Bore Vs. Stroke...... - Chevelle Tech
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1999 -- Tech Files - reference area
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Old Feb 18th, 00, 4:24 PM
Horsepower69 Horsepower69 is offline
Join Date: Feb 2000
Posts: 17

Is it true that an engine with a big bore and short stroke will produce more horsepower than torque?? Will an engine with small bore but long stroke produce more torque?? My last question is: will an engine with a big bore and long stroke produce good torque and horsepower??


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Old Feb 18th, 00, 10:04 PM
IgnitionMan IgnitionMan is offline
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Old Feb 18th, 00, 10:21 PM
DZAUTO DZAUTO is online now
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Ditto. You catch on quick.

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Old Feb 20th, 00, 3:27 AM
robzr robzr is offline
Join Date: Dec 1999
Location: Chicago, IL US of A
Posts: 11

bore:stroke ratio is something that I'd like
to discuss, hopefully some people out there
are willing... here's some tidbits of
knowledge that I can share with ya:

When bore is greater than stroke, the engine
is called oversquare I think. I guess that
means a large stroke engine is undersquare?

One important factor is that a large bore
engine will have greater area for the valves
than the same displacement engine with a
larger stroke. Large valves (in relation to
displacement) are better for higher rpm power.

A shorter stroke means less distance for the
piston to cover with each revolution, there
fore the pistons velocity, and hence
acceleration is lower than that of a large
stroke motor. Less acceleration means less
force (stress) on the rotating assembly, so
the motor can safely rev higher. However,
force = mass * acceleration, and a larger
bore motor will have heavier pistons. I'm
guessing that this still works out in favor
of the large bore engine, though, as large
bore engines can rev higher.

I think the only other factor that could come
into play here would be the actual motion of
the piston/rod. Longer stroke motors will
have a lower rod:stroke ratio. However I
believe that a higher rod:stroke ratio is
better for power throughout the rpm range,
so it would seem like the large bore engine
wins out here.



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Old Feb 20th, 00, 5:30 AM
Gene Chas Gene Chas is offline
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Join Date: Apr 1999
Location: Buffalo, NY
Posts: 1,525

And small bore/long stroke combinations can handle more compression than big bore/short stroke combinations.

Gold #62/ACES
67 SS396/L88
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Old Feb 21st, 00, 12:00 AM
Schurkey Schurkey is offline
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Within the general limits of production V-8 car engines produced from WWII to about 1995 or so, I think that Bore/Stroke ratio is overemphasized.

Look at the difference between Buick 455 and Olds 455 engines:

Buick has 4.32 bore and 3.9 stroke. Big bore, short stroke. Very oversquare.
Olds has 4.125 bore and 4.250 stroke. Small bore, long stroke. Very undersquare.

The Buick should be a high rpm screamer, and the Olds could go into a John Deere tractor...

Except BOTH engines are famed for low rpm grunt, and neither one will rev like a 454 Chevy.

Ford used to advertise thier 427 as being like a "race engine" because of the big bore/ short stroke.

Chevy's 427 has almost identical Bore/stroke, and Chevy stuffed them in two ton potato trucks, in addition to L-88 Corvettes.

True enough, bore/stroke makes a difference when you're talking Formula 1, Nascar, even some wild ass motorcycles (Suzuki's GSXR 750's come to mind, also Honda's oval piston wonder/nightmare.)

For all the rest of us, Carburation and manifolding is MUCH more important. Cylinder head flow capacity is MUCH more important, Combustion chamber quench and swirl is MUCH more important, reciprocating/rotating weight is more important and perhaps rod length is more important, too.

Far too many engines are blown up because the valve train was over-revved, rather than the bottom end fragging because of a long stroke.
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Old Dec 22nd, 04, 4:01 PM
wrencheadblues wrencheadblues is offline
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just what I needed to help me building my tall deck 427 trk blk - thanks let me know if you have any tall deck parts
CPE= 1930 3window coupe / Trk= 1966 elky big blk 4spd / DROPTOP=1966 SS convertible 2nd owner / 1966 drag car 427
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Old May 9th, 06, 12:22 AM
david5 david5 is offline
Join Date: May 2006
Posts: 1
Default Bore/stroke 101/73 that

I am wondering about the new BMW R1200S... The Germans made them with
Bore/stroke 101/73 that produces 122 HP at 8250rpm...

My questions is,,, if I would reduce the stroke to 56 instead of 73... what would the HP outcome...? I wonder about that....

Does anyone have an idea about the above?
I love the way the BMW R1200S looks... Great design...

I was planning on buying a SP2/RC51 but I might swith to BMW if HP works out well...

Please let me know
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