Tuning aggravation with VE over 100

**Dieselsj** · 10-26-2021

I've been logging and tuning and it has been going well. I had an area where VE wanted to be over 100. So I dropped the fuel rate in the settings which brought the test of the table down but I still have cells that want to be over 100. I'm running the stock injectors up at 20psi. I have adjusted the fuel flow all the way down to 90lb and still have a series of cells that are at 99 and during my last drive it still maxed out the BLM. The rest of the VE is fine with my lowest value being about 52.

I can keep dropping the fuel rate values but how far is ok? I mean I guess it is really just a number in a calculation so theoretically it can be a low as I need it to get the table in line.

So this is probably just a sanity check posting. How far below your actual flow rate have you needed to go to get your VE under control?

7427 ECU.

**kur4o** · 10-26-2021

I woudn`t touch the fuel flow rate. It is much better to increase the cyl volume constant, to get the same results..

**dave w** · 10-26-2021

I think it's OK to adjust injector flow. I've always tuned by adjusting injector flow.

In my way of thinking, injector flow and cylinder volume are algebraically the same . . . see formula for Base Pulse Width (ECM 1227747)

The 16197427 has an injector flow constant and a displacement constant, providing the same algebraic logic.

dave w

BPW 1227747.jpg

**Dieselsj** · 10-26-2021

Thanks Dave. It was actually reading some of your old posts that turned me on to the concept of tweaking those constants to move the entire VE up or down.

I'll just go with the thought that I stumbled onto some magic number of pipe size and length on the exhaust that is just making the engine super efficient in that section of the table.

I'll tweak the constants again and see what happens. Since the lowest VE I have right now is in the 50s, I do have room to bring the rest of it down again.

Thanks gentlemen.

**dave w** · 10-27-2021

My "Fuzzy" Injector Math would be . . . If 13 PSI Factory Pressure = 61 lb/hr injectors

My "Fuzzy" Injector Math would be . . . If 61 lb/hr injectors @ 20 PSI = 76 lb/hr

Possibly a margin error of +/- 10% of 76 lb/hr (68 lb/hr ~ 84 lb/hr)?

What an injector is rated to flow . . . Hmmm?
What an injector is actually flowing . . . Hmmm?
What injector flow is programmed into the chip . . . Hmmm?

dave w

**Dieselsj** · 10-27-2021

Originally Posted by dave w

My "Fuzzy" Injector Math would be . . . If 13 PSI Factory Pressure = 61 lb/hr injectors

My "Fuzzy" Injector Math would be . . . If 61 lb/hr injectors @ 20 PSI = 76 lb/hr

Possibly a margin error of +/- 10% of 76 lb/hr (68 lb/hr ~ 84 lb/hr)?

What an injector is rated to flow . . . Hmmm?
What an injector is actually flowing . . . Hmmm?
What injector flow is programmed into the chip . . . Hmmm?

dave w

Factory big block 1987 injector flows 90lbs @ 13 psi.
What are they actually flowing? That is a great question to which I don't have a definitive answer.
Injector flow programmed into the chip (assuming you mean into the .bin) - I started at 110 (90lb @ 20 psi = 111lb) and I'm all the way back down to 90. Even if the factory were 80lb (I read somewhere they were actually 80) then at 20psi they should flow about 100lb.

I should have time to play with it today and I'm going to drop it to 80 in the tune and see what happens.

**dave w** · 10-27-2021

Fuzzy Injector math . . . 90 Lbs / Hr @ 20 PSI = 111 Lbs / Hr.
Fuzzy Injector math . . . 80 Lbs / Hr @ 20 PSI = 99 Lbs / Hr.

+/- 10% on 111 Lbs / Hr = 100 Lbs / Hr ~ 122 Lbs / Hr.
+/- 10% on 99 Lbs / Hr = 89 Lbs / Hr ~ 109 Lbs / Hr.

Getting back to one of your questions, "how far below the actual flow rate has been needed" . . . I don't recall going any lower / higher than 10%, based on "Fuzzy" injector math.

Personally, I prefer stock fuel pressures. . . simplifies Injector Parameters

dave w

**brian617** · 10-29-2021

Verify that you have solid 20lbs of fuel pressure in all throttle positions while driving. Used one of the "18#" TBI springs once that was very ineffective of maintaining advertised fuel pressure. After chasing my tail, it finally went in the trash.

**Dieselsj** · 10-29-2021

Originally Posted by brian617

Verify that you have solid 20lbs of fuel pressure in all throttle positions while driving. Used one of the "18#" TBI springs once that was very ineffective of maintaining advertised fuel pressure. After chasing my tail, it finally went in the trash.

Yep, I do. Using an aftermarket remote FPR and have a block-off plate on the injector pod where the stock one would be. I have a gauge on it and it holds 20.

**Dieselsj** · 10-29-2021

Originally Posted by dave w

Fuzzy Injector math . . . 90 Lbs / Hr @ 20 PSI = 111 Lbs / Hr.
Fuzzy Injector math . . . 80 Lbs / Hr @ 20 PSI = 99 Lbs / Hr.

+/- 10% on 111 Lbs / Hr = 100 Lbs / Hr ~ 122 Lbs / Hr.
+/- 10% on 99 Lbs / Hr = 89 Lbs / Hr ~ 109 Lbs / Hr.

Getting back to one of your questions, "how far below the actual flow rate has been needed" . . . I don't recall going any lower / higher than 10%, based on "Fuzzy" injector math.

Personally, I prefer stock fuel pressures. . . simplifies Injector Parameters

dave w

Yeah, if I could find an injector that flowed enough at stock pressure. I was >95% on duty cycles before I bumped the pressure.