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305 heads on a 350.1st hand experience only please!

Discussion in 'The Garage' started by 3car, Sep 10, 2003.

  1. 3car

    3car 1/2 ton status

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    heres the deal.i have a 90'truck 350 shortblock thats fresh,with flattop pistons with 2 valve releifs.i believe deck height is stock.the heads i want to use are 305 heads from an 86'monte carlo ss,305 h.o. with 1.84/1.50 valves,and 58 cc chambers,because i have them,and they are fresh.i guess i will get the combustion chambers polished,and use a thick head gasket to lower the compression ratio a little,but will it still be to high for 93 octain gas? /forums/images/graemlins/confused.gif /forums/images/graemlins/crazy.gif
     
  2. chevyracing

    chevyracing 1/2 ton status

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    I ran 305 heads on a 350 on 89 octane with no problem. I had to use the 305 exhaust manifolds though because the rear holes were not correctly spaced on the 350 manifolds.

    The biggest issue is they flow like crap.

    John
     
  3. 3car

    3car 1/2 ton status

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    thanks chevyracing,also your signature rocks!
     
  4. 83ZZ502_Jimmy

    83ZZ502_Jimmy 1/2 ton status

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    I could only run 93 and it still pinged under load. Plus they absoutely sucked as far as power goes. They just dont flow enough to do anything. I know you may want to try and use them , but IMO its not worth it, cause you'll be swapping them again soon enough.

    John
     
  5. wrathORC

    wrathORC 1/2 ton status

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    A "good" 305 head flows 135cfm. A "good" 350 head flows 165cfm. With many hours on a die grinder you can get up to 160cfm out of a 305 head. This means that you're still better off with 350 heads on a 350. Plus, you still are losing to the shrouding problem of the heads.

    If you have someone polish them then have them CCed as well.

    Let's assume the "dish" for the reliefs are 3.1cc (usually four are from 6 to 6.5cc). Let's say you choose a .041" thick headgasket. With 58cc heads you're around 10.5:1.

    If you've already got a lot of money tied up in the 305 heads then use them. Otherwise, sell them and get some 350 heads. You can probably sell that driver side 305 head for around what a freshly machined set of 350 heads cost at a machine shop. Those driver's side 305 heads off Monte Carlo SSs were only used on those cars, nothing else. They're getting rare and expensive.
     
  6. 3car

    3car 1/2 ton status

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    thanks for your input guys,you have convinced me. /forums/images/graemlins/thumb.gif
     

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