Well, i am pretty sure they are right. I normally trust what other people post, but when i was calculating the 23% pulley i started to figure out the graph was wrong. I was somewhat leary about the original numbers so i grabbed a stock crank pulley and measured it and came up with was posted above.

With 19% customer we have always told people to stick to the stock redline, no higher. The problem with this is most all the chip tuners let the thing rev to 7500. This is way to high! Again, we need our own user tunable ECU so we can lower it ourselves.

As with anything the more you spin it, the quicker it will wear out. The JCW car obviously tuned their SC to be right on the edge of the SC redline, and it is a 100k car.

 

Could someone with strong math skills please re-calculate the engine redline (relative to the SC redline) for the -15%, -16%, -17%, and -19% combinations (Crank & SC Pulleys)?

 

some clarification might be in order here.

That graph is a least a couple of years old and the crank pully used was stock. The M45 Redline was obtained by Randy from Eaton and as far as I know the 17200 rpm number is accurate.

The stock SC pully allowed for the engine redline to be set to well above 8000 without redlining the SC (obviously there are other concerns about the engine redline but the SC would not be the gating factor until over 8k).

For every other SC pully mentioned the engine redline was adjusted such that both the engine and the sc hit the redline at the same time.

hope that helps

Chuck

EDIT: Ok I worked through the number from that graph and I too get some discrepencies. It does look like the crank pully size used was about 5.16 but it varies (I assume there was some rounding done). soon as I get out of the fab I'll do some more numbers

 

Isn't redline 6800 rpm?

 

So are you saying that the redline (maximum safe rpm) would be the same for a modded car with a -17% SC pulley and a modded car with a -15% SC Pulley & a +2% Crank Pulley?

 

Alta,

I have something for you to calculate. What would be supercharger redline with at 21% reduction?

As far as dyno testing goes... Wouldn't there be a larger margin of error if you were to go as far as tune for each setup? I would think it is difficult to tune everything perfectly for all the different combinations.

If I was going to do any dyno testing it will be the following: 19% vs. 23% or 21% with GIAC and JCW injectors. However the GIAC is tuned for the 19%. Does anyone see any problems with this?

 

Here are numbers on the M45 from another source:

http://www.lightweightmiata.com/sc/sc.htm

 

This math is pretty easy! Is it really the case that you all can't do it yourselves or is it just easier to ask someone else to do it?

Matt

 

If the stock SC pully has diameter of 2.565 and the stock crank pully has diameter of 5.48 and the SC redline is 17200 (all numbers are now suspect in my mind)

This is what I get for engine redline

........stock ...2% ..5%
stock 8051 7893 7667
-15% 6843 6517 6517
-17% 6682 6551 6364
-19% 6521 6393 6211

that was done simply by multiplying the pully ratios by the redline of the SC.

Its been awhile since I've had to use my brain for anything so if someone wants to check my simple math please feel free.

Chuck

 

totally correct. But I couldn't read the numbers because of formatting.

So, for the math challenged.... This is Engine RPM at SC redline...

(Crank RPM @ SC Red Line) = ((SC Pully Diameter)/(Crank Pully Diameter)) times 17,200 (SC RPM at Red Line)

Here's the chart another way. If you run the Mini at 7000 rpm, the SC will be running at.....

sorry, the editor choked on the charts. So I've attached a graphic.....

so, if you run a 21% reduction sc pully, and a 5% oversize crank pully, remember to order a spare SC, and don't forget the larger injectors!


Matt

 

Math-challenged: Thanks! I really appreciate this!
Reading-challenged: Think you could take one more swing at the formatting?

 

When I pasted into the editor, everything was so pretty. Then I saw the post. I had it almost all edited by hand, and then I hit the back button by mistake and lost all the edits. I finally gave up and attached it as a jpeg!

Call me computer challenged!

Matt

 

cdconsor & Dr Obnxs: Thanks for running the numbers for us. (And for being good natured enough to take a little ribbing, Dr Obnxs. )

Now for the next question, which combination will yield more "under the curve"? I suppose this is where emprical data is required. But is it possible that you could use your vast powers of reasoning and analytical thought to theorize? (Yep, you got me. I'm still using flattery in a blatant attempt to get someone else to do the work )

A comparison of the power produced by varous combinations prior to the adjusted redlines would be quite interesting indeed. I suspect that in the end it will come down to how the car will be driven. For example, a car that is driven only on the street might get by nicely with the extra power produced by overdriving the SC a bit more. Whereas a car that is driven on the track might need the extra revs.

Ya know, when I say it like that it doesn't sound like new information at all, does it?

 

That isn't an easy calculation. It may even take less time to bolt on all the hardware and dyno to find out! Even if you could get the boost and temp out of the SC just from it's RPM, the IC efficiency is a function of car speed. The filling of the cylenders is a function of manifold pressure and RPM (and other stuff I'm sure), and the power per spark is a function of so much stuff my head starts to spin! that isn't just algebrea, but it's fluid dynamics, thermodynamics, materials science and a whole lot of CPU! That being said, there is engine simulation software around that can do a very good job. I don't have it and don't know what it takes to get proficient at it, but I'm betting a parts vendor who gets it and gets good at using it could have quite an advantage in designing power adders......

