Originally Posted by REVIT93RX7

Just to add some humor here, I think this is a terrific thread very informative. How about we swap a 6.1L Hemi in the thing and call it the HEMIFIRE!

Originally Posted by TemjinX2

After talking with a couple of people and getting feedback from both forums. I'll probably just experiment with the stock pulley since its already off the car. I'm going to talk to some machine shops probably tomorrow.

Originally Posted by REVIT93RX7

Just to add some humor here, I think this is a terrific thread very informative. How about we swap a 6.1L Hemi in the thing and call it the HEMIFIRE!

Originally Posted by TemjinX2

After talking with a couple of people and getting feedback from both forums. I'll probably just experiment with the stock pulley since its already off the car. I'm going to talk to some machine shops probably tomorrow.

Originally Posted by Mr. Max

That's what I was thinking. If I'm going to screw one up, I'd rather it be the stock one. I'm not sure I'll ever use it again (maybe warranty work on the bolwer) and the stock one will be much cheaper to replace. Think about how many code three owners are on this site alone with stock pulleys sitting on the shelf.

Originally Posted by TemjinX2

yeah thats what i figured too..if i mess up on the stock pulley, i can just trade my code3 pulley and some cash for a stock pulley when i want to put the car back to stock.

Originally Posted by Mr. Max

I would think you could trade the Code3 for a stock pulley and get some cash back on top of it, quite a bit of cash.

Originally Posted by Forza1

Hi, I'm a new owner, and I'm glad to have found this forum, you guys are very knowledgeable. I've been doing a lot of research, and I think the problem with the 185mm pulley lies in the supercharger.

The factory AMG unit is the AMG-S105-IHK unit from IHI. This is essentially the same as the Lysholm LYS1600ax unit. I've hosted the maps for both respectively:






Now if you notice, the supercharger is rated at a maximum of 15000RPM. There are some C32 AMG articles floating around claiming 20,000RPM. I see nothing that AMG did to the Lysholm unit to make it spin that much faster safely. If anyone has any more information on this, please to share it.



Using this formula: Crank pulley(mm) / Supercharger pulley(mm) = (Ratio) * Engine RPM = Supercharger RPM

Now it should be noted that stock rev limiter is 6,000 RPM, but some chips(may want to ask your tuner) are 6200RPM which can make a large difference(more on that later)...


Heres some math gratuitously stolen from a BrianBrave post:


155 / 74 = (2.10) * 5.8K = 12,180 SC RPM (Factory)

178 / 74 = (2.41) * 6K = 14,460 SC RPM

181 / 74 = (2.45) * 6K = 14,700 SC RPM

185 / 74 = (2.50) * 6K = 15,000 SC RPM


Code 3 pulley = 65mm (so I've read) although waldig hinted it may be 63mm(?) can someone measure?

155 / 65 = (2.38) * 6K = 14,280 SC RPM

178 / 65 = (2.74) * 6K = 16,440 SC RPM (Stacked)



Now, lets look back at the graphs. To figure out where we are exactly, we can use this formula to find our Compression Ratio(y-axis):

Pressure out / Pressure In = (MaxBoostGaugeReading - IntercoolerPressureDrop) + Ambient) / (SCInletPressure + Ambient) = Compression Ratio


We'll say your boost gauge reads 15psi, and the intercooler has a 2psi pressure drop, SCInletPressure is how hard the SC is sucking, and I would use a number like -.5 or -1 for this. Ambient is 14.7psi.

((15-2)+14.7) / (-.75+14.7) = 27.7/13.95 = 1.9856


So drag your finger up the y-axis on the map to 1.98(I'm using the IHI map). The x-axis is going to be the amount of air the engine flows. This will be different depending on a few factors. General rule of thumb is 150CFM per 100HP so if BrianBrave dynos consistent 362rwhp as per his post, we get 3.62 * 150 = 543CFM. This is a rough figure, but it should have us looking in the right area. Converting to match the graph, this equates to: 15.37 Cubic meters/min so lets use this for x-axis.

