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:

AMGS105IHKIsentropic.jpg

Lysmap.jpg


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

 

Welcome, very interesting stuff there. I see we have another problem solver here. Great to have you aboard.

 

Thanks for the GREAT POST!! Very interesting. Is the temperature curve shown in the diagram WITH Intercooling or WITHOUT Intercooling? 110 Degrees Celsius at stock boost (15PSI) seems to be measured at the outlet of the SC without Intercooler...

 

Excellent information and post!!!!! I want to add a 185 to my wife's car too but safely. LET HE & Johnson pump on the way, should probably consider split reservoir and meth injection for higher boost.

Also, I didn't know the C32's came with larger injectors? Are we exceeding the duty cycle of the stock ones on the 185 pulley or do you know the percentage that's being used throughout the rpm range?

 

He speaks alot like Pat Polson from the 60's
I guess my question as a more than satisfied owner of a 185mm is, what is this problem you speak of?
There is far less a problem than there is a lot of people that will argue non issues. The Crank Pulley vs. the Code3 debate will go on forever. For what reason is beyond me. This is not a Chevy vs. Ford debate, we all run the same engine. So like some of us, post times, challenge on the road courses and hope for proof in the way of either butt dynos, water brake dynos or first across the line. I can draw a schematic showing why we can't get to the moon, BUT WE DID!
I'm sitting here in Montana with between 406 and 409 crank horse, if you want to dought, bring it on I will take all comers.
And as I always say, Enjoy the Ride...
Mike

 

Those diagrams are almost always shown WITHOUT intercooling.

 

Nice to meet you. Very interesting post, definitely helps to explain the workings of the S/C and pulleys.

 

A well reputable vendor will tell you that the c32 injectors have been flow tested at 39lbs and that the srt6 ones are identical(though he didnt actually flow test the srt6 ones).

As far as a replacement s/c we all like and have discussed that idea but no one will fork up the cash to be the first...

I need to drink some coffe and look at those graphs more..

 

Please allow me to get back upon one of my basic beliefs related to the supercharger. Building boost.

The S/C data provided above AND taken at face value reinforces my point, and that is the boost provided is a function of the Pressure differential across the s/c [inlet to outlet pressure]. Colder weather adds to the boost as we all know, because the inlet air is DENSER TO BEGIN WITH.

If you have a boost ratio of 2.2 or other number, going beyond that is possible at the cost of lower efficiency and much greated stress - heat - input power.

I have instrumented and measured the inlet pressure at the throttle body. Using the standard Needswings CAI inlet and filter, I was getting a VACUUM of 30" of water column. That LOW restriction intake has about 1 PSIG of pressure loss due to velocity turbulance and amounts for 1 out of 14.7 or about 7% loss in density. The stock intake is much worse than that!!

By adding a second cold air inlet I was able to get 1 MORE PSIG OF BOOST without any other changes. THis is in part of why I was able to hit 20 PSIG of boost with the 178 mm pulley alone. THIS GAIN IS DUE TO EVEN LOWER INTAKE RESTRICTION, FREEING UP MORE ATMOSPHERIC PRESSURE TO REACH THE THROTTLE BODY.

Your S/C only compresses what is delivered to the input and there is where the output [Boost] comes from. A 6.8% gain in H/P is A BIG TIME gain and up to about 20 HP. I have shown this on the dyno and the gain is most prominent at the LOW rev end. THis is where you lose time on the track - just getting it rolling - going.

I have addressed many issues [technical] with a very mixed forum response; however the proof is in your hands. Just remove your intake at the throttle body for a short test, and watch your boost gauge to confirm the results for yourself.

Intercooling helps reduce the charge temperature and again increases the density of the inlet air within the cyclinders. The cooler the better; for both power and a greater safety margin for detonation prevention.

I will be doing some testing of the S/C boost with a185 size pulley this spring. I have now run the 178 [ currently], the 181 pulley , the Code 3, and the combo 178 & code 3 "stacked" pulley setup. The 185 is the last step in the evaluation phase, as I want to uncover information and the power locked within.

