Which Gearbox? Quaife??
Discussion
I want to run a sequential box in the car, Rx7
With budget in mind...x-trac and Recardo are a little out of my budget!! What would be the gearbox of choice??
My thoughts are
Hewland
Quaife
Elite
Apart from Hewland Ive heard mixed reviews about the other 2.
Ive seen that Block uses a gearbox by Maktrak, an ex hewland employee....does anyone have any information on their gearbox? Cant find a website about it
With budget in mind...x-trac and Recardo are a little out of my budget!! What would be the gearbox of choice??
My thoughts are
Hewland
Quaife
Elite
Apart from Hewland Ive heard mixed reviews about the other 2.
Ive seen that Block uses a gearbox by Maktrak, an ex hewland employee....does anyone have any information on their gearbox? Cant find a website about it
lolMy experience with motorsport dog/sequential boxes in general is that they fall into exactly 2 categorys:
1) expensive and good
2) everything else
I have a quaffie HD 6 speed sequential in my car, it's OK, seems tought enough, but the shifts are a bit ropey (not an issue now i have paddleshif system doing the work for me) and it's f'ing heavy! but for just under £7k nothing else gets too close (equivalent Hewland etc would be easily double that)
ETA: i think a lot of people get into trouble with sequential boxes because they add one, add some flat shift device (ign cut etc) then expect to be able to shift in zero ms flat, and actually, to do that needs a lot more than just a decent gearbox (like minimised engine rotational inertia etc!)
If you do the math, slowing 0.3kgm^2 of engine by 1000rpm in 50ms is a pretty large number ((0.5I x(omega^2)) and that energy needs to go somewhere!
1) expensive and good
2) everything else
I have a quaffie HD 6 speed sequential in my car, it's OK, seems tought enough, but the shifts are a bit ropey (not an issue now i have paddleshif system doing the work for me) and it's f'ing heavy! but for just under £7k nothing else gets too close (equivalent Hewland etc would be easily double that)
ETA: i think a lot of people get into trouble with sequential boxes because they add one, add some flat shift device (ign cut etc) then expect to be able to shift in zero ms flat, and actually, to do that needs a lot more than just a decent gearbox (like minimised engine rotational inertia etc!)
If you do the math, slowing 0.3kgm^2 of engine by 1000rpm in 50ms is a pretty large number ((0.5I x(omega^2)) and that energy needs to go somewhere!
Edited by anonymous-user on Tuesday 21st September 17:41
I think you need to bear in mind when selecting a gearbox that you need to size it for the application.
Putting it in the simplest terms, gearboxes are sized principally by torque rating, and the more torque you have the bigger the gears. The bigger the gears, the more load on the synchros and the baulkier and slower the gearchange.
You can make a small torque capacity gearbox take a higher torque by making the low gear ratio numerically lower e.g. going from a 3.6:1 1st gear to a 2.2:1 1st gear. You can get the ratio spread back by using an overdrive top gear.
That said, when you use overdrives you need to counteract them with numerically higher final drive ratios e.g going from 3.1:1 to 4.3:1 and in RWD applications you run the risk of hitting 1st order bending frequency. You counter this by using a two piece propshaft - each piece is stiffer than a long piece and so the frequency is raised, alternatively use a very long gearbox tailshaft.
So when it comes to the RX7, to get the very best out of it, it really helps to understand exactly what the engine is delivering and what ratios you need to extract every possible amount of performance from the vehicle.
I think you also need to think carefully about why you want a sequential gearbox and what problems you are going to fix by having one, against the problems you will make by having to re-engineer your car.
Putting it in the simplest terms, gearboxes are sized principally by torque rating, and the more torque you have the bigger the gears. The bigger the gears, the more load on the synchros and the baulkier and slower the gearchange.
You can make a small torque capacity gearbox take a higher torque by making the low gear ratio numerically lower e.g. going from a 3.6:1 1st gear to a 2.2:1 1st gear. You can get the ratio spread back by using an overdrive top gear.
That said, when you use overdrives you need to counteract them with numerically higher final drive ratios e.g going from 3.1:1 to 4.3:1 and in RWD applications you run the risk of hitting 1st order bending frequency. You counter this by using a two piece propshaft - each piece is stiffer than a long piece and so the frequency is raised, alternatively use a very long gearbox tailshaft.
So when it comes to the RX7, to get the very best out of it, it really helps to understand exactly what the engine is delivering and what ratios you need to extract every possible amount of performance from the vehicle.
I think you also need to think carefully about why you want a sequential gearbox and what problems you are going to fix by having one, against the problems you will make by having to re-engineer your car.
GavinPearson said:
I think you need to bear in mind when selecting a gearbox that you need to size it for the application.
Putting it in the simplest terms, gearboxes are sized principally by torque rating, and the more torque you have the bigger the gears. The bigger the gears, the more load on the synchros and the baulkier and slower the gearchange.
You can make a small torque capacity gearbox take a higher torque by making the low gear ratio numerically lower e.g. going from a 3.6:1 1st gear to a 2.2:1 1st gear. You can get the ratio spread back by using an overdrive top gear.
That said, when you use overdrives you need to counteract them with numerically higher final drive ratios e.g going from 3.1:1 to 4.3:1 and in RWD applications you run the risk of hitting 1st order bending frequency. You counter this by using a two piece propshaft - each piece is stiffer than a long piece and so the frequency is raised, alternatively use a very long gearbox tailshaft.
