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Old 02-27-2008, 10:57 AM
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Default Throttle position and boost

It appears that to have an ECU control boost it is based on throttle position. In a car that makes perfect sense, in an airplane, it doesn't.

full power = 2800 RPM = 31.5 manifold pressure
Cruise power = 2500 RPM = MP of around 26

It seems to me that the throttle position in both cases should be full open if boost is required to produce that amount of power and not partially closed to tell the ECU to produce a lessor amount of boost. Why impede air flow just to tell the ECU how to control the turbos.

I think, to make the system more efficient, i may go to a separate boost controller

I mean, here i am making a more efficient intake manifold, I'm going to hand file flanges to improve air flow and then - what - partially close the throttle at high boost conditions!!!

What am i missing
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Old 04-19-2008, 01:38 AM
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Default Re: Throttle position and boost

Air fuel mixture and rpm
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Old 04-19-2008, 11:00 PM
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Default Re: Throttle position and boost

I figured it out - a potentiometer attached to the throttle that only moved the actual cable first 75%, then it is all potentiometer movement to tell controller to increase boost

actual throttle plate will be wide open from 75% to 100% of throttle position
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Old 12-02-2009, 07:02 PM
gilbert drieux gilbert drieux is offline
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Default Re: Throttle position and boost

Hello Dust,
I think potentiometer attached to the throttle is not good to read "power".
It is better to use a Lambda sensor on exaus pipe to know actual air/fuel ratio.
When sensor voltage is 0.5 volt, ratio is 14 (stochiometric...).
You need :
1 - engine cylinders' capacity (i.e. Lyc O-235 is 235 cubic inches => 117.5 ccinch aspirated per turn),
2 - rpm,
3 - air intake pressure,
4 - air temperature (at carburator),
From those data you compute "standard" air volume per minute; and air masse per minute,

5 - applying "Lambda", you get fuel mass consumption per minute,
6 - using fuel density, you get fuel volume / mn; multiplied by 60, is fuel volume per hour.....

I'm currently trying to build such a device....

Lambda sensor (from car) + LED bargraph display is now operatinal to trim mixture....
Just need some sensor more, and a little unit to compute as above (with data table to link lambda sensor voltage to air/fuel ratio.
That work fine ..... in an Excel sheet !

Regards,


Gilbert.
VE F-PMPZ; Lyc O-235,
@ LFPK Coulommiers / France
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Old 12-03-2009, 11:21 AM
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Default Re: Throttle position and boost

Well, it is hard to explain, but ifin i can't, well i better not do it!

the throttle position will tell the ECU how much manifold pressure i want. Full throttle, i want 31.5 Inches Mercury (IM) 80% throttle i want 25 IM. and so forth.

To me after having made a free flowing intake and exhaust manifolds, it seems silly to obstruct it with a partially closed throttle plate at less than full power but with the turbos workin to keep IM pressure up.

that is why the difference. the ECU will have IM temp, pressure to work with and i will develop fuel tables that are optimized for all conditions.

i will also have wide band ox sensors to tell me the A/F ratios and the CHT's and EGT's to gauge performance and to trim fuel to each cylinder for even EGT's. I will only have 2 of the sensors, but will be able to switch them around to give me the info needed.

Right now i am making sure that i have the proper sensors installed so that when i get to that point i can solidify my thoughts and have the proper info with which the ECU can manage the engine.

Am i making any sense?
It is sooooo complex, maybe we should talk on skype?
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