20g - fuel pump; 190 or 255

[athlete3344]

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?

 

[4gfun]

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?

I was in your shoes for a while, but don't recall the exact research that I performed. It seems that if you are going to run "a lot" of boost, the 850s and 190lph FP will be insufficient.

If I had a 20g, I'd be running it at very high boost levels. I hope someone will give you more granular data soon.

 

[Macspsi]

I just put on my walbro 255 and 880 injectors and a 20g should be plenty fuel for the 47lbs that these turbos are capable of producing. Just remember if you dint have a fpr you have a chance of running rich during idle and at cruise. If you follow the same route as I just said you should be fine.

 

[athlete3344]

Ideally, I would like to perform calculations to check the setup. Ive been reading threads on "this is what I run" and "this should work", and those are great! But I would like to perform a check on my fuel system via calcs and confirm them with some of the more proficient members which contribute to the forums (which is always very much appreciated).

 

[Macspsi]

Well most members here most likely will tell you the same exact thing as I did. Not to many ddifferent fuel options when you're running a 20g. I picked a 255 and re-wired it and 880's so I know I won't be maxing out my fuel system when I bump the boost up to about 25psi. Are you running pump 93 e85?

 

[AWD Sebring]

My buddy had a similar setup with a gt35r a single walbro 255 and 850's on 93 and if you want to get a little more out of it get some meth...

 

[athlete3344]

Ill be running pump 93. Ive done my research in checking various fuel options for a 20g, and Im fairly certain my setup will be sufficient.

As the next step, I would like to calculate at which point I will max out a rewired 190. I would also like to determine operating conditions at various points for 850cc injectors with a rewired 190.

This is purely for a double check, and in addition to learn how to perform the correct calculations to match a turbo to a fuel system.

 

[4gfun]

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.

 

[Macspsi]

http://www.dsmtuners.com/forums/articles-tuning-ecu/366003-injector-fuel-pump-supported-airflow.html that thread should help you out

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.

Not to question your intelligence but wouldn't an air to fuel ratio of 11.1 consider to be rich not lean correct? Since its air/fuel meaning higher air reading would mean higher the ratio number and lower air reading or higher fuel reading would mean lower number. And being 14.7 is about perfect 11.1 would be considered to be rich? But from my research 11.1-11.3 seems to be a good mixture at wot so you should have no reason to worry about running out of fuel

 

[AWD Sebring]

^^^^^^ from what I remeber you want to be in the 10.8-11.2 range on 93, correct me If im wrong. But 11.1 would be on the lean side, but still an acceptable range..

 

[LandSpeed-DSM]

^^^^^^ from what I remeber you want to be in the 10.8-11.2 range on 93, correct me If im wrong. But 11.1 would be on the lean side, but still an acceptable range..

Every setup will like something different. Don't fixate on a number as "right."

 

[GSLENK]

I already have the 190 rewired, and I would like to confirm the number of pounds I can safely run.

I put the 20g on with the oem fuel pump.I ran out of pump rather quickly. Any boost above about 15psi or so and I couldn't add enough fuel.I think a 190 would be pushing it. Honestly it is only $100 for a plug and play kit, and an hour of your time.

Less if you are good, and less $$$ if you sell the 190.And it will allow you to max out the 20g on pump gas.

Once you break 24-25 psi you wont wanna stop till its done. Stop selling yourself and car short. Just do it.

 

[athlete3344]

Guys, its very simple. I would like to run a calc to determine the number of pounds which will max out a 190. Im not trying to argue, or disagree, or try to push use of a 190 over 255.

This is more than just determining if a 190 will work or not. For me, this is taking a step to become educated for the future when I choose a larger turbo, diagnose fuel problems, planning ahead, etc etc.

Thank you for the injector flow rate link, thats a step in the right direction.

 

[Macspsi]

Guys, its very simple. I would like to run a calc to determine the number of pounds which will max out a 190. Im not trying to argue, or disagree, or try to push use of a 190 over 255.

This is more than just determining if a 190 will work or not. For me, this is taking a step to become educated for the future when I choose a larger turbo, diagnose fuel problems, planning ahead, etc etc.

Thank you for the injector flow rate link, thats a step in the right direction.

That should also have an equation for calculator the amount of flow for the fuel pumps. But there are only so many options for fuel pumps so there really is barely any need to know such equation. Either you're going to have a 190 255 dual hanger 255 or 450 those are the most common.

 

[LandSpeed-DSM]

Since you say you actually want to learn, I'll take the liberty of assuming you can do basic algebra and use Google.. here is a brief guide!:

Step 1.) Find published "flow v. pressure v. voltage" figures. Convert volume to mass using specific gravity of the fuel you intend to use.

Step 2.) Rough plot of your engine's demand flow on the compressor map for your turbo choice.

Step 3.) See if your pump can sustain requisite fuel mass flow at worst case Air/Fuel ratio, max total "combined fuel pressure" and voltage under maximum likely mass airflow determined in step 2.

Step 4.) Pick a bigger pump because even with a re-wire our stock electrical systems are crappy and the voltage that gets to the pump will drop under load.

Step 5.) Learn to search and see that this has all already been explained to painstaking detail in several threads for you, at least twice in the last few months for that matter.

Step 6.) Have epiphany and realize that it is cheaper to build a fuel system once, that you won't outgrow.. potentially several times. Save $$$ (Guilty )

Good luck!

 

[jayson427]

It must be pretty hard to type turbo fuel calculator into Google.

