I just fitted a gauge (to the fuel reg pressure line)
At full throttle at about 4 to 6k my boost gauge sits hard on 6psi.[]
Has anyone else fitted a boost gauge.
SLK230 1998 with Pulley kit.
I know all of that what you did written, but i am telling you that at full throttle is air bypass valve FULLY CLOSED (90% PWM signal), and we still get only 10,5 PSI at 4000 rpm, instead 21 PSI (if i get 10,5 PSI at 2000 rpm at full throttle, then logicaly we should get 21 PSI at 4000 rpm at full throtttle, but WE DONT!!). Why? Where is that pressure lost (remember bypass is closed at full throttle)?
I don't know if the compressor generates a linear pressure/rpm curve while deadheaded, but it's a very safe bet to say that it does not while flowing (at varying flow rates no less), which of course is the condition it is operating under while the engine is running.
The blower is limited by Eaton to about 14,000 rpm, at a 10 psi pressure boost that requires a draw of 25 hp. Once you start to go much above 14,000 rpm the rotors start to lose efficiency and the pressure curve will drop off. There is a limit as to what this unit is designed to do, when left in stock form.
Bruce, to reach 14.000 rpm at SC, you have to spin engine to 6000 rpm, and you must have crankshaft pulley at least 220mm AND SC smaller pulley 83 mm. Only than you can reach cca 14.000 rpm. So, all people who only have cranshaft overdrive pulley do not have to be afraid, because even at 6000 rpm their SC do not reach 13.500 rpm. Even with maximum available cranckshaft overdrive pulley the revs of our SC are still safe beyond 14.000 rpm.
My SC with this pulleys reach cca 14.500 rpm at 5800 engine rpm and i have cca 220 mm cranshaft pulley AND BRABUS S1 83 mm SC pulley. My boost reading with this pulleys write after the SC (at the ALU outlet) is 1,0 BAR (14,5 PSI) at 2000-6000 rpm. Now is here anybody who can tell me, why my readings at 6000 rpms are not 3 BAR (3 times more revs = 3 times more boost)?
The blower is limited by Eaton to about 14,000 rpm, at a 10 psi pressure boost that requires a draw of 25 hp. Once you start to go much above 14,000 rpm the rotors start to lose efficiency and the pressure curve will drop off. There is a limit as to what this unit is designed to do, when left in stock form.
One graph they don't have on that page is pressure vs. flow. 10psi is the max pressure at a minimal flow rate - a condition it's not likely to encounter with the engine WOT at 6000 rpm. Although the first graph indicates that the pressure does not drop significantly as flow increases.
One graph they don't have on that page is pressure vs. flow. 10psi is the max pressure at a minimal flow rate - a condition it's not likely to encounter with the engine WOT at 4000 rpm. Although the first graph indicates that the pressure does not drop significantly as flow increases.
Agree. even though pressure stays the same flow increases.
Also Steve J found the rotors bleed of a lot of boost. He is getting a unit modded to decrease the clearences.
Bruce, to reach 14.000 rpm at SC, you have to spin engine to 6000 rpm, and you must have crankshaft pulley at least 220mm AND SC smaller pulley 83 mm. Only than you can reach cca 14.000 rpm. So, all people who only have crankshaft overdrive pulley do not have to be afraid, because even at 6000 rpm their SC does not reach 13.500 rpm. Even with maximum available crankshaft overdrive pulley the revs of our SC are still safe beyond 14.000 rpm.
I don't think I said that it wasn't safe to go above 14,000 rpm, but I think it's fairly obvious that that is where the design limits are. Go faster and gain less, it's called diminishing returns.....
My SC with this pulleys reach cca 14.500 rpm at 5800 engine rpm and I have cca 220 mm crankshaft pulley AND BRABUS S1 83 mm SC pulley. My boost reading with this pulleys write after the SC (at the ALU outlet) is 1,0 BAR (14,5 PSI) at 2000-6000 rpm. Now is here anybody who can tell me, why my readings at 6000 rpms are not 3 BAR (3 times more revs = 3 times more boost)?
