Injector size qustion

[sleepinGSX]

Does a 550 and 750 or so size injector work the same. Im talkin about regular use and performance wise. Im thinkin that it would b the same, except the larger injectors can flow more fuel but im not sure. I hope this makes sense. Someone inform me please..

 

[L2RTSiAWD]

A 720cc injector will flow more fuel everywhere even at idle which is the bad part. That is why you need to choose the injector best suited for your app.

Later,

 

[DSMotorsport]

The other thing to consider is that anything really large (600 and bigger) tend to have a problem with idling simply because even though you might have 50% adjustment on an afc to take fuel out at idle, the realistic limit on injectors is that they cannot function with pulsewidth (amount of time the injector is open) less than 2.0 to 1.8milliseconds.

1.8MS of pulsewidth on a 720cc injector is still too much fuel for a 2.0 with 4 injectors.

 

[DSMotorsport]

basicly if you don't have a need for anything larger than 550cc unless your are going to make 450+hp, then the 650cc injectors can help. Putting injectors that are bigger than needed is wasted $, and will cause idle and tuning headaches.

 

[Mistaspakles]

Once you go with a Big 16G Ported/Clipped, you might want to move up to at least 625's. I know someone that has run out of fuel with the Big 16G and 550's.

 

[ILOSE]

Originally posted by Mistaspakles
Once you go with a Big 16G Ported/Clipped, you might want to move up to at least 625's. I know someone that has run out of fuel with the Big 16G and 550's.

That is completely wrong. Every car with a big 16 or larger does NOT need at least 625's. Please don't post this as fact.

 

[DSMotorsport]

I would base injector size on power output (or mph assuming similar weight car) definatly NOT turbo size.
I would run : (assuming near full weight 1G awd)
450cc injectors up to about 107-110mph
550cc injectors I have personally gone 120mph on
650 injectos I woudn't use untill atleast 117-118mph

Anything over 650/660cc is just not needed. If you are trying to drown the engine in fuel to keep it from knocking and keep egt low, then you have other problems, and it's not running out of fuel!

 

[Mistaspakles]

I'm not saying that you "have" to get 625's if you run a big 16G. All I'm saying is I know someone who has run out of fuel (because of the 550's) with his big 16G (and supporting mods of course).

 

[Formz]

Originally posted by Mistaspakles
I'm not saying that you "have" to get 625's if you run a big 16G. All I'm saying is I know someone who has run out of fuel (because of the 550's) with his big 16G (and supporting mods of course).

he probably has a clogged fuel filter or his pump isnt working properly.

 

[GreenGSX]

One thing that were missing is that it really matters if your car is a 1G or a 2G. 1G cars have good timing maps and 550's will work great into the 11's with the right tuning. 2G cars have awful timing maps so they respond well to larger injectors. Not because they really need all that fuel but because the larger injectors allows them to pull back with the AFC and gain better timing. It can make a 12.8 car run 12.3's just by switching to bigger injectors.

Another thing to consider is that things like tip-in enrichment gets kinda wacky with big injectors. Good fuel pressure control can be a real savior when trying to tune so a AFPR, although not nessecary, comes recommended.

Tim

 

[DSMotorsport]

Originally posted by GreenGSX
One thing that were missing is that it really matters if your car is a 1G or a 2G. 1G cars have good timing maps and 550's will work great into the 11's with the right tuning. 2G cars have awful timing maps so they respond well to larger injectors. Not because they really need all that fuel but because the larger injectors allows them to pull back with the AFC and gain better timing. It can make a 12.8 car run 12.3's just by switching to bigger injectors.

Another thing to consider is that things like tip-in enrichment gets kinda wacky with big injectors. Good fuel pressure control can be a real savior when trying to tune so a AFPR, although not nessecary, comes recommended.

Tim

True...both 1g and 2g will respond with more timing becuase of larger injectors and trimmed down MAF signal. Even though 650's could make a car run better becuase of the timing, it is still WRONG to say that 550's did not supply enough fuel. How can a big16g car run out of fuel on 550's when MANY dsm guys have gone 120's+ mph on 550 injectors.
the fastest mph a 16g car has gone is 117. so unless this car is a record setting 16g car by about 4-5mph....it's not running out of fuel from the injectors

 

[BatmanGSX]

Nate, I've seen plenty of people max 550s out on a 105mph car. This is because they are scary and have no idea what they are doing. They put a 16G, 550s and an AFC on and there AFC settings are like +30%!

When I max out my 550s I'm going to turn up the fuel pressure. People seem to be against this but I see no problem with it. Assuming that I run no more than 25psi of boost I should be safe with up to almost 60psi of base pressure. That makes 550s into 645s, well within the range of an AFC's adjustibility. I probably won't even need to go that high. I think when people were running 10s on a 550s/20G combo they were running 55-58psi of base pressure. I just want an 11.xx out of my 550/20G combo.

