Any Feed back on the JHM light weight crank pulley?

[ArthurPE]

Since his 12.84, he has added a JHM lightweight flywheel, 4 JHM lightweight rotors, and added stock sized gutted downpipes (2.5"). With these mods, in worse conditions (around density altitude 1800 feet this time vs. around 500 feet when stock) he ran 12.2 @ 112.98 mph on 98 octane gas at the same track (Palm Beach International Raceway).

But how much of that gain is due to the lightweight flywheel, how much due to the lightweight rotors and how much due to the gutted downpipes?

Since 3 things have been changed at the same time there's no way of knowing which made a positive difference, which (if any) made a negative difference and which made no difference.

and were there software changes to tie it all together?
not to mention 98 octane fuel

those traps times are ~7-9% power torque gains, 30-40 HP at the crank, with the weight loss factored out, 20-30 maybe

we're talking about a change due solely to a pulley

[sakimano]

But how much of that gain is due to the lightweight flywheel, how much due to the lightweight rotors and how much due to the gutted downpipes?

Since 3 things have been changed at the same time there's no way of knowing which made a positive difference, which (if any) made a negative difference and which made no difference.

Yes, I'm well aware of that, however we've seen people run at the dragstrip befor eand after gutted stock downpipes and there's not a massive change. Same with octane. The lw parts certainly do their job to help the car accelerate and this was just a good example of a car with very simple LW mods and a decat, and still no tune...yet it ran the fastest non-supercharged time yet (and faster than many of the PES/VF supercharged cars lol).

It's very easy to brush off results if your goal is to find a reason to ignore them and it's very easy to say 'this was changed/that was changed' thus the results are just a good guideline of what's working and what's not. If you think reducing 18 lbs of rotating mass at the crank is not helpful unless someone shows you some kind of proof that you deem acceptable, that's fine. I think lots of other people understand that it will help and will do the modification to their cars and enjoy the results. The fastest accelerating cars in the world are the US domestic market cars which enjoy a massive aftermarket, and all platforms focus on reducing rotating mass where possible. It's not a co-incidence.

Exactly how effective it is will be hard to demonstrate, and even if I had a quarter mile or pbox or vagcom log comparison for you of a LWFW+LWCP only car vs. stock, you'd find a way to point to a myriad of reasons that it is not be a justifiable result.

To that end, what would be sufficient proof of a modification like this working to satisfy you?

[sakimano]

Since his 12.84, he has added a JHM lightweight flywheel, 4 JHM lightweight rotors, and added stock sized gutted downpipes (2.5"). With these mods, in worse conditions (around density altitude 1800 feet this time vs. around 500 feet when stock) he ran 12.2 @ 112.98 mph on 98 octane gas at the same track (Palm Beach International Raceway).

But how much of that gain is due to the lightweight flywheel, how much due to the lightweight rotors and how much due to the gutted downpipes?

Since 3 things have been changed at the same time there's no way of knowing which made a positive difference, which (if any) made a negative difference and which made no difference.

and were there software changes to tie it all together?
not to mention 98 octane fuel

those traps times are ~7-9% power torque gains, 30-40 HP at the crank, with the weight loss factored out, 20-30 maybe

we're talking about a change due solely to a pulley

I'm not sure what you're asking. I mentioned the fuel. There is no tune.

I'm not saying 'here's proof of the exact results from x'.I think I was pretty clear that there were other mods to muddy the waters. I'm saying 'focusing on reducing rotating weight such as LWCP, LWrotors, LWFW help the car accelerate faster and here is an example of a great result with just decatted DPs and an octane boost + a bunch of LW parts'. If you think an RS4 with a decat on 98 octane could run 12.2 @ 112 I will have to disagree. Nobody has been anywhere near that yet with those mods.

Exactly how fast will these mods make you? I am not sure, and more importantly I'm not trying to convince you. I get the impression you and petroldave will never modify your cars anyway. I have done a myriad of stock testing with my car using a PBOX, using the dragstrip, using VAGCOM logs....and I will do even more when I'm modified. I did this with my last Audi as well, and produced some of the fastest times for that car considering a very modest modlist power wise (tune/exhaust)...while focusing on freeing up the car by reducing rotating weight.