So when it comes to the RX7, to get the very best out of it, it really helps to understand exactly what the engine is delivering and what ratios you need to extract every possible amount of performance from the vehicle.
I think you also need to think carefully about why you want a sequential gearbox and what problems you are going to fix by having one, against the problems you will make by having to re-engineer your car.
Wise words, but the Rx I am going to be running has been rebuilt from the ground up. As far from standard as you can possibly imagine!Putting it in the simplest terms, gearboxes are sized principally by torque rating, and the more torque you have the bigger the gears. The bigger the gears, the more load on the synchros and the baulkier and slower the gearchange.
You can make a small torque capacity gearbox take a higher torque by making the low gear ratio numerically lower e.g. going from a 3.6:1 1st gear to a 2.2:1 1st gear. You can get the ratio spread back by using an overdrive top gear.
That said, when you use overdrives you need to counteract them with numerically higher final drive ratios e.g going from 3.1:1 to 4.3:1 and in RWD applications you run the risk of hitting 1st order bending frequency. You counter this by using a two piece propshaft - each piece is stiffer than a long piece and so the frequency is raised, alternatively use a very long gearbox tailshaft.
So when it comes to the RX7, to get the very best out of it, it really helps to understand exactly what the engine is delivering and what ratios you need to extract every possible amount of performance from the vehicle.
I think you also need to think carefully about why you want a sequential gearbox and what problems you are going to fix by having one, against the problems you will make by having to re-engineer your car.
I don't see your point about the 2 piece prop, surely that just adds flex at the joints? It looks as though I am going to go with the MakTrak box, as this offers everything I need from the box, and John is both very helpful and very knowledgeable. Great box and can handle the torque....as demonstrated on Mr Blocks car.
Ive run a 4.3 instead of the 4.1 previously, but with the increase of power I now have there is little point. You can select the gear ratios, and I have a calculator that will show me the rev drops between the gears. This can be altered with the use of drop gears, which are quick and easy to change between circuits.
It comes with the strain gauges built in, so I can get the ECU to handle the flat shifts. As for the engine, that is built proof! Will rev to 13k, although the turbo will have given up the ghost way before that, but it will allow the engine to roll with the punches when over runs occur.
JontyR said:
I don't see your point about the 2 piece prop, surely that just adds flex at the joints? It looks as though I am going to go with the MakTrak box, as this offers everything I need from the box, and John is both very helpful and very knowledgeable. Great box and can handle the torque....as demonstrated on Mr Blocks car.
You need to know the speed your car will run at, and covert that back to propshaft rpm. Then convert that to revs per second to get propshaft frequency.Let's suppose your car is geared and tyred such that at top speed the propshaft will run at 140 revs per second - 140 Hz.
If your propshaft is a long one that is good and heavy it might have a natural frequency of 120 Hz. Once you run above that you overload the part and risk failure. That is inadvisable.
The fix for this is to raise the frequency of the prop, by going to a bigger diameter, shorter shafts (e.g. 2 piece) or using materials that raise the frequncy, e.g. carbon fibre. All have pros and cons.
Regarding your selection of transmission, customer support is clearly a good thing to have, but without fundamentally understanding the applications engineering behind this you will have more gearbox torque capacity than you actually need. I'm not saying that you should be concerned from a budgetary expense, more from a lap time one.
GavinPearson said:
JontyR said:
I don't see your point about the 2 piece prop, surely that just adds flex at the joints? It looks as though I am going to go with the MakTrak box, as this offers everything I need from the box, and John is both very helpful and very knowledgeable. Great box and can handle the torque....as demonstrated on Mr Blocks car.
You need to know the speed your car will run at, and covert that back to propshaft rpm. Then convert that to revs per second to get propshaft frequency.Let's suppose your car is geared and tyred such that at top speed the propshaft will run at 140 revs per second - 140 Hz.
If your propshaft is a long one that is good and heavy it might have a natural frequency of 120 Hz. Once you run above that you overload the part and risk failure. That is inadvisable.
The fix for this is to raise the frequency of the prop, by going to a bigger diameter, shorter shafts (e.g. 2 piece) or using materials that raise the frequncy, e.g. carbon fibre. All have pros and cons.
Regarding your selection of transmission, customer support is clearly a good thing to have, but without fundamentally understanding the applications engineering behind this you will have more gearbox torque capacity than you actually need. I'm not saying that you should be concerned from a budgetary expense, more from a lap time one.
We are going to be running 300 x 18 with a 705 diameter.
I'm going to look at the types of props that MakTrak recommend, but I will read up on what you are saying about the resonance.
I'm sure the engine is going to be at the top of the Torque range of the box, should be running over 600bhp..not sure on the ft lbs until the engine has been on a dyno.
Max_Torque said:
What's the rotational inertia of an RX7 rotary engine like?? probably could be quite good if you fit a dinky flywheel and multiplate clutch too??? that would really help with fast dog shifting!
Rotor 1 is 4106.4g and Rotor 2 is 4106.1gThe clutch and flywheel weigh in at 2.1kgs
JontyR said:
Max_Torque said:
What's the rotational inertia of an RX7 rotary engine like?? probably could be quite good if you fit a dinky flywheel and multiplate clutch too??? that would really help with fast dog shifting!
Rotor 1 is 4106.4g and Rotor 2 is 4106.1gThe clutch and flywheel weigh in at 2.1kgs
but, from those low masses the rotational inertia is probably very small too !!
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