Engine/Transmission (1994 - 1998) Boost questions - stock setup

[tomblue01]

From what I've read here, about 20psi boost is max for our 12 valves. Having recently installed mine, I have a performance ?:

4th gear [NV4500]; WOT going uphill. ~ 2300 rpm
Boost will climb to ~16psi, but only momentarily. It then falls to 10psi where it remains until I let up on the throttle. Should this happen?

When I'm in 2nd and trying to accelerate hard, I might build 12psi of boost. Is this because of the turbo lag & the fact that I'm only in 2nd for a few seconds?

 

[GAmes]

I'm guessing that is empty with with no trailer. Sounds normal to me.

 

[tomblue01]

Correct: empty & no trailer.

 

[Bob4x4]

My 94 would hit 18-19 right out of the box.It would drop a bit after it flattened out.10 psi is not right test fuel psi and check for boost leaks.

 

[Woodenhead]

You mention accelerating hard in 2nd gear, what about in the bigger gears? 2nd gear doesn't really load things up much.

On a stock to lightly modified 12V figure 1psi for each 10hp you're producing. My 215hp stock motor would produce 21-22psi boost when I'd load it up. How much hp you're using and boost you're producing will depend on how much you are loading up the engine. Towing with your foot to the floor or accelerating hard you should see maximum boost, in your case this should be around 20-22psi for your stock 215hp engine. If you're only seeing 12psi then something isn't right, possibly a boost leak of fueling issue. How are the EGTs?

 

[tomblue01]

I didn't focus heavily on EGTs. ~900ish going up the hill. Always in the green. Was at a big box store the other day. Found a 4" PVC cap, 4" diameter rubber hose... I think it was a short coupling hose of sorts. Just need to grab a schrader valve and two clamps and purchase/assemble everything. Bike pump and soapy water are standing by!
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Does your boost stay high, or does it max out and drop down a bit?

 

[Woodenhead]

I didn't focus heavily on EGTs. ~900ish going up the hill. Always in the green. Was at a big box store the other day. Found a 4" PVC cap, 4" diameter rubber hose... I think it was a short coupling hose of sorts. Just need to grab a schrader valve and two clamps and purchase/assemble everything. Bike pump and soapy water are standing by!
___

Does your boost stay high, or does it max out and drop down a bit?

Sure the boost drops off. Again, it all depends on load, as the speed increases at some point the rate of acceleration and load decreases. Keep it loaded with fuel pouring in then the boost stays up, less load, less fuel...less boost. Put it to the floor in neutral and wind it up, no load...no boost. Along with all this, if you're only making 12psi of boost you're only making about 1/2 the power you should be. You'd likely notice that thing being a dog.

Watch yourself with the pressure test, if that plug comes loose it'll have a lot of pressure behind it...not that I've ever seen that happen before :-laf.

 

[Missouri Mule]

If your putting the pedal to the floor your blowing black smoke out your tail plpe. That black smoke is hot burned fuel.. That unburned fuel is not going make the turbine wheel spin like it should.
I know it is hard to do. Try depressing the go pedal slowly until you feel the engine and turbo are syinced then you can press it down the go pedal further dowm.
I have it 22 psi then the waste opens. On the on our steep small hills running 70 I can hit 14-15 psi.
On my liner I do the same thing except the liner is governed in each gear. But with the vp44 pump and the torgue straight lining from 1500 to 2500 rpm I have plenty of get up and go.

 

[fest3er]

I've found two reasons for boost to drop. (1) There's a problem with fuel delivery (air gets sucked into a line, fuel pump cannot supply fuel fast enough, fuel filter is clogged, etc.) (2) The boost line to the gauge is old and hardened and allows air to escape, thus lowering the pressure reading.

 

[SSage]

Sounds normal, boost will drop off unless your pulling hard up a hill or something and higher rpm cause it to defuel.

My 12 valves ran 10 psi or less at 70 mph on the interstate. You should see around 18 psi at 2,000 rpm I think. I haven't had a stock truck in a long time. They do defuel fairly quick when you rev them up, thats why many of is run 3K or 4K governor springs.

Its always a good idea to test for air leaks though, you will usually find more than you expected.