DASC RPM vs. pulley size vs. psi ???

[JiXer]

I am still doing some research, but thought I would drop a new thread in hopes for a quick answer.
I am building an M44 with a DASC kit to put in my e30:

M42 Crank in an M44 to drop compression ratio to around 9.5, Straight intake running MegaSquirt off of MAP, 42# injectors, stock cams, Full length headers, 3" exhaust, map switched to run 91 octane on the street and 99 octane on the track.

I have a crank pulley from a 1998 318ti (6-Rib, measures 5.75" on the outer lip). I calculate it to run the M62 blower at 13,824 RPM at 7,200 engine rpm with the 3" pulley that came with the kit (bought it used off of an e36 M42, not sure what pulley size that is).

I want to max out the boost/hp within reason and figure 12 psi will get me what I am looking for. I know thats on the outer reaches of that compression ratio, but with the MS and knock detection, I figure its worth a try. I cannot find any solid info on what psi to expect out of this set up at those redline numbers. I could get a 2.75" pulley for the blower, to get the blower up near its redline (at engine redline), but I am not sure where that would leave me considering the potential for diminishing returns. I do not plan on running water or methanol injection. The blower is old and the rotors have a few nicks and some of their coating is wearing off, so I don't want to spray them and I don't want to spin them any faster than I need to.

I am also uncertain as to where to start with my cam settings. I am going to keep the stock M44 cams, but I figure I should tune out some of the overlap.
However, I am not sure which direction to take which cam.
I figured I would start with both at a neutral setting, but I don't know enough about where that leaves them to know if that is best.

Any help is appreciated.
Thanks.
J. Farina
Big Fish Motorsports

[xxxJohnBoyxxx]

Hey I responded to your PM before I knew you posted a thread. How are you measurering your pullies? I've never found a 3" SC pulley or smaller. The smallest I've found is a 3.2". To measure correctly run a string around the pulley belt area, measure the string then divide by 3.14 (pi) for the pulley size. I think a 3.4" pulley would get you around 12psi with the large crank pulley. I don't know the size of the large crank pulley but will measure it when I have my engine out in a week or two. If a 1997 318is M44 has the same pulley as your 1998 then it is the large pulley. If you spin the SC with a 3" pulley with a large crank pulley I think the SC would have tons of boost low and loose pressure up high. Magnuson states their MP-62 starts to loose efficiency over 14psi. I've cranks out 16.7psi with a 3.2" pulley last winter but can't get over 15psi this year due to 3" exhaust mods that helped to get the spent charge from backing up in the combustion chamber. I would consider running the water/Meth injection for two reasons. 1. to cool the charge and blower since there is no intercooling and 2. to help seal the rotors to the case on a worn SC. The coating is very thin on the rotors and if it's missing in areas the water/meth with help it seal. You should have no problems with 12psi on a 9.5:1 engine and see nice power with the 12psi of boost since your filling a larger combustion chamber at 9.5:1 with that 12psi. Good luck and ask away at any questions you might have and the board will try to help. Do you know the maximum rpm for a MP-62 blower? I would like to know what that is and who gave you that information. I'm interested??

Originally Posted by JiXer

I am still doing some research, but thought I would drop a new thread in hopes for a quick answer.
I am building an M44 with a DASC kit to put in my e30:

M42 Crank in an M44 to drop compression ratio to around 9.5, Straight intake running MegaSquirt off of MAP, 42# injectors, stock cams, Full length headers, 3" exhaust, map switched to run 91 octane on the street and 99 octane on the track.

I have a crank pulley from a 1998 318ti (6-Rib, measures 5.75" on the outer lip). I calculate it to run the M62 blower at 13,824 RPM at 7,200 engine rpm with the 3" pulley that came with the kit (bought it used off of an e36 M42, not sure what pulley size that is).

I want to max out the boost/hp within reason and figure 12 psi will get me what I am looking for. I know thats on the outer reaches of that compression ratio, but with the MS and knock detection, I figure its worth a try. I cannot find any solid info on what psi to expect out of this set up at those redline numbers. I could get a 2.75" pulley for the blower, to get the blower up near its redline (at engine redline), but I am not sure where that would leave me considering the potential for diminishing returns. I do not plan on running water or methanol injection. The blower is old and the rotors have a few nicks and some of their coating is wearing off, so I don't want to spray them and I don't want to spin them any faster than I need to.

I am also uncertain as to where to start with my cam settings. I am going to keep the stock M44 cams, but I figure I should tune out some of the overlap.
However, I am not sure which direction to take which cam.
I figured I would start with both at a neutral setting, but I don't know enough about where that leaves them to know if that is best.

