supercharger boost problem
Discussion
Can anyone offer any suggestions?
I've fitted an Eaton supercharger to the standard compression ratio Renault F7R (Williams) engine, worked that to give 6.6psi boost I would need a 1.95:1 ration. Problem is that now its running the gauge shows 14psi (with or without exhaust fitted). Far as I can see the formula and calculation are right!!?
I've fitted an Eaton supercharger to the standard compression ratio Renault F7R (Williams) engine, worked that to give 6.6psi boost I would need a 1.95:1 ration. Problem is that now its running the gauge shows 14psi (with or without exhaust fitted). Far as I can see the formula and calculation are right!!?
OK, so is that calc to give the boost pressure? Looks fairly sensible, have you measured teh temperature? Do you have an intercooler? That calculation only looks at the volumetric effect of the air, but I would expect that the temperature rise through the SC may give an additional 50% pressure rise as the air tries to expand; still not enough to give 14 psi though!
I assume your measured 14psi is gauge rather than absolute? (ie it goes to zero with the engine off?)
The reason position may be important is that if the sensor plane is perpendicular to the airflow it will read static rather than total pressure which is lower, but in this case you seem to be getting a high pressure so I don't think that's the problem. Incidentally, I assume that this pressure reading is at WOT? If you are throttled back, then the engine cc will drop dramatically as the throttle reduces flow through the engine...
I assume your measured 14psi is gauge rather than absolute? (ie it goes to zero with the engine off?)
The reason position may be important is that if the sensor plane is perpendicular to the airflow it will read static rather than total pressure which is lower, but in this case you seem to be getting a high pressure so I don't think that's the problem. Incidentally, I assume that this pressure reading is at WOT? If you are throttled back, then the engine cc will drop dramatically as the throttle reduces flow through the engine...
Hi
Temp is ambient/very low as I've only run it for 30 seconds each time. No intercooler fitted because the boost is supposed to be really low to avoid damaging the engine (hence why I'm not running for long periods); the gauge is dropping back to and starting off at zero. The output on the Eaton M45 (ex Cooper S) has an output at 90 degrees to the rotor plane and the gauge pickup is inline with the flow (not at 90 degrees). Pressure reading is at tick over and it raises when revs applied (dont know what WOT means). Your thoughts are making me focus on the gauge/ siting of the gauge, but I never thought the position would make such a big difference (8psi)
Thanks for your help so far
Temp is ambient/very low as I've only run it for 30 seconds each time. No intercooler fitted because the boost is supposed to be really low to avoid damaging the engine (hence why I'm not running for long periods); the gauge is dropping back to and starting off at zero. The output on the Eaton M45 (ex Cooper S) has an output at 90 degrees to the rotor plane and the gauge pickup is inline with the flow (not at 90 degrees). Pressure reading is at tick over and it raises when revs applied (dont know what WOT means). Your thoughts are making me focus on the gauge/ siting of the gauge, but I never thought the position would make such a big difference (8psi)
Thanks for your help so far
Sorry,
not sure what you mean here? Do you mean the "air chamber" after the throttle body? Would just before the throttle boy give a lower reading do you think? This would obviously be a much easier operation as I can just tap into the pipework rather than having to remove bits of engine?
Thanks
not sure what you mean here? Do you mean the "air chamber" after the throttle body? Would just before the throttle boy give a lower reading do you think? This would obviously be a much easier operation as I can just tap into the pipework rather than having to remove bits of engine?
Thanks
I don't think the positioning of the sensor is your problem. You may be getting some errors, but I doubt it would indicate double the actual pressure.
With regards to temperature, the question was about teh temperature coming out of the SC, rather than the ambient temperature. As the SC compressors the air, it gets hotter, so you may think you've got 2 x the air, but actually get more than 2 x the pressure as it expands. Feel the SC housing or inlet manifold and see how hot it is; if it's almost too hot to touch, than that'll probably cause a 25% further increase in boost rpessure (but still not double).
WOT is Wide Open Throttle. The engine capacity in your calculation assumes that the throttle is wide open; ie a 2 litre engine only takes 2 litres of ambient air (every other revolution) when your foot is to the floor. At lower throttle openings, it takes in less air. I suspect that what is happening, is your supercharger is trying to deliver the air into the engine at the correct flow rate, but the closed throttle is putting back pressure on the supercharger.
With regards to temperature, the question was about teh temperature coming out of the SC, rather than the ambient temperature. As the SC compressors the air, it gets hotter, so you may think you've got 2 x the air, but actually get more than 2 x the pressure as it expands. Feel the SC housing or inlet manifold and see how hot it is; if it's almost too hot to touch, than that'll probably cause a 25% further increase in boost rpessure (but still not double).
