I have a '92 F150 with a 300/6. I'm ready to start doing some significant mods to improve performance. Before I start, however, I am going to get some baseline dyno #'s,
as well as 1/4 mile e.t.'s. I want to bypass the smog pump
for these tests. Does anyone know what part# a short belt,
the correct length for the smog pump bypass, would be?

 

With AC, the length is 93.5".

You should be able to ask for that specific length at the parts store.

 

anyone no the belt size for one with out a/c ? im doing away with my smog as well

 

Thanks Ghog. That's a start. I was hoping that someone had tried a specific belt that had worked for them. The a/c compressor will stay for now. I can bypass that as well, but it is no measurable loss as long as the clutch is not engaged. So either belt would be fine. Anyone?

 

i think silver streak said w/o the smog pump the belt was 87". not sure if that was with or w/o A/C. easy way to check it get some string and route it around the pullies u can and measure the lenght.

 

I posted this here (https://www.ford-trucks.com/forums/s...ighlight=belt+), I have a '91 with a 300 and no A/C:

Seems like 82" worked on my '91 w/o A/C. Can't remember for sure though.

Just go to NAPA with a wrench to pull back the tensioner so you can get the belt on and off. Then ask them if you can try different length belts. The one that fit was just a touch long and the tensioner was almost at the end of its travel but it was OK and the next shorter one was way too short.

I guess it was 81" (https://www.ford-trucks.com/forums/s...ighlight=belt+):

In case anyone is interested for reference. The stock belt on the truck is 97 inches long. An 81 inch belt fit but it's just a little long, the tensioner is right at the end of the indicated range. An 80.5 inch belt would be better if you could find it.

And here (https://www.ford-trucks.com/forums/s...ighlight=belt+):

If it doesn't inject air into the head behind the exhaust valves (look for the rail under the top of the intake manifold with a check valve and hose running to it toward the front of the engine) it won't be as big of a deal if you want to bypass it.

With no head air injection the air pump just injects air into the exhaust after the O2 sensor to help the catalytic converters do their job. I have no head air injection on mine and gutted the pump, cleaned it good, welded everything shut and filled it with light motor oil. I don't worry about the bearings crapping out on me now. I tried a belt that bypassed it but it was just a tiny bit long and squeaked. Some people say that this plugs the cats but I can't see it being a problem if the motor's running right and is tuned right. I have several other vehicles that don't pump air into the cats except when the motor's very cold and they've never had trouble with cats.

The motors that do have the air injection behind the exhaust valves can't do without the pump without the computer getting confused and making them run wrong.

 

Thanks for the help. I'll do the Napa test fit thing to get a belt for my tests. I'm not to concerned about the cats. They will either be replaced or I might forget to put any on at all. The memory is the first thing to go...