So I burned my first tank of gas on this new engine and I'm only getting 14 MPG. That is 95% 70 MPH interstate driving. What I can do to improve my mileage? Holley 850 CFM 4150 Carburetor 68 Primary Jets, I think a 5.5 Power Valve. (It desperately needs higher power valve, Engine Begs for more fuel under load on the interstate) Timing 34* All in under 2000 10* Vacuum Advance Could the incorrect power valve make my mileage suffer?
Gotta ask, why an 850 DP on only a 350 with automatic and only a 3.42 gear? Are you planning on spining 8000rpm? Poor airflow thru the carb (cuz it's too big IMO) means poor atomization, larger droplets, less mileage and efficiency. And BTW too much timing too quickly isn't good either.
He has a 2004R, so the 3.42's become 2.29's. Holleys were never known for mileage, especially the DP's. I think a good Q-jet is in order, but Cason will never go for that, or an MSD:laugh:
If your looking for economy, a holly carb shouldn't be you first choice,let alone and 850 cfm. Sounds like WAY to much carb for a 350 unless you plan on turning about 8000 rpm. Q-jet it!!
A Holley 850 double pumper and your surprised your not getting good gas mileage? They arent exactly known for economy. The mileage problem is a result of the mechanical secondaries. I bet you would see an improvement with a 0-3310 750 vacuum secondary if your dead set on a Holley. Or you can just put a Q-Jet on it and have the best of both worlds. A well built Q-Jet is awesome. Ask Chris Gullo (v8sky) how nice my Q-Jet ran on his 72 convertible.
It's in your secondaries...Stop looking for it so hard with your right foot:moonu: I do have to agree though, back the timing to stock spec, put a q-jet on it, and drive like grandpa if you want mileage. Otherwise flog it and be happy with 14-15mpg.
Or you can just put a Q-Jet on it and have the best of both worlds. A well built Q-Jet is awesome. Ask Chris Gullo (v8sky) how nice my Q-Jet ran on his 72 convertible.[/QUOTE] >>Yep, Jason said it - it did wonders for my engine! I now have one of Ken's (tech8) rebuilt Q-Jets which works beautifully as well on my 350.
What kind of fuel pump are you using? Also, I agree with the Q-jet suggestion. Check out Sean Murphy Induction's website: http://www.smicarburetor.com/ His Stage II Q-jet would be perfect for you (he even has a BOP-specific model), and "only" around $360-$380. A lot of racers swear by his Q-jets. Since you apparently have enough funds to attend a university AND build a muscle car, I'm going to assume that you're not a "starving student", and that the >$400 price of one of their Q-jets wouldn't break your bank... (I'm only partly joking)p --Chris
Chris- Ive been going through some forgotten parts I had and guess what? I found not one, but two 72 350 Q-Jet cores yesterday. ou: Im pretty sure they're 7042240's. Left over from my 72 GS-350. Man, I miss tht car. Oh well, cant keep them all http://www.v8buick.com/showthread.php?t=125124&highlight=fun+drive
Are you still running the Burton intake? If you are that & the big Holley probably contribute to very low intake velocity at cruise speed. I'm guessing RPM at 70 is in the 1700 to 1900 range? The low intake velocity could cause poor atomization & poor fuel distribution. Also if you just rebuilt this engine it will pick up some mpg as it breaks in.
I like the 850 cfm carbs on hot 350s but not on stock ones. You will get the best milage with a 77 and newer Q jet with Adjustable Part Throttle mixture. The Q jet is the best carb for fuel milage in my opinion. I know you have to set up the TV cable for your 200r4 trans but keep in mind there are q jets that come on 307 olds engines that have the linkage for the TV cable... There are also aftermarket kits to hookup the TV cable on any q jet or you can modify it your self.
What shape is your suspension in? Have you had an alignment recently? Repack the wheel bearings (or replace w/new)? What size/type rims/tires are you running? Brakes dragging? These are a few things to look at also that might be robbing your fuel efficiency as well.
