pp2 at 6007.us
Mon Oct 10 16:46:00 EDT 2005
>It's odd to me.......someone posted last week suggesting a subject of
>"getting higher gas mileage" from your Vair.....NO ONE responded!
Well the first and most obvious cost savings is to be able to run regular
instead of premium.
Other than that if the primary goal is MPG and cannot begin with a turbo
then the best start with a 110 hp engine, accept the cost of premium, and
learn to drive for economy which is specific.
Had posted a number of possibilities for DFI (digital fuel injection) which
has the most potential for improvement that is the "poorly controlled leak"
that is the HV carb. Does not even have any metering rods (e.g. Carter AFB
or Rochester "M" series which includes the monojet which is very crude but
there) to lean out the cruise. Even a variable venturi SU HD-4 would be
better but is a sidedraft.
Next issue is the driving conditions. Best is a steady state cruise at the
minimum rpm you can get into top gear. PGs have an advantage there since
are at 1:1 as low as 15 mph (with some slip, have not plotted actual rpm
yet, one of the things I have planned.
For Interstates obviously the best choice is a 3.08 gear for minimum rpm,
3.27 is next and tall rear tires make possible for the rest. Ideal would be
2400-2600 rpm at 70 mph but is hard to achieve with a 3.55.
Next, everything related to tuning needs to be optimized. Need to find the
"sweet spot" for advance for your car (is a little different for each).
Invest in a manifold vacuum gauge and find settings that provide the
highest reading at steady state cruise.
Worst thing about driving for maximum MPG is the constant attention,
requires as much as any race, for any advantage such as turning the engine
off & coasting as much as possible (my wife thinks it amusing when coming
up to a known light that is going to be red awhile that I shift to neutral
and when a/c is not required, turn off the engine. Of course it helps to be
confident that the engine will fire back up on the first 1/2 turn of the
Biggest factor is not no accelleration but no sudden changes (just like
racing). If in a 45 mph zone then holding the throttle constant and
allowing variations in speed will give better results than holding 45
exactly. Get to speed as quickly as possible without engaging "power
enrichment" and then try to stay smooth and constant with minimum braking
(turns the momentum you spent gas to achieve into heat).
I don't know what the drag coefficient is for the Corvair (expect LM is
better than EM but really only important over about 60 mph) but the car has
a low profile and (to me) smooth lines. Best is a coupe. Worst is a convert
for two reasons, one curable. First the roofline is not as smooth. Second,
the cocktail shakers represent over 50 lbs of extra weight.
Biggest factor in MPG is where you drive. Five mile hops to the store and
such with lots of traffic is terrible. Steady state at a "sweet" speed
(needs to be enough to be operating efficiently in top gear but no faster)
is best. Have no numbers on Corvair as yet (still getting it right) but
last weekend the 3800 (231 cid, 3300 lbs) that was reading 17.2 mpg 20
miles from fillup due to stop and go was up to 23.6 after 120 mile round
trip to picnic. Long stretches at 60 mph (sweet spot) over 30 mpg. On
cruise. Without trying. I *know* the Corvair can do better with 90 cubic
inches and 1000 lbs less.
I really like digital feedback FI because it does not require tuning once
programmed properly. Can do the same with carbs just requires periodic
Anyone try Clark's variable fan pulley, seems to make sense ?
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