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 Post subject: Calculations for new injectors
PostPosted: Mon Jan 08, 2018 3:00 pm 
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Joined: Thu Jul 28, 2011 4:10 am
Posts: 813
ECU Model: S100 Pro
I'm going to change the injectors on one of my cars as they are just about maxed out.
They are 241cc (@ 3Bar) x 4 but installed and running @3.5Bar
I want to change then to some I have
359cc x 4 and reduce the fuel pressure to 3.0Bar

I'm thinking that the fuel pressure reduction would need an increase in injector duration of 7% to compensate.
And the increased injector size would require a 49% reduction in duration.
Therefore a total duration reduction of 42% across the map would leave me with the same fuel into the engine.

Does that sound anything like right?


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 Post subject: Re: Calculations for new injectors
PostPosted: Mon Jan 08, 2018 3:11 pm 
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Joined: Tue Aug 02, 2011 12:08 pm
Posts: 2852
Location: Norn Iron
ECU Model: No ECU
Just give it a try and scale it up/down until idle AFR's are close to where they were. But you would still need to check everything under load, dont take it for granted.


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 Post subject: Re: Calculations for new injectors
PostPosted: Mon Jan 08, 2018 3:14 pm 
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Joined: Thu Jul 28, 2011 4:10 am
Posts: 813
ECU Model: S100 Pro
Yeh, but I'd like to be a bit more scientific about it :)


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 Post subject: Re: Calculations for new injectors
PostPosted: Mon Jan 08, 2018 4:14 pm 
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Joined: Tue Aug 02, 2011 12:08 pm
Posts: 2852
Location: Norn Iron
ECU Model: No ECU
Science only takes you so far....after that, the force is required...( or some guessing )

And injector behaviour, dead times etc....can all add variables as to how things act under load. Although if all the data is correct...they differences should be reduced.


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 Post subject: Re: Calculations for new injectors
PostPosted: Tue Jan 09, 2018 4:07 am 
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Joined: Fri Feb 28, 2014 1:03 pm
Posts: 1030
ECU Model: S40 Pro
Distributor: DTA
Firmware Version: 79
There are a couple of calculators here that should help:

http://www.deatschwerks.com/fuel-calculators


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