Any help is appreciated.
Thanks.
J. Farina
Big Fish Motorsports

[xxxJohnBoyxxx]

Another cheep solution to having to run 99 octane at the track is the water/meth system. At a 50/50 mix the methanol injected is 118 octane and will raise your 91 octane much higher during boost only. So you can run 91 for daily driving and let the meth system increase your octane during boost only. It's the best of both worlds because a 99 octane on 9.5:1 with no boost will loose power. I run 93 octane day driving with water/meth during boost to 15+ psi with no issues for 25,000 miles on a 10:1 stock M44. You want the least amount of octane the motor will run safe on and if octane is too high you loose power since it is a much slower burn and flame travel which is needed only when adding boost or advancing timing so you don't get detonation. Snow systems is the best in my opinion for less then $400. It is completely tunable for your motor and I run maybe 5 gallons of methanol per year at $2.36 per gallon...Much cheeper then filling up with 99 octane. If you track the car you will want a oil cooler and cooling system mods to keep everyting in the motor cool during a beating at the track

[JiXer]

Pulley size: I just measured with a caliper across the middle to the outer edges. I know its not precision, but I figured for initial discussion that is was negligible. However, that would suggest that my pulley is even smaller?

Meth: I have just heard so many bad things about what that stuff does to blowers and the rotors are getting hard to come by, so a rebuild could become a problem. My plan is to do what I have to to hit my target boost of 12 psi and run the car to see where it ends up. If at that point, I feel I need to spray it, than I will take that step.

Heat: Yes. I am very concerned about this. However, I am not sure how to go about improving the cooling system without spending big bucks. I am thinking about running an M20 radiator with an e36 fan shroud/reservoir, but I haven't looked in to the practicality of that yet.

Oil Cooler: I really want to do this as well. Do you know of a kit or an affordable solution to add one to an M44?

I was thinking about possibly venting the hood right above the blower too and maybe even spraying it on the outside like you would an intercooler, although both of those things may turn out to be little more than a waste of time.

J.

[xxxJohnBoyxxx]

Originally Posted by JiXer

Pulley size: I just measured with a caliper across the middle to the outer edges. I know its not precision, but I figured for initial discussion that is was negligible. However, that would suggest that my pulley is even smaller?

Meth: I have just heard so many bad things about what that stuff does to blowers and the rotors are getting hard to come by, so a rebuild could become a problem. My plan is to do what I have to to hit my target boost of 12 psi and run the car to see where it ends up. If at that point, I feel I need to spray it, than I will take that step.

Heat: Yes. I am very concerned about this. However, I am not sure how to go about improving the cooling system without spending big bucks. I am thinking about running an M20 radiator with an e36 fan shroud/reservoir, but I haven't looked in to the practicality of that yet.

Oil Cooler: I really want to do this as well. Do you know of a kit or an affordable solution to add one to an M44?

I was thinking about possibly venting the hood right above the blower too and maybe even spraying it on the outside like you would an intercooler, although both of those things may turn out to be little more than a waste of time.

J.

No the pulley is bigger then 3". Use the caliper to measure the diameter from rib to rib. Your rib to center is radius of the pulley circle or half it's diameter. At 3" radius would be a 6" pulley diameter which is not a pulley for a DASC. I estimate by looking at the crank pulley it is 6 inches or less diameter on my car. The DASC pulley's come in 3.6", 3.4" and 3.2". A large crank pulley and 3.2" DASC pulley gives me 16+ psi. Medium crank pulley and 3.4" DASC is around 12psi. Small crank pulley and 3.6" SC pulley (Standard from Downing) will make 8.5psi. On the large crank pulley that I have every .1 inch smaller makes 1.5 psi increase. The 3.6" stock DASC pulley made almost 10 psi out of the box on my car due to the large crank pulley. I will measure my crank pulley as soon as I pull the motor out in a week or two

[JiXer]

Originally Posted by xxxJohnBoyxxx

No the pulley is bigger then 3". Use the caliper to measure the diameter from rib to rib. Your rib to center is radius of the pulley circle or half it's diameter. At 3" radius would be a 6" pulley diameter which is not a pulley for a DASC. I estimate by looking at the crank pulley it is 6 inches or less diameter on my car. The DASC pulley's come in 3.6", 3.4" and 3.2". A large crank pulley and 3.2" DASC pulley gives me 16+ psi. Medium crank pulley and 3.4" DASC is around 12psi. Small crank pulley and 3.6" SC pulley (Standard from Downing) will make 8.5psi. On the large crank pulley that I have every .1 inch smaller makes 1.5 psi increase. The 3.6" stock DASC pulley made almost 10 psi out of the box on my car due to the large crank pulley. I will measure my crank pulley as soon as I pull the motor out in a week or two

You are confused. I did not measure the radius. The full outer diameter of the SC pulley is 2.97" Rib to rib would measure slightly less. Do you measure in the valley of the rib or at the crest? I'm sure it doesn't matter much, but fo ID purposes between different pulleys, it might mean something?
So if I am running the 5.75" crank pulley and a 3" SC pulley, I might be over revving the blower. So for 12 psi and safe revs, I may want to run the 3.4" pulley: http://pulleyboys.com/bmw.html
$90 seems pricey for a pulley?

J.

