The Boost with My Roots Blower?
05-04-2003, 12:05 PM
#16
Three Wheelin'
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Any,
With a roots blower flow is proportional to RPM, look at the flow graft flat line.
You may have to speed up the blower, wrong size pulleys.
Check the throttle plate opening, do you really have ¼ at ¼ opening, 1/2 at ½ throttle opening. You may need to adjust the throttle cable. On roots blowers the throttle is mounted at the intake of the blower, the closer it is to the intake valve the more RESPONSIVE the engine will be.
The intakes pipes and throttle body opening could too small, choking off the flow. Do you have a bypass valve if so checks the vacuum signal responses with a gauge, also make sure that the diaphragm is working? Making it all work is the hardest part.
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With a roots blower flow is proportional to RPM, look at the flow graft flat line.
You may have to speed up the blower, wrong size pulleys.
Check the throttle plate opening, do you really have ¼ at ¼ opening, 1/2 at ½ throttle opening. You may need to adjust the throttle cable. On roots blowers the throttle is mounted at the intake of the blower, the closer it is to the intake valve the more RESPONSIVE the engine will be.
The intakes pipes and throttle body opening could too small, choking off the flow. Do you have a bypass valve if so checks the vacuum signal responses with a gauge, also make sure that the diaphragm is working? Making it all work is the hardest part.
<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />
05-04-2003, 04:24 PM
#17
Drifting
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I am no expert.
Normy,
As per Corky Bell author of "Supercharged!" ROOTS type blowers have a volumeteric efficency as well as engines. To figure boost you need to know the system VE ratio, engineVE to blower VE. Since I was never able to get a figure for the VE of the S4 engine I have to experiment.
Steve and Normy,
Notice that the lines on the graph start at 4000 rpm for the blower. Who knows what happens before this? Using a pulley ratio of about 1.65:1 the blower will not reach 4000 rpm until the engine reaches 2424 RPM. So with my setup idle to 2424 rpm is still uncharted territory.
By the way I have 2 crank pulleys one just over 7" and the other at 5.25". SC pulley is 3.12".
With the 5.25" crank pulley the pulley ratio is about 1.65:1. At 6300 engine rpm the blower should move around 600 cfm. If the S4 engine had a VE of .85 at 6300 rpm then it would need 470 cfm. ((600 cfm/470 cfm)x316 stock HP))-30hp to drive blower = 373 system HP. This is a bit conservative ,as I rounded down a bit. I expect around 390 crank HP with the 5.25 pulley.
Now with the 7.2" pulley PR = 2.30:1. SC will spin at a max of about 14400rpm and move about 870cfm. ((870/470)x316))-45= 539 crank HP.
Rick,
Thanks for the post. I will give a full low down soon.
Cheers,
Andy K
Normy,
As per Corky Bell author of "Supercharged!" ROOTS type blowers have a volumeteric efficency as well as engines. To figure boost you need to know the system VE ratio, engineVE to blower VE. Since I was never able to get a figure for the VE of the S4 engine I have to experiment.
Steve and Normy,
Notice that the lines on the graph start at 4000 rpm for the blower. Who knows what happens before this? Using a pulley ratio of about 1.65:1 the blower will not reach 4000 rpm until the engine reaches 2424 RPM. So with my setup idle to 2424 rpm is still uncharted territory.
By the way I have 2 crank pulleys one just over 7" and the other at 5.25". SC pulley is 3.12".
With the 5.25" crank pulley the pulley ratio is about 1.65:1. At 6300 engine rpm the blower should move around 600 cfm. If the S4 engine had a VE of .85 at 6300 rpm then it would need 470 cfm. ((600 cfm/470 cfm)x316 stock HP))-30hp to drive blower = 373 system HP. This is a bit conservative ,as I rounded down a bit. I expect around 390 crank HP with the 5.25 pulley.
Now with the 7.2" pulley PR = 2.30:1. SC will spin at a max of about 14400rpm and move about 870cfm. ((870/470)x316))-45= 539 crank HP.
Rick,
Thanks for the post. I will give a full low down soon.
Cheers,
Andy K
05-05-2003, 01:28 AM
#18
Three Wheelin'
Firstly, congratulations on the progress of your project!
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">I was never able to get a figure for the VE of the S4 engine I have to experiment. </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">On page 32 the last paragraph, Corky says it's reasonable to use 80% VE for two-valve engines, and 88% for four-valve engines.