Hey Nate, I just bought an FPR, gauge and few other stuff from you the other day.

 

[DSMotorsport]

Hey...hrm well this proves that advertizing on this board is good...customers and DSMtuners are atleast on the same page!

well...105mph car woudn't go any faster if you put 650's in it, so it's a null point. it's the tuning, not the injector that's messed up.

11.xxx is no problem for 550's. And i think you are correct about the base pressure....Switzer,shep and some of the other guys that hav gone 10's (that "might" have been on 550's) definatly had big base pressure...no doubt there. As for at what pressure injectors start to act wierd from too high of pressure? I don't know..im certainly not an injector expert. IMHO people go up bigger than 550's to early....
you can make up the little differance with higher base pressure.

 

[BatmanGSX]

Originally posted by DSMotorsport
Hey...hrm well this proves that advertizing on this board is good...customers and DSMtuners are atleast on the same page!

Actually I got your name from somewhere else. I also added to your "good guy" review there.

well...105mph car woudn't go any faster if you put 650's in it, so it's a null point. it's the tuning, not the injector that's messed up.

I know, that was my point. I think some people have a hard time understanding what is actually going on with injectors/airflow/duty cycles etc. They don't realize that 100% duty cycle on 450s will still be 100% duty cycle on any injector unless they can scale the airflow way down. I watched a guy install 550s because his duty cycles were 100% on the 450s. Then as he is "tuning" his car he is turning the AFC up. He couldn't grasp that just putting 550s in didn't lower his duty cycle at all.

EDIT:
Also, on the pressure thing, I've heard that at around 85psi the injector can flake out and possibly stick open. I'm not sure if I believe that is an inevitability. I see turbo Honda guys running insane base pressures. Also I think it depends on if you are using "peak hold" or "saturation" injectors... maybe that is for duty cycle. I'm no injector expert either but 55psi (of base fuel pressure) and 25psi (of boost) comes out to be 80psi. That should be near, but below the theoretical limit.

 

[NosLaser]

I personally maxed out 550's on a small 16g, but that was with a dry kit. I was already cramming MUCHO pressure in there, so the only logical next step was more volume. For a street car, adding fuel is a nice way to be able to run more timing on pump gas, however people with an AFC obviously have no way to run extra timing. Ideally, you want to be able to burn the fuel you are using, as running too rich can sometimes be as bad as running too lean i.e. washed cylinders, etc. Most 16g setups are fine with 550's, although I think 1G guys can't get away with it as MUCH as 2G guys. If you have a nice method of tuning (PMS, Haltech, etc.) then you can actually utilize a larger injector and potentially make more power. I ran out of injector, and realistically couldn't add any more pressure, so I saw a huge increase from 550's to 660's.

Regards,

 

[rca90gsx]

I ran 117.37 mph on a small 16g, with 550 cc injectors. This was done with 38 psi of base fp, so IMO there is still plenty of injector too go. If you are having fuel issues running slower than that, look elsewhere, it's not the injectors. BTW... I used a hard wired supra pump with stock lines and filter just for the record.....

Richie
and no the car wasn't super lean either, it had a 0 knock sum for the entire pass.

 

[TURBOSPYDER]

Anyone have AFC settings for both low and high throttle for 720cc injectors? I wanna compare and try out your settings. I know all cars are different.

 

[MaineDSM]

Originally posted by rca90gsx
I ran 117.37 mph on a small 16g, with 550 cc injectors. This was done with 38 psi of base fp, so IMO there is still plenty of injector too go. If you are having fuel issues running slower than that, look elsewhere, it's not the injectors. BTW... I used a hard wired supra pump with stock lines and filter just for the record.....

Richie
and no the car wasn't super lean either, it had a 0 knock sum for the entire pass.

That's good info, but I've seen datalogs of people running a small 16G to 110+mph traps that had above 90% duty cycles on the injectors. This is at a nice, tunable fuel pressure level, like your example.
BTW, what do you use for a FPR?

I've also heard that running above 90% on the injectors is not good. That may be a load of crap, but better safe than sorry.

Anyway, I plan on getting 660s for my car, which has a T28 now, but may have something bigger later. The DSMLink lets me set dead time, so it really doesn't matter if I get injectors that are too big. Although I have heard 720s can act a little funky at idle, even with a DSMLink. 550 and 660s have a dead time of 180ms, whereas 720s are something crazy, like 500ms. This suggests they are constructed in a different way, to take so long to open.

Brent
'96 Talon AWD