[ArthurPE]

so no tune
punched out cats
LW flywheel
lighter rotors
98 octane

and it picked up 0.65 sec and over 5 mph trap in conditons that would yield 7% LESS HP due to the alt density?
and the track is basically at sea level


something doesn't add up
no tune so the 98 oct should give no power gain
the cats without a tune may cost HP
flywheel and brake discs gained that much? something doesn't jive, that's over 50HP
SC cars run those times and they have 80-100 HP gain

even if the brake rotors are 10 lb lighter at an 0.6' radus
less torque required T = 0.6 x 10 ~ 6 lb ft, sounds like a lot, except it is AFTER the gearing/torque multiplication
6/4.11 (final drive) ~1.5 ft lb
after division by the tranny ratio''s it becomes less that 1 for 1, 2, 3 & 4th
so the rotors offer no accel advantage, although the unsprung weight will improve handling

same goes for the flywheel, oem flywheel vs LW flywheel, yes it MAY accelerate a bit faster, perhaps, if not in gear
but put a load on the engine and the flywheel wt delta becomes such a minute portion of the weight the engine must propel (4000 lbs or so) it will have no effect what so ever...

what is the FW diameter and weight for each?

there is also the concern of balance/harmonics/dampening once again

[sakimano]

so no tune
punched out cats
LW flywheel
lighter rotors
98 octane

and it picked up 0.65 sec and over 5 mph trap in conditons that would yield 7% LESS HP due to the alt density?
and the track is basically at sea level


something doesn't add up
no tune so the 98 oct should give no power gain
the cats without a tune may cost HP
flywheel and brake discs gained that much? something doesn't jive, that's over 50HP
SC cars run those times and they have 80-100 HP gain

even if the brake rotors are 10 lb lighter at an 0.6' radus
less torque required T = 0.6 x 10 ~ 6 lb ft, sounds like a lot, except it is AFTER the gearing/torque multiplication
6/4.11 (final drive) ~1.5 ft lb
after division by the tranny ratio''s it becomes less that 1 for 1, 2, 3 & 4th
so the rotors offer no accel advantage, although the unsprung weight will improve handling

same goes for the flywheel, oem flywheel vs LW flywheel, yes it MAY accelerate a bit faster, perhaps, if not in gear
but put a load on the engine and the flywheel wt delta becomes such a minute portion of the weight the engine must propel (4000 lbs or so) it will have no effect what so ever...

what is the FW diameter and weight for each?

there is also the concern of balance/harmonics/dampening once again

I agree it was a pretty hard to believe result, but it was a really good driver (he previously held the 370Z all motor record) and a really quick track. He posted video and timeslip. PBIR is where many cars set records. IT's NHRA and IHRA certified, so I'm not concerned it's 'cheating'...but track prep is apparently excellent. I asked him if he could log his car so we could see if the previous owner had put a tune on, but he was pretty sure it wasn't tuned. He has asked JHM for a tune but has to wait for their new server system to be ready to launch (for RS4/S5 flashing).

His stock time was 12.84 @ 107.7 so his modded time was 0.58 seconds quicker and 5.2 mph faster trap. For the record I went 12.75 @ 108.3.

it should be noted that the RS4 likes race gas. Most RS4s pull timing to some degre, and race gas will help you eliminate most of that. 'RS4tony' dyno'd something excellent on 100 octane with just JHM LWFW, JHM rotors and I believe piggies and ecs h-pipe.

