350ci Chevy Help

[ALAN GEDDES]

Bought a sweet 81 Chevy shortbed stepside with a 350 with quadrajet, headers etcetra. 3 speed auto trans. Sucks gas like a shop vac. What can I do to help with mpg ? Regear rearend ? 700r4? tranny, change carb ? Suggestions please as I have no experience with these things. It's a low mileage stock rebuilt engine. Friend offered a new 600cfm edelbrock carb to replace old quadrajet but I don't know if that would help or not. I'm getting 10 - 11 mpg around town and keeping my foot out of it. Is that the best I can expect? But the tear sure does look good behind it and I can carry firewood and stuff.

[purplepickup]

It depends on how much money you want to spend. To keep it cheap I'd definitely take the Edelbrock and get rid of the quadrajet. You'll probably need an adapter to bolt the edelbrock on but it would be better to get an aluminum intake. The basic Edelbrock performer is good and if you don't want to spend that much Holley and Wieand are good. There are some chinese Edelbrock knockoffs that are less than $100 and they're better than the stock one too. Maybe a set of headers and make sure it's tuned properly and you should get 17+mpg.

If I were you, before I changed rear ends (unless the gears are extremely low) I'd look into getting a 700R 4speed overdrive tranny if you still want to spend more money. That way you'll still have the gears to haul wood and tow but you'll have the low rpms for cruising.

My pickup is over 400 hp and it gets 20+mpg on trips with the cruise set at 70. It weighs over 3500 lbs with me in it. I don't have overdrive but when I built the engine I knew what I wanted and matched the parts to make it very efficient.

[SteveH]

Allen,

In '81 the manufactures had a hard time making the smog numbers mandated by Washington, and they had not installed computers that were worth a flip yet.

I agree with George on the carb swap. The Edelbrock 600 is a good carb as long as it is the electric choke model. The manual choke model is jetted for horsepower, and the electric choke model is jetted for economy.

The stock manifold is also not good. It is the EGR model....recycles exhaust gas back into the intake to help with emissions, but hurts power and mileage.

The main thing that really hurt performance and milage back then was tuning. The easy thing to fix is ignition timing. I would get an adjustable vacume advance unit. Set it for no more than 10 degrees of vacume advance and then adjust the timing so you get 35 degree advance with cyntrifical advance fully advanced and vacume disconnected.

The hard thing to fix is the cam timing. Back in those years they retarded the cam timing also for emissions. To fix that, you need to take the timing chain cover off and I would replace the timing chain set with a double roller set and advance the cam timing 4 degrees.

With all of these things done, you will have lots more power AND get better fuel mileage.

[ALAN GEDDES]

Thanks for the input guys. Is the 700r4 a direct swap ? The carb my friend offered is the electric choke version. It was too small for his engine and he only used it for about 30 minutes and went to a 750cfm. I know what he paid for it and can get it for almost nothing.

[purplepickup]

Thanks for the input guys. Is the 700r4 a direct swap ? The carb my friend offered is the electric choke version. It was too small for his engine and he only used it for about 30 minutes and went to a 750cfm. I know what he paid for it and can get it for almost nothing.

No, the tranny swap isn't a direct bolt in. If you have a 350 tranny it's shorter and the crossmember will need to be modified. Then there's the differences in 700R4's throughout the years. Personally, I don't think it would be worth the trouble unless you're going to do a lot of highway miles. If you still want to swap trannys I can help get you some answers.

If you do what Steve suggested you probably will see some big improvements. If the guy with the carb has the manual, make sure you get it. It has an easy to follow tuning matrix type chart if needed. It's available online too http://www.edelbrock.com/automotive/eps_intro.html . Edelbrock carbs are very easy to tune. Any changes you might need can simply be made by changing metering rods and/or springs and that only requires removing two screws while the carb is still bolted on. I've had a lot of experience tuning so PM me if you might need something.

[Woody]

700r transmisions with overdrive are not built strong enough for towing in overdrive, since they can get very hot. 400 turbo hydromatic is the animal for hauling. I had to install coolers and was told by a transmission guy that rebuilt my 700r with overdrive stock models need to be beefed up alittle to accomodate the additional strain of highway towing and not to tow in overdrive period, but in drive. They were made and installed for fuel economy and not built for heavy towing capability like a 350 and 400 turbohydromatics. It all made sense to me, when they cracked the case and I looked inside. Hope this helps

[SteveH]

Allen,

I agree with everyone on the 700r4. It's not built for towing in OD, the rear crossmember will have to be moved, and the drive shaft will have to be shortened. B&M makes a speedometer cable driven switch that you would have to install to get the lockup torque converter to lockup.

I've put one in one of my street rods, and it works good there, but I don't tow with it.

You would probably never recoupe the money spent for the conversion in fuel savings.

[ALAN GEDDES]

Thanks for the input. I will go ahead with the carb first and see if that helps. Did some on line checking and don't see how the tranny change would save me much when you figure in the cost of it and the mods required. Good thing it isn't going to get used a whole lot.

[bg]

I have an 84 with a 305 and a 700r4 tranny. Mileage is around 19 on the highways.

The 700r4 is a mostly direct swap. You should have a TH-350c with a 9" tailshaft, making a 700 a almost painless bolt in. The cooler lines have to be 'adjusted' a little and a crossmember from a 87 with a 700r4 makes things somewhat easier. You'll need a tv-cable and dipstick tube matched to the 700.

My total for swapping the 700 in came to just under $1000, but the old 350 had died anyway. My transmission came from someone in NC, if you want to go that route, shoot me a PM and i'll give you the contact info.