Rookie

OK, a little EFI 101 for me. Is there a specific duty rate injectors need to run between? I assume not at 100%, but is there a not below 50%? I'm collecting parts. If I buy a Holley HP EFI and 8-60lb injectors, would the injectors be sufficient for 550-575HP NA, and then transferred to an injector plate for 650-700HP supercharged twin throttle body? Would the HP EFI be the right choice? From my readings it's the same programming as the Dominator just minus 20/20 I/O's

Young Performance

Ideally, you want to stay under 85% duty cycle. You can go over that but if you run them at 90%+ for extended periods, it will take it's toll on the injectors. It's hard on the pintle in the injector, not to mention the injector will overheat. At 100% duty cycle, you have 12 ms at 5000 rpm and 10 ms at 6000 rpm of available time. That's physics and you can't change it. So you shoot for a pulse width of 85% or less of those numbers at those rpms.

The simple thing is to just go large on the injectors. However, going to large can make it a real ***** to tune down low. The pulse width becomes so short that it is very touchy to tune. It depends on the resolution of the ecm. Some may only be able to change .05 ms at a time, where others are .01 ms. You could have a situation where at idle, changing the pulse by .05 ms may change the AFR's by 1 point or more. Fuel pressure also plays a role. Injector size is figured at 3 bar, or 43 psi. If the pressure is higher, the injector will flow more than it's rated. There is an easy formula to figure it out.

Location of the injector will also determine the power it can support. In most Whipple's, the injectors are on the inlet side of the blower just inside the throttle plates. That suction from the blower will help the injectors to flow a little more. While it doesn't actually make vacuum at the throttle plates, that air moving through there at such a high rate will help to pull the fuel in. Now if the injectors are in the intake runners of a SC engine, they are having to fire against the pressure in the intake . This is a deterrent to the fuel flowing. For example, (8) 65 lb injectors in a Whipple can support over 1000 hp at 50 psi. of base pressure. You are a little over 85% duty cycle, but only at upper rpms. Those same injectors placed in the intake runners will only get you about 900 hp.

In your case, (8) 50 lb injectors will support about 800 hp NA or supercharged if they are on the suction side of the blower. You could get away with 50 lb injectors, but I would go for the 65 lb injectors though. When you step up later to the blower, you will be pushing the 50's. With the NA engine at 550 hp, it may be a little tricky at idle, but nothing that isn't doable. With either engine, run the pressure at 40 psi to help at idle. When you go SC, boost reference the regulator so that the pressure will rise with boost.
Eddie

sutphen 30

the newer efi's can handle bigger injectors w/ low pulse width.This is an idle quality thing,old days it was harder.now you can run down to 1msec and it will idle.Then the other question,,you can run up to 90%,I wouldn't push it much harder than that(I have but by accident,then went bigger injectors,no damage to ecu,injectors or motor).we took the risk,that was our deal,,as for the norm,,don't go more than 85%.if your boosted injection time is up around 13-15msec,,its time to go bigger(assuming afr's aren't to rich).
and then there is the staged injection,small injectors for idle and such and monster injectors for big power.
my 2 cents.

HaxbySpeed

Yep, Rookie you'd have no problem running 60's. There's no problem getting good idle and driveability on a 5.3L running 160# injectors with the Holley HP. The disc style injectors work better too when you start getting up in size, but for your app you could run any style. Running high duty cycle is hard on the injector coils, because the injector is almost wide open all the time. Running too high a pressure to compensate for not being able to run an adequately sized injector is what's hard on the other internal parts in the injector. On a draw through boosted deal, I like to run without boost reference, so that the lbs/hr on the fuel table is more accurate.

BUP

have no idea what happened to some of my post so redoing some of it.

Duty cycle is the % of time the fuel injector is open versus the total time between firing events. Technically you do not want to continuous flow fuel injectors over 80 % duty cycle to be an the very safe side as many stock OEM's have thrown this rating out as well. Yes you can go up to 90 % but not for continuous levels.. Also technically 3 bar is 43.5 psi.

Basically STOCK and NOT over your top MPI marine engines using 3 bar / 43.5 PSI / fuel injectors for most apps from most of the marine OEM's for your STANDARD MPI V-6 and V-8's.

The new Volvo Penta direct injection V-6 in the combustion chamber fuel pressure is 2250 PSI in which is something like 1500 bar rated. Anyways just throwing that out as to what's available this year on the marine side for fuel injection. The 5.3L GM will be available in July from Volvo Penta in which is direct injection as well. Mercruiser for its smallblock just like its 4.5 V-6 will have its block made and not using direct injection fuel injection but the standard rail / fuel injection / MPI. Both Volvo and Mercruiser are now using true wideband O2 sensors but only before the CATALYST.

Injector dynamics works in conjunction with Bosch and currently IMO has the best fuel injectors on the market along with a lot of current R&D with the help from Bosch plus they run a lot of F1 programs. I have learned a lot off these guys and a lot from the auto tuner guys when it comes to fuel injection. Marine fuel injection has some catching up along with their outdated ECM's. Just saying because currently there is stand alone aftermarket ECM's for the auto / race market and more coming that can be used on the marine side but not many at all using them - Sterling is one of the few big names. Also MEFI - 7 is available and GM is pushing it with their GM GEN V Marine base engines to the marine OEM Engine Manufacturers.

Some of the current marine Engines manufacturers are using E-controls for their ECM's. Indmar with the Fords and the LS packages along with Volvo Penta - even for their direct injection engines . Anyways just posting some of the new stuff for this year on the OEM side.

Rookie

I assume I still use my Crane HI-6M ignition boxes, coils, distributors, but what about my knock modules? Does the Holley have its own built in knock module and I just keep my knock sensors? Do I have to buy new oil psi, water temp, 2 oil temp and water psi senders? Or does it just read off my old senders?

Tibbstoy2

Personally, between my research on this thread and even more so, I used Holley's forums on HP EFI:
http://forums.holley.com/forumdisplay.php?49-HP-EFI

The Holley threads go into extreme detail. From do's/don'ts of wiring, how-to's on synchronizing timing and ignitions, troubleshooting, working with MSD, DIS, 2 wire vs 1 wire knock sensors and calibration... etc... I also felt like the Holley EFI software had very good help sections and went into great detail on the how-to's. Even better, Danny the moderator on the EFI forums is very helpful and really quick to help.

Buying from Haxby is definitely a good idea though - his knowledge being marine specific helps as well.

Having gone through the Holley multiport conversion a couple years ago, and upgrading to DIS ignition, I felt more than up-to-speed and ready to attack having gone through the research part before I bought anything. No videos needed... I spent a lot of time tinkering with the Holley software as well (free, so why not tinker). I machined my better flowing intakes (holley ones are not ideal), and angled the injectors to hit the back of the intake valves... I am VERY happy with the results.

Tibbstoy2

You have a lot of options for keeping existing knock sensors. You basically set the sensitivity (up to 2 sensors per engine) by running the boat on the data log on some typical days when you know you have good fuel. From that, you can experimentally determine the appropriate setting.

http://forums.holley.com/showthread....=knock+sensors

Since you're in the GR area, feel free to PM me I can be of any help... I wish I had a local helping hand when I was going through it!

mmb

What distributor do you use for the efi to control timing and assuming you do not want a crank trigger. I only want to use 1 coil also.

rvander68

I use the MSD 8366. I swapped the ignition module to GM HEI module though due to reported issues (I have no first hand knowledge of this but did not want to take a chance) with the MSD module.