What's the full combo? 340-360 seems high for a basic bolt-on car. I run 24's in my car (302, E cam, ported GT40 irons, Edelbrock intake, 75mm TB, full exhaust, and 175 shot with no issues.

 

I'm in the same range and upgraded my FMS 24's to TFS 30's last fall. They look just like the Accel injectors. Not enough mileage on my car since it went into winter storage last fall, but I didn't notice any ill effects with my C&L and 30# tube after I switched.

 

What's the rest of your combo? the combo in my Thunderbird (see sig) has 24lb injectors, stock replacement Motorcraft FPR, and a Walbro 155lph pump. Traps around 100mph in the 1/4 mile at a 3700lb+ race weight. I haven't gotten any lean codes so I assume it's ok. Then again I could be totally wrong...

 

Combo with those numbers:

Gt-40x heads, e303 Cam, Typhoon intake, 70mm TB, 73mm Mass Air, K&N, 1-5/8 to 3" long tubes, catless x-pipe, flowtech terminator mufflers, flowmaster tailpipes, 3.71:1 gears, TKO-600, aluminum driveshaft, 3190lb race weight.

Changes:

155 lph pump, Edelbrock Performer lower ported and matched to typhoon upper, BBK fuel pressure regulator, pullies, 3G, exhaust combo with ground clearance and the same or slightly better power. New race weight 3100-3140.

I still don't know how the 88lph pump handled that.

 

340-360 at the crank w gt40x's? Not likely my man, I'd guess you're around 270 some odd at the wheels which would be like 300 or so at the motor. You'll be ok with 24's.

 

340-360 is reasonable for engine HP, which is all that matters to an injector. Engine design efficiency matters, but is pretty consistent for our engines in good condition.

 

Have you had it at the track? What has it trapped (e.t., mph)? You can get a good estimate of horsepower from a 1/4 mile run.

 

I was able to run a 13.1 with a 2.0 60' (poor traction) and trap 105.4 MPH in the 1/4 mi

 

which is why I went with 30 over 24 for my combo. I'm right around 350-360 crank hp

 

I can't find good 30lb injectors at a decent price though. FRPP 24lb injectors are only $200. I have read too many bad things about Accel and the TFS ones are supposedly made by Accel. Why did ford have to stop making 30lb injectors?

The injectors I had seemed to be in bad shape, one was a little bent at the tip from removing the pintle cap. I ordered FRPP 24lb injectors.

Hopefully they can handle the occasional 87-93% duty cycle.

 

Where have you read bad things about Accel/TFS injectors?

The old yellow colored units didn't review well, but I haven't found any negative posts about the newer stainless steel body design. I also noticed a set of like new 30's in the Corral classifieds for $220.

 

It seems the Chevy guys don't like them and the new Bosch 3 style injectors atomize the fuel better. I would rather have a ford injector, for $78 less, not have to replace the MAF, and probably never exceed its limitations without a power adder or new/rebuilt lower end.

Are Accel Fuel-Injectors any good? They seem to be the most affordable ($240 - $390) for set of 8. - Corvette Forum

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Are accel injectors any good? - LS1LT1 Forum : LT1, LS1, Camaro, Firebird, Trans Am, Engine Tech Forums

 

My Thunderbird is making around the same power as your car. Get the 155lph pump in the tank and roll with it. If you get a deal on some good 30lb injectors snap them up and run them.

 

I've been thinking about the 24lb vs 30lb injector debate recently as the engine in my Thunderbird is in that 340-360HP at the flywheel range. With the 24lb injectors the car has now it doesn't throw a code 86 (adaptive limit reached) so I assume the 24lb injectors are enough. I don't expect the car would run any better/faster if I switched to 30lb injectors and if your car isn't throwing a code 86 it probably wouldn't benefit from 30lb injectors either. I could be totally wrong but it seems that in my case (and probably yours as well) 24lb injectors are enough. I'm running a stock replacement Motorcraft FPR as well (39psi non adjustable) for what its worth.

 

Anything "adaptive" isn't relevant in open loop (when you are putting the injectors to good use)...and EEC-IV isn't checking your A/F ratio @ WOT.

Running a Walbro 255, I've run 24lb injectors @ 41psi base fuel pressure and had enough for AFR-165s and about the same cam. Probably could have used 30s for my combo, but 24s did it with no issue.

I spend the extra money on a 255lph pump and a wet kit over the 155 instead of the injectors...24s should be more than enough

 

If you're getting the car tuned, you could even run 42's or 60's. Buy what you can get a good deal on.

I have the red top, 30lb. injectors in mine.

 

I think at this point I'm better off just picking up a Lightning MAF and 30lb injectors when I get the car tuned. I'm guessing the 24lb injectors and calibrated MAF are fine for now. Doing some calculations at ~345hp flywheel 24lb injectors are at about a 90-95% duty cycle at 39psi. I'm in the okish range. For now.

 

Just some food for though. I know a guy who has a Thunderbird similar to mine (TW170 heads, stock HO cam, GT40 intake) who has a quarter horse. With his combo and 24lb injectors (stock fuel pressure, 39psi) he was hitting 95% duty cycle at 5500rpm. He's since upgraded to 30lb injectors. I've got a bit more cam and intake than him so I'm probably around there at WOT as well.....

 

Totally believable. My 30's show 80% or round about I think.