Notice where this puts us on the map..... For reference, 35 kW is 46.9 horsepower(!). Also notice temperatures. This is at only 15psi! Some users report boosting to 21psi with the 185mm pulley. This not only puts the supercharger in the "red zone", but also exponentially increases the temps(110*C is extremely HOT air entering the engine for combustion), and also the power requirements(notice how the pink power lines on the IHI chart get closer and closer together the faster it spins). Also, increasing the cars redline to 6200rpm will spin the supercharger roughly 500RPM faster than the numbers above(sub 6k for 6.2 or 6200). One should keep in mind though that the 185 is spinning the SC faster throughout ALL rev ranges when compared to a 181 or 178. This means boost max boost comes on faster, and will give the car a better bottom end. Very beneficial until the losses come into play. That being said, I wouldn't be surprised to see a 185mm pulley car dropping off towards the high end on the dyno(exponential parasitic losses). Don't get me started on stacked...




Based upon the above data, here are my thoughts:


1. A 185mm pulley car will not benefit from an increased rev-limiter. They should ask the tuner to leave the stock 6000RPM, or even 5800RPM for safety.
2. Because of the extreme heat issue related to the output temps of spinning the supercharger that fast, I would recommend alcohol or meth injection for the sole purpose of cooling the intake. I think this would make a big difference at say above 18psi if the ECU tuners gets some seat-time and get the tuning down.
3. I would recommend the 181mm pulley as the best matched for our cars without worry or hassle.
4. I would also suggest that since the parts are readily available at any dealership, the SRT-6 guys purchase the C32 AMG injectors which are about 20% larger.


Also, Lysholm is the manufacturer of Whipple systems(the whipple and lysholm are identical). I like the idea of the Code3 pulley(or SC pulley in general) over the crank pulley because it is easier to change, more reliable, and appears to be lighter weight than the stock unit. Now a 2.5" pulley(64.7mm) for a whipple charger can be seen here.

I don't see why we couldn't run one of these on our cars if we were to remove the electromagnetic clutch that engages the SC at 1600RPM. Far out there, but it's a LOT cheaper, and easily available than $600-1500 pulleys.


It's late, and that was a lot of typing! Hope its coherent. Please post up any thoughts you have on any of this.



I'd like to see someone with a 185mm pulley have a new tune made with 5700RPM shift points, and post back to see if it improves his 1/4 mi times.

Also, let me know if you have a cheap cold-air intake, or cheap 181 / 185mm pulley kit for sale(must have better water pump bearing). Looking to pick up one of these and get to the track soon!





-D

Originally Posted by Web 3.0

Great post but something is wrong with the numbers on the IHI map..

First off, the rule of thumb you use is correct at 1.5 CFM per HP, the only point I would like to add there is that it is used to calculate crank HP. You also have to take into account drive-line loss as well as parasitic loss at the supercharger. If you consider the latter two figures then it is physically impossible for the IHI map to be the right one for the SRT, which makes the second map the most logical choice.

In fact, you are off the map by 565 cfm / 1.5 = 376 at the crank - 60 hp (45 kw) to drive the SC = 316 * .81 (drive-line loss) = 255.9 RWHP max theoretical RWHP on that map.

Note: The typical Front engine/ Rear wheel drive car loses 19% from the crank to the wheels. The typical blower running at high psi will consume 30 - 50 crank HP. I also calculate the pressure ratio as achieved including the pressure drop so in my calculations I am assuming a PR of 2.4 at 20 psi.

So, on the other side of the coin and looking at 362 RWHP we come up with the following:

362 * 1.19 = 430 crank + 60 hp for parasitic loss = he is producing 490 HP at the crank!

490 * 1.5 = 735 cfm which is more like (20.7) m3 at a PR of 2.4 puts you in the 59% efficiency range.

Ultimately you reach a point of diminishing returns with any supercharger as the efficiency goes down and the parasitic loss goes up. At some point, the additional psi of boost loses ground to the other two and the top end HP peaks. However, once you reach this plateau, you will usually still see a rise in low end torque with the next step in pulley size to a certain point.