[2000jack]

I have a 29 Tudor that gets 8 mpg. It has a SBC 350 with Chevy Vortec heads (the truck type that supposed to be for better mileage). I have, everything less than 2000 miles on it, new gas tank, lines, gas filters (two), gas cap, K&N air filter, properly functioning thermostat. No apparent fuel leaks, I go into the garage after 4 or 5 days and I smell nothing. Fuel pump less than 2500 miles Choke works fine. Idles good. A new out the box Holley in which I dropped the jets from I believe was 65 to 63. The Holley tech did not recommend to go any lower. I have it timed at 8 degrees advanced. The exhaust pipes are black carbon. Some one suggested that I get a new power valve with the lowest amount of Hg, but I see that the go from 10.5 Hg to 1 Hg on Summit. What is a good street number and how do these things work?

[454C10]

read this.

http://www.corvette-restoration.com/.../Timing101.pdf

[454C10]

and this.

http://www.bob2000.com/carb.htm

[454C10]

8mpg in the city or highway?

what is the curb weight?

what gears and transmission type?

the cam determines the right power valve.

bigger cams require smaller numbered power valves.

the higher the the number the sooner it comes on.

a mild cam will run snappy with a 8.5 but will get better city mpg with a 6.5.

a mild small block should get 10 city/16 highway with a 3.08 gear and th350 trans in a 3800 pound ride.

[2000jack]

Originally Posted by 454C10

8mpg in the city or highway?
Ans. [I]Not much City where I am so it is backl roads and highway[/I]
what is the curb weight?
Ans. around 3200 pounds

what gears and transmission type?
Ans. 2.92 & TH350
the cam determines the right power valve.

bigger cams require smaller numbered power valves.

the higher the the number the sooner it comes on.

a mild cam will run snappy with a 8.5 but will get better city mpg with a 6.5.

a mild small block should get 10 city/16 highway with a 3.08 gear and th350 trans in a 3800 pound ride.

These are the numbers I would love to have

[ericnova72]

Need to tell us what cam, compression ratio, rear gears, are you using the vacuum advance??

Total mechanical advance you have, to go with your 8° initial??

[cobalt327]

X2, need the low-down on your combination.

There's a current THREAD that deals w/power valves (last couple pages) as well as other tuning parameters on a Holley carb. A search here will also get you a lot of info.

[2000jack]

Originally Posted by ericnova72

Need to tell us what cam, compression ratio, rear gears, are you using the vacuum advance??

Total mechanical advance you have, to go with your 8° initial??

I believe it is 25 so that it has a total of 33, not a total of 40 with the old style heads. I bought the motor as a new rebuilt from Phoenix Engine. I have the cam specsIntake 442 @288 and the exhaust 465 @298. Also they gave me @.50 lift 214 int. and 224 exhaust. Standard flat top pistons. 8 inch Ford rear with 2.92 gears. Standard HEI distributor.

[Hippie]

What Holley are you running?

I went from 7 MPG with a 15,000 mile 9 to 1 twenty over 318 with Edelbrock SP2P, 727 auto and 2.94 gears to 13 average in my '86 Dodge D150. The truck had a totally trashed 1850 600 on it when I took possession. I slowy got it up to 9 MPG with a good tune up, replacement of a defective fan clutch, hotter thermostat and repair of too many tiny vacuum leaks in the heater controls to count. I then replaced the 1850 with a fresh 6619 and with some jetting and addition of a two dtage power valve eeked 10.5 out of it. After about 3 months I replaced the Holley with a remanufactured Q-Jet I pulled off a '93 W-150 Cash for Clunkers victim in the boneyard and immediately picked up another 2.5 MPG. Over the course of all this my idle vacuum went from 15 to 23. I set the idle mixture on the Q-Jet and that has been it. I believe there's more to be squeezed out of it but I needed a break from it so for now I'm just enjoying my 85.7% mileage increase.

Just saw the post with your cam specs, that's not exactly a mileage/RV cam. You may not believe this but I think you're going to want a little lower gear. At highway speed you're probably not into the power curve, or "up on the cam" so the engine is lugging slightly. Lower RPM only helps mileage to a point, too low and it actually hurts mileage. Plus something to keep in mind is aero drag, a '29 isn't the most aerodynamic thing on the road. It may be light but it's pushing a lot of air at 60 MPH.

[2000jack]

Originally Posted by Hippie

What Holley are you running?

I went from 7 MPG with a 15,000 mile 9 to 1 twenty over 318 with Edelbrock SP2P, 727 auto and 2.94 gears to 13 average in my '86 Dodge D150. The truck had a totally trashed 1850 600 on it when I took possession. I slowy got it up to 9 MPG with a good tune up, replacement of a defective fan clutch, hotter thermostat and repair of too many tiny vacuum leaks in the heater controls to count. I then replaced the 1850 with a fresh 6619 and with some jetting and addition of a two dtage power valve eeked 10.5 out of it. After about 3 months I replaced the Holley with a remanufactured Q-Jet I pulled off a '93 W-150 Cash for Clunkers victim in the boneyard and immediately picked up another 2.5 MPG. Over the course of all this my idle vacuum went from 15 to 23. I set the idle mixture on the Q-Jet and that has been it. I believe there's more to be squeezed out of it but I needed a break from it so for now I'm just enjoying my 85.7% mileage increase.

It is a 600CFM non adjustable float 4 barrels. I have to go to storage to get the exact number.

[454C10]

yes, not a gas mileage cam. and too much cam for the gear ratio.

need more initial timing with that cam. try putting the vacuum advance on a manifold source. should have 8 mechanical plus another 15 to 20 from the vacuum advance at idle. so that makes 23 to 28 at idle.

I would reduce the total amount of mechanical advance in the distributor so you can run more initial.

[2000jack]

Originally Posted by 454C10

yes, not a gas mileage cam. and too much cam for the gear ratio.

need more initial timing with that cam. try putting the vacuum advance on a manifold source. should have 8 mechanical plus another 15 to 20 from the vacuum advance at idle. so that makes 23 to 28 at idle.

I would reduce the total amount of mechanical advance in the distributor so you can run more initial.

If I understand you correctly, you believe that the valves are staying open too long at low rpm so that the some of the gas is flowing out the exhaust before it has a chance to fire?

[454C10]

bigger cams need more timing at idle. more timing allows for a leaner mixture.

furthermore, a cam that big also requires more rpm at idle and more throttle opening. this causes the carb to idle past the transition slots which make it run very rich at idle. more timing will increase idle speed and allow the throttle blades to be closed more and operate in the idle circuit.

did you read the 2 links I posted at the start of this thread? It is all in there.

[454C10]

"An engine with a performance camshaft will also respond well to more initial timing because, at lower engine speeds, the air velocities are reduced due to valve overlap and the air/fuel mixture is poor. Therefore, advancing the initial timing provides longer time for this poorer mixture to burn in the cylinder"

quote from a engine tuning web site.

[ericnova72]

First step, you need to get the initial timing up to around 15-20° initial. You are going to have to modify the distributors advance limit slot under the mechanical advance mechanism due to the fact that you need to keep the total below 40°.

Common mod for those of use that do performance on a regular basis, but it sure does seem to throw people a curve ball when you tell them they will have to dissassemble the distributor and modify it, that there isn't some bolt-on solution.

Well, there is one bolt-on solution...a $300 MSD Billet Distributor that is fully adjustable.