Gallileo60

Ok, I guess im a little dense here, cuz im having trouble figuring this out.....If you make (Or buy one) your reg adjustable, how do you measure the pressure after the reg??? I can see several spots to measure the pressure before the regulator, but where after???? Am I just over looking something really easy, or do I not even know where the reg is on my TBI???? Thanks for the help, and HAPPY EASTER TO ALL.........

golden

I think it's integrated at the rear of the TBI unit where the feed line is .

Gallileo60

Thats what I thought, but how do you measure the pressure on the output side of the regulator???????? Someone please explain...Thanks........

RBob

iTrader: (1)

The fuel pressure is to be measured at the feed line to the TBI unit. The output side of the regulator just dumps the fuel back to the tank (return line).

RBob.

Gallileo60

RBob, forgive me, but I dont understand this....How is the pressure to the ijectors regulated????I thank you for your answer, but could you explain a little more, or tell me where I might learn about this??? I have read all the stickies, and I understand how to make my unit adjustable, but I just dont get how you know what the pressure going to the injectors is....Thank you very much for your reply....I know this sounds simple, but im just having a little trouble grasping the concept....I see how it works on carbs, and on TPI's, but ive looked at mine for awhile, and am lost...............Tom

RBob

iTrader: (1)

The TPI & TBI fuel pressure regulation is almost the same. Only difference is that the TPI fuel pressure changes with manifold pressure. This is to keep the same differential pressure across the injectors (the injector outlets are exposed to manifold pressure on port setups). TBI injectors are not exposed to manifold pressure, so the fuel pressure typically remains constant. I say typically as it is possible to set up the FPR as manifold referenced (VAFPR or VRFPR setups for hi-po use).

On the stock TBI, the feed line to the TBI unit first goes to the injectors, the fuel passage then goes to the FPR, with the output of the FPR exiting the TBI unit as the return line to the fuel tank.

The TBI unit, is the same as the TPI is: a return style regulator. The FPR sits down stream of the injectors. It maintains fuel pressure upstream, at the injectors. Whatever fuel is not required to maintain pressure at the injectors is just returned to the tank.

RBob.

Gallileo60

Well if I understand you correctly, damn im gonna buy a book on this subject.....Anyway, I think im leaning out on the big end, so my theory is that if I up the FP, I might get a little more power....From what ive read this is common at this stage in the game...I just installed the injector pod spacers, and am thinking of doing a intake this week, or next...Am not sure what intake to go with tho....What are you using, and why??? Am going to do the adjustable reg this week, if time permits...Thanks for your help, and HAPPY EASTER..........Tom

iggy1991

Look at the picture. MY best luck was to get a 1-15psi gauge and use a T-fitting to go in the middle of the rubber pressure hose up front on the drivers side. That way you can measure it at all times.

Gallileo60

RBob, thank you so much for your explanation....I am still having a bit of trouble figuring this out tho....

Iggy1991, what picture are you talking about?????

Dont know why im having so much trouble with this, I generally pick up stuff prett quick, but I just cant get how having a regulator after the injectors controls the pressure on the injectors....I kinda get it, it seems that if you slow down the flow back to the tank on the return line it will increase pressure to the injectors....Is that how it works??????
I dont remember a rubber line on the front, I thought mine had 2 steel lines...Will look later today.....Thanks all.....Tom

beatercoprice

What are you guys saying? That all the fuel in the feed line will be at the pressure the regulator is set at? Meaning that you can get a fiarly accurate reading by measuring the pressure right before the fuel enters the TBI?

RBob

iTrader: (1)

Yes.

However need to clarify the 'all the fuel in the feed line' part. The further back from the TBI you go, the higher the pressure will be in the feed line. There will also be some pressure drop across the fuel filter. So the feed line between the tank and filter will be at a slightly higher presssure then at the injectors.

Placing the gauge at the under-hood rubber line connection works. Fender side or engine side.

RBob.

Gallileo60

Wow, what a strange way of doing it.....I've got to get past my Holley fuel pump, regulator, carburator way of thinking.....
RBob, so by letting more or less fuel back into the tank, you raise or lower the pressure????? Is that it????????? Am I getting it?????? Im about to pull my hair out..........Thanks, Tom

beatercoprice

You feed a given amount of pressure into the TBI at all times, whatever fuel the TBI doesnt use it sends back to the tank.

Gallileo60

So you force it to use more by letting less go back to the tank, is that it?????? Thanks..

zipfast

iTrader: (2)

Hope this picture helps to put all the marbles back in the jar.

beatercoprice

Judging by that pic yes you are correct... I think. lol

Gallileo60

I want to thank everyone for their patience, and help on this subject...I think I see how it works now...........Tom