Any Feed back on the JHM light weight crank pulley?

[Teutonic Tuner]

Ok, devil’s advocate here with a few questions...

This thread was started by asking the question if a JHM part developed specifically for the S4 would work on the RS4 so let's keep it in context

If they spent so much on it, and it works for the B7 RS4, why don't they list it on their site? Is it because it hasn't been ‘fully’ tested on that specific engine and it would be 'at owners risk' if it was fitted and caused issues?

Not sure what the exact differences between the S4/RS4 engines are other than pistons & heads/valves, but would these changes affect the engine balance and require a different crank pulley to the S4? An easy way would be to find out if the OEM crank pulleys are the same on both engines…

I don’t think that anyone meant to slag off JHM by the way…

[PetrolDave]

Not sure what the exact differences between the S4/RS4 engines are other than pistons & heads/valves

The RS4 engine has a different bottom end to the other FSI 4.2 Audi engines to handle an 8250rpm rev limit, the S4 engine is closer to the Q7 4.2 V8 than the RS4 engine.

Oh and the S4 engine is indirect injection not FSI.

[ArthurPE]

I'm not sure whom you say I 'worship' that works for Ford, but they do not work for JHM, as you say they consult, but most companies like Ford restrict key personnel from outside work with non-competes and covanents
who is this wonder engineer?

JHM is shadetree compared to the dozens of PhD's at Audi with 100's of years of combined experience
why do you defend JHM so vigorously and attack all others? I have no vested interest in any tuner...you appear to have some...
this is not a US site, so in other words it is reasoned, and I have had differences of opinion with MRC and was not banned...and MRC did not attempt to ridicule or stiffle the discussion, they just presented their technical arguement, something you have NOT done...you try some logical bally-hoo, Audi MUST have left a bunch on the table (due to cost, reliability, whatever) which is only an assumption, logic would dictate if they did so, adding more would hurt relability and imply the cost to benefit ratio does not make sense for the mod...

the only way they could get 500 HP is by raising compression, displacement and powerband redline, or some combination,, not by bolting on ancillary do-dads

you are making cost rationalizations withot one technical proof that is is better, improves performance...and even if it may add afew HP (dobt) I bet that it offset by increased engine wear due to lessoned balance/dampening...I've done the rotational interia calcs for both at various rpm's and it's not even 1 HP of drag, or 1 lb ft of force to accelerate the difference...

perhaps the mass IS the factor, and they chose steel to get a higher density, smaller volume, for a given mass...less mass is probably detrimental in a SYSTEM balanced for a given mass
the cost of the pulley is not in the raw material but the manufactuer, it may be 10% of the total cost, and even if it is twice as much it is moot on a $5 device on a $70k car, especially if doing so added power...but consider, althoug aluminum may cost twice as much, you only need 1/4th as much, so material is a wash...

the 'new' car RS5 is not really any faster, and is a bit lighter, and the torque is identical, what changed is power because they raised the redline
P = T x rpm = 414 x 8200/7600 ~ 445, the rating of the 'new' engine, they did so by providing dual intake tract, so the engine won't be starved at the higher rpm

now you may ridicule me and call me clueless but you will not change my mind, I must assume your defense of JHM mods (or anyones similar mods) is for the benefit of others

arthur do you not know JHM's team? One of the members is one of those OEM engineers who you worship in your posts. He works at the performance division of Ford (SVT) and is able to help JHM with product development.

To say they are 'shade tree' is a ridiculous comment. I'd like to see you say that about MRC while you're at it...you'll be banned in all likelihood. Further, to say things like 'if it could be lighter/faster/better it would have been' and to say that JHM is 'out-thinking' Audi is missing a very important fact - Audi is constrained by budget, emissions, noise regulations, mass affluent general public need for a cushy car etc. They could have made the RS4 500 hp at the crank from the factory. They choose not to. They weren't out-thought by JHM. JHM just offered what Audi chose not to give us.

