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Calculations for new injectors

Posted: Mon Jan 08, 2018 3:00 pm
by Rob Stevens
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?

Re: Calculations for new injectors

Posted: Mon Jan 08, 2018 3:11 pm
by stevieturbo
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.

Re: Calculations for new injectors

Posted: Mon Jan 08, 2018 3:14 pm
by Rob Stevens
Yeh, but I'd like to be a bit more scientific about it :)

Re: Calculations for new injectors

Posted: Mon Jan 08, 2018 4:14 pm
by stevieturbo
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.

Re: Calculations for new injectors

Posted: Tue Jan 09, 2018 4:07 am
by Alex DTA
There are a couple of calculators here that should help:

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