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> ..and move about 870cfm. ((870/470)x316))-45= 539 crank HP. </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Although your numbers are reasonable, you are not taking into consideration the loss of charge density due to heat which is magnified again since you’re not using an intercooler.
870 cfm requires approximately 12 psi of boost, or a Pressure Ratio (PR) of 1.82. The discharge temp of the supercharger is the Ideal Temp Gain made by the supercharger divided by the it’s thermal efficiency, which is 55% for a roots blower:
((PR^0.28 – 1) x Absolute Temp) / SC Thermal Efficiency)
(100.04 / .55) = 181.88 degrees, which is the Real Temp Gain.
Finally, using our Real Temp Gain, we can calculate the Density Ratio (DR) which ends up being .75. Taking your calculation of 539 crank HP and multiplying by our DR .75 we end up with only 404 HP which is quite a difference.
If an intercooler with 85% efficiency is employed, our DR calculates out to .95 which ends up giving us 512 HP, a 100 horsepower gain.
Now for the important part, the heat generated by the combination of compression ratio and the supercharger.
To make a long story short, a non-intercooled roots at just 5 psi (..1,167.38 degrees) generates more heat than the max of 1,075 degrees listed on page 37 .
Now that 1075 is ‘an arbitrary’ figure from Corky, and the actual number will vary for an engine type. But the question is, how much variation for an S4 and it’s favorable aluminum heads and pent-roof combustion chamber?
Well, the light bulb finally flickered when I recalled that Mark at FAST ran his centrifugal blower non-intercooled at 5 psi with apparently no problems (..a 32 valve ’85?). The combination of 10:1 compression ratio at 5 psi of non-intercooled boost produces a seemingly ‘S4 safe’ combustion chamber temp of 1,167, 92 degrees over the 1,075 'max'.
So the question is, will a roots with it’s greater heat output due to it's worse thermal efficiency be able to run at 5 psi too? It’s combustion chamber temp comes out to be 1,210.79 degrees, 44 degrees more than the new ‘S4 safe’ number. Hopefully it will; time will tell.
Since there’s no intercooler, I wouldn’t try to run more than 5 psi at this point.
Since detonation is the true bane of a supercharged engine, it is paramount to be able to accurately detect and monitor if and when the phenomenon occurs.
So the question is, does anyone know how to tap into and monitor the spark-knock sensor?
If one were able to do this, blowing up supercharged engines due to detonation before they’re dialed in would almost become a thing of the past.
The best of luck, and thanks for keeping us posted! If you have the time, read thru Chapter 4, 'The Balance of Heat' as it's very informative. Try to get your car onto a dyno as soon as possible so you can dial in your air/fuel ratio so you won't inadvertantly run lean and detonate.
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">I was never able to get a figure for the VE of the S4 engine I have to experiment. </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">On page 32 the last paragraph, Corky says it's reasonable to use 80% VE for two-valve engines, and 88% for four-valve engines.
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> ..and move about 870cfm. ((870/470)x316))-45= 539 crank HP. </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Although your numbers are reasonable, you are not taking into consideration the loss of charge density due to heat which is magnified again since you’re not using an intercooler.
870 cfm requires approximately 12 psi of boost, or a Pressure Ratio (PR) of 1.82. The discharge temp of the supercharger is the Ideal Temp Gain made by the supercharger divided by the it’s thermal efficiency, which is 55% for a roots blower:
((PR^0.28 – 1) x Absolute Temp) / SC Thermal Efficiency)
(100.04 / .55) = 181.88 degrees, which is the Real Temp Gain.
Finally, using our Real Temp Gain, we can calculate the Density Ratio (DR) which ends up being .75. Taking your calculation of 539 crank HP and multiplying by our DR .75 we end up with only 404 HP which is quite a difference.
If an intercooler with 85% efficiency is employed, our DR calculates out to .95 which ends up giving us 512 HP, a 100 horsepower gain.
Now for the important part, the heat generated by the combination of compression ratio and the supercharger.
To make a long story short, a non-intercooled roots at just 5 psi (..1,167.38 degrees) generates more heat than the max of 1,075 degrees listed on page 37 .
