Timing a custom supercharged engine
02-28-2015 | 08:20 PM
#41
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From: chicago
I was just discussing this today on the phone with another oso member who wants to try it on his big power blower motors. I have yet to purchase anything though. Its not really feeling like spring is anywhere near!
02-28-2015 | 08:59 PM
#43
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From: Algonac MI
I think you are on the right track. I would be very concerned running an SC engine with locked out timing. In an efi engine (speed density, ie, MEFI), everything is based off of MAP (manifold absolute pressure) Timing is based on load. Take a supercharged efi engine making roughly 1000 hp. At 100 kpa (no vacuum, no boost), it may have 30 deg at 5000 ramping up to 35 deg at 6000 rpm. Depending on boost, it may have a small negative number to remove some timing once it is in boost. That may only be 1-3 deg. That will depend on rpm and boost. The higher the boost and lower the rpm, the more negative the number (taking out more timing) At higher rpms and lower boost levels, no timing is taken out.
Now, at a Kpa level lower than 100 ( in vacuum) the timing may be 36-40 deg. The lower the Kpa (more vacuum) the more timing it will have. So, at 5000 rpm and 80 Kpa, it may have 38 deg., at 90 Kpa it may have 35 deg and at 100 Kpa it may have 30 deg. Anything over 100 Kpa is boost. If the boost is say less than 5-6 psi, than the timing may stay at 30 deg. If boost is over 5-6 psi, you may start taking out 1-2 deg. That may also increase as boost increases.
This is what really sets efi apart. There is unlimited tuning to be done to the spark curve. You can add as much as it wants when the load is light ( high vacuum) and then start taking it away as load increases. As rpm catches up, you can start putting it back in.
Also, with the Mefi (not sure about others), it has what's called "idle spark stabilization". This will add or remove timing to keep a smooth idle and prevent the engine from stalling. You can program it to add as much as you want. It's not uncommom for it to add 20+ deg and raise the timing to 40deg at idle. It's really nice when you have a boat with 41" props and 1.24:1 gears. It's a tremendous amount of load when you put it in gear. The IAC will open up and the timing will come way up to keep it idling so that it may only drop 100-200 rpm from neutral. With a carb engine, you would look like you are swinging numchucks on the throttles.
Of course, you also have the protection of a knock sensor. With the Mefi, you can not only control when it listens, but the sensitivity of it. You can compensate for a noisy solid valvetrain, drivetrain noises, etc. You can change the temp at which it listens if you have a worn out engine with some piston slap when it's cold......and on and on. It will do just about anything you want it if you spend the time.
Hope this helped shed some light on it. I tried to simplify it as much as possible.
Eddie
Now, at a Kpa level lower than 100 ( in vacuum) the timing may be 36-40 deg. The lower the Kpa (more vacuum) the more timing it will have. So, at 5000 rpm and 80 Kpa, it may have 38 deg., at 90 Kpa it may have 35 deg and at 100 Kpa it may have 30 deg. Anything over 100 Kpa is boost. If the boost is say less than 5-6 psi, than the timing may stay at 30 deg. If boost is over 5-6 psi, you may start taking out 1-2 deg. That may also increase as boost increases.
This is what really sets efi apart. There is unlimited tuning to be done to the spark curve. You can add as much as it wants when the load is light ( high vacuum) and then start taking it away as load increases. As rpm catches up, you can start putting it back in.
Also, with the Mefi (not sure about others), it has what's called "idle spark stabilization". This will add or remove timing to keep a smooth idle and prevent the engine from stalling. You can program it to add as much as you want. It's not uncommom for it to add 20+ deg and raise the timing to 40deg at idle. It's really nice when you have a boat with 41" props and 1.24:1 gears. It's a tremendous amount of load when you put it in gear. The IAC will open up and the timing will come way up to keep it idling so that it may only drop 100-200 rpm from neutral. With a carb engine, you would look like you are swinging numchucks on the throttles.
Of course, you also have the protection of a knock sensor. With the Mefi, you can not only control when it listens, but the sensitivity of it. You can compensate for a noisy solid valvetrain, drivetrain noises, etc. You can change the temp at which it listens if you have a worn out engine with some piston slap when it's cold......and on and on. It will do just about anything you want it if you spend the time.
Hope this helped shed some light on it. I tried to simplify it as much as possible.
Eddie
02-28-2015 | 11:55 PM
#44
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I will only add that watching the spark stabilization at idle with my MEFI is truly astonishing. Within 1-3 seconds after start the IAC and ignition have the motor idle tamed nicely, in spite of the mildly aggressive cam. Watching the timing graph at idle is like watching the EKG of a heart attack patient on crack. It's all over the place, but the idle is nice. Great stuff.
03-01-2015 | 10:30 AM
#45
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From: Toronto, Canada
Anytime I can get a friend to spend money, I feel great! Mike, I think you might be a perfect candidate for this. You think Dave down at the dyno would be up for playing with this setup? Maybe when we can bring yours down to the dyno, and skype Eddie in for some live tuning assistance
03-01-2015 | 10:52 AM
#46
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From: cleveland ohio
I called down to daytona sensors last week. The lady that answers gave me the owners cell phone number.
