GavDavs Mk2 2gr-fe swap

[gavsdavs]

First plot appears to be dyno of 2 different cars - car 1 is 196bhp. car 2 is 271 bhp. Date is 19/12/05
Are you saying these are both 2GR ?

Second plot appears to be 2 runs of the same car - run 1 is 282bhp, run 2 is 276bhp, date on that is 07/11/08 ?

The dates appear not to be reliable, the dynos are different. I don't follow how these represent a gain in power.

Think about it. A flywheel stores rotating energy (that's what it's for), so a heavier flywheel can store more energy and add smoothness, but it can't add horses or torques. Its always going to be swings and roundabouts (revviness/stall-iness vs driveability).

http://www.lotustalk.com/forums/f25/...-torque-85900/

[Paul Woods]

I'm not knowledgeable enough on the subject to be able to comment 100%, but i do know using the heavier fly is resulting in more torque being present in the midrange, Phils dynos are from his 1mz days running the TRD SC, the only thing to change on those plots were the flywheel from steel to Fidanza, either way it's also been noticeable on the road. I agree the fly cannot affect BHP, but something is going on with the torque figure.

[gavsdavs]

Here is my thinking. Imagine a single, or twin cyliinder engine - far fewer actual driving pulses coming down the crank.

A really light fly will
- mean the engine will stall when you declutch when stationary with zero throttle. There isn't sufficient mass to keep it spinning.
- add and lose revs more quickly
- permit the pulsing of the pistons firing through to the transmission with very little damping effect and 'feel rough'
- not need very much effort on the part of the engine to add, or lose RPM.
- Very low parasitic effect.

A really heavy fly will
- require the engine put more work in to gain revs, but conversely mean the engine looses revs more slowly.
- larger parasitic drag on the crank - the engine has to put more effort into have the fly gain RPM, before moving the mass of the transmission/weight of the car.
- damp the crank pulses much more, so the driven transmission has much smoother rotation coming into it.
- if the engine has been revved up in neutral, you can declutch and the rotational inertia will move the car, whereas a lighter fly will not have that rotational inertia and the engine will be more prone to stall.

The effect is much more noticeable on single or twin cylinder engines and a lot less so on mutli-cylinder engines.

Flywheel weight can't add or remove power or torque, but it can change the perceived effect

I am surprised you can actually feel an effect when on the move as the difference should really be negligible but physics says - heavier fly = the engine has to put more work in to change the rotating speed of the fly before its done anything to the speed of the car.

[Paul Woods]

What about the stored kinetic energy in a heavier fly? Surely a heavier fly, once spinning, is actually helping rotate the crank due to it's inertia.... there seems to be logic in that, a lighter fly would not aid the crank rotating as much as the heavier one would?

I know the heavier one is going to take more effort to spin at lower RPM, but can you see the thinking once it's spun up? Old boys use massive flywheels on old traction engines to keep them turning easier, hard to get going but once running a heavy fly takes very little effort to turn due to its massive stored energy compared to a light one..... that's the way I see it, but I'm no expert in that area.

[gavsdavs]

What about the stored kinetic energy in a heavier fly? Surely a heavier fly, once spinning, is actually helping rotate the crank due to it's inertia.... there seems to be logic in that, a lighter fly would not aid the crank rotating as much as the heavier one would?

It only helps when the gearbox is spinning more slowly than the crank is. When you re-engage the next gear - the energy stored in the fly (where it is spinning faster than the transmission) is imparted into the transmission.

This will feel like a little surge forward as you let the clutch out when changing from 2nd to 3rd (for example). Once you are "in gear" - where the crank is locked to the transmission by 'being in gear' - the fly becomes parasitic again.

I know the heavier one is going to take more effort to spin at lower RPM, but can you see the thinking once it's spun up? Old boys use massive flywheels on old traction engines to keep them turning easier, hard to get going but once running a heavy fly takes very little effort to turn due to its massive stored energy compared to a light one..... that's the way I see it, but I'm no expert in that area.

They use them because they want a smooth driven effect - and they only have one or two input pistons - so an undamped traction engine would be really 'lumpy' - not what they want.

The RPM speed isn't relevant to the power seen at the gearbox - though the effect of the fly is lesser the more revs you have. You'll only likely notice a difference one way or the other - at low revs.

[Paul Woods]

Hmmm, I get and agree with all of that, but this leaves us with one big elephant in the room, Phils dynos, and the only thing to change in those runs was the flywheel......

[gavsdavs]

Hmmm, I get and agree with all of that, but this leaves us with one big elephant in the room, Phils dynos, and the only thing to change in those runs was the flywheel......

Those plots confused me - Which was the before and after.?
Were they taken on the same day? (

Either
-the engine is combusting differently and better (most likely)
-there was fresh oil and a reduction in drag somewhere in the drive train (possible, but the difference is going to be hard to measure unless it was really bad before the change)

An increase in flywheel weight cannot increase engine power output.

We are talking about 1/2/3% here, as you have said what matters is how it feels.

[Paul Woods]

No I know it cannot increase power, but perhaps the torque band is being moved as a result of the work the flywheel is doing, I really don't know, just guessing.

[MRV6]

Sorry for the confusion. The first plot was with my 1mz n/a engine, the second with the supercharger ( all on one plot) the mapper overlaid them to show a before and after. The third one is with the lighter flywheel which was actually a turbo flywheel.

Just found this.

[geoffmunt]

Back in the day when I had my turbo, I had 2x dyno runs on the same dyno, 1st with original clutch, fly and cat. 2nd with Helix clutch, Fidanza & decat.

If I remember rightly (and could dig out the original graph I guess), BHP went up from 293 to 299, whilst torque dropped from 271 lb/ft to 264 lb/ft. However these were the extrapolated flywheel figures, the bhp at the wheels actually went up a lot, from (IIRC) 240 bhp to 270bhp.

Make of that what you will, but seems to indicate lower transmission losses with the lighter fly (might have been getting a bit of clutch slip beforehand, can't remember now).

FWIW, I'd agree with Gavdav's analysis of what's going on, the car 'felt' more torquey with the original fly but it was most certainly quicker in it's final incarnation.