Forza1, thanks for the stimulating and thought provoking article.

Enjoy, Woody

 

Can someone provide a synopsis for someone like me who doesn't know what all of that means? Is the 185 not good to run then? What about a 178 and the new midsize s/c pulley that code3 is coming out with?

 

Nice write up with some great information. Always feel free to use anything I’ve posted on forum – it’s there to share.
Regarding the Supercharger RPM – the max RPM the SC will see with the 185mm @ 6150 RPM is still under maximum limit that is determined by the SC bearings . I hit maximum engine RPM (6150) in first, second, third gear (and only for a moment between shifts).

I’ve never gone fast enough to hit redline RPM beyond that (other then on a Dyno) – and I’ve had my SRT6 up to 170MPH – So if you still have the factory speed limiter set on your ecu….. But I have been “road course” driving and kept the RPM’s revved up in both second and third gear (around 5,500 RPM) with no issues.

Regarding Heat – One of the first mods I installed after the 185mm pulley was an IAT gauge – for just this reason. I mounted the sensor near the factory sensor (to see what the ECU sees) – and never had an issue. Keep in mind that my IAT sensor is copper clad and will read a little higher than the tip due to the air distributer is mounted on. But even so - - IAT’s are not an issue for me. I’ve never even heard of anyone having this issue with any size crank pulley. Spray water/meth if you want – but I don’t need it.

The 100*C (230*F) IAT you mention is well over the SC cut-off temp set by the ECU. The max IAT I see with the larger HE and split reservoirs is around 145*F on a hot summer day - boosting hard – on cooler days I see around 95-110*F when boosting.

When I go back and look at the first map you posed and keep my eye around the 70*C line I like what I see. It tells me I’m staying right in the “Sweet Spot”.

 

Must be - That's why it graph is labeled "Test Stand" and my IAT differ so much.

 

My interpretation summary. The 181 pulley is the largest to be used before efficieny starts to be lost from heat issues. OP choice is Code three pulley because it is easier to install, lighter and has greater reliability. Basically what is being stated is that the 185 creates to much boost and the extra boost generates more heat which results in a lower amount of efficiency which translates to less power. Hope this helps

 

thank you. that does help. I appreciate it..............................

BrianBrave, it appears that you feel otherwise about your 185? Is that correct?

 

I have nothing to contribute to the discussion, other than to say thank you to all you guys who do all of this research and testing. I have an engineering degree so I can pretty much follow what you guys are talking about, so that helps a little. However, this is the main reason that I keep delaying buying any new pulley because it seems like people are learning something new about this car/engine everyday. Exciting stuff, thanks again!

 

Thanks guys! Just trying to figure everything out and help the community.

SLK32Germany, It does appear that they're showing non-intercooled results probably for a more standardized result. Anyone have the upgraded intercooler and 185mm?

Montana, you and waldig are my favorite posts to read on here. To answer your question, the "problem" with the 185 is why they aren't beating the 178mm cars at the 1/4mi track. I think they are through the midrange, but not on topend where the 178mm cars are running much more efficiently.

240M3SRT, For the injectors, this should be easy enough, lets just compare the injector part numbers for SRT-6 to C32.

Woody, I agree with you, I think the stock airbox setup is a POS. Lots of gains to be had there. I want to hear back your findings after the 185 pulley goes on.

Anyone want to take a guess as to how much the IC is cooling the air?

 

I wouln't say that I feel otherwise, just that my experience with the 185mm pulley (installed two weeks shy of one year and over 12K miles) - - is different then those who don't have one installed and expect something else.

Before I installed mine - I expected the possibility of these very same issues - that's why Erick offerd me to exchange it with a 181 or 178 if I had issues or was not happy.

I'm Happy - Very Happy!

Only you can decide what you want and what your comfort level is.

 

thanks for input Brian!

 

Forget pullies can't we just use a bigger whipple unit?

 

Here is the link for more detailed review of this post, Woody

http://www.opcon.se/index.asp?sPage=1&langID=1&cID=14