383 tuning help

[Fast355]

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.

Simply advancing the base timing will also not work very well. The TPI heads you are running like about 34* of timing at WOT not the 38* mentioned above. 38* is for the older slow burning smog heads. With 20* of idle timing when you advance the timing to 12-16 as mentioned above you end up with 32-36* of idle timing which is too much for the mild cam you have. The advance curve is also slower in the ECM than what the TPI heads need. The TPI heads like about 16-20* of timing from 1,000 rpm through about 2,400, then up to about 30* from 3,000-4,600 and finally on to 34* above 4,600. The TBI heads have a substantially different timing advance requirement.

I have been through converting a 305 HO with 14022601 heads to TBI and had to make massive changes to the chip in both timing advance and fueling to make it run correctly. To give the little 305 with the mild 204/214 @ .050 cam and headers enough to drink I had to run 350 injectors at 14 psi.

Finally....I am not even going to get started on why someone would pull the 191/193/810 swirl port heads off and put even worse TPI heads on.

[daveosx]

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.

450 HP Hour requires 9.16 Gallons per hour of Gasohol.
Mechanical efficiency of stock motor is 49% with new pistons rings increased compression and roller cam 76-80%

At 6lbs per gallon thats 54.96 PPH

The injectors will provide at stock fuel pressure 336HP no problem.
At 18psi like I recommend they will flow reliably at 74-75PPH

Simply advancing the base timing will also not work very well.

I agree base timing is really not that important but the 0degrees as stated would cause the exhaust vales and pipes to over heat at idle.
At 3000 RPM GM HEI will reach no knock retard maximum advance after 30 seconds.
That has been the normal for all SBC since the beginning.
Setting the timing to 38 degrees at this point sets the distributor phasing and the maximum no knock advance possible.
At 4200 and up knock will retard the timing 4-5 degrees no problem.

At 4200 shift point the roller rockers will make noise this is not knock but will retard the timing an additional 2-3 degrees.

The TPI heads you are running like about 34* of timing at WOT not the 38* mentioned above. 38* is for the older slow burning smog heads. With 20* of idle timing when you advance the timing to 12-16 as mentioned above you end up with 32-36* of idle timing which is too much for the mild cam you have. The advance curve is also slower in the ECM than what the TPI heads need. The TPI heads like about 16-20* of timing from 1,000 rpm through about 2,400, then up to about 30* from 3,000-4,600 and finally on to 34* above 4,600. The TBI heads have a substantially different timing advance requirement.

On this one I can authoritatively say that since I wrote the GM service bulletins on Corvette and Camero TPI ignition timing with aluminum heads.
That the timing retard for these heads was solved in 1991 with the new knock sensors and EST modules.
Yes there is a different module for the corvette and the sensors are different.
This was not for the cast iron vortex heads only the aluminum.
Same device was mirrored in 1996 with the different EST and Knock sensors on the LT-4 engines because of the roller rockers.

As for the power available and RPM capabilities of the GEN1 and GEN1.5 TBI engines with stock injectors and HEI
Here is a snap shot of a 1984 Corvette I am tuning tuning at @7400 RPM with no Knock and only a 4ms Pulse width on the Crossfire TBI injectors.
There is no load attached to the motor so no HP rating.
IMG_1401.JPG

[Fast355]

450 HP Hour requires 9.16 Gallons per hour of Gasohol.
Mechanical efficiency of stock motor is 49% with new pistons rings increased compression and roller cam 76-80%

At 6lbs per gallon thats 54.96 PPH

The injectors will provide at stock fuel pressure 336HP no problem.
At 18psi like I recommend they will flow reliably at 74-75PPH

My experience and wideband both disagree with your HP potential of the TBI injectors.

350 with TBI heads, stock TBI cam, 1.6 roller rockers, Edelbrock 3704 intake manifold bored to 2", 454 TBI unit with 350 injectors, doug thorley tri-y headers, dual 2.5" exhaust into a X-pipe in my 1983 G20 van put down right at 200 RWHP and 300 RWTQ. Stock injectors at 14 psi were insufficient over 4,000 rpm to feed the stock long block. They went static, duty cycle above 100% and the engine misfired terribly and fell flat on its face before 5,000 rpm. I swapped to a Marine regulator and injectors from a 405 HP Mercruiser 502. Those are high pressure 61s that deliver 105 lb/hr @ 32 psi. I could turn the engine 5,500 rpm after with no fuel issues. I put a Weiand 177 on the same engine and used a rising rate FMU. At 10 psi boost it took 50 PSI of fuel pressure to feed the engine. I went 13.7 @ 101 mph in a 5,300 lbs G20 van with the Weiand 177 on the stock longblock, 700r4 with stock 1,600 rpm converter, and 3.08 gears turning P295/50R17s.

