Refresh costs 71 307 vs 86 305

Discussion in 'Engine Topic' started by Matt T, Sep 29, 2016.

  1. Matt T

    Matt T Veteran Member

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    Advice?
    Yes, I know they both suck and everything is old tech.
    Goal: (finally) get it running--cheap and reliable:
    -original to this car 307, sitting out of it for over 25 years. Complete unknown.
    -'86 t/a (parts car) 305. I got it running yesterday. It had not run in maybe 20 years, but obviously basics still work. It smokes but runs pretty smooth considering.

    RockAuto: 305 kit (no machining) ~$400. 307 kit ~$200. The 305 kit is Sealed Power components and the 307 is off-brand/unknown. I've got to check the parts lists. I figured the 305 would be cheaper--newer and way more of them around?

    My wife rightly points out, why put money into another motor you don't want to keep? Actually she asked why even keep the 307 when I explained it was original but not actually valuable. (I also have a 350 core that I planned to build for the longer term, higher $ version.)I could put the ignition, intake, and fuel parts from the 305 on the 307 since I now know they work.
     
  2. grzewnicki

    grzewnicki Veteran Member Lifetime Gold Member

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    I agree with your wife...Build the 350, I wouldn't waste my time on either of the other motors. If it came down to the 305 or 307, probably the 305 since maybe it has less miles on it (?) and is known to run. What's your plan, just a hone, fresh bearings and go?
     
    Last edited: Sep 29, 2016
  3. Damon

    Damon Veteran Member

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    Unless you have some special attachment to the 305 or 307, I wouldn't waste my time rebuilding either of them. If you just need it running and mobile, drop in the 305 as-is to get you from A to B. Otherwise, build the motor you want from the start. Every dollar you waste on an "interim" motor is a dollar you no longer have to build the one you really want.
     
  4. Crusty75

    Crusty75 New Member

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    Rebuild the 307 core and top it off with a healthy cam and the heads off of the 305 and you'll have a pretty good running motor
     
  5. 70-camaro

    70-camaro Veteran Member

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    I did a 307 bored it 30 over, Comp cam,305 601 casting heads, edelbrock intake and Pro-form carb. Real torquey with 355 gears. Of course you wouldn't have to bore it.
     
  6. giggity

    giggity Veteran Member

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    It wont cost any more to build the 350 as it would the 307. Do it right the first time, or dont do it. in the end your will spend more time and money doing both.
     
  7. tom3

    tom3 Veteran Member

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    Throw some cast rings/bearings, seals and gaskets in the 307. Backyard rework the 305 heads for it and put it back in the car. Might surprise you. Have some fun with it while you plan out the next move.
     
  8. Cataldo

    Cataldo Veteran Member Lifetime Gold Member

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    I see two options, 307 or junk yard vortec 350. '86 305 doesn't even have the perk of being a roller motor, IIRC.
     
  9. shad_van

    shad_van Veteran Member

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    it depends on what your looking for out of your car. if you just want it running I say go with the 305 as it is already running, but there are other reasons for choosing the 305 as well.

    the 305 had a 3.736 bore and a 3.48 stroke. the smaller bore than the 307 but a longer crank. it will make more bottom end torque, and that is what you want in a street car. if your looking to do it with out rebuilding the engine this is the way to go.

    the 307 has a 3.875 bore and a 3.25 stroke. the larger bore will help the engine breath better at higher RPM, but the 307 was never really a performance motor. I say clean it up, give it a rattlecan rebuild, and put it on an engine stand in your garage and use it as a trophy. that way you have it if you ever need it and want to put it back to factory.

    in reality neither motor is going to be better than a 350. which has a 4.00 in bore and a 3.48 in stroke. you get the torque and the better breathing. Also GM put them in everything, so they are cheep. it should be cheaper to rebuild a 350 than either the 307 or 305. the rock auto enginetech kit RCC350A for a 350 is only $140! it does not include a cam and lifters. add a seal power cam and lifter kit KC274 from rock auto for another $99. that is less than $240 for a complete rebuild kit. don't forget to add the cost of machine work for the block, crank, and heads as well. the last time (about 2 years ago) I had a 350 bored and honed it was $200 bucks and an exchange crank for $75 dollars and reconditioning the rods cost just under $100 and they installed the new pistons on them for me for free. a $200 of a valve job and you are still under $825 for a completely rebuilt 350. it would be a solid running motor, in the 250-275HP range, depending on the factory heads.

    Throw on a set of headers, a performer manifold and a Edelbrock or Holley carb and it should bin in the 300-325 range.
     
  10. thrasher

    thrasher Veteran Member

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    With all things presented here the 350 and your wife sound like the only things to keep and spend money on.
     

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