i need gas mileage!!!

[tssievert]

i have a 350 with the small valve heads, they were the smallest valves listed, i don't remember the numbers.  it is in a 79 full size truck, i have a 3 speed auto (th350) 307 rear gears and i can't get better than 11 mpg. do i need to get different heads? carb? what? if i can't get this to work, i do have a chance to trade the combo off for a 4.3 with a 5 speed out of a 93 full size. how hard would it be to install that?
thanks for the help
troy

[roundedline]

The 4.3L isn't going to get much better mileage to warrant the swap.  You should be able to get close to about 15mpg.  Is the 11 you are getting average mileage?  Do you do alot of short trips?

What kind of carb are you using now?
What is the current state of the motor?  rebuilt, original
what is the current state of tune for the motor?

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project

[Lt.Del]

As Chris mentioned, more  info would be great.  But if your engine is original, 11 mpg should be about it depending on the mileage (of the engine).  I have a full size 79 big 10.  Before I put new stuff in it, it was a 350 w/ a th350 and that was the mileage i was getting. I threw in a new 383 engine and a th350c transmission (w/ the lock up torque feature) and new edelbrock qjet carb.  I can now get about 15-16 mpg on the interstate (w/ the converter locked) and about 12 mpg in town driving.  I have the same rear end as yours, which is kind of high...great for interstate, bad for city driving.

I would check all your vacuum lines to ensure no leaks which rob mileage.  You have a lot of vacuum lines if all stock.  

SgtDel    

Edited by: SgtDel at: 1/31/06 3:47 pm

[tssievert]

the engine has recently been rebuilt. the heads are new and everything is within spec. the reason i suspect the heads is that i got 11 before the rebuild and 11 after. the heads i purchased have the exact same size valves. the carb is just a reman qjet (bought a new one during rebuild) there are no vacuum leaks.  timing is set per specs.  the only reason i have questions is that i heard somewhere that the small valves meant crappy mileage. soooooooooooo will the big valves get me better mileage?  SgtDel.. what size valves were on your original compared to your 383?  oh btw that 11 is 60mph on the 40 mile highway trip to and from work

[Lt.Del]

I found an engine builder out in Arizona (I am in Va.) via the internet and I liked his packages and price. I ordered his 383 engine but wanted the 4 bolt main and an RV cam for torque at the lower RPM's, especially due to the higher rear gear I have.  Here are the specs of the engine.  With about 335hp and over 400 ft lbs of torque, this is all I need.

That 11mpg on the highway is really bad w/ your rear gear.  You have to get single digits in the city.

The valves on the original 350 were the small ones, I believe. I haven't opened her up yet.  Still trying to figure out what I am gonna do w/ it.

SgtDel

383 stroker  

Edited by: SgtDel at: 1/31/06 7:23 pm

[ChevyGuy]

What rearend gears do you have and what kind of transmission do you have?

[ChevyGuy]

Sorry I was sleeping there you already posted that. What are the casting numbers of your heads? What kinda stuff you have on your motor as far as ignition, intake, etc? Bigger valves will help depending on what your combination is in heads and cam.  

[tssievert]

what would it take to install a 700r4 and is the price worth it.  also what about TBI?

Edited by: tssievert at: 2/1/06 5:56 pm

[1976Scottsdale]

TBI is okay, but there is some work involved.  As far as a 700r4, I think someone posted how to "home bake" your own lockup kit for less than what Jegs and summit get.  Other than that, you will need to move you transmission crossmember and change driveling length, not too bad.

For the record, My 78 that decided to buckle a piston had a 400 hp built 327 bored 30 with a hopped up cam and it got about 10-13 on the highway with 3.07 lockers front and rear got around 3-5 in town, a converted np203, a th350, and 31.4 inch tires on 89 octane gas with and edelbrock 1406 600cfm e-choke on a gm iron manifold.  New engine will be a 350 with a rv cam, 750 Q-jet with hot air choke, 53cc heads, Street Dominator intake, 1 3/4" headers and 2.5" pipes w/ flowmaster 40's.  Ought to get maybe 2.  

Edited by: 1976Scottsdale at: 2/3/06 8:59 pm

[shaved80]

gas mileage? what's that?