tuffxd

hey guys, i have found a 3/71 gmc blower for sale seems to be in good nick was wondering if it is big enough to add a good power increase to a 302 if i could spin it fast enough or would i be wasting my time coz its to small? any oppinions would be greatly apreciated coz im ripping my hair out at the moment trying to find a similar project on the net lol.

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Finally back in an XD

 

gus351

HI ToughXD,
Yeah, unfortunately you are right, unless the motor was bone stock, a 3/71 is too small for a V8, even a 302.
They simply don't flow enough air to feed 5 Litres.
As they are not efficient in design either, you couldn't overdrive one fast enough to get the required airflow you need.
For any V8 of 5 litres or more, a 6/71 is required. Tough 351's will use 8/71's or even larger for drag use.
Keep an eye on ebay or the trading post. Be careful with used ones as many need a major overhaul, new teflon seals etc, bearing kits or machining if foreign bodies have been sucked in to them.
Maybe talk to some reputable speed shops, they often have used ones lying around and may be able to help you out.
cheers
gus351

tuffxd

thankyou gus351, the plan is to freshen up the old 302 i got lying around and use it in my burnout car i figured if i keep it stock apart from decompress it i can get resonable torque and power without spending a fortune, wont rev it to hard prob 5500 to 6000 max. so yeah its just tryin to find a 6/71 at the right price i dont care if it lookes terrible coz it just gunna be a dirter. what is your oppinon n 4/71's that way i only need to 1 boost referenced carb.

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Finally back in an XD

gus351

hi tuffxd,
a 4/71 would probably be ok for a stock 302. you'll need to beef up your coil and electrics too.
Blown Clevos work better with protected tip plugs around the 7 heat range.
You'll have to pull a lot of timing out of the engine, about 24-26 total, but don't worry that's how blowers are set up.
If you want a little more insurance, a couple of hundred dollars for a water/ methanol injection kit for when you do burnouts might be worth considering. It will help prevent detonation and enable you to run a bit more timing safely.
The safe limit for a roots blower is around 8-10lbs of boost
cheers
gus351

funny1

funny1