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 TemjinX2

courtesy of the crossfire forums