PSA: FLEX FUEL with stock injectors

[vollosso]

I've been tuning some flex fuel turbo cars for a while, but we run big injectors. I did a stock injector flex the other day and its way out of injector for ethanol, it actually surprised me how bad it is.

So heads up if you're stock injectors and ethanol you are way out of duty cycle. (I guess unless you only make like 275whp?)




anyway heres some data for your consideration, this is a stock engine, high mileage, ebay headers, a turner box, and some muffler.

It's tuned and makes 330whp. It's been running this way for a few years I think we did the box and tune back in 2021.


Before we switched to e85 I logged injector time and look at the graph below at 330whp it peaked at 83% duty. For reference most people say 85% is the limit.

I also uploaded the data here also if you want to look at it yourself, Excel.






Then re-tuned it on e85 with big injectors and made 365whp. Pretty nice.

[Tbonem3]

Ya we know. Ethanol isn't as explosive as gas. We're trying to figure out now if bolt ons (v1s, airbox, cams), alone, are enough to max out duty cycle.

[vollosso]

Ya we know. Ethanol isn't as explosive as gas. We're trying to figure out now if bolt ons (v1s, airbox, cams), alone, are enough to max out duty cycle.

Yeah id say 100%.

83% duty on e10....

e30 needs 13.9% more fuel. (you get that from stoich: 12.9/14.7)

so unless your goal with running e30 is only to make 290 whp (Which we make more than that on completely stock cars with just a tune) youll need more injector. Forget cams and mods.

[Sharocks]

Ya we know. Ethanol isn't as explosive as gas. We're trying to figure out now if bolt ons (v1s, airbox, cams), alone, are enough to max out duty cycle.

Apparently it is.

I'm happy with the power levels I have but if I was considering going for more, I'm absolutely upgrading the injectors.

[Tbonem3]

I'm glad I'm happy with 330whp or whatever I have. Just keep dialing in the chassis and dropping weight.

[mrgizmo04]

When was the last time those injectors were cleaned and trued? Can owner send them off to get tested to show the delta?

This is not news, been discussed on the forum many times. There were data points that with some mods, including box/headers (maybe mild cams also, don't remember at this point), "safe" range was around e45-50, and obviously decreased with heftier mods and fbo.

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[jet_dogg]

^this guy asking the important questions

How can anyone make a conclusive assessment on the efficacy of 20 year old God-knows-how-many-mile injectors so matter of factly? Start with new or at least balanced and blueprinted injectors then make an informed opinion.

[vollosso]

When was the last time those injectors were cleaned and trued? Can owner send them off to get tested to show the delta?

This is not news, been discussed on the forum many times. There were data points that with some mods, including box/headers (maybe mild cams also, don't remember at this point), "safe" range was around e45-50, and obviously decreased with heftier mods and fbo.

Sent from my SM-G950U using Tapatalk

I didn't know it had been discussed so extensively..

Now im curious.. let's double check my data, and sort of weed out the injector clogged theory, with some math.


Simple question.. What's the required fuel flow on e85 and pump to support 400bhp?


To calculate the required fuel flow for an engine, we can use BSFC... I'm not a huge fan of this, but since we don't believe logged data lets try it..

Fuel Flow (in lbs/hr) = Horsepower x Brake Specific Fuel Consumption (BSFC)

Typical BSFC values:

• For gasoline (pump gas), it's around 0.5 lbs/hp/hr
• For E85, it's typically higher due to the higher fuel consumption, about 0.65 lbs/hp/hr

Let's calculate the required fuel flow for 400 brake horsepower. or 320-340whp depending on your desired loss rate.

For gasoline:

Fuel Flow = 400 hp x 0.5 lbs/hp/hr = 200 lbs/hr

To convert this to cc/min (a more common measurement for fuel injectors), we'll use the fact that 1 lb/hr ≈ 10.5 cc/min. Therefore:

Fuel Flow = 200 lbs/hr x 10.5 cc/min = 2100 cc/min (350cc/injector)

For E85:

Fuel Flow = 400 hp x 0.65 lbs/hp/hr = 260 lbs/hr

And converting to cc/min:

Fuel Flow = 260 lbs/hr x 10.5 cc/min = 2730 cc/min (455cc/injector)

So... we know the factory e46 injector is 268cc @ 3bar...

Let's calculate the new flow rate at 5 bar.. here's the math:

New Flow Rate = Old Flow Rate * sqrt(New Pressure / Old Pressure)

New Flow Rate = 268 cc/min * sqrt(5 bar / 3 bar) = 345cc/min

345 cc/min at 5 bar of pressure.

In summation:

The s54 injector flows roughly 345cc, and calculated fuel needed for 400bhp (320-340whp) on gasoline is 350cc per injector. This calculation paired with the collected dyno data above I believe is enough to stop guessing. The factory injectors aren't enough or your car needs a retune because its suboptimal.

One last calculation, we know to run 400bhp on e85 we need 455cc/min injectors.

How much power can we make on e85 and e40 with stock injectors?

We will ignore the fact that we would hope to make more hp on e85...

Total fuel flow = 345cc/injector x 6 injectors =2070cc

And converting to lb/hr:

Fuel Flow = 2070cc/min / 10.5 cc/min = 197lb/hr


Lets calculate power for e85:

Hp = 197lb/hr / 0.65 lbs/hp/hr = 303bhp


Lets calculate power for e30:

Hp = 197lb/hr / 0.62 lbs/hp/hr = 317bhp

So... yep... the dyno data and my statements are spot on to the standardized math... Someone else run a testo log on a dyno and post the hp, rpm, and injector opening times.

[enjoy_m3]

So you're running a 450cc injector to get that 360hp?

[vollosso]

So you're running a 450cc injector to get that 360hp?

440cc @ 3 bar or 560cc @ 5 bar.

[mrgizmo04]

How are you getting the true "e" from e85 that you are tuning for? Sounds like you are doing a static tune. E85 varies between the stations quite significantly.

There is no doubt with larger injectors you can jam for e out of it. I think stock injectors net around 20whp because exactly, they max out of the flow ccs.

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[vollosso]

How are you getting the true "e" from e85 that you are tuning for? Sounds like you are doing a static tune. E85 varies between the stations quite significantly.

There is no doubt with larger injectors you can jam for e out of it. I think stock injectors net around 20whp because exactly, they max out of the flow ccs.

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Custom code in ecu and wired in ethanol sensor. Full flex. Ignition and fuel control. 3 wires.

[heinzboehmer]

Custom code in ecu and wired in ethanol sensor. Full flex. Ignition and fuel control. 3 wires.

Standalone or stock ECU?

[vollosso]

Standalone or stock ECU?

stock.

[heinzboehmer]

stock.

Very cool. It always seemed possible to reuse one of the inputs on the DME for a flex fuel sensor, but never looked into it too much. Good to hear you have that working.