Tire size/MPG

[ALAN GEDDES]

Been thinking for a while about re- gearing my 81 GMC PU. Looks like I am about stuck with what I have. Anybody have any idea what a 2 inch taller rear wheel would do for my highway mileage which right now is between 9 and 10 mpg. 350ci/350 auto so am not overly concerned with losing a little acceleration.

[Nitetimes]

It's been my experience doing that that it mostly depends on each vehicle. On some it does nothing at all, some it makes very little difference, I've had a couple that it really made a big improvement and even had one that got worse. The biggest drawback I've found is that it tends to make around town driving mileage a little less.

[purplepickup]

....my highway mileage which right now is between 9 and 10 mpg. 350ci/350 auto.

Alan, you should be getting better mileage than 10 mpg. You might want to check the carb to make sure it's jetted and set up correctly. Headers and unrestricted air intake help too. My pickup weighs 3400 lbs, has over 400 hp and gets 20+ mpg on the highway if I keep the speed down. It's a 350/350 combo too but it's tuned very well.

The bigger tires will help some if you have a really low (3.70-4.11) rear axle gear ratio but if you have a high ratio (3.00 or less) you will probably get worse mileage around town like Nitetimes said. You might want to consider switching trannys from your 3 speed to a 4 speed overdrive. You'll still have good acceleration but engine will run at low RPMs at highway speeds. I know people getting 22-25 mpg with mild 350's and OD trannys. A transmission swap is only an option economically if you plan to keep the truck for a long time and use it a lot to make the savings in gas offset the cost of the swap. Of course it would increase the resale value too.

[ALAN GEDDES]

PP< Engine is stock but only 10k on it. Headman headers, dual cats and low pressure pipesinstalled by previouse owner. Stock 25 year old Quadrajet on stock intake. I can lay my hands on a new 600cfm Edelbrock and intake at a good price. Think that would help at all ? I'm a VW/ foreign car guy. Don't really know a lot about working on this GMC. Not to worried abput city mileage as I bought as primary tear puller and most of our trips seem to be 650 to 800 mile round trips.

[purplepickup]

I can lay my hands on a new 600cfm Edelbrock and intake at a good price. Think that would help at all ?

Everyone has a favorite brand of carb and mine is a 600 Edelbrock. I'd suggest you get it. Some people will tell you that it is ready to run right out of the box and they do run good the way they come but they all need to be fine tuned for your engine, altitude, and driving conditions to get the best mileage. Edelbrocks are really easy to tune once you understand them. Here's a helpful thread about tuning an Edelbrock from a car forum I'm on: http://www.roddingroundtable.com/forums ... php?t=3506 If the carb doesn't come with an owners manual one is available online and there are links to it in my post on that thread.

If you have more questions about carbs or just getting better mileage in general, feel free to join that forum and ask. There's a lot of knowledge there and people are very helpful and friendly. There are some people that like quadrajets too and can give you tips on tuning yours if you don't get the Edelbrock. Quadrajets do have very small primaries and might very well be a good carb for economy. I just haven't had much luck tuning one. And don't worry about not knowing much about what you're asking if you do post questions....remember the only dumb question is one not asked. I'll bet you can increase your mpg to at least 17 or better.

I'm sure you'll get some more input here too. Good luck.