720cc injs. with only afc???

[93jdmlaser]

I am upgrading to a 50 trim to I have to replace my rc550s a bigger size. I was told the 680s mite be on the edge of being to small. The only thing I have as of now is an afc to control my injs. Can I get away with 720s for now with just my afc to tune or will I have to use 680s?

 

[DSMJim]

I know guys who used 720cc with the afc but you get a crappy idle and other related problems. None of that with 650cc.

I have 650cc injectors now with my 50 trim and went 12.1 on pump gas if that makes a difference. Car runs like stock.

 

[GPTourer]

I had crappy idle with my Denso 660's until I got my AFPR.

 

[Jclipse]

720's will be a bit much for your 50 trim without dsmlink or a standalone. My friend has 660's running a 50 trim and is almost out of the afc's range of taking fuel away at 21 psi.

 

[93jdmlaser]

Ok I wanted to go with pte 680s but I was told yesterday that they wouldnt be enough. Also since you have a 50 do you know how good the internal gates are? Thanks

 

[pneumo]

Denso 720's tend to idle poorly because they have a long deadtime. The ammount of time the injector needs to be open at idle is shorter than the ammount of time it takes to open and close the injector. So it makes the idle lumpy. I don't mind the lumpy idle on my car.

Smaller injectors have shorter deadtimes, so they idle better. Another option is to get the 680's along with an adjustable FPR, then raise the fuel pressure to increase the flow out of the injectors. That way you get the nice idle/ shorter deadtime of the 680s plus the flow of 720's. Increasing the fuel pressure by just 5 psi will make 680's flow like 720's. Or you could go with more pressure if you wanted to.

Your 2G MAF should keep the SAFC settings far enough away from the lower limit of the adjustment range. But it also depends on how much you raise the FP since raising the FP means you'll have to lean out the SAFC settings even more.

 

[93jdmlaser]

Aslong as 680s will be enough to support my 50 trim thats all I care about.

 

[mirkoelek]

i know its stupid question for you guys, but what is FPR

 

[Quazz209]

Adjustable Fuel Pressure Regulator

 

[DSMJim]

Aslong as 680s will be enough to support my 50 trim thats all I care about.

Did you not read what I posted or did I waste my breath? Honestly whats the matter with people around here now a days..


I SAID I RAN 12.1 @ 115MPH WITH 660CC ON A 50TRIM ON PUMP GAS.

What part of this statement is leading you to believe they will not be enough? When you go faster than I did feel free to ask me if they are enough or not.

 

[UPGRADED2G]

YES YES YES. I needed this info a long time ago. Now i can sleep at night. Im going with 650s, my AFC/AFPR/255 pump. Does the fact that the SAFC2 has more adjustment increments (up to -50/+50 or -60/+60, i think), make it better at handling these 650s than the five button AFC would? I knew someone who had problems controlling 660s with his 5 button AFC on a ported and clipped 20g, thus the question.

 

[ftltalon]

i have denso 720's, idles perfect, my hi throttle settings are high 20s-lows 30's on a e16g at 20-22psi. i know 720's are alot for a e16g but i am going bigger and didnt want to upgrade twice

 

[RoasT BeeF]

I have Denso 720's and I had a hard time tuning them with just the AFC. The thing with me was that I had to correct so far that I was getting way off the timing map. I was getting around 40 counts of knock and 35+ degrees timing. I got a dsm chip with injector comp and it has helped a TON. I got the knock down to 3 counts and I get about 25* timing now. Car runs WAY better. I still need an AFPR though.

 

[ftltalon]

you were still getting 35* timing with 40 counts of knock ?

 

[btrux06]

ya i run 720s afc and stock ecu and idles good and very tuneable. maf translator and gm maf made it idle even better, wasnt so good with my old 2g mas setup.

 

[NeOzz1]

Would a DSM Chip ordered for bigger injectors fix the rough idle?

 

[DSMJim]

The larger the injector you run the more you dial the AFC back the less air the ECU thinks is there. If you have logged your timing before you know that your at about 35-40 deg advance while driving part throttle for good fuel economy. When you put a large injector in and dial the air flow back the ECU gives more timing because it's not seeing the real air flow sort of like part throttle driving. What happens is you end up with huge timing numbers like what has been stated above.

A good fix is a chip that compensates for injectors, it doens't change air flow but injector pulse width time and the like so that your not in a situation where your dealing with huge timing numbers and crazy knock as a result. Even with 650cc you'll get around 25deg of timing which is a lot. 20 is good on a turbo car 25 is getting scary.

I plan on going to a larger injector and was going to use the ignition retard feature on my MSD to start pulling timing at 5000rpm to combat the problem. Have not tried this method yet so don't know if it will work, but I did put the timing retard on once by accident and it yanked my timing way back and took almost a second off my 1/4 time ..

 

[btrux06]

timing doesnt always sky rocket just cause u got bigger injectors, say u have 550s and only running at 80 percent duty cycle then ur timing will go up to around 25, with no knock. if u upgrade to 720 when u dont need to right now then ur duty cycles will be down to only 55 percent ruffly and then ur timing will go too high, but if got a big turbo and flowing anough air to need 90 percent duty cycle with 720 you end up wit the same airflow reported to the ecu and same duty cycle and same timing as u were getting back when u had smaller turbo and 550s. u just got to make sure ur going to need or use up all the big injectors u get and run them in the 85 to 95 percent area and u wont have a high timing problem. this is atleast what ive learned and experienced with going from 16g turbos and 550 up to my current 50 trim and 720 with stock ecu. i run my 720 int ot the 90s even more and timing doesnt go crazy, also i set my base timing to on1 which probaly helped a bit. another thing is keep ur fuel pressure as low as u can so that ull need little more duty cyle to be low knock free, which will raise ur airflow alittle and lower ur timing alittle.

 

[RoasT BeeF]

As stated before...

The ECU will pull timing when there is knock. If you are tuned, this will not happen.
But here is the catch... Too much timing will make you knock, and then the timing is pulled back further than it should be for the best power. Too little timing and you aren't making as much power as you could be.

It's a big balancing act with the SAFC because when you remove fuel, you get more timing (due to the altered airflow signal).
As you lean it out you may not only knock because of less fuel, but because of more timing.

For instance - In a case where the timing is causing the knock: Lower the base fuel pressure a bit, add more fuel on the SAFC, and you end up with the same amount of fuel -- but less timing!

In case you're wondering why -- it's because the timing curve is a slope from high to low when plotted against airflow. If you increase the airflow signal to add more fuel, you are lower on the timing map.

 

[UPGRADED2G]

on my t25 i get 11-15 timing @ WOT, with a bad Mass airlow sensor.

 

[paul s]

I run 119/11.9 last year on 50trim and 650s, 45psi base pressure..

 

[DSMJim]

I run 119/11.9 last year on 50trim and 650s, 45psi base pressure..

Yeah Paul, but we all know that 11.974 is really a 12.0 except that you took a pee just before that run. !

 

[paul s]

Hahahaa, yes I know that, I made sure not to eat that morning..