Your statement that if it could have been lighter it would, would imply that the car couldn't be improved upon from the factory. Ever bought 2 lbs of aluminium vs. 6lbs of steel? Guess what...aluminium is bloody expensive, especially when you're buying 20,000 lbs of aluminium vs. 60,000 lbs of steel. Want to talk about the 26 lb stock steel flywheel vs. the JHM 13lb lightweight flywheel? Again...'if it could be lighter it would'. Well...Audi chose to buy 260,000 lbs of steel for the flywheels rather than 130,000 lbs of aluminium.

Further, on performance, If Audi gave us all they could, why didn't they run the dual intake setup the RS5 and B8 RS4 got (and that they had already developed for the S6/S8 before the RS4, as shown below)? Why didn't they run 2.75" exhaust as JHM and MTM (MTM stands for Motoren Technik Mayer, started by someone you'd call a shadetree engineer...when in fact Roland Mayer was a long time Audi engineer). Why didn't they run forged wheels? Why didn't they run ceramic brake rotors as standard? And the tune that helped them develop an extra 30 hp at the crank on the newer cars from a similar engine with a dual clutch DSG and launch control in the tune? You really think Audi gave us everything possible, and that they can't improve upon the B7 RS4 engine as it was from the factory?

Not only could they have improved it...they did in the next gen. The new car is faster even though it's much larger and heavier. So what happened? Maybe...just maybe...Audi left a bunch of power/performance on the table with the B7 RS4 as they always do, knowing they would re-use this type of engine (NA 4.2 V8 FSI) on two more RS platforms that they'd need to sell from 2012 to 2014.

[ArthurPE]

for those who give a damn let's look at a very basic calc on the torque required to turn the pulley
say 1.5 pound vs 6.5 pounds at a centroid radius of 3" (0.25')
T = F x r
F = weight (lb force)
T = 6.5 x 0.25 ~ 1.6 lb ft required to accelerate the pulley provided by the engine torque (parasitic loss)
vs 1.5 x 0.25 ~ 0.4, so you MAY pick up 1.2 lb ft of torque or 0.3%
I'm guessing less since it looks like the alum piece center of mass is at a greater radius than the steel ones...
and the actual radius is likely smaller than 0.25, so less than 1 lb ft less torque is required to accel the lighter pulley at the same rate as the heavier

so the engine will deliver say 318 at the crank vs 317...will that make the car faster?
is it worth the cost and risk of tampering with the system?

steady state power, won't type out the calcs, assuming a pulley type flywheel (7800 rpm, 3" radius)
6.5 lb 1000 joule of energy required to spin it
1.5 300 joule or a difference of 700 joule, sounds like a lot
difference/savings is 700 joule = 0.00026075429 horsepower hour
it frees up fraction of a HP for an hour of operation at a constant speed
should raise top speed at least 1" per hour

[BlingBling]

arthur do you not know JHM's team? One of the members is one of those OEM engineers who you worship in your posts. He works at the performance division of Ford (SVT) and is able to help JHM with product development.

To say they are 'shade tree' is a ridiculous comment. I'd like to see you say that about MRC while you're at it...you'll be banned in all likelihood. Further, to say things like 'if it could be lighter/faster/better it would have been' and to say that JHM is 'out-thinking' Audi is missing a very important fact - Audi is constrained by budget, emissions, noise regulations, mass affluent general public need for a cushy car etc. They could have made the RS4 500 hp at the crank from the factory. They choose not to. They weren't out-thought by JHM. JHM just offered what Audi chose not to give us.

Your statement that if it could have been lighter it would, would imply that the car couldn't be improved upon from the factory. Ever bought 2 lbs of aluminium vs. 6lbs of steel? Guess what...aluminium is bloody expensive, especially when you're buying 20,000 lbs of aluminium vs. 60,000 lbs of steel. Want to talk about the 26 lb stock steel flywheel vs. the JHM 13lb lightweight flywheel? Again...'if it could be lighter it would'. Well...Audi chose to buy 260,000 lbs of steel for the flywheels rather than 130,000 lbs of aluminium.