Now that 1075 is ‘an arbitrary’ figure from Corky, and the actual number will vary for an engine type. But the question is, how much variation for an S4 and it’s favorable aluminum heads and pent-roof combustion chamber?
Well, the light bulb finally flickered when I recalled that Mark at FAST ran his centrifugal blower non-intercooled at 5 psi with apparently no problems (..a 32 valve ’85?). The combination of 10:1 compression ratio at 5 psi of non-intercooled boost produces a seemingly ‘S4 safe’ combustion chamber temp of 1,167, 92 degrees over the 1,075 'max'.
So the question is, will a roots with it’s greater heat output due to it's worse thermal efficiency be able to run at 5 psi too? It’s combustion chamber temp comes out to be 1,210.79 degrees, 44 degrees more than the new ‘S4 safe’ number. Hopefully it will; time will tell.
Since there’s no intercooler, I wouldn’t try to run more than 5 psi at this point.
Since detonation is the true bane of a supercharged engine, it is paramount to be able to accurately detect and monitor if and when the phenomenon occurs.
So the question is, does anyone know how to tap into and monitor the spark-knock sensor?
If one were able to do this, blowing up supercharged engines due to detonation before they’re dialed in would almost become a thing of the past.
The best of luck, and thanks for keeping us posted! If you have the time, read thru Chapter 4, 'The Balance of Heat' as it's very informative. Try to get your car onto a dyno as soon as possible so you can dial in your air/fuel ratio so you won't inadvertantly run lean and detonate.
05-05-2003, 02:44 AM
#19
Drifting
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Laguavlin,
Where have you been all this time? Thanks for the new reading material. Please be on the lookout for my posts on this topic. I am going to read your whole post then respond.
Andy K
Where have you been all this time? Thanks for the new reading material. Please be on the lookout for my posts on this topic. I am going to read your whole post then respond.
Andy K
05-05-2003, 08:53 AM
#20
Three Wheelin'
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Where have you been all this time? Thanks for the new reading material. Please be on the lookout for my posts on this topic.</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">I have been following your project with great interest the entire time. You certainly have some big brass ones to pop a roots onto your car! I'm sure everyone on this board is impressed with your accomplishments so far as a roots install is much more involved than a centrifugal.
With that said however, you're probably 60-70% done as you've got quite a bit of work ahead of you in the form of tuning. You've made it this far, you can certainly make it the rest of the way.
I would say to go ahead and nail down the air/fuel ratio first, then go after and address your boost issues next.
Now that I've said that, I can't help but think about the indicated 10 psi of boost you reported which you really don't want to be running as you're not cooling the charge.
Well, try to be patient and don't rush ANYTHING.
With that said however, you're probably 60-70% done as you've got quite a bit of work ahead of you in the form of tuning. You've made it this far, you can certainly make it the rest of the way.
I would say to go ahead and nail down the air/fuel ratio first, then go after and address your boost issues next.
Now that I've said that, I can't help but think about the indicated 10 psi of boost you reported which you really don't want to be running as you're not cooling the charge.
Well, try to be patient and don't rush ANYTHING.
05-05-2003, 12:07 PM
#21
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Your best option is to get the thing to a dyno, and do a few runs with a wide band o2 as well as a stand alone knock sensor.
Monitor it VERY closely. I recall hearing people with 6 psi of boost on a stock S4 lower end grenading ring lands with no detonation ever being detected.
I think if you keep it down around 5-6 psi, you will be alright. Remember, you have 10:1 pistons and no charge cooler. Your Threshhold for detonation will be pretty low...don't grenade it!
My goal is 14 psi at the manifold, but I am turbocharged and on 8:1 compression with a charge cooler (hopefully a bigger one soon!). Also, my motor starts at only 230 HP, so I have to shove more boost to get the same power you can make with just 5 psi. You should be able to make 420-475 HP with that engine pretty easily. Your stock fuel pump is probably good for 475 HP, so make sure you check its flow rate at the fuel pressure you intend to run.
Good Luck and keep us all posted. There seems to be a lot of people going the forced induction route with the 928!
Monitor it VERY closely. I recall hearing people with 6 psi of boost on a stock S4 lower end grenading ring lands with no detonation ever being detected.
I think if you keep it down around 5-6 psi, you will be alright. Remember, you have 10:1 pistons and no charge cooler. Your Threshhold for detonation will be pretty low...don't grenade it!
