Can someone please fill in the blanks for me or tell me the formula to work it out, I am thinking about building a stroker 1275 motor and would like some capacitys, bore size Vs stroke. The block is currently Std bore.

78mm
79mm
80mm
81mm Std bore 1275 +030 1300 +060 1330
82mm
83mm
84mm
etc

Thanks.
David.

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The formula is as follows:

Bore in inches
Stroke in mm

((((pi x ((bore + overbore) x 25.4)^2)/4) x stroke) x 4) / 1000

Basically you use pi x D^2 / 4 to find the area of a circle, multiply that by the stroke, multiply by 4 (4 cylinder) and divide by 1000 to the numbers to cc's.

Hope that helps.

Otherwise, here is a table I prepared just before:

Bore (in) Bore +0.030" Bore + 0.060"
Stroke (mm) 2.780 2.810 2.840
78 1221.4 1247.9 1274.7
79 1237.0 1263.9 1291.0
80 1252.7 1279.9 1307.4
81.28 1272.7 1300.4 1328.3
82 1284.0 1311.9 1340.1
83 1299.7 1327.9 1356.4
84 1315.3 1343.9 1372.7

<edit> if you "quote" this post the table formatting comes out heaps better.

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or use this calculator
http://www.ajdesigner.com/phpengine/engine_equations_cubic_inch_displacement_b.php

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Thanks guys, That was just what I was after.

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sorry for the hi-jack but can you de-stroke a crank ?

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120bhp with 450kg just fun waiting to happen

We were prob. drunk when we set it up last and thought this will be a good idea

Yes.

if i use an uncracked 1100s b/j crank how far un-stroked can i go ?

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120bhp with 450kg just fun waiting to happen

We were prob. drunk when we set it up last and thought this will be a good idea

depends on the wear of the big end journals, but basically the maximum offset is the difference between large and small journal sizes for the diamter, with the centre of the journal is then offset by half this number.

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the world is a book, and those who do not travel read only a page
66 Mini Minor sponsored by http://www.lifeonthehedge.com.au/ The Dog Harness Specialists
It was a pleasure ausmini. I'll miss all you misfits and reprobates

'Bohrung' means bore, 'Hub' means stroke

red - std. cc
green - std. overbore
blue - other popular oversizes

Helpfull? (may contain the odd rounding error)

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If you are prepared to grind the crank more undersize than usual, you can get more stroke (or less stroke if destroking).
Matt Read aka TheMiniMan holds the record I think, he did a couple with the crankpins at -.080".
But to do this, he had to corner the world market of -.080" bearings...

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

With a good [std size] 1.750" B/J crank you can shift the center by 3mm to 1.625 [allowing for clean up] and this X by 2 will add 6mm to the overall stroke.
If you want to de-stroke then just use a 998 crank[1275 crank 81.28 -6 =75.28 and 998 is 76.2 mm] with spacers in the block and caps[2" to 1.750"] or new steel caps.

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www.minisprintgt.com

so if i put a 998 crank into a 1275 block with a 120" over bore i would get 1298cc.

thats cool

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120bhp with 450kg just fun waiting to happen

We were prob. drunk when we set it up last and thought this will be a good idea

Might be cool for the track (if 1300cc limit) but give me more cubes for road use. A 1445 stroker's torque would suck the doorhandles off your 1298.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

And stick a 16 valve twin cam head, fuel injected and a blower on it then you will make some HP

_________________
Research is the difference between speculation and investment. Anyone who copys some one else will always be second
www.minisprintgt.com

s/sedan rules not force fed and under 1300. So i figure if I have a big bore and a small stroke I should have the best of both.

_________________
120bhp with 450kg just fun waiting to happen

We were prob. drunk when we set it up last and thought this will be a good idea