Further, on performance, If Audi gave us all they could, why didn't they run the dual intake setup the RS5 and B8 RS4 got (and that they had already developed for the S6/S8 before the RS4, as shown below)? Why didn't they run 2.75" exhaust as JHM and MTM (MTM stands for Motoren Technik Mayer, started by someone you'd call a shadetree engineer...when in fact Roland Mayer was a long time Audi engineer). Why didn't they run forged wheels? Why didn't they run ceramic brake rotors as standard? And the tune that helped them develop an extra 30 hp at the crank on the newer cars from a similar engine with a dual clutch DSG and launch control in the tune? You really think Audi gave us everything possible, and that they can't improve upon the B7 RS4 engine as it was from the factory?

Not only could they have improved it...they did in the next gen. The new car is faster even though it's much larger and heavier. So what happened? Maybe...just maybe...Audi left a bunch of power/performance on the table with the B7 RS4 as they always do, knowing they would re-use this type of engine (NA 4.2 V8 FSI) on two more RS platforms that they'd need to sell from 2012 to 2014.

Agreed.

[adsgreen]

I'm somewhere in the middle...

I don't doubt for a second that audi have talented and creative engineers. But they don't have a monopoly and there's plenty of telented 3rd party independant engineers. That being said... there's plenty of talented engineer wannabees and sometimes it's hard to see through the crap.

Audi engineers like it or not are restricted by a budget - I bet they'd love to put in things that didn't make the final build but as with everything in life it's about compromise. They could have stuck the kitchen sink in and ended up with a 100k-200k RS4 that very few people bought. At the time they had to price it inline with the perceived main rival so it had to be M3 money (plus a small amount of wiggle room).

As for the new 4.2V8 - as arthur said, completely down to the minor jump in RPM limit. The twin airbox setup allows better breathing at high rpm but only realy made use at the new higher limit. The torqie is identical as the air getting in is the same.
I believe that Audi took the decision seeing how reliable the unit has been in the R8 and RS4 that some compromise on the contingency could be safely made as this gives an immediate boost in power for minimal expense. For an NA engine the rulle of thumb for the best way to increase headline bhp is to simply up the RPM limit. I've not seen the B8 chassis so don't know if there is some packaging issue from the B7 platform that restricted what could be put where. For example, the non FSI V8 with twin airboxes may have fit as there was space where as in the RS4 bay the FSI pumps and plumbing restricted the available space. I don't know if this is the reason and purely conjecture but shows there are limitations.

With regards to a LW crank pulley - the V8 in the RS4 really is an impressive piece of work (as is the BMW v8). Getting V8's to rev over 8k rpm reliably without using a flat plane crank is a real impressive achievement. With this setup balance is everything. Spinning a unit at 7k is considerably less demanding than 8.5k and may be a compromise too far. Not saying it couldn't be done but would need some good bench testing.

As for balance - as above, whenever I've gone this route I've had the whole assembly balanced as a unit. By that I mean engine out and in bits then the flywheel, crank pully, crank and clutch balanced as a whole unit. To me it's the only way to do it properly and it's very easy to replace parts that individually are "within a tolerance" but collectively be out enough to cause excessive wear.

For the crank pulley? Well, I've never had one done that increased power. It's very hard to be subjective as the one main effect I always used it for was improved throttle response. Personally, I don't think it adds much at all.
One point to bear in mind when considering rotating masses of the engine - there is a sweet spot to be had as although not so much of a problem with a v8, but certainly on an I4 the engine combustion pulses are relatively far apart and in the gap between them the engine is trying to slow down. The flywheel and other masses help store this energy reducing the drop off so you can actually lose some torque if you go too low (as I understand it). As above... it's all a compromise.

[sar]

I'm somewhere in the middle...