At least part of what you seem to be experiencing is blow by at the rotor lips. As I stated before, there are limits as to what these blowers are capable of. One of those limits is caused by the clearance between the rotor lip, and the housing that it runs in.
You mean in our system? The first graph does indicate that at any given rpm, the compressor outlet pressure does drop as flow increases. It's a small graph to read, but it looks like a 5-10% increase in flow will cut the pressure in half.
If pressure in our system stays the same as system flow AND rpms increase, that would indicate one of two things:
1) The flow/pressure/rpm curves of the compressor match perfectly with the flow/pressure/rpm curves of the system. While possible, this seems highly unlikely.
2) The excess pressure and flow generated by the compressor is being bled off in varying amounts at various rpms to maintain system pressure. This seems more likely.
Has anyone ever blocked off their bleed valve to see what max pressures they could get at various rpms? It would take a heartier soul than me to blindly experiment with that.
One graph they don't have on that page is pressure vs. flow. 10psi is the max pressure at a minimal flow rate - a condition it's not likely to encounter with the engine WOT at 6000 rpm. Although the first graph indicates that the pressure does not drop significantly as flow increases.
I think what you may be missing is the fact that this blower is actually a positive displacement pump, what goes in, WILL come out the other side, provided you stay within the parameters set by the factory. The lip seals and rotor end gap will leak more and more air as speed and pressure start to build up, and that will limit the pressure that this blower can put out. Keep in mind also that the end bearings were designed to have a finite life span at the loads that the unit was designed for. If you crank up the speed, you change the loads and how they are taken on these bearings, that will shorten the lifespan some, and maybe a lot.
Oh no, I'm not missing the fact that it's a PD compressor at all. The first curve on that page backs up my assertion that at any given rpm, as flow increases pressure decreases. If you were pumping something uncompressable, like water, then sure flow would be the same at any pressure (within system and pump limits) with a PD pump. But since air is compressable, PD air compressors do not flow the same at any pressure.
Oh sorry Bazzle I didn't mean from a permanent and practical standpoint, just an experimental one, to see what the compressor was capable of in our system throughout the rev range.
Oh no, I'm not missing the fact that it's a PD compressor at all. The first curve on that page backs up my assertion that as flow increases, pressure decreases. If you were pumping something uncompressable, like water, then sure flow would be the same at any pressure (within system and pump limits) with a PD pump. But since air is compressable, PD air compressors do not flow the same at any pressure.
I agree with you, and at least part of the decrease in flowrate has to do with the clearances around the rotating parts. There is going to be blow by, that's a fact of the design of the unit. It has limitations.
Ok, given all that, and to come full circle back to Snogard's question, I think it's a safe bet to say that:
Given the fact that system psi is defined by many variables (compressor rpm, system flow, and compressor psi/rpm/flow curves) it's not at all guaranteed (and in fact highly unlikely) that if the compressor generates x psi at y rpm in this sytem, that it also generates 2x psi at 2y rpm, except in the case of excess compressor capacity and artifical pressure limiting specifically designed to meet those conditions.
I am still 100% sure that if i get exactly 1 BAR at 2000 rpm at full throttle at 6000 rpm, meassure at kompressor ALU outlet, and if i get THE SAME 1 BAR at 6000 rpm at full throttle, meassure at thge same place, that this is not rotor looses, nor kompressor uncapabilities, but some kind of sensor who tells ECU to open the bleed valve at 1 BAR.
It is TOO MUCH linear (2.000-6.000 rpm exactly 1,0 BAR) too say that rotors loose pressure or that kompressor rich his maximum. Eather case should come out as GRADUALY smaller pressure when rpm goes hi.
You said that when we go MUCH BEYOND 14.000 rpm then dewsign limits come in. And i am telling you that WE DONT GO beyond 14.000 rpm! The pressure 1 BAR (in my case)is exactly the same from 2000 to 6000 engine rpm (so from cca 5000-14.000 kompressor rpms the pressure is the same)!
