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20g - fuel pump; 190 or 255

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athlete3344

10+ Year Contributor
347
17
May 1, 2010
Tampa, Florida
I am trying to find out how to calculate the amount of fuel required for a 20g at various pounds of boost. From researching, I found 850cc injectors will be sufficient (which I already have), but the type of fuel pump has pretty much been split down the middle.

I already have the 190 rewired, and I would like to confirm the number of pounds I can safely run. Would anyone please be able to step through the calculation with me or provide a solid link?
 
Absolutely false.

Even that could be debated, but not in this context...

As an [object] approaches the speed of light its relativistic mass will theoretically increase.

So, don't forget to factor that into your equation somehow. You know, for when your system is so efficient that it is moving air near the speed of light.

athlete3344 said:
I work as a process engineer and graduated chemical engineering.

If you are as smart as your accolades suggest, then you should realize how pointless such an equation is.

Keep buying parts with a "bare-minimum" mentality (directed by your theoretical equations, computations, and subsequent assessment, in perfect worlds) and see how far that gets you. A lot of people here know all about this, myself included.

#### it... Lets piece this thing together. Here's the ideal gas law... PV=nRT
 
"Hey guys, math is better than two decades of people learning what works and what doesn't".

I usually hear this sort of sentiment from guys who barely made it out of HS. ROFL

Your modern existence revolves around math.

You can bet almost everyone in this community that has pushed their setup in the last 24 years did plenty of math along the way.

Now stop drooling on everything. :thumb:

Apply that tortured 'logic' to anything else and you'll see how ignorant it is, bridges for example:

"We don't need models and simulations, people have done this for millennia!"

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"Oh, right."
 
Meh.
Without taking the real-world variables into consideration, math is only as good as the person applying it. 100% of everything we've ever built has been improved due to the original version falling over/exploding. If your models and simulations fail to take those experiences into consideration, then nothing ever improves. He's asking a question that the answer to have been provided a million times over, except he would much rather take the chance that his math is correct...when real-world results from the past 24 years have shown that the math isn't necessary. How is his alternator? Will the voltage output be ok? How about chassis grounds? Stock fuel lines? How well was the pump installed? How clogged is the fuel filter? Rewired pump? Math usually assumes a 100% base, when in actuality, it's far less, and without those factors considered...the answer is useless.

Math in itself isn't bad, it's when it's used to provide answers that are 100% correct on paper without any real world testing...that's when it becomes a hindrance.

Take that bridge you posted. It fell down because the math omitted a crucial variable...wind ;).
 
Even that could be debated, but not in this context...

As an [object] approaches the speed of light its relativistic mass will theoretically increase.

So, don't forget to factor that into your equation somehow. You know, for when your system is so efficient that it is moving air near the speed of light.



If you are as smart as your accolades suggest, then you should realize how pointless such an equation is.

Keep buying parts with a "bare-minimum" mentality (directed by your theoretical equations, computations, and subsequent assessment, in perfect worlds) and see how far that gets you. A lot of people here know all about this, myself included.

#### it... Lets piece this thing together. Here's the ideal gas law... PV=nRT



Thanks for the laugh. I like how you assume Im trying to get by with the bare minimum (is the hyphen really necessary?). Purposely, I didnt state what my intentions were, only that I wanted to perform calculations. My only intention from this thread was to gain a fundamental understanding. If you lack the ability to understand, thats fine.


Once again, thanks for the contributions to the thread. Arguing is pointless since you dont want to do math.
 
Maybe I am wrong. I recall being told I'd need at least 1000cc injectors and a 255 to run heavy boost on a 20g. I run 650s and a rewired 190lph on my e316g and I am close to maxing out at ~20 psi. On cold nights, my A/F ratio can approach 11.9:1 at WOT even though my open loop maps are set at 11.1:1 under WOT.

Scares me a bit.

Maybe you just need to adjust your tune. the openloop maps are not a representation of the exact AFR but rather and numerical guide....Especially in colder weather you may need to richen the tune in boost some to compensate for the colder denser air...doesn't necessarily mean you are running out of fuel pump/injector.
 
I would say just get it over with and save the time and money now and go with a rewired 255 and an afpr to top it off. You will be happy and it will serve you for a long time depending on the goal. But, should support the 20g just fine.

I am running the same setup I mentioned and it hasn't done me wrong yet on tdo6 20g 25psi on e85.
 
I would say just get it over with and save the time and money now and go with a rewired 255 and an afpr to top it off. You will be happy and it will serve you for a long time depending on the goal. But, should support the 20g just fine.