I don't doubt for a second that audi have talented and creative engineers. But they don't have a monopoly and there's plenty of telented 3rd party independant engineers. That being said... there's plenty of talented engineer wannabees and sometimes it's hard to see through the crap.

Audi engineers like it or not are restricted by a budget - I bet they'd love to put in things that didn't make the final build but as with everything in life it's about compromise. They could have stuck the kitchen sink in and ended up with a 100k-200k RS4 that very few people bought. At the time they had to price it inline with the perceived main rival so it had to be M3 money (plus a small amount of wiggle room).

As for the new 4.2V8 - as arthur said, completely down to the minor jump in RPM limit. The twin airbox setup allows better breathing at high rpm but only realy made use at the new higher limit. The torqie is identical as the air getting in is the same.
I believe that Audi took the decision seeing how reliable the unit has been in the R8 and RS4 that some compromise on the contingency could be safely made as this gives an immediate boost in power for minimal expense. For an NA engine the rulle of thumb for the best way to increase headline bhp is to simply up the RPM limit. I've not seen the B8 chassis so don't know if there is some packaging issue from the B7 platform that restricted what could be put where. For example, the non FSI V8 with twin airboxes may have fit as there was space where as in the RS4 bay the FSI pumps and plumbing restricted the available space. I don't know if this is the reason and purely conjecture but shows there are limitations.

With regards to a LW crank pulley - the V8 in the RS4 really is an impressive piece of work (as is the BMW v8). Getting V8's to rev over 8k rpm reliably without using a flat plane crank is a real impressive achievement. With this setup balance is everything. Spinning a unit at 7k is considerably less demanding than 8.5k and may be a compromise too far. Not saying it couldn't be done but would need some good bench testing.

As for balance - as above, whenever I've gone this route I've had the whole assembly balanced as a unit. By that I mean engine out and in bits then the flywheel, crank pully, crank and clutch balanced as a whole unit. To me it's the only way to do it properly and it's very easy to replace parts that individually are "within a tolerance" but collectively be out enough to cause excessive wear.

For the crank pulley? Well, I've never had one done that increased power. It's very hard to be subjective as the one main effect I always used it for was improved throttle response. Personally, I don't think it adds much at all.
One point to bear in mind when considering rotating masses of the engine - there is a sweet spot to be had as although not so much of a problem with a v8, but certainly on an I4 the engine combustion pulses are relatively far apart and in the gap between them the engine is trying to slow down. The flywheel and other masses help store this energy reducing the drop off so you can actually lose some torque if you go too low (as I understand it). As above... it's all a compromise.

+1 nailed it...

[RSKiwi]

I'm somewhere in the middle...

I don't doubt for a second that audi have talented and creative engineers. But they don't have a monopoly and there's plenty of telented 3rd party independant engineers. That being said... there's plenty of talented engineer wannabees and sometimes it's hard to see through the crap.

Audi engineers like it or not are restricted by a budget - I bet they'd love to put in things that didn't make the final build but as with everything in life it's about compromise. They could have stuck the kitchen sink in and ended up with a 100k-200k RS4 that very few people bought. At the time they had to price it inline with the perceived main rival so it had to be M3 money (plus a small amount of wiggle room).

As for the new 4.2V8 - as arthur said, completely down to the minor jump in RPM limit. The twin airbox setup allows better breathing at high rpm but only realy made use at the new higher limit. The torqie is identical as the air getting in is the same.
I believe that Audi took the decision seeing how reliable the unit has been in the R8 and RS4 that some compromise on the contingency could be safely made as this gives an immediate boost in power for minimal expense. For an NA engine the rulle of thumb for the best way to increase headline bhp is to simply up the RPM limit. I've not seen the B8 chassis so don't know if there is some packaging issue from the B7 platform that restricted what could be put where. For example, the non FSI V8 with twin airboxes may have fit as there was space where as in the RS4 bay the FSI pumps and plumbing restricted the available space. I don't know if this is the reason and purely conjecture but shows there are limitations.

