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Making a square motor
sander288 - May 14th, 2009 at 03:36 PM

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

RISKYBUG - May 14th, 2009 at 05:58 PM

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

sander288 - May 14th, 2009 at 09:19 PM

looking online actually I just found some motors with a similar combo, but I suppose there is a reason why this isn't done anymore

http://www.thesamba.com/vw/forum/album_page.php?pic_id=200551 
http://www.thesamba.com/vw/forum/album_page.php?pic_id=329477 

mnsKmobi - May 15th, 2009 at 01:09 PM

Quote:
Originally posted by sander288
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 - May 17th, 2009 at 02:25 PM

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 - May 17th, 2009 at 07:05 PM

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!

Craig Torrens - May 17th, 2009 at 09:22 PM

Quote:
Originally posted by mac76
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 - May 18th, 2009 at 03:35 PM

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.:)