My goal is 14 psi at the manifold, but I am turbocharged and on 8:1 compression with a charge cooler (hopefully a bigger one soon!). Also, my motor starts at only 230 HP, so I have to shove more boost to get the same power you can make with just 5 psi. You should be able to make 420-475 HP with that engine pretty easily. Your stock fuel pump is probably good for 475 HP, so make sure you check its flow rate at the fuel pressure you intend to run.
Good Luck and keep us all posted. There seems to be a lot of people going the forced induction route with the 928!
05-06-2003, 01:27 AM
#22
Drifting
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Lagavulin,
I honestly haven't read the whole book.
I have been working under the "Build it and they will come" precept. And it has worked. With "they" being people like yourself, who for instance put the PR into prespective, even as it relates to this project. "They" will help me along and have a right to some credit. Thanks for doing the math. But it is not the math that matters. An objective statement based on calculations or actual experience is worth a million times more than the passing of hearsay. Thanks for your support!
I have never planned on going with more than 5 psi without intercooling. I have gathered from various readings, mainly here that I shouldn't pass that #. I started this post to figure out what level of boost I really have. I only saw 10psi for a split second. I don't think it would have held 10psi, but I was not going to find out given the golden rule of 5psi. Instead of laying down huge strips of rubber and grinning ear to ear (ok, well I did a little of each) I came back here to ask you guys about measuring boost with with a roots.
Your next mission should you choose accept it is to figure the boost generated using the 5.25:3.12 pulley ratio. Then the 7.2:3.12 ratio.
John,
Thanks for your contributions on my topics. I have learned from them as well as your own topics. I have to ask though who are these people that have smashed ringlands? I have yet to see real proof of this.
If anyone can bringforth a real person that actually smashed ringlands of an S4 on 6 psi then they will get their choice of any tool from my tool kit (jack, pump, spare included) or my single remaining tweeter speaker grill.
14psi, 8:1 CR, Air to air intercooling, sounds familiar. Ah, 959 rings a bell. Speaking of that The 959, and S4 share the same combustion chamber and valves. A design meant to shed hot spots and lower possibility of detonation. It seems that they would have done something to those S4 pistons too.
I hope to get the car to a dyno this weekend. Does anyone know of one in Torrance or surrounding area?
Steve,
That was a good question about the throttle being opened by 1/2 at 1/2. It is not. At 1/2 of bell crank travel the buterfly seems to be at about 1/8. It is very progressive after that. I wonder how changing that would affect the bowden cable operation?
<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />
Andy K
I honestly haven't read the whole book.
I have been working under the "Build it and they will come" precept. And it has worked. With "they" being people like yourself, who for instance put the PR into prespective, even as it relates to this project. "They" will help me along and have a right to some credit. Thanks for doing the math. But it is not the math that matters. An objective statement based on calculations or actual experience is worth a million times more than the passing of hearsay. Thanks for your support!
I have never planned on going with more than 5 psi without intercooling. I have gathered from various readings, mainly here that I shouldn't pass that #. I started this post to figure out what level of boost I really have. I only saw 10psi for a split second. I don't think it would have held 10psi, but I was not going to find out given the golden rule of 5psi. Instead of laying down huge strips of rubber and grinning ear to ear (ok, well I did a little of each) I came back here to ask you guys about measuring boost with with a roots.
Your next mission should you choose accept it is to figure the boost generated using the 5.25:3.12 pulley ratio. Then the 7.2:3.12 ratio.
John,
Thanks for your contributions on my topics. I have learned from them as well as your own topics. I have to ask though who are these people that have smashed ringlands? I have yet to see real proof of this.
If anyone can bringforth a real person that actually smashed ringlands of an S4 on 6 psi then they will get their choice of any tool from my tool kit (jack, pump, spare included) or my single remaining tweeter speaker grill.
14psi, 8:1 CR, Air to air intercooling, sounds familiar. Ah, 959 rings a bell. Speaking of that The 959, and S4 share the same combustion chamber and valves. A design meant to shed hot spots and lower possibility of detonation. It seems that they would have done something to those S4 pistons too.
I hope to get the car to a dyno this weekend. Does anyone know of one in Torrance or surrounding area?
Steve,
That was a good question about the throttle being opened by 1/2 at 1/2. It is not. At 1/2 of bell crank travel the buterfly seems to be at about 1/8. It is very progressive after that. I wonder how changing that would affect the bowden cable operation?
