Hey guys!!

Everyone seems to be using 15% reduction for SC...but why don't you use 19% SC? doesnt 19% give you more boost? what would be the pros and cons for having 19%??

Please teach me~

 

Search, there are many threads on this. I think those that favor 15% believe it is optimal from a reliability standpoint, no change in belt, can point to the JCW pulley for warranty justification, and possibly closer to optimal efficiency when it comes to the temperature of the compressed air relative to volume.

 

Something about water pumps or whatever.

mb

 

Depends on what you intend to do also. For us track rats 19% does not play well when you live in the upper range of the rev counter. See above.

There have been multiple discussions on this, search is your friend.

 

I've read on NAM about the 19% burning up the SC. do a quick search and you'll pull up a ton of threads

 

I just discovered that if you do a search for "Do a search on NAM", 3 of the top 20 or so results are threads entitled "which pulley?" or "choosing a pulley"

 

1. If you track or spend a lot of time in high revs you can get the oil too hot

2. More prone to belt snaps lose the belt lose your cooling you're riding a flat bed until you get a new one.

3. Prone tobelt slippage even with a smaller belt.

4. Need to for other mods, ECU injectors

5. Search shall set you free

 

Agreed, do a search as there have been tons of threads and almost as many opinions on this topic.

In short, it's all about what you are looking for and what the duty cycle is for the car. For example, the vast majority of my time is spent driving back and forth to work, 90+ mile round trip on rural highways with speed limits between 45 and 60mph, so most of my miles are spent in 5th or 6th gear at low rpm. On the weekends, I autocross and run it up to the 7300rpm rev limiter if the course calls for it. That amounts to seconds at very high rpm. I find the increased mid and low range power of the 19% to be beneficial while autocrossing, and more pleasant putzing back and forth to work. I don't do track days. At this point, I've got over 112,000 miles on the car / clutch / supercharger. A 15% pulley was installed at 33,000 miles, and swapped to a 19% about 10,000 miles later. That makes roughly 69,000 miles with the 19%. I've never broken a belt (replace them every 9-10 months as preventative maint.) or had any other issues related to the pulley.

Others with different duty cycles or less carefully installed pullies will have different results. IMO, getting the pulley lined up is a VERY big deal for belt life.

Scott
90SM

 

I got the 15% because I am pretty sure I couldn't handle the 19%.

dan

 

To small of a pully on a roots type charger is inefficient, due to heat gain. At low rpm's the 19% produces more power, but, at higher rpm's the 15% actually produces more power. Couple that with water pump cavitation and reducing the life of your charger to 65,000 miles. not really worth it to me.

 

Love my 19%, I autocross my car 10 times a year and do a few DE's. never had a problem or belt break. But you do need to take into account ECU and injectors. 19% = grins for me as I pass modded mustangs.......

15K on 19%
6K on GIAC and injectors

 

here is more reading then you ever wanted on 19% pulleys.

https://www.northamericanmotoring.co...ght=19%25+GIAC

enjoy!

 

i was told by minimainiauk that the M45 starts to become inefficent at 13psi and above!!

Chris.

 

Also here is more info
http://store.webbmotorsports.com/ind...in_page=page_3

I'llseeif I can find the WRR from waaaaaay back that covers it as well.

 

Well, all positive-displacement superchargers have a pretty steep dropoff in "power increase per pound of boost" as you increase the boost. As a result, I don't know that it's possible to draw a "line in the sand" as to exactly *when* they become "inefficient".

It's amazing just how much power the supercharger itself takes to turn it once you start to raise the boost.

One of my supercharger design books talks about an engineer that set up a test rig where he had an engine on a stand, driving a Roots-type supercharger on a different stand, connected via a belt. The supercharger discharged into a chamber so that the engineer could control the pressure in the chamber to see how much power it took to drive the supercharger at a particular boost level.

The engine he originally used to drive the supercharger was a pretty stout Chevy 350 small-block, but when he tried to raise the supercharger boost over about 20 psig, the Chevy 350 locked up - it flat-out couldn't turn the supercharger. He had to build a 454 big-block to continue the test.

I don't remember the exact results, but at 20 psig of boost, it took something like 500 horsepower just to drive the supercharger. Of course, the increase in engine power is more than the power required to drive the supercharger, so you still get an overall power increase.

 

you right mate, i was just trying to ilistrate at a point (give to me not that i have worked out myself) the M45 'charger starts to drop in efficency. and im sure its alot lower than most think!

its the same problem with the turob guys. people think that simple runing the turbo or 'charger harder will make more boost. it will but are you actually moving more air???????

you reach a point where you are not moving any more air just heating the air more. this is when you REALLY need to look for a BIGGER power adder!

alternatively if you are still in the RPM limits of the blower (ie you are not over spinning it) then you could look at ways to reduce presure! things like porting the head, fitting a very effective exhaust and fitting a more effective (not just bigger) intercooler or charge cooler might actually reduce to boost but increase power!

thanks Chris.

 

If the supercharger is going to die at 65,000 miles, please don't tell mine that it is way,way overdue! Having run both 15% and 19%, there is a noticable increase in low to mid-range power with the 19%, but not an obvious difference at high rpm between the two. I'm not arguing that the 15% doesn't have the supercharger running at a speed at which it is more efficient when the engine is at very high rpms, just that it isn't obvious from the driver's seat. Calling a Roots blower efficient at any rpm is sort of stretching it anyway. Don't forget that a 15% pulley can spin the supercharger just as fast as a 19%. It just takes a few more engine rpm to do it.

The reason that some people may see more belt problems with smaller pullies is a function of belt wrap and the subsequent amount of load applied to the belt. A much bigger impact on belt life is how accurately the pulley was aligned with the rest of the belt drive components.

I've also seen absolutely no indication of water pump cavitation, but again I do not spend prolonged time at high rpm the way a road racer would. My oil and coolant temperatures stay very, very reasonable and at almost 113K miles my engine is doing just fine by all external indicators.

As I posted above, it is all about duty cycle and how an individual car is used. On something as complex as an automoblie, saying that any part will last X miles for everyone just isn't remotely accurate.

Just for the record, for those that don't already know, engine durability testing and development is my profession. We have direct access to more analysis and testing tools at work than any of the MINI vendors do with the possible exception of BMW, and if it is engine driveline specific (as opposed to the rest of the car) I suspect we have BMW beat pretty soundly too. It's a shame I can't put my own engine on the test stands, though I have brought a few other parts in for failure analysis by the metalurgists, like suspension parts.

Scott
90SM