carb changes for elevation

[4404spdcharger]

I was living in Houston when I bought my 68 Charger R/T 440 4 spd and then moved to Colorado at 9000 ft.   I re-jetted the AVS carb to .095 primary and .085 secondary from stock jets.  Now I'm in Ft Collins at 5300 ft elevation.  Anyone got any suggestions about the size jets to use at 5300 ft?  How about you Troy, any suggestions?  The engine has been bored 30 over but otherwise is bone stock.

[elacruze]

Here's a great chart you can apply to your jets.

http://www.ultralightnews.ca/rotax503/rotax2strokepdf/mainjetcorrectionchart.pdf

[BSB67]

Do you know if the Rotax engine jet-change flow is proportional to carter/holley jet-change flow?

[femtnmax]

At my elevation of 5000 feet the suggested jetting in Edy's avs booklet was not even close.  Tuning with an O2 sensor made all the difference.

[elacruze]

Do you know if the Rotax engine jet-change flow is proportional to carter/holley jet-change flow?

Fluid dynamics don't change for manufacturer.

[BSB67]

Do you know if the Rotax engine jet-change flow is proportional to carter/holley jet-change flow?

Fluid dynamics don't change for manufacturer.

I think you miss my point.  That chart is for Rotex jets.  The factor for multiplying might not be the same for Holley or Eddy jets.  Multiplying a Rotex jet number (unitless) by say .94, may correspond to a different flow rate change than multiplying a holley jet number by .94. 

[elacruze]

Do you know if the Rotax engine jet-change flow is proportional to carter/holley jet-change flow?

Fluid dynamics don't change for manufacturer.

I think you miss my point.  That chart is for Rotex jets.  The factor for multiplying might not be the same for Holley or Eddy jets.  Multiplying a Rotex jet number (unitless) by say .94, may correspond to a different flow rate change than multiplying a holley jet number by .94. 

I'm not suggesting that if you have perfect jetting at a certain altitude that you can use this table and expect perfect jetting at a different altitude, it's just a tool to give a general idea where to go, air and holes being pretty much the same at any altitude. Flow rates between jet brands may change, but the fluid they all pass doesn't; Air will behave the same in holley brand, rotax brand, Keihin brand jets relative to their branded sizes. The difference in flow rates between rotax and holley jets is moot, since you won't be replacing one with the other.

[BSB67]

Do you know if the Rotax engine jet-change flow is proportional to carter/holley jet-change flow?

Fluid dynamics don't change for manufacturer.

I think you miss my point.  That chart is for Rotex jets.  The factor for multiplying might not be the same for Holley or Eddy jets.  Multiplying a Rotex jet number (unitless) by say .94, may correspond to a different flow rate change than multiplying a holley jet number by .94. 

I'm not suggesting that if you have perfect jetting at a certain altitude that you can use this table and expect perfect jetting at a different altitude, it's just a tool to give a general idea where to go, air and holes being pretty much the same at any altitude. Flow rates between jet brands may change, but the fluid they all pass doesn't; Air will behave the same in holley brand, rotax brand, Keihin brand jets relative to their branded sizes. The difference in flow rates between rotex and holley jets is moot, since you won't be replacing one with the other.

Let me try again.  If a properly tuned engine is move from mean sea level to a higher elevation and requires 8% less fuel, it will not matter if it uses Rotex or Holley jets, it will require 8% less fuel.  What I don't know is if the multipyling factor found on the Rotex chart will result in the same % change in fuel reduction as a holley jet.  Remember, jet size is a unitless number.

Said differently. multiplying a rotex jet by .94 might be a 5% reduction in fuel flow, and multiplying a Holley jet by .94, may result in a 10% reduction in flow.   It is possible that they are the same.

[elacruze]

I see the issue.

I failed to point out the the table only works if you know the actual measured orifice size, which may not relate linearly to the stamped jet number.

[71bee]

I have researched & experimented with a ton of "proper" jetting/calibrations for altitude. I tell yah, it's a hit & miss proposition. here in Utah (4100 ft), I found that by merely throwing in a set of slightly thicker Carter AVS# 4966 metering rods, my car ran perfectly as opposed to doing what Carter recommended (dropping a primary jet size.)

I think you should run beautifully with going 1 size smaller on your primary jets.