AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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- Jan 19, 2014
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Continuation of post 86
If your vehicle can break traction at zero mph, and continue to spin say to 20 mph, at WOT, then you don't need any more stall than you already have. Spinning just slows your ET. You need to deal with the tirespin first, then you can think about a higher stall.
Unless you just want to spin tires,lol.
But if you cannot spin to 20ish, or cannot even break traction, with the current combo, then; assuming the engine is healthy and has reasonable pressure, and the tune is at least decent, then; the cheapest, fastest, easiest solution is to increase the stall-speed, so that when you gas it at Zero mph, the rpm spools up to where there is more available power.
But be careful; Once the rpm is above the stall-speed, the TC is no longer of much benefit, over any other TC.
With 3.21s, in 2.45 first gear, and 28" tires;
2000 rpm is ~19mph, 2400 is ~23mph, 2800 is ~27, and 3200 is ~31mph.
So, if you have a 2000TC and are doing 27mph, the TC ratio is down towards the 1.1 end of the scale, as will be any other TC. And if you have a 2800TC, it will be about the same.
The take-away here is that the TC can only help you below it's point of minimum ratio. In other words; if your engine is gutless at 27mph, in first gear; then no stall, 2800 or less, is gonna change that. At this point, you need more cylinder pressure. And if you are already pressured to the max for your available gas, then you need a bigger rear gear,or a bigger engine, but NOT a cam! Cams do not make power. A bigger cam moves the operating rpm up higher and the new higher more efficient rpm, is what makes the power. But, generally, the bigger cam gives up pressure at the lower rpms to get that higher operating rpm.
How the stall works.
The TC is a Torque Convertor. It accepts the engine torque and multiplies it to a new higher number (at WOT of course). This number depends on the resistance on the output side, and on the input torque. It is expressed as a ratio. The ratio could be a high as 2.0 or as low as about 1.1. For most exercises I use 1.8@Zero mph, and diminishing to 1.1 at 90mph.
Your crank instantaneous torque, gets multiplied by the trans ratio, and the rear end ratio, and the hydraulic ratio inside the TC, and arrives at the rear axles at this much higher number. If that number is small, then you get no tirespin/no tire chirp. If that number is huge, for a streeter, then you just have to upshift right away.
So that number has to be in-between somewhere.
To break the tires loose at zero mph, the tires don't care what size engine you have, or what trans you have or anything other than the number. And the more traction you have, the bigger the number needs to be.
By personal experience, my 295 BFGs or Cobras, need about 2500 ftlbs into the axles, to break traction. But I have a clutch, so I can just rev it up, dump it and we are burning rubber.
Take a look on that graph I posted, which is for a 5.2Magnum, but is probably pretty close to your LA360. At 2000rpm ( a typical stall), the torque is around 275 ftlbs. Into the rear axles, at Zero mph,this would be;
275 x2.45 x3.21 x the TC multiplier, which I'll guess to be 1.8=3890, which is plenty to get the tires spinning. But as soon as the tires break loose, the TC multiplier moves towards 1.1, and as the revs go up, and the torque increases into the TC, so the multiplier moves back towards 1.8. So the TC is like a 2-speed gearbox that is automatically varying it's ratio, anywhere in-between 1.8 to 1.1, in response to the Torque Differential between the In side and the Out side..
So let's say you got the tires spinning and the Rs up to 2800, and on the graph I see 292 ftlbs (WOT). Lets suppose the tires are still spinning at 20mph. And suppose the TC ratio is down to 1.3 (sure, still guessing). Your new number is
292 x2.45 x3.21 x1.3=2985 ftlbs into the rear axles. By 20 mph, I think you will need more than this to keep on spinning, so you will have to rev it up; But I'm guessing.
Now, lets look at the same scenario but with a 2800TC.
Back to zero mph, and with 292 crank ftlbs the number looks like;
292 x2.45 x3.21 x1.8= 4133 which is waaaaay overkill, unless you got some seriously sticky tires.
Again, by 20 mph, the number might be down to 2985,again. So to continue spinning, you will be needing; more rpm, more torque, or a bigger engine.
