Author Topic: S.B.Chevy Q-Jet base plate & intake modifacations for Gas Mileage?  (Read 1487 times)

Offline AHotRod

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Cliff,
Last Wednesday I ordered a SR-Kit for a Q-Jet #17059203 which is a '79 Corvette 4-speed unit that I'll install on a factory GM aluminum Q-Jet intake manifold, which will go on my daily-driver Model A Coupe.

http://i267.photobucket.com/albums/ii283/LimeSqueezer/PurplePounder016.jpg[/img]]

When I ordered a bag full of parts from you to build a Q-Jet for my Chevy II Wagon a while back, I also bought your book which you autographed for me, Thank You.  Excellant book.

With gas prices continuing to go through the roof, I decided 2 weeks ago to change to a smaller camshaft, tighter torque convertor, Weiand dual plane intake, and all I had around that was ready to bolt on was a Barry Grant 650 Demon  >:( which produces 11-12 MPG each day on my 65 mile round trip to work.

http://i267.photobucket.com/albums/ii283/LimeSqueezer/SparkPlug001.jpg[/img]]

Since aftermarket dual-plane intake manifolds are seperated and sealed, I studied the GM intake and the bottom of the carb.

http://i267.photobucket.com/albums/ii283/LimeSqueezer/QJet001.jpg[/img]]

The areas that I point out are not allowing the intake or the Q-Jet to be totally sealed from side-to-side. My thoughts are to use Marine-Tex and fill these areas.

http://i267.photobucket.com/albums/ii283/LimeSqueezer/QJet005.jpg[/img]]

Here also ....

http://i267.photobucket.com/albums/ii283/LimeSqueezer/QJet004.jpg[/img]]

And here .....

http://i267.photobucket.com/albums/ii283/LimeSqueezer/QJet009.jpg[/img]]

And I planned on using the FelPro 1905 4-hole gasket shown here in the middle ....

http://i267.photobucket.com/albums/ii283/LimeSqueezer/QJet002.jpg[/img]]


Will this work? 

Should I build this carb as stock? .... or follow one of your recipes.

Here is the run down on the Coupe:
Weight: 2530 w/driver
Rear gear: 3.55
Rear tires: 28" tall
Convertor: TCI - acts like stock
Engine: Chevy 355 
             9 - 1 compression ratio
             Hyd Roller - .462 Int. / .470 Exh. lift with 1.5 Roller Rockers
                                 210* "  /   215* "  duration @ .050
                                 Lobe Centerline - 110*
                                 68* overlap
             Vacuum @ idle - 17.5 "
             World Sportsman II heads w/2.020" int. valve / 1.600" exh. valve

The majority of my driving is between 50-60 MPH, or 2200-2700 RPM cruise speeds.

I really would appreciate your ideas, thoughts and comments before I recieve the kit from you so I can do this correctly.

Best regards,
Glenn










Offline Cliff Ruggles

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Re: S.B.Chevy Q-Jet base plate & intake modifacations for Gas Mileage?
« Reply #1 on: January 09, 2011, 07:21:52 AM »
I would not block the tranfer areas between each side.  I've never found any advantage anyplace doing this, and when I tested spacers a few years ago, the 4 hole spacer provided the worst results everyplace. 

It woln't hurt anything to let one side of the dual plane intake see the other side, and there may actually be a few benefits from allowing this to happen, much like adding an "H" or "X" pipe in the exhaust system ahead of the mufflers.  In the intake manifold specifically, the air to each cylinder stops for an instant when the intake valve closes, much like getting a door slammed in your face.  This puts little shock waves into the incoming air stream.  It may help distribution, and airflow to allow one side to see the other to minimize their negative effects.  I'm not sure about all this, but I do know it has an effect on power output, and may effect efficiency and fuel economy as well?

The dyno and dragstrip testing we did a few years ago with intakes/spacers showed more power and quicker ET with more MPH with a small cut-out between the secondaries.  We saw benefits as well with a semi-open spacer, solid across the front and open between the large secondaries.  This testing further supports letting one side see the other side.

Another thing not to do is remove the entire divider on dual plane intakes between both sides.  Right on the dyno we saw a BIG drop in mid-range power and torque doing this, with only a couple of additional HP at really high rpm's benefit.  Maybe too much of a good thing?

In any case, it's all about application, and the total combination of parts, etc.  Keep us posted on the testing, and the results.  You will find that the APT system in the carburetor will allow you to have full control of the A/F ratio at light load/part throttle.  With the triple venturi area in the carburetors primaries, the fuel milage will be considerably better than any Holley or Holley "clone" once you nail down the best setting(s)......Cliff

Offline AHotRod

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Re: S.B.Chevy Q-Jet base plate & intake modifacations for Gas Mileage?
« Reply #2 on: January 09, 2011, 02:00:31 PM »
Thanks for your reply Cliff,
Based on the information that I gave, should I follow recipe #1 on this carb for daily driving?
I'd preferr not to run a choke on the unit.