With regards to a LW crank pulley - the V8 in the RS4 really is an impressive piece of work (as is the BMW v8). Getting V8's to rev over 8k rpm reliably without using a flat plane crank is a real impressive achievement. With this setup balance is everything. Spinning a unit at 7k is considerably less demanding than 8.5k and may be a compromise too far. Not saying it couldn't be done but would need some good bench testing.

As for balance - as above, whenever I've gone this route I've had the whole assembly balanced as a unit. By that I mean engine out and in bits then the flywheel, crank pully, crank and clutch balanced as a whole unit. To me it's the only way to do it properly and it's very easy to replace parts that individually are "within a tolerance" but collectively be out enough to cause excessive wear.

For the crank pulley? Well, I've never had one done that increased power. It's very hard to be subjective as the one main effect I always used it for was improved throttle response. Personally, I don't think it adds much at all.
One point to bear in mind when considering rotating masses of the engine - there is a sweet spot to be had as although not so much of a problem with a v8, but certainly on an I4 the engine combustion pulses are relatively far apart and in the gap between them the engine is trying to slow down. The flywheel and other masses help store this energy reducing the drop off so you can actually lose some torque if you go too low (as I understand it). As above... it's all a compromise.

I have to agree (with what little my Engineering knowledge allows me to understand and form an opinion with). ads well reasoned without the excesses of 'personality'.

[sakimano]

Good input all around. I'll just say this

1. Freeing up rotating weight helps the car accelerate faster. There's a reason forged wheels, light tires, lightweight flywheels and crank pulleys exist for just about every platform out there...and there' s a reason cars fitted with those parts accelerate faster. They free the car up from the burden that's upon them, and unsprung, rotating weight is the best burden to rid your car of (as long as it's done safely!). They're not adding power or torque to the engine's output...they're reducing the overall drag and power vs. weight that these cars fight everytime they move.

2. Audi most certainly did not give the car 'all they could'...and if Arthur believes that they gave it all they could other than diminishing return gains due to reliability, I think he's ignoring emissions, costs, and the most important factor, subjective feel for their target market who they were asking $70,000 or 55,000 pounds from.

Most people don't want a car that is touchy and loud and all the other characteristics of one that performs as best it can given it's engine...and when I say most people I don't mean people like us who join forums to talk cars. We're weirdos. Of the 10,000 RS4s sold, maybe 1000 owners have signed up on forums, and maybe 200 have posted more than 100 times. We're weirdos relative to the other 9000+ RS4 owners who don't pursue RS4 knowledge or performance in anywhere near the perfervid manner forum regulars do. I love a car with an epic exhaust tone like the RS4s with milltek downpipes/catbacks. Not everyone does though, and I'd be in the minority - that's a key fact Audi has to consider.

3. Saying they can't get 500 hp out of the RS4 engine without cranking compression through the roof is definitely up for debate. A few carbon clean, good running stock cars have dyno'd 320 whp at 034 motorsports in California for example. Do your math to figure out how to get that back to 420 peak crank hp...23.8% drivetrain loss. Two of those cars when running well with full 2.75" catless exhaust, JHM tune etc. dyno'd 360-370 whp. Apply your 23.8% drivetrain loss to that and you're at 472-485 hp. No raised redline yet. No intake improvment yet. I know it's not that simple etc. etc. however there's plenty left on the table for these cars and 500 hp is not ridiculous at all. Our cars fall off at about 7500 RPM. I shift at 7500 RPM when I'm running flat out. There's 500 rpm that could be making a good bit more power, and Arthur you touched on the RS5/RS4 dual intake design. There's certainly room for improvement there, but whether it's financially worth it in the aftermarket is up for debate. We know Audi knew this dual intake design would feed the engine well, as they did it with the other cars with some engine bay space.

