Need more fuel

[RideFord94]

So I've made an extensive amount of airflow mods to my motor. I can elaborate if any would like, but the real subject here, is that I was reading on rogue performance that through a certain formula. He was able to assume that the stock ranger injectors at 14 lbs can support maximum of 150 hp N/A even less with induction. Now, I've swapped my original motor with a 97 windstar 3.0. Through research I've discovered that these are 17 lbs injectors. So I've also read that most ecu's can self tune for an injector up to about 20% larger. Does anyone know if they are plug and play, or is there more work involved than it seems. I believe this to be a staple in the usual ranger modifications IF IT WORKS, because if you were to add 5 - 10 hp your injectors wouldn't be able to handle the additional horsepower. Thereby making any mods effectively useless. Any thoughts, ideas, concerns, complaints?

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[RonD]

You will probably want to Google: speed density vs mass air flow

Speed density was the older Ford system that used a MAP sensor to calculate fuel/air from preprogrammed tables in computer memory.
Mass air flow is the current system using a MAF sensor for fuel/air, this is calculated on the fly no tables.

MAF system are more accurate(efficient) and tend to have a better throttle response than MAP systems, which is why they are currently used.
But MAP systems have been the popular choice when maximizing engine output.

You most likely have a MAF system now, you never stated the year of the computer being used.

Up to a point the MAF should work for you, as it is air "flow" based, but it does have limits until chipping the computer or changing the computer is an option.

 

[RideFord94]

I do have a MAF system on my 98 Ford Ranger 3.0. But even if the MAF could trim the fuel to maximize every ounce of power. Through the formula, And I don't remember what the formula was, but it basically said that 14 lbs at the injectors max out at 150 hp. Now I figure with this theory that the 17 lb injector will be more in my area of 170- 180 hp. I also attribute my observation that my truck with cai and free flowing exhaust always ran better at 3/4 throttle than at WOT to this assumption/theory.

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[RideFord94]

So do you think 14 lb can support more than 150 hp with a stock tune/MAF system? Or do you think 17 lbs would be better for that application? I realize nobody has really broached the subject of injector swaps but from what I've read it might be one of the first mods you should do when trying to squeeze more power out of your 3.0.

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[RonD]

In general stock injectors on any vehicle will have a 20% "over need" factor.

Only changing to larger injectors will only turn on a CEL and not increase power, in most cases, because O2 sensors will cause computer to lower the dwell(open time) of the larger injectors and then computer will turn on the CEL because O2 and dwell time are outside of preset parameters.

Because you have increased the available air flow the larger injectors might help, but you usually need to get a longer dwell cam or turbo to need that much extra fuel.

But what I would do first is to get a live scanner since you have OBDII and watch fuel trims when above 3/4 throttle, if they are leaning out then you may have reached current injectors max flow.
But, since you mentioned changing the exhaust I would think that could be the limiting factor in RPM torque curve.
Exhaust system don't add power, they change when you get power, stock exhaust is tuned for mid-band.
Most popular "headers" lower the power band, to give better acceleration, but then power drops off sooner at higher RPMs.
IMO, that would be your 3/4 throttle issue.

 

[RideFord94]

Yes. The exhaust is with high rpms in mind. Now generally with the 20% over feed I don't discredit. But tell me if this makes any sense. ( Formula) fuel injector size = HP x BSFC(brake specific fuel consumption) ÷ (# of cylinders × injector duty cycle) SO 150× .45 ( generic N/A bsfc) ÷ (6 × .80) = 14.05 which would mean no 'over need'. Make any sense? Rogue performance goes on to say that there is none of the normal 'slop' to make up for poor spray patterns or clogged injectors.

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[RonD]

Rogue is a good site.

But if there wasn't 20% margin then cold start rich mix wouldn't be possible when driving on the highway, and that grey cloud of over rich exhaust would never happen when MAF or Computer F*ed up, lol.

The calculations have the margin built-in.
Drop BFSC down to .4 and recalculate, you will get 12.5

BSFC of 40%(.4) is more common now, some newer Ford engines get down to 36%(.36) at higher RPMs.

 

[RideFord94]

That makes sense. Now for a hp goal of 170 conservatively. Do you think 14 lb will get it done at high rpm?

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[RideFord94]

That formula tells me just barely. And I was hoping to be closer to 180 anyway. Looks like I'm going to the dyno.

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[RonD]

As you increase "potential" horse power you will want to go to a larger injector.

But generally any "bolt-on" upgrade, with the exception of a turbo, will not need larger injectors.

 

[RideFord94]

Thanks RonD! It was a nice discussion. Had you seen rogue performance before?

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[stmitch]

If your truck is a 98, and not Flex Fuel, it should have 19 lbs injectors stock. Flex Fuel trucks had 23ish lb injectors.

I'm curious about your breathing mods. What have you done that the stock injectors might have trouble with?

 

[RideFord94]

Well for one the 17 lb I injectors are much larger in comparison to ranger stock although that may not say much.

As far as my mods go I have
Modified MAF housing

Bored/Polished throttle body w/ plans to 'half-shaft'

Modified upper/lower intakes ported/polished/gasket matched

Lightly ported heads polished on both sides

Lightly polished combustion chamber

3 angle valve job and all new gaskets on the motor

Full cai/Sri w/ 3 inch induction pipe

Cat delete w/ plans for new high flow
And a poorly installed flow master 40

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[stmitch]

Physical size has very little bearing on flow. Your mods may be approaching the edge of what the stock 19lbs could handle, but they are likely fine for everyday use. If you want to maximize the potential of your mods, then I'd suggest having it tuned professionally. A way to look at AFRs would be helpful too.

 

[ab_slack]

I have to agree with Ron and comment here. Doesn't sound like you are going to get so much more air. Without some pre-compression of intake air, or cam dwell increase to give piston more opportunity to suck in air, only so much is going to go into the cylinder particularly at high RPMs. The only thing you pick up are pressure drops in the intake which is more of an incremental improvement. Sure you will pick up a little but probably not really running out on the injectors.