RMC List - Picnic

Mon Aug 15 14:53:29 EDT 2022

Mike:

What I was told about carburetors and air/fuel ratios is that an IC engine depends upon both the VOLUME of air being passed through the engine and the MASS (weight of air). It is the kinetic energy of the air passing through the jet that primarily creates the needed atomization, not just the volumetric  (air) flow.The kinetic energy is the gas (air) velocity times the mass of the air. Thus, as the altitude increases and the air density decreases, kinetic energy required for fuel atomization decreases. Compensation is needed.

But there is more. What about the fuel? The fuel needs to pass through the orifice in the jet. The jet (orifice) in a carburetor resists the flow of the fuel thus a slightly larger jet reduces the fuel flow resistance. Therefore, the bigger jet adjusts for the altitude's reduced kinetic energy as dictated by the lighter, lower density air. Less air kinetic energy is compensated by lowering the fuel flow resistance imparted to the fuel by the jet.

Modern FI systems have MASS FLOW sensors for this reason. The atmospheric pressure sensor determines the altitude variable and the ambient temperature sensor provides the temperature variable, the computer determines the available atomization kinetic energy. The signal then is used to set the air/fuel mixture under various throttle position (and exhaust oxygen) settings.

Hope that helps!

Ken Scifttner

> On Aug 15, 2022, at 12:13 PM, MICHAEL PIPER via RMC-List <rmc-list at corvair.org> wrote:
> 
> My $0.02- 
> 
> The high alcohol fuel will boil if you look at it cross-eyed.  It also has more oxygen on it so to compensate you can make the fuel/air mix richer to cut down on detonation.  I have two 140 engines and they tend to detonate easily.  I don't know what jets I have but they are bigger than stock.
> 
> In the mists of time, using leaded fuel, the old rule was to advance the timing 1/2 degree per 1000 feet of elevation, or 2 1/2 degrees at 5000 feet.  That did not work well in my 140 engines.  I've had detonation issues so I'm pretty close to the book timing advance.
> 
> Be very careful when putting rubber hoses in the engine bay.  If you loose a belt and cut a line, you have the makings of a fire if the pump keeps running.
> 
> I've put electric fuel pumps in the front near the right front wheel or back by the left rear wheel.  If the pump is low in the system it does not need to suck fuel to speak of.  If it is the engine bay where Mikey's is it will need to lift fuel to the carbs.  If it's hot due to the engine plus you are sucking on the fuel, that could enhance vapor lock chances due to reduced atmospheric pressure.
> 
> Regards,
> 
> Mike 
>> On 08/15/2022 11:34 AM Paul Jarrett Sr <pjarrettsr at yahoo.com> wrote:
>> 
>> 
>> 
>> Why would you increase jet size at higher altitude?
>> 
>> On Monday, August 15, 2022 at 11:18:34 AM MDT, JOHN DAWSON via RMC-List <rmc-list at corvair.org> wrote:
>> 
>> 
>> Mikey: 
>> all of the issues you mention could contribute to the surging, but it was a hot day and having the electric fuel pump inside the engine compartment could be a major contributing factor.
>> 
>> Sounds like a vapor lock or a heat-related fuel issue, as what happened to me just two miles from home and my electric fuel pump is located up front near the tank; but is subject to all the heat radiating up from the hot asphalt pavement. The 10% ethanol in the fuels we have in the metro area does not help one bit either.
>> 
>> Most important in setting the car up for 5280' elevation is to advance the ignition timing by about 3 - 5 degrees and maybe having larger jets in the carbs (go from 49 to 51). I've been able to get by with just advancing the ignition. And always spend the extra money on the 91 octane "Premium" fuel...even if it has ethanol in it.
>> 
>> Make sure that you've replaced all the rubber fuel hoses with an ethanol-compliant hose (Gates 4219BG for instance) This is available at most auto parts stores (I've purchased it from O'Reilly's recently)
