jet needle area?
Turbo Mini Forums

Does a change in jet area (hole) by about 30% (0.90 to about 1.2) would change all the fuelling curve by a linear 30 % with the same needle or does it will have an exponential increase as the jet is unmasking the hole?

fab

As fuel pressure rises it will indeed be non linear.

good q fab , i think that the needle profile remaining the same ,and the hole getting bigger ,would mean the ratio of needle to hole would change as it got further and further out of the hole eg ,as rpm rose .so if we had a 3 square inch hole ,and a 2.5 square inch area needle in it that would give .5 square inches at tickover ,and then a 2 square inch needle at rpm ,that would give a 1 square inch hole for fuel , but then take the 3 square inch hole ,and make it 3.5 square incch ,then at tickover it'd be 1 square inch ,but at rpm it would be 1.5 square inch ...
so the ratio of enrichment tickover to rpm has changed and its not linear.this written at an early point with 8 hr jetlag so may be even more drivell than i usually come out with .
regards robert

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

also, back to basic maths, a circles area increases exponentially with its diameter, so adding an extra 30% to its diameter will give more than 30% will give more than 30% increase in area...

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

will give more than 30

...just incase you didnt get it earlier LOL

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

well so an other needle is needed!

after a day of reflection it's not that bad!
easier to swap a needle than a jet.........even if it need more work to sort fuelling first.
thanks
fab

If you are struggling for fuel....fit a 0.125" needle into the carb, and drill/ream the jet out to 0.125"

Due to me making my own plenum, and not replacing the restrictor at the mouth of the carb as per factory plenum, I had to do this to get enough fuel from the carb ( as well as a bigger needle valve and larger reservoir )

Another option go make it lift more fuel is a smaller restrictor at the mouth of the carb to speed up air over the jet.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

thanks but not struggling with fuell, just a weigher one,
about the restrictor,a good tips when you leave it is to use an "airstream boost sensing", a 30/45° angled (tune the angle to adjust) tube producting into the airstream just after the compressor outlet tubing this one blowing in the carb float by the vent tube