will a stock flywheel help with torque? ??

[Frak]

Why are you sceptical of torque figures from dyno's? They are accurate if you understand what's going on. I operate an engine and chassis dyno on a daily basis. What many don't understand with the chassis dyno, is the torque figure you get will be at the wheels unless the dyno has the facility to work out derived torque(basically torque at engine ignoring gearing).

If an engine is say putting out 100NM and the car has a 1st gear of 3:1 and a diff ratio of 4:1, then the torque TO the wheels(not at the wheels will explain in a second) would be 1200NM, this is where some guys get confused as they think this is what the engine is putting out, it's not.

Now lets say the same engine is now in 4th gear 1:1 then the torque to the wheels is 400NM, a gear box multiplies torque but NOT power.

So they are actually not crazy figures but legit figure.

Now some dyno's will get the kw figure, back work it using an rpm input and give derived torque, which is much closer to engine figure and will not alter regardless of what gear the run is done in.

Now another thing I hear is, do it in this gear or that gear. Now all things being equal, no wheel spin etc etc, regardless of what gear you do it in the power will be the same BUT the torque at the wheels will be different, lower gear, higher torque(because of gear ratio) and higher gear, lower torque BUT the power figure will be the SAME.

The reason is, 1st gear has high torque but low speed, 4th gear has lower torque BUT higher speed, this is basically the relationship, torque and speed.

Now this torque to the wheel figure of for example 1200NM will actually be lower torque AT the wheels as the tyre diam is usually larger than the roller diam so that 'gear ratio' will reduce torque......just like an overdrive gear, so using above engine example a gear box with 0.85 ratio would now have 85NM coming out of gear box and still using that 4:1 diff ratio would now be 340NM. So going from 4th gear to 5th gear would drop the torque from 400NM to 340NM, but remember we had 1200NM in 1st gear.....but lower road speed

So Torque figures on a chassis dyno are legit but you cannot compare torque at the wheels with torque at the engine......derived comes close and is much more accurate but will still be lower than actual engine torque figure but much more realistic..


Now flywheels are a storage device nothing more, nothing less, they do not add torque they do not take it away, what they are designed to do is store energy to keep the engine spinning over smoothly until the next torque pulse. If you have a small capacity engine with a heavy flywheel it will probably operate smoothly at low rpm, now fit the same engine with a very light flywheel, the engine still makes the same torque BUT now at lower rpm it may not have enough inertia to keep the engine turning over smoothly to the next torque pulse so torque fluctuations affect how smooth the engine is. You may find after fitting a light flywheel that the engine is not as smooth at low rpm OR it may not even like operating at lower rpm and you may have to go down one gear to increase the rpm, in fact what you have done is increase the number of torque pulses in that given time frame. Of course all the other benefits quicker revving etc I'm not going into as it's been well documented.

Also I find amusing sometimes when people say things like 'that engine's shit has no torque, or not the torque of a bigger engine', for example, lets say we have 2 engines, one engine (engine A) has 210NM at peak revs to 6500rpm, the other makes engine(engine B) 170NM peak BUT revs to 8500rpm. Now lets say in 4th gear we want both to max out at 200km/h, (using 195/50/15 tyre) engine A would need a 3.5 diff ratio and engine B a 4.3 diff ratio, so engine A would have 735NM TO(not at) the wheels and engine B 730NM, very similar, so you can see what gearing can do to an engine with less torque and we still get the same speed.

[Hen may possibly be a nut]

I agree entirely with your long post Mr Frak. My point was that many people don't know what is going on and will quote at the wheels torque figures from dynos, thinking it relates to the engine. You often see totally unrealistic numbers being spouted, hence my distrust of quoted torque figures.

[slider4life]

4.3 ratio car revs at 4000rpm a 110klmh