What Engine for 500BHP
Discussion
Been back in touch with GKN & they finally admit the joints are marginal...
Quote
"With that amount of torque and gear ratios you state the joints are going to struggle, even the bigger one. But vehicle weight, tyre size etc. determine if the torque can actually be put down on the tarmac, thus protecting the driveline."
Un - Quote.
I have filled in a full questionaire for power torque, gear ratios, tyre size, weight etc, so now just waiting to see what they say.....
Quote
"With that amount of torque and gear ratios you state the joints are going to struggle, even the bigger one. But vehicle weight, tyre size etc. determine if the torque can actually be put down on the tarmac, thus protecting the driveline."
Un - Quote.
I have filled in a full questionaire for power torque, gear ratios, tyre size, weight etc, so now just waiting to see what they say.....
The issue is few race cars similar to ours have the torque we do.... F1 cans are around half...
Also with the tyres nice and warm I have been able to give the car absolutely full throttle in first gear, and can easily do so in 2nd gear on track.
I want a lightweight, high torque option for fifty quid lol
Also with the tyres nice and warm I have been able to give the car absolutely full throttle in first gear, and can easily do so in 2nd gear on track.
I want a lightweight, high torque option for fifty quid lol
I think you hit the nail on the head there, our engines have way more torque than more normal race cars 
Heard back from GKN - they say that I have 3558Nm at the wheels in 1st (with a saftey factor) and my inner joints are good for 3700Nm and the outer 100mm ones 2600Nm, but they do have an option of a 2900Nm joint So basically they are too small.
I have done the calc for 2nd gear and come out with 2103Nm, so the plan is to stick to launching in second for now.
Ultimately I either need to up size the outer joints and have new shafts or feed wheel speed into the ECU and limit boost in 1st gear......
Heard back from GKN - they say that I have 3558Nm at the wheels in 1st (with a saftey factor) and my inner joints are good for 3700Nm and the outer 100mm ones 2600Nm, but they do have an option of a 2900Nm joint So basically they are too small.
I have done the calc for 2nd gear and come out with 2103Nm, so the plan is to stick to launching in second for now.
Ultimately I either need to up size the outer joints and have new shafts or feed wheel speed into the ECU and limit boost in 1st gear......
turbonutter said:
... feed wheel speed into the ECU and limit boost in 1st gear......
That should be easy enough to implement and cheaper than shafts. Or fit a switch to the gear linkage to detect first gear selection. You will need to limit torque to about 380lb/ft in 1st gear.Edited by stevesingo on Tuesday 20th August 10:11
I have no idea how GKN calculate their shaft torque estimation, because it is actually very difficult to come up with a decent number (especially with a turbo engine)
Consider the following:
1) Can your turbo charger "keep up with your engine" in 1st gear (unless you're running launch ALS, i'd suggest no) i.e. in 1st , your engine accelerates so fast that the steady state boost is never reached. As such, youre engine isn't producing the steady state torque output
2) Engine inertia. On a launch and on a gear shift, the engines inertia gets transmitted through the powertrain. This can be a very big number indeed (a massive torque spike in effect) How torsionally stiff your powertrain is,makes a big difference to the shape of this spike at the wheels
3) Torsional vibration from cylinder firing events introduces a higher frequency cyclic loading. Again, the stiffness and the rotational inertia of your powertrain influences the magnitude of these transmitted loads. "racing cars" with low inertia designs can often work their transmissions very hard at high frequencies leading to fatigue failure
By the time you have all these different interactions of effects (and luckily you haven't got things like ABS / traction control inputs to worry about!) accurately calculating the actual driveshaft loadins is really very difficult. So, back to the beginning, just taking the max theoretical torque in 1st gear, and adding a safety factor based upon experience probably isn't such a bad idea! ;-)
Consider the following:
1) Can your turbo charger "keep up with your engine" in 1st gear (unless you're running launch ALS, i'd suggest no) i.e. in 1st , your engine accelerates so fast that the steady state boost is never reached. As such, youre engine isn't producing the steady state torque output
2) Engine inertia. On a launch and on a gear shift, the engines inertia gets transmitted through the powertrain. This can be a very big number indeed (a massive torque spike in effect) How torsionally stiff your powertrain is,makes a big difference to the shape of this spike at the wheels
