Why cant custom larger injectors be made? It seems like some cars are capable of more power but are limited by injectors. Is it that difficult to make custom ones or is there another problem?

 

RC Engineering and others can increase the flow of injectors, but there is probably a reason why he chose to let them be.

 

You can run any injector with the factory ECU using the Acceleronics VersaFueler, which provides the proper peak and hold drive characteristics for low impedance injectors. I ran 96 lb/hr injectors on my supercharged street Camaro for years with absolutely no driveability problems.

You can find more info at acceleronics.com. I can't say any more since I'm not (yet) a site sponsor. If the 6-speed community accepts the concept of running large, low impedance injectors while retaining the factory ECU, I'll gladly become a site vendor.

Jeff

 

There are bigger injectors available that do not require direct drivers...
750's . Siemens/Genesis. They also have bigger ones...

 

I have tested many large, high impedance injectors on my fuel injector flow bench. They can be reasonably well flow matched at long pulsewidths, but at the short pulsewidths you see at idle and cruise, I have found them to be very poorly matched. In fact, in the first set of 8 "60 lb/hr" Siemens injectors I tested on the flow bench, the highest flowing injector flowed twice as much fuel as the lowest flowing injector at a 2.0 ms pulsewidth. You can't fix that with a tune!

I know many will say they are running large, high impedance injectors with no problems, and that may be true. Statistics says that not every set is going to be mismatched. I wonder, though, if the car would perform even better with a set of matched low impedance injectors.

The reality is that large, high impedance injectors open much more slowly than the equivalent-sized low impedance injector. Their high impedance limits the amount of current in the injector coil to about 1 amp, which is why the stock ECU can run them without frying its output transistors. A low impedance injector coil will draw 4 amps when it is opening (which will fry the ECU!). That's 4 times as much current, which translates into 4 times as much power available to open the injector valve.

The real problem with the high impedance injectors is the variation in opening time. I measure the minimum pulsewidth required for injectors to produce a visible output. I've seen as much as 0.5 ms variation in a set of big high impedance injectors. This variation in opening time is what causes the wide variation in flow rate at short pulsewidths. Low impedance injector opening time variation is 0.1 ms or less in my testing.

Please PM me for any more details - I don't want to hijack the thread or get banned!

Jeff

 

MidnighTT
That's excellent information. It would be interesting to know what the GT700 is using: high or low impedance.

 

great write up.... I have 680s currently and my car runs well.
I have no issues at idle. My back up option is to go with low impedance injectors with direct drivers....
markski

 

Now Markski cant you go with a larger injector and crank it up to 1.7bars or will that compromise idle and drivability?

 

Im upgrading to 750s just about 15 % more then what I have... Im doing the simple swap and then some calibration when Todd has time. My car actually is good for 1.4 bars... then it slightly gets lean at 1.5 bars.... so I really want to run about 1.6 bars thats it. Can I do 1.7 sure I can... the injectors theoretically are good for 2 bars... I just don't want to blow it up...
markski

ps my current injectors are fine at idle.

 

Just FWIW, I ran 1000cc (96 lb/hr) low impedance injectors on my supercharged street Camaro for 4 years with absolutely no driveability issues. Smooth idle, crisp throttle response, and the NGK BKR9EIX plugs stayed clean.

Jeff

 

I agree with what you are saying. That is why we are using peak/hold (low impedence) injectors. They are 1100 cc. They open and close much faster at low rpm and keep the motor smooth on the engine dyno from 7400 to 9500 rpm's. The other injectors just can't properly handle the low and high rpm ranges due to there slowness in these areas.

 

I have successfully run low impedence (peak and hold) injectors with an ecu that was not designed to drive them. All it took was about $40 worth of inline resistors. No ecu damage, no idle problems, smooth power delivery. The application was in a 1.8L Miata, turbocharged with 274rwhp using RC Engineering 55lb (550cc) low impedence injectors. I'm no wizard...this is a common, well known trick to avoid damaging the ecu injector drivers.

 

Chris You Rock!!!!!!!!!!!!!!!

 

Yes, the resistor box is a well-known trick, but by using it you are denying the low impedance injector the 4 amps of opening current it was designed to use to open quickly. You are limiting the injector to 1 amp or less to save your ECU injector drivers. It will open and flow fuel, but you are compromising its performance. The resistor box is more or less like putting the stock exhaust behind a turbo engine designed for 800hp and saying it runs fine. Yes it runs, but it could run better!

Jeff

 

Great Info......