Jets for quadrajet at high elevations?

Aaarrghh · August 17, 2016, 04:49 PM

Hi, I've been driving around at about 100' elevation, but planning a drive to New Mexico. At one of my planned stops, the elevation is over 7,000 ft. Southern NM is generally over 4,000 ft elevation. Can someone recommend what jets to put in my quadrajet for the thinner air at those heights? There must be someone on this forum that operates in that environment.

BTW, here's a good vid abut how to change jets:
https://www.youtube.com/watch?v=4BU7FfDXXi8

Rickf1985 · August 17, 2016, 06:18 PM

Not a clue but unless you plan on staying there for months I don't think it is worth the trouble to change jets. The only time I changed jets for people outside of racing and high performance boats was when they moved to a much higher altitude and were staying up there all the time. If you really have to know contact Sean Murphy at SMI.

https://www.smicarburetor.com/

bluebird · August 19, 2016, 06:39 PM

Qjets are unlike any other carb ever built. The jets both front and back have metering rods that restrict the fuel flow, and are opened by the amount of vacuum created by the engine. May not be as bad as you think. When GM built cars and trucks with those carbs, they didn't know where they were to be sold.

Rickf1985 · August 19, 2016, 07:17 PM

Not exactly true Bluebird, Remember the Carter AFB? Now known as the Edelbrock Performer. They use the same needle and jet setup but the quadrajet had the advantage of the small primaries and the HUGE secondaries. The AFB did not use needles on the secondaries but when you are that far into it who needs metering? :)rotflmao

beaverman · August 19, 2016, 09:39 PM

Man Carter AFB, worst carb ever made! hated them damn things!

Rickf1985 · August 19, 2016, 09:52 PM

But the reincarnation as the Edelbrock has changed them drastically.

bluebird · August 19, 2016, 11:13 PM

Well I haven't had an AFB for over 40 years, so I don't remember much about them. I do know the Qjet is the best street carb, if set up correctly. I know a couple guys that even prefer them to a holley for drag racing. I still prefer the holley for racing, easier to tune for me. I had a guy come last year when I was selling all my extra parts and bought at least 10 Qjets and all my extra tunning parts. I did keep 1 800 cfm Qjet because I still have a 77 Trans Am and it may need a carb sometime or another.

Aaarrghh · August 20, 2016, 07:45 AM

Quote from: bluebird on August 19, 2016, 06:39 PM
Qjets are unlike any other carb ever built. The jets both front and back have metering rods that restrict the fuel flow, and are opened by the amount of vacuum created by the engine. May not be as bad as you think. When GM built cars and trucks with those carbs, they didn't know where they were to be sold.

Yes, adjusting the height of the metering rods may be all that's needed for 4000'. Unfortunately, my carb doesn't have an access hole in the top to do that. I'd have to take the top off (ugh).

BTW I found a route that doesn't go over those extreme elevations. My MS Streets and Trips doesn't consider elevations, so I had to do a little more research.

BrianB · August 20, 2016, 09:47 AM

Your Qjet should work ok at 4000'. I just returned from Alaska to NY state and spent a lot of time above 3000 feet.

Rickf1985 · August 20, 2016, 09:57 AM

You consider 4,000 ft extreme? Try Loveland pass (11,990) or Wolfcreek pass(10,857). I have done both in an old Peterbuilt with a 450 HP Detroit diesel. Let me tell you that diesels do not like high altitudes with no air! You want to talk about smoke!!! And I KNOW someone is going to post that song. :)rotflmao :)rotflmao :)rotflmao

And I had many Chevy pickups passing me and they were not blowing smoke and they all would have been running quadrajets. The diesels were the only ones suffering. And the humans, try walking to the bathroom when you are used to sea level!

BrianB · August 20, 2016, 03:48 PM

C. W. McCall

Aaarrghh · August 22, 2016, 09:16 AM

Naw, 4k' isn't extreme. I was talking about the road to Alamagordo going by Cloudcroft that's at 8600 feet. That's where I didn't want to go. Certainly if I got up to Durango I'd be looking for tailpipe smoke, but thanks for telling me about those Chevy pickups. Anyway, People in the Mile-high city probably don't have a problem with their quadrajets. Now if I was to migrate up to Santa Fe or Los Alamos (7100') next summer, might I get better performance by re-jetting?

Rickf1985 · August 22, 2016, 10:39 AM

Maybe, but only if you planned to live there and stay there. You have to remember that with the lower barometric pressure it also affects the application of the needles in the jets so there is a lot more to the equation than just less air. Again, there are hundreds of thousands of Chevy trucks living at high altitudes that have never been modified.