73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Performance => Topic started by: shackleton on May 13, 2007, 11:34:15 am
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I just signed up and was hoping someone could shed some light on an issue I have with my '80 High Sierra 25.
I bought the truck with a 400 in it and soon blew that motor. I replaced it with a 350 from Marshall (some local shops advised me this was not the best choice but I was in a bind and needed something quickly as the truck was out of state when it met it's maker). This truck is sheerly a work horse and to be used for hauling a horse trailer and various menial tasks. It doesn't get much road time(<2000 mi/yr) but I'm not happy with it's performance.
It has an Edelbrock intake, is linked to a TH 400 and a 14 bolt rear end (the t-case is a 205 for what it's worth). It's bogging on the low end almost like it's loading up with fuel that won't clear until I put it in neutral and rev for a bit. Also power gets sapped quickly when pulling the trailer through the hills. This leads me to think I'm having a carb issue combined with incomplete combustion.
I was thinking of a Holley avenger or truck avenger at 670 cfm. Also I want to bump up the ignition and am wrestling with the HEI upgrade or going full bore with the MSD 6AL.
The other wrinkle is that I live in the foothills outside of Denver at ~8000' above sea level. I tried to give you the whole picture but I started running long and tried to rein myself in. If there is any other info you need let me know and I will try to provide it. Does anyone have any thoughts about this? Thank you in advance for your input.
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At higher elevations the last thing you need is more fuel since there's less air pressure. DO NOT over carb it. I would go through and perform a tune up - set your timing and rebuild your carburetor. If your carburetor is shot and you don't have the carb overhaulin skillz pick up a reman'd Q-jet for about $250 bucks.
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Thanks for the reply. I was looking at a new carb basically to make sure I had the go power necessary when hauling. I believe that carbs sold for altitude come with a different needle and spring kit to compensate. I've never bought a carb up here so I don't know if the different configuration works or not. Is it your opinion that adjusting it won't work and just play it safe with a lower flow? Do you think the Holley options will be ineffective or that I won't get the return on my dollar or both?
Thanks for the input
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Basically any performance carb out of the box is going to be rich in all modes of operation so they will just bolt on and work for most applications. In a high elevation there is less air pressure therefore you need to step down the amount of fuel being meterd in slightly. A stock Qjet should work just fine. As far as it's ability to perform - Those Qjet carbs have huge secondaries. When you stomp on it you'll now it.