Any suggestions?

[Govern]

I know it's been touch on a lot but I'm getting stumped.. Having poop fuel economy 8mpg tops. That's w a very light foot. This is what I have done to improve the issue but it still occurs

1 new msd dis
2 new wires
3 plugs gapped at 40
4 sealed all vac leaks
5 new edelbrock 600 tuned w vac gauge
6 new air filter
7 initial timming is at 12 advanced
8 vacume gauge reads 20-21hg at idle which I think is really great for a old 350
9 bfg tires inflated to 30 psi 35"
10 456 gears
11 700r4 trans

Reading on here people w similar combos are reporting closer to 12-14 mph and tips? Am I missing something

[dieseldawg142]

gears-4:56's are not for mpg's, even with a od, be thankful you have that, i got a t400 with 4:56's & 38's. turns at 31-3200 at 55mph-maybe 5mpg's if i'm lucky.
personally i would throw 3:73's in it. some will say 4:10's, but for the expense of regearing, your not going to see a big increase in your mpg's.
i ran 35's on my k5 with 3:73's, more than enuff power, but still reasonable on fuel

[Govern]

I think 456 w 35"a and and overdrive is a nice combo only turning 1700 rpm at 60 mph.. You would expect that to yield better mpg

[dieseldawg142]

yeah, thats pretty reasonable rpm's.
brakes are'nt dragging?
maybe put synthetics in your axles, t-case, etc
i have 33's on my stepper with 3:73's & run the tires at 35 psi (BF M/T's) & manage about 15 on the freeway,12-13 in town (350 tbi), so i dont think you will get huge changes, but yes, it would be nice to bring that 8 up to 12 or so

[Govern]

O yea if I could go from 8 to 12 id be ecstatic. Brakes are fine fluid in diff is new not sure if synthetic tho. I'm not a huge fan of the tires they r alittle noisy but when u are coasting at a high speed it doesn't drop down in speed very fast like some other nobby tires..

[Govern]

I plan to buy a set of summit headers, x pipe and 2.25 pipe do you think they would help the economy much?? Currently it has manifolds and cherry bombs

[dieseldawg142]

Originally Posted by Govern

I plan to buy a set of summit headers, x pipe and 2.25 pipe do you think they would help the economy much?? Currently it has manifolds and cherry bombs

might get a small increase, but most likely you will blow that playing with your throttle listening to them new headers!

[Govern]

Haha good point. Really the truck rarely goes over 2300 rpm so would headers really even come in to play? Aren't they more top end ?

[donut]

New distributor with 12* initial. Total? When does it start? All in?

Initial is a starting point. Ideally 32-36* by about 3000rpm, then see where the initial lands. I would imagine MSD is close to what you want, not like cheap e-bay unit that didn't start advancing until about 1800 rpm. (there is a good sticky in the engine and drivetrain FAQ on playing with advance curves. sbc ignition timing iirc)

My K-20, an x-pipe wouldn't work. ended up with H-pipe. (transfer case...)

[Govern]

12 initial, never checked the total. Instructions seemed like you set the initial and waalaa your good. Did you just solve my problem? Do I need timing tape to set the total timing currently it just has the little metal comb looking thing

[donut]

http://67-72chevytrucks.com/vboard/s...d.php?t=290498 Start reading. I use a timing tape and standard timing light. Many folks use a dial-back light.

This may or may not help, for all I know your MSD already has a good curve. Were there any instructions?
Chinese dizzy benefited greatly from this, drive ability greatly improved. Stock HEI in the C-30 hasn't been checked yet, though PO did throw in initial advance.

I honestly don't know if I solved your problem, but it's something you haven't looked at yet. It's actually a combination of little things that add up.

[piecesparts]

#1, Check the type of drivng that you do. All Highway, all city, mixed
#2, Check timing with a timing light that has advance capability to ge the total timing
#3, How much effort do you expend to get up to speed---tire combo calcs
#4, Are you positive the carb is set to the optimum jet settings or are you running rich
#6 inflate the tires just a little more to go to 37 to 38 psi