How do you calculate the required injector sizes?

I have the Holley TBI with 44lb/hr at 11 psi (I think maybe 12 psi).

How can I be sure these are the right size?

Thanks.

 

(Horsepower*BSFC)/(#of injectors*(max duty cycle%/100%)) will give you what each injector should be.

If you had for example, 400 hp, a BSFC of .45, 4 injectors, and desired a max duty cycle of 85%, it looks like this:
(400*.45)/(4*(85/100))=52.94 pounds per hour for each injector.

Those holly injectors are rated at 11 psi (.75 bar) I believe, so they should still flow 44 pph. If you up the pressure, the new flowrate is:
SQRT(New pressure/Old pressure)*Old Flowrate.
44's at 16 psi are 53 pph.

Hope this helps.

 

Kewl, thank you!

 

You need to ask your question a little better if you ment to ask how to calculate the injector constant for the ecm.
Since I have a feeling that's what you're trying to ask then I'll tell you how easy it is. You have 4 injectors, normal TPI has 8. So you take your ratings of 44 and multiply by .5 to come up with the ecms injector constant. So in the bin you'd have the injector constant set to 22#.
Can I ask how you plan on running these injectors off of the 7730? I don't remember seeing any plans for overcoming the whole load problem. You need 4 injector drivers but you only have 1. Oh, and since you're using such small injectors on a big block I can only recommend turning up the fuel pressure! Stock TBI BBC injectors were 80#, half of that is 40 so you're looking at running the injectors static if you plan on making more than ~240hp . You're cheapest fix would be to increases the fuel pressure. The holley FPR can be made adjustable by just drilling out the brass cap. Grab a 4mm allen key and increase the pressure. I recommend getting your injectors up to a 50# rating at LEAST.

 

Thanks for the reply.

I originally got this setup from Howell Fuel Injection (howell-efi.com). They are still selling the Holley 4 barrell with the 7730 ECM.

The are running the injectors in an offset diagonal between the two drivers, with the injectors in series.

It's been running for six years now, not my daily driver. But it has been lean in AE, primarily MAP AE, or AE after TPS delta at least. I am still not clear on how the 7730 does AE MAP after MAP and TPS settle....

I am planning on running 15 psi and re-tuning.

 

I just thought of something, of course, I would have no way to confirm it. But, couldn't changing the micro second opening rates in the table

"INJECTOR PULSE WIDTH CORRECTION VS. BATTERY VOLTAGE"

compensate for this lack of fuel pressure (BPW)?

Apparently, howell-efi added .488 to ALL of these tables from the AXCN.bin

Does this table affect ALL other tables? AE, PE?
I know it affects idle and BLMs....

 

Sorry, it will not change the amount that the injectors will flow when they reach 100% duty cycle (no injector turn on time at 100%, because the injectors are always on, thus they are not continually turning on as when not at 100% duty cycle). It will, however, richen the entire map, and will have more of an effect (% change) at low PWs (low MAPs) than high MAPs.

Also, as stated in other posts by other people, the 730 only has 1 injector driver (but two wires that go out to the wire harness) (I don't know this personally, but it's what the guys in the know say).

Most systems, but not sure about this one, will have the VBatt offset on each injection, and with that, the VBatt offset is not taken into account when doing multipliers to the Base, such as PE, and warmup.

 

Don't use the battery voltage compensation table to add more pulse width. Like redngold said, if the injectors flow x amount in t time then that's the most they're going to flow! You reach 100% duty cycle and the injectors are just sitting there fully open, stuck open .
As for Howell EFI, I'm not there tech support and to be honest, I don't want to be. So do me and all the rest of the guys on the board a favor and give em hell. Last time I tried to get some information regarding their dual TBI setup they told me they didn't sell them but weren't going to tell me how they did it because it was a "secret." I've got the e-mail still saved to prove how worthless some people really are in life.
Call Howell up and demand that they help you clearify a few things. If they don't, then post a thread on the Aftermarket Review board. Next step would be to crack open the case and take a gander at the electronics. They MIGHT have doubled up the FETs to increase the current capacity. Also, to be completely sure of this, you ARE using a holley 4 barrel TBI where the injectors are above the throttle blades correct? I mean it isn't that 4 barrel Accell TBI which has the injectors right below the butterflies or is it?
Again, Howell tech support should get you all the answers you (and we) need about the system so please go that route so some progress can be made.

 

JPrevost, what accel tbi are you referring to? Do you have a link? I had a guy interested in designing something like that for aftermarket sale, but if it's been done, I should let him know. Thanks in advance.

 

Thank you for clarifying that information.

YES, I do have a 4 Barrell HOLLEY TBI. I presume it is a stock computer, as I have two of them, and there is no difference either in my ALDL or "seat dyno" when I have changed them out before. I can take it apart and check, if I can find out where on the PCB the drivers are supposed to be.


I see what you are saying about the duty cycle now with the batt voltage change. That must be why my motor "dies" at around 4K or so....

I have since changed the TPI BATTVOLT compensation table back to stock (90L98MAN8D.bin).

I have also since increased my fuel pressure to just above 15 psi (this is as far as my gauge goes), but it still varies.

Doing this has taken me from previous chip burned tuning of 128 - 126, after fuel-pressure and batt voltage change I am not at 138.

It DRIVES a LOT smoother now, even though MY VEs are pretty far out.
Back to the VE tables.

Yes indeed Howell is worthless. Every time I call them, they want to charge me to burn me another chip, but they never got it right the first time. So now I am doing it myself, I still have a lot of learning to do. Even though i have been trying to tune this for the last year.

Perhaps it is time to go to a 7747 with 4 driver board. Bummer.