DCOE jetting help please

[AndyIA]

Ok, recently moved from a mile high to 860 ft. elevation. I'm running dual 45 DCOE's with 34mm chokes, 292 cam, headers, high compression pistons, etc.. Does anyone have a good jetting recipe for my altitude? TIA.

[dapbmw]

Altitude compensation: Reduce main jet size 0.05 for every 5000 feet of DENSITY altitude. Density altitude is dependent both on temperature and air pressure. Although calculating actual density altitude is a fairly complex operation, you can approximate it with actual altitude with this forumla:

Density Altitude = 75 feet * (Outside Air Temperature F - (59F-Altitude/300)) + Actual Altitude

This is a crude measure and you may wish to stick with Actual Altitude to avoid overleaning in warm weather.

To change behavior over the mid to high range of RPMs (more than 1/6 throttle), change main and air correction as follows:

For a given air correction jet, a larger main will flow more fuel across the RPM range.

For a given main jet, a larger air correction jet will reduce fuel flow in the higher RPM range.

In general, for racing, the air correction jet will be smaller than the thumb rule above, and the main jet larger. This allows for more fuel flow over the whole range, and further enrichment at high RPM. For economy, the thumb rules are close but may require small adjustment. The question is, why are you looking for economy instead of power at Wide Open Throttle?

[dapbmw]

125 main 175/180 air

[Brendan_Lopez]

Hi,

What size jets are you running?

In general, you want to run smaller mains @ altitude. In your case going from mile high to 860 ft you'll have to richen a bit.

Weber offers this setting (from Pat Braden's Weber book)

BMW Alpina

38 venturis

5 aux venturi

125 main

170 air corrector

F9 emulsion

40 pumpjet

70 pump bleed (exhaust)

45 F8 idle

2.25 needle valve

My Alpina spec sheet indicates (10:1 w/ 300 deg)

38 venturis

5 aux venturi

130 main

200 air corrector

F9 emulsion

45 pumpjet

60 pump bleed (exhaust)

55 F8 idle

2.00 needle valve

I have a list of BMW DCOE jet settings from various books/literature I can add to the FAQs if anyone is interested.

BL

[AndyIA]

Thanks everybody for the replies. Currently (and the carbs were never properly jetted before) installed:

140 mains

170 Air Correctors

f9 emulsion tubes

050 f8 idles

so would 125 mains and 175/180 air correctors get me to a proper running set-up?

[meyekel]

140 mains and 170 airs seem awfully rich to be running at 5000 feet. i'm in denver and am using 120 mains and 200 air correctors and that seems to be about right even a tad on the rich side. i'd use the above posts as a basis to start with.

mike r

[vintage_car]

Is the larger the main jetting the more fuel you get as well as the air corrector?

[Guest Anonymous]

Altitude compensation: Reduce main jet size 0.05 for every 5000 feet of DENSITY altitude. Density altitude is dependent both on temperature and air pressure. Although calculating actual density altitude is a fairly complex operation, you can approximate it with actual altitude with this forumla:

Density Altitude = 75 feet * (Outside Air Temperature F - (59F-Altitude/300)) + Actual Altitude

This is a crude measure and you may wish to stick with Actual Altitude to avoid overleaning in warm weather.

To change behavior over the mid to high range of RPMs (more than 1/6 throttle), change main and air correction as follows:

For a given air correction jet, a larger main will flow more fuel across the RPM range.

For a given main jet, a larger air correction jet will reduce fuel flow in the higher RPM range.

In general, for racing, the air correction jet will be smaller than the thumb rule above, and the main jet larger. This allows for more fuel flow over the whole range, and further enrichment at high RPM. For economy, the thumb rules are close but may require small adjustment. The question is, why are you looking for economy instead of power at Wide Open Throttle?

It is never nice to pass work off as your own, if you choose to quote someone's work please reference it. This is taken verbatim from the www.teglerizer.com site. A great reference for DCOE jetting and tuning.