[ArthurPE]

12.84 @ 107.7
12.2 @ 112.98
12.84 - 12.2 = 0.64 sec (I said 0.65)
trap 5.2, I said over 5
still can't buy it

[ArthurPE]

http://www.stealth316.com/2-calc-hp-et-mph.htm
using these estimators, the best I've found
4000 lb car
108/113
all three add 60 HP or so, and stock at 108 is 393-414, close to rating

ET 12.2 to 12.8
60 to 100 HP gain, ave 80 or so

using 4000/420 HP
13.3/108.5
13.15/109
12.35/110
avg 12.95/109 or so

this does not factor in the 7-8% power the density altitude cost during the faster run

[adsgreen]

There is I way I can believe just reducing unsprung and rotating mass by 6kg or so makes that much difference on its own.
One of my track cars (that weighed under 1500lbs to start with) went from conventional to funky composite brakes and lighter wheels that shaved of 16kg total and it made virtually no difference to the cars straight line.

The bit I don't like is the comments 'won't show up on the dyno'.
Why not? The dyno is testing how fast the car accelerates a known mass. The total mass being accelerated is the combined weight of the engine rotating mass, drivetrain, unsprung mass and dyno.
So logic states to me that reducing any of the non dyno mass would give a higher reading?

[sakimano]

There is I way I can believe just reducing unsprung and rotating mass by 6kg or so makes that much difference on its own.
One of my track cars (that weighed under 1500lbs to start with) went from conventional to funky composite brakes and lighter wheels that shaved of 16kg total and it made virtually no difference to the cars straight line.

The bit I don't like is the comments 'won't show up on the dyno'.
Why not? The dyno is testing how fast the car accelerates a known mass. The total mass being accelerated is the combined weight of the engine rotating mass, drivetrain, unsprung mass and dyno.
So logic states to me that reducing any of the non dyno mass would give a higher reading?

You had a typo in your first sentence. Don't know what you're saying.

If you don't think reducing sprung weight helps acceleration, I don't know what to say to you. Having made a few of these mods to my own car in the past and seeing gains identifiable in logging and acceleration, I disagree with you...and we'll just have to agree to disagree. I mean, I'm happy to have more people out there think this stuff doesn't work. Means less fast cars out there. Do me a favour...go to the BMW and AMG forums and convince them that reducing rotating unsprung weight doesn't help acceleration while you're at it. Tell the world of cars that lw wheels are a waste of money. Our cars could use the edge!

I won't pretend to understand the part about the dyno. I agreed with your thinking until two different dyno operators explained that the LW parts don't impact results. I have heard some say that in fact heavy parts may help dyno results. Something to do with the load/resistance with a dyno.

[adsgreen]

Typo due to iphone.
Just to be specific - I am well versed enough to know that reducing unsprung weight is will help acceleration. Thats not the point I was making.
In my experience reducing 6kg will not give equivilent to 60bhp difference on a 1700kg car.
I've had track cars tuned so the idle had to be over 2k just to stop the bloody thing from stalling. In a racing start against other not so compromised cars there was nothing in it. Where it did help was to make gearshifts much quicker with less stress on the drivetrain/synchros and balancing the car mid corner was easier.

Reducing unsprung mass has many other positive effects than engine rotating mass - to the point I'd say the link between the two isn't that great. For example, reducing engine rotating mass will do feck all to slow a car down but reducing unsprung will.

The reason why it won't show up on a dyno is that I suspect for a street car the difference is below the tolerance of the dyno to read (which can be a surprisingly large amount).
Granted it may not have any affect on crank hp however in terms of available power at the wheels it by definition must have an affect that can be measured.
Otherwise how do you explain magically accelerating faster with no increase in the effective driving force at the wheels?!?

[PetrolDave]

It's very easy to brush off results if your goal is to find a reason to ignore them and it's very easy to say 'this was changed/that was changed' thus the results are just a good guideline of what's working and what's not

To that end, what would be sufficient proof of a modification like this working to satisfy you?

The acceleration changes from ONE modification at a time.

As a Professional Engineer with 35 years experience I can think of many occasions where more than one thing has been changed at a time and the assumption of which change made the difference was wrong.

Now when I'm fault finding or looking for improvements I only ever change ONE thing at a time.

