hey guys what is the stock fuel pressure on my 305 tbi? and also the mallory 3-port regulator is wut i need to switch to carb right? wut is the 3rd port for?thanks

 

i think one of the tech articles on ultimate TBI said 42 PSI.

 

43 for a TBI car? I don't think so. FSM says 9-13psi is range that it could be set at from the factory.

 

ya TBI fuel pressure is way lower than TPI. TPI has 8 injectors that need fuel pushed through them, TBI just has 2 big good flowing ones that don't need as much pressure.

 

"Q: What fuel pressure setting will give me the best performance?

A: The stock setting is 42 PSI. Much track testing has showed that any type of increase will greatly benefit both horse power and torque. Here's some dyno testing on a stock 350 motor which substantiates those claims:

42 PSI (stock) 46 PSI 50 PSI
RPM Torq HP Torq/diff HP/diff Torq/diff HP/diff
------------------------------------------------------------------------
dyno numbers are shown here, but are too long for the post.

It shows that by increasing the fuel pressure to 50 PSI, results in maximum torque increase of 58 ft-lbs (along with a much flatter torque curve) and a maximum horse power increase of 19 HP over stock. 46 PSI also provides a noticable increase which should work well for day-to-day street driving. An adjustable fuel pressure regulator (see Chap 5.2) is required to increase the fuel pressure."

 

That's a good qoute from the FAQ not the Ulitmate TBI tech article. And I'm sure it is accurate. But it applies only to TPI cars. Not TBI.

The TBI cars run at a much lower pressure. Once again the factory service manual states that normal operating pressure ranges from 9-13psi. Most people with modded cars can turn it up 1-5 psi. But that's about it. My 9C1 ran about 12psi stock. Now with the vAFPR it runs about 12psi at idle and 17psi w/o vacuum.

 

sorry about that, it doesnt say whether it was for TPI or TBI, and somebody told me if i switched to carb i would have to have a lower fuel pressure, so i figured the article was for TBI.

 

NotDads,
How difficult was the vAFPR install? I'm thinking of doing this on my '93 5.7 truck. Just wanted some info from someone who's done it this mod. Thanks, SC.

 

Installing it was easy. Just swapped out the top of the TBI unit. What's that six torx bolts? And ran a vacuum line to it.

Tuning it was another thing.... You can't just swap it onto your truck and go. You are going to have to spend some time tuning and adjusting it. But the results are worth it IMHO.

I started a big thread on this sometime ago see this thread.

https://www.thirdgen.org/techbb2/sho...highlight=vfpr

CD

 

Thanks. I read through the whole thread. Thanks again, SC.

 

you would have to lower the pressure from 9-13 to 5-7