newguycls55

I am moving forward with some engine mods. I've heard different things about 172mm vs 180mm pulley kits.
Can someone knowledgeable go over with me the difference? and also the reliability of each? I've heard 180mm is not for daily driver, and 172mm is much more reliable, is that correct?

dyno

the bigger it is, the quicker you get overheating issues you then have to cope somehow ... except you need it only for a one fourth mile run or you live in a very cold area

you can find a lot on this subject by using the search function. you will also find a naive table showing a supposed relation between pulley dia and HP increase

about two years ago the question was deeply discussed and the consensus, at that time, was for a pulley close to 170mm as the best option .
...today it's moving forward
btw,

jmf003

+1 on the suggestion to search. There's a ton of good information already posted.

A larger pulley increases the supercharger's boost more than a smaller pulley, but you already knew that. This thread has a good description on the amount of boost relative to pulley size: https://mbworld.org/forums/w211-amg/...ize-boost.html.

All things being equal more boost makes more horsepower. The problem is our cars have load limiters built into the ECU and TCU. If you exceed one of the load limiters the ECU will reduce power output. The workaround to this constraint is ECU (and sometimes TCU) tuning to increase (or even remove) the load limiter.

More boost also makes more heat. Too much heat in the air intake will also cause the ECU to reduce power. The workaround to this constraint is to increase the capacity of the intercooler cooling system.

If you ensure that limiter and cooling are not constraints then a 180mm pulley will make more horsepower than a 172mm pulley.

Would it really be less reliable than a 172mm pulley? If you did a full bore statistical analysis it's likely the MTBF (Mean Time Between Failure) is lower for the bigger pulley simply because it's making more power but I doubt the difference would be noticeable over the normal life of a car. I have no qualms about running a 175mm VRP pulley on my car.

dyno

if you disagree with something else I wrote, you can tell me explicitly..

jmf003

I'm not following you here.

I used "+1" to explicitly agree with you about the value of searching for extra info.

I don't particularly disagree with anything you wrote and my comments are generally similar to yours with respect to cooling.

A Robinson

If you increase the diameter of the crank pulley then the blower spins quicker which creates more boost. More boost more HP correct? However we have no idea what PSI this represent becuase nobody puts a boost gauge in their cars. Not even the tuners which i find odd. Obviously the stock blower is only going to flow but so much air. I would like to know how much boost can be ran on pump gas using the stock blower and fuel system. Also what size pulley is needed to achieve this boost level.

Best,

A Robinson

If you increase the diameter of the crank pulley then the blower spins quicker which creates more boost. More boost more HP correct? However we have no idea what PSI this represent becuase nobody puts a boost gauge in their cars,which i find odd. Obviously the stock blower is only going to flow but so much air. I would like to know how much boost can be ran on pump gas using the stock blower and fuel system. Also what size pulley is needed to achieve this boost level.

Best,

dyno

sorry, I misunderstood that our common thinking was only the value of searching !
LOL

dyno

your last question is more complicate but again, you can find alot of info through search.

Summing up, first thing you must have an accurate view at this chart.





Let's try to do the homework together :
with Stock pulley we are at about 62% efficiency, with the blower running at about 10K rpms (at engine redline) and a discharge air temp of 100+ degrees C.
Max allowed blower rpm is declared at 13,500rpms, with a max pressure of 2.2 times the natural pressure. therefore it is 2.2-1 = 1.2BAR

we know that Stock SC pulley is about 91mm;
- stock crankpulley is 151
therefore Ratio is 151/91 = 1.659 ratio
.. meaning that at engine redline of 6500, the blower will run at 10,784rpms

the result you are looking for should be 13500/6500= 2.07 ratio
therefore the theoretical max crank pulley is 2.07x91= 188mm
and you get 1.2BARs of boost.

obviously, it depends on where your engine limiter is at ! ... a 7000rpm engine limiter would allow a maximum of 175mm crank pulley


but, keep in mind there is a reverse relationship between efficiency and boost level, as the graph and common sense suggest ..


personally I prefer to obtain the power more from inside the engine than from outside (the blower)
.. but this is only a matter of tastes ..I like so much high revving engines

newguycls55

Wow. the response is very detail and very technical. which I am completly lost.