[xxxJohnBoyxxx]

Originally Posted by JiXer

You are confused. I did not measure the radius. The full outer diameter of the SC pulley is 2.97" Rib to rib would measure slightly less. Do you measure in the valley of the rib or at the crest? I'm sure it doesn't matter much, but fo ID purposes between different pulleys, it might mean something?
So if I am running the 5.75" crank pulley and a 3" SC pulley, I might be over revving the blower. So for 12 psi and safe revs, I may want to run the 3.4" pulley: http://pulleyboys.com/bmw.html
$90 seems pricey for a pulley?

J.

I'm confused I saw middle to edge instead of accross middle to edge. My error. I'm stumped since you have a SC pulley I'm not aware of. If my crank pulley is 6" then you might be ok. I will try a measurement tomorrow so you can calculate my blower rpm and go from there. Sorry about that. Good news is I have the 3.4" and 3.6" pulley's if you want to try them. I could send both and you keep the one you like for half the price of a new one. Both are in excellent condition with less then 100 miles on each

[JiXer]

Originally Posted by xxxJohnBoyxxx

I'm confused I saw middle to edge instead of accross middle to edge. My error. I'm stumped since you have a SC pulley I'm not aware of. If my crank pulley is 6" then you might be ok. I will try a measurement tomorrow so you can calculate my blower rpm and go from there. Sorry about that. Good news is I have the 3.4" and 3.6" pulley's if you want to try them. I could send both and you keep the one you like for half the price of a new one. Both are in excellent condition with less then 100 miles on each

Yeah. That would be awesome if you could hook me up.
My other option is to just get a smaller crank pulley. I could probably do that even cheaper and that would keep the AC compressor, PS pump and alternator spun up higher. Haven't really thought that through yet.

J.

[xxxJohnBoyxxx]

Originally Posted by JiXer

Yeah. That would be awesome if you could hook me up.
My other option is to just get a smaller crank pulley. I could probably do that even cheaper and that would keep the AC compressor, PS pump and alternator spun up higher. Haven't really thought that through yet.

J.

Smaller crank pulley actually will slow down all accessories. Think of like a 10 speed bike the bigger on the crank and smaller on the tire gear makes the most overdrive. Smaller on the crank and larger on the wheel is for mountain climbing.

[JiXer]

Originally Posted by xxxJohnBoyxxx

Smaller crank pulley actually will slow down all accessories. Think of like a 10 speed bike the bigger on the crank and smaller on the tire gear makes the most overdrive. Smaller on the crank and larger on the wheel is for mountain climbing.

Yeah. I just had a brain fart there. Now that I've had a chance to think about it though, I would want to go the opposite way and spin the accessories slower to create less parasitic loss on the system. The reduced drag on the crank would be a good thing considering the added drag of the blower.

I believe alternators hit there peak efficiency at low RPM, PS is the same way, and I will rarely use the AC, so I think I might go that way.

So what pulleys are out there? I don't want less than 5 ribs. I don't want to deal with belt slippage.

J.

[xxxJohnBoyxxx]

I have the exact same pulley as your crank pulley 5.75" outer edge. So with a 3.2" SC pulley it's 15psi summer and 16+ psi in winter. I would go with the 3.4" sc pulley for 12 PSI. Can you post a picture of the DASC? That would help me a lot. Also are you sure it's a MP-62 gen 3 supercharger by magnuson? I would trade my 3.4" or 3.6" sc pulley for your 3" if our SC shafts are matching

[JiXer]

Originally Posted by xxxJohnBoyxxx

I have the exact same pulley as you crank pulley 5.75" outer edge crank pulley with a 3.2" SC pulley at 15psi summer and 16+ psi in winter. I would go with the 3.4" sc pulley for 12 PSI. Can you post a picture of the DASC? That would help me a lot. Also are you sure it's a MP-62 gen 3 supercharger by magnuson? I would trade my 3.4" or 3.6" sc pulley for your 3" if our SC shafts are matching

Yes. I am sure its a gen 3 M62. I may look for that smaller crank pulley first, but I will keep you posted.

J.

[xxxJohnBoyxxx]

Originally Posted by JiXer

So what pulleys are out there? I don't want less than 5 ribs. I don't want to deal with belt slippage.

J.

pulleyboys(dot)com go to the DASC section

[JiXer]

Originally Posted by xxxJohnBoyxxx

pulleyboys(dot)com go to the DASC section

Sorry. I meant what type of CRANK pulleys are out there.
I need at least 5 ribs and would like it to be under 5.75".

J.

[xxxJohnBoyxxx]

Originally Posted by JiXer

Sorry. I meant what type of CRANK pulleys are out there.
I need at least 5 ribs and would like it to be under 5.75".

J.

I can't answer that but call Jim @ Downing Atlanta and he can tell you the different size crank pulleys. There are 3 that I'm aware of but I don't know the actual sizes.

Want to trade out the 3" pulley you have? I would like to try it and see if I can make more a few more pounds of boost...