p.rite.sh

ok, so when we look at some charts that show 300 horsepower and 300 on the torque i notice the torque peak is a lot lower rpm than the bhp rpm...eg

4000 for peak torque
6500 for peak bhp

when do you up shift, 4000 or 6500? and why?

thanks

arumdevil

it's not quite that simple, you need to know what the whole torque curve looks like. Ideally you want to change at a point that's going to land you at the beginning of the highest part (more or less) of the torque curve.

So peak torque might be 250lb/ft at 4000 but at 5000 you still have 230lb/ft which is not that much less but then suddenly drop off after that. So you shift at 5000 which in the next gear is say 3000 at which point you have 220lb/ft - so your changes keeping you, on average, in the highest part of the torque curve.

The above figures are just for example, you'd have to check out your torque curve in relation to your gear ratios for accurate figures, or experiment (boost gauges helps, but you can feel it).

dunx

iTrader: (3)

Smooth changes are best with the torque similar before and after the shift.

Fast changes need to be up around peak power.

IMHO

dunx

gallois

it is not as simple as that either, even though torque drops off relative to bhp, acceleration is still relatively linear due to the fact that although torque is the 'load', bhp is the 'speed' at which the load is moved.....put simply 300ft/lbs at 2500rpm will behave like 150ft/lbs at 5000rpm. So using that example, if your torque at 5000rpm is in excess of half of that torque at 2500rpm, it will accelerate stronger at 5000rpm. So that needs to be considered also.........in reality, due to design characteristics, in a decent petrol car, redlining before changing gear will give optimum acceleration.

arumdevil

Sc0oby

is there anyway to run high torque n less horsepower like those in wrc cars?

arumdevil

should be doable by remapping for that, but unless you have some reason to keep the bhp down it's kind of counter-productive - may as well map for maximum safe boost all through the rev range.

GazJenno

Torque is the amount of energy the engine produces to rotate the crank measures in Nm or Joules. Power (Not BHP but power in KWatts which can be converted to bhp by multiplying by 1.341) is measured in J/s and so is the amount of work done over a given time.

So if you produce 40Nm at 2000RPM and can still produce 40Nm at 6000RPM then your power will be greater at 6000RPM. If you produce 40Nm at 2000RPM and 20Nm at 4000RPM you will have the same power at both engine speeds.

so if your engine produces X amount of torque early in the rev range but can hold the same amount of torque through the rev range then the power will increase with the engine speed hence why they peak at different points.

Also, Torque is a function of displaced volume and Power is a function piston area.... I think lol

Gaz

arumdevil

torque is a function of distance (from axis) x force (or put simply, of the components of the running engine). Power is a function of torque x engine speed (as in your examples above.)

p.rite.sh

so when would i shift at the top torque levels and when would i shift at the top power level?

i think i may be getting confused...

GazJenno

The distance your reffering to is the stroke yeah? obviously when you have a greater stroke you have more leverage of your crank giving the greater torque. A greater stroke also increases the displaced volume which is kind of what I meant. If two engines have the same piston area then the one with the greater displaced volume or stroke will produce more torque.

Anyway theres quite alot of variables that will determine torque and power, I was just trying to explain how you can have peak torque at one engine speed and peak power at another.

Also the OP was talking about a car with 300BHP and 300torque but what units? Would be nice if all the power graphs used SI units lol

Gaz

GazJenno

Sorry I missed the shift part of your post.... I was talking about the differences in peaks.

Shift wise, I would say change at the maximum engine speed that still feels like its pulling. You can usually feel a point where the RPM is still gradually increasing but the pull doesnt feel great.... that correct arumdevil? Post 2 & 4 explain it pretty well tbf.

Gaz

arumdevil

agreed.

p.rite.sh

ah ok, that makes sense - many thanks for your replys

Sc0oby

looking foward for more low end torque as you when comapare to an evo the subaru has less torque down low. i have a JDM V8 sti twin scroll unit and already been remap using open ecu but would still like to get more low end torque as i dont usually revs it up to 8k rpm