The Basics of EFI Conversion
 

There's a lot of experience and brainpower on this board among members who have gone through the conversion from carb to EFI or from stock EFI to modified EFI. This is a subject that I would like to learn more about and I'm sure others would too.

All I know is a little bit about injectors. A little knowledge is always a dangerous thing.:rolleyes:

Q. If Johnny had eight 50 lbs/hr injectors operating at a duty cycle of 75%, how much horsepower could he support without raising fuel pressure?

A. I get 600 HP. Is that right?

I have seen custom setups with 16 injectors which could presumably support 1200 HP and work well at low speeds by using only eight injectors. I see that there are now 65 lbs/hr injectors good for 780 HP or 1560 HP with 16 of them. How do you drive 16 injectors? What's the difference between high impedance and low impedance injectors?

Let's thrash this subject like we used to thrash tech subjects on this board. Winter's coming, bench racing season is upon us!

This is a subject that I would like to learn as much as possible about as well. What is the formula you use for determining the maximum horsepower from a particular set of injectors??

If my parts ever get here we will see how 95 lbs /hp injectors work out.

Holley's web site had the formulas for coming up with what injector to use with what max HP.

I'm here to help so throw your questions at me. I have extensive knowledge of EFI systems in automotive applications, but I'm sure marine systems are very similar. I know my MPI system is.

Later
Roby

(# of injectors ) * ( injector size Lbs/hr ) * (duty cycle)
-----------------------------------------------------------------
( 1/2 Lb of fuel per hour per hp)

eg. for 38 lb injectors

8 * 38 * .90
--------------- = 547 hp
.5

The 50lbs inj. at 75% DC @ .50 BSFC will support 600hp.

A supercharged engine might run @ .58 BSFC therefore the 50lbs. @ 75% DC will only support 520hp.

Some ECU's and some injectors don't mind running 90% DC some don't like it and will heat up.

Most supercharged engines also have a 1:1 boost regulated fuel pressure regulator to keep the fuel flow to the engine constant.

The fuel pump, Fuel lines, Fuel pick-up all need to be larger to support EFI and even larger to support EFI Blown. You need a lot bigger pump
to support 600hp EFI Blown then 600hp carb natural.

I knew I shoulda paid attention in math class!!!!

Finally got 2000cfm throttle body, fast ecm, 8 injectors, wiring harness, fuel rails, & most of my sensors today. The only one they forgot to ship was the wide band O2 sensor & the manual (who needs that stinking manual). At least I was able to pull it off the web site. Since it has taken over a month to get the parts I was worried something would be missing.

Hope to call you next week TC & see if we can do a trial fitting with the 2000cfm throttle body.

I have had several engines with modified ecu's, one that was changed from carbed to EFI, a cent. supercharged EFI, and currently working on a two Merc. 575's one old 540ci merlin head,and a 575 SC. Also working with different combinations of headers and other mods on a 496 HO. All have turned out rather well.

Has anyone run an Accel Gen 6 ECU on a boat motor?

Thanks
Dick