I'm wondering if the '7730 $8D system will function correctly with the injector flow set to 50 lb/hr? Maybe there is a practical limit on the injector flow rate for the $8D system?

I'm hoping to hear back from someone who is willing to share information about using 50 lb/hr injectors with a TPI system.

The SBC 400 TPI system has an aftermarket High Flow Throttle Body, and a set of aftermarket High Flow Runners. The cam is a Competition Cams 292 grind. The vehicle is classic 56 Chevy Belair.

Maybe I should plan on using 24 lb injectors?

Thanks in advance,
dave w

 

I have run 127 lb injectors....50's are not a problem. High impedance that is. 730 wont do low z, need a 749 to do that

 

I run 30 Lb injectors in my 406, have them at 52 psi for a net of around 36 lbs.
Works well and idles good at 800 with 236/242 hyd roller.
I have HSR intake, the TPI wouldn't flow enough to need 50 lbs anyway unless your boosting.

 

Sorry to hi-jack the thread...

JP, what idle vacuum do you get with that cam? I'm thinking ahead to something like a 427 sbc and will want to get a cam that gives me similar idle characteristics as my current 350 (i.e., not bone stock, but not lopey either... just enough to know that it's not stock). I know the larger displacements tolerate larger cams, but I'm not sure how large is too large.

 

50-55 Kpa at 800 rpm in gear with a quasi-loose 2400 converter.
Rolling the load drops to 45-48 Kpa.
Howards retro roller, HRS-CL120265-12 at Summit. (290/296 adv duration 0.634/0.640 lift)

406 @ 10.6:1, Sportsman II modified Iron heads, HSR,
I do run small primary longtube headers (1-5/8 x 3", then 3" all the way out), that will have some effect.

 

How would you rate the idle quality? Lopey? Severely lopey? Slightly more than stock?

 

You will def hear that cam in a 400's inch motor

Alot if it depends on exhaust setup tho

Heres my 9:1 comp turbo motor back in 09. 400" with 233/233 112 lsa hyd roller. Fast idle at startup but end it tames down alittle. 900-950 rpm to keep alternator happy



And this was 730 ecm with 80 lb injectors

 

The engine starts and runs (poorly) on 24lb injectors. Actually, the engine runs about the same as it did with the 50lb injectors. So I'm thinking I might have a fuel delivery problem, the fuel pressure very slowly bleeds off. The fuel pressure bleed off time is almost an hour after the fuel pump is shut off. The fuel pressure is above 20 PSI for almost 30 minutes. I've been thinking the fuel pressure should bleed off to almost 0 psi fairly quick, like within a minute or less? Am I thinking correctly?

I've been thinking maybe I should try bypassing the factory TPI pressure regulator and convert to the OBD2 "Corvette" return-less fuel filter / pressure regulator set up. Thoughts about the retrun-less system are welcomed.

The 1956 Belair has an aftermarket off the shelf ready "EFI Fuel Tank".

dave w

 

Actually the pressure should hold long after you shut the engine off. You could have a leaking regulator or something leaking on the pressure line within the tank.

 

Maybe the Corvette return-less system is not a good plan, I'm thinking $8D would require an injector flow table like the ones pictured (return-less vs. manifold vacuum referenced)

dave w

 

Manifold vacuum controls the fuel rail pressure to keep the injector flow correct at different MAP levels. A table is not used.
$8D also uses battery volts or fuel pump volts (selectable) for the injector voltage compensation.

 

Thanks for posting the functional description and theory of operation of the VRFPR.


I was wondering "What IF" I used the "Corvette" Return-Less fuel pressure regulator. After some research, I've decided using the "Corvette" Return-Less fuel pressure regulator would NOT be a good plan with stock $8D code.


dave w