TPI-Formula350-

quick question.. I have been tuning the APAP bin with tuner pro RT and my prominator.. I was thinking there was a place in the constants to tune duty cycle for the injectors, but I cant find it! Maybe there is a different version of tuner pro i'm thinking of that is able to tune injector duty cycle????

doc

FWIW: I have used TunerPro and TunerCat and neither have a constant or other for tuning the duty cycle. In fact, you do not want to tune the DC, it is what it is. You put in the correct injector flow constant, you tune the MAF or VE tables, the BLMs end up near 128 +-6. You get the fueling at WOT right for about 12.8:1 AFR. The injector DC will be whatever it is.

TPI-Formula350-

thanks Doc... Guess i was mistaken....one thing, you stated that I put in the correct injector flow constant... R u just refering to putting the correct injector lb size into the constants? thanks

doc

Yes, I am a strong believer in putting in the correct flow constant for the injector and tune other things. I've got 30s in my HSR 395, so I have the injector constant set at 30.0 because I am running the fuel pressure for the 30#/hr rating of the injectors. IMO, you should put in the correct flow rate, taking into account higher or lower fuel pressure than the injector is rated at.

TPI-Formula350-

yeah... I have the FI sizes in the constants set to 30 being I'm running 30 LB ford injectors. So I'm wondering if the motor makes say 485HP at the flywheel, to support that HP with 30lb injectors I'd have to crank the adjustable fuel pressure regulator to approx 60lbs to support that 485HP..correct?

doc

For 485 Hp and DC = 80%, the injectors would have to flow about 37.9#/hr. A Ford 30#/hr injector at 60psi would flow about 36.74#/hr. So to achieve 485 Hp (at the flywheel), you simply would be running at a higher DC which is not as bad as most people claim because how long are you at that high throotle? If we are talking about the 1/4 mile dragstrip, its only about 12 seconds. Injectors can run at 100% duty cycle for 12 seconds without major problems. (at least one dragracer tells me) 30#/hr Ford injectors running at 60psi and 100% DC, theoretically can make 588 Hp at the flywheel. So your 485 Hp at the flywheel is certainly within reach as far as the injectors are concerned.

TPI-Formula350-

ok, sounds good but your losing me in one area. you said I cant change the DC using tuner pro RT in the constants.... So how do I get to 100% DC??

gsjmtntman

Check this out also.
https://www.thirdgen.org/forums/diy-...or-offset.html

doc

The Duty Cycle (DC) is a calculated value. It is the ratio of the amount of time that the injector is open (flowing fuel) divided by the amount of time for the crank to make one revolution. You do not want to reach 100% because that means the injector was open the entire time the crank made one turn. The injectors fire once per crank turn. 100% DC means that the injector is open all the time, it has gone "static".

The formula is: %DC = RPM * PW / 600 where the pulse width is in msec

For example, if at 4,772 RPM, the Pulse Width is 8.2 msec, then the duty cycle is 32.6%.
(4772) * (8.2) / 600 = 65.2

EDIT: I had to edit this reply. I had posted the DC for my LS1 car. For our batch fire cars, the divisor should be 600, not 1200.

TPI-Formula350-

ok so if I understand correstly...if I needed to get more out on my 30lb injectors I'd have to go about it in two ways. 1. for example...I can raise my fuel pressure up to say 50lbs from the stock setting of 43lbs...2. if the car was being dyno tuned the DC could be raised above the stock 80% by changing the MAF and VE tables..correct??

doc

There is nothing stock about the injectors at 80%. See, I know that you are operating under a false impression, and I have not been able to get you off of that. Call me I sent you me cell #.

If you need more more, for example, at WOT then you can increase the fuel pressure OR invrease the values in the PE vs RPM table.

Once again you do not tune the injectors for Duty Cycle. You only want the injectors NOT to run at 100% DC for along time, short burst is OK.

TPI-Formula350-

thanks Doc... Im understanding it all alot better after the call..