<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />
Andy K
05-06-2003, 10:29 AM
#23
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Call Marc at Devek. He has experience with one S4 that smashed on a load dyno at 6-7 psi. They were running that car for sustained periods (i.e. minutes) under boost, so that certainly may have contributed.
Marc also dismantled an early Callway single turbo car with smashed ring lands. The rumor was that car ran on 6 to 8 psi of boost, no charge cooler, but water injection. 8.5:1 compression. I suspect someone turned up the dial on it once... and for all. That car now has a Euro S engine in it. The owner still has the Callaway kit from the car.
Quick Carl smashed a ring land on his supercharged 928 on 11 psi with no charge cooler. I think he is about 8.5:1 or 9:1 compression. He has some pictures.
I know of at least two Callaway 928s and one Callaway 944 that suffered this failure as well.
I think as long as you control detonation, you will be just fine. Make sure you have a bit of extra fuel in there to avoid any lean situations.
Now, with that said, my car never had an issue on 8-9 psi. There is also another twin turbo Callaway 928 that resides in NY. The owner claims to have run 14 psi on the stock internals...not sure I would do that! Mine ran quite well for 20 years. I also heard of two Callaway 944s on stock, machined pistons running 12 to 14 psi at the manifold. Those engines ran a steel liner. The second (14 psi engine) blew a ring land after the owner covered the air entrance to the charge cooler with a bra. That owner put 951 pistons in his car.
I looked at it this way: I wanted to up the boost and not worry about ring lands taking a dump on me. Most OEM turbo engines run on forged pistons, so I bit the bullet now and I am in the process of upgrading. I would have felt safe to about 10 psi, but not north of there.
I'm not saying what you have won't work, because I think it will. I am saying you need to be very cautious with monitoring your air fuel ratio and be very aware of detonation...sometimes it can't be heard and this is the kiss of death to a blown engine.
Detonation will also destroy the strongest forged piston out there, no questions asked. I just didn't feel safe running high boost levels on those pistons, given the track record.
Anyway, dyno that thing and let us all know how much POWER it has. My guess is it should be around 400-450!
Marc also dismantled an early Callway single turbo car with smashed ring lands. The rumor was that car ran on 6 to 8 psi of boost, no charge cooler, but water injection. 8.5:1 compression. I suspect someone turned up the dial on it once... and for all. That car now has a Euro S engine in it. The owner still has the Callaway kit from the car.
Quick Carl smashed a ring land on his supercharged 928 on 11 psi with no charge cooler. I think he is about 8.5:1 or 9:1 compression. He has some pictures.
I know of at least two Callaway 928s and one Callaway 944 that suffered this failure as well.
I think as long as you control detonation, you will be just fine. Make sure you have a bit of extra fuel in there to avoid any lean situations.
Now, with that said, my car never had an issue on 8-9 psi. There is also another twin turbo Callaway 928 that resides in NY. The owner claims to have run 14 psi on the stock internals...not sure I would do that! Mine ran quite well for 20 years. I also heard of two Callaway 944s on stock, machined pistons running 12 to 14 psi at the manifold. Those engines ran a steel liner. The second (14 psi engine) blew a ring land after the owner covered the air entrance to the charge cooler with a bra. That owner put 951 pistons in his car.
I looked at it this way: I wanted to up the boost and not worry about ring lands taking a dump on me. Most OEM turbo engines run on forged pistons, so I bit the bullet now and I am in the process of upgrading. I would have felt safe to about 10 psi, but not north of there.
I'm not saying what you have won't work, because I think it will. I am saying you need to be very cautious with monitoring your air fuel ratio and be very aware of detonation...sometimes it can't be heard and this is the kiss of death to a blown engine.
Detonation will also destroy the strongest forged piston out there, no questions asked. I just didn't feel safe running high boost levels on those pistons, given the track record.
Anyway, dyno that thing and let us all know how much POWER it has. My guess is it should be around 400-450!
05-06-2003, 03:32 PM
#24
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Tim Murphy's S4 was running 8psi of boost for a year or more, with no intercooler. Even with some leaner than optimum air/fuel ratios before he got that straightened out, there were no problems with the stock 10:1 pistons. Running a boosted car on the dyno for long periods of time is not a good idea unless there's a lot of airflow provided over the intercooler, if it has one that is.
