better gas mileage

[janderson]

i have a 66 c10 with a small block 305 4 barreled carb hi rise intake, 350 turbo tranny with overdrive, and 4:10 geared rear end it changes gears pretty fast so it would get in to overdrive fast was my thought but anybody have something similar they can tell me the gas millage on. Also anyway to make it get better gas mileage cheaply.

thanks justin

[Rich 5150 69]

What is your carb and intake manifold.

[pmkrew]

Tire height may help also, and it will depend on how you want to drive ie; highways or byways...

[janderson]

holly 660 carb, i don't know the brand of the intake but it is high preformance and high rise intake.

[pmkrew]

that's alot of carb for a 305...

[jocko]

agree with pmkrew. 660 seems like a bit too much. isn't 660 a center-squirter? Seems a 600 or even a 450 would be sufficient (if you're concerned with mileage). Just my 2 cents (worth about a penny).

You mentioned an overdrive. What kind/type, etc? Gear Vendors u/o?

[janderson]

the man i bought this truck from was trying to make it a street legal drag truck and yes it is too much it isnt adjusted just right and it floods out easily. but i am only 17 and trying to fix the truck to make me through high school so it was cheaper to use what was on it.
don't know the gear vendors on the transmission just that it is a 350 turbomatic with an overdrive.

[blackmopar]

'gear vendors' is the name of the company - not, 'what gear vendor did you use'

a gear vendor brand over/under splits each gear - so if you have a 3spd auto - you get 6, and so on.

i didnt know a th350 had an overdrive option - i thought that was a th400. but if im wrong id love to know more about it

[blackmopar]

i must be missing something here - unles thers something radically done to this 305 that we dont know about - the 660 is certainly too much carb and im guessing the high rise intake is a single plane - youre 17 - you know computers better than any of us - sell both on craigslist and grab a mild dual plane with a holley 1850 - youll be MUCH happier and pass a couple gas stations that you used to have to stop at to boot

[65Guy]

Turbo 350 and 400 are both 3 speed non overdrive trannys!

[janderson]

ok so i am wrong on the overdrive not much experience in mechanics. It may help to know that the 305 has a competion cam and is a high compression engine. the man i bought it from told me this and he was a mechanic. If i was going to sell that motor and get another what would yall suggest.

[65Guy]

just because the guy was a mech. It doesnt mean jack. Un less you tare the engine down you wont know what you have, just my .02.

[janderson]

thats true but i have to go on what he said because i don't really want to tear the engine down.

[jocko]

janderson,
no worries - you've come to the right place for help. Now that you've given us a little more info, maybe this will help.

65guy is correct - the TH350 and TH400 are 3 speed automatics that are non-overdrive (i.e. their 3rd gear ratio is 1:1). An "overdrive transmission" (in other words, the "overdrive" is built into the transmission itself) has a top gear ratio that is less than 1:1 (like .64:1, etc) so that the engine turns less rpm for a given speed on the highway compared to a non-overdrive trans. An "overdrive" (stand-alone unit - the "Gear Vendors" thing I mentioned) is something you bolt onto the back end of a non-overdrive transmission to get some of the advantage of an overdrive as well as split the gears of the automatic trans. "Splitting Gears" means that the overdrive unit you bolt onto the trans actually provides a high and low for each gear - so a 3-speed TH350 becomes a 6-speed, a 700R4 essentially becomes an 8-speed, etc etc.

Enough on that. In YOUR case - if the mechanic knew enough to tell you it had a TH350 trans - recommend you look under the truck and see if there's a mechanical chunk of metal bolted between the end of transmission and before the driveshaft. That is where an "overdrive" would be mounted if it's external (like a Gear Vendors unit). If it's not there, you may want to give your "mechanic" a holler, he may have stiffed you.

When I look at your setup - the 4.10 rearend is what jumps out at me as your main fuel mileage killer. You probably can't afford a lower (numerical) gear right now, so I'll skip over that. If you have a friend with a 3.55 or 3.42 or 3.anything laying around, mow his grass or wash his car until he lets you have it....

As for a hi compression 305, that's a bit of an oddity - not many folks hot rod the 305. Not that it can't be done. But generally speaking, you'd get better performance for the buck with a 350 and a Holley 600 carb or Edelbrock Performer.

Having said that - understand you are trying to work with what you've got since $ are tight - so I'd have to agree with blackmopar - your best, most cost-effective improvement is to sell the 660/manifold combo and go with a dual plane intake and Holley 600 (or even a 450). Since you mentioned the mechanic said it's got a big cam or something like that, you' really ought to get an appropriate cam grind for very mild street use also. I know the money is adding up, but keeping a wild cam in a toned-down 305 will not give you the results you are looking for. Summit Racing Equip offers very inexpensive upgrade kits to do all that and you could recoup much/some of the cost by selling the carb/intak combo you currently have - some racer somewhere will want it. Understand money is tight, so that is probably the cheapest way to approach this.

If you were rolling in bucks, a REAL ovedrive transmission would be the ticket (700R4 is a good option) but I am sure that's beyond the wallet. I know it was when I was 17!! It still is! So, bottom line, I think you could see a decent improvement in gas mileage and, more importantl, probably an increase in perf and driveability with the above swap. If you can not drive the car while you sell the old stuff then get the new stuff, great, otherwise you'll need to buy first then sell the old stuff to recoup some of the expenses and swap it all in the driveway on the weekend so you can keep driving it to school during the week.