The exhaust alone with 2 cats including one RIGHT at the end of the tri-y headers chokes the engine of the ability to remove damaging heat and evacuate the exhaust gases. Certainly not good for the motor (but requred by emissions). No x-pipe costs us valuable exhaust scavenging (but keeps the car nice and quiet for typical first time buyers...the ones Audi cares about). Neck downs in the catback to 2.36" also hurt flow (but preserve a refined sound). You don't think the Milltek guys on this site with something as simple as 2.5" downpipes with one high flow cat, and a 2.36" milltek catback with an h-pipe crossover are making power gains over stock? MRC has boatloads of dynos to show you the truth. These would do zero harm to the car...and would yield gains. Sounds incredible too...but again that starts to get a bit too loud for typical first time buyers.

None of this is damaging the engine if you eliminate the bad parts of the exhaust design...it just makes the car a little less refined/quiet and maybe not ideal for the well heeled buyers who had $70,000 or 55,000 pounds sterling lying around back in 2006-2008...the buyers Audi targeted when designing the car from 2003-2005.

[sakimano]

Not sure what the exact differences between the S4/RS4 engines are other than pistons & heads/valves

The RS4 engine has a different bottom end to the other FSI 4.2 Audi engines to handle an 8250rpm rev limit, the S4 engine is closer to the Q7 4.2 V8 than the RS4 engine.

Oh and the S4 engine is indirect injection not FSI.

Yes, the S4 is multiport, not FSI. In fact the the S4 (BHF) engine is not related to the FSI standard (S5/Q7) or the FSI high revving (RS4, R8 and the new version in the RS4/RS5) at all. Shares only displacement and cylinder count and I think displacement is actually only shared by rounding. Even the metallurgy of components is quite different.

It is the S5/Q7 that is the sister engine that shares the bottom end with the RS4, but the S4 engine is a second cousin at best.

Ok, devil’s advocate here with a few questions...

This thread was started by asking the question if a JHM part developed specifically for the S4 would work on the RS4 so let's keep it in context

If they spent so much on it, and it works for the B7 RS4, why don't they list it on their site? Is it because it hasn't been ‘fully’ tested on that specific engine and it would be 'at owners risk' if it was fitted and caused issues?

The B6/7 S4 4.2 (MPI) engine's crank is externally balanced and the pulley is incredibly precisely designed for that engine. NOT SWAPPABLE TO THE RS4 IN ANY WAY!

The OP didn't in fact ask that question, but I thought I'd clarify it just in case it wasn't clear. JHM has also developed a crank pulley for the RS4...I know 3 people who have them on their RS4. Like many of JHM's other RS4 products, they developed them over a year or two including extensive testing on their own RS4 (they bought one so they could test and develop parts for us).

They have sold their tune/exhaust/crank pulley etc. to a few customers who agreed to be part of the next stage of beta testing, but until they go full retail release with these products, consider them unavailable for now.

[ArthurPE]

the bottom line:
is the risk and cost worth the benefits?
risk: tampering with a balanced system (as was said, the WHOLE rotating system is balance, along with each component) not only for mass distribution, but total mass
mass has a dampening effect, less is not better when it comes to a asymmetric system (as opposed to say a symetric one like a wheel)

cost: not sure but install might take a few hours at least, it's pretty tight in there, lol

benefits, I think most can agree negligable, and most likely not measureable
definitely not measureable using on track timing, as shown above, can't be more that 1 lb ft or a fraction of a HP, shouldn't cost power but who knows. it's complex

I've come to the conclusion the only way to get substantial power on this car is the supercharge, then 500-540HP (crank) is realistic (not the 600 some are saying)
supercharging effectively raises compression ratio by stuffing more air into the same volume, ie, 1/2 atm of boost basically increases Cr by 50% and with it power
rule of thumb 1 atm = 100% power increase (assuming air/fuel/timing/charge cooling is matched) or 100/14.7 psi ~ 7% increase per psi of manifold pressure
but with a supercharger 30% is lost driving the sc, so 5% per psi is a better number (6% with a turbo)
put 5% of net boost using a SC on an RS I would expect ~ 414 x (1 + (5 x 0.5)) ~ 515 HP, now in these crazy days people will say that isn't a lot, but considering how fast the RS4 is stock, another 25% power can only make it faster, not to mention basically elevating the entire torque curve 25%

[sakimano]

I do agree the benefits are small, but on a platform where you can't just crank the boost to make gains, you need to dig to find acceleration improvements. A lightweight crank pulley and flywheel shave 18 lbs of rotating mass at the crank. That's a nice find.

