Jeep Strokers

27lb injectors seems to be the norm for a 4.7 stroker. E85 has an air/fuel ratio of about 9.7, while gasoline is 14.7, so E85 requires 1.5 the amount of fuel for the same amount of air. That would mean that I need a fuel injector that will flow 1.5 times as much fuel as a I would need for gasoline. This can be accomplished by using an E85 conversion kit (ex: http://www.change2e85.com) or using larger fuel injectors. Even with an E85 conversion kit the fuel delivery would benefit more from an increased volume over the same amount of time (this is larger injectors) versus the same volume over a longer period of time (this is the conversion kit). I will need EV1 connectors for my 97 TJ.

So I can go for larger injectors and the conversion kit. I figure that I will want a 36lb injector as they will deliver 1.33 times the fuel of a 27lb and still be reasonably priced. I'm thinking the F87E-375. These have an impedance of 14.5 Ohms.

I could go as with 42lb and not even need the E85 conversion kit. That makes me think that I want the Bosch Green Tops. These have an impedance of 14.4 Ohms and from the photo look like they are EV1 connectors as well. They are reasonably priced at $280 for a set of six. These will run a bit rich though at 1.67 times the fuel that I need at 49psi. Can I change my fuel pressure or is that an OBD I only thing? Then again I'm basing this "rich" opinion on the assumption that 27lb is the perfect injector for a 4.7. I'd still rather be running rich than lean.
Using the data found here this injector will deliver 1.55 times as much fuel as a 27lb injector.

What impedance do I need for my injectors?

This thread on JeepForum discusses a couple options for converting to E85. None of the options in the OP are upgrading to larger fuel injectors. I like the simplicity of not having the piggy-back computer of a conversion kit. There are less parts to break, it keeps the underhood area much neater, the piggyback computer probably isn't water resistant enough for offroading, and it's cheaper to not have to buy it.

My calculations use the Fuel Flow Calculator (which follows Dino's math on his page) here:
http://kgparts.com/index.php?page=fuel-calc
Assuming that 27lb injector is 27lb at 3 bar pressure (old injector) and whatever pressure the new injector is stated as being measured at (new injector).

Thoughts, opinions, recommendations?

In practice I don't think many (or anyone) is running 27# injectors in a 4.0 Stroker, I have a 4.6 and run 19 pounders just fine (though I'm cammed for low torque so it's easier for them to keep up. The last guy around here I recall running 27's was having very clear symptoms of severely rich condition, and didn't seem to want to believe his injectors were causing his problem.

The Mustang 5.0 came from the factory with 19# injectors...feeding 230 horses Several GM LS/LT 350 combination's have 25# injectors and even the late model Corvette application only had 27# injectors and it's somewhere around FOUR HUNDRED HORSES.

So IMO 27# injectors are way overkill for most Jeep strokers and even some radical strokers. I think even 25# blue tops are (usually) overkill for most of us.

So applying that to E85 I think you should notch your prospects down one, look at 30lb red tops with 36's being your high end of the range. Unless of course you're going to do some forced induction.

Just my Opinion

Doesn't the mustang and corvette engines have eight cylinders ( injectors?)

Just a note, I am currently using the Mopar 42lb injectors and running them at 80-85% duty cycle.

Plechtan wrote:Doesn't the mustang and corvette engines have eight cylinders ( injectors?)

Yes .. that always gives us two extra.

Plechtan wrote:Doesn't the mustang and corvette engines have eight cylinders ( injectors?)

They are v-8"s but sometimes if you find a good set it's nice to have two spares!

Plechtan wrote:Doesn't the mustang and corvette engines have eight cylinders ( injectors?)

Fiveomotorsport sells the 42lb injectors in sets of four, five, six, or eight. They sell several injectors in sets like that, but it's not a bad idea to have spares.

SIXPAK wrote:Just a note, I am currently using the Mopar 42lb injectors and running them at 80-85% duty cycle.

Can you tell me a little about your engine? This is the most that I could find. I was just worried that flowing that much through the injectors would drain the fuel from the system and starve other injectors but nobody has mentioned that yet.

I've also received other feedback that 27lb is not too much for a 4.7 and is actually ideal.