3) Torsional vibration from cylinder firing events introduces a higher frequency cyclic loading. Again, the stiffness and the rotational inertia of your powertrain influences the magnitude of these transmitted loads. "racing cars" with low inertia designs can often work their transmissions very hard at high frequencies leading to fatigue failure
By the time you have all these different interactions of effects (and luckily you haven't got things like ABS / traction control inputs to worry about!) accurately calculating the actual driveshaft loadins is really very difficult. So, back to the beginning, just taking the max theoretical torque in 1st gear, and adding a safety factor based upon experience probably isn't such a bad idea! ;-)
andygtt said:
Maybe we should put rubber doughnuts in our shafts similar to some prop shafts lol
It's not unusual for driveshafts that are designed to take massive loadings to twist massively under full load, being designed this way allows the 'spike' to be absorbed protecting other driveline components. Not that much different to having a doughnut 
It's worth noting that "Load sharing" in the joints is absolutely critical too. Because the component parts are so hard and in-elastic, minor dimensional tolerances massively change the load paths, and can easily overload individual sections of the joint leading to a "cascade" failure.
If you imagine two very smooth metal blocks, being held apart by two other smooth metal blocks, if one block was only 0.01mm longer it would take the entire load, and the shorter block would take none.
This is why these joints tend to precision honed, and it is imperative that they are not disassembled! (i.e. each ball must stay in it's own particular socket). The higher the quality of the joint, the more important this becomes, and often the only difference between the "motorsport" joints and the OEM ones is a tighter dimensional tolerance (selective fit).
If you imagine two very smooth metal blocks, being held apart by two other smooth metal blocks, if one block was only 0.01mm longer it would take the entire load, and the shorter block would take none.
This is why these joints tend to precision honed, and it is imperative that they are not disassembled! (i.e. each ball must stay in it's own particular socket). The higher the quality of the joint, the more important this becomes, and often the only difference between the "motorsport" joints and the OEM ones is a tighter dimensional tolerance (selective fit).
Some Good points made above, especially about not dissembling the CV joints - I had dismantled one, when I change the nearside driveshaft, but it was the untouched one that failed! I will remember that for the future though!
As for the Drive Shaft angle, the shafts are about 1/2" lower at the inboard end static, plus about 1" squat. The nearside shaft runs a steeper angle as it is shorter, but it was the offside joint that broke...
I will have a look at the driveshaft shop & see if they can offer anything, but for now the plan is to torque limit 1st gear and see how things go. Until I can get the limit in 1st gear, no launches in 1st, only in second
As for the Drive Shaft angle, the shafts are about 1/2" lower at the inboard end static, plus about 1" squat. The nearside shaft runs a steeper angle as it is shorter, but it was the offside joint that broke...
I will have a look at the driveshaft shop & see if they can offer anything, but for now the plan is to torque limit 1st gear and see how things go. Until I can get the limit in 1st gear, no launches in 1st, only in second
andygtt said:
Wonder what torque you need to have at the wheels to achieve a wheelie :-)
Guess it depends on weight, but I'm guessing like me you are just over 1000kgs and we both have most of the weight in the rear lol
Definately going to need stronger CV's for a wheelie Guess it depends on weight, but I'm guessing like me you are just over 1000kgs and we both have most of the weight in the rear lol
Yes we are similar weights - my Stratos is 1060Kg 60% on the rear axle...................
Max_Torque said:
Your going to need about 9100Nm at the rear axle to wheelie (assuming 1060kg, 40/60, and a 2180mm wheelbase). You will also need a rear tyre mu of about 2.2! (Which is why you car generally spins it's rear wheels and doesn't wheelie.....)
Not much chance of getting that much torque through the gearbox - or that much grip from the tyres......Sticky tyres is what you need. And a very grippy surface.
https://www.youtube.com/watch?v=ej5Y4bRmtXg&fe...
https://www.youtube.com/watch?v=ej5Y4bRmtXg&fe...
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