Help on where to hook a fuel pressure gauge Big Cam with a PT pump

If you mount it permenent I recommend using 1/8 copper line and a ball valve.
The reason is I found a bigger line to the gauge makes the return to idle lazier and drop in rpms to shift much slower. 1/8 line does not seem to effect that. The ball valve is a safety measure to cut fuel off to the cab if line or gauge pops. My small cam 350 will hit 300 psi if floored and in a high gear. These are the gauges I use. They are the only ones I could find in a 2 in diameter that went above 300psi.

 

You guys are talented with pictures, circles and arrows. I am not but that helps me to understand I may have explained it poorly. That is the steel tube ( like a brake line ) just in front of the fuel solenoid. It connects to the engine block side of the pump. The other end of the line connects to the aftercooler above it.
It works like this but I do not remember the pressures. The AFC ( air fuel control ) limits the amount of fuel that can be injected until there is sufficient air ( boost ) around 1500 - 1550 RPM on the engines I was most familiar with. If this system does not hold pressure you will have limited fuel.
The STC is a whole different conversation but probably not where to start. When you start the engine watch the oil pressure gauge. At the same time you get oil pressure the sound of the engine should change. If it does not you have an STC problem. However if it does that does not mean it is all OK.

 

Bad idea

 

So I’m gathering that the second line going to the STC “box” coming from the rear of the head is the oil pressure signal line? And that the STC uses oil pressure to regulate timing using fuel pressure?

I’m off to get some fittings to test the AFC and also fittings to hook up my pressure gauge. I’ll post my findings and hopefully I’ll be closer to resolving my power issues.

I’m not crazy in thinking that not being able to keep speed at only 50k am I?

I keep hearing people saying how well big cams pull, and right now it pulls about as well as my C8.3 Cummins loaded to the same weight.

I'm guessing that it should be capable of grossing 80k and it be manageable (it used to be a tractor) so I’m really looking forward to getting this thing running the way it should!

 

So I just got the fuel pressure gauge hooked up and took it for a quick rip, gauge never went over 185, and that was on a hard pull up a pretty big grade in 8th (it’s only a 9 speed). Boost never went over 15.

Does that sound low to you? Should I drill the throttle shaft and turn up the pressure a little?

I live in Pittsburgh and was going to have Pittsburgh Power rebuild my pump, bump my governor to ~2300, and throw a button in it. They said they could give me somewhere in the 500hp range, I’m wondering where I am now on power with 15 psi and 185 psi of fuel.

Shane

 

That sounds pretty normal. Cummins never really had many pump codes that put the pressure above 200. 15 psi of manifold pressure is about right.
Drilling out the throttle shaft will richen the flow more than raise the pressure but it will make the throttle crispier. You can back out the afc screw ( the allen screw above the throttle shaft) a 1/4 turn at a time to fine tune the flow for throttle response to the turbo boost pressure but too much will make it black smoke.

If you don’t mind me asking. What engine are used to pushing? The reason I ask is because guys that are new to the classic truck thing and are used to big torque and 500+ hp are always disapointed in the lower feel of power the older engines have. It’s a culture shock so to speak.
They operate and feel a lot different.
Some guys learn to love it and some can never get used to it.
That being said. I’m not saying there is a problem with your engine or not because I’m not there to see how it is pulling. Normal or not.
It is a gorgous truck.
The whole idea behind the Formula engine was economy. Better mpg’s with the gross hp at a lower max rpm. Two of the ways they did that is by lowering governor from 2100 to 1900 rpm and running lower fuel pressures.

 

Thank you, I’m not really used to anything in particular, but have driven Detroit 60’s, which I know is no comparison, but my buddies 400 will eat this thing alive...hell, my 10 ton F800 with a mechanical 8.3 will pull just as hard loaded to the same gross (50k)

I drilled the shaft, it was 3 turns out when I started, went 2 more (5 total out) how many is safe to do? Is there any harm in doing so? What’s the difference between that and doing a button? I’m getting close to 200 psi now...

What would you suggest to start with to wake this thing up a little?

Shane

 

With the engine idleling and you standing at the throttle shaft snap it with your hand. Don't go wide open. Just snap it a 1000 rpm or so. If it has a crisp feel and a snappy sound and a quik puff of smoke from stacks you’ve got all your gonna get from the shaft screw. Fine tune the afc screw with the throttle shaft screw the same way. 4 to 5 turns out on throttle shaft is about max. Anything more won’t do anything other than make it loose enough that it can eventually fall out. 3 to 4 turns out on afc is max. That one has a lock nut on it so it won’t fall out.
The button is what is going to give you the biggest psi increase. Best thing to do is take yours out and see what number is in there already. Then you can decide what you need to do.

 

When you get the old button out take it to you local fuel pump shop. Go down two sizes and ask for two hundred RPM's worth of shims to add to it. That will help.
Do not stand in it under load for long periods of time.
Did you ever check the throttle lever?

 

I’ve tried to check to see if it “breaks” all the way, which I’m not exactly sure how to tell, all I know is that if I push the petal down to the floor, the shaft turns to full lock...