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Thread: Engine builders with dyno experience?

  1. #1
    Member JUNIOR BUILDER
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    Engine builders with dyno experience?

    Still looking for an answer to my previous post. Is there a gain in horsepower from a standard bore to a .030 bore? Taking into consideration that the larger the bore each time, the heavier the piston. Has anyone done any experimenting on the Dyno in this area? Looking for knowledge to inform the track where I race that there is no reason to throw away our engines just because they wear beyond the .030 bore that is allowed. thanks, Don Gordner
    Safety is only what one makes of it!!!!!

  2. #2
    Senior Member RACING JUNKIE
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    There is no replacement for displacement.

    When it doubt, bore it out.

    Sure a .030 over motor will make more power than a standard bore, a .060 over motor will make more power than a .030 over.

    How much more power? That depends on your HP per CID.
    -WJ Birmingham

    OneBadGMC.com

  3. #3
    Administrator RACING JUNKIE bjuice's Avatar
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    many people cannot get in their mind the cubic inch theory and thats cool..we have all been there..some of us still are...lol ...

    when i was starting out..it was desrcibed to me this way.....

    think of a cylinder as a coffee can.....the bigger ( bore/stroke) you make the coffee can the more contents it will hold...

    contents = air and fuel..
    which causes a larger explosion = equals more power..


    this is how i would explain the cubic inch theory to anyone starting out..


    a rule of thumb i have always been told is 1.5 hp per cubic inch...a good engine builder with top of line parts has seen 1.75/ 2hp per cubic inch. ( naturally aspirated)


    the old saying is has always been ( no replacement for displacment)

    this only holds true if your engine is naturally aspirated,,turbo's, nos,blowers will make a 355ci think its a 632ci..

  4. #4
    Member JUNIOR BUILDER
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    What about the weight of the pistons??? Wouldn't the weight of the piston in the new bore counter the new bore itself?
    Safety is only what one makes of it!!!!!

  5. #5
    Senior Member RACING JUNKIE fla1976's Avatar
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    Bore size

    The actual piston weight difference between a standard bore and a 0.030 is negligible. That is if you use the same type piston. If you are going from a cast to a forged piston, you will usually add weight. I personally believe the added strength is worth the weight. The added power comes from more capacity , more power. Just boring the engine will boost the compression alittle also. The volume of the cylinder is larger but the head volume stays the same, so the compression will be greater. There's the old saying, "When in doubt, punch it out".

  6. #6
    Senior Member RACING JUNKIE jmarksdragster's Avatar
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    One thing to consider, more bore on a stock blocks make the cylinder walls thinner. If you can't keep the cylinder round you may lose HP. It will depend on the block and how much wall thickness you have, as well as how much power you are trying to extract. What about using sleeves to keep it at .030?
    Mark Whitener
    http://racingfuelsystems.myfunforum.org
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  7. #7
    Senior Member MASTER BUILDER
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    We had 1 guy years ago, that ran a 412 in a super gas car. The factory block cracked, and was un-usable. So, by them Dart had blocks available. We used a new Dart block, and he wanted to stay at 4.125 bore, basicaly standard. His old block was 4.185. Obviously new pistons were used, but they were the same Je piston, except for a 4.125 bore, otherwise, all his old parts went back in. Engine went from 685 hp, to 650hp. .060 over in that case was 35hp.

    Other good examples, are big block chevy's, from a 540 to a 565, no other change, your talking 35-40+hp there too. 25 cubic inch, is a lot, and its all from increasing bore size. Part of the gain is from unshrouding from the bigger bore, plus the added cubic inch. Do the math. If you have a given combo making say 850hp, at 540 cubic inch, thats 1.57hp per cubic inch. Now, add 25 cubic inches, and simply multiply 565 times 1.57 and you get 887, thats 37hp. And that is a common gain, from just the bore size on those engines. But again, your gaining a lot of cubes.

    Frank
    Advanced Performance
    www.get-ap.com

  8. #8
    Senior Member MASTER BUILDER
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    Sleeving all 8 on a stock block works ok for street engines that are low comp ratio but in a race application even a 3/33 wall sleeve weakens the deck enough that its hard to keep a head gasket in the engine.the center bolts are the problem.we tried that years ago and the deck wasn't strong enough for even a 150 shot.
    The stock blocks we have dynoed made more power at .030 over than @ .060 wall flex and poor ring seal really show up @ .060,this was on 13.5-1 alcohol engines.Bill
    Hendrens Racing Engines
    1310 U.S. Hwy 221 North
    Rutherfordton N.C. 28139
    828-286-0780 Bill, Steve, Mike
    www.hendrensracingengines.com

  9. #9
    Senior Member RACING JUNKIE
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    Quote Originally Posted by bjuice
    many people cannot get in their mind the cubic inch theory and thats cool..we have all been there..some of us still are...lol ...

    when i was starting out..it was desrcibed to me this way.....

    think of a cylinder as a coffee can.....the bigger ( bore/stroke) you make the coffee can the more contents it will hold...

    contents = air and fuel..
    which causes a larger explosion = equals more power..


    this is how i would explain the cubic inch theory to anyone starting out..


    a rule of thumb i have always been told is 1.5 hp per cubic inch...a good engine builder with top of line parts has seen 1.75/ 2hp per cubic inch. ( naturally aspirated)


    the old saying is has always been ( no replacement for displacment)

    this only holds true if your engine is naturally aspirated,,turbo's, nos,blowers will make a 355ci think its a 632ci..
    If you read his other post, you'd know that he's talking N/A for a roundy round application. Maybe it was just more fun trying to belittle me?
    -WJ Birmingham

    OneBadGMC.com

  10. #10
    Administrator RACING JUNKIE bjuice's Avatar
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    What ?.....geez...if you think i was trying to belittle you..i APOLOGIZE...WOW !! :shock: ..


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