What Size Injectors Do I Need?

Flade · Feb 26, 2016

Hi, I am getting ready to build up my 94 GT vert a little. The engine is stock except for a CAI. I have a set of GT40 heads and Explorer intake. I plan to add a larger throttle body, MAF & EGR, plus a cat back exhaust. The car is a daily driver, so it need to be reliable. Do i need to move up to 24lb or 30lb injectors? Will the stock furl pump keep up? Anything else I should upgrade? Should I consider a mild cam upgrade to?

Gearbanger 101 · Feb 27, 2016

The stock 19lb/hr injectors will be sufficient for those mods. If you're going to upgrade anything, I'd change out that tired old stock 88lph fuel pump for something in the 155lph range, or better.

If you're looking for bang for the buck mods for that very, consider a rear gear change. A set of 3:73's added to the rest of your proposed mods will make it feel a lot more lively around town.

jozsefsz · Feb 27, 2016

You could probably expect to make around 40 extra hp with the heads and intake. I don't think the MAF & Throttle body will add much more, but personally I'd upgrade to 24lb injectors and get a calibrated MAF to go with it. The 19's might handle it just fine, but I think that's borderline risking going lean by exceeding a reasonable duty-cycle. A better cam could also help, but to some degree changing the cam just pushes the power curve up or down the RPM's unless you make more dramatic changes (like a set of more pricey heads) and will probably give you some driveability issues unless you want to do a tune too. A nice Walbro fuel pump is fairly cheap, and since our cars are 20+ years old now, a replacement is in order so may as well upgrade.

The gears are a good idea as Gearbanger mentions (especially on an automatic), though the tradeoff is mileage and top-speed on a daily driver, and I wouldn't do them if you're considering going forced induction at any time in the future.

Flade · Feb 27, 2016

Thanks, the car is a 5 speed. I was considering upgrading the rear gears. I was thinking 3.55 so I won't give up too much highway mileage. I can buy a set of used 24lbs injectors for $50 so I wil go with that and a new 155 lph fuel pump. I was thinking I should get a tune chip to tie it all together.

Gearbanger 101 · Feb 27, 2016

The stock 19lb/hr injectors will support the fuel requirements for your above mods. So unless you realistically plan on making more than 280+hp, don't bother with the 24's....its money better spent elsewhere.

Noobz347 · Feb 27, 2016

Gearbanger 101 said:
The stock 19lb/hr injectors will support the fuel requirements for your above mods. So unless you realistically plan on making more than 280+hp, don't bother with the 24's....its money better spent elsewhere.

^this^

jozsefsz · Feb 27, 2016

I'll have to disagree with you guys on the 24's, 19's are probably safe but borderline. At stock power + 50hp, you'll be at around 90% duty cycle, which is not generally what you want for max reliability (you should be aiming for around 80% max).

And if you're considering upgrading MAF, might as well do them at the same time and give yourself some room to grow in the future (plus, heck you'll have the intake out anyways so why put old junk back in). It doesn't hurt that my opinion is related to 20+ year old injectors which are prone to failure at some point soon anyhow, and a 90+% duty cycle is just what you need to have them stick open until the end of time. Which makes for a long trip home, as I've been there.

A decent set of newer injectors can also help you pick up power and economy with optimized spray patterns, clean baskets, more stability at the low slope, and 20 years of advancement in technology.

On the rear gears, make sure to check out what you have right now. There were different options available, so check your door-tag to see what you already have. Might save you a few bucks if you were already good from the factory.

M=2.73:1
Z=3.08:1
E=3.27:1

Flade · Feb 27, 2016

I bough the car new, so I know what it has. At the time I upgraded to the better 3.08 gears. The 3.27s were only offered In the automatics. I also picked up a used BBK 70 mm throttle body so I think to be safe I'll go with the 24 lb injectors.

This guy is selling a set at what looks like a fair price:

https://okaloosa.craigslist.org/pts/5427028614.html

Noobz347 · Feb 28, 2016

I would never waste money on 24 lb injectors. Like gearbanger said, unless you have better heads than GT-40s and... (what cam?), along with some great flowing LTs, then the 24s are a waste. If you decide to put blower on what you have, then 24s are too small.

