

When the engine is under full load and producing max torque the shear forces through the clutch will be same in 4th or 5th, i dont see how they would be any less in 4th... Its not like the engine is suddenly producing more torque at the flywheel...

I think what Hunt is saying is that it requires more effort to turn the wheels in 5th, therefore it is more likely for the clutch to slip in 5th than it is in 4th. That's why you always notice it first on the motorway before it starts getting bad in lower gears.

[Malcolm]

When the engine is under full load and producing max torque the shear forces through the clutch will be same in 4th or 5th, i dont see how they would be any less in 4th... Its not like the engine is suddenly producing more torque at the flywheel...

you sure about that mr engineer?

Actually I can understand why you, being trained in the discipline of civil engineering, would struggle with this - it is after all a dynamic problem which is outside the scope of your knowledge

[xsspeed]

When the engine is under full load and producing max torque the shear forces through the clutch will be same in 4th or 5th, i dont see how they would be any less in 4th... Its not like the engine is suddenly producing more torque at the flywheel...

you sure about that mr engineer?

Actually I can understand why you, being trained in the discipline of civil engineering, would struggle with this - it is after all a dynamic problem which is outside the scope of your knowledge

Amen

[method]

Haha yeah, i don't know much about dynamics at all. Ill admit that! I always think of things statically. Hence my max torque description No idea what the forces are doing dynamically. When buildings and bridges start moving you are in the shit!

So there is more load on the clutch in 5th gear then? I cant see why seeing as clutch and engine are on the input side but thats nice to know!

[postfach]

I've made a simple diagram to help you understand.

Imagine yourself as a clutch, and gear ratios as the length of one side of a see saw. Now imagine that you, the clutch, want to keep the see saw level (not slip).

As you cycle through the gears, it takes less turns of the engine to make the same number of turns at the wheels. This means more work from the engine, more strain on you, the clutch.



The higher the gear, the harder you work, until eventually after many thousands of km, you start getting tired, and because its more work to keep the see saw level in a higher gear, you start losing your ability to do so in those gears first.

[method]

Thats a awesome diagram, but i still dont get it!

The reason being because if the engine say only produces 100nm of torque max at the flywheel under full load. So no matter what the gear ratio you can only output so much power. So in a lower gear you are still putting out the same power, but you just accelerate much faster

That would mean that no matter what gear you are in there is never more than 100nm of torque than that going through the clutch plates right?

I always thought the reason slipping clutches are more easy to spot in higher gears is because the engine is producing its max torque for longer.

Is my thinking fundamentally flawed? Im pretty interested

[xsspeed]

IIRC and bear in mind its been a long time since i did machines and mechanisms at uni, the different gears alter the power:torque ratio (i think thats the right saying?) as seen by the diff, which in turn has a ratio, (but remains constant), and this is then what the flywheel sees. Now i cant remember if this is the final ratio or if companies or whoever takes into account the wheels?

I believe that this is why it is suggested to do your dyno runs in whichever gear corrsponds closest to 1:1 ratio as then you are getting the power & torque produced by te engine?

I'm a bit fuzzy round the edges, as I said its been a while, someone else will have a more definitive answer for you though.

Edit: as for slipping clutches i'm not sure but engine working harder theory above sounds right in my mind.

Edit 2: Oh yeah and torque is the rotational equivalent of a moment iirc, hence the drawing above, and beaming a beam and pivot drawing you should be able to grasp it. Changing gear is like changing the point of the pivot.

[molex]

I'm having trouble getting my warrent of fitness sorted in time.. I've fixed all issues outstanding, unfortunately I had a picky bugger and he wants a low volume cert for a front mount Any chance I can still run in the drags without a current wof? Car is definitely up to standard.

[cat007]

You'll be fine.
I wont have a wof altho I'm up to spec

My mates bike isnt even road registered let alone a wof

[RomanV]

Think of it this way, if your wheels are up in the air, then there's next to no load on your clutch, because there's no resistance from the ground etc.

No matter how much torque the engine throws at the clutch, it's never gonna make it slip.

The higher a gear you're in, the more 'resistance' the rest of the drivetrain is putting on the clutch, making it want to slip.

[Lith]

Thats a awesome diagram, but i still dont get it!

The reason being because if the engine say only produces 100nm of torque max at the flywheel under full load. So no matter what the gear ratio you can only output so much power. So in a lower gear you are still putting out the same power, but you just accelerate much faster

Say you weigh 100kg, go and jump from 3 metres up into a swimming pool. You feel it, but the water gives way and you don't get much shock back so its not a real biggy. Now do the same thing onto a slab of concrete, I bet your legs are inclined to either bend to absorb the shock, or break....

When you jump onto the concrete the forces you exert on your legs at the moment of "impact" are no greater, but the resistance is far greater when hitting the concrete. Imagine the water being 1st gear and the concrete being tapped out in top gear - think of your legs as being the clutch, or the last point of contact between the force and the recipient of the force.

[deaf_rattle]

dyno shoot out and cruise was awesome

[Malcolm]

Think of it this way, if your wheels are up in the air, then there's next to no load on your clutch, because there's no resistance from the ground etc.

No matter how much torque the engine throws at the clutch, it's never gonna make it slip.

The higher a gear you're in, the more 'resistance' the rest of the drivetrain is putting on the clutch, making it want to slip.

Exactly what I was going to say.

[snwtoy]

Couple of photos







Link to full gallery will be posted when I've processed them all

[IH8TEC]

woop woop, PB for me, 12.59@ 181.6kmh

turned out to be a pretty good day, once fog cleared the track dried alot, pro import guys laid heaps of rubber down which i loved but still need a prepped track as i'm losing too much time on the start and in second gear.

all in all, pretty good day, some really nice cars turned up. cheers to all the organisers and marshalls, and the sponsors of the day.

[method]

Day went real well, nicely organised.

Thats a nice trap speed ih8tec, if you had some grip for your launches im sure you would be able to rip some awesome times!

I was still battling with my clutch, car was launching fine.. could line lock in first but as soon as i hit 3rd gear it started falling apart. No chance for the clutch in 4th either. Had to try feathering the throttle a bit in 3rd and 4th.

Managed a 14.92 @ 147.2 which i was real happy with considering the circumstances. Esp seeing as my car dynoed 87kw haha!

Ill be back for another go once its all sorted!

The rubber layed down by the pro imports helped a heap with the launches and traction in second!

[IH8TEC]

hence why i was trying to run in lane 1 haha. went one run in lane 2 and lost heaps of time.

trap speeds are down 5kmh on the last car but times are faster. need a nice cold night.

[escortman]

damn i wished i could of raced sounded like a mean day

[cat007]

Yeah it was an awesome day.
Totally loved it.
Shame about the prepped, or lack there-of, track.
Lane 1 was the best for me as well - I managed a 13.63 @ 169kmph - I just couldn't get anything in first - it was a joke - AND I was still in 3rd at 170kmph a little disturbing.....

[SilverTe]

Awesome run event guys. I gapped it at lunch but by the sounds of it should have stayed since the track got alot better. Ran a 14.1@176k with no tractin until 4th haha.( I was in the blue silvia)