I am running the same setup I mentioned and it hasn't done me wrong yet on tdo6 20g 25psi on e85.

I agree completely, except not taking the steps to learn how to size a fuel system is not a waste of time for me and requires just the electric use from my laptop. The value I gain from this exercise is immeasurable to me.
 
I went back and looked what I did when I was doing this. I never used the "turbo" or the turbo air flow in my calculation either. I started with my target HP. Then determine how much fuel you need to flow to support this HP and what line pressure (boost) will be for your fuel lines. Thenmake sure that your fuel pump(s) can flow enough fuel (at your planned line pressure). Lastly, make sure your injector are big enough to flow this volume of fuel at the IDC your targeting.
 
Maybe you just need to adjust your tune. the openloop maps are not a representation of the exact AFR but rather and numerical guide....Especially in colder weather you may need to richen the tune in boost some to compensate for the colder denser air...doesn't necessarily mean you are running out of fuel pump/injector.

Not to hijack, but you might be right.
 
Thanks for the laugh.

Arguing is pointless since you don't want to do math.

You are welcome. (I certainly was digging for a laugh) :thumb:

Sorry for being abrasive. I do this to everyone that asks to be spoon fed. It didn't seem as though you wanted to do this purely for sport. It appeared you wanted to mathematically justify not having to upgrade to a 255 from your 1st post, ergo my "bare-minimum" statement. Indeed I should have spelled it "bear mini-mum" to relay my intent.

"The math" has already been done with the following assumptions:

2g car, 11:1 target AFR, 43 psi fuel pressure, etc...

http://www.dsmtuners.com/forums/articles-tuning-ecu/366003-injector-fuel-pump-supported-airflow.html

Maybe you can ask Nathan for his magical formula?

Here's another formula. Even though I don't want to do it all for you, I can throw you some puzzle pieces.

New_Flow_Rate = SQRT (New_pressure / Old_Pressure) * Old_Flow_Rate
source: RC Fuel Injection

I played around with his data for you. You should know that pumps have an operating pressure limit, and that fuel pressure rises 1:1 with boost pressure.

I read in a walboro publication that the max operating pressure is 85psi. That means that max boost you could ever run on it is 42 psi (at 43 psi FP).

Using the data provided, and expecting a 20g to max out at 40-45 lb/min airflow, it should be clear that a 20g can exceed the limits of your 190 at around 26 or 29psi (on pump gas at 43psi fuel pressure) depending on the efficiency and max airflow ratings of the turbo. I personally would not run it to the edge like how others have stated. Safety margins are a nice. If you are not running at 43psi, feel free to do the conversions for flow rates (again, provided for you).

I will let you look at the data and charts to decide if a 255 is a better choice or not...

Everyone has told you what you should/might take into consideration. Dust off your engineering books, and put it together already. Or at least make an attempt better than mine and I will give you an honest attempt also.

What turbine are you running btw?
 

Attachments

  • fuel pump comparison.xls
    22.5 KB · Views: 70
Nothing magical about math, but I guess the purpose of this thread has changed a bit as Ive been tinkering in excel.

I guess ideally this went from determining limits of a few different turbos, to creating a user friendly excel sheet with pump curves for various fuel pumps showing where they will be operating for a given turbo and pressure.

Im still trying to get the ins and outs, but something else to consider is I have access to a flow simulator at work that is excellent at predicting pressure drops at a given flowrate and pipe diameter. I think bringing everything together to create a fuel system model is the goal, but it will take some time as I am busy.

Thanks for the input though, everyone here has given me more then enough feedback and information for me to get started - just gotta find some time.
 
Lambda 1.0 = Stoich for any fuel. It's a unitless measure of oxygen ratio.

1.0 being the amount required to burn the full fuel mass injected.
<1.0 would describe a rich condition, or excess fuel
>1.0 would indicate there is excess air, or a lean condition.

So from that table for pure gas, we commonly round up to 14.7:1 AFR as being stoich (Lambda 1.0)

The equivalent gasoline AFR for a reading of "0.78 Lambda" would be: 14.7 AFR * 0.78 Lambda = ~11.5:1 AFR, a fairly common WOT target Air:Fuel fraction on pure pump gas.

Does that make sense?

Oxygen sensors ("Nernst Cells") actually output a voltage which is translated to the Lambda ratio, and then you take that ratio to whatever the known stoich value is for the fuel you are running to determine AFR.

Gasoline containing 10% Ethanol will have a Lambda 1.0 of ~14.13:1 AFR, richer as a result of the proportion of Ethanol added.
 
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