Ah, the good ol days. Keep up the good work!
(and if you don't find an overdrive behind your transmission, go kick your mechanic in the shin).
jocko

[blackmopar]

my bad on the 400 - i know better just mispoke - i am thinking he might have a 700r4 behind the 305........? thats the only practical thing i can think of whats going on without seeing pics, yea?

or do you have a big ol chunk of metal bolted where your tailshaft would be- that looks like this? its the GV over/under unit for a th350


i cant imagine someone would throw 2500 bucks at that behind a 305 but that sjust me i spose

[janderson]

i don't think it has a external over drive but the man never told me it had overdrive i just assumed.It sould be a 350 turbo i put a filter kit in it for a 350. To help clarify things this truck had a 350 in it with that transmission and rear end. the mans son was scared of the dark and his son was driving home one night when it began to run hot but he kept driving because he didn't want to pull over. So he blew the motor up, they built this motor and put in it. after about 5,000 miles the leaky holly caught fire and burnt the distributer and plug wires up. the man left it sitting for ten years when i found it and bought it.
Changing the carb and intake will definitely be on my list so maybe i can afford to put some gas in it.

thanks for all the help

[pmkrew]

Here is my take on this scenario...
Nothing wrong with a well built 305, I had plenty of friends with them in camaro's and trans ams in the 90's that ran plenty respectable and theyre good engines if taken care of (not run hot).
The carb is flooding your engine out; you need to do some tuning on it or replace it with a 550 HOLLEY if you can get one. Dual plane or single plane, I doubt you'll see much difference in fuel economy but a dual plane will provide a little more feeling in the seat on a smaller cid engine on the bottom end. Maybe try craigslist in your area and relist your stuff, OR that carb is popular and good so I would hang on to it for another day (bigger engine).
You could also try for fuel economy to disconnect the rear throttle blades or adjust them to come in real late (further toward the floor) to help with the heavy foot syndrome (you are 17, I remember those days). I would try to change your jets, squirters and power valves (if equipped) down a couple sizes to help with the flooding. (There is a member here ( ON 67-72 FORUM) that specializes in holleys maybe he could offer some guidance)
Check your floats and fuel pressure and make sure it's about 7psi if your using an aftermarket pump.
Your "mechanic" may have been mistaken when calling your th350 a "overdrive" it is probably a "lock up" type transmission which means the torque convetor is designed to lock up for fuel economy instead of allowing any slippage at cruising speeds. Kind of an overdrive but not really. Reference your trans pan design (shape) and make sure it is a th350 and if it is a lockup it should have some electrical coming off of it or an empty plug where it should be hooked up.

Figure out what you have for sure and work from there.
Good luck! And remember we all pretty much started where you are today...

[blackmopar]

agree with PMkrew - you dont need to sh*tcan the 305 - its fine - just not set up right - my buddy ran a 305 in his 68 camino (lb for lb dont think much lighter than our c10s really) and it was fun! not mugh torque but a powerglide held in 1st got booby attentnion whereve we went - n lets be real - at 17 thats what were trying to accompish here (hell at 37 thats what im still tryin to accomplish)

best advice so far - lets TRULY id what you have - im still kinda skeptical at what this mechanic sold you - if you cant alone - post pics here and we'll help ya!

[TwoFiftyShifter]

Yeah man, keep your motor and sell your intake and carb setup for something more economical. Without knowing the cam and compression specs of that 305, a smaller carb may even.help performance too.

Jocko, nice work on that post I was just about to explain that whole thing so you saved me a few mins!

[janderson]

once again thanks and i was confused on the transmission it is just a regular 350 turbo. As to the motor i agree i have driven it and like the 305, can i put a intake and carburetor on it without changing the cam. There is a man in my town that has a large junk yard of cars and trucks. I think he has a early 60 c10 i don't know if it has a motor or tranny but i think i can trade him for a rear end and a carburetor and intake for a 67 mustang body i have here. And maybe have another project later to pictures this weekend.

[neto]

I wonder if a TBI fuel system can be adapted to it?

[Captainfab]

Not very easily if it has a 'cam' in it.

Originally Posted by neto

I wonder if a TBI fuel system can be adapted to it?

[astrochimp]

FWIW-
I am now getting 18.5 highway with my 63. 305, 3sp man, electric fan, 373 gears, 255/70/15 (heavy) tires. I have a early 70's factory intake and late 70's Q-jet.

In town, not so good- I drive about a mile and half to work, top speed 30, and because of the 10 deg temps have warm up time. My choke is not quite right, BUT- truck starts and runs on the 2nd crank even at -10 deg and sitting all weekend!!!! I will do some tuning on the choke when it is warm knowing it will start is worth a couple of mpg this winter.

David

TLDR- You can probably trade your intake and carb for a factory intake and q-jet, and should have a better running truck with better mpg.

[Rich 5150 69]

I agree with David, pull at least the holley off and go with an quadrajet if your looking for milage, retime your motor, (HEI if you don`t have one ) I get 18.5 with mine as well 350/350/373 gears, slightly less on freeway when spinning the motor at higher rpms, usally around 17.

[janderson]

that makes me feel a lot better I like my truck and want to be able to keep driving it. Can i put the intake and carb on there without a new cam.