PDA

View Full Version : FAQ: Injectors - Brands, Sizes, etc.



GenerAznX
12-06-2005, 05:30 PM
I did some searching but was unable to find anything detailed.

There are some things that i want to know about injectors,

1. how does increasing injector size improve performance?

2. What are the down sides of injectors that are too small? too large?

3. What is the best size for safc w/ stock turbo?

4. what is injector "duty cycle"?

5. what are the differences between the different brands? ie denso, RC, precision, etc.

6. which is better? why?

7. What are the differences between the different types? ie pintle, disk, ball, etc.

8. which is better? why?

i hear that the denso is the best, just wanted to know why. and i have also hear mixed things between 720cc and 660cc.

Thanks!

if we get some good answers, maybe we can move this to the FAQ section.

EvoPwr
12-06-2005, 05:40 PM
I did some searching but was unable to find anything detailed.

There are some things that i want to know about injectors,

1. how does increasing injector size improve performance?

2. What are the down sides of injectors that are too small? too large?

3. What is the best size for safc w/ stock turbo?

4. what is injector "duty cycle"?

5. what are the differences between the different brands? ie denso, RC, precision, etc.

6. which is better? why?

7. What are the differences between the different types? ie pintle, disk, ball, etc.

8. which is better? why?

i hear that the denso is the best, just wanted to know why. and i have also hear mixed things between 720cc and 660cc.

Thanks!

if we get some good answers, maybe we can move this to the FAQ section.


1. more fuel
2. not enough fuel, too much fuel
3. 660cc or 720cc
4. meh
5. denso works great, i heard rc 1000cc are good.
6. different people have different opinions, i and many prefer denso.
7. meh
8. meh

leaveit2bevo
12-06-2005, 05:41 PM
heres what has been proven to work and most are running denso 720cc injectors

Mr. B.K.
12-06-2005, 05:56 PM
Not trying to be a smart ass, but this will help answer some of your questions

http://auto.howstuffworks.com/fuel-injection.htm

Blak94GSX
12-06-2005, 05:59 PM
The stock injectors are Denso 550cc and different types of injectors have different "dead times" or how long it takes for the injector actually open after the ECU tells it to. Since the stock ECU is designed around the Denso injectors, continuing to use Denso injectors seems to work better.

The answers to your questions vary depending on the engine management system you are using, but basically if you are using an AFC or some kind of piggyback that controls airflow, going to a larger injector gives more timing advance. Selecting the proper size injector gives just the right amount of timing advance. Too large and there is too much timing advance, resulting in knock and then too little timing because the ECU pulls out all of the timing due to knock. Too small of an injector and you don't get the optimal timing curve.

If you are using a standalone system like the AEM EMS, you can compensate for the injector dead time and size independently of the timing, so the type and size of the injectors are much less critical. In general you want to go with a pretty big injector since there is no real downside when running a standalone. I recommend 1000cc injectors for AEM EMS users.

"Duty Cycle" is a measure of how much time the injector spends ON during each crank rotation. If the injector duty cycle is 50% the injector is ON for 50% of the time and OFF for 50% of the time. Injectors are basically electric solenoids using a wound wire coil (electromagnet) so if the injecto duty is too high the electrical coil can overheat and result in problems. This is more of a theoretical problem than a real problem. Most modern injectors are fine at 80-100% duty cycle. The rating of an injector is based on 80% duty cycle, so a 550cc injector pumps out 550ccs at 43PSI of fuel pressure and only 80% duty cycle. At 100% duty cycle it puts out more than 550cc per minute. The problem is that the duty cycle to fuel quantity isn't exactly linear, and it gets increasingly non-linear after around 80%.

ANTHONY
12-06-2005, 06:20 PM
what he said!!!! :roll:

GenerAznX
12-06-2005, 06:23 PM
Thank you so much scott.

That was the type of answer i was looking for.

Can you speak to injector sizing in conjuction with safc?

I have heard denso 720cc, and more recently 660cc injectors.

Blak94GSX
12-06-2005, 06:40 PM
Denso 720s for higher octane fuels and Denso 660s if only running 91 octane. The 720s work good on most cars with pump gas, but the 660s give slightly less timing advance and work on all cars. The 720s give more power due to the higher timing curve but on some cars for whatever reason this is too much timing resulting in knock and the timing being pulled heavily by the ECU.

So either is good.

GenerAznX
12-06-2005, 06:47 PM
Denso 720s for higher octane fuels and Denso 660s if only running 91 octane. The 720s work good on most cars with pump gas, but the 660s give slightly less timing advance and work on all cars. The 720s give more power due to the higher timing curve but on some cars for whatever reason this is too much timing resulting in knock and the timing being pulled heavily by the ECU.

So either is good.



thanks again scott,

so would it be safe to say, 660cc for street only car w/good margin of safety. 720cc for occasional track days with race gas, and tuning closer to the edge?

so start with 720cc and if you have that rare knocking problem then change to 660cc?

would it be also safe to say that when possible the 720cc injector would be preferred?

GenerAznX
12-07-2005, 12:59 AM
What is the difference between denso and RC injectors?

evofosizzo
12-07-2005, 01:11 AM
What is the difference between denso and RC injectors?


i think Desno are single nozzle, and i know forsure RC injector have mutiports nozzle.

i dont think all denso's single nozzle, i would like to know as well.

turbolarry
12-07-2005, 02:01 PM
What is the difference between denso and RC injectors?


i think Desno are single nozzle, and i know forsure RC injector have mutiports nozzle.

i dont think all denso's single nozzle, i would like to know as well.


Densos (Greddy's too) are pintle tip. They supply our stock injectors and when you look at them they look like the have two nozzles very close together... pintle tip.
Just about all other injectors; RC's, Fuel Injector Clinic, PTE's, etc., are all Delphi style with a finer multiport nossle.
Which is better? Pintle tips are good to 80%IDC and after that those two nozzles dump in fuel; not in a good spray, but in whole drops kinda dump. That excess fuel keeps things safe when you push it too hard, but makes tuning it a little more difficult. The multiport nossles have a better spray pattern for better atomization and have been accurate to 90%IDC. After that though, they go lean... just when you don't want them to.
So again which is better...?
:?

Blak94GSX
12-07-2005, 02:41 PM
The RC Engineering stuff is Lucas type. They also use Denso injectors if you ask nicely.