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Making a square motor

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sander288 "Bolt-on Master"

1,404 posts · joined Aug 2008 ·

#712342
I was browsing through an old holden brochure the other day and was reading how the old FE's etc had square motors, and I was thinking what a square motor would be like in a bug, as I know we tend to always be over-square with a small stroke and big bore,

For example how do people think a 77 bore x 76 stroke would run? is it even possible?

food for thought I thought
BMW R65 LS
1967 1300 Deluxe
Swing-axles FTW ❗

RISKYBUG Seriously Crusin Dubber

187 posts · joined Mar 2008 ·

#712373
i don't think that would be much good
there is a ratio of bore to stroke for a good donk
little pistons with that kind of stroke i dont think would be worth trying

mnsKmobi Wolfsburg Wizard

589 posts · joined Aug 2002 ·

#712560
sander288 wrote:I was browsing through an old holden brochure the other day and was reading how the old FE's etc had square motors, and I was thinking what a square motor would be like in a bug, as I know we tend to always be over-square with a small stroke and big bore,

For example how do people think a 77 bore x 76 stroke would run? is it even possible?

food for thought I thought
small stroke and big bore is probably because it is easier to change the p & cs then the crank!

mac76 Learner Dubber

12 posts · joined May 2009 ·

#712951
problem with going smaller with the p&c is you have to runn smaller valves which is no good for hp! square as in 94 X 94 is great but no room for a crank that big and the engine would be very wide with a decent rod ratio. I have been pondering building a 2ltr motor for hillclimbs using a oxyboxer case with 101.6mm p&c and a custom 62mm crank but you would need to rev the tits off , but it would be a great little combo with massive valves and heaps of hp potential. so what i am saying i believe over square is the way to go.

sander288 "Bolt-on Master"

1,404 posts · joined Aug 2008 ·

#713006
I agree I just was putting it out there, over square always seems to produce the best results and is a bit easier, I remember a conversation with stan pobjoy about over square and stroking motors, which did take a couple of hours but the point was porsche have been making boxer motors for years and have stuck with an oversquare combo and it works best and is more reliable becasue of the smaller crank.
Cheers all!
BMW R65 LS
1967 1300 Deluxe
Swing-axles FTW ❗

Craig Torrens 6 times Australian, 7 times State Hillclimb Class Champion

8,040 posts · joined Jan 2003 ·

#713046
mac76 wrote:oxyboxer case with 101.6mm p&c and a custom 62mm crank but you would need to rev the tits off , but it would be a great little combo with massive valves and heaps of hp potential. so what i am saying i believe over square is the way to go.
My combo that I'm doing at the moment is 66mm stroke x 103mm pistons.


psimitar Son of Jim - Creator of Good

2,506 posts · joined Jan 2009 ·

#713172
if I remember correctly, a longer throw crank creates more torque but you need a big enough explosion to keep it running smooth so there's a limitation to the size of piston you can use.
They did this with the Sierra Cosworth and made the 2L into a 2.4L just by using a longer throw crank. Due to the turbo charging they could make sure the bang was big enough but didn't have to dial the PSI up by much to create a very lazy motor that pulled like a V8. Ended up being marketed at the caravaning brigade.🙂
madness is in the eye of the beholder 👍