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Discussion Starter #1
Two questions:

1. Can I use 75W-90 synthetic oil in the front of my 6-71 blower? I hope so because that's what I filled it with. I went to NAPA and they had a special on Valvoline 75W-90 syn and the tag on the blower did not say which 90W oil to use.

2. Belt deflection. I've got the belt and idler assembly all finished and everything is bolted on. How "loose" should the belt be? I'm running a 54-tooth upper and a 48-tooth lower, 8mm belt, 1600mm long (69").

Thanks!

john
 

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AKA Lee in KC
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1. Snythetic should be fine.

2. BDS told me to set a straight edge between the drive pulley and the driven pulley on the non-idler side, then measure deflection mid-way between the pulleys. They said 3/4" to 1" would be about right.

You are running about 12-13% under-driven. Is that what you intended? I'm running mine at 1:1 (48-48) and getting only about 6 lbs. of boost at 5,000 rpm.
 

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Your oil should be fine. As far as the belt, adjust it as mentioned above. Error on the side of too loose rather than too tight. Tool loose will not cause damage, too tight will put added stress on the crank, and blower bearings. You will be shocked at how much the blower "grows" when it's warm. Always double check your belt tension once the engine is warm.

Engine and blower size along with other variables will determine how much boost is made. I run an 8-71 at 10% underdriven and make 12lbs of boost on a small block.
 

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Discussion Starter #4
Thanks everyone. Just so I am sure on this 1" of play, I measured down halfway between the pulleys (the long run) and set it so that it moves a total of 1" back and forth at this point. When all warmed up, how much should it move at this point so I know how much slack, if any, I can take out when cold?

Sure wish that black box would show up today. I'm dying to get this on the street before old man winter makes me put it away till spring!

Actually, I'm trying to make it to the Southern Super Heavy Shootout VI down in Commerce, GA this coming weekend. www.sshs6.com for those wanting to read up on it.

Cheers

john
 

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Technical Support Barry Grant
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Check with your blower manufacture, some do not like synthetic oil for their seals.
 

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I would suggest setting your belt so it will "deflect 3/4 -1" not back and forth but if you push it in. It is much better to error on the side of to loose. When it is warm you do not want the belt like a banjo string, you wtill need a little play not a bunch but, enough to know it's not stressing the crank and blower bearing. It's a feel thing. You will know it once you fire it up and see how much it grows.

Tech @ BG, Good point about the synthetic oil. Probably not an issue but, better safe than sorry.
 

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Technical Support Barry Grant
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I've got superchargers from different companies, one uses syn, while the other can't....
 

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Discussion Starter #8
Ok, so total movement should be 1.5-2" at the centerpoint. I'll loosen it up a tad and then see how it goes.

Thanks everyone!

John
 

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2" will probably be a bit too much but, I bet 1.5" will be close.
 
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