[tcb] Re: Dual vs. Single
- From: theresabuckner@xxxxxxx
- To: tcb@xxxxxxxxxxxxx
- Date: Tue, 17 Sep 2013 23:22:27 -0400 (EDT)
Sammie If you have less air filter at high altitude , will that help ??
Without turbo to force the air , does carb size or head / valve size make the
difference ??
-----Original Message-----
From: sammie smith <bugcollections@xxxxxxxxxxxxx>
To: tcb <tcb@xxxxxxxxxxxxx>
Sent: Tue, Sep 17, 2013 8:03 pm
Subject: [tcb] Re: Dual vs. Single
Julie: You got me to thinking about your lack of power at altitude. For a
reciprocating engine to run (fire to occur) you need three elements; fuel, air
& ignition. Changing jets for altitude will result in a more proper mixture of
the fuel and air (less fuel for less air). But, the problem at high altitudes
is not mixture, it is lack of air. From my aircraft experience: Most
reciprocating normally aspirated aircraft engines power an airplane at a max
altitude of about 13,000 to 15,000 feet. They fly great at altitudes up to
about 9.000-10,000 feet, but after that the engine loses so much power that at
some point there is not enough power to maintain flight. The problem is lack
of air (O). Without oxygen you cannot get a decent explosion in those
cylinders. The answer in aircraft, and has been known for a long time, is
supercharging (now turbocharging) to force more air into the cylinders.
So you can change carbs and jets all day long, but you are not going to
overcome the effects of lack of oxygen on a normally aspirated engine. More
horsepower (and less reliability) along with bigger carbs will help some. But
when you get to 9,000-12,000 feet elevations in your car, bus or whatever your
horsepower is going to be way down.
I used to own and fly a VW powered aircraft. It would climb great up to about
9,000 feet. After that the rate of climb started dropping off dramatically.
One day I decided to see just how high it would fly. I made it to 13,500'. At
that point it no longer had enough power to climb. Some of that is
attributable to the much thinner air making the wings more difficult to fly,
but primarily was due to the fact that the engine simply did not have enough
power to pull it any higher.
In summary: I would go with what you got. Unless you want to turbocharge it
or supercharge it (also with decreased reliability) you are just gonna have to
live with much less power at altitude.
From: Julie <julie.hey.ho.lets.go@xxxxxxxxx>
To: "tcb@xxxxxxxxxxxxx" <tcb@xxxxxxxxxxxxx>
Sent: Monday, September 16, 2013 11:09 PM
Subject: [tcb] Re: Dual vs. Single
My only real mountain driving was with my fancy engine. Honestly I was slowed
down a whole super duper a lot by the altitude. My guess is that the 40 Kadrons
had something to do with it.
Mt Shasta is a bunch higher.
Some say just stab that engine in the DC and go for it. Some say switch out
the carbs to a single. (My mechanic says no to that idea.). I have been
leaning towards having a new engine built. I need one for my zebra Bus
anyways.
Ugh! I can't decide. And once I am on the mountain, it will be too late.
On Sep 16, 2013, at 9:52 PM, sammie smith <bugcollections@xxxxxxxxxxxxx> wrote:
Julie: You are basically correct. However, unless you are running some large
carbs, such as dual weber 44s I don't think you are going to notice the
difference, e.g. for a PIC 34, stock carb on late model dual ports, you might
notice some decrease in power at high altitudes, like 8-9,000 feet.
But trying to rejet the 34 to compensate is not going to help much. If I were
going to drive continuously at high altitude and running weber 44s I would jet
them for that altitude. I live at 350 feet above sea level and jetted my 44s
for that altitude. When I made the California cruise I went through altitudes
as high as probably 9,000 feet. I could detect no difference in power. Had I
pulled the plugs and looked at that altitude the engine was probably running a
bit on the rich side.
Conclusion: I would jet it for where you live and not worry about it. I don't
know what the altitude of
Mt. Shasta is, but I wouldn't go through the process of changing the carb jets
to climb it. If you were gonna live there at that altitude all the time, then
yeah. But getting the jetting exactly correct is difficult, and if you get it
too lean you can burn your engine up. Having it too rich is not really gonna
hurt anything. You want to err on the rich side, not the lean side. If you
have it jetted for Austin the only thing that's gonna happen on Mt. Shasta is
that you will be running a bit on the rich side; not a problem. If you have it
jetted for the top of Mt. Shasta then you are gonna be running lean at lower
altitudes, not a good problem.
What engine are you going to run and what carbs will you have on it? Maybe we
can be more specific on jetting.
From: Julie <julie.hey.ho.lets.go@xxxxxxxxx>
To: tcb@xxxxxxxxxxxxx
Sent: Monday, September 16, 2013 8:39 PM
Subject: [tcb] Dual vs. Single
I don't understand carbonation throughly. But I do know that when you take a
well running Bus into higher altitudes the mixture of fuel to air gets off and
you run rich which slows you down and can fowl your spark plugs until you can
cruise at a fast speed for awhile to clean the spark plugs off.
So here is my question, would the effect be equal if one Bus had a single carb
on the engine as another Bus that has dual carbs? Or would one set up be more
finicky or sensitive to the thinner air over the other?
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