MSefi.com read only forum (Jan.15,2018)

Anyone know what the max PSI is for a GM TBI unit? I know there were some 454cid setups that ran around 20 PSI, but I’m curious how much higher they could go for 2 reasons – increasing flow rate of the injectors and also using a more-common MPI pump instead of a low-pressure TBI pump (limited choices).

1. These are side-feed injectors and from what I can see they might not have fuel ‘above’ the pintle, thereby fuel pressure would not be trying to keep it closed (like a typical Bosch-type injector) therefore leakage would only be a function of the TB gaskets. Can anyone confirm that?

2. My next question is about using a more-common high-pressure MPI pump with GM TBIs. I am concerned that the higher pump flow at the low pressure might overcome the internal FPR and cause a pressure rise at idle (and/or gasket leakage on the TB). I could remove the internal FPR and install an external one, but I’d rather avoid that expense unless I have to. Would an MPI pump flow too much fuel volume and overcome the regulator spring?

We've used a high pressure Walbro 255 pump with a stock GM TBI regulator and didn't have a problem. Not sure about where the injectors max out though.

Matt, I was hoping to hear from you, you always have good info! You'll be getting an MS2 order from me someday soon.

That's good news on the pump, that allows me to build for the future and do either TBI or MPI without a pump swap.

Yep, that was the idea with the Nova, two different fuel setups without replumbing the whole car.