And graphs you posted clearly shows that looses thruu rpms are irrelevantly small. I am talking about 300% loses, not few% that graphs are showing....
So saga continues....I am more and more possitive that some kind of sensor tells ECU , which open the bypass when predefined pressure is riched.,....
I am still 100% sure that if i get exactly 1 BAR at 2000 rpm at full throttle at 6000 rpm, meassure at kompressor ALU outlet, and if i get THE SAME 1 BAR at 6000 rpm at full throttle, meassure at thge same place, that this is not rotor looses, nor kompressor uncapabilities, but some kind of sensor who tells ECU to open the bleed valve at 1 BAR.
Agreed, but that was not the question I originally responded to. The original question you asked was why does system pressure not double when system rpm doubles, and as you can see from the above discussion, it is highly unlikely except in the case of excess compressor capacity and artificial pressure limiting specifically designed to meet those conditions.
The question above is why does system pressure stay the same as rpm and flow change, and the answer to that, similar the answer to the previous answer, is that it is highly unlikely that system pressure would remain the same as system flow and compressor rpm change. So yes, it is highly likely that at some points on the rpm curve, and possible all points on the rpm curve, the system pressure is being artificially limited.
Agreed, but that was not the question I originally responded to. The original question you asked was why does system pressure not double when system rpm doubles, and as you can see from the above discussion, it is highly unlikely except in the case of excess compressor capacity and artificial pressure limiting specifically designed to meet those conditions.
The question above is why does system pressure stay the same as rpm and flow change, and the answer to that, similar the answer to the previous answer, is that it is highly unlikely that system pressure would remain the same as system flow and compressor rpm change. So yes, it is highly likely that at some points on the rpm curve, and possible all points on the rpm curve, the system pressure is being artificially limited.
Bazzle@
Why do you think that boost reading (measured from the line of the FPR) is max 0,6 BAR (O.K. sometimes 0,7-0,8, but for very short time) at 2000 rpm and the same (0,6 BAR) at 6000 rpm? It would have to be 3 times more (1,8 bar), because kompressor have 3x more revs at 6000 rpm than at 2000 rpm. But the boost is always 0,6 BAR??? I know that engine is using this kompressed air, but it can not be that linear (the same pressure between 2000 and 6000 rpm)?
Am I missing something here or what?
It seems to me that if the blower develops .6 bar at 2,000 rpm, and you turn it 3X as fast, you will get three times as much air, BUT, the engine will use air from that blower three times as fast. The net result is still .6 bar plus or minus a small amount assuming that the blower/engine combination is reasonably balanced.
How do you think there can be 3X the pressure boost if the engine is sucking air 3X as fast as it does at 2,000 rpm?
Am I missing something here or what?
It seems to me that if the blower develops .6 bar at 2,000 rpm, and you turn it 3X as fast, you will get three times as much air, BUT, the engine will use air from that blower three times as fast. The net result is still .6 bar plus or minus a small amount assuming that the blower/engine combination is reasonably balanced.
How do you think there can be 3X the pressure boost if the engine is sucking air 3X as fast as it does at 2,000 rpm?
I get max. 0,6 BAR with bigger crankshaft pulley at 2000-6000 rpm and i get THE SAME max. 0,6 BAR with bigger cranskaft pulley AND smaller kompressor smalller kompressor puley at 2000-6000 rpm. In other words; you can turn kompressor anywhere from 10000- 20000 rpm and you never get more than 0,6 BAR. So obviosly there is some sort of sensor or switch, who opens bypass at 0,6 BAR. The big question is where is that sensor and how can we make it that it doesnt open bypass at 0,6 BAR but maybe at 1 BAR.....
'The boost pressure is determined indirectly from the boost pressure map on the basis of the following parameters: -engine speed -air mass -throttle valve position'
If there was a pressure sensor for boost control, then a pulley kit would have no effect to increase boost...........the ECU would just adjust the air bypass valve to control the boost
ECU remapping would be the only answer............just be thankful they used the indirect method that can be tricked to some extent by the pulley kit
Very good thinking, Bruce.
