Turbo, Fuel Pump, And Injectors

[teknicalissue]

Hello once again!

I created the following thread Here

Not understanding how the FPR works. Knowing how it works now it opened new questions on the correlation between turbo, injector and pump.

I'd Like to know what is the process to choosing the correct injector size. I've seen plenty of threads asking "what injector should I use" but haven't read anything that explains why people recommend X size.

before you respond, I've seen This Page which explains the fuel pump and Injectors but it doesn't help me (Or maybe I just don't understand) how people choose an injector based on the provided data.

To add more to the confusion.. I've read that the flow of the Turbo is important to choosing injectors. I've looked online and found compressor maps for a td06 20g but again, I seem to hit a dead wall combining all the data together.

I have goals for 400 - 500hp. As of now I have DSMLink v3, wideband, DSMLink boost solenoid, Fuel Lab FPR, walboro 255HP (Rewired), td06sl2-20g and wideband/boost gauge. I'm at a point where I need to choose Injectors but don't really wanna ask what injectors because I'd like to know how people come up with the numbers.

Thanks!

 

[1990dsmkid]

most will buy the biggest they can get. That way they work now and when you want more you can grow and dont have to waste more money on other injectors. This in my opinion is the best way to go so get yourself some 1200 or bigger and be done with it

 

[teknicalissue]

I understand that, But based on the PSI i'm going to be shooting for my goals, I need to be aware of the Pumps capabilities as well. I think I read somewhere that at some point i'm gonna need dual wally's if I wanted 30PSI on my engine (67 total PSI) which will hinder my pumps flow.

I understand that based on what I read, But i don't understand how the numbers say that (which I believe is important to know considering that I'll be doing the tuning myself as well)

 

[jayson427]

Your right it's about the flow of the turbo and what's called duty cycle. When people say they max out their injectors they are close to 100% duty cycle. So most people like to be around 85% but if you want room to grow you get bigger injectors. Since you have dsm link you can tune in big injectors with no issues. There is a formula to figure it out but I don't know it off hand. Hope this helps.

 

[teknicalissue]

Helps a little. A large chunk of what's confusing me is that there is sooo much data and little explanation. For example I use this site to calculate injector size based on my HP goals (injector Site) I put 600HP a BSFC of 0.6 4 injectors and 0.8 injector duty cycle.

That gives me a flow rate of 112.5 Lb/Hr for 1181.25cc's

Does this mean that my pump has to flow 112.5 Lb/Hr???

that would make no sense considering that based on this page
(Page) My wally would pump 4068Lb/Hr. That means one single Wally pump can handle a non existent 19687.5cc injector as it would require a flow of 1875Lb/Hr... which my injector apparently meets based on the thread.

Something is not adding up!

 

[LandSpeed-DSM]

It's all right there in post #6 from your other thread, bold for emphasis:

You always want more fuel then you expect to need at any point in normal operation. You do not want the fuel system to be the "bottleneck" in power production, that is how things become.. melty/explodey

The best way (in my opinion) to approach this is determine first how much Power (air mass) you need for your goals with the car. Having a familiarity with engine demand flow and compressor maps is going to be key to this route however.

Then determine what fuel, we'll use pure gasoline (no ethanol "E0") for discussion.

Now pick a worst case (Rich) target AFR for that fuel at peak airflow. I usually use 15-20% margin for safety. So on gasoline (E0) If you expect to be running as rich as 11.0:1 AFR or Lambda 0.75; 15% more fuel would put you around 9.5:1AFR

Let's say your goal is 450awhp on an average setup, this will likely require about 50lbs/min mass airflow. At 9.5:1AFR, this is going to require about 5.25lbs/min fuel. Find the specific gravity of your fuel at a likely temperature and convert mass flow rate to volume flow rate. Now pick your injectors so they can support 5.25lbs/min fuel flow or ~700cc/min injectors. Recommended max injector duty cycle is 80% (industry standard) this means you would want 880cc/min injectors. Automotive fuel injectors are rated at 43.5psi (3bar) standard.

