1992 chev full size van-mpg

My 1992 G20 conversion van with the 350ci throttle body has 59k miles. I tow a ten foot long light enclosed trailer and only get 12 mpg at 55-60 mile per hour. Oxygen sensor was replaced, no improvement. I am installing a cat back 3" exhaust w/Ravin muffler tomorrow. Does anyone know if I have room to install a throttle body spacer, and is there any thing else anyone can suggest (hopefully that they have tried) that can improve my miles per gallon? I run 6 ply radials @ 35 psi. Thanks

I wouldn't complain.
My 95 3/4 Ton Conversion van is VERY heavy. I drive 80% highway miles. It gets 13 mpg in Winter, when I warm it a few minutes before driving.
Summertime it gets 15-16 Hwy.
I pull a 6,000 # race car/trailer and it gets 10MPG hwy.
I use 5w30 oil in winter, 10w30 in Summer. Radial tires with 45 PSI. (NOTE: Ride was smoother at 35 PSI, but tire wear is better & mpg is 2-3 better at 45 PSI. Check yoru tire sidewall in fine print it will say what the max pressure can be. Some tires it is only 35 #, some will go to 50-55 or more).

Thanks for the response Jim. Since that post in 2004, I have mpg information after installing the Raven flow thru muffler and 3" exhaust. I now get 13.5 mpg pulling the 10', 1800lb trailer at 60mph, still air. Van now has 95K and still pulling 19" mercury at idle. I guess this is as good as it gets.

Marquetry Man,
That is a decent increase in mileage, percentage-wise around 10% or so better.
Tell me, did the exhaust system help your power output?
My van has 130K miles on it, but it has been rather doggy since I got it with 72K on it 4 years ago. I know a 350 should pull better than this one, I really think the Cat Conv is too small, or maybe partially plugged-up. Am considering a high-flow Cat & larger exhaust from Cat-back, as you have done. Mainly looking for more power, any boost in mileage would be considered icing on the cake. I don't know what rear gear ration these vans have, but mine might be too tall for this heavy of a vehicle. Thanks for youor reply. -Jim.

Yes, power and mpg increased with the addition of a improved flow cat and the raven flow through muffler and 3" pipes. Sound is really great too-----real deep throated rumble at idle, though perhaps a little loud cruising on the highway. I, too, have a conversion van so I'm carrying extra weight. Actually, with the van fully loaded with approximately a little over 1thousand pounds, I get 15.5 mpg in still air when I'm not pulling the trailer. The trailer's wind resistance is hard to overcome. The trailer is only three inches taller than my van, and is narrower. I tried a full width wind deflecter on the rear of the van, but this didn't seem to help any.

Hi all i too have a 95 discovery, conversion, on the way from SC to NY i got 17-18 mpg, i was complaining before i read your posts, just today i was looking into air intake, what is that cover half way down to the air filter, i opened it up, stuck a jamb in there, and now i feel more power from dead stop, and so far gas gauge didn't move in about 20 miles.:banghead: why restrict airway?!? any help is appreciated.
bob