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Old 03-15-2008, 09:26 AM
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altitude effects on supercharging

Im just wondering, does altitude cange any "rules of thumb" when it comes to supercharging? I live at 4500 feet my driving takes me from 3500 to 7000 feet within 30 min either way i go. I've always heard you shouldn't supercharge a 9.5-1 ratio street motor, just for kicks it's a 350 sbc 64cc heads with 9.5-1 comp ratio. I'd like to just put a Weiand 142 or 177 kit on. Also does altitude affect carb sizing?

I've never heard anything about it just thought i'd start some trouble!

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Old 03-15-2008, 10:19 AM
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you can supercharge anything , Its just a matter of how much boost you can run . with 9.5:1 and pump gas you are only going to be able to run about 4lbs of boost . also you should have a forged bottom end .As to elevation you will find it depends at how high you do your tune , I would think if you do it at sea level your amount of boost would be lower at the higher elevation , if you did it at a high elevation you may have detenation at sea level due to gettimg more could probally see the difference .
I dont think i would supercharge a 9.5:1 engine, I am in the process of building a 8.5:1 supercharged motor now .
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Old 03-15-2008, 12:13 PM
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The elevation is going to dictate your mixture. With a supercharger that is going to become more critical the higher you get. The 2 most critical tuneable factors in a supercharged engine are A/F ratio and ignition timing.
You are already living on the edge at 9.5 to 1. I would think unless the pistons are forged you are flirting with disaster. I broke the pistons in a 9to 1 engine that didnt get pushed all that hard. That is with a 142.
If you want to get the boost benifits from the supercharger be sure the engine can support it. If you dont you will be tearing it apart sooner or later to repair the damage.

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