Now through assumed previous knowledge (Engine Demand/Compressor Maps, etc.), you have found a turbo that will produce 50lbs/min airflow at 30PSI boost on your setup.

This is where the 1:1 rising rate fuel pressure regulator comes in. In order to maintain that flow rate across the body of the injector the same pressure differential needs to be maintained for consistency in the tune and injector scaling. Try tuning a Turbo/SC converted Honda with a returnless system and factory FPR, and you'll grow to really appreciate our fuel systems.

So If we have 43.5PSI base pressure, and max boost of 30psi, while still needing to supply 5.25lbs/min of fuel we now have our criteria for finding a pump. The pump (flow rated by pressure and voltage) needs to be able to deliver that 5.25lbs/min @ ~74psi total fuel pressure. Pump flow falls off fast as pressure increases and/or voltage drops. This is why pump re-wires are a huge deal, as seen in the chart here:

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Look at the difference a mere 1.5V at the pump makes!


I typically put together a spreadsheet for my builds to put all this in one place that is easy to digest. Here is the sheet for the Magnafuel pump in my car now and what it can support at a given pressure and voltage for a variety of potential fuels and fuel temperatures:
https://docs.google.com/spreadsheet/ccc?key=0Ahi5eTgzfWg_dHh3RGpienAyYXRrNUF3c2Y0cEwyNlE#gid=0

Consider also that this does not account for pumping losses and pressure drop from the rest of the fuel system: fittings, lines, filters, etc.

Hope this helps.

Combined fuel pressure, boost plus base, is more a concern for pump sizing. That is unless you are trying to "stretch" injectors that are too small at their rated 43.5psi base pressure.. which proper sizing in the first place should aim to avoid.

But as discussed later in the thread, build your fuel system once if you can, make it upgrade proof so to speak.

 

[teknicalissue]

Let's say your goal is 450awhp on an average setup, this will likely require about 50lbs/min mass airflow. At 9.5:1AFR, this is going to require about 5.25lbs/min fuel. Find the specific gravity of your fuel at a likely temperature and convert mass flow rate to volume flow rate. Now pick your injectors so they can support 5.25lbs/min fuel flow or ~700cc/min injectors. Recommended max injector duty cycle is 80% (industry standard) this means you would want 880cc/min injectors. Automotive fuel injectors are rated at 43.5psi (3bar) standard.

How did you get the Bold data?

Like, how do you know 450awhp requires 50lbs/min? Isn't this different per turbo and air density?
I'm assuming you got the 5.25 doing math from the AFR?

I Could just buy dual pumps and giant injectors... But it takes the fun out of learning how things work

 

[LandSpeed-DSM]

On pump gasoline you can expect to make 7-10whp per pound of air.. drivetrain losses, tuning, engine setup, dyno type weather etc. determine that. So for 450whp, it would not be unreasonable to expect to need 50lbs/min airflow.

Using a 15% margin of safety on my example of 11:1AFR gives us about 9.5:1AFR. Dividing mass airflow by the 9.5:1 ratio gives us about 5.25lbs of fuel for 50lbs of air. Making sense?

I used known density figures at a likely temperature to convert mass flow rate to volume flow rate. This is where I got my about 700cc/min injector size when accounting for the 4 injectors. Then using the industry standard of 80% max duty cycle 700 becomes close enough to 880cc/min injectors, which are actually offered in that size.

