Is there anywone hwo runs more than 15 psi on C38 (or C30 - 94) supercharger ?
reading the "parked" chapter I've seen max 10-12 psi on these ...
I'm looking to use this kind of spg on a M50NV engine, triyng to get around of 350whp ... but I'm concerning about the Rotrex recommendation to not use often these spg for more than 9psi ...
any input is welcome , thank you
' 99 E36 316i Compact, 83kw
i don't think anyone on here runs more than 10.5 psi on the c38
Centrifugal superchargers all use some sort of internal drive mechanism and have maximum recommended rpm. The rpm matters more than the psi since psi will vary depending on engine displacement and VE for the particular application. However, supercharger makers (and turbo makers) also do not like people to exceed certain efficiency limitations. Pushing the blower too far will result in decreased efficiency, whch creates more heat.
One risk with pushing a supercharger too far is that if it fails, it may send metal into your engine. I would not exceed the maximum rpm by much. Consider using the next larger blower. If that won't work for your needs, try a turbo. There are many more turbo sizes to choose from than there are centrifugal or positive displacement superchargers.
I know the C38 is good up to 14psi on the S52 engine. Above that, you might be asking for trouble.
It is not safe to go by psi alone. Improve the VE on an S52 by adding headers, M50, cams, track pipe, rear exhaust, etc., and you would have to spin the C38 as fast on this S52 as you would to spin it to 17 psi on a stock S52. You have to look at efficiency charts and the blower rpm curves, with the blower rpm curve being the more critical of the two to a certain point.
Guys, I'm not talking about overreving the blower - is not needed to do this for blowing 14psi in M50B25 engine with a C30-94 or a C38 unit ... more, reading the supercharger maps, it seems that both units are quite efficient at this pressure on the related engine ..
I'm just wonder why there are not so many people doing this ... is something that I've missed in my calculations ?
' 99 E36 316i Compact, 83kw
People are not spinning the blower much faster than AA recommends because relatively few people have modified AA Rotrex C30 and C38 kits. The limits wil be learned sooner or later. My personal view is that there is a limit to how fast you can spin the blower when it is driven by the stock accessory belt system. I just don't know what that limit is and no one else seems to know, either. A heavier duty tensioner and a wider belt custom, wider accessory pulleys would help, but the best drive system is a dedicated blower drive system like Dinan and RMS use. AA, for example, converts to 8 rib pulleys on the E46M3 Rotrex kits (still part of the accessory drive, but wider belt and pulleys).
If you're seriously trying to max out a c38 you may want to just go turbo from the start.
Active Autowerke C38 stage 2 on 95 dakar yellow M3, 30k miles
.080 mls headgasket, ARP headstuds and obd2 valve retainers; Stewart water pump; Dunlop Z1's on staggered CSL's.
387whp, 296wtrq --- girls dig dakar
I've developed previously 2 custom supercharger kits and a turbo setup ... in my opinion is more easy and more reliable to use spg than turbo ..
on the other hand, i use my car for daily driving and time to time for 1/4 mile race ... for this kind of usage, I think that the cf spg is more appropriate
@ pbonsalb :
I'm thinking to use a AC pulley engaging the supercharger (as a dedicated driving system) and a heavy duty belt (Lemforder)
in my calculations, is no need to spin a C30-94 blower more than 85k rpm achieving 14psi (M50NV) .. and the spg rev limit is 100k ..
please take a look to the map:
http://www.w2wpowertrain.com/images_...ger_range1.pdf
@ Marco, I've understand that you sell Rotrex units - what's your opinion in this issue ?
Thank you,
Last edited by kaliE36; 12-25-2007 at 02:48 AM.
' 99 E36 316i Compact, 83kw
I can't remember whether the AC pulley is 5 rib or 6 rib. If it is 5 rib, the belt cannot handle as much load as a six rib. On the other hand, the routing will be shorter if the drive is dedicated. I also can't remember the diameter of the AC pulley, but think it is maybe 5 inches. Smaller diameter means more chance of slippage. It might work, though. You can always try. Have custom pulleys machined if you need them. If you were willing to space the blower out further from the motor, you could probably build your system using an RMS or Dinan Vortech crank pulley. The 6 inch ones go for $250 used when you can find them and the 5.25 inch ones go for about $100 used. If max rpm is 100k and you are spinning to 85k, I would not worry. The max rpm on my Vortech is 50k and I spin to 48k. With a centrifugal, you don't spend long at max rpm. If I was building an autobahn car that would be run at maximum rpm for extended periods, I would to make sure the blower was in a good efficiency range at that speed -- closer to 70% than 65%.