WOT is Wide Open Throttle. The engine capacity in your calculation assumes that the throttle is wide open; ie a 2 litre engine only takes 2 litres of ambient air (every other revolution) when your foot is to the floor. At lower throttle openings, it takes in less air. I suspect that what is happening, is your supercharger is trying to deliver the air into the engine at the correct flow rate, but the closed throttle is putting back pressure on the supercharger.
Crofty2011 said:
Sorry,
not sure what you mean here? Do you mean the "air chamber" after the throttle body? Would just before the throttle boy give a lower reading do you think? This would obviously be a much easier operation as I can just tap into the pipework rather than having to remove bits of engine?
Thanks
Well...we dont actually know where you have positioned your throttle, or blower...or anything really....not sure what you mean here? Do you mean the "air chamber" after the throttle body? Would just before the throttle boy give a lower reading do you think? This would obviously be a much easier operation as I can just tap into the pipework rather than having to remove bits of engine?
Thanks
Just reading again, another thought, if I read correctly, your current pressure sensor is fitted upstream of the throttle body, and what I was trying to describe in my earlier post, is that I think this is your issue.
You normally measure boost at entry to the engine, ie after the throttle body in the inlet manifold just before it splits into the individual ports. It's this pressure which you worry about for detonation etc. as this is what the engine sees, not the pressure upstream of the throttle body. Is there anywhere you can tap the pressure in there? Or is there an existing ECU pressure sensor you can tap into to read?
You normally measure boost at entry to the engine, ie after the throttle body in the inlet manifold just before it splits into the individual ports. It's this pressure which you worry about for detonation etc. as this is what the engine sees, not the pressure upstream of the throttle body. Is there anywhere you can tap the pressure in there? Or is there an existing ECU pressure sensor you can tap into to read?
Good morning, thanks for your help so far.
I've re checked calcs and ratios and they all indicate 6.6 psi. I've considered the positioning of the gauge pick up and can see how that would give a false reading if positioned before the throttle valve, so thats my next job!
Thought I'd try to explain the set up for you to comment on:
M45 Eaton supercharger, air filter (pipercross) with MAF sensor fitted in to it. Pipework is 76mm bore alluminium and this goes directly from the supercharger outlet to the throttle body. From the throttle body back is bog standard. I had hoped that the MAF sensor would work with the ECU and the Lambda sensor to sort out the right air/fuel mixture. The funny thing is that when this is running (although there is no load on it) there is no detonation and it sounds sweet?
Thanks again
I've re checked calcs and ratios and they all indicate 6.6 psi. I've considered the positioning of the gauge pick up and can see how that would give a false reading if positioned before the throttle valve, so thats my next job!
Thought I'd try to explain the set up for you to comment on:
M45 Eaton supercharger, air filter (pipercross) with MAF sensor fitted in to it. Pipework is 76mm bore alluminium and this goes directly from the supercharger outlet to the throttle body. From the throttle body back is bog standard. I had hoped that the MAF sensor would work with the ECU and the Lambda sensor to sort out the right air/fuel mixture. The funny thing is that when this is running (although there is no load on it) there is no detonation and it sounds sweet?
Thanks again
Crofty2011 said:
I had hoped that the MAF sensor would work with the ECU and the Lambda sensor to sort out the right air/fuel mixture. The funny thing is that when this is running (although there is no load on it) there is no detonation and it sounds sweet?
Thanks again
Is the lambda narrow or wideband? (count the wires going into it,anyhing less than 5 is narrow) as its only designed to achieve a 14.7:1 afr on an oem engine, not the richer mixtures required for forced induction.Thanks again
+1 on what others said about positioning of your boost gauge.
Ok, so now I'm really in the realms of "no knowledge"! First of all I've checked the lambda and there are 4 wires???
Secondly,just after the throttle body is a vacuum pipe that links into the fuel pressure regulator on the fuel rail. Although obviously there has to be "pressure" inside the airbox I dont fully understand where I would need to reposition the gauge connection to as surely it will show vacuum if placed incorrectly? There is an existing connection which I have connected to (just after the vac pipe) and that shows vacuum of 8psi at tick over, reducing to zero as revs are applied. Any further suggestions?
Thanks
Secondly,just after the throttle body is a vacuum pipe that links into the fuel pressure regulator on the fuel rail. Although obviously there has to be "pressure" inside the airbox I dont fully understand where I would need to reposition the gauge connection to as surely it will show vacuum if placed incorrectly? There is an existing connection which I have connected to (just after the vac pipe) and that shows vacuum of 8psi at tick over, reducing to zero as revs are applied. Any further suggestions?