 

[jbeaton9292]

Im agreed just go big and be done enless money is no issue im doing 2200 ### i can get a good deal on dw's and im gonna tune out the extra and if i want more later tune again and not worry about fuel cut no sense in saying hiw does it work i feel

 

[teknicalissue]

On pump gasoline you can expect to make 7-10whp per pound of air.. drivetrain losses, tuning, engine setup, dyno type weather etc. determine that. So for 450whp, it would not be unreasonable to expect to need 50lbs/min airflow.

hmmm.... This may be unrelated to fuel.. How do you find what 50lbs/min is in boost? Also, I can't help but noticed you used 9WHP X Lbs/Min = Total HP

So for my application I would need 45Lbs/min for a total of 405

Using a 15% margin of safety on my example of 11:1AFR gives us about 9.5:1AFR. Dividing mass airflow by the 9.5:1 ratio gives us about 5.25lbs of fuel for 50lbs of air. Making sense?

Wouldn't 15% be 9.3:1 instead of 9.5? (11*0.15=9.3)

When you say divide mass airflow by the 9.3:1 I'm assuming you mean 45/9.5 which then gives me 4.8 (rounded) lbs of fuel for 45Lbs/Min

*Phew*

I used known density figures at a likely temperature to convert mass flow rate to volume flow rate. This is where I got my about 700cc/min injector size when accounting for the 4 injectors. Then using the industry standard of 80% max duty cycle 700 becomes close enough to 880cc/min injectors, which are actually offered in that size.

Could you provide an equation for those density figures?

EDIT: Just noticed that my 20g will def not be making 66lbs/min. I'll be topped off at 45lbs/min... hahaha Shoulda researched fuel BEFORE I bought the turbo
EDIT2: updated my responses to reflect 45psi

 

[LandSpeed-DSM]

I did those figures mentally with some rounding when I typed them up on my phone yesterday, so not too bad if I do say myself! Specific gravity and/or density can be found on the MSDS for these fuels. How it changes with temperature is a curvilinear function if I recap which means its faster to just remember a couple figures to give you a spectrum to work with.

I lifted the number in my spread sheet for my current pump in your other thread from an old textbook which is what I used. This stuff is all algebra and applies to pretty much any application. You can get a feel for it quickly.

If you want 600whp.. especially if auto or auto/awd you will need a 60mm or larger turbo and can count on a fairly high boost pressure/rpm/ve combo to reach those parts of the turbos compressor map that move that much air mass the closer you stay to "only" 60mm inducer size.

So think HX40Pro, GT3586R, FP Red, and S200sx sized turbos at minimum. The other problem here is because of the boost you'll be forced to run and that will land you in less efficient pays off the maps.. race gas, E85 or pump grad with men injection will be a must. Unless you plan to run a pump gas street tune at lower boost, using race gas and full boost only at the track which is common.

On a GT4202, HX52 or s400sx there is a good chance of doing it on pump gas alone but the other tradeoffs of running turbos that large for only 600whp outweighs the benefits.

 

[teknicalissue]

I did those figures mentally with some rounding when I typed them up on my phone yesterday, so not too bad if I do say myself! Specific gravity and/or density can be found on the MSDS for these fuels. How it changes with temperature is a curvilinear function if I recap which means its faster to just remember a couple figures to give you a spectrum to work with.

I'm creating a "Basic" version of your sheet on my google drive hahaha
Good guesstimating!

I lifted the number in my spread sheet for my current pump in your other thread from an old textbook which is what I used. This stuff is all algebra and applies to pretty much any application. You can get a feel for it quickly.

Yea, thank you so much for your help! I'm getting a better understanding of how everything is working out

I think I need a little bit more info though.. to get the CC I want and figure out the flow rate for my pump..

If you want 600whp.. especially if auto or auto/awd you will need a 60mm or larger turbo and can count on a fairly high boost pressure/rpm/ve combo to reach those parts of the turbos compressor map that move that much air mass the closer you stay to "only" 60mm inducer size.

I'm on a manual 1g.. future plans are for a dog box.. I'm slowly gonna go all out on my DSM haha

Based on the various equations given, I created a simplified sheet with the above information. Let me know if there something I need to change or to add

https://docs.google.com/spreadsheet/ccc?key=0AkycI6tzGsiDdFAzc2pXVThCX0loOTdOY1RYVkJQZkE&usp=sharing