Injectors

[Matt99]

Im building the 4.6 stroker. It was bored 40 over. I kept the head stock I was curious on what injectors i need to use for the 4.6? What did you guys use?


Thanks ahead!!!!!

[FrankZ]

I used 24# FMS injectors. Keep in mind that the actual flow rate will vary based on the fuel pump pressure. What is the output pressure of your fuel pump?

[Matt99]

I was told that i did not need a new fuel pump or regulator is this true? If so why?

4.6L Low-buck, low CR "rockcrawler"

Jeep 4.2L 3.895" stroke crank
Jeep 4.2L 5.875" rods
Silvolite UEM-2229 +0.030" bore pistons
Increase piston dish volume to 30cc
8.75:1 CR
Crane #750501 192/204 degree camshaft
Ported HO 1.91"/1.50" cylinder head
Mill block deck 0.035"
Mopar/Victor 0.043" head gasket
0.058" quench height
Ford 24lb/hr injectors with stock 39psi FPR for '87-'95 engines, stock injectors with stock 49psi FPR for '96 and later engines
234hp @ 4500rpm, 311lbft @ 3300rpm

[FrankZ]

No you don't have to, but you might want to consider going with an adjustable Fuel Pressure Regulator to fine tune your motor. Here's some info to help you determine the proper injectors for your rig...

Injector sizing

Stroker engines require oversize injectors to provide adequate fuel and prevent pinging due to lean air/fuel mixtures. Click on the image to the right.
To calculate optimum injector size, use the following formula:

Injector flow rate (lb/hr) = [Expected HP x 0.5 (BSFC)] / [no. of cylinders x 0.8 (injector duty cycle)]

The actual injector flow rate from each injector depends on the fuel pressure (FP) in the injector rail. Most injectors have rated flows at 43.5psi fuel pressure. The actual flow rate from each injector is:

Actual injector flow rate = Rated injector flow rate at 43.5psi x square root of (FP/43.5)

Take from Dr.Dyno's website:
http://www.jeep4.0performance.4mg.com/stroker.html

BTW, taking .035" off the block seems extreme. I'd suggest removing a minimal amount to get a flat surface and no more. Same goes for the cylinder head.

[Matt99]

Ok what has everyone else done for there strokers?

[Matt99]

I was told that i did not need a new fuel pump or regulator is this true? If so why?

4.6L Low-buck, low CR "rockcrawler"

Jeep 4.2L 3.895" stroke crank
Jeep 4.2L 5.875" rods
Silvolite UEM-2229 +0.030" bore pistons
Increase piston dish volume to 30cc
8.75:1 CR
Crane #750501 192/204 degree camshaft
Ported HO 1.91"/1.50" cylinder head
Mill block deck 0.035"
Mopar/Victor 0.043" head gasket
0.058" quench height
Ford 24lb/hr injectors with stock 39psi FPR for '87-'95 engines, stock injectors with stock 49psi FPR for '96 and later engines
234hp @ 4500rpm, 311lbft @ 3300rpm

This says for 96 and later engines i can use stock injectors with stock 49psi FPR so i do not have to upgrade righrt?

[FrankZ]

I'm not 100% sure to be quite honest. I do know that in 97 the fuel pressure went up to 49 PSI (from 39 in the 96 and older XJ's) with a non-adjustable regulator built into the pump assembly. I'll have to defer to some of the other folks here as far as the maximum pressure available (via the pump and regulator) for your rig.

No sure I'm helping much on this one.

[John]

Im building the 4.6 stroker. It was bored 40 over. I kept the head stock I was curious on what injectors i need to use for the 4.6? What did you guys use?


Thanks ahead!!!!!

What year fuel pump will you be using, OBD1 or OBDII. What color are the tops of ypur injectors?
John

[Matt99]

Im using all my stock stuff out of my 99 cherokee.

[FrankZ]

Sweet! Your fuel pump is the same as mine and the regulator is non-adjustable at 49PSI. Grab some 24# Ford Injectors (closer to 26+ with your pump) and you're golden!!

[Matt99]

Sweet! Your fuel pump is the same as mine and the regulator is non-adjustable at 49PSI. Grab some 24# Ford Injectors (closer to 26+ with your pump) and you're golden!!

What does the 24 injectors come out of? I need to get some asap that is all thats holding me back!

[FrankZ]

http://www.jeep4.0performance.4mg.com/tech_specs.html

[aaronkeiser]

So If im running 39 psi fuel pump with 24lb ford injectors, what would the voltage be on my adjustable map sensor? I know its hard to say but what would be the range.

[FrankZ]

Maybe I missed it but I didn't see anything in your posts reguarding adding an adjustable map sensor. FWIW, I didn't add one to my 97 and haven't had any fuel delivery issues.

[gradon]

My early 96 (1/96) XJ has the 49psi rail w/o return line/regulator and the 23.2lb injectors. If I had the 39psi rail, I'd definitely have an adjustable FPR and MAP. I have an adjustable MAP on now set to 5.0V. I'll remove it and the Jet 2 since the PSC1-003 can tweak the MAP at different RPMS(it didn't come in today, so maybe tomorrow. . .).