Thanks
In your installation, do you have anything to take the load off the blower under part load conditions? Without that it's going to get extremely hot and wear out prematurely. You should ideally have an outlet downstream of the blower output (between the blower output and the throttle, in your setup) which opens under part load conditions to relieve the pressure across the blower. A vacuum actuated throttle does the job nicely, Supercharger UK do a nice one that bolts onto a flat surface and has a hose spigot on the outside. If you're using mass airflow sensing then the outlet from the valve should be fed back in upstream of the blower intake.
If your boost calculations are purely based on mass flow and volume, you may have neglected the effects of charge heating. For example if your blower is forcing 50% more air into the engine than the engine would have taken normally aspirated, you don't get 0.5 bar boost you get a lot more (exactly how much depends on how efficient the blower is in that region). Eaton publish the data to enable you to work all this out, on their web site.
If your boost calculations are purely based on mass flow and volume, you may have neglected the effects of charge heating. For example if your blower is forcing 50% more air into the engine than the engine would have taken normally aspirated, you don't get 0.5 bar boost you get a lot more (exactly how much depends on how efficient the blower is in that region). Eaton publish the data to enable you to work all this out, on their web site.
8psi is not vacuum.
What sort of weird markings does your gauge have ?
The original signal to the FPR, would do fine for a gauge take off.
I would expect the car to run fine at idle, and perhaps light loads.
There is no chance in hell of the factory ecu compensating for the supercharger at heavier loads though.
What sort of weird markings does your gauge have ?
The original signal to the FPR, would do fine for a gauge take off.
I would expect the car to run fine at idle, and perhaps light loads.
There is no chance in hell of the factory ecu compensating for the supercharger at heavier loads though.
Crofty2011 said:
Ok, so now I'm really in the realms of "no knowledge"! First of all I've checked the lambda and there are 4 wires???
Secondly,just after the throttle body is a vacuum pipe that links into the fuel pressure regulator on the fuel rail. Although obviously there has to be "pressure" inside the airbox I dont fully understand where I would need to reposition the gauge connection to as surely it will show vacuum if placed incorrectly? There is an existing connection which I have connected to (just after the vac pipe) and that shows vacuum of 8psi at tick over, reducing to zero as revs are applied. Any further suggestions?
Thanks
If you are seeing vacuum, then its in the correct place - that is the "manifold pressure"Secondly,just after the throttle body is a vacuum pipe that links into the fuel pressure regulator on the fuel rail. Although obviously there has to be "pressure" inside the airbox I dont fully understand where I would need to reposition the gauge connection to as surely it will show vacuum if placed incorrectly? There is an existing connection which I have connected to (just after the vac pipe) and that shows vacuum of 8psi at tick over, reducing to zero as revs are applied. Any further suggestions?
Thanks
Also, your fuel pressure regulator needs to be a 1:1 type, which increases the fuel pressure as the "boost" increases. The reason there is a fuel pressure regulator at-all, is so the injectors see a constant pressure differential.
To try to explain simpler ( i hope):
Most typical injectors run at 3 bar (43psi) - if you were running 3 bar of boost - no petrol would actually squirt out - and if you were running 50psi boost - you would in theory force air back up into the injectors!
So the idea is to raise the fuel pressure inline with boost pressure. Also, the opposite is true - when the car is in vacuum, the fuel pressure is reduced for the same reason - otherwise too much fuel would get "sucked" out of the injectors.
considered the bypass and decided I can fit it once the supercharger is up and running, - can the vac be activated by "t" ing into the fuel regulator vacuum? I assume that you mean the bypass valve when open in idle conditions needs to be looped back to non-pressure/air filter side? I understand where you're coming from with the heat generation, but so far I've run it from cold for about a minute and it has never had time to get hot and the pressure has still been 14psi. I think the suggestions made so far about my taking the feed from pre throttle body may be causing a false pressure reading but don't understand the relationship between vacuum/pressure generation in the air box?????
If the air pressure gauge is connected to the air box (after the throttle valve there is a vac pipe that connects to the fuel regulator in the fuel injector rail) then at idle the gauge shows vacuum and then as revs are applied the vac turns to pressure. Am I right to assume that if I revved to 6000rpm the pressure gauge would show 6psi (as I originally worked it out to be?)
Thanks for you input, its really appreciated.
If the air pressure gauge is connected to the air box (after the throttle valve there is a vac pipe that connects to the fuel regulator in the fuel injector rail) then at idle the gauge shows vacuum and then as revs are applied the vac turns to pressure. Am I right to assume that if I revved to 6000rpm the pressure gauge would show 6psi (as I originally worked it out to be?)
Thanks for you input, its really appreciated.
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