turbo fuel ????'s

[Dsc Motorsports]

im in the process of turboing my 91 ranger and just wondering on a safe size injector to run i wont be running but 7psi and i dont want to go over board with it!

[Bill G]

You should be safe with 19lb yellow top injectors from a 5.0 mustang

[Dsc Motorsports]

hmmm! think itll be enough!

[Bill G]

If your'e not going to run over 7 psi, your stock injectors will work. But to be on the safe side, you can add the yellow top injectors. There was a guy here named George who ran 18 psi with the yellow tops and he said it never ran lean.

[V8RangerBoy]

A typical "ballpark" calculation for injector size is:

(Flow * max duty cycle * cyl #) / BSFC for the motor.

In other words, multiply the flow rating of the injector (lb/hr) times the maximum duty cycle (typically no more than 80% for reliable operation) times the number of cylinders. Then divide this value by the BSFC (brake specific fuel consumption - Google it if you want, it's a wierd value). BSFC for a normally aspirated motor is about .5. Supercharged - .6, turbo'd - .65.

So, for my truck for example, the stock injectors flowed 19lb/hr. I used 80% duty cycle, and it's a V8. This was also in prep for the turbo, so I used .65 BSFC. (19 * .80 * 8) / .65 = 187.5 - the stock injectors were good for roughly 190hp under boost. Obviously, I knew they had to go. An N/A 5.0 makes more than 190. Went up to 39lb/hr's - moved the ceiling up to about 385hp.

Keep in mind these values are by no means exact, but it will let you know if you're in the ballpark. Or way the hell out for that matter! Are you turbo'ing a 2.3 or what?

[Dsc Motorsports]

yea its a 2.3L 5-speed got a tdo4 turbo. so if i keep the boost down i can prob get by with the stock injectors for a while? what do yall think i should do on the mass airflow sensor??and how much can the stock one take before i becomes useless?

[V8RangerBoy]

Yes, with low boost stock injectors are probably fine. I'm not extremely familiar with the 2.3 turbo setups or with the 2.3 itself, but from what I've gathered from briefly reading around the stock injectors seem to hold up well for low boost. Whatever you do though, stay away from the FMU route like a Vortech blower kit uses... nothing but bad news with those - they're a super-halfass way of getting extra fuel.

As for the MAF, I would either A) find the specs of the MAF off of one of the 2.3 turbo coupe's to compare with, or B) just get a MAF from a turbo coupe. Those are bound not to peg out, and I would imagine that the wiring is most likely plug-and-play since both meters would be pre-OBD II.

The range of the meter also depends on how it is set up. Mounting the meter draw-thru will give the meter slightly more range before pegging than mounting it blow-thru will. The drawback here is that mounting draw-thru means that you have to not run a blow-off valve, recirculate the blow-off valve, or tune for the little hiccup that venting out the metered air will cause. If you choose to go blow-thru though, make sure that there is at least 6"+ of straight tubing before and after the MAF. Cutting corners here will cause you some serious headaches later. Definitely invest a fair amount of time researching this area - the MAF is very very important from both a tuning and driveability standpoint.

[Dave R]

As for the MAF, I would either A) find the specs of the MAF off of one of the 2.3 turbo coupe's to compare with, or B) just get a MAF from a turbo coupe. Those are bound not to peg out, and I would imagine that the wiring is most likely plug-and-play since both meters would be pre-OBD II.
A nice idea but, unfortunately, turbocoupes did not use MAF meters. They used a modified speed density system and yes, the VAM (Vane Air Meter (the modified part of the SD system)) does peg out. Ford didn't 'perfect' their MAF systems until late '90/early '91.

[Dave R]

Then divide this value by the BSFC (brake specific fuel consumption - Google it if you want, it's a wierd value).
Nothing really weird about it, it's a measure of how efficiently any given engine converts fuel into horsepower. The closer the number is to zero the more efficient the engine is, the further away the more wasteful it is.

[V8RangerBoy]

Nothing really weird about it, it's a measure of how efficiently any given engine converts fuel into horsepower. The closer the number is to zero the more efficient the engine is, the further away the more wasteful it is.

Wow, finally someone with a decent and simple explanation :) good to know.

Bummer on the MAF deal. Haven't heard of SpeedDensity systems consistently providing results to jump up and down about :( could be wrong though, could have just been set up incorrectly.

[Dave R]

Wow, finally someone with a decent and simple explanation :) good to know.
I never really understood why people think it's some 'magical' thing. And BTW, the type of induction has nothing to do with an engine's (B)SFC. Most modern computer controlled engines are capable of getting into the .50-.55 range. T'is one of the reasons that there have been no great mileage advances in vehicles for the past 15 years or so. My '93 Escort commuter car gets 32-34 MPG average driving, as do most 'modern' vehicles of it's size.


Bummer on the MAF deal. Haven't heard of SpeedDensity systems consistently providing results to jump up and down about :( could be wrong though, could have just been set up incorrectly.
Other than Mega-Squirt, and perhaps a few of the limited production motorcycle builders, nobody uses SD anymore. The VAM on forced induction engines was a way to tell the computer how much air was being forced into it, since, obviously, the simple rpmXdisplacementXMAP calculation wasn't going to cut it, especially as Ford chose to use a MAP sensor that couldn't read pressure. MAF systems are better, in the long run and thanks to the modern vehicle computer's ability to be reprogrammed much easier to get right.