>> 
>> The PowerGlide in of itself is probably not the main culprit other than it's just a two-speed transmission, and therefore does not allow for keeping the engine rpm up a bit when going uphill (unless it's in "L" and then the rpms may be a bit too high...)
>> 
>> Hope this helps
>> 
>> Be safe out there
>> John Dawson
>>> On 08/15/2022 10:46 AM Mikey Spaulding <mspaulding166 at gmail.com> wrote:
>>> 
>>> 
>>> Interestingly, twice on my drive home while heading uphill, I had a sort of surging in the vehicle and seeming loss of power, almost like it was stalling out.  The last time it happened on Federal, I slowed down to about 30mph (not intentionally) before making it to the top of the hill.  Once past the crest, I had no more problems.  Any ideas as to what gremlin could cause this?  Would it be related to not having the carbs tuned to this elevation since bringing it from Minnesota, where my elevation was 912' asl?  Or is this more a transmission issue with the PowerGlide? 
>>> 
>>> Thanks for any help and ideas! 
>>> 
>>> Mikey
>>> 
>>> On Sun, Aug 14, 2022 at 9:08 PM MICHAEL PIPER via RMC-List <rmc-list at corvair.org <mailto:rmc-list at corvair.org>> wrote: 
>>> My red Corsa has an Airtex solenoid style pump, the white car has a Carter vane style pump.  Both are low pressure pumps.  I think the problem with the red Corsa is the wiring in the engine bay vs the pump.  I wiggle the wires by the bulkhead connector and off it goes.  The problem has been very hard to duplicate sitting in the garage. 
>>> 
>>> Maybe I failed to pay my dues to the gremlin union.
>>> 
>>> Hope this is a little helpful.
>>> 
>>> Mike
>>>> On 08/14/2022 8:54 PM JOHN DAWSON via RMC-List <rmc-list at corvair.org <mailto:rmc-list at corvair.org>> wrote:
>>>> 
>>>> 
>>>> That darn gremlin may have been passed over from Mike's car to my sedan...
>>>> the electric fuel pump decided to take a coffee break as I was waiting at the light at Orchard and Broadway on the way home. was able to get the car to a safe place and 30 minutes later, the pump was back to work...and of course that was after calling AAA for a tow and letting Karen know that I'd be a little late getting home.
>>>> 
>>>> BTW: what type of electric pump have you used on your daily drivers?
>>>> 
>>>> Great to see you and Linea today.
>>>> 
>>>> Be safe out there
>>>> JD
>>>>> On 08/14/2022 5:04 PM Eric Schakel via RMC-List <rmc-list at corvair.org <mailto:rmc-list at corvair.org>> wrote:
>>>>> 
>>>>> 
>>>>> Good time, good people, enjoyed the cars and company. Special thanks to Mike Piper, who once again did “Corvair gremlin” duty so the rest could drive trouble-free! And thank you, Dale, for getting this up so quickly!
>>>>> 
>>>>>  
>>>>> Eric S.
>>>>> 
>>>>>  
>>>>>  
>>>>> From: RMC-List <rmc-list-bounces at corvair.org <mailto:rmc-list-bounces at corvair.org>> On Behalf Of Dale N. via RMC-List
>>>>> Sent: Sunday, August 14, 2022 3:57 PM
>>>>> To: Corvair - RMC Email List <rmc-list at corvair.org <mailto:rmc-list at corvair.org>>
>>>>> Subject: RMC List - Picnic
>>>>> 
>>>>> 
>>>>> 
>>>>> Hello RMCrs,
>>>>> 
>>>>> We got together for the Wilshire Memorial Picnic today.
>>>>> As usual, it was a combination of pleasant weather, almost too much food, and not enough conversation.
>>>>> Never seems to be enough time to catch up with everyone.
>>>>> 
>>>>> If you were unable to attend, you missed a good time and we missed you.
>>>>> 
>>>>> Check this link for a few photos from the gathering.
>>>>> 
>>>>> https://www.rockymountaincorsa.org/2022-08-14-picnic/ <https://www.rockymountaincorsa.org/2022-08-14-picnic/>
>>>>> 
>>>>> Dale
>>>>> 
>>>>> _______________________________________________ 
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>> 
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> _______________________________________________
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