Question about fuel injection from a newbie

[Ed Wright]

Originally Posted by pbp1

Not to kick the hornets nest, But
There is potential power to be gained by running over sized injectors.

I assume that CMRacing is referring to the possibility of Phasing the injector "Event" in relation to the intake valve opening and closing.

I have found some power doing this with the FAST XFI system, but I will tell you that there is no guarantee that you will find anything, and there is no set strategy that will work on every application.

If your intake duration is say, 288 degrees, that equals 40% of a complete engine cycle. So if your strategy is to only have the injector open while the intake valve is open, then you must keep your injector duty cycle equal to or less than 40%.

You may not make any more power this way than you do with smaller injectors at 80% duty cycle, but there is definitely the potential to!

As far as going over the recommended 80% duty cycle max, there are two good reasons not to do this.
One, many injectors are not linear above 80%, meaning that because of poor pintle control at high duty cycle, the pintle may never close at 80-85%. This means that at 80%, you may be getting 100% of the injectors flow potential, therefore, the ECU assumes that there is 20% more fuel that it can add that is not really there.
Two, if you have your engine tuned to run above 80% duty cycle, and you go somewhere where the air is really good, you could easily run out of injector.
The 80% rule of thumb is not there to keep from damaging the injectors or the ECU, it is to make sure that you don't get into a situation where the engine needs more fuel than the injectors can supply.
I am not bashing anyone who is running their injectors above 80%, just making those watching aware of the dangers.

I don't run injectors at, or above 80% duty cycle. I do work with injector timing, or phasing. I like to end the injector pulse just before the intake valve closes.

[Darrel Goheen]

After testing Friday night I learned one thing for sure. My 4th gen f-bodies will not hook on just any track as I've been told. I made 7 runs and only hooked on three of them! As for fuel pressure test, as near as I can tell it made the et .02 quicker going from 45 lbs to 60 lbs fuel pressure. Another discovery I made....I normally launch with a 2 step. I normally run 124 mph. I tried footbraking and the et was the same but I went 127 mph. I also tried a footbrake pass the next day just to make sure and I went a high 126. I *think* it may be lean at launch on 2 step and it likes the additional fuel that it gets by footbraking. Sound right? I just don't understand the faster mph and no et change.

[ss3011]

I think you may read lean on the two step , because some of the fuel is not burned and allows O2 to pass through the engine . Does two stepping change the 60 ft time ?

[Darrel Goheen]

Originally Posted by ss3011

I think you may read lean on the two step , because some of the fuel is not burned and allows O2 to pass through the engine . Does two stepping change the 60 ft time ?

You can't tell anything about an O2 reading while on the 2 step. No 60' change. Only mph.

[Signman]

The highest load and fuel demand during a run is when the car leaves and when it goes in to high gear.

[Darrel Goheen]

I will be tuning (richening) the launch area to see if I can get the same performance on the 2 step that I do footbraking.

[Dan Fahey]

Originally Posted by cmracing

You are wasting your time and money unless you fix your power issues to your fuel pump. Raising the pressure will make things worse!

You should have a 10 gauge wire feeding the fuel pump. All the EFI cars I wire have a relay in the back, close to the battery, 20 amp fuse between the battery and relay. All wiring from battery to relay to fuel pump is 10 gauge. I also use a 4 pole battery disconnect switch. The smaller terminals on the switch are used to remove the power from the relay coil so when you hit the disconnect switch the engine stops immediately even if you have a working alternator (which I highly recommend you do).

I had a friend with a BS/A swap between 42lb/hr injectors and 60lb/hr injectors within 10 minutes for back to back passes. With keeping the A/F the same, the car ran identical. Don't listen to people telling you that large injectors are a problem.

Been doing this since 1986 and I'm not on here trying to solicit business. Several here know me. I don't have time or the inclination to take on any new projects anyway, just trying to steer you straight.

If you can't get and maintain 12.5 volts at the fuel pump park the car! Get a working alternator and that pump will be MUCH happier at 13.5 to 14.0 volts. So will the injectors.

This is a smart preventative maintenance mod that is overlooked.

Our B-Body Impala/Caprice community also suffer from Fuel Pump Problems.
Key issue; GM used just enough gauge size for their Harnesses.

Over time you have dodgy fuel pumps, burned wires, corroded connectors and blown fuses.

Last week the Caprice Wagon Fuel Pump fussed at 240,000 miles.
Bought a Racetronic Harness a while back which has a larger gage wire.
Installed it with a new Delco Fuel Sending Unit and Fuel Pump.

All of a sudden the Fuel Gauge works properly again and drivability improved.

D