If your vehicle can break traction at zero mph, and continue to spin say to 20 mph, at WOT, then you don't need any more stall than you already have. Spinning just slows your ET. You need to deal with the tirespin first, then you can think about a higher stall.
Unless you just want to spin tires,lol.
But if you cannot spin to 20ish, or cannot even break traction, with the current combo, then; assuming the engine is healthy and has reasonable pressure, and the tune is at least decent, then; the cheapest, fastest, easiest solution is to increase the stall-speed, so that when you gas it at Zero mph, the rpm spools up to where there is more available power.
But be careful; Once the rpm is above the stall-speed, the TC is no longer of much benefit, over any other TC.
With 3.21s, in 2.45 first gear, and 28" tires;
2000 rpm is ~19mph, 2400 is ~23mph, 2800 is ~27, and 3200 is ~31mph.
So, if you have a 2000TC and are doing 27mph, the TC ratio is down towards the 1.1 end of the scale, as will be any other TC. And if you have a 2800TC, it will be about the same.
The take-away here is that the TC can only help you below it's point of minimum ratio. In other words; if your engine is gutless at 27mph, in first gear; then no stall, 2800 or less, is gonna change that. At this point, you need more cylinder pressure. And if you are already pressured to the max for your available gas, then you need a bigger rear gear,or a bigger engine, but NOT a cam! Cams do not make power. A bigger cam moves the operating rpm up higher and the new higher more efficient rpm, is what makes the power. But, generally, the bigger cam gives up pressure at the lower rpms to get that higher operating rpm.
How the stall works.
The TC is a Torque Convertor. It accepts the engine torque and multiplies it to a new higher number (at WOT of course). This number depends on the resistance on the output side, and on the input torque. It is expressed as a ratio. The ratio could be a high as 2.0 or as low as about 1.1. For most exercises I use 1.8@Zero mph, and diminishing to 1.1 at 90mph.
Your crank instantaneous torque, gets multiplied by the trans ratio, and the rear end ratio, and the hydraulic ratio inside the TC, and arrives at the rear axles at this much higher number. If that number is small, then you get no tirespin/no tire chirp. If that number is huge, for a streeter, then you just have to upshift right away.
So that number has to be in-between somewhere.
To break the tires loose at zero mph, the tires don't care what size engine you have, or what trans you have or anything other than the number. And the more traction you have, the bigger the number needs to be.
By personal experience, my 295 BFGs or Cobras, need about 2500 ftlbs into the axles, to break traction. But I have a clutch, so I can just rev it up, dump it and we are burning rubber.
Take a look on that graph I posted, which is for a 5.2Magnum, but is probably pretty close to your LA360. At 2000rpm ( a typical stall), the torque is around 275 ftlbs. Into the rear axles, at Zero mph,this would be;
275 x2.45 x3.21 x the TC multiplier, which I'll guess to be 1.8=3890, which is plenty to get the tires spinning. But as soon as the tires break loose, the TC multiplier moves towards 1.1, and as the revs go up, and the torque increases into the TC, so the multiplier moves back towards 1.8. So the TC is like a 2-speed gearbox that is automatically varying it's ratio, anywhere in-between 1.8 to 1.1, in response to the Torque Differential between the In side and the Out side..
So let's say you got the tires spinning and the Rs up to 2800, and on the graph I see 292 ftlbs (WOT). Lets suppose the tires are still spinning at 20mph. And suppose the TC ratio is down to 1.3 (sure, still guessing). Your new number is
292 x2.45 x3.21 x1.3=2985 ftlbs into the rear axles. By 20 mph, I think you will need more than this to keep on spinning, so you will have to rev it up; But I'm guessing.
Now, lets look at the same scenario but with a 2800TC.
Back to zero mph, and with 292 crank ftlbs the number looks like;
292 x2.45 x3.21 x1.8= 4133 which is waaaaay overkill, unless you got some seriously sticky tires.
Again, by 20 mph, the number might be down to 2985,again. So to continue spinning, you will be needing; more rpm, more torque, or a bigger engine.
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