05-07-2003, 12:56 AM
#25
Three Wheelin'
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> Your next mission should you choose accept it is to figure the boost generated using the 5.25:3.12 pulley ratio. Then the 7.2:3.12 ratio.</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Damn, it's deep in enemy territory and no turning back once under way... Alrighty then.
In order to do that, we need to know some specs on the Eaton M112, most significant is the displacement per revolution. This link provides the details:
<a href="http://www.automotive.eaton.com/product/engine_controls/M112.html" target="_blank">http://www.automotive.eaton.com/product/engine_controls/M112.html</a>
Since it’s listed as 1.84 Liters/Rev, we need to convert to cubic feet per revolution. The conversion factor is 0.0353147, and we get:
(1.87 Liters/Rev) x 0.0353147 = 0.065 cubic ft/min (ft^3/min)
Now we will see what size crankshaft pulley we need in order to produce 5 psi, and we will need to calculate the required supercharger speed:
Supercharger Speed = (Desired CFM) / (SC Displacement/Revolution)
At this point we don’t know the CFM we’re shooting for so we’ll need to calculate the Pressure Ratio (PR) and use that result and multiply against the normally aspirated CFM.
PR = (14.7psi + boost) / 14.7psi
PR = (14.7psi + 5psi) / 14.7psi = 1.34
Our stock airflow rate in CFM is calculated as such:
CFM = (cid x rpm x 0.5 x VE) / 1728
CFM = (302 x 6,200 x 0.5 x 0.88) / 1728 = 476.8cfm
And now the desired CFM we are after with supercharging:
Desired CFM = (Stock CFM) x PR = (477 CFM) x (1.34 PR) = 639 CFM
Now we have everything needed to calculate the required supercharger speed using the following calc:
Supercharger Speed = (Desired CFM) / (SC Displacement/Revolution)
Supercharger Speed = (639 CFM) / (0.065 ft^3/min) = 9,831 RPM
9,831 RPM is within range as the link states the M112’s max is 12,000 RPM.
Now we need to calculate the pulley ratio to determine how large the crankshaft pulley must be with respect to the SC pulley:
Pulley Ratio = (SC RPM) / (Max Engine RPM) = (9,831 SC RPM) / (6,200 Max Eng RPM) = 1.59
Now that we have the pulley ratio, we can now calculate the required crankshaft pulley diameter:
Required Crankshaft Pulley Size = SC Pulley x Pulley Ratio
Required Crankshaft Pulley Size = 3.12” x 1.59 = 4.96”
So we end up with a crankshaft pulley that’s supposed to be 4.96” in order to produce 5 psi. Well, Andy K only has a 5.25” and a 7.2” pulley which will both produce more than the target of 5 psi. What will those pulleys produce, boost-wise?
We will now work backwards.
Crankshaft Pulley Size = SC Pulley x Pulley Ratio
Pulley Ratio = (Crankshaft Pulley Size) / (SC Pulley)
Pulley Ratio = 5.25” / 3.12” = 1.68
So 1.68 is the pulley ratio we have in the toolbox to work with.
Next, we need to find the speed at which the supercharger will turn with the pulley ratio.
Pulley Ratio = (SC RPM) / (Max Eng RPM)
SC RPM = (Pulley Ratio) x (Max Eng RPM)
SC RPM = 1.68 x 6200rpm = 10,416 RPM
So we will be turning the supercharger at 10,416 RPM with this pulley setup. The next question is, how many CFM will it produce at that speed?
SC RPM = (New CFM) / (SC Displacement/Revolution)
(New CFM) = (SC RPM) x (SC Displacement/Revolution)
(New CFM) = 10,416 x .065 ft^3/min = 677 cfm
So now we know that we will produce 677 CFM, and with that, we can calculate the amount of boost:
New CFM = PR x (Stock CFM)
PR = (New CFM) / (Stock CFM)
(14.7 + boost) / 14.7 = (New CFM) / (Stock CFM)
(14.7 + boost) = [(New CFM) / (Stock CFM)] x 14.7
boost = [[(New CFM) / (Stock CFM)] x 14.7] – 14.7
boost = [[(677cfm) / (477cfm)] x 14.7] – 14.7 = 6.16 psi
So the pulley combination of 5.25” and 3.12” will produce 6.2 psi.
