4 Hole Bosch Injectors max HP and Tune -4.6 PI


Dec 29, 2017
Bought a 98 Mustang GT recently. The guy I bought it from had built a 4.6 PI motor for it. The motor has ported PI heads that flow 27 percent better then stock, it’s .20 over, race balanced rotating assembly. He used the yellow 4 hole skinny Bosch type 3 injector. I stuck a Trick Flow plenum and ported 70mm Throttle body off a econoline on it, weld in Dynomax mufflers, no air silencer and worn out k&n. ( Fix to be a mac I found on eBay for $16 ) going to can tune it with a CARB legal Tune has well.

I live in CA and they have really really cracked down on tuneing stuff. LMR won’t even ship tuners here. Neither will Amazon a whole bunch of companies won’t. So I was basically forced to buy a I3 that’s carb legal with canned tunes. I should be able to adjust timing And some other stuff has well.

This is the injector part number.

This injector cross references with a bunch of others and appears to be 19lb same has the one that comes in the Explorers that people put on the mustang.

I have read on here before that they actually flow closer to 22 to 24 at 43.5. Is this accurate because this site says they are actually 18.25?

According to my calculations and what the guy who built the motor said I would have to be pushing 300 to 320hp at the crank. He says it was a 300hp motor and that’s before I put mods on it.

I saw a set of heads like this put on a car and it picked up 36HP. Granted that was a engine on a stand with no accessories and long tubes.

So what’s the max HP I can get out of 19s? Because I’m trying to figure out what to do about injectors if Iam in fact maxing their duty cycle and there is more power on the table.

Because I can’t just tune for 24 pound injectors. See the dilima? That will be disabled in the tuner from my understanding.
No custom tunes either. Disabled on CARB tuner.

Like I have seen dyno reports of people putting 280 to 290 on the ground on 19 pound injectors. How are they doing that if 19 pound injectors can only support 300hp at the crank or so. 290 to the ground that’s like 340 to 350HP

Last night I read a dyno report on a 98 pi swap and it was 289 to the wheels.

I know on these 98s they have some funky fuel setup so I can’t just raise fuel pressure on the 19 pounds.

My thoughts are stick 21 pound injectors from a newer new edge in it. It wouldn’t be has rich has 24 pound injectors but I read Ford didn’t even change the tune when they whent from 19 to 21 in the new edge. I have to pass smog. So I don’t want to be swapping injectors every few years.

Or just Leave these or find some thing close to it.

Anyone got any other ideas if in fact I’m maxing the injectors out? I will no more once the tuner comes in and I data log it some to see if the injectors are maxing out.

Or does anyone know how to adjust fuel pressure on a 98 mustang? It has the welded on fuel pressure regulator.
  • Sponsors (?)


New Member
Oct 9, 2020
for a 300 hp motor you need 24,s and a proper dyno tune. upgraded maf also. And some compression,a good port and CAMS! Not even California can change physics.

a canned tune will not work on a 300 hp pi 4.6 car, to get to that place, you NEED cams, no canned tune covers a cam swap, of a maf change, and a very select bunch of parts , that support that power, and some luck as well. This took us years to achieve 300 hp with the pi motor, and no one did it on 19 pound ejectors.
and lastly a proper tune, by a knowledgeable tuner. 300 rwhp is no easy task with a pi motor. Rwhp is much lower than crank hp. And no one races motors on engine stands. So……show me a 300 rwhp hp pi 4.6 car running a stock maf and 19 pounders, I will show you a car about to blow up. Not happening.

best answer, leave California, I did!