Honda / Acura K20a K24a Engine Forum banner

21 - 36 of 36 Posts

·
Registered
Joined
·
184 Posts
How are you sizing your injectors?

Without using an online calculator, I was wondering how you guys are sizing your injectors. I tend to stay away from the online calculators because some give different results. However, they are off by very little so no big deal. I just like to do it written out instead to keep a log of things.

Anyhow, here is what I have been doing in the past. Is anyone else doing the same and getting the correct results they need/anticipate?
-----------------------------------------------------------------------------------------------------------------------------------------------------------------
On a highly modified turbo setup:

BSFC = 0.65
Duty Cycle = .90 (injector dynamics run between 92.5% - 95% duty cycle)

Based on this info, looks like I'll be bumping up to 2000cc injectors:

(Max HP 900) X (BSFC 0.65)
----------------------------------------- = --->
(num of inj 4) X (duty cycle .90)


585
----- = 162.5 lbs/hr per injector
3.6


Assuming I am going to run 30psi of turbo pressure, that puts my static fuel pressure from 43.5 to 73.5.

Now, 73.5 / 43.5 = 1.6896 and sqrt(1.6896) = 1.2998 or 1.3

Finally, converting my 162.5 lbs/hr per injector to cc:

1 lb per hour = 10.5cc roughly

(inj 162.5) X ( conversion 10.5) = 1706.25cc + 1.3 fuel pressure difference = 1707.55cc

So, I need 1707.55 injectors. Rounding it to the next available size with some level of comfort, I'll need:

2000cc Fuel Injectors
----------------------------------------------------------------------------------------------------------------------------------------------------------------

What are you guys doing to figure your sizes? Are you doing the same? I have always been iffy about adding in my assumed static fuel pressure under boost. However, if I take that out of the equation (1.3), it's a very small change that doesn't really affect how much bigger my injectors should be. Now if I were using a fuel pressure regulator beyond a 1:1 ratio reading, say a 6:1, then I can see factoring this in.

Any thoughts?


Sent from my iPad using Tapatalk
 

·
Registered
Joined
·
238 Posts
Re: How are you sizing your injectors?

You're using that mechanical engineering degree too much. Big boosted hp + e85 = 2000cc no matter what calculations you tell me. Beauty of the ID2000 is the ability to run very high base pressure. They still emit the same spray pattern & characteristics at 100psi that they do at 70psi. So 60psi base + 30-40psi of boost is still fine.
 

·
Registered
Joined
·
184 Posts
You're using that mechanical engineering degree too much. Big boosted hp + e85 = 2000cc no matter what calculations you tell me. Beauty of the ID2000 is the ability to run very high base pressure. They still emit the same spray pattern & characteristics at 100psi that they do at 70psi. So 60psi base + 30-40psi of boost is still fine.
I should be using the degree, I paid good money for it ;). Anyway, I am just factoring in all aspects of EFI as I am using best practices for tuning to apply to my own build once its complete. So detail is key for me. None of this, "Big boosted hp + e85 = 2000cc no matter what" deal. I need justification and full understanding of why settings are the way they are. You wouldn't want your tuner (assuming you don't tune your car) telling you the same thing, right?


Sent from my iPad using Tapatalk
 

·
Registered
Joined
·
244 Posts
Re: How are you sizing your injectors?

Fellow mechanical engineering degree (err, in the making currently) here, and I agree completely with unix. There are calculations for a reason, and it's because they work.

Your math looks good to me, it really is only going to get you to a ballpark figure anyway, but it's better than a blind guess.

Just make sure the fuel pump you use can also move the lb/hr that you need fuel wise at the pressure (max) that you plan to run it at.
 

·
Registered
Joined
·
184 Posts
Fellow mechanical engineering degree (err, in the making currently) here, and I agree completely with unix. There are calculations for a reason, and it's because they work.

Your math looks good to me, it really is only going to get you to a ballpark figure anyway, but it's better than a blind guess.

Just make sure the fuel pump you use can also move the lb/hr that you need fuel wise at the pressure (max) that you plan to run it at.
Got it. I was running my numbers hoping that I would need at least 1000cc injectors and compensate any more fuel needed through my injectors through a rising fuel pressure regulator with something like a 4:1 ratio. This way I wouldn't have to deal with rough idle issues which such big injectors.

