[QUOTE=Fast355;68671]A pair of 61 lb/hr TBI injectors are good for 205-210 hp @ 85% duty cycle at the stock 13 psi and if they were static, meaning on all the time, good for about 250 hp at most. Most engines run around 1/2 lb/per hr/per hp. 61 lb/hr x 2 injectors /.5 bsfc = 244 hp. Even if you were running a Vortec head and had a very good BSFC around .45 that is still only fuel for 270 hp.
What injectors would you recommend for my set up?? Thanks for any help
[QUOTE=C2500;68791]Keep the same injectors, get a fuel pump for a 1993-1995 Astro/Safari van with a 4.3 "W" vin code CPI engine and get your hands on one of the 28-32 psi marine TBI regulators. That will boost your 61 lb/hr injectors up to about 104 lb/hr each. At that point you are good to over 350 HP at 0.50 bsfc and 85% duty cycle. I am sure you can get a TBI to run to 7,200 rpm without load at 4 msec, but when you go to full load that same rpm would require a good 4-5x the fuel. Because the TBI injector fires twice per crank rotation, 4x per complete engine cycle, at 5,000 rpm you have something like 6 msec between injector firings. At 6,000 rpm you have 5 msec between firings injector. During that time you need to stay under 85% duty cycle and factor in both intake and closing times of the injectors. If it takes the injector 300 usec to open, its going to take roughly the same time to close. So that 5 msec cuts down to 4.25 msec to stay under 85% duty cycle and finally allowing opening and closing times it drops to 3.65 msec to spray the necessary fuel accurately without running the injectors static. What will happen if you get to 100%+ duty cycle is the the engine will develop a high rpm misfire and if you get into the 110% range it will quit pulling all together under load. Running an asynch fueling strategy will help this condition but you should closely watch the air/fuel mixture distribution if you run that.Originally Posted by Fast355
Fast, Thanks for the above post. I have a new Delco EP376 pump Not sure what it is but I’ll look it up. I would think you want a AFR in the 13’s at wide open correct? I got a wide band hooked up and an LM1 on the seat next to me and went for a drive..Runs fairly well driving it normal but it has a lean heasation if you run at 25mph and lightly step on the throttle.. Also I went WO up a hill and in no time the AFR went into the 17’s. Not good
So I’m trying to tunerPro up and running as that’s another challenge with my limited skills with a laptop..
Delco EP 376 pump. Will this do?
http://www.gmtuners.com/tech/fuel_pumps.htm
Last edited by C2500; 01-13-2018 at 09:01 PM.
You want a cast iron head small block around 12:1 under and near peak tq and about 12.6:1 at peak hp. Those heads usually like a pretty quick advance curve and about 30-34 total advance at WOT. Cruise timing can be upwards of 42 at 3,000 and no load. If you set the initial timing at the distributor to 10* and set the Initial timing in the .BIN to match you can experiment up to about 52* of timing to see what works best at cruising speeds without load. Generally to get the no load timing right, I will use my Autoprom, hold the engine at a steady 1,200 rpm. Look at the timing cell the engine is running in KPA wise, holding the throttle steady, I will then slowly advance the timing until the RPM stops rising. I will repeat this process at every RPM value of the timing table up to about 5,000 rpm. For a good starting point you can then interpolate the values down to your WOT timing. Works well as a starting point for me.
Last edited by Fast355; 01-13-2018 at 09:22 PM.
Looking at that chart that pump should be fine, good for 550 hp @ 32 psi. I did not realize you had already upgraded the pump.
Fast pumps not in yet I have it here new inn the box and was asking if that one will do and it will.. Thanks
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