So, I'm now getting a whopping 11.5 mpg average.
86 ta, 709r4, non lockup, 343 posi rear, 31" mud tires, carb non computer 355 just built. L98 heads, holley dual plane intake, holley 600 vac secondary, point type dizzy, headers with true dual straight pipes, and my timing set at 16* advance, full advance is in the area of 34*..
Stock non roller cam from an 83 truck.. runs like a mad ape!
just..good god, 11mpg average? Mostly highway..
could my lack of overdrive cause this?

I've got a v8 Mercedes that I average 22mpg with, I drive both the same way.. which is not aggressively.

 

I'm guessing you mean 700R4 and not 709r4.
a 700R4 is a overdrive trans. The rear should be a 3.42, (my guess is 3.23), 3.08 2.73 or? Unless it was swapped.
Sounds a little low but 31" mud tires really?

 

Yes, droid RAZR M keyboards just suck haha.
My torque converter lockup isn't hooked up, it was originally a tpi car and trans was blown. Removed all computer junk and put in new trans, haven't hooked up a lock up yet.

Yep, 3:42. Again, crappy keyboard. Yes, its an off road vehicle, soon to be lifted 8". As of now though, stock suspension.

Running 9.2:1 CR on 87 octane, with 75 jets and a 6.5 PV. My jets might be a little big.. threw em on the 305 before I swapped it just to have some fun haha

 

Yeah, with that computer junk, lockup and the TPI you would be getting well over 20mpg. (I got 27mpg mildly modded back in the day)

My TPI computer junk is now running a 4??ci miniram SBC untuned and getting 22mpg. (making 650hp plus)

Carbs can work well but they take more work than most people want to put in them.

 

Aint she just a beauty?




More info, there's no ac either. Plugs gapped at... .025 if I remember correct, point gap at .019 with new points, wires, condenser, cap..

 

Nothing against tpi and such, I just got the Car for $600 with 36k original miles from a kid who butchered the hell out of it..was no saving that.. cheapest option was to go carb, plus I like/prefer carb's.

With my motor setup, even with 31" mudders, driving conservative, 11mpg avg sounds..waaay low..

 

Ummm....yeah. It's like a train wreck, you know it's going to be ugly, but you just have to look.

 

POINTS AND CONDENSER? WTF is wrong with you? You have gone backwards in everyway you possibly could !!!

 

Tried vacuum advance one wire HEI. They are CURSED for me.
I blew 8 coils and modules in 2 months, running the same ignition as I currently am. Went to point type, has ran like a beauty ever since.
Haha yes its a ******* rocket. She doesn't win any beauty contests, thats for sure. Was a rust free 36k original mile tpi trans am

 

30 years of driving GM HEI cars and trucks and I had one ICM go out and that's it. They aren't as problematic as you may believe.

 

That may be true, but for me, they're cursed. Tried an accel one, multitude of different coils and modules, was getting 13v at coil with a perfect ground, still kept blowing em. Yet never tripped the 10a fuse always used Arctic Silver thermal paste, good ground strap internally.. they would work great for a bit, then jus blow without warning.

 

36k miles and rust free...so how was it butchered? I'm just wondering.

The 31" tires are what is killing you, that and probably your carb tune.

 

For example: I have a 27" tire, a 750 double pumper holley (it looooooves fuel) and still get 14 driving it "spiritedly" lol

 

 

How do you have the stacks/exhaust hung? just curious. Looks like it would flop around quite a bit.

 

The electronics were FUBAR. ecu shot, half the harness looks like a high school kid hacked at it, the maf was shot, 5 injectors were seized, and the harness was a joke at best. Example, turning it over would roll the windows down and pop the hatch. To this day, with my headlights on, my left blinker doesn't work, yet with em off it does.
Transmission kinda had first and reverse if ya sweet talked it and got it in the mood..
The only thing it had going for it was new seats and carpet, posi disc rear, and rust free.

Not that I didn't wreck it, I did and I know it.


And where my stacks make a 90 behind the door, I bolted em to Tue body using two main caps from another SBC and some all thread, theyre actually pretty tight, aside from when the nuts on the collector occasionally wiggle loose.

Would simply having too large of jets cause this bad of mileage?
I'm running 75 jets, haven't had time to check my plugs to see what they looked like. I know when th3 305 was in, they were coooooovered in carbon. Looked like bed liner..

Power wise it runs like a mad ape, and doesn't blow any color of smoke or smell like gas.. carb only has a base tune/tuned by ear right now. Started at 1 1/4 turns on the idle screws and backed em out till it ran smoother. New needle and seat..recently rebuilt, manual choke always open..

 

That's pretty hilarious about the windows. I've been in cars with similar..."issues". haha.

Possibly but again, anything can be tuned down to run decent. If you have the time you can try sofa's holley tuning routine. I haven't done it, but alot of people have and swear by it.

https://www.thirdgen.org/forums/carb...ey-tuning.html

 

That didn't seem to help.
Didn't adjust transition slot, didn't have time, but took my 75 jets out, put in 70s, still running rich/blowing black smoke, popped in a 8.5 PV (highest local speed shop had), made it run worse, idle screws had no effect.

Popped a 6.5 back in, and dropped down to 66 jets, and it ran even worse. Blew enough black smoke to be confused for a diesel. Switched back to 70 jets, same PV, and it runs fine again, just still rich. On heavy throttle it'll blow black smoke, plus on startup.

Also, now if I quickly blip the throttle and let off, it dies. Doesn't matter the speed. Already adjusted my accelerator pump as well.
The 150 mile range really sucks. Especially working 20 miles away being my DD.