 

Here is ACCEL's recommendation for fuel injectors:

Ford Racing also some examples on page 3 of their guide:

https://fordperformanceracingparts.com/download/tipsPDF/EFI_TechTips.pdf

 

Based on replies in this thread, some data logs of people with similar combos, and injector sizing recommendations I'm going to pick up a set of red top 30lb injectors. They can't hurt and will give me some breathing room when ever I swap in a more aggressive cam.

 

1 vote for keeping what you have. 24# injectors are fine, and if you already have them, and an MAF tuned for them, you're wasting money to swap 'em. If you don't have an AFPR, get one before you go to a dyno. You're at the high end of the range for what I would use 24 lbs injectors for. However, I've personally pushed 24s as high as ~320rwhp. You're probably in the 270-280 rwhp range give or take.

 

You tell him to save money on the injectors.... then you tell him to burn money on an adjustable fuel pressure regulator. Only time the adjustable fuel pressure regulator makes a meaningful change is the initial start after install or adjustment. As soon as the car is in closed loop the EEC will adust injector pulse duration and remap the fuel trim tables to get everything back to where it was before. The only time increased fuel pressure will be beneficial is if your running too small an injector. Ie the injector is too small and duty cycle is 95 to 98 %. Ramping fuel pressure up will enable the EEC to decrease duty cycle. Idle and low load cruise trim will get whacked out with the crutch.... not to mention the decrease in pump life.

 

What is the problem with my advice again, Kim?

Yes, $129 (Accufab) AFPR is far less expensive than $320 (OP's estimate).

Yes, increasing the fuel pressure will cause the idle and partial loads to be "whacked out" for a bit until the EEC IV's adaptive learning adjusts.

Yes, the bump in pressure will lessen the DC at WOT, which is the entire point.

Yes, hypothetically running increased fuel pressure is harder on the fuel pump. It has worked for decades without causing pump failures. It beats spending $500 or more on a chip and tune.

 

Nothing. My brain was locked on the other response where the person said at WOT adaptive EEC didnt affect the mechanical adjustment. So many people get an adjustable fuel pressure regulator and tinker with a few pounds one way another and have no clue that so long as the injector drive is within the 60 some percent to 95 percent the EEC simple tunes out thst fuel pressure bump. In the case where we are dealing with a small injector pushing pressure will allow the EEC to shorten injector pulse duration.

 

mine makes 305rwhp (350ish crank) on stock 19s. I do want 30s and a new tune but it sucks ford racing doesn't make 30s anymore so I may just get 24s. I have a 155 walboro btw.

 

Cool. Can you verify how much the EEC IV can adjust the trims? I'd read long ago that it was 12.5% in each direction, lean or rich, for a total window of 25% adjustment.

Back to the OP for a bit:

Check out this link: Fuel Injector Calculator - Pro-M Racing, LLC.

Pro-M makes the best aftermarket Mass Airflow Sensors on the market. They know everything about injectors, and they recommend maintaining a 90% duty cycle at WOT.

Here's some math for your car using your worst case 360hp estimate, which I believe to be a very high estimate.

360hp * .5BSFC = 180lbs/hr fuel requirement
(180 lbs/hr) / (8 injectors) = 22.5 lbs/hr per injector
(22.5 lbs/hr) / (24 lbs/hr) = 93% duty cycle at WOT assuming 39psi base fuel pressure (stock)

So, at 360hp with 24lbs/hr injectors at stock fuel pressure, you should be running ~93% duty cycle. Now lets calculate the fuel pressure that would be required to drop from 93% duty cycle to 90%:
(22.5/x)=.9
22.5/.9 = 25 --> you need a 25 lbs/hr equivalent fuel injector or greater. So:

sqrt(x psi/39 psi) * (24 lbs/hr injector) = (25 lbs/hr injector)
x = (25/24)^2 * 39
x = 42.32 psi

So round up and set your base fuel pressure, vacuum source removed from the AFPR, to 43 psi.

I recently bought a 155lph fuel pump to handle the 24-30lb injectors and HP I will be making. However, not much has changed with my setup and I'm surprised how fast the car was before considering I was running a stock pump. How is it that I was able to run a 13.1 with a 2.0 60' (poor traction) and trap 105.4 MPH in the 1/4 mi while being so fuel starved? Where's Scooby?

I can only guess that it wasn't stock. It's entirely plausible that at some point before you owned it, it may have gone out and was replaced with a bigger pump. 88LPH stock fuel pump should be good for no more than 290 crank hp, and that's pushing it. Even Ford upgraded the stock fuel pump to the 110LPH pump in the '93 Cobras, which only made ~235 rwhp.

 

I ended up swapping on a set of FRPP 30lb EV1 red top injectors and a C&L 099 purple sample tube into my 76mm MAF. The car runs great, just like it did with the 24lb injectors. Drive ability is the same and surprisingly the idle is slightly smoother.

 

Glad to hear that! I like my 30's better too, but I've been having problems with MAF meters. My 73mm C&L with the stock electronics and 30# sample tube runs fine. However I just purchased a brand new PMAS 80mm MAF that is supposedly calibrated for 30's but the computer throws codes.

Code 66 (Mass Air Flow sensor circuit below minimum voltage) which leads to
Code 98 (Hard fault is present - FMEM mode)

PMAS hasn't replied to my emails, so I'm going to have to call them to confirm the calibration. I also suspect I'll need to install it again and measure voltages.

 

Excellent result! Glad you're happy

 

Has any tuning been done to the stock computer, Tom?