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Calculating engine sizes?

4K views 32 replies 8 participants last post by  shultzjr 
#1 ·
hi all,

I have been trying to get 1130cc and 1250cc for the engine sizes of the v-rod and I have been unsuccessful. And yes I am sure I am using the right formula size=(num.cyl)X(stroke)X(pi)X(radius squared) so where's the rub? Does harley-davidson use metric or the english system in its' engineering? Please show examples.
What is the max size the v-rod can be bored and stroked with stock case and cylinders?

thanks,
charles......
 
#2 ·
The calculation is done using english units. Displacement = (2.835)X(3.14)X(3.94/2)(3.94/2)= 69.095 cubic inches. To convert to cc's multiply by 16.387 which should give you 1132.26 which is rounded to 1130.

Some people have produced 1550 cc's V-Rod motors.
 
#5 ·
Is this what you were thinking of?


1130 bore = 100mm
1250 bore = 105mm
Stock stroke = 72mm
Destroyer stroke = 75mm
"1/4" stroke = 78mm
"3/8" stroke = 81mm
"1/2" stroke = 84.5mm

1130 with Destroyer Crank = 1178.1cc
1130 with "1/4" crank = 1225.2cc
1130 with "3/8" crank = 1272.4cc
1130 with "1/2" crank = 1327.3cc

1250 with Destroyer Crank = 1298.9cc
1250 with "1/4" crank = 1350.8cc
1250 with "3/8" crank = 1402.8cc
1250 with "1/2" crank = 1463.4cc (hmmm.....a thought for next year)
 
#14 ·
I don't think that you will find many people telling you that increasing the stroke will not effect the longevity of the engine.

You will also find it hard to argue that when you have the additional power you tend to use it more often and add stress to the rest of the engine components.
 
#12 ·
I just looked at the Falicon website and they call out 1/2" with 84.5mm in parentheses. Now you have me wondering. Maybe they just round off to 1/2mm in there ads.

If this is true, we really should have been having CP make the pistions with offsets other than .125".

On the 1/2" stroke engine I am building now, the new result would be that the piston would actually be .0081" from the top of the stroke.

Not much to be concerned with, but worthy of note.
 
#13 ·
I just looked at the Falicon website and they call out 1/2" with 84.5mm in parentheses. Now you have me wondering. Maybe they just round off to 1/2mm in there ads.

If this is true, we really should have been having CP make the pistions with offsets other than .125".

On the 1/2" stroke engine I am building now, the new result would be that the piston would actually be .0081" from the top of the stroke.

Not much to be concerned with, but worthy of note.
CP does not make the pistons with .125" offset. They are .115".

Stock stroke compression height = 1.195"
1434cc piston compression height = 1.080"
Net difference = .115"
 
#20 ·
So, If the Falicon 1/4" stroker crank is actually 81mm or 3.18898" and the 1/2" stroker crank is 84.5mm or 3.32677" and the pistons are offset by .115" and the rods are .125" shorter, then this is what I get:

On a 1/2" stroker engine, the piston offset, plus the rod difference is .240" or 6.096mm shorter. Half the increased stroke would be .246063" or 6.25mm. The net result would be that the pistons are .006063" or .154mm higher than stock.

On a 1/4" stroker engine, the piston offset is .115" or 2.921mm. Half the increase in stroke is .11811" or 3mm The net result would be that the pistons are .00311" or .079mm lower than stock.

I must say that I am quite a bit more informed through this thread than I have ever been. At the same time, I wonder how we ever got to having rods decreased by .125" and pistons offset by .115" when the increase in sroke have always been done in mm's.
 
#21 ·
So, If the Falicon 1/4" stroker crank is actually 81mm or 3.18898" and the 1/2" stroker crank is 84.5mm or 3.32677" and the pistons are offset by .115" and the rods are .125" shorter, then this is what I get:

The 1/4" is actually 78mm stroke. The 3/8" is 81mm. You can see the 81 stamped in my crank below.




On a 1/2" stroker engine, the piston offset, plus the rod difference is .240" or 6.096mm shorter. Half the increased stroke would be .246063" or 6.25mm. The net result would be that the pistons are .006063" or .154mm higher than stock.

This could very well be the idea behind Eagle using the obscenely thick head gaskets that they do on the 1550 we ran with this last weekend. Thicker then I ever would use PLUS they were all gooped up with sealant.

On a 1/4" stroker engine, the piston offset is .115" or 2.921mm. Half the increase in stroke is .11811" or 3mm The net result would be that the pistons are .00311" or .079mm lower than stock.

OK, now figure out mine at .115 piston and -.062 rod length using 81mm (+9mm) stroke.

I must say that I am quite a bit more informed through this thread than I have ever been. At the same time, I wonder how we ever got to having rods decreased by .125" and pistons offset by .115" when the increase in sroke have always been done in mm's.
See the bolds above.
 
#23 ·
Ken you are correct, I called out the wrong size in mm for the 1/4" stroke, but the calculations were correct size I used a 6mm increase over stock.

I really like the sharing of information on this thread. I'm pretty sure I am not the only one that learned a thing or two today. Good stuff.
 
#29 ·
If so, the 3/8 build should have rods that are .062" or 1.5748mm shorter and pistons with a .115" or 2.921mm for a total of .177" or 4.4958mm. Based on an actual stroke of 3.18898" or 81 mm, half the increase stroke would be .177165" or 4.5mm. That would put the piston .000165" or .0042mm higher than stock....nearly perfect.
 
#33 ·
As a beginner (in bike engineering) some of you guys out there know a $hit load more about this stuff than I do. My area of excellence is computers and I was disturbed that some of the numbers weren't coming out in the beginning. From my observation sportster sizes are all done in english units and the problem comes when one goes from english to metric and back. One also gets "better" numbers when rounding is NOT done. So here is what I found:

Sportster XL883L = 883.5846cc with 3in bore and 3 and 13/16in stroke.
use 25.4 mm per inch and use 2.54x2.54x2.54=16.387064 to 1 for converting ci to cc. and back if needed.

For v-rod early motors were 100mm bores and "bigger" ones were 105mm bores the stroke is the same at 72mm. They come out to 1131.42857... and 1247.40000.

Several wishes on my part: harley would use all metric and no this is not a compitulation to the japanese since it is the future. So when they say a bike is a 750cc it better damn well be from 749.5 to 750.5cc. and hopefully 749.9999. second: I hope that harley can increase the gas mileage for the v-rod, I know, most owners want HORSEPOWER but at a 55mph speed limit and increasing gas prices how fast do you think you can go before you end up in jail.

end of my rant.

thanks to all,
charles.....
 
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