It's great to talk about magic spray patterns and all but most of that applies to much larger injectors that have been improved to help provide better manners at cruise. Not all that long ago, 60lb injectors were track only. Why? Because they wouldn't idle or part power worth a crap and were high impedance. That end of it has improved. 19lb Ford OEM injectors? They're still some of the best in that size (nearly bullet proof) and there's not significant spray pattern improvement from other brands either. At least, nothing that's measurable on a dyno.

Plot your end game and figure out what it is you need to get you there. For the cost of injectors and a throw-away tune (or the cost of a custom tune) along with whatever "calibrated meter" (I really don't like that description) you get to toss in with, and I could have had sub-frame connectors, an aftermarket fpr (much cheaper than 19s if there's already a good fuel pump behind it).

Sometimes 24s will run without tuning issues while other times it won't. There are tips and tricks for making it work but you'd still need a good adjustable fpr.

Just a ball park rule of thumb for injectors:

\

Middle of the road for 19's is 300-320ish we'll say. What do you need to do to your combo to get there?

jozsefsz · Feb 28, 2016

Noobz347 said:
Middle of the road for 19's is 300-320ish we'll say. What do you need to do to your combo to get there?

Here's the source of our disagreement.

With a 94-95 302 BSFC's going to be around 0.52 (not the most efficient engine), so that brings your 100% duty-cycle max hp to 290.
Factor in that you're running at 39 psi and not 43.5 (unless you want to adjust your tune) and you're at 260.
Factor in that you want to run at 85% BSFC max and you're now at around 220.

Ford wasn't a generous benefactor that threw in oversized injectors back in '95.

Riddle me this Mr. Noobz, why did Ford decide to use 24lb injectors in the '95 Cobra when it put out a whopping 240hp?

Because... to run with factory reliability you want your duty cycles low, and running let's guess 250hp with GT40 heads and explorer intake, you're best off running 24's.

You can squeak by on 19's all day long. You might never see an extra HP. But as the op has a set of 24's lined up for $60 personally I'd go with it (buyer beware on used injectors though, I've gotten my share of duds). If you're already planning to upgrade the anemic MAF that tops out at not much higher flow-rates than the injectors, it's a good time to upgrade. And that 'calibrated' MAF can easily be tuned in for greater injectors if you ever want.

As to better injectors with more mild-mannered low-ends, I've tuned my car with Bosch-style EV1 injectors and there's a noticeable difference in idle smoothness, low-end grunt, fuel consumption, and emissions (they test where I am). It'll cost you a bit more than $60, but I think they're excellent. They show almost no need to set a different lo-slope in the tune in my experience.

Noobz347 · Feb 28, 2016

You can more than squeak by. Done it... many times. Save the injector and MAF for when it matters. Boost.

Gearbanger 101 · Feb 28, 2016

Ok, I'm gonna leave this here and I'm done with this back and forth.

Hundreds.....literally hundreds of 5.0L owners have run the combination the O/P has outlined above with 19lb injectors with nothing but success. Realistically, an iron GT40 top end is only going to net you about 265-270hp on a good day. Adding 24lb injectors to this combination does nothing but complicate the build and add unnecessary expense. On the expense side, the added cost of the 24lb injectors, plus matching MAF meter and/or tune, depending on how you do it and complications included in driveability issues presented (because let's be honest....calibrated meters are ).

Quite frankly, if I ever got to the point where I thought changing injectors was a necessity, I wouldn't even waste my time with 24lb'er. I'd go right for 30's that'll suit ANY N/A power level you could throw at a 302, or jump right up to a set of 42-60lb injectors if forced induction was in the cards.

@Flade FWIW, with that top end, an injector, MAF meter and throttle body swap aren't effective mods. You'll fork out several hundred dollars for a gain of about 5-6hp.

If you want to pick things up, spend the money on gears. Don't worry about the mileage. The difference in gas mileage between your 3.08's and a set of 3.73's is all of 2-3mpg. Small price to pay for a big "seat of the pants" feeling.

My buddy has an '88 GT, converted to mass air. He bought my old BBK 70mm MAF meter (which is what size the one on your '94 is now) and my old Explorer top end with a comp XE264HR camshaft. He had a full exhaust and 65mm throttle body and made 269rwhp. His A/F ratio was rock solid, all the way to red line. If you're that worried about feeding it up top, go ahead and spend $75 on an adjustable fuel pressure regulator and add 5psi of fuel pressure to the mix. It's not going to hurt anything.

