whats the most you can overdrive a 671? - Page 2 - Hot Rod Forum : Hotrodders Bulletin Board
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Old 09-15-2010, 02:34 PM
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Quote:
Originally Posted by darkostoj
everybody seems to be getting super confused here. I just wanted to know how much you can overdrive a 671 until the boost charge gets too hot...thats all. You guys are going to make me drill and tap the intake for an IAT here!

no one seems confused but you. You can't ignore the boost pressure. It can overheat in an underdriven condition if the boost pressure is outside of the normal operating (efficiency) zone. Its the same for turbo chargers and centrifugal blowers. An IAT sensor would be a good idea.

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Old 09-15-2010, 03:22 PM
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For what it's worth, BDS's boost chart for the 6-71 only goes to 17 pounds. From that I would infer that the most you can over-drive a 6-71 before you have "issues" is 17 pounds, which on a 350 is 30% overdriven.
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Old 09-15-2010, 03:35 PM
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Originally Posted by XNTRCI-T
For what it's worth, BDS's boost chart for the 6-71 only goes to 17 pounds. From that I would infer that the most you can over-drive a 6-71 before you have "issues" is 17 pounds, which on a 350 is 30% overdriven.
I don't think the BDS blowers are built the same as the weiand ones, I could be wrong though.


GET THE BLOWER CHART FROM WEIAND. Its the only way to have a solid answer, every application is different.
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Old 09-15-2010, 03:47 PM
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Quote:
Originally Posted by turbolover
GET THE BLOWER CHART FROM WEIAND. Its the only way to have a solid answer, every application is different.
Good point. I only tossed out BDS because that's what I have and I knew they had a chart. Don't know anything about Weiands.
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Old 09-15-2010, 03:57 PM
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The chart you are looking for will look something like this-
http://upload.wikimedia.org/wikipedi...ciency_map.jpg

However this one does not have blower speed nor cfm listed, both of which are required.

Weiand's chart does show that a 350 with 30% overdrive should produce about 24 psi (which will vary with each engine), BUT you're looking at a minimum of a 450 outlet temp (probably closer to 600 in operating conditions), which will rise dramatically in anything longer than 1/8 mile.
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Old 09-15-2010, 04:08 PM
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Quote:
Originally Posted by darkostoj
so after 8-12 psi the boost charge just gets too hot then?
This is probably the most you would want to run the 671 and be safe. Anything after 12lbs and you really start to heat things up inside the engine. I have a 2.8 Kenne Bell on my Mach-1 and I run 17lbs of boost on a street tune, but, the KB is intercooled. My IAT-2 temps run about 170 degrees, (This is charge/boost temps that get forced into the engine, post supercharge. I bet if you push 12 lbs out of the 671 which is an old roots style blower and non-inter cooled, your IAT's would be well over 250 degrees. At this point, the 671 becomes a heater....
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Old 09-15-2010, 05:09 PM
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1)Check into Water/Alcohol injection or a Superchiller.
2) Rule of thumb unless you have a 144,177, or 250(ie not your 6-71) never overdrive beyond 25%, so if you need more check into a 8 or 10-71.
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Old 09-20-2010, 10:22 PM
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It's true you can run a 6-71 at 70% over. We did it on alcohol. Drag race only and not really a stock 6-71. It really stumbled at the top end and required multiple high speed valves but it sure got with the program off the line.

If you are talking about a street blower and more or less stock clearances I think about 25 % over would be about the max that the blower would survive at using E-85. I would approach it gradually and monitor both temp and boost. I can't imagine running more than 15 pounds boost without an intercooler. I'm basing this on running no more than 4500 rpm sustained....like in a boat.

I run 5% under and 8 pounds boost at 3/4 throttle and I put a lot of miles on. It can get pretty dog gone hot even cruising at 13 inches of vacuum on a 98 deg day at 3000 rpm.
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