But.
I get max. 0,6 BAR with bigger crankshaft pulley at 2000-6000 rpm and i get THE SAME max. 0,6 BAR with bigger cranskaft pulley AND smaller kompressor smalller kompressor puley at 2000-6000 rpm. In other words; you can turn kompressor anywhere from 10000- 20000 rpm and you never get more than 0,6 BAR. So obviosly there is some sort of sensor or switch, who opens bypass at 0,6 BAR. The big question is where is that sensor and how can we make it that it doesnt open bypass at 0,6 BAR but maybe at 1 BAR.....
Frankly I don't see anything you have said as obvious here.
(1) Did you have a manifold pressure gage on the car before and after the installation of the bigger crank pulley?
(2) Did you have a manifold pressure gage on the car before and after the installation of the smaller blower pulley?
(3) Just how sure are you that the drive belt isn't slipping on the blower pulley? The blower absorbs AT LEAST 25 hp in it's normal operating trim, and with the stock pulleys. Increase the crank pulley and reduce the driven pulley and you will run into problems with power transmission. How effective that small belt is at getting power to the blower comes into question.
Using the numbers in your signature the blower speed at an engine speed of 6,000 rpm is 16,875 and at 6,200 rpm it is 17,375, that is well over the blowers limit, and the internal losses begin to take effect. If you don't believe me, look up posts by Steve Johnson, he has done the most with these blowers on this board.
Frankly I don't see anything you have said as obvious here.
(1) Did you have a manifold pressure gage on the car before and after the installation of the bigger crank pulley?
(2) Did you have a manifold pressure gage on the car before and after the installation of the smaller blower pulley?
(3) Just how sure are you that the drive belt isn't slipping on the blower pulley? The blower absorbs AT LEAST 25 hp in it's normal operating trim, and with the stock pulleys. Increase the crank pulley and reduce the driven pulley and you will run into problems with power transmission. How effective that small belt is at getting power to the blower comes into question.
Using the numbers in your signature the blower speed at an engine speed of 6,000 rpm is 16,875 and at 6,200 rpm it is 17,375, that is well over the blowers limit, and the internal losses begin to take effect. If you don't believe me, look up posts by Steve Johnson, he has done the most with these blowers on this board.
1.On ALU kompressor outlet (before intercooler):
a) With big crank pulley: 0,8 BAR at 5000+ engine rpm
b) With big crank and small kompressor pulley: 0,8 BAR at 2500+ engine rpm
2.On FPR pipe:
a) With big crank pulley: 0,6 BAR at 5000+ engine rpm
b) With big crank and small kompressor pulley: 0,6 BAR at 2500+ engine rpm
So IT IS OBVIOSLY that anything over 0,6 BAR at Throttle body is blowen out. Smaller kompressor wheel only makes full boost (0,6 BAR) come in sooner. But i can do whatever i wont with overdrive ratio, and i cannot get more than 0,6 BAR at Throttle body.
Now about my ovedrive kompressor rpm ratio:
Exact measurments of my crank pulley at belt line: 220 mm (stock=185 mm)
Exact measurments of my kompressor pulley at belt line: 90 mm (stock=cca 98 mm)
Maximu engine rpm (auto trans,preFl 230K) 5.800 rpm
220:90x5800= 14177 rpm
So very safe kompressor rpm even at maximum engine rpm .:thumbsup: So i dont think that 177 aditional rpm bring drastical looses....
P.S. This days we experimenting (on German mercedes forum) with bypass valve; we discovered that this valve IS NOT mechanicaly fully closed when full throttle is pressed. So we think this is the answer where to boost larger than 0,6 BAR (at throtlle body) goes....
No I dont. USA models have one from what Ive seen.. You can get a tapping for a guage from there .
EDIT: I see you have measured at both sides, foget this post.
Bazzle
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