Pully Clarification

[Ilikemike]

I've been thinking about an underdrive pully kit for my 2013 M3 but have heard that BMW engineers have designed the M3 to shut off accessories during hard sprints..... essentially nullifying the advantage of having a underpully. Does anyone know for a fact that this is what BMW has done?

[coloradoe92m3]

During full throttle your car shuts down a/c and alternator. Still drives power steering and water pump. Things you really in my view don't want underdriven. Pulley's have never made sense to me given the biggest drag of the alternator and a/c is not a problem in full throttle but everyone has an opinion

[Ilikemike]

So, the numbers I'm seeing in terms of HP and TQ from the manufacturers of the UDP's should be increases in comparison to a functional (shut off's engaged) BMW engine on full throttle?

[momo3605]

Originally Posted by Ilikemike

So, the numbers I'm seeing in terms of HP and TQ from the manufacturers of the UDP's should be increases in comparison to a functional (shut off's engaged) BMW engine on full throttle?

The 10 or 11 hp are produced from underdriving the power steering and water pump, or whatever is actually underdrived. Those are real world dynos, so those gains will be correct.

My question is, do you also gain hp when you're on partial throttle? I imagine you'd get more power on partial throttle since AC and alternator are not shut off? And if not, then you should at the very least still get some additional power from underdriving the power steering and water pump.

[FogCityM3]

I datalog extensively and have the electronic performance steering wheel. Temperatures post the pulley (I have the Dinan which is the most aggressive) barely budge (1-3 degrees if even that) on the track for both coolant and oil. Highest oil temp I've seen is mid 240s and coolant at about 195-200. The only thing I notice is that you have to run the AC slightly cooler in normal driving and on cold start the car is actually smoother with the pulley. Granted, I have not tracked in above 80 degree weather up here, so maybe its different if you run in extremely hot temperature climates.

[coloradoe92m3]

Its well documented steering gets ennaturally heavy and coolant temps rise. For 3 ho not with it

[FogCityM3]

Not to get drawn into the Longwong Tit-For-Tat exchanges, but for the potential benefit of those considering a pulley, didn't notice heavier steering at all.... actually had to get the bpm servo done to even notice a difference for me personally. Also, as I said my own logging differs from assertions of significantly higher temperatures at least where I live/track. 8-12 bhp gain is also well documented, and cited and tested by Dinan (whom I would believe a lot more than someone with 10 different usernames and 9 prior bans).

[Vic311]

Pullies are probably the most overrated mod, second only to air scoops.

[momo3605]

Originally Posted by Vic311

Pullies are probably the most overrated mod, second only to air scoops.

Why would you say that? 11hp for $300 is pretty cheap power...

[Ilikemike]

Agreed, $27.00/hp is cheap....

[SenorFunkyPants]

Originally Posted by momo3605

Why would you say that? 11hp for $300 is pretty cheap power...

I would interested to know where the 11bhp comes from....anyone can put up a dyno graph to show whatever gains they like, doesn't make it so. I read up about the bhp consumption of water and power steering pumps a while ago and there isn't a 11bhp gain to be made even if you disconnected them both completely. Removing a water pump and replacing it with an electric one run off its own battery gave a saving of ~3 bhp and using an electric power steering pump would save ~4 or 5 bhp.
A 20% underdrive of those components isn't going to give you much.

[pbonsalb]

I have run a pulley for a couple of years. I have not noticed higher coolant temps, but I have also not tracked the car or datalogged. Any difference in steering feel is very slight. The only change that I definitely noticed is that the AC underperformed slightly at the same setting, something easily remedied by turning it up.

I have seen dynos over the years that show gains from just a pulley. I'd like to think they are accurate. Dinan tests parts it sells, and it sells a pulley.

Some say an intake does nothing. Some say a K&N filter is bad for your engine. Some say a rear exhaust does nothing. You have to sort through the claims, do what research you can, and buy the mods you are comfortable with.

[Ilikemike]

That's still a question I don't think has been answered (seniorfunkypants).
If the measures are taken at the rear wheels with the same car, with the 'disengagement of accessories' (claimed to happen under full throttle (on this forum)) then it seems any differences in hp/tq are likely 'real'. But if the measures are made at the flywheel then how do you know that the stock engine is running as it normally would, i.e., are the switches that control the disengagement of the car's 'accessories'.. being turned off. I'd hoped one of the retailers would have explained how the readings were taken but no luck so far.

[happos2]

Originally Posted by coloradoe92m3

Its well documented steering gets ennaturally heavy and coolant temps rise. For 3 ho not with it

Well I shall document otherwise. I am not trying to justify my pullies, however, I have never noticed unnaturally heavy steering since adding the pullies. I have seen comments both ways on almost every single pulley thread created.

Can't comment on the cooling though as I have never data logged nor done a back to back test.

[tom @ eas]

Originally Posted by Ilikemike

I've been thinking about an underdrive pully kit for my 2013 M3 but have heard that BMW engineers have designed the M3 to shut off accessories during hard sprints..... essentially nullifying the advantage of having a underpully. Does anyone know for a fact that this is what BMW has done?

We posted a short article on pulleys here a while back that breaks it down:

Bang for the Buck Mods: Macht Schnell UDPs & Dyno Findings
http://www.m3post.com/forums/showthread.php?t=649151

Hope this helps.

[regular guy]

Originally Posted by coloradoe92m3

Its well documented steering gets ennaturally heavy and coolant temps rise. For 3 ho not with it

I was thinking now would be a very good time to ask for "Data & Concrete Proof Over Everything."

Originally Posted by FogCityM3

Not to get drawn into the Longwong Tit-For-Tat exchanges, but for the potential benefit of those considering a pulley, didn't notice heavier steering at all.... actually had to get the bpm servo done to even notice a difference for me personally. Also, as I said my own logging differs from assertions of significantly higher temperatures at least where I live/track. 8-12 bhp gain is also well documented, and cited and tested by Dinan (whom I would believe a lot more than someone with 10 different usernames and 9 prior bans).

I guess I wasn't the only person to notice the new persona.

[Vic311]

Originally Posted by SenorFunkyPants

I would interested to know where the 11bhp comes from....anyone can put up a dyno graph to show whatever gains they like, doesn't make it so. I read up about the bhp consumption of water and power steering pumps a while ago and there isn't a 11bhp gain to be made even if you disconnected them both completely. Removing a water pump and replacing it with an electric one run off its own battery gave a saving of ~3 bhp and using an electric power steering pump would save ~4 or 5 bhp.
A 20% underdrive of those components isn't going to give you much.

It comes from cleverly crafted marketing material which dupes gobble up.

No way a pully is giving up gains of 11HP.

[regular guy]

Originally Posted by Vic311

It comes from cleverly crafted marketing material which dupes gobble up.

No way a pully is giving up gains of 11HP.

This was the first, and may still be the most relevant (and independent) test done on a pulley. The pulley was the only mod since baseline. Best of all, was done on a Dynapack which would be the most reliable dyno for this type of test as well. FYI: Dinan uses Dynapack as well.

Gain: 9 hp.

http://www.s65dynos.com/showDyno.php?recID=15

[Ilikemike]

Thank you 'regular guy,' that's what I was looking for!

[momo3605]

That's 9 whp too! At the flywheel that's closer to 15hp or so

[SenorFunkyPants]

So if a 20% underdrive pulley is worth ~15 bhp at the flywheel what would a 100% underdrive be worth? 75 bhp?

[dereksM3]

Edit: Not worth the debate.