If you ahve one of the setups with the fuel pressure regulator in the tank, you face a problem of dropping fuel pressure overall as you go to bigger and bigger injectors. The design of the fuel line and fuel rail (their relative sizes) will prevent some injectors from having lots of pressure and some less... the restriction is the fuel line, in-tank pressure regulator, and fuel pump.

If you have a regulator up front... your most likely restriction becomes the fuel pump and fuel line, causing a restriction before the regulator. again, the fuel rail is usually sufficient in volume to provide even pressure to all injectors, no matter what injector size.

I wouldn't even begin to venture a guess on where the current "weak point" is, or how much HP the stock fuel systems can support.

lafrad wrote:I wouldn't even begin to venture a guess on where the current "weak point" is, or how much HP the stock fuel systems can support.

All these references to HP and calculators I've seen relating fuel flow rate to HP all assume that the fuel is 14.7 stoichiometric gasoline, correct?

PolloLoco wrote:Can you tell me a little about your engine? I've also received other feedback that 27lb is not too much for a 4.7 and is actually ideal.

This is a drag only motor with an aftermarket ECU. Not sure if the HP but I did go to 100% duty cycle on a 30# injector so this is why I went to the Mopar 42lb (39 actually). Ported head had been ported for max flow in the lower lift areas to accomodate a lift rule camshaft per our Association rules. Over 14:1 comp which may be a bit on the high side. Induction was cobbed together by me and uses three 87-90 stock jeep TB's. Jesel rockers and a CV products belt drive.

Yes V8's generally have two more cylinders

Just being a smartass Pete, to take your unstated question seriously (because it's definitely a worthwhile point) Yes V8 (small blocks in this case) have more injectors and in our case smaller bores than our I6. So ostensibly they can use smaller injectors than the bigger bore I6. Undoubtedly that's what you were hinting at with your question This is not the first time I've seen this point brought up. believe it or not

If you think of it in terms of cylinder per cylinder injector pulse for injector pulse Yes the similar displacement V8 (such as the ford 5.0) 19# needs to flow less than an I6 with the same injector and pressure... But beside idle and just off idle with "sequential" FI; thinking in terms of one injector pulse to feed one cylinder per cycle really isn't whats happening. So that muddys the waters which is why injectors are usually sorted out with total horsepower and not engine size or cylinder displacement. The problem is that once things "get going" (batch fire) so to speak any single injector is feeding a mass of AIR (or Horsepower) regardless of the displacement of the particular cylinder the air/fuel is going into.

There's other factors that muddy the waters as well, like: All those V8's are larger displacement have higher horse power and almost all of them Rev several hundred if not a thousand RPM's higher than the 4.0 stock fuel system. So yeah the I6 has relatively big bores and good CFM flow needing a bit larger injector, but they are closer than most people think due to the factors I just mentioned.

So a 19# can feed my RV cammed stroker but it's admittedly probably at 90% duty cycle doing it... at WOT it' might even be maxed but it works and I've not burnt anything up in 60k miles of rented mule useage. A 24# works and probably plenty even for a higher RPM cam (like the street cams most people put in their budget strokers with the longer duration and overlap).
But IMO 27 is just going to get you worse idle and low torque with a factory fuel system. Just like putting on too large a Carburetor does... big droplets of fuel instead of finely atomized fuel leads to poor lower RPM performance. A 27 pound injector at factory PSI is basically shooting a stream like a squirt gun right onto the back of the valve... Not to mention that the factory ECU is probably going to fight a battle that's outside its programed fuel tables to try and deal with a 27# injector.

The computer is blind to the type of fuel and injector size I use. All the computer will do is signal the injector to deliver fuel for x amount of time, either based on it's programed tables in open loop or feedback from the O2 sensor in closed loop. It will need to deliver extra fuel for E85 due to the different AFR.

What I am trying to find a solution for is what size injector would be proper for E85? I want to go as large as needed without using too large of an injector that then draws too much fuel from the rest of the fuel system causing other issues; how much is too much?

Buy a stand alone fuel injection first. You're wasting your time with the stock stuff.
Rule of thumb is .5 pounds of fuel per hour per HP.
Add 20-30% more for E-85.