I am going to install an underhood fuel pressure guage to help with tuning my motor. Will I be better off with a 0 to 15 psi range guage or a 0 to 30 psi? What would be best?

 

0-30 is better I think.

I think GM TBI runs best at about 20psi anyway...

 

The stock TBI pump wont even push 16 PSI through a stock regulator. I think my old TBI ran around 14 PSI max.

Eh, just use a 30 psi one....

 

If you plan on modding your motor, which I assume you have given the need for a gage, than I would go with a 0 to 50 psi or more. Although the stock pump won't produce over 15psi or so, as mentioned, an aftermarket one (for a multiport set-up) can produce 50+.

 

I have an actron 7817 pressure guage.I haven't had a chance to use it yet but I think it reads from 0 to 100,I have to go home and check.

 

The GM TBI injectors start to leak somewhere around 30 psi (or so I've read in a few places, I've never tried to run them that high). So I think the 0-30psi gauge is ideal. Besides, if you crank the fuel pressure up that high (30+ psi) you'll have so much flow that you probably won't be able to get the thing to idle properly anyway (with decent size injectors anyway).

"DEATH TO ALL BLUE OVAL DONKEYS!" That is beautiful

 

I don't think I'd buy into GM TBI injectors starting to leak at 30 psi. Main reason is that GM runs them at 28-32 psi on the '94-'95 BBC trucks. Myself, I've run a SBC TBI unit at a higher pressure then that. No leakage at all, and they do idle.

RBob.

 

That is nice to know, I've been wondering about it for awhile. Take two 90 lbers @ 30+ psi supporting over 550 hp. What size motor would be necessary so that the idle pulse width wouldn't be too low beyond the injectors' ability to cycle properly (assuming a motor with components capable of making 550 hp, of course).

More to the point, what's the minimum pulse width TBI injectors can deal with? Perhaps someday I'll consider supercharging or nitrous and I'd like to know that.

 

Once a BBC injector at 22 psi gets to 0.1 - 0.2 msec it gets a little iffy. At that low of PW the fuel flow is not all that stable.

Once the fuel pressure is above 18 psi or so, best is to use a vacuum referenced fuel pressure regulator. This reduces the fuel pressure at lower MAP. There by increasing the required PW. Really works out nice. On the other hand, this shouldn't be done with stock TBI code, it doesn't work out too well.

RBob.

 

I'm running the 90#/hr injectors on my car at 17psi. Overkill, I know. It idles just fine too, so I know you can go at least that high and still be able to tune the idle in good. I think my BPC is at 61.

 

Actually, that's a specific question I've been wondering about for a long time. You should have enough fuel for 400 hp. At one time I had 90 #ers on an essentially stock LO3 (BPC set at 68,l IIRC) and it idled fine . However, I'm in the process of building a rather strong 334 and was wondering how low I could go with the BPC if I needed to crank the fuel pressure.

Just curious... why did you go to 17psi and set the BPC so low? You seem to have a fairly strong L03, but did you actually run lean with the 90s at a lower pressure? Were you running nitrous or anything?

 

Well I had been running them at 11 psi all along, and did a good amount of tuning with them at that setting. Then I installed a Walbro 190 and it jumped to 17psi. I figured I'd try to get it to idle like that without trying to dial down the pressure and it was fine, so I left it. I was actually surprised at how much the pressure spiked with the Walbro.

 

i ran an aeromotive with the weaker of two springs(0-20) at 17 lbs. swapped cams and required more fuel so swapped in a 20-50 spring and set to 23 lbs and all was well. 80 lb inj's. so easy to adjust FP with the Aero. my gauge is 0-30.

Casey: i was with a BPC of 83. however my VE was maxed at 100 so i moved BPC to 100 to allow more fuel in VE2(EBL).

 

Gentlemen,

With EBL, there now is another solution. Variable BPC settings allowing use of a VAFPR. I've been using it for the past 2 weeks with very good results. Runs 11.5psi at idle and 20psi at WOT. This is with the larger spring that comes with the Aeromotive 13301 VAFPR. All hail RBob!

 

I only wish the EBL had provisions for Variable BPC settings above atmospheric pressure. Think BOOST.

 

That can be done

RBob.

 

maybe someone else can elaborate on "asynch" fueling at idle. before EBL my tune would fall into asynch in CL idle. expected with high FP and large injs. engine responded to the transition not too well. now running OL at idle with EBL and idle is much improved. i dont think there is a down side to running a bit rich at idle is there? i believe there is a way to run asynch-OL idle but have not yet looked into it. well aware of the VAFPR with EBL. will investigate that next season.

 

That would be great.

My fuel pressure now is like 15 @ 50 KPA idle, 20 @ 100 KPA and 27 @ 155 KPA(7 PSI boost). With 90# injectors, this works GREAT.