Rotrex CF units are very well designed (C38) I think with a custom pulley set someone could see 15psi. The C38 has a max pulley rpm of 12k and an impeller rpm speed of 90k. I'd like to see someone MAX out the C38........................... 15psi is not maxed out IMO
The max PSI for C30-94 on an e46 know to me is 10.5
C38 - 12 PSI
Stock compression is the main restriction IMO, not the Rotrex blower "limited" capabilities.
Malina, this is an e46 325? You have an intercooled kit? Which pulley is producing 10.5psi for you, 90mm or 85mm? Have you made any other mods to increase VE such as headers? Thanks.
^ Yes, intercooled, M54B25. 90 mm is regular pulley size for AA C30 kit (8-9PSI). One needs atleast 85 mm pulley, larger injectors and software, of course, to boost over 10.5 PSI. I still have a complete stock exhaust (shame on me).
Wouldn't using an 85mm pulley on a C30 bring the impeller speed past what Rotrex says is safe in terms of RPM's for the unit?
The 85mm pulley can be run on the 30# injectors and base AA 325 m50b25 kit tune per AA, at least on good 93 octane fuel. I am not sure about the m54. You should ask AA if you have not already. The 85mm will not go above the 100k rom limit. Besides, how often and long are you hitting redline?
I wonder why people are spreading this nonsense about C30 being maxed out @ 8-9PSI? Any technical, mechanical info to support? I was able to squeeze 10PSI @ 6800 with just a 97 octane instead of 93 without any pulley or software upgrade. Take a look at the last page and find pulley sizes that C30 can support.
http://www.w2wpowertrain.com/images_...ger_range1.pdf
C30 with 8PSI is a conservative setup IMO. If you wish to safely bring up the boost level, call AA.
I believe people were saying the C30 is maxed at 8-9psi on the S50 & S52 engine. Like it was already said once in this thread by pbonsalb, the psi is based more on the VE of a particular engine, not just the impeller speed and the amount of air from the supercharger.
Also, just because there are pulley sizes that go as small as 70mm listed on the Rotrex site it doesnt mean that a 70mm pulley can be safely used with a C30 mated to an S52 engine. Rotrex doesnt just make these units for our BMW's, but for a wide range of vehicles with varying crank and accessory pulley sizes that will spin the blower at different speeds when compared to our cars that have the same size s/c pulley.
The technical data that is important is the peak impeller speed of 100,000 rpm's that is listed on Rotrex's site. Now I do not know the math to figure out the impeller speed of the unit with various pulley sizes, so you may be 100% correct when you say that more boost can be produced safely from the C30.
Does anyone know the math to figure out the inpeller speed?
is very simple to calculate the impeller speed ... you will need to know both diameters for crank pulley and spg pulley and engine rpm's ...
the formula will be like :
Impeller rev = Engine rev * (Crank Pulley diameter/ Spg Pulley diameter) * 9.49.
That becouse the spg internal gear ratio is 9.49.
by ex: if I will use a 12.5 cm AC pulley and a 10.0 spg pulley, at redline (7.000), the impeller speed will be: 7.000*12.5/10.0*9.49 = 83.037 rpm
btw: when I'm talking about boosting a M50B25 engine with more than 14 psi, I've understand a full rebuilt low compression engine (I'm thinking about 8.5 - 8.8 :1 CR), not a stock 10.0:1 CR engine
So, we talking just about the spg capability to produce reliable high boost, not about if the engine will withstand this ...
The engine rebuild is in progress now: enlarging and polishing ports
On the other hand, I want to use a spg that leave me some room for upgrade ...
now, the first goal is to achieve 350whp from a fully rebuilt 2.5 engine, M50 intake, polished ports, Dbilas cams, free exhaust, 7.200 redline and 15 psi from a cf spg (I belive that goal is achiveble)
anyway, I want to leave enough room in this setup to increase boost to 18-20psi to get 400 whp ... (for this I will need bigger injectors, bigger fuel pump, a new gearbox + rear differential, new clutch and many others )
Last edited by kaliE36; 12-27-2007 at 03:15 AM.
' 99 E36 316i Compact, 83kw
@ pbonsalb: you're right about the A/C pulley, I think that there are just 5 ribs ... but I'm thinking to machine a new one with 8 ribs - to avoid slippage ...
on the other hand - I think that is by far more safe to use another belt than the accesories belt to engage the spg ... if something will occur, and the belt will fail - you will still have the water pump and alternator engaged ...
anyway, in a previous cf spg setup (12psi on a M50B20 engine) I've used the stock 6 ribs accesories belt to engage the spg .. no slippage
' 99 E36 316i Compact, 83kw
^Very useful info! Thanks KaliE36
This is very useful info.
Does anyone know the exact size of the crank pulley diameter on the S52. I heard 5.25"....anyone know if that is correct?
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