Parallel Plumbing 84 Dual TBs


Mar 24, 2008
I thought there would be interest in this. I have been struggling with feeding a 383 in my 84. On the dyno we noticed a fuel pressure drop from 20psi to 15psi with a TPI pump. Pressure started to drop off at 4000rpm and at 5500rpm the pressure was at 15psi. Needless to say this indicated a severe fuel delivery issue - the TPI pump should be able to supply enough fuel - I have a LT1 pump in the wings just in case the motor needs more fule. One way to cure this is to parallel plumbing the TBs. The regulator is a bypass regulator hooked up to the return side. I am also removing both regulators and will have a plate welded in place. The injector tops are at the weld shop and should be done in a couple days. Hopefully this setup will supply enough fuel to feed the motor so it can be all it can be.

I also plan on redoing the fuel lines to use hardlines once I get stuff setup. This was a exercise in getting it plumbed and working. The airpump at this point is nothing more than a pulley - it is gutted. I may fab up a airpump delete for the 84 sometime in the future.

What adapters fit the stock TB adapters (hex shaped steel fittings)? When I did this, I removed those also and used a dellorto adapter fitting (available from russell & earls) as the tb thread is the same as on dellorto carbs.
I believe it is a 5/8-20 to -6AN adapter used on carbs. Tom (buc) picked it up when he was at Parker Fitting. I looked around for the Dellorto stuff but I could not find it.
A few items.
I'm using an LT1 pump in my '84 turbo. Seems to do the job well (and the best part, I got it free).
I needed to change the fuel lines when I changed out the dual one barrels for the 454 two barrel TBI. I struck out finding the correct fittings, so I used the front half of the fitting (that screws into the 2bbl TBI), cut and TIG welded to the back half of the fitting the attaches to the fuel lines. Worked well, and unnoticeable.
What's the max fuel pressure that TBI injectors can deal with? TT and I have discussed this in the past. Just curious if anyone has any definitive information.
Should be easy to test, all you need is an ECM toa ct as a driver and then in a testing setup for the injector crank up the fuel pressure. I'm betting on right around 20psi is when the pressure is too high for the pintle to close.

The part number for the Dellorto fittings: 991945ERL ; 12mm x 1.25 gasket ring seat to -6 AN
Just a side note on pressure Marck. I had my 80# @26psi for a while, but wasn't comfortable with that setting and here's why. When I first modified my FPR, I set it to about half way (spring tension) and the FPG went to 35psi and fuel went everywhere out the compensator side. I blew a brand new bladder.:amazed:

I went down to 22psi after that just to be safe, but thats not enough FP for my beast. We are working on a modified setup right now that will cure the FP issue I believe.:thumbs:
Are you moding up the 2.13 TBs? What FPR did you decide to go with, Aeromotive? I've alway thought parallel lines was the way to go. Are you going to make up hard lines after getting it all layed out?
I am still running the 2.0" TBs. Yes it is a Aeromotive regulator. Hard lines are in the future. For now I am tyring to fix my fuel delivery issues.
For those folks interested the DC (duty cycle) dropped dramatically and are now more consistent - 75%-80% range.