Some of your numbers are off. You have: Stock Crank Pulley : 74mm S/C - - Ratio = 2.0270, this ratio gives stock crank pulley at 150mm, but stock pulley is 155mm, so 155mm/74mm = 2.094 Ratio.

That changes some of your numbers.

So for a stock 155mm pulley, S/C pulley would need to be reduced to
64.4mm to equal the boost of 178mm Crank Pulley running @ 6,200 Engine RPM (155mm/2.4054 = 64.4mm)
63.4mm to equal the boost of 181mm Crank Pulley running @ 6,200 Engine RPM (155mm/2.4459 = 63.4mm)
62.0mm to equal the boost of 185mm Crank Pulley running @ 6,200 Engine RPM (155mm/2.5000 = 62.0mm)

This also means Stock Crank Pulley (155mm) would need a 51.6mm S/C Pulley for MAX supposedly safe S/C RPM (18630 S/C RPM) (155mm/3.005 = 51.6mm where 3.005 = 18630RPM / 6200RPM).

To reach this MAX "safe" S/C RPM:
178mm Crank Pulley would need a 59.2mm S/C Pulley
181mm Crank Pulley would need a 60.2mm S/C Pulley
185mm Crank Pulley would need a 61.6mm S/C Pulley

Now, as of right now, we don't have the actual size of Code3's S/C pulley, but he posted over on mbworld that "...the new sc pulley is no more than .5" smaller than the stock one". 0.5" = 12.7mm -> Stock S/C pulley: 74mm - 12.7mm = 61.3mm for Code3 (again, NOT the official size as of this posting. Hasn't been officially announced yet. I'm just using this number as the SMALLEST size to expect). That puts their pulley maximally at 0.3mm SMALLER then what you want for a 185mm Crank Pulley for your max safe S/C RPMs. Their S/C pulley would put you at 18,711 S/C RPM @ 6200RPM and 21,140 S/C RPM @ 7000RPM (for a ratio of 3.018 = 185mm/61.3mm)

After all those calculations, it looks like 10% under max S/C RPM may not be a good idea, See this thread: talking about 192mm crank pulley

A 192mm Crank pulley gives:
192 Crank Pulley : 74mm Stock S/C - - Ratio = 2.594
Engine RPM @ 6000 - - S/C RPM = 15564
Engine RPM @ 6200 - - S/C RPM = 16083 - Rev Limiter W/Tune
Engine RPM @ 7000 - - S/C RPM = 18158

He was getting detonation at WOT with that pulley and no tune, so 15,564 S/C RPM is too much for the fuel system at WOT. This is REALLY close (64 RPM) to a 185mm pulley running at a tuned 6200 RPM (15500 S/C RPM)

Brian, you haven't had detonation at WOT with the 185mm crank pulley, have you? I don't remember reading anything saying that you had.

Assuming you haven't, that tells us that things start to go bad with a ratio somewhere greater than 2.5 (185mm crank pulley/74mm stock S/C pulley = 2.5) and less than 2.594 (192mm/74mm=2.594)

Crank Pulley / Code3 S/C Pulley (at guess of .5" smaller then stock):
155mm/61.3mm = 2.528
178mm/61.3mm = 2.904
181mm/61.3mm = 2.953
185mm/61.3mm = 3.018

So the numbers say their S/C pulley should NOT work well with anything but the stock crank pulley.


Now, Brandon did say that his pulley dyno'ed a bit less then the 185mm pulley. From the numbers above, the S/C pulley needs to be 62.0mm to equal the 185mm crank pulley ratio. 74mm - 62.0mm = 12.0mm -> 12.0mm/25.4mm per inch = .47inch, really close to .5". So we now know that their pulley CAN'T be 61.3mm and has to be bigger then 62mm (equivalent to 185mm crank pulley) and less then 63.4mm (equivalent to 181mm crank pulley).

So if we use 15500 S/C RPM as the max safe RPM @ 6200 engine RPM (Ratio = 2.5) this assumes 185mm crank pulley produces max safe S/C RPMs:

178mm Crank Pulley would need a 71.2mm S/C Pulley
181mm Crank Pulley would need a 72.4mm S/C Pulley
185mm Crank Pulley would need a 74.0mm S/C Pulley

So you can't use their S/C pulley with any after market crank pulley.

Of course, my math could be wrong...

 

why not just use pi and figure out the exact circumference of the stock pulley and the bigger pulleys and at different RPMS... distance over time= speed... I am sure if I had the right tools to measure the exact diameter of the stock pulley and the S/C pulley there wouldn't be no guessing... math + physics = exact science... no opinions no other answers!... but I forgot schools now teach how to have high self esteem and integrate... not how to calculate the circumference of a circle or know what speed is

with the data YOU gave me(155mm crank, 74mm S/C pulley) this is what is correct for STOCK pulleys... in reallity with our cars... not ratios out of diameters difference...

the circumference is the distance the belt is moved after one rotaion.
the formula is 2xpixR... we already have 2R = 155(stock)
155pi = 3.141x155 = 485.855mm
74pi = 3.141x74 = 232.434mm
485.855mm/232.434mm = 2.090
so every rotation per minute = 2.090 rotations of the S/C

5800rpm(stock)= 5800x2.090 = 12122
6175rpm(tuned ecu)= 6175x2.090 = 12905.75

you can use these formulas to know what is really going on under there
I appreciate everybody trying to calculate and get a good answer why our max is so low and our stock is so high well I don't know the max but I KNOW the stock(if of course those pulley diameters you posted are correct)

 

I do know math and physics and how to calculate circumference. And I know that speed is the magnitude of a velocity vector


You don't need to calculate 2*R*Pi, because we're looking at ratios.

