I have bought an adjustable fuel regulator (photo below), does the adjustment bolt need a locking nut ? Will normal vibration let it go out of adjustment or is it fine with just the bolt ?
The reason i ask is that i have seen some for sale with locking nuts on them.
the other question is in relation to the vacuum line, i doubt that it was put there because GM had a spare vacuum line left over, so what was its original purpose and what are the pros and cons of blocking it off ?

 

Adjusts fuel pressure to suit engine running conditions
Stock typically 39 psi at low engine load like cruise / idle ; 45psi at WOT when more fuel is needed
If you block it you will have full fuel pressure ( what ever you set AFPR at ) all the time meaning you will be burning more fuel than needed

 

To add to the above post the vacuum line helps at idle when you do not need or want the full fuel pressure. With the new style injectors now available this may not be an issue. But with the old factory injectors it was. Mine does not have a lock nut. It is hard enough to adjust without having to worry about the lock nut.

 

thanks for that info guys, so i take it its best to block off the vacuum to set the fuel pressure then plug the vacuum line back in for driving ? or do you set the pressure with the vacuum line still on ?

the unit had a 5mm bolt that was only 10mm long, the housing is 5mm thick, I dont see how it would be long enough to adjust anyway, so I tapped it out to 6mm and put a longer bolt with lock nut in.

 

That is factory method.
You set the MAX pressure you want ( no vac ) and engine vac lowers it when required

 

thanks rodj

Im going to put Bosch 3's in and fit the adjustable regulator while everything is apart, will be borrowing a fuel gauge tonight and check the current fuel pressure before I pull everything apart.

 

Hi
I have an adjustable fuel press regulator and find the pressure changed over time. a lock nut or spring is heaps better .
I ended up putting a few washers in and having it set to 45 psi with the screw tight ...... has not changed over the last year .... previously had to check the fuel press monthly.

 

Hi Gerard, i cant see how it would be good to not have a lock nut, I have put a longer 6mm bolt in to get plenty of adjustment. I hooked up the fuel gauge this morning, 38 psi with ignition/pump on, and 38 psi at idle, so the pump and diaghram spring must be good, now i have a baseline.
i like the engine setup on your profile, what sort of rwhp is that worth ?

 

If thats the bolt your using, you may have a hard time adjusting it once its on the car.You have to be able to get to it from the side..Its hard enough to adjust with a regular bolt..WW

 

thanks WW7, i put that one in coz its nice and shiny, when i put the reg in i will look at putting in a normal bolt.

 

I see yours is an 85. The change to Bosche III injectors and adjustable regulator is a good mod for that year. The 85 ran larger injectors than later years (24# vs. 22#) and lower pressure. So basically the fuel was squirted rather than sprayed. You'll find with the new setup that 45 psi is a good maximum pressure (vacuum disconnected). According to TPiS dynos it will increase Hp. The increase is due to better atomization of the fuel resulting in more efficient burn.

 

Hi yes the lock nut is a must on fuel press regulators . I have installed the bosch type 111 injectors on my 85 and was very impressed.
Hi blackausvette... i have not had the vette dyno tested with the supercharger,the car did a 13.4 sec quarter before i installed the vortech supercharger with cold air intake extractors removed air pump and cat converter removed with high flow mufflers and fuel press from std 29 psi to 45-50 psi. Now with the supercharger just lots more power everywhere, 8 psi boost normally cuts 1 to 2 secs of the quarter mile time as per procharger / vortech kits for vettes .I have installed the normal vette air filter set up to comply with Australian rules that state you cannot have an intercooler and a pod filter... anyway is better now that it doesnt pick up the heat from the exhaust
Am running 8 psi boost thru the intercooler and the mass airflow sensor after the intercooler. the standard computer copes fine, have a vortech FMU that adjusts the fuel pressure per psi boost to ram more fuel through the injectors. Just wears the tyres more :rolleyes
Anyway i love the extra power and the supercharger noise ....
when i first had the car around 12 years ago it did 14.5 sec quarters with some minor mods and tuning 13.4 now with the blower should do low twelves ..... i know of one vette a 93 running 12psi boost doing 10 sec quarters .. its tempting more boost but i will have to strengthen the engine /trans/axles and diff... have already had to replace the alloy shaft/ axles between the diff and wheels
... thinking of putting a smaller intercooler in so i can run the air conditioning without the car overheating with the a/c on

Cheers ... gerard

 

Just a little clarification to previous posts.

The reason for the vacuum line is so that the regulator is vacuum-referenced. This ensures that a constant pressure differential is maintained across the injectorsunder all load conditions. This is critical to proper fueling calculations by the ECM.

Can you run an engine with the vacuum line plugged? Yes, but even with re-tuning, the engine would not receive best fueling under all conditions.

Some newer cars have used atmospheric-referenced regulators, but that is just for simplification, not performance. These atmospheric-refenced cars, however, use different fueling algorithms. The C-4 fuel routines in the ECM require that the differential pressure across the injectors remains relatively constant under all operating conditions.

Lower fuel pressure at idle does not equate to lower fuel flow because you still have the same pressure differential between the injector inlet (regulator outlet pressure) and the injector nozzle (manifold vacuum).

Idle = lower manifold pressure = lower fuel pressure
High load = higher manifold pressure = higher fuel pressure

The fuel still "sees" the same pressure drop as it sprays from the injector.

I hope this helps explain things...

 

There is vac in the manifold ; not pressure
Hi vac at idle
Lower vac at WOT

 

0 PSIA = approx. 30" Hg (vacuum) = approx. 14.7 PSIV = 0" Hg (absolute) = 0 ATM
approx 14.7 PSIA = 0" Hg vacuum = 0 PSIG = 0 PSIV = 1 ATM

PSIG is referenced to atmospheric pressure.
" Hg (vacuum) is referenced to atmospheric pressure, but is negative.
PSIV is referenced to atmospheric pressure and is also negative.
PSIA is referenced to a perfect vacuum.

Higher vacuum equates to lower pressure.

<<<<<<<<<<<<<<<<< Lower pressure <<<<<<<<<<<<<<<<<<<<
0 ATM--------------------1 ATM----------------------2 ATM
0 PSIA---------------approx. 14.7 PSIA------------approx. 29.4 PSIA
approx. 30" Hg-------------0" HG-------------------approx. 14.7 PSIG
>>>>>>>>>>>>>>>>> Higher pressure >>>>>>>>>>>>>>>>>>>>>

I hope all of this makes sense????

 

I would toss that thing in the trash and get a holly adjustable fuel pressure reg. Looks like it's been monkey rigged.

 

I wouldn't buy a Holley. I've read too many complaints of them failing/leaking. And they use a special diaphram, so you can't replace the diaphram with a factory style one from the parts store.

 

I know mine has a funky spring in it. I have never heared there was a problem. Mine has been 100% issue free.

 

I had read of several who had problems with the Holley diaphram leaking to where I went with the stock style adjustable hat. The other problem is with Holley, you can't use the stock style diaphram. So, if/when the diaphram goes bad you can't get a new diaphram from the local parts store. Not sure if you can get just the diaphram and not the whole assembly. I've only seen the Holley's sold as a complete unit.

 

That is crappy. I will say this, it sure looks good.