[Dsc Motorsports]

yall are sending this stuff right over my head!!haha

my maf is the blow throught type! so is there any way i can use my stock one maybe if a get a burned chip!

and i want to run a bov!! but if i dont have to that would be great (save some dough)

[V8RangerBoy]

I never really understood why people think it's some 'magical' thing. And BTW, the type of induction has nothing to do with an engine's (B)SFC. Most modern computer controlled engines are capable of getting into the .50-.55 range.

Those values are pulled straight from a tech article in a Mod Mustang magazine I have. You're 100% correct on most modern vehicles being able to get into the .5's, simply because of the computer's ability to constantly seek stoich 14.6-14.7. But (I just replied to that other post about why I have mine set so rich) because a more rich AFR is desirable at WOT for forced induction, (like I am set for, 11.5:1) this cuts the BSFC down from .5's to .6-.65 at WOT. Because a supercharger is usually more 'linear' and 'predictable' about the boost curve, you can get away with a more lean WOT mixture, hence why I referred to the .6 value for S/C'd applications. Under cruise, any engine will pull around .5 though, correct.

[Dave R]

Well, unless there has been some revision in the laws of physics since I was at university, maximum power, regardless of induction type, is derived with an A/F ratio in the 12.5-13.3 range. Less than that and your loosing power and pissing fuel away.

[Evil Ranger]

Well, unless there has been some revision in the laws of physics since I was at university, maximum power, regardless of induction type, is derived with an A/F ratio in the 12.5-13.3 range. Less than that and your loosing power and pissing fuel away.

Maybe... but you are most likely pinging. That lean and you'll be losing power because you will have to pull so much timing. I'd stay at 11.7, or λ=.8 leaving enough cooling for slight fuel and weather changes and then you can keep the spark up to about 3° away from the spark knock limit.

For the amount of time you are at WOT the lower lambda wont make that much difference... a little bit of extra fuel can go a long way toward providing a knock safety margin for the occasional bad tank of gas.


Edit: Come to think of it look at the graphs from any of the LA3 and PK* computers... and the fuel switch... They really needed to keep it rich and fat. I mean given how sloppy the VAM was at determining how much air was going through them the AF on those cars at WOT was in the mid 10's.

[rocket5979]

Well, unless there has been some revision in the laws of physics since I was at university, maximum power, regardless of induction type, is derived with an A/F ratio in the 12.5-13.3 range. Less than that and your loosing power and pissing fuel away.



Running a 12.5-13.3 AFR @ WOT in a boosted setup is asking for trouble. Much too lean. There are more factors that come into play than just power and fuel economy here. Now if you were recommending those AFR's on a N/A vehicle then that would be ok.

[Dave R]

There are more factors that come into play than just power and fuel economy here.
Factors such as?

[rocket5979]

Factors such as?



Engine safety and detonation to name a few. Running that lean of an AFR at WOT in a boosted vehicle will lead to a much much higher chance of damaging engine internals or at the very least lifting the heads and blowing a gasket. If you are running a lighter vehicle then you can usually get away with a little leaner of an AFR due to less load being placed on the engine but not quite the range of high 12's to low 13's though. Like I said, the AFR's you mentioned would be good for a N/A vehicle but not a boosted one where the engine is more prone to detonation. The "extra" fuel in the boosted engine will keep things cooler and allow much less chance of detonation.

One other thing worth mentioning is that leaner does not always equal more power in an internal combustion engine. I have tuned vehicles before where going a few more points lean would not do anything for power gains.

[Evil Ranger]

Factors such as?
Directly from Garret's website...

Leaner AFR results in higher temperatures as the mixture is combusted. Generally, normally-aspirated spark-ignition (SI) gasoline engines produce maximum power just slightly rich of stoichiometric. However, in practice it is kept between 12:1 and 13:1 in order to keep exhaust gas temperatures in check and to account for variances in fuel quality. This is a realistic full-load AFR on a normally-aspirated engine but can be dangerously lean with a highly-boosted engine.

Let's take a closer look. As the air-fuel mixture is ignited by the spark plug, a flame front propagates from the spark plug. The now-burning mixture raises the cylinder pressure and temperature, peaking at some point in the combustion process.

The turbocharger increases the density of the air resulting in a denser mixture. The denser mixture raises the peak cylinder pressure, therefore increasing the probability of knock. As the AFR is leaned out, the temperature of the burning gases increases, which also increases the probability of knock. This is why it is imperative to run richer AFR on a boosted engine at full load. Doing so will reduce the likelihood of knock, and will also keep temperatures under control.

There are actually three ways to reduce the probability of knock at full load on a turbocharged engine: reduce boost, adjust the AFR to richer mixture, and retard ignition timing. These three parameters need to be optimized together to yield the highest reliable power.

[Dave R]

Thanks dave.

[mxracer652]

Hello guys, I'm new here, but regarding the OP's question, I do not think 19s will suffice for 7psi and here's why:

Even though this is the SOHC, the laws of physics & chemistry still apply. I was seeing into the 80s% duty cycle (80% being considered maxxed out) with the 24s that came stock on the SOHC & only 5psi boost, BUT 68psi fuel pressure. The high fuel pressure makes those 24s function more like a 28. With fuel injectors, err on the high side, and don't listen to anyone who says big injectors don't idle. I'm running 39.5s now on E85, and it fired right up yesterday morning when it was 5 degrees. If I were you, 36s.

Edit: That is ASSuming the rest of the system is up to par and you're talking about a 6cyl.

[rocket5979]

With fuel injectors, err on the high side, and don't listen to anyone who says big injectors don't idle. I'm running 39.5s now on E85, and it fired right up yesterday morning when it was 5 degrees.



100% true. The "big injectors don't idle" stuff is a thing of the past. My 60's idle and drive like stock too.