And the pulley combination of 7.2” and 3.12” will produce 13.99 psi.
It is interesting to note that besides producing an unusable amount of boost, the supercharger will spin at 14,322 RPM, far above it’s max of 12,000 RPM.
In order to do that, we need to know some specs on the Eaton M112, most significant is the displacement per revolution. This link provides the details:
<a href="http://www.automotive.eaton.com/product/engine_controls/M112.html" target="_blank">http://www.automotive.eaton.com/product/engine_controls/M112.html</a>
Since it’s listed as 1.84 Liters/Rev, we need to convert to cubic feet per revolution. The conversion factor is 0.0353147, and we get:
(1.87 Liters/Rev) x 0.0353147 = 0.065 cubic ft/min (ft^3/min)
Now we will see what size crankshaft pulley we need in order to produce 5 psi, and we will need to calculate the required supercharger speed:
Supercharger Speed = (Desired CFM) / (SC Displacement/Revolution)
At this point we don’t know the CFM we’re shooting for so we’ll need to calculate the Pressure Ratio (PR) and use that result and multiply against the normally aspirated CFM.
PR = (14.7psi + boost) / 14.7psi
PR = (14.7psi + 5psi) / 14.7psi = 1.34
Our stock airflow rate in CFM is calculated as such:
CFM = (cid x rpm x 0.5 x VE) / 1728
CFM = (302 x 6,200 x 0.5 x 0.88) / 1728 = 476.8cfm
And now the desired CFM we are after with supercharging:
Desired CFM = (Stock CFM) x PR = (477 CFM) x (1.34 PR) = 639 CFM
Now we have everything needed to calculate the required supercharger speed using the following calc:
Supercharger Speed = (Desired CFM) / (SC Displacement/Revolution)
Supercharger Speed = (639 CFM) / (0.065 ft^3/min) = 9,831 RPM
9,831 RPM is within range as the link states the M112’s max is 12,000 RPM.
Now we need to calculate the pulley ratio to determine how large the crankshaft pulley must be with respect to the SC pulley:
Pulley Ratio = (SC RPM) / (Max Engine RPM) = (9,831 SC RPM) / (6,200 Max Eng RPM) = 1.59
Now that we have the pulley ratio, we can now calculate the required crankshaft pulley diameter:
Required Crankshaft Pulley Size = SC Pulley x Pulley Ratio
Required Crankshaft Pulley Size = 3.12” x 1.59 = 4.96”
So we end up with a crankshaft pulley that’s supposed to be 4.96” in order to produce 5 psi. Well, Andy K only has a 5.25” and a 7.2” pulley which will both produce more than the target of 5 psi. What will those pulleys produce, boost-wise?
We will now work backwards.
Crankshaft Pulley Size = SC Pulley x Pulley Ratio
Pulley Ratio = (Crankshaft Pulley Size) / (SC Pulley)
Pulley Ratio = 5.25” / 3.12” = 1.68
So 1.68 is the pulley ratio we have in the toolbox to work with.
Next, we need to find the speed at which the supercharger will turn with the pulley ratio.
Pulley Ratio = (SC RPM) / (Max Eng RPM)
SC RPM = (Pulley Ratio) x (Max Eng RPM)
SC RPM = 1.68 x 6200rpm = 10,416 RPM
So we will be turning the supercharger at 10,416 RPM with this pulley setup. The next question is, how many CFM will it produce at that speed?
SC RPM = (New CFM) / (SC Displacement/Revolution)
(New CFM) = (SC RPM) x (SC Displacement/Revolution)
(New CFM) = 10,416 x .065 ft^3/min = 677 cfm
So now we know that we will produce 677 CFM, and with that, we can calculate the amount of boost:
New CFM = PR x (Stock CFM)
PR = (New CFM) / (Stock CFM)
(14.7 + boost) / 14.7 = (New CFM) / (Stock CFM)
(14.7 + boost) = [(New CFM) / (Stock CFM)] x 14.7
boost = [[(New CFM) / (Stock CFM)] x 14.7] – 14.7
boost = [[(677cfm) / (477cfm)] x 14.7] – 14.7 = 6.16 psi
So the pulley combination of 5.25” and 3.12” will produce 6.2 psi.
And the pulley combination of 7.2” and 3.12” will produce 13.99 psi.
