High Altitude Compensator (1 Viewer)

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Feb 12, 2015
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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
 
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.
 
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.
 
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?
 
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.
 
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.
Trying my luck with this old post. I own a HJ45 which came with the same HAC as yours but with no connection tube, may I ask where does the tube from the HAC go to? 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).

View attachment 3048162

But I see from your photos you have a B engine.
Yes I do have the B diesel engine
 
Trying my luck with this old post. I own a HJ45 which came with the same HAC as yours but with no connection tube, may I ask where does the tube from the HAC go to? Thanks!

As far as I know the purpose of the tube is just to keep gunk out of the HAC. It needs a reading of atmosphere to work properly and the tube is meant to reach a place where water/dirt won't easily get in.
 
For the gasoline guys…. I have a HAC in a ‘85 2F motor transplanted into my ’74 FJ-40, and drive my truck up Mount Lemmon (2500 - 8000’) regularly.

My truck seems to run better & have more power above 5000’. It’s prettier amazing!
 

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