. carb jetting

[66hcs-conv]

Hi gang,

1966, 289, 2V, single exhaust

We have moved from 7500 feet altitude to 5000 feet.

Anybody got any idea what size jets I should be using, or how much larger I need to go for 2500 feet lower altitude?

Thanks for your help. Dave

 

[Mosesatm]

Here's a little plug-in-the-numbers website.
http://www.bgsoflex.com/holley.html

Holley recommends 1 jet size for every 2000 feet.

 

[66hcs-conv]

Thanks for the web site & the information.

The Holly web site recommends a higher numbered jet for a higher altitude.

The Ford shop manual recommends a lower number jet for a higher altitude.

The shop manual says a # 48 jet for "altitude". Problem is they don't say what altitude they are talking about.

I be confused !

 

[Mosesatm]

Thanks for the web site & the information.

The Holly web site recommends a higher numbered jet for a higher altitude.

The Ford shop manual recommends a lower number jet for a higher altitude.

The shop manual says a # 48 jet for "altitude". Problem is they don't say what altitude they are talking about.

I be confused !

It seems to me that the car will run rich at higher altitudes, due to less oxygen in the air, so the carb will need smaller jets.

 

[davidathans]

It seems to me that the car will run rich at higher altitudes, due to less oxygen in the air, so the carb will need smaller jets.

i concur. But he is going from 7500ft down to 5000ft, so there will be a higher oxygen concentration, therefore he will have to increase his jetting or he'd run lean. If he were moving up to the higher altitude then he would need to decrease his jetting, but he is moving from a higher altitude to a lower altitude therefore he will need bigger fuel jets.

 

[66hcs-conv]

It seems to me that the car will run rich at higher altitudes, due to less oxygen in the air, so the carb will need smaller jets.

Correct. I agree, the higher in altitude, the smaller the jet.

The Ford manual calls for a # 50 jet, for "normal" operation and #48 for "altitude" operation. Assuming the altitude operation is for Denver, that would follow the 1 jet size for every 2,000 feet rule, and I would go 2 sizes down from a # 50 jet to a #48.

I'll give that a try, drive it, and take a look at the plugs.

THANKS for the input.

You new Mustang owners with fuel injection are missing all this fun!

 

[rvrtrash]

You new Mustang owners with fuel injection are missing all this fun!

Yes, these new cars are just no fun at all---very boring. :grin:

Steve