the flyin' scotsman

Was curious what changes I might expect if using 24lb new injectors in a 87 S4?

apparently the 19lb items are NLA!!!

Leon Speed

What about Roger, he should sell 19 lbs ones, or Five-o-motorsports.

the flyin' scotsman

As always roger is my 1st choice for parts.

The other suppliers have OEM units on their sites for only $120 - $190 ea!!!

Manfred

If you know your horsepower at the flywheel you can use this calculator:
http://www.witchhunter.com/injectorcalc1.php4
They recommend the injector you chose run at about 80% of maximum duty (ie don't come in under the wire with your injectors, leave a little room to spare for future modifications that might increase your HP).
I think 24lbs in an S4 is about right. I just had 24lbers put in my GT and I think I could've gone just a bit bigger. I suspect either 19 or 24 will work for you but 19 is cutting it closer to the top end. Let us know what the calculator says.

Dan

993turbo

Im planning on 24's in my GT, when I do the sharktuning.

ROG100

You will see very little difference but have additional capacity for tuning in the future.

The 19Lb are available if you look around. In this case the customer has easier access to 24Lb.

Tom in Austin

Do the 24 lbs affect the displays on digital dash? Seem to recall that was discussed in the past ...

jcorenman

For a relatively stock motor, I think the answer is "none".

There's a couple of things to consider. First, the "19 pound" rating is just a number. Injector flow rate depends on pressure, and is usually spec'ed at 39.15 psi. I haven't seen the spec's for the factory injectors, but the "19#" Ford Motorsports M-9593-C302 actually flow 20-21# at 39.15 psi.

The factory fuel pressure however is 55psi (3.0 bar), so the actual flow rate for the 19# injectors is 23.5-25#.

There is another effect, however-- it takes time to open the injectors, for the stock 19# injectors this is around 0.95 ms. This depends on voltage and pressure of course, and reduces the amount of fuel that can actually be injected. What the factory does is half-cycle the injectors above 5100 RPM, instead of one injection pulse per engine revolution they go to one pulse per two revolutions, to reduce the effect of opening-time.

And of course with Sharktuning you actually gain some headroom at the top end, because the factory tune is overly rich at WOT (AFR in the 11-12 range). If you tune WOT to a more reasonable 12.5-13:1 AFR then you will not only gain some HP (around 15hp if computer models are to be believed), but also reduce injector pulsewidth which gains some headroom.

So net-net, the stock 19# injectors are fine for the stock 315-330 BHP (crank), and still OK in the 320-350 range (x-pipe, Sharktuning, etc).

So why consider changing to 24# injectors? Two reasons: When you get into cams, bigger exhaust, etc, then you do start running out of headroom with 19# injectors.

But also with larger injectors that have a bit quicker turn-on time (i.e. 4-hole disc-style injectors), you can easily dispense with the half-cycling above 5100 rpm, and just run normal cycling all the way up. There is no evidence that this is worth any real HP, but the more uniform fueling can't be bad.

jcorenman

Yep, improves the calculated fuel-mileage about 20% which messes up the indicated mileage, and miles-to-go. No effect on outdoor temperature however.

ROG100

Does affect the MPG numbers on the digital dash as well as the fuel gauge 50/25 check range warning.
The gauge and low fuel light are not affected as they take the reading direct from the sender.

928mac

Roger what is the going price for your 4 hole? new and rebuilt.

Speedtoys

I got my 19lb ford injectors off Ebay for $80.

Imo000

The original 19lb units are the same as the ones found on all stock 5.0L Mustangs, from the late 80's early 90's. They are orange in colour, the 24lb for units are bule and the Linclon Mark VIII had then.

the flyin' scotsman

Thx all.

Jim, appeciate your detailed advice.

Roger, my 'NLA' comment was given to me via my customer who has done some research sourcing new Ford 4 hole 19lb and not any comment directed at you or your fantastic service. Ive advised that the items are available hence my first post indicating the $190ea OEM units should he want to make that choice.

GregBBRD

Jim:

Are you saying that for a stock engine without any tuning that a 19 pound injector is going to deliver a similar amount of fuel that a 24 pound injector does and the OP can use either one, in a stock application?

This is how I interpreted the original question.

I understand that a 19 pound injector delivers a lot more fuel at 3 bars of pressure...but a 24 pound injector is also going to proportionately deliver more fuel than 24 pounds, at 3 bar.