2*R*Pi = D*Pi

Dcrank*Pi/Dsc*Pi=Dcrank/Dsc. Pi divides out. When can do the math with just the pulley diameters. Your calculated ratio of 2.090 differs from mine of 2.094 because of rounding.

I noticed you used lower RPMs for your calculations. Are those the actual RPM limits of our engines? I thought it was 6000 stock and 6200 with a tune. I was using the same values Brian used. He asked someone to check his math so I did. It was really late when I did all this, so I didn't break out a ruler and actually measure the diameters of our stock pulleys to verify Brian's numbers.

I figured Brian knew what the sizes are and went with that. Besides, I'm really interested in the new S/C pulley being developed and was wondering myself if we could use it in conjunction with the after market crank pulleys.
I enjoy doing math (yeah, I'm weird like that) and had some free time, and no one else checked Brian's numbers, so I did.

 

Thank you very much. Very interesting.

Bruno

 

I was under the impression the 192mm pulley spun the s/c much closer to the s/c limit than what you calculated...if your calculations are correct its not even close, which is good.

As far as the fuel systems limits i thought it was determined that both the injectors and fuel pump were more than suffecient for turning up the boost near the s/c's max. I thought it was the tuning that was necessary at that point in time to eliminate detonation...? Maybe i need to re-search.

 

Yeah, it turns out his problems at WOT were due to the fact he had headers installed. When I read the thread, the headers were still being fabbed. I missed his post were he stated they got installed. He made a post in a different thread (the LET headers thread) stating he had no problems with the 192mm pulley UNTIL he installed the headers. Here is that post: https://www.crossfireforum.org/forum...9&postcount=69

So that means we don't yet know what ratio will give us fuel problems at WOT WITHOUT headers. It could still be possible to combine the S/C pulley with an aftermarket crank pulley after all. Hopefully Code3 will do just that and post info.

As to the 192mm running the S/C at near max, someone posted that, but didn't show their calculation. They just stated a number. I wish more people on here would show their calculations, so that others could verify the numbers.

I'll try to actually measure my S/C pulley today, so we can be sure of the size. My calculations above are based on the size Brian stated. I don't think he's lying, he just never said were he got that info. And I haven't had the chance to do more research to verify.

 

I measured the stock crank pulley (which I have removed and replaced with LET's 185mm pulley) with a steel machinist's rule, my calipers weren't big enough so the numbers could be off a little, and the stock SC pulley when I had the belt off. My numbers were pretty close to post #10 in this thread.

To add more to this discussion, it's my understanding the limiting factor turns out not to be the maximum SC RPM, that's just the mechanical limitations of the SC, but it's the Bosch ECU.

When the ECU is in the open-loop mode (yer rippin' down the road) - once the MAP sensor signals the ECU with a 22-24PSI reading, (that's just about MAX boost of my 185mm pulley) the ECU then stops adjusting the fuel maps. Once this happens, and if MAP continues to rise, you will begin to run lean because the ECU will no longer try to add more fuel to keep up with the increasing air supply (A/F ratio). The lean A/F ratio will be detected by the O2 sensors, the ECU will signal a CEL and begin to pull timing. There's been talk of a MAP clamp so as not to signal the ECU of overboost, but I'm not sure how that would solve the issue of fuel map selection by the ECU.

I think this is what what was happening to AMGrasoul who was running the 192 pulley - he was just over boosting the MAP sensor and creating a lean condition, as the cylinders heated up he would pre-detonate, causing all kinds of issues...

 

Is the MAP sensor the limiting factor meaning it simply needs to be upgraded with one that can read more boost? Or is it that the ecu cant adjust fuel maps past a certain point, and if so will a tune solve the problem?

All these dollars we spend on big pullys, headers, etc are pointless past a certain level if the ECU cant handle the necessary calculations.

This would definitely be nice to know.

 

My understanding is that it's the ECU

No - We just need to balance the mods; unless you were going to run flat out at WOT for long periods of time. Pulling hard off the line is my main performance goal - not so much increasing top speed.

With the 185MM pulley my SRT will reach max PSI when I am in the Tiptronic mode - but only momentarily before shifting into the next gear.

When I took the SRT6 out to the desert for a high speed run, I believe I hit around 23-24PSI running flat out at 165-170MPH - (but I was to busy with my eyes on the road and did not think to sneak a glance) but that engine RPM was momentary as well. It might be a concern if I went wide-open for say 10-15 miles but I had my ECU tuned to run just a tad richer. I have never had CEL since installing the 185mm pulley.

 

what about installing a diode to trick the ECU just a little bit to where a bigger pulley and higher boost wont scare it... not too much though... otherwise it will run very lean... but the way i see it the SRT6 enigine runs very rich stock(that's why I get under 20mpg on the freeway) so a diode will not give us too much trouble with that, we just need someone with a wideband A/F to try it out someone BRAVE