One For Lawsy

[Lawsy]

I went away then tried to edit my above post, but it wouldn't let me... damnit.

Anyways, I might as well add more to it now :D

For a flywheel torque value, well... The reality is that there is no point trying to accurately calculate it. It could be anywhere from 600 - 630, but you'll never know without putting it on an engine dyno and checking....

The reason for this is, you have a torque converter. Torque converters do just that, they convert extra RPM into torque and heat. They, in a sense convert, power into torque as well, giving power peaks at lower wheel speeds and torque peaks at lower wheel speeds also. The max power would be lower at the wheels but the max torque will be higher at the wheels... So with this in mind, and considering you dropped 80nm through the driveline then you'll probably never really lose more than 80nm then, up untill a rediculous amount of power that is, because the extra RPM being forced upon the torque converter will cause it to slip a little bit more (not much more though because the pressure through the converter would be greater as well) and converter just a few more rpm into added torque at any given wheel speed while it struggles to lock

If it was a manual though, which say had 60nm as the total loss, and as a rough guess add 5nm of loss with every 100nm increase in torque at the wheels...

So if you made 600rwnm in a manual, you could say you roughly had 670nm at the flywheel. Or something like that, I really don't know... It's too inaccurate to bother with, we'll never get it right until someone puts there 350rwkw motor on an engine dyno, before 350 and after 350kw, to test it out.

This could all be rubish, so just tell others you have about 550 at the wheels and you'll stay out of trouble

550 twisties can tow (and accelerate hard with) 5 tonne rigs up hills at 100km/h... Keep that in mind before sneezing at it!

[Flukey]

  Lawsy said:

I went away then tried to edit my above post, but it wouldn't let me... damnit.

Anyways, I might as well add more to it now :D

For a flywheel torque value, well... The reality is that there is no point trying to accurately calculate it. It could be anywhere from 600 - 630, but you'll never know without putting it on an engine dyno and checking....

The reason for this is, you have a torque converter. Torque converters do just that, they convert extra RPM into torque and heat. They, in a sense convert, power into torque as well, giving power peaks at lower wheel speeds and torque peaks at lower wheel speeds also. The max power would be lower at the wheels but the max torque will be higher at the wheels... So with this in mind, and considering you dropped 80nm through the driveline then you'll probably never really lose more than 80nm then, up untill a rediculous amount of power that is, because the extra RPM being forced upon the torque converter will cause it to slip a little bit more (not much more though because the pressure through the converter would be greater as well) and converter just a few more rpm into added torque at any given wheel speed while it struggles to lock

If it was a manual though, which say had 60nm as the total loss, and as a rough guess add 5nm of loss with every 100nm increase in torque at the wheels...

So if you made 600rwnm in a manual, you could say you roughly had 670nm at the flywheel. Or something like that, I really don't know... It's too inaccurate to bother with, we'll never get it right until someone puts there 350rwkw motor on an engine dyno, before 350 and after 350kw, to test it out.

This could all be rubish, so just  tell others you have about 550 at the wheels and you'll stay out of trouble

550 twisties can tow (and accelerate hard with) 5 tonne rigs up hills at 100km/h... Keep that in mind before sneezing at it!

Lawsy,

No sneezing here, I can assure you. Just big fat grins everytime I drive it

Again, thanks for the input. Its good to see we have one rocket scientist in the place.

[Power]

  Lawsy said:

  IH8PORK said:

dat alot of twisn powa. Not that I know but that seems like a big increase in torque compared to kws. that's >50% nm increase. I like!!!!

You'll notice that whatevet the percentage increase in torque is, at any given rpm point, that that same percentage increase applies to the power as well..

Ok, so it has tractive effort stated, and just after 120km/h the TE curve flattens, this is most likely about 500 rpm after max torque...

But it doesn't really matter because tractive effort doesn't need an rpm value to convert anyway.

Lets take 6500 as your true max tractive effort, about 10km/h before the curve flattens.

Torque = (rolling radius x Tractive effort) / total reduction x 1000

T = (300mm x 6500N) / 3730

T = 523nm at the rear wheels. Which is a damn good effort.

I take rolling radius as this.

You have 245/40/18's, total diameter is 25.5 inches. Minus an inch for tyres with a profile of 40 or more, running between 35- 45psi in the tyres. For working it out with lower profile tyres, take less than an inch. Say, 1 - 2 cm depending on just how low the profile and how much pressure is in the tyres. If you are on the dyno, simply measure it! Get a square, stick it ontop of the tyre and measure from the square to the ground. Easy!

So 300mm is a nice, non fudged round number to use for this calculation...

So that's it, you have nearly 530 tooheys news pushing your car allong....

What's the rolling radius for Dunlop SP300A's 235/45/17 ?

Thanks.

EDIT: 39-40.5 psi at rears

Edited 18/08/05 12:56 AM by Power

[Lawsy]

  Power said:

What's the rolling radius for Dunlop SP300A's 235/45/17 ?

Thanks.

EDIT: 39-40.5 psi at rears

31.5 cm is the radius.

Minus 2cm for 'squish' factor and you get 295mm rolling radius..

Theres actually a fair bit to this though, its actually not a blanket "this will work for every tyre" figure. It all depends on the type of tyre, the compount, the pressure, the sizes... Everything.

Cup tyres with 25psi have stiffer sidewalls, but the contact area is made of sticky rubber so soft you can ball it off with your fingers. The sidewalls on these tyres don't squish at all, but the tread itself does. Therefore they squish less than a road tyre, even though they run 25-30psi vs our 35 - 45psi.

So if you have mega sticky rubber with stiff as crap sidewalls, your tyres may act totaly different on a dyno.

Another thing is that because of centrivical forces, the tyre is going to want to expand outward as speed builds. This may only have a 3mm effect but its worth mentioning, as I will normally round up to the nearest 5mm, because I can...

I'd like to correct my above post as well.

I actually took a little less off the radius by about half a cm than I posted above. I forgot that I originally took an inch and a bit of the diameter and not the radius, so if you wanna work it out, how I do it is this. I'll keep it to cm or mm as its allot less confusing.... (and rounding (usually up, see above) to the nearest 5mm is allot more accurate than 0.5 of an inch, but rough enough to not be confusing).

This seems to work for pressures between 35- 45psi.

Profiles for tyres wider than 235, squish factor. Taken from the Radius, not diameter.

30 - 35, 1.5cm

40 - 45, 2cm

50- 55, 2.5cm.

Even if you have 285's, which obviously makes the sidewalls taller (as the profile is a ratio dependant on width) the pressure in the tyre relative to this aspect ratio is what counts, so it will still only squish 1.5cm if you have 285's...

Infact, it will probably squish a little less. This is because the area of sidewall vs contact patch on the road is lessoned (and the pressure spreads accordingly, keeping the sidewalls more upright).

Hope that helps. If anyone wants to know anymore, just PM me. I check the forums every 2-3 days or so (sometimes every day if I'm really bored).

And I'm no rocket scientist, but thanks for the compliment.