Sanzomat
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| posted on 29/6/26 at 01:18 PM |
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Changing to higher flow injectors (tunerstudio/Speeduino)
I'm not the sharpest tool in the box so forgive me if this a daft question...
My Locost with an R1 bike engine (4XV adapted for EFI using respaced 5PW throttle bodies) is currently running the standard injectors (230cc/min)
When it was mapped 4/5 yrs ago on a rolling road the tuner advised that the injectors were reaching 100% duty cycle not far beyond 11,000rpm so he set
the rev limiter to 11k to avoid it going lean when the injectors couldn't deliver any more flow. He advised that it wasn't ideal for them to
go that close to 100% duty and suggested I should get bigger injectors and then re-map it.
I procured some bigger flowing injectors (from Hobbsy on here) but as the car was running well and I didn't fancy forking out on a another
rolling road session so soon I left it how it was. Fast forward four years and maybe 20 track days I'm getting a top end misfire (above 10k rpm)
so wondering if the advice the tuner gave has come true and the injectors are failing (or it could be something else...) so I'm thinking time to
put the injectors I bought several years ago into the car.
So, finally getting to the point...
Tunerstudio uses a constant called "required fuel" which I believe is the time in milliseconds that the injector needs to open to give Stoic
AFR at max load.
The replacement injectors are 320cc/min (old ones 230). If I change this constant to 230/320 x "current value of constant" and leave the VE
table as it is then the current map should then give the same amount of fuel i.e. less milliseconds at more flow = same fuel delivered???
As such is the only reason to get it remapped just to check that other possible variables such as time delay for opening and effect of spray pattern
on burn speed (and thus spark timing) aren't making a big difference?
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JAG
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| posted on 29/6/26 at 01:57 PM |
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quote:
If I change this constant to 230/320 x "current value of constant" and leave the VE table as it is then the current map should then give the
same amount of fuel
I agree with your theory and the maths makes sense - however I only have a basic understanding of fuel injection so I can't be sure that the
outcome you and I imagine is exactly what will happen.
Do you have an Air-Fuel-Ratio Guage that you can use to better understand this change?
If not it might be a good time to invest 
Having said all that I'd do it and learn 
Justin
Who is this super hero? Sarge? ...No.
Rosemary, the telephone operator? ...No.
Penry, the mild-mannered janitor? ...Could be!
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Sanzomat
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| posted on 29/6/26 at 02:12 PM |
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quote:
Originally posted by JAG
quote:
If I change this constant to 230/320 x "current value of constant" and leave the VE table as it is then the current map should then give the
same amount of fuel
I agree with your theory and the maths makes sense - however I only have a basic understanding of fuel injection so I can't be sure that the
outcome you and I imagine is exactly what will happen.
Do you have an Air-Fuel-Ratio Guage that you can use to better understand this change?
If not it might be a good time to invest
Having said all that I'd do it and learn
Thanks JAG, I do have an AFR gauge and I can collect data logs whilst driving. If the car was on the road then I'd be tempted to go that way but
hasn't been MOT'd since 2015 and therefore not taxed (or insured) so mr plod might get upset if I tried. As its only used on track days
I'll either have to bite the bullet and find the money for a mapping session or do a track day and maybe take it a bit easy until I'm happy
the AFR (and spark advance) is okay but taking it easy on a track day might not work for me!!!
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scudderfish
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| posted on 30/6/26 at 08:48 AM |
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Yep, your maths is correct and should get you in the right ball park
https://vetuner.co.uk
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gremlin1234
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| posted on 30/6/26 at 10:01 AM |
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would it be silly to
insure it for road use
get an mot
tax it for summer
then road tests could be done.
maybe cheaper than rolling road session, and you get to enjoy the car on the road.
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Sanzomat
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| posted on 30/6/26 at 10:16 AM |
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quote:
Originally posted by gremlin1234
would it be silly to
insure it for road use
get an mot
tax it for summer
then road tests could be done.
maybe cheaper than rolling road session, and you get to enjoy the car on the road.
Hi Gremlin, I have considered going down that route but 1) as the car is primarily for track days it'll spend most of its time at either full
throttle or no throttle so WOT is where where the map needs to be most accurate and its hard to maintain steady full throttle on the road! 2) I also
have a GTM Spyder which gives me my on road kit car enjoyment!
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