Gas Mileage
- Thread starter Clarkwb100
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I'm thinking it's too much of a good thing. Run a tank in D instead of OD and see how it compares.
It will give you an idea what 3.73 or 4.10 gears will behave like on the highway with OD.
That was my initial thought. Eledbrock carbs, being fairly generic instead of application specific, need to be tuned correctly right out of the box, regardless of what you put it on.. (altho some people say the box it comes in does better when bolted onto the intake than the carb does, but I digress..) Optimally, I would throw an Air/Fuel meter on it, but the plug color would tell us a lot here.
Great idea! I hadn't thought of that.
-Gonz
I'm not certain what you mean by "power circuit in carb" but engine is definitely not taxed, I don't think this engine has seen 2500 rpm yet. Folks here in Texas have generally commented that the Holley Avenger is not the way to go with this set up and almost all have said "get an Edelbrock" carb". WOuld this have the same problem? If changing out the carb is the answer, specifically what carb should be considered? Is this an out of the box fix or do I need to go thru a carb tuner, again?
Thanks
Don't listen to anyone that says "just get an edelbrock". Power circuit is the fuel circuit that is active at WOT. Most carbs have an idle circuit, power circuit, some kind of part throttle circuit, and some kind of accelerator pump (or squirter, on a holley) that gives an extra squirt of fuel when you crack the throttle so it wont lean out.
What he means by lugging is when a car is in high gear (in this case overdrive with your 200r4 transmission, which is a .67:1 gear) and it's being asked to do more work than it can because it's at a gearing disadvantage. It;s at such a low RPM the engine wants to idle, but usually when you're in overdrive you are at speeds of 45+mph. The suggestion of driving around in Drive (drive being 3rd gear, a 1:1 gear), will put the engine higher in the rpm range in the meat of the torque curve. This is why automatic transmissions "kick down". You cant do it to yours, but on a th350 for example, you can unhook the kickdown cable, floor it at say 55mph, and it will choke on fuel, sputter for a bit, until it recovers and slowly starts to raise in rpm. Pop the cable back on, it shifts down to 2nd (1.52:1 in a th350), and rpms shoot up right into the engines best rpm for passing/etc. BUT, your gears also play a role in that as well. With a 200r4, your 2.56:1 rear end gears are too high. They just are. It's making your engine lug. tbh you should actually get better mpg in D than OD. As said, Swap gears to at least something in the 3s. 3.08, 3.42, 3.73 are all common junkyard 7.5 10 bolt selections. You can buy 3 series gears for your 2 series rear end and have a competent shop install them. You car will feel spunkier around town, and in theory you will get better gas mileage. The best carb for gas mileage by far is a quadrajet due to their small primary barrels.
Long Story Short:
Your high gears (lower numerically) coupled with your overdrive are lugging your engine making it inefficient and wasting fuel. Upgrade your rear gears to something shorter (higher numerically). Maybe your converter as well. These old school engines like to generally be around 2,000-2,800ish while cruising at highway speeds (60-70mph usually) for best efficiency and performance and fuel economy.
Edit: My calculations show that your setup with 2.56 gears, your 27.01" tall 255/60/15s, and your .67 overdrive, at 65mph will only be at 1385 rpm. Way too low. That's basically fast idle, when the engine idles high when it's cold. So the engine is basically idling at that point. in Drive (1:1), it would only be 2000rpm. you could be in 1st gear at 65mph and be at 5200rpm, basically redline. that's nuts. with say... 3.73 gears... at 65mph in overdrive you'd be at 2000rpm. you could put 4.56 in there (lol) and only be at 2400rpm. I mean these calculations are just from a calculator, they dont take into account wind/rollig resistence, etc but it's always been at least +/-200rpm for me. If you want to run the whole 1/8th mile in 1st gear like I used to (I had 2.41 gears, now I have 3.42), but it wouldn't be as fun as 3.73s around town while still maintaining good rpm on the highway.
Your high gears (lower numerically) coupled with your overdrive are lugging your engine making it inefficient and wasting fuel. Upgrade your rear gears to something shorter (higher numerically). Maybe your converter as well. These old school engines like to generally be around 2,000-2,800ish while cruising at highway speeds (60-70mph usually) for best efficiency and performance and fuel economy.
Edit: My calculations show that your setup with 2.56 gears, your 27.01" tall 255/60/15s, and your .67 overdrive, at 65mph will only be at 1385 rpm. Way too low. That's basically fast idle, when the engine idles high when it's cold. So the engine is basically idling at that point. in Drive (1:1), it would only be 2000rpm. you could be in 1st gear at 65mph and be at 5200rpm, basically redline. that's nuts. with say... 3.73 gears... at 65mph in overdrive you'd be at 2000rpm. you could put 4.56 in there (lol) and only be at 2400rpm. I mean these calculations are just from a calculator, they dont take into account wind/rollig resistence, etc but it's always been at least +/-200rpm for me. If you want to run the whole 1/8th mile in 1st gear like I used to (I had 2.41 gears, now I have 3.42), but it wouldn't be as fun as 3.73s around town while still maintaining good rpm on the highway.
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The Holley can be tuned for mileage. Do you have a square and spreadbore manifold? If it is just a squarebore manifold a Street Demon 625 or even better a their 750 tuned to YOUR motor will give better mileage than the Holley both with an ideal tune. First do the drive in D test, it will prove how 3.73 gears will behave for mileage.
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