I called to ask about the MAP sensor and its application in regards to a NA application.
He told me that there was no advantage to collecting manifold pressure data in a NA application. I was wondering if I could use the data to program in more timing under a light load/high vacuum condition.
The part of the MAP sensor operation that I'm having difficulty wrapping my head around is that the Delphi map sensor is a 0-5 volt pressure transducer. Great for measuring a boosted application as in turbo or SC applications. I would think you would need a sensor with a negative/atmospheric/positive range to measure vacuum and boost. That said, I'm not sure what the range is for the Delphi map sensor. I did read that the Delphi sensor sees manifold vacuum and manifold positive pressure as a value above zero in the 0-5 volt signal.
I need to do some more research to determine if there is any advantage to collecting MAP in my application.
It may be that the map data could be used in addition with the rpm at a given time to plot the 3d timing table.
I called to ask about the MAP sensor and its application in regards to a NA application.
He told me that there was no advantage to collecting manifold pressure data in a NA application. I was wondering if I could use the data to program in more timing under a light load/high vacuum condition.
The part of the MAP sensor operation that I'm having difficulty wrapping my head around is that the Delphi map sensor is a 0-5 volt pressure transducer. Great for measuring a boosted application as in turbo or SC applications. I would think you would need a sensor with a negative/atmospheric/positive range to measure vacuum and boost. That said, I'm not sure what the range is for the Delphi map sensor. I did read that the Delphi sensor sees manifold vacuum and manifold positive pressure as a value above zero in the 0-5 volt signal.
I need to do some more research to determine if there is any advantage to collecting MAP in my application.
It may be that the map data could be used in addition with the rpm at a given time to plot the 3d timing table.
03-01-2015 | 11:16 AM
#47
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From: cleveland ohio
Looking at the Delphi PDF files, it appears that barometric pressure nets a voltage output of just under 5 volts and as vacuum is created in the manifold, the voltage output decreases proportionally.
Not quite sure how a positive manifold pressure is quantified with such a transducer.
I'm sure I'm missing something pretty basic here.
Not quite sure how a positive manifold pressure is quantified with such a transducer.
I'm sure I'm missing something pretty basic here.
03-01-2015 | 11:29 AM
#48
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From: Vancouver BC
Different sensors have different calibrations, 1 bar 2 bar, etc. For a 1 bar (atmospheric ) sensor, 5 volts is 105kpa/14.7psi/0" vacuum/1 bar. Depending on how you want to read it. When your engine pulls a vacuum, it is still reading pressure, unless you boat in space, there will always be pressure in your intake, even though we call it vacuum, it's only pressure below atmospheric - 14.7psi
03-01-2015 | 11:31 AM
#49
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From: Vancouver BC
Also, I agree in an NA marine app, due to the very linear load vs rpm, there would be very minimal gains to timing vs map instead of timing vs rpm. You can use the rpm as your load curve
Last edited by HaxbySpeed; 03-01-2015 at 07:23 PM. Reason: add
03-01-2015 | 07:19 PM
#50
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From: chicago
I know on my personal boat, and some of my boat buddies boats, which are heavy twin supercharged engine vee bottoms, the rpm/load/manifold psi, is not very linear to rpm.
For example, our lake can be as calm as can be, where a duck can leave a noticeable wake. Then there are days it can sink freighters. So, on some days, I could be out running say 65mph, drives trimmed out, tabs fully raised, light on fuel, and be say 0 inches on the gauge at 4000RPM. Then there are days when its sloppy rough, I got a full 220 gallons of fuel on board, some fat chicks, drives tucked, tabs dragging, and be at 3-4lbs of boost at 4000RPM.
For me, I'd want to take advantage of the map sensor function. This whole concept was around way back in the days of vacuum advance distributors. High vacuum, lots of timing. Low vacuum, not so much timing. It actually was a good setup for its time, but most guys would get angry and plug the vacuum advance , mainly because they just didnt understand it. I remember the first time I saw a sun distributor machine, thought it was the coolest thing ever! I had aquired a mint condition one several years back. Like a dummy I sold it to a guy, I should have kept it. It would have been cool to put in my magic room someday.
For example, our lake can be as calm as can be, where a duck can leave a noticeable wake. Then there are days it can sink freighters. So, on some days, I could be out running say 65mph, drives trimmed out, tabs fully raised, light on fuel, and be say 0 inches on the gauge at 4000RPM. Then there are days when its sloppy rough, I got a full 220 gallons of fuel on board, some fat chicks, drives tucked, tabs dragging, and be at 3-4lbs of boost at 4000RPM.
For me, I'd want to take advantage of the map sensor function. This whole concept was around way back in the days of vacuum advance distributors. High vacuum, lots of timing. Low vacuum, not so much timing. It actually was a good setup for its time, but most guys would get angry and plug the vacuum advance , mainly because they just didnt understand it. I remember the first time I saw a sun distributor machine, thought it was the coolest thing ever! I had aquired a mint condition one several years back. Like a dummy I sold it to a guy, I should have kept it. It would have been cool to put in my magic room someday.
Last edited by MILD THUNDER; 03-01-2015 at 07:27 PM.