[ArthurPE]

how would it be measured on a dyno?
the dyno wheel weighs the same and it's rate of accel and mass is used to determine the torque/force, and to derive power
now if what you are saying is that the engine would have less losses and deliver more to the dyno wheel, hence spooling it up quicker, perhaps
think lighter rotors on the front of a RWD car on a dyno

but my point was it is so small of a % of total mass that even if a LW flywheel did allow the engine to spool up faster, it is 1/100ths of the total mass, and any difference is lost in the noise

the point is, gain 1 ft lb at the wheel. it is only 1/(tranny x diff ratio) at the engine

[adsgreen]

how would it be measured on a dyno?
the dyno wheel weighs the same and it's rate of accel and mass is used to determine the torque/force, and to derive power
now if what you are saying is that the engine would have less losses and deliver more to the dyno wheel, hence spooling it up quicker, perhaps
think lighter rotors on the front of a RWD car on a dyno

That was my logic - I think it's fair to say that any steady state reading of an engine output will be the same for a lighter flywheel than stock.

But if the claim is that a lighter flywheel accelerates the car significantly more as a whole faster then the only way is by reducing losses making more effective power at the wheels.
This should be very obviouls from a wheel or hub dyno esp if the margin put forward above is true.

[sakimano]

Typo due to iphone.
Just to be specific - I am well versed enough to know that reducing unsprung weight is will help acceleration. Thats not the point I was making.
In my experience reducing 6kg will not give equivilent to 60bhp difference on a 1700kg car.
I've had track cars tuned so the idle had to be over 2k just to stop the bloody thing from stalling. In a racing start against other not so compromised cars there was nothing in it. Where it did help was to make gearshifts much quicker with less stress on the drivetrain/synchros and balancing the car mid corner was easier.

Reducing unsprung mass has many other positive effects than engine rotating mass - to the point I'd say the link between the two isn't that great. For example, reducing engine rotating mass will do feck all to slow a car down but reducing unsprung will.

The reason why it won't show up on a dyno is that I suspect for a street car the difference is below the tolerance of the dyno to read (which can be a surprisingly large amount).
Granted it may not have any affect on crank hp however in terms of available power at the wheels it by definition must have an affect that can be measured.
Otherwise how do you explain magically accelerating faster with no increase in the effective driving force at the wheels?!?

I see. However I don't see where the 6 kg = 60 hp thing came from?

As for the dyno thing, I'm with you in logic. It's something I'd love to have explained properly to me.

[ArthurPE]

this is the equation for time to change pulley/flywheel speed, from N1 to N2 (N = N2-N1)

t = (0.003257 x N x W x R^2)/T
t in sec
T in lb ft = 300 lb ft
W in pounds = 10 pound vs 20 pounds
R in feet, 0.5, com of a flywheel
N in RPM, delta, use 4000, say 4000 to 8000 rpm

t (10 lb) = 0.11 sec
t (20 lb) = 0.22 sec

this is why it can't be measured, insignificant, now throw the weight of the car into it, 4000 lb vs 10 lb delta

another thing to note, although it only takes a fraction of a second to change the speed of the flywheel, this assumes instantaneous application of the torque
in a car ther is slip, inertia of the engine, response of throttle/control system
our car
0-60 5 sec or so
1st 4-8k 2 sec
2nd 5-8k 3 sec
5 sec for 9k rpm or 0.55 sec per 1000 rpm or 2.2 for an avg of 4000
the flywheel takes 1/10th of that, in the total load the engine sees the flywheel weight is miniscule

these equations can be found in the std handbook of mechanical engineering, they are used to size motors/pullies for mechanical systems

if we use brake disc, same 10 vs 20 lb, same 6" radius
assume 300 lb ft, gear ratio of 10: over all, so 750 lb ft per corner
speed change say 35 to 70 mph ~ 4000 to 8000 in 2nd or 400 to 800 rpm for the wheel
since rpm is 1/10th as much and torque is 10 times as much the time difference is 1/100th as much!
0.0011 sec or so
with no load, wheel on a jack, put the car on the ground and you are comparing <0.1 lb ft or so vs 750 needed to propel the cars mass