Also, I was planning on not blocking the heat crossover so as to heat the intake and achieve better atomosation which should yeild a increase in fuel economy.

Comments?


Glenn

Offline Cliff Ruggles

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Re: S.B.Chevy Q-Jet base plate & intake modifacations for Gas Mileage?
« Reply #3 on: January 10, 2011, 05:07:01 AM »
I don't have a choke on my own carb, for at least 15 year now, and don't even miss it.  If it sat outside in a snow drift and I used it in the Winter months, it would have a choke on it!

Good idea to leave the crossovers open.  This shortens warm up times considerably, and helps atomization of the incoming air/fuel charge.

Even with the crossovers blocked off or missing, the intake eventually heat soaks anyhow, just takes a LOT longer.

The heads on my new engine don't have crossovers in them at all, and it takes a LONG time for the engine to warm up in cool/cold weather.....Cliff

Offline omaha

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Re: S.B.Chevy Q-Jet base plate & intake modifacations for Gas Mileage?
« Reply #4 on: January 10, 2011, 11:48:54 AM »
I cant believe that fuel milage is that bad with a vehicle that weighs ~2600.  I would suggest keeping the crossover also. Id  run a 190 thermostadt, to see what might help. Q-jet and jetted correctly and correct curve in the distributor, I would think that you would get at least 16-18 (or more??) at that rpm.
Oh well, must be neet to have a daily driver like that, do you drive it in the rain too??  Nice ride!!

Offline AHotRod

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Re: S.B.Chevy Q-Jet base plate & intake modifacations for Gas Mileage?
« Reply #5 on: January 10, 2011, 06:18:24 PM »
I do run a 190* thermostate in it now, and yes, it's almost unbelievable that the gas mileage is this bad. I Only have a 10-1/2 gallon tank, so I have to buy gas every night on my way home. Today it rained all day long ( yes, I drive it EVERY day) and driving a fenderless car helps keep folks from tail-gating  ;)
Todays gas mileage was a womping 12.02 MPG  :(

As to my ignition curve, it's at 20* before TDC @ idle and 33* total @ 1600 rpm at this moment. I've been moving it each 2 days, it's been from 32* - 36* so far with just a minor difference so far.

Glenn

Offline AHotRod

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Re: S.B.Chevy Q-Jet base plate & intake modifacations for Gas Mileage?
« Reply #6 on: January 10, 2011, 06:21:06 PM »
Cliff,
Based on the information that I gave, should I follow recipe #1 on this carb for daily driving?

Glenn


Offline Cliff Ruggles

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Re: S.B.Chevy Q-Jet base plate & intake modifacations for Gas Mileage?
« Reply #7 on: January 11, 2011, 04:06:25 AM »
I'd use the second recipe for idle fuel with that much cam in a 9 to 1 350 cid engine.

You talked about timing, how much vacuum advance is being added?.....Cliff

Offline AHotRod

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Re: S.B.Chevy Q-Jet base plate & intake modifacations for Gas Mileage?
« Reply #8 on: January 11, 2011, 06:20:21 PM »
Cliff,
I have no vacuum advance, only mechanical advance.
What do you recommend?
I can set it up with vacuum......

Glenn


Offline omaha

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Re: S.B.Chevy Q-Jet base plate & intake modifacations for Gas Mileage?
« Reply #9 on: January 11, 2011, 10:05:41 PM »
Well, you gotta have a vacuum advance for the street use [jus my opinion].
It should have a ported source on the carb [hopefully]. And always run a ported source for street use.
This will get you the best milage. I'll bet you pick up 5 mpg with a vacuum advance. Id say; 16 degrees initial and 34-36 total mechanical and 10 degrees in the vac advance that starts in at 13 inches off of a ported source. these are all general figures to start at.  the one I am not too sure about is the 13 inches starting point of the advance can. I am not sure what such a light car would want as far as the "cut in" point of tha vacuum advance. Is there room for an HEI?

Offline Cliff Ruggles

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Re: S.B.Chevy Q-Jet base plate & intake modifacations for Gas Mileage?
« Reply #10 on: January 12, 2011, 05:34:25 AM »
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

Offline AHotRod

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Re: S.B.Chevy Q-Jet base plate & intake modifacations for Gas Mileage?
« Reply #11 on: January 12, 2011, 07:25:48 PM »
I'll bet you pick up 5 mpg with a vacuum advance. Is there room for an HEI?

+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

Offline AHotRod

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Re: S.B.Chevy Q-Jet base plate & intake modifacations for Gas Mileage?
« Reply #12 on: January 12, 2011, 07:30:03 PM »
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

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

Offline Cliff Ruggles

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Re: S.B.Chevy Q-Jet base plate & intake modifacations for Gas Mileage?
« Reply #13 on: January 13, 2011, 05:03:50 AM »
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

Offline 1985C10

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Re: S.B.Chevy Q-Jet base plate & intake modifacations for Gas Mileage?
« Reply #14 on: January 23, 2011, 07:09:37 AM »
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.
« Last Edit: January 23, 2011, 07:19:14 AM by 1985C10 »