hooleyboy

I fairly new to F/I. For those who dont know I'm doing a AMG supercharger retro-fit on my C55. I'm in the tuning stages, so the project is just about done. Only thing is we had a custom machined pulley that is 4.5 inches or 114.3mm's pressed onto the stock pulley.

We tapped the surge tank to monitor boost On the dyno. We are only showing about 5psi or a touch less. The stock E55 pulley is 152.4mm's or 6 inches.

So my question is what kind of boost level would i expect with the stock E55 crank pulley? We are thinking with my very free flowing exhaust setup i'm loosing boost out the tail pipes.. sort of say?

shardul

iTrader: (1)

stock e55 should boost up to 11.6 psi in 4th gear at 6k rpms

stock - your custom size = 38.1

for every mm you increase on the pulley you gain .2psi

38.1 x .2 = 7.62 psi

4.8 (your boost) + 7.62 = 12.42 a bit higher than stock

so in other words your boost level is where it should be with a 114.3mm pulley.

someone correct me if i am wrong.

splinter

What was your technician’s workaround on the bypass valve?

hooleyboy

Thats a bit high for were i want to be. Strangely My pulley is 4.5 inches wide and the stock E55 pulley is 6 inches wide. I just dont get it. why 6 inch pulley an put down 11.6psi and my 4.5 inch pulley only putts down 5psi max even dips into the 3's IDK

hooleyboy

Yes. I believe I have a block of plate

HYEPWR

Id aim to undershoot. Its easier to make a bigger pulley than change a blown engine. Make a 125-128mm pulley and see what happens. Should be very close.

hooleyboy

I'm very nervous about the shop wanting to use my an E55 stock crank pulley at 11.1C/R

correction: I have a 101.6mm stacked SC pulley and that makes 5psi of boost. so... for every 20.32mm's I make 1psi of boost.

152.4mm (stock E55 pulley size)

152.4 / 20.32 = 7.5spi of boost??? or does the math not work that way?

AMGSC

The 55K blower has an 2:1 step up internal SC gear ratio so. every fractional increase or decrease doubles the intended effect measured at the crank pulley. This is probably why you lost double the intended reduction and now have 3-4 psi instead of 6-8psi.

hooleyboy

My pulley has 101.6mm diameter. Stock E55 pulley is 152.4 diameter

101.6mm pulley has a circumference of 319.024mm

Math for my crank pulley:
C = 3.14 X 101.6
C = 319.024mm

Math fro E55 crank pulley
152.4mm pulley has a circumference of 480.06mm
C = 3.14 x 152.4
C = 480.06mm

Making the difference in circumference 161.036mm between my custom pulley and the stock E55 pulley

480.06 - 319.024 = 161.036mm difference.

I have no Idea what this math^^^ means for my boost levels.

hooleyboy

My pulley is a 25% (Basically) reduction over the E55 stock pulley

does that mean for every 25% reduction in crank pulley size I lost 50% or.. for every 25% increase I gain 50%? So... If I increase to the stock Crank pulley that is 25% bigger i will get 10psi of boost rather than 5psi peak boost?

HYEPWR

Although the engines are both the same displacement and you are using the same SC as us, the efficiencies of your car is a bit different. I bet your car is already putting down ~400rwhp at 5psi. In other words the SC is flowing the same amount of air for you at 5psi as our cars at 10psi. Remember--your compression Ratio is 11:1 vs 9:1 for us. Our engines, running 9:1 CR and 15psi (big boys)have an effective compression ratio of 18.3:1. For you to get to the same level at 11:1 CR would mean a max boost preassure of 9.5psi.

I realize that this doesnt help you with your problem. Im just trying to tell you that the MAX i would ever go is 9.5psi. I have no idea what type of pistons and rods come stock on the C55 engine. If you miscalculate the pulley size and get 9,10,11psi....it might be KABOOM for your engine.

You cant really compare psi. You need to look at airflow...or rwhp. Get a slightly larger pulley made--one that is slightly bigger than your current 105mm. 10mm more sounds good. Then meassure your boost psi. Then you will have 2 data points SPECIFICALLY for your car. So 10mm pulley increased boost 1psi--->so each mm=Xpsi

Thats how Id do it. Worse case senario is that you spend ??$500? for a slightly bigger pulley....pick up 0.5-1psi and 20rwhp===which is still pretty good.

Why dont you PM Ahmed (blackbenzz)he has a clk with a similar setup I think.

hooleyboy

I was looking at the efficiency chart of the Lysholm SC and it makes sence that there is a boost drop off at high rpm's Due to my pulley at 5psi dropping out of the efficiency range.??? If i get a pulley made arounf 127-130mm I think I will be were i want to be.

and yes, I'm only putting down around 400whp on a dyno dynamics after A/F adjustments.

AMGSC

Your pulley's circumference is actually 33.54% smaller than the stock pulley when I do the math. So stock is 11.7psi, at 2/3 your should have been 7.8psi but due to the 2:1 step up gearing inside the SC you actually reduced your the stock boost by 2/3 which calculates to 3.9psi. This is what you are reporting as your actual boost right now correct?

Whatever you do don't go over 8psi unless you plan on rebuilding the engine soon.

hooleyboy

The stock supercharger pulley is 76mm and the crank supercharger pulley is 152mm..... 76 & 152 = 2:1 ratio between pulleys

I need to get to a 1.75:1 ratio between pulleys

That would mean keeping the supercharger pulley at 76mm I would need a crank supercharger pulley 133mm
76 & 133 = 1.175:1

or I could try and machine down the supercharger pulley from 76mm to 65.5mm.
I would need to machine off 10.5mm of the supercharger pulley to get the ratio of 1.75:1 butting at a nice boost level.

HYEPWR

I wouldnt touch the SC pulley....others have tried. There is less than 5mm(IIRC) of meat on the SC pulley before you damage it. Others have tried---it doesnt work.....UNLESS you arent using the elctromagnetic clutch?? and your Sc is always "on".

Why are you soo greedy?? 400rwhp on a 3600lbs car is great. Thats 117-118mph car. YOU Greedy bastrad!! lolol..

As far as "boost" is concerned--your sig says you have exh manifolds which changes the picture even more. I think going from 101 to 132mm might be too much. Remember that the boost on a E55 actually SPIKES at 2200rpm and then tapers. So 11.7 at 6000rpm may be 13psi at 2200.

just go slow and be carful

shardul

iTrader: (1)

good read sir