But for beyond the table, this isn't your day....

Matt

 

Well, OK.

It's been a good day all the same. Thanks for all the useful info.

 

I know my numbers got posted on the page before this one, so they may have been over-looked.
eMini,
I know you had a wink but what was it that you douted? It took the Dr. for people to listen?
This is what i posted as an average.

15% 2.511 Ratio and SC RPM of 17600
17% 2.57 Ratio and SC RPM of 18000
19% 2.63 Ratio and SC RPM of 18400
23% 2.77 Ratio and SC RPM of 19400

Sorry i just feel like i was left out ...


Anyway, the area under the curve is really easy to find out when on the dyno. Next weekend or mid week we have a customer that we are installing a bunch of parts on his car while on the dyno and of course one is the pulley. We will have time to swap out to a larger pulley and do a 23% combo. We will go from the 19% to the 23% and calculate the area under the curve. Should be very telling if a higher boost lower engine redline will have an advantage over less boost higher redline. Fun times to come!

 

Oh yeah! Finally have anticipation for something new. Please post dyno graphs! This will deffinately determine what I spend a little bit of money on.

 

hehe... well the redline you are right it is 6800 but i actualy ment rev limiter.

Frans got mine below stock. i hit it ones and that why i know its some where between 6800-6900

but by lowering the Revlimiter you also lower the red line


By the way ALTA2, i did not overlooked your number but to be honest it scares me to look at them...
i have like i said the 19% and the light weight crank pulley... do you personaly feel like i am abusing my blower?
becuase if i am... i think the 19% pulley and 2% crank will without a dout make you change blower very often...

 

Please forgive me, but you misunderstand. I didn't miss your post. And, I didn't doubt it. To the contrary, I took it as fact. You posted the SC speed at an engine speed of 7000 rpm with a variety of SC pulley sizes.

What I wanted was to see adjusted redline values for engine speeds that would keep the SC at or below its redline. And because my math muscles have gotten very weak, I persuaded others to perform the calculations using combinations of crank pulleys and SC pulleys.

And when I posted: The reason it didn't sound like new info was because you had already posted: Rest assured, I heard what you said, and I believed it. I was just looking for a little more info. And, looking back on it now, I think repeating much of what you said, may have helped to crystalize my thinking a bit.

Though the education I'm getting is cool, my interest in this subject is not simply academic. When I read your announcement of an overdrive crank pulley, I was immediately attracted to the idea of getting -19% effective rate w/o the belt slip & tensioner issues. Furthermore, I really like the idea of shifting the torque curve lower into the rev range.

The testing you're talking about performing sounds very promising. Selfishly, what I'd love to see is a comparison of a -15% SC pulley and a -17%/+2% combo. I don't think I'm brave enough to go beyond 19%. Though I understand the principle that by adjusting the redline downward, you can produce more boost earlier without endangering the SC. And, by installing a larger/more efficient intercooler to compensate, there is a possiblity of more area under the curve, even with the reduced redline.

As you said, fun times to come.

 

Well with all this SC over driving stuff going on, and this weekend we confirmed the 4% crank pulley works, who is going to be the first with the 23% reduction!

eMini,
No worries, it was supposed to be kind of a funny anyway. Over the next couple of weeks we are doing some dynoing of the crank pulley/SC pulley combos. We will absolutely post graphs of a 15% pulley 17% pulley, and 19% pulley, all with area under the curve and theroetical engine redline. We too are excited.

 

Cool

 

...if air is compressed it heats up. Now, I'm not a scientist - read disclaimer below - but, by this point in our evolution we should be able to determine a given heat value for a given amount of compression. I realize we can find out via the dyno, But wouldn't a more educated first step include a compression/heat calculation as a way to point to a pulley/crank combo that might reach a point of deminishing return?

 

Michael, on this note I will mention that the Alta IC and the M7 hood scoop (modified) makes a lot of nice coooool air.

 

There's a lot that goes one here. For instance, leakage would need to be known. And this would be a function of SC RPM, ambient pressure, and manifold pressure. Also, the degree that the air heats under compression isn't really described by an ideal case (which would be called adiabatic compression, where the walls of the compressor are taken to be perfect insulators). anyway, it's a messy calculation. I'm sure that Eaton has nice curves to show boost and temp as a function of SC RPM, maybe even for a range of ambienter pressures etc.

So when it comes down to all this, it gets messy fast. Hence my earlier post about just bolting on the combos, and tuning for max power. Short of real, high end engine simulation software, testing will be the fastest way to get the numbers.....

Matt

 

Onalsed,

Do you mean that you had to modify the M7 scoop as well to accommodate the Alta IC and optimise performance? Please elaborate since I am getting a M7 scoop very soon :smile:

Henry