[ame=http://www.google.com/search?hl=en&redir_esc=&client=ms-android-boost-us&source=android-browser-suggest&v=141400000&qsubts=1388783124202&q=turbo+fuel+injector+calculator]turbo fuel injector calculator - Google Search[/ame]

Pick a link

 

[Mello]

All the math for this is fairly simple. First thing is to convert all the units so they are the same. I use cc, mins, & cc/m. You need to get the air flow so it's using volume and not mass (ie: lbs/min to cc/min). Pick the IDC & target AFR and layout all the values and add up the totals need for your injector and cross reference it to the fuel pump flow rate. You will need to know the pumps flow rate vs line pressure. This means you need to pick the PSI boost you plan to run to see when the pump is going to start maxing out. Lastly you are going to have to make some assumption regarding your barometric pressure because the volume of air changes with temperature (pick to the extreme). Also, as the amount of fuel being pumped through the fuel lines increases the line pressure is going to go up and this will impact the pump flow rate. This isn't a linear relationship meaning that at first the line pressure will slightly increase but as more fuel is trying to be pushed the pressure will go up faster & faster. This is a system and everything needs to be balanced with each other. When in doubt go bigger (round up) so you have a safety margin. Remember Google is your friend and if all else fails just take the advice given.

 

[99ECLIPSEGSXDSM]

10psi = 46.48lbs/min
11psi = 45.89lbs/min
12psi = 45.26lbs/min
13psi = 44.58lbs/min
14psi = 43.86lbs/min
15psi = 43.09lbs/min
16psi = 42.28lbs/min
17psi = 41.43lbs/min
18psi = 40.54lbs/min
19psi = 39.60lbs/min
20psi = 38.62lbs/min
21psi = 37.60lbs/min
22psi = 36.53lbs/min
23psi = 35.42lbs/min
24psi = 34.26lbs/min
25psi = 33.06lbs/min

 

[LandSpeed-DSM]

All the math for this is fairly simple. First thing is to convert all the units so they are the same. I use cc, mins, & cc/m. You need to get the air flow so it's using volume and not mass (ie: lbs/min to cc/min). Pick the IDC & target AFR and layout all the values and add up the totals need for your injector and cross reference it to the fuel pump flow rate. You will need to know the pumps flow rate vs line pressure. This means you need to pick the PSI boost you plan to run to see when the pump is going to start maxing out. Lastly you are going to have to make some assumption regarding your barometric pressure because the volume of air changes with temperature (pick to the extreme). Also, as the amount of fuel being pumped through the fuel lines increases the line pressure is going to go up and this will impact the pump flow rate. This isn't a linear relationship meaning that at first the line pressure will slightly increase but as more fuel is trying to be pushed the pressure will go up faster & faster. This is a system and everything needs to be balanced with each other. When in doubt go bigger (round up) so you have a safety margin. Remember Google is your friend and if all else fails just take the advice given.

Volume changes.

Mass is constant.

Use mass units.

 

[athlete3344]

I work as a process engineer and graduated chemical engineering. I appreciate the steps given and I will search around a bit more. Overall, I feel if I can better understand the fuel system then it will be 1 more piece to the puzzle that is understood.

Thanks all for the help!

It must be pretty hard to type turbo fuel calculator into Google.

turbo fuel injector calculator - Google Search

Pick a link

No it isnt hard at all, but you are assuming whatever calculator you find is correct for your particular situation. I prefer to have a firm understanding of the calculation before blindly following a random google found calculator.

 

[Mello]

^^^ Mass is not constant. Mass is temperature dependent and different at different temps. Turbos are volume devices and is why all pressure maps shown in lb/min are "corrected mass air flow".

 

[Boost Demon]

Here's some info by Real Street Performance on the Walbro255 in a comparison test against some other pumps, not sure if this helps at all.

Fuel Pump Comparison Test : Real Street Performance Engine Parts, Pistons Rods Cams Valvetrain and More


Also, here's some flow testing done by the guys at RRE which helps illustrate the importance of doing the fuel pump rewire if nothing else:

RRE Instructions

 

[LandSpeed-DSM]

^^^ Mass is not constant. Mass is temperature dependent and different at different temps. Turbos are volume devices and is why all pressure maps shown in lb/min are "corrected mass air flow".

Absolutely false. The word you may be thinking of is "density" which is temperature dependant.. which is why the volume will change with respect to temperature.

A 5 Kg mass of oxygen at 10*C is still 5 Kg at 70*C, but because the density decreased, the physical space it occupies at the same pressure is greater.

Turbochargers are turbine-powered gas-compressors. The compressor "wheel" is literally a centrifugal compressor.

Because we are dealing with a ratio that involves both gasses and liquids in a system with very dynamic temperatures and pressures including phase changes, you need to use mass.

End of discussion.

 

[athlete3344]

That and mass is just easier in general to use for calculations. The more conversion factors you can remove from a problem, the better off you are. This is especially true when dealing with cfm, scfm, any other type of volumetric flow rate.

And thank you all for the replies. This has been a most useful discussion.

 

[4gfun]

http://www.dsmtuners.com/forums/articles-tuning-ecu/366003-injector-fuel-pump-supported-airflow.html that thread should help you out



Not to question your intelligence but wouldn't an air to fuel ratio of 11.1 consider to be rich not lean correct? Since its air/fuel meaning higher air reading would mean higher the ratio number and lower air reading or higher fuel reading would mean lower number. And being 14.7 is about perfect 11.1 would be considered to be rich? But from my research 11.1-11.3 seems to be a good mixture at wot so you should have no reason to worry about running out of fuel

You must have missed part of my post. Take a look. I am running as lean as 11.9:1.

14.7:1 would certainly be too lean under WOT.

11.1:1 is how I have my maps setup under WOT as a compromise. However, it is leaning out to 11.9:1 on cold nights.