These LW parts don't show up on the dyno...and a crank pulley isn't going to make you go 'wow!' but again, it's one of those 'every little bit helps' parts.

On my B7 S4 I had a JHM LWCP (-5.5 lbs), LW rotors (-20 lbs) and a tune/downpipes/catback. With the rotors, I noticed an immediate difference when pulling out of the dealership. The crank pulley was done with tune/exhaust so I honestly couldn't really comment on it. I had to trust it was helping. Same with intake spacers...I had to trust it.

if you don't trust JHM, you won't buy the crank pulley or intake spacers. There's a little faith you have to have that a part is helping when it's effects are small enough that you may not be able to discern a difference on their own.

As for cost, i agree there...the crank pulley for the S4 was $350. Install is something most of us can do in our garage to be honest so not so concerned about that...but it's about $200 if you can't. That's $550 for a very modest gain. I did mine because the front end was already coming off the car. It should be noted that I sold my JHM crank pulley after 2 years of use for $300 when I sold the car...thus it cost me $50 overall. Certainly worth it and that's something to think of. The up front cost of the part is significant but it doesn't lose value, thanks to no competition, and the fact it's not a part that will wear out.

[PetrolDave]

I do agree the benefits are small, but on a platform where you can't just crank the boost to make gains, you need to dig to find acceleration improvements. A lightweight crank pulley and flywheel shave 18 lbs of rotating mass at the crank. That's a nice find.

But will the lightweight crank pulley and flywheel actually make a noticeable acceleration improvement?

Or are they just about bragging rights?

[sakimano]

I do agree the benefits are small, but on a platform where you can't just crank the boost to make gains, you need to dig to find acceleration improvements. A lightweight crank pulley and flywheel shave 18 lbs of rotating mass at the crank. That's a nice find.

But will the lightweight crank pulley and flywheel actually make a noticeable acceleration improvement?

Or are they just about bragging rights?

JNAUT in Florida ran 12.84 @ 107.7 in his RS4 bone stock on 93 octane fuel (he was the stock record 1/4 mile time before I pipped him last month with my 12.75 @ 108.3). 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). That is pretty compelling.

Hopefully someone will chime in, but theory has it that a lb dropped of unsprung rotating weight is worth about 7 lbs of sprung weight dropped. So 18 lbs offers the acceleration gains of about 120 lbs of sprung weight dropped. If you want to test the accleration effects of 120 lbs, do a log in 3rd gear going full bore from 3000-8000 rpm and measure your time in vagcom. Then do it again with two 60 lb sandbags in your car. If you were racing a buddy, that's about a car length in a typical pull. Doing a pull stock against someone with just a LW flywheel and a LWCP would be interesting. Tough to find someone with that exact modlist as most who opt for the flywheel have done a clutch.

Considering we will have to replace our flywheel eventually (and our rotors etc.) if we can garner some acceleration gains out of these parts without sacrificing quality or braking performance say in the case of the rotors vs. stock, I'm all for it. On my B7 S4 I changed out the stock front rotors for JHM lightweight front rotors (10lbs lighter than stock each rotor = 20lbs) and as I said above, this you could actually feel. The car ripped through RPMs a little quicker. I log my car using vagcom and measure RPMs per second in 3rd gear WOT. To see how quickly it goes through the RPMs. The rotors were good for 20 RPMs/second gain (I believe it was 470 vs 490 rpms/second same day, done before and after the install). I was kinda shocked...I just needed new rotors so I grabbed those from a friend who was parting his car out, but the difference was significant.

[PetrolDave]

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.