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Ways to tell a 305 from a 350

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Ryan88Jimmy, Jun 27, 2000.

  1. Ryan88Jimmy

    Ryan88Jimmy Registered Member

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    While I had the tranny off my dad had a look at the flexplate, and he said that I must have a 305 because there were some weghts on the flexplate. He says that 350's were internally balanced and that 305's were externally balanced. When I checked my option codes that I found in the glove box, it said that I had the 350 from the factory.

    Now my question is, is there any other way to tell the diff between a 305 and 350? Also, maybe the previous owner used the wrong flexplate?? Man, I don't want no stinkin 305 ;)

    Ryan88jimmy
     
  2. James90

    James90 1/2 ton status

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    read every thing you can find on your K5 and you might find out what you have I sure hope you have a 350 what kind of gas mileage do you get

    [​IMG]Go prepared
    </font color=red>90 k5 soon to be big, bad, and mean
     
  3. chevidog

    chevidog Registered Member

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    305's and 350's are both internally balanced, the only small block that is not internally balanced is the 400. Could the engine be a 400? It could be a 400 flexplate installed on a internally balanced motor (305, 350), but the thing would have shook like tazmanian devil since it would have been terribly out of balance. Without literally measuring the stroke of the crank I don't believe that you can distinguish a 305 from a 350 unless you match the code on the front of the pass. side block in front of the head with a reference manual. If the flexplate was trully from an externally balanced engine, then you are probably looking at a 400.
     
  4. Ryan88Jimmy

    Ryan88Jimmy Registered Member

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    Whoops, I meant to say that my dad had said that 400's were externally balanced. And since they stopped producing 400's years ago, it must mean that someone had installed the wrong flexplate.... I think [=

    As far as gas mileage goes, I've never really wanted to find out :) besides, if I did it would be in litres/kilometer. And that wouldn't do anyone any good ;)

    Also, my truck is an 88 Jimmy

    Ryan88Jimmy
     
  5. ken

    ken 1/2 ton status

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    THe stroke of a 305 and 350 are THE SAME. Only the bore size is different. The only sure way to tell without miking the bore, is to look up the casting # of the block. Check Mortec's site www.mortec.com for casting # info.

    ken
     
  6. MudRebel350

    MudRebel350 1/2 ton status

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    According to the specs page here it sez they stopped making the horrible 305 in 1988 so there you go. I had an 87 with a 305 and it sucked on gas and everything else. The 350 in my jimmy gets better mpg's than the 305.

    J.D.
    88 Gmc Jimmy
     
  7. 4x4blazer

    4x4blazer 1/2 ton status

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    One thing to keep in mind here is that the engine you are running now may not be the original engine. I would only trust the casting number.
     
  8. Bruiser

    Bruiser 1/2 ton status

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    Casting number

    I have the guild to small block casting numbers, if you post it here or e-mail it to me I will look it up. That will tell you if it is a 305 or 350.

    Vincent Michels
    1978 Blazer
    Bruiser (Frost white/Black top/ Light Blue interior)
     
  9. Ryan88Jimmy

    Ryan88Jimmy Registered Member

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    Yeah when I bought the truck the salesman said that there had been a fresh targetmaster or whatever 350 put in 20k kilometers ago. Wasn't sure if that guy was full of it or he just didn't know what he was talking about

    Also found out today that 350's 87 and up did have an external weight on the flexplate. So I pulled the tranny and flexplate off for no reason :(

    Ryan88Jimmy
     
  10. 87Blzr

    87Blzr 1/2 ton status

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    Does the engine have center bolt valve covers? If not its a pre 87. If it was a 400 it would also have a different harmonic balancer. Because the 400's are externally balanced the balancer isn't smooth all the way around. Its hard to explain but it has some material removed part way around for balancing. If its a targetmaster then it should say targetmaster on the valve covers. Targetmaster engines don't come with centerbolt valve covers no matter what the year. What are the numbers on the block pad underneath the alternator? Also if its a later model engine (later as in late eighties) then the displacement in liters is cast into the block at the bellhousing flange on the drivers side. Hard to see with the engine in the truck but not impossible. Should say 5.0 or 5.7 Should also be a G meaning a gas engine

    87 K5 Siverado, 68 SS 396 Camaro
     
  11. Logan

    Logan Registered Member

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    >Now my question is, is there any other way to tell the diff between a 305 and 350?

    Hehehe, just stomp on the gas pedal! You can always spot the 305, because nothing happens. ;)

    -Al.
    '84 GMC FS Jimmy
    Getting it's 350 Heart Transplant TODAY!
     
  12. blazer72

    blazer72 1/2 ton status

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    All 400 also say 509 on each side of the block, this is cast into the block the numbers are about a inch tall. There were some replacment 400's out there for a time. I thought the target motors came with dampers and flywheels anyway. Plus there is know way that any SB other than a 400 would live with that flywheel on it for long and never for what 20K miles!
     
  13. Blazin'Grrl

    Blazin'Grrl Registered Member

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    Hey, I'm extremely offended! My 83 Blazer has a 305 in it, and it runs just as good as anyones 350! It gets 15 mpg and I take it mudding with no problem at all. :P

    <font color=purple>Sarah</font color=purple>
    <font color=purple>[​IMG]'83 K-5 Silverado Blazer[​IMG]</font color=purple>
     
  14. BlazerBoy

    BlazerBoy 1/2 ton status

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    I dont think anyone meant to offend you, I think the boys meant that the 350 is stronger and more powerful than the 305. I have owned a 83' with a 305 that ran like a champ never had a problem. I also have my 87' with a 350, it also runs great, but is much more powerful. Yet does get worse gas mileage then the 305. Its a trade off.

    BlazerBoy
    http://generalblueballs.coloradok5.com
     
  15. 87Blzr

    87Blzr 1/2 ton status

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    Be careful with the 400 casting number. 509 is legit for 70-71 4bolt and 74-80 2bolt. But also 817 can be used for 72-80 2bolt and 511 can be used for 70-72 4bolt. As far as the 305 vs 350 the 305's aren't a good motor to build because of the small bore. It makes it harder or impossible to add big valve heads and they didn't make any performance versions. BTW I don't consider a 195 horse TPI 305 "performance". There is nothing wrong with a 305, just no reason to have one if you can have the advantage of a larger motor in the same package. Kind of like the big blocks. If you had a choice between a 396 and 427 which would you choose? Most would say the 427 because why take the smaller displacement motor when you can have the larger in the same package? I will have to say that I believe that the 350 will give better gas mileage in certain instances. A friend used to have a 97 ford f350 with a FI 460. Had plenty of power and got fair gas mileage. We accidently totalled it badly, wasn't our fault though. The truck he bought in its place is a 97 f350 with a 351 FI. Much less performance with worse mileage but same gear ratio and trans. We contribute it to the fact the 351 must work and rev so much more to do the same things the 460 did. Just taking off the 460 barely had to rev to get the truck going. The 351 tries pretty hard and has to rev more. Its a heavy truck to move around. I suspect the 351 will wear out faster than the 460 would have also due to how much harder it has to work

    87 K5 Siverado, 68 SS 396 Camaro
     
  16. James90

    James90 1/2 ton status

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    I just like big thinges big K5 and I want a big block 502 to replace my 350 that would be nice

    [​IMG]Go prepared
     

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