It is interesting to note that besides producing an unusable amount of boost, the supercharger will spin at 14,322 RPM, far above it’s max of 12,000 RPM.
05-07-2003, 02:17 AM
#27
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In the words of Bill and Ted...
"Whoa"
Ya know, if you could grade posts on here, that one is theee bench mark to grade against! Great info and clearly explained. Thnx. I cut and paste that whole thing to my "porsche" file...just becasue!.
<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />
"Whoa"
Ya know, if you could grade posts on here, that one is theee bench mark to grade against! Great info and clearly explained. Thnx. I cut and paste that whole thing to my "porsche" file...just becasue!.
<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />
05-07-2003, 04:12 AM
#28
Drifting
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Tony,
In the words of Captian Willard "Absolutely g@&*$# right".....and may I add, with only 28 previous posts. What if you compared this to the majority of the "White GTS" replies? What we have here is Big 3 quality with only 28 previous posts. Makes me wonder who else is out there.
Lagavulin,
You are the man. Your post saved me a lot of time and it is among the best of replies I have seen. It has the great positive value of being based on pure and simple figures. While you were calculating and posting I was able to determine with large certainty that the Lightning intercooler would fit under my SC. I am relieved to see that I won't need it to produce 423 crank hp at 5psi according to the <a href="http://www.superchargeronline.com/hp_calculator.asp" target="_blank">SC HP calculator</a> . Team work! Does that figure sound right you? I hope you will tell us soon. (check out the HP calculator with 14 psi and 3 core intercooler, 595 at the crank).
I feel confident in dynoing the car with the 5.25 crank pulley now, not for max power but fo tuning and to begin to work out the bugs.
We need a graemlin to symbolize hats off. Until then this will have to do <img border="0" alt="[burnout]" title="" src="graemlins/burnout.gif" />
Andy K
In the words of Captian Willard "Absolutely g@&*$# right".....and may I add, with only 28 previous posts. What if you compared this to the majority of the "White GTS" replies? What we have here is Big 3 quality with only 28 previous posts. Makes me wonder who else is out there.
Lagavulin,
You are the man. Your post saved me a lot of time and it is among the best of replies I have seen. It has the great positive value of being based on pure and simple figures. While you were calculating and posting I was able to determine with large certainty that the Lightning intercooler would fit under my SC. I am relieved to see that I won't need it to produce 423 crank hp at 5psi according to the <a href="http://www.superchargeronline.com/hp_calculator.asp" target="_blank">SC HP calculator</a> . Team work! Does that figure sound right you? I hope you will tell us soon. (check out the HP calculator with 14 psi and 3 core intercooler, 595 at the crank).
I feel confident in dynoing the car with the 5.25 crank pulley now, not for max power but fo tuning and to begin to work out the bugs.
We need a graemlin to symbolize hats off. Until then this will have to do <img border="0" alt="[burnout]" title="" src="graemlins/burnout.gif" />
Andy K
05-07-2003, 02:06 PM
#29
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Sounds like a good plan for you to stay sub 10. The 8 psi number is certainly valid, since this owner has had no issues with piston ring land failures. Again, it is all about controlling detonation. I would think 5-6 psi would be perfect.
If you look in all the publications, 10 psi on 10:1 compression is a no-no.
With that said, I have a 93 Audi S4 5 cylinder...9:1 compression running 21-24 psig at the manifold...yes that is gauge pressure, not absolute pressure. The "recommended" limit on such a compression ratio is about 10 psi, but my motor continues to survive with 205,000 miles on the clock.
That animal is bulletproof. Now if I could only run that much boost through the 928...?
If you look in all the publications, 10 psi on 10:1 compression is a no-no.
With that said, I have a 93 Audi S4 5 cylinder...9:1 compression running 21-24 psig at the manifold...yes that is gauge pressure, not absolute pressure. The "recommended" limit on such a compression ratio is about 10 psi, but my motor continues to survive with 205,000 miles on the clock.
That animal is bulletproof. Now if I could only run that much boost through the 928...?
05-07-2003, 09:14 PM
#30
Drifting
Lagavulin, ditto on what Tony and Andy said!!!!! Absolutely great post. One of the most well broken down, well thought out responses ever!!!!!! You're not even helping me, and I'm thrilled to read your response. :-)