Flade · Feb 28, 2016

Jozsefsz,

Thanks for that detailed reply. I am interested in hearing about your use of teh Bosch EV1 injectors. Do they swap right in? Do they require a custom tune or different fuel rails. For a daily driver the improved idle and Low end performance sounds worth looking in to.

Flade · Feb 28, 2016

Gearbanger, I have heard others say that the 94GT has a 70mm TB, but elsewhere I see it listed as 58mm. Compared the the 70mm BBK I have, it looks tiny. I am planning to use the BBK so I should have a very similar setup to your friend. If I can get in the 270 range I'll be plenty happy.

Gearbanger 101 · Feb 28, 2016

Flade said:
Gearbanger, I have heard others say that the 94GT has a 70mm TB, but elsewhere I see it listed as 58mm. Compared the the 70mm BBK I have, it looks tiny. I am planning to use the BBK so I should have a very similar setup to your friend. If I can get in the 270 range I'll be plenty happy.

No, the MAF meter is 70mm. The throttle body is 60mm (actually only 58mm). Even the '94-'95 Cobra's only got a 60mm throttle body. You could put the 70mm BBK on if you'd like, but you're not going to see any performance gain.

I misspoke earlier. I meant my buddy put my old 70mm BBK MAF on, not throttle body. He actually re-used the 65mm throttle body from the Explorer manifold.

FWIW, I've got a 70mm throttle body feeding my stroked and poked H/C/I 331....and consider the difference in airflow between our two engines.

jozsefsz · Feb 28, 2016

Gearbanger 101 said:
Ok, I'm gonna leave this here and I'm done with this back and forth.

Fair enough, but you'll forgive me that I don't put any stake whatsoever in how many people have done stupid as a basis for technical decisions. I'm an engineer and I prefer scientific data and design specifications as my rationale. At those power-levels you're exceeding the duty cycle the injectors are designed to handle. It will work just great, until it doesn't. Your army of amateurs who have slid by doesn't impress me.

The Op stated he wanted reliability for a daily driver, and has an opportunity to pick up some 24's for cheap. I say go for it if you're already changing MAF. It's what Ford did with the Cobra, and for good reason. You say go big or go home, which is fine, but that's not the only answer. I agree that cranking up the fuel pressure can address the problem the exact same way as going 24's, but that either requires a tune or matched MAF as if you were upgrading the injectors. Going to 24's doesn't open up as much opportunity as 30/36/42 or more, but you can get away with a calibrated MAF at that small a change (30/36/42 will NEED a tune).

@Flade you're welcomed my man. if you're interested in the Bosch injectors, the EV1 style just drop right in, same connectors and all. you'd need to do the same things as with any injector upgrade, depending on the size.

addermk2 · Feb 29, 2016

I love these threads.

Don't dick around with old injectors. Buy a brand new set that have zero miles.

As for the stock 19s. Every car I've had, they just get thrown in the trash.

Injector technology has coke a LONG way over the years. There is truth to the notion of spray patterns being improved. Better part throttle driveability, fuel mileage, and reduced emissions can all be had with a newer style injector.

My car runs 83# EV14s with a base pressure of 55psi. So basically 96# injectors. I can run my car in the shop without setting off the CO detection system, and I don't have cats.

Bam Bam · Mar 1, 2016

addermk2 said:
I love these threads.

Don't dick around with old injectors. Buy a brand new set that have zero miles.

As for the stock 19s. Every car I've had, they just get thrown in the trash.

Injector technology has coke a LONG way over the years. There is truth to the notion of spray patterns being improved. Better part throttle driveability, fuel mileage, and reduced emissions can all be had with a newer style injector.

My car runs 83# EV14s with a base pressure of 55psi. So basically 96# injectors. I can run my car in the shop without setting off the CO detection system, and I don't have cats.

What Maff calibration are you running with those injectors? I purchased a 95 GTS which I'm trying to figure out what I actually have. Guy said 306 with aluminum GT40x heads, 1.7 RR, E Cam, trick flow track, 75mm t body, unequal shorties, UDP, 24lb injectors but they are Black in color and are matched to Mass. This car has been a pita to get right. Came with a tweecer had no clue what I was doing. Last 2 months a lot of research and loaded the J4J1 cobra tune and modified it. Runs great now but took forever. I need to change the mass it looks stock want to upgrade to a larger one and then address injectors.

The car runs surprisingly good for the mods. It feels like a low 12 second car. Would have whipped my SRT8 charger with bolt ons. Scratching my head on cam also it raps pretty hard for an e cam?

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