This is why running numbers is great because you know exactly where you stand and figure out what type of fuel combinations you can go with depending on your expectations. If my numbers would have given me say 900cc, I could have gotten the 1000cc injectors and compensate the rest with a rising regulator. However, there don't seem to be injectors from ID between 1000cc and 2000cc. I wouldn't want to compensate 700ish/cc's using a rising regulator.

Thanks for your response. Your input and suggestion is appreciated.


Sent from my iPad using Tapatalk
 

·
IMAKEBOOSTATIDLE
Joined
·
6,916 Posts
Re: How are you sizing your injectors?

I can hook you up with some 2000s for a good price :dude:


im running e85 on my setup with a walbro 400 e85 pump and ID2000s :)
 

·
Registered
Joined
·
238 Posts
Re: How are you sizing your injectors?

Whatever makes you happy. It's definitely nice to have the knowledge to be able to figure this stuff out. I know a handful of excellent tuners so I don't even bother.
 

·
Registered
Joined
·
287 Posts
Re: How are you sizing your injectors?

I am confused about the pressure adjustment.

Injector flow is usually rated at 43.5psi or 3bar. This is correct.

Injector flow is proportional to the fuel pressure differential across the injector.

So if you run an indexed (to manifold pressure) fuel pressure regulator (and it is the linear kind, as most of us use), then the fuel pressure pressure differential across the injector will stay the same al all boost levels i.e. usually your static FP of 43.5. So the turbo pressure adjustment, below is wrong.

You can cheat by making a smaller injector flow more fuel by raising the static fuel pressure. This is very benefitial for NA engines as higher static fp (up to 70 psi) improves fuel atomization.

Running static 70 psi in a turbocharged engine bcomes a problem for the fuel pump. At 30 psi boost, you will need large volumes of fuel (500lbs/hr) at 100 psi. There are not too many fuel pumps capable of that. 100 psi in the fuel line with 30 psi inthe intake manifold, still puts the injector at 70 psi head and it is still happy.

In any case 2000cc injectors are required.

Anton

.....
Assuming I am going to run 30psi of turbo pressure, that puts my static fuel pressure from 43.5 to 73.5.

Now, 73.5 / 43.5 = 1.6896 and sqrt(1.6896) = 1.2998 or 1.3
....

Any thoughts?


Sent from my iPad using Tapatalk
 

·
Registered
Joined
·
184 Posts
I am confused about the pressure adjustment.

Injector flow is usually rated at 43.5psi or 3bar. This is correct.

Injector flow is proportional to the fuel pressure differential across the injector.

So if you run an indexed (to manifold pressure) fuel pressure regulator (and it is the linear kind, as most of us use), then the fuel pressure pressure differential across the injector will stay the same al all boost levels i.e. usually your static FP of 43.5. So the turbo pressure adjustment, below is wrong.

You can cheat by making a smaller injector flow more fuel by raising the static fuel pressure. This is very benefitial for NA engines as higher static fp (up to 70 psi) improves fuel atomization.

Running static 70 psi in a turbocharged engine bcomes a problem for the fuel pump. At 30 psi boost, you will need large volumes of fuel (500lbs/hr) at 100 psi. There are not too many fuel pumps capable of that. 100 psi in the fuel line with 30 psi inthe intake manifold, still puts the injector at 70 psi head and it is still happy.

In any case 2000cc injectors are required.

Anton
Good info here Anton. This is by all means why we usually run more than one pump at these fuel line pressures since usually one fuel pump is not sufficient. For instance, running two walbro 255 intank or one intake and one inline. My calculations above were just to size injectors. However, this is not to say that we need to forget about how much the pump should deliver firsthand.

I really appreciate your info here...thanks!!


Sent from my iPad using Tapatalk
 

·
Registered
Joined
·
184 Posts
Having the injector pour fuel into a closed intake port is not good at all.So keeping all of this in mind.
Signal,

Quick question..when you say that pouring fuel into a closed intake port is not good, are you referring the intake valves? I thought that having the injector pour fuel on the valve right before it opens would help it vaporize better since at the precise moment the valve is hot and then continue to pour fuel while the valve is open. Then close the injector when the valve closes.

Or, are you referring to throttle bodies/ports that use sequential injectors settings in pairs like on a carburetor type manifold or ITB's?

Thanks


Sent from my iPad using Tapatalk
 

·
Registered
Joined
·
4,294,967,295 Posts
Discussion Starter #34
I was referring to pooling. Yeah, the injectors typically spray and hit the valves (assists with cooling the valves too) but we don't want the injector at 100% duty cycle and creating large droplets of fuel in the port.
 
21 - 36 of 36 Posts
Top