Can I get the pulley kit without ECU flash or Tune? how much power would I gain with only Pulley kit. and no flash, no tune, no heat exhange.
and what are my risk or downside to just Pulley upgrade. (include new water pump pulley)

jmf003

I had the VRP 175mm pulley installed without an ECU tune and immediately ran into the load limiter. As a result my car was no faster with the 175mm pulley than it was with the stock pulley. I then got the VR600 ECU tune and the car became MUCH faster.

The bottom line is, you need an ECU tune to get the benefit from a larger crank pulley.

Cooling is a bit more complicated. A larger pulley generates more heat in the intake but it's only a problem when the temp reaches/exceeds the overheating threshold (140F?). Depending on a bunch of factors including ambient air temperature, the stock heat exchanger setup on your CLS, and other factors such as how hard you run the car, you may or may not need additional cooling.

You can always add cooling later so there's no risk in trying to get by with stock cooling. That said, your car will run stronger in more diverse conditions if you upgrade the cooling.

dyno

JMF, 140 deggree in graph is Centigrade.
but this Temp is before Intercooler work ..

NEWGUY, the graph is surely complicate but it's enough for you to read what I typed below it.


replacing a pulley is not a great job and also the cost should be affordable from anybody sitting into a car like this ..
therefore you can simply try what you thing better, you make your errors .. you learn and maybe you will later on do something different.

what I can tell you is that after my "small" 161mm pulley (that equals to about 166mm total diameter, depending on the dimension of the outer rim. id est, the same dimension as the first Renn and Klee pulleys, think), and everything else stock, I felt the car stronger .. maybe to its limit without stepping to a tune, to an exhaust work, etc....

but, again, this depends to some extent to each one's tastes: in general I don't like so much Forced Induction engine's behaviour: I really hate the lack of low end in turbos; this car was my first experience with Kompressor and must say that I appreciate very much the help that the kompressor gives at low till mid ... IMHO, trying to put a jumbo pulley into a Kompressor is like trying to transform it into a Turbo .. and, simply, it does not work ... too much parasitic power loss !

so, in conclusion, if you go bigger than 161/166 (ID/OD), be prepared to go further on along the mods' chain ..

best

A Robinson

A properly sized turbo will make more torque, more horse power, and reach its target boost level quicker than a comparable sized supercharger "every time"

Best,

dyno

for example.. 911TT or Mitsu ?
suggest me one with those characteristics, able to rev till at least 7000 rpm stock, and it will be my next car


... or maybe next AMG 55TT with M278 DE55LA motor



it's a pity that the SLS will still have the 63 ..

A Robinson

I love the 63 for its simplicity and power. However im a forced induction freak

MJ50

use RENNtech, VRP or ASP pulley kit and u'll be fine for daily driving...

Simon @ evosport

I would personally not use any pulley that is just a modified factory pulley or a pinned on enlargement.

But to your question, 175mm seems to be the magic number. We've tested larger pulleys and while theoretically it should make more boost, the car does bleed off the excess boost so there is no realized gain. So bigger pulley does NOT mean more power. There may be other downsides to larger pulleys if not addressed, like additional heat buildup, etc.

jikjak

wont u get more hp and tq with a 180mm pulley if u upgrade the cooling system?

whats the most boost we can hold and how can we make the car hold more if it starts to bleed boost?

dyno

I keep one of these on my furniture like a fine piece of engineering ... springs and clutch inside ... really beautiful, it's a "Master of Complications"

.. btw, this is what I call "169mm" pulley because 175 is its OD

Simon @ evosport

Not with regard to the issue of boost bleeding. Our Kompressor Cooling Upgrade (KCUP) maintains power that otherwise gets lost when heat soaking is an issue.

Our tests have shown that there is no real value to a 180mm pulley. With a smaller and larger pulley test, we can measure the boost on the dyno with no change in boost or realized power. With regards to controlling boost, you would need to control the actuation of the valve. Again, there may very well be downsides to overboosting the motor.

Simon @ evosport

Speaking of complications, I have a version I wear on my wrist

dyno

except chrono, the only complication I ever desired was ... just to stay on topic ...

the STAR WHEEL




... a kind of Salterello

AMGSC

I read that the Kleemann Autorotor can run up to 26psi so do you think it is realistic to install a 172mm crank pulley with a 60mm SC pulley to achieve 26psi or 1.87 Bar on a reinforced/rebuilt engine?

jikjak

so 175mm is the biggest size the pulley should be?
is a cooling upgrade still required for a 175mm pulley?

what kind of gains can i expect from going from a kleeman 168mm pulley to a 175mm pulley?

MJ50

yes