High Altitude Compensator

Joined
Feb 12, 2015
Messages
42
Location
Dominical Costa Rica
I have a 76 & 77 BJ40 here in Costa Rica, one w/ an HAC. The 76 is my current daily driver and does well w/o HAC. I live @ 4650 ft and my shop is located @ 3300 ft. The 76 has no issues climbing the mountain back home. My question: what is the purpose of the HAC? 77 is close to completion and will be exported to CA as my vehicle, NFS. We'll build to order but the project 77 is being built as a collector as are all my builds but this is my first Toyota
20220622_085413.jpg
. Any information about the HAC purpose and or function would be appreciated. Thanks.

20220524_072054.jpg
 

John in Utah

SILVER Star
Joined
Oct 20, 2017
Messages
669
Location
Moab
The general idea is to limit the maximum fuel setting on the pump by replacing the fuel stop screw with a diaphragm that changes position based on ambient pressure.

The pump on your 77 should look like the photo below. It’s basically a silver puck with a hose on one end that is exposed to ambient, and some bellows on the pump side. There’s a 17mm lock nut you can loosen to screw the whole puck in or out to adjust the fuel stop position (max fuel setting)

681FACA3-8F3A-4257-887D-85ADC7ED6D38.jpeg


I have a HAC and live at a similar altitude as you, but it’s hard to tell if it does anything meaningful. Sounds like you have no problem without one currently.

At the end of day, tune your fuel so you aren’t getting excessive black smoke/EGTs and it’ll be fine.
 

1911

chupacabra
Joined
Aug 11, 2006
Messages
7,036
Location
Parker County, Texas
My question: what is the purpose of the HAC? ... Any information about the HAC purpose and or function would be appreciated. Thanks.

In gasoline 2F engines, the HAC advances the ignition timing an additional 6 degrees, and bleeds air into the primary low and high-speed circuits in the carb (to lean the mixture) when you get above 3,930' elevation. I have it on my truck; it helps quite a bit when I drive mine in the Rocky Mountains (sometimes well over 12,000' elevation).

IMG_0864.JPG


But I see from your photos you have a B engine.
 
Joined
Feb 12, 2015
Messages
42
Location
Dominical Costa Rica
In gasoline 2F engines, the HAC advances the ignition timing an additional 6 degrees, and bleeds air into the primary low and high-speed circuits in the carb (to lean the mixture) when you get above 3,930' elevation. I have it on my truck; it helps quite a bit when I drive mine in the Rocky Mountains (sometimes well over 12,000' elevation).

View attachment 3048162

But I see from your photos you have a B engine.
Yes I do have a B series diesel motor. Needed @ high elevations for a diesel?
 
Joined
Feb 12, 2015
Messages
42
Location
Dominical Costa Rica
The general idea is to limit the maximum fuel setting on the pump by replacing the fuel stop screw with a diaphragm that changes position based on ambient pressure.

The pump on your 77 should look like the photo below. It’s basically a silver puck with a hose on one end that is exposed to ambient, and some bellows on the pump side. There’s a 17mm lock nut you can loosen to screw the whole puck in or out to adjust the fuel stop position (max fuel setting)

View attachment 3048157

I have a HAC and live at a similar altitude as you, but it’s hard to tell if it does anything meaningful. Sounds like you have no problem without one currently.

At the end of day, tune your fuel so you aren’t getting excessive black smoke/EGTs and it’ll be fine.
Thanks for the info.
 

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