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S.B.Chevy Q-Jet base plate & intake modifacations for Gas Mileage?

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Cliff Ruggles:
For best fuel economy, use a vacuum advance.  How much timing to add with it depends on the total engine combination.  Typically, the more efficient the engine, the less timing will be needed.

You only need to add the timing at light load/light throttle for most applications, so we concur with using a well located ported source to operate the advance.

There are a LOT of folks who will debate the source of the advance, MANIFOLD vs PORTED.  Most don't have a clue as to how the advance works in the first place, the rest are trying to "crutch" a lean idle problem with too much initial timing.

In any case, an engine like yours with good heads, decent compression ratio and small cam will like about 10-15 degrees from the vacuum unit at cruise. 

From the testing I've done, this will improve fuel economy a couple of MPG's, and maybe more if you get an adjustable unit and play around with exactly how much to add over a few tankfuls of fuel.....Cliff

AHotRod:

--- Quote from: omaha on January 11, 2011, 10:05:41 PM ---I'll bet you pick up 5 mpg with a vacuum advance. Is there room for an HEI?

--- End quote ---

+5 MPG with a vacuum advance?  I hope your right, I'll add that to my "To get done list " ASAP  8)

No, I don't have room for a HEI, I currently have a old GM Tach drive distributor that I converted with a Chrysler relucter wheel and magnetic pickup years ago and it's fired by a Jacobs Ignition system. It's at full advance by 1600 RPM now, so I'm not certain on how a vacuum advance is going to improve it.  '

I must be missing something here .....  ???

Glenn

AHotRod:

--- Quote from: Cliff Ruggles on January 12, 2011, 05:34:25 AM ---For best fuel economy, use a vacuum advance. 
From the testing I've done, this will improve fuel economy a couple of MPG's, and maybe more if you get an adjustable unit and play around with exactly how much to add over a few tankfuls of fuel.....Cliff

--- End quote ---

Cliff,
Since the Coupe is buring up a 1/2 tank each day, I have to re-fill everyday, so I've got a record chart that I carry in the car that I record the mileage and gallons every night.

Currently it varies from 11.55 - 12.79 MPG each day  :'(

Glenn

Cliff Ruggles:
Lots of room for improvement, IMHO.

Last time I checked the Ventura with the old 514hp 455 cid engine, it was 11-13 mpg's for "normal" driving, not highway driving.

It still goes up near 180 miles or so on 14-15 gallons of fuel, but it's difficult, if not near IMPOSSIBLE to go thru an entire tank with an engine making near 600hp and not do a few FULL THROTTLE BLASTS!

I would think the little SBC can get over 15 mpg's in a much lighter vehicle when you get it all ironed out?......Cliff

1985C10:
I love your little Model A.  Have you considered a 700R4 for improved fuel economy?  With a well tuned mild engine, Q-jet, and OD trans you should be able to hit 20 mpg easy in something that light.

Also something else occurred to me about our combination.  Your 200cc heads, while excellent performers, cut valuable intake velocity by having too big a cross sectional area for such a mild engine.  I bet something like L31 vortec heads would help low-end and mid-range torque considerably.  Obviously you are already invested in those heads, so if the budget is a constraint at all, it probably wouldn't be worth changing.  But I'd bet that move would net you a gain in mpg.  I'm no expert, it's just a thought.

Good luck with this endeavor.  Please report back with your results.

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