61# injectors are good for about 72 lb/hr @ 18 psi. I have once flowed one on an injector bench in 4 psi increments from 10 psi through 62 psi. The high pressure injectors will reliable open up to about 70 psi, however above about 50 psi the increased pressure does very little to increase flow.

[C2500]

Sorry for the confusion guys I sent that post on timing with my phone..Any way I set 0* with the spout disconnected..shut it off and reconnected the spout then started and timing is in the 20* mark at idle..

[C2500]

Ed just sent me back my chip with an adjustment and told me that the bored TB I have may be junk. Any way here’s his chip anyone recognize it??88F05DCB-AC87-4152-9A11-7217D769995B.jpg

[lionelhutz]

The i on that memory chip appears to be an Intel mark.

[C2500]

I spoke to Ed and he said to set timing at 0* with spout disconnected.. Can’t help but all this is confusing what some are telling me and what others are saying. I’m sure there are way to do this and all get to where it should be..I need someone to help me figure this out..
Also tuner pro web help never seems to help..lots of unanswered questions there...

[daveosx]

The calculation for HP to pounds of fuel is universal not a short cut it's just the physics.
1 HP = 2545 BTU’s per hour

Gasoline is 5.92 lbs per gallon
Gasohol is 6.1 Lbs per gallon

Flat head ford is rated at 49% Therodynamic Efficiency and BTU per pound is based on that .
Modern engines run from the factory at @76%.
Theoretical 18000 BTU per pound of gasoline is based on 49% conversion ratio.
Stock 1979 and up engine is @76% or 28000 BTU per pound of gasoline.
Rings valve seats and throttle plate sealing provides 80% on typical modified engine or 29000BTU per pound.
1 LBS of fuel on a modern modified engine should produce 11.4 HP
Parasytic Loses valve springs, piston skirts, oil pump timing chain ETC lower the net power.

pumping 130 Gallons of air and 9.16 Gallons of fuel on that motor will yield 335 HP


C2500s engine build is the Super Chevy magazines Test mule for carboration and the same build is typically 450 HP.
These motors with carb are routinely dynode with 650 and 700 CFM at 450 HP

As far as your results I understand you are commanding the injector to open and close.
Have you put a scope on the injectors them selves while running and confirmed that you are getting the actual commanded on period.
I alter the ignition with CDI after the module and give a solid 5v pp signal to the reference line.
I get @7400 rpm no load at 4ms on 65/68 TBI injectors
I have seen refurb ECM with cheap slow Mosfet installed could be a slew issue rather than injector flow.

In example I had a 1995 Impala/caprice with 1996 LT-4 Corvette, Radically ported iron heads 280cc intake runners, 194/160 with orange ZZX Beehive springs, 1.6 roller rocker crane rev kit lifter springs, .575 intake .560 exhaust 117lsa cam, SPO timing chain on steel gears, Low RPM water pump drive, HyperUtetic Pistons with tungsten Disulfide coated skirts, Rods drilled with piston squirters, copper shim head gaskets final compression ration 10.8 : 1, HMV55HV millings with 5W-50 oil, oil cooler trans cooler, 4L60E with 4.3L convertor, truck low gear spray, Steel drive shaft GM 10bolt 3.73 with Eaton Posi.
TH ignition system was/ is triggered using opti spark pick up CDI box and twin coil MSD coils. Ford 4cylinder ecoboost injectors in sequential mode rather than batch.
Routinely ran at 7500RPM and even peeked it a few times at 8500rpm.
According to iPhone pocket Dyno and Cats Tuner dyno hit 600HP on regular basis.
Never drag raced the car just street racing.
Have driven the car at Taledega at over 180MPH and at Daytona over 160

[C2500]

[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

[Fast355]

[QUOTE=C2500;68791]

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

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.

[C2500]

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

[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

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.

[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

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.

[C2500]

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