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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: vince311 on April 08, 2009, 12:36:32 pm
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I recently installed a Goodwrench motor...and am running a Weiand stealth intake w/ a 600cfm carb. My mpgs aren't great....and I'd like to try running a 2-barrel carb.
Question: Is there a universal adapter plate, to go from a 4-barrel intake to a 2-barrel carb? I've searched Jegs/Summit...with no luck.
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Going to a two barrel carb won't increase your mpgs. It will limit your power at WOT. When you are cruising you are only using half of a four barrel carb, so in essence, your engine thinks the carb is a two barrel. Play with your ignition timing. My Goodwrench likes about 14-15° initial and about 35-36° total with the vacuum advance on the full vacuum port. Also for less than the cost of a new two barrel you could pick up a stand-alone wide band O2 sensor and dial in your A/F ratios.
What kind of carb are you currently running? If it's a Holley with straight-leg boosters, you could talk to a carb shop about installing stepped dog-leg boosters for finer fuel atomization, which could improve your fuel effeciency.
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Vince, Yes they are available, Trans Dapt & others make them, however even is correct, you will end up with the best results with a properly tuned & working Q-jet as long as you keep your foot out of it (or limit the secondaries in some way) The primaries throttle blades/bore, jet area & the accelerator pump circuit are smaller on the Q-jet than the 2bbl. Lorne
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I have done the 2 barrel swap in the past and it was a waste of money. A finely tuned 4 barrel and engine tune will get better results. You wont be happy with the swap. Yes, if you keep the pedal floored you will get worse mileage with the 4 barrel, but if its driven normally, the 4 barrel will do just fine.
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The key to this is a Q-jet 4bbl with small primaries. A Holley with the same size primary/secondary won't cut it.
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Since he said 600 cfm, I assume we are either talking a Holley or Edelbrock carb.
Vince: If your quest is solely max mpgs you might consider either swapping back to a Q-jet (you would need a spreadbore manifold) or swapping over to TBI (not as expensive or complicated as you might think).
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Thanks for the feedback. Couple additional details:
- Holley 600cfm carb is currently installed (I also have a Holley Avenger 670, but assume that will be even worse mpg)
- I think my wife is going to kill me if I spend anymore on this "daily driver" :-)
- I've been driving the truck for a couple weeks now, since the motor swap. Finally have the timing adjusted so that the pinging is gone.
- Have not figured the mpg using a super "light foot". Have been driving it normal, and getting somewhere around 9 mpg. yikes!!
- Trying to find the simpliest, least expensive route...for better mpg. (like under $100)
- I'm learning a lot from the folks on the forum, thanks!
- I could go with a Q-Jet. Is there an adapter plate from square to spreadbore? TBI...not 100% sure what that involves.
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Adapters that convert square to spreadbore and vice versa are known power killers. I would suggest finding a spreadbore manifold like the edelbrock 2101, if you really want to go back to Q-jet. I would experiment with the calibration of the Holley before spending alot more money.
How you drive is very important to getting max mpg's. Highway cruising speed, how aggressively you accelerate from a stop, and amount of time spent idling are all very important factors that play into gas mileage. The heavier and less aerodynamic a vehicle is the more sensitve it is to the first two factors. You can't complain about poor gas mileage until you have made free and easy adjustments to your driving style.
What is the rest of your combination? If the answer is a TH350 with 3000 stall and 4.11's in the rear, you may be fighting a losing battle here. Overdrive and a lockup converter go a long way in the battle for higher mpg's.
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Do you have the dual or single plane weiand? And just to back up a few previous comments, Q-jet, ignition timing & driveline configuration. TBI is a nice alternative but if you want it to be cheap you'd need a donor vehicle. I'm converting my mutt into tbi.
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He's got a squarebore dual plane. A Weiand Stealth manifold is the equivalent of Edelbrock's Performer RPM.
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You might also go with a powervalve with a lower setting. Or even a dual stager. Also jet it down some perhaps? What jets are in there now? What do your plugs look like?
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i'm time-limited here, but we need to establish a base-line mpg and then we can tweak here and there (this coming from the self-appointed 73-87 truck mpg "expert")
For some rock solid proven mpg improvments consider a tonneau cover for the bed.
Also, refer to my post concerning mpg's. Sorry don't have time to provide a link.