Injection pump question, B engine

[LCkoolJ]

Can anyone tell me what this line is for on the fuel pump? It blew off last year on my way up to the Whipsaw and my turbo, which normally puts out around 10 psi, spiked up to 20 psi and the truck lurched forward like I gave it a shot of nitrous! The only thing was the engine ran on for a few seconds after dropping the throttle, so the response was all off. I'm wondering if there's an opportunity to work with that line a little to get a bit more performance out of the turbo?

[lostmarbles]

My advice is "don't mess with it".

Sure you will notice BIG power increases when you mess around with either of those two hoses - but that is only because they control the diaphragm movement - which in turn controls the rack movement - which in turn controls the amount of fuel dumped into your cylinders.

So your power increases are achieved by burning much more fuel than usual - and prolonged running under these conditions is not advisable if you want your engine to last.

The rearmost hose on your injector pump (actually on the diaphragm-housing at the end of the injector pump) is the "vacuum hose". It is connected to a venturi tube that sits in the throat of your intake manifold. When your foot is off the accelerator, the butterfly valve in the throat is closed. The venturi tube provides another path around the closed butterfly - so the air flow through it greatly increases. This in turn greatly increases the vacuum produced in the tube (by venturi-action)which sucks the diaphragm back. And since the diaphragm is connected to the rack - the rack moves towards the low (idling) fuel flow setting.

Foot flat down sees the butterfly go "wide open" = minimal flow through the venturi = minimal vacuum = rack moved (by spring pressure) to the maximum fuel quantity end of the scale.

The other hose that you ask about is the "reference pressure hose" for the diaphragm. It senses the "intake manifold pressure just upstream of the butterfly valve".

If you want to see your engine go wild - pull off that vacuum hose while your engine is idling!!!! The revvs will go "through the roof" in a millisecond. (See if your engine holds together at its revv limit?)

[LCkoolJ]

Thanks for the advice. So question then, if I crank my fuel way up will that also allow more air through the intake ie higher turbo boost?

[lostmarbles]

Originally Posted by LCkoolJ

Thanks for the advice. So question then, if I crank my fuel way up will that also allow more air through the intake ie higher turbo boost?

Well "more fuel + more air" is certainly the way to go to get more power. But I don't know what the humble B engine can take. (Most people turbo the 3B engine rather than the B, so I suspect the B engine is more fragile.)

From what I read here on MUD - the B engine has no "piston skirt oil-jet cooling" whereas the 3B apparently has this feature. And people seem to think this feature is particularly desirable for turbos. (The B engine probably has other "weaknesses" too.)

But hey - I'm getting way out of my depth. I'm certainly not the person to talk to with regards to turbos (or any other attempt at gaining more power).

I hope those with experience in this area (I have none) will chime in and give you advice now.



Ps. I'm of the old-school opinion that most power gains come with the price of "reduced engine life". (And I intend my engine to last forever )

[LCkoolJ]

As far as I know the piston skirt oil-jet cooling is the only difference. Other than that the motors are virtually identical. There might be a slight difference in displacement, but other than that its the same sh*t, different pile. The only reason I didn't do a swap to the motor out to a 3B was that the B had been rebuilt to factory spec, and only has about 30,000 kms on it. I know other guys that have turbo'd B engines, and they work great. Just have to be a little more careful with EGT's thats all!