RKT 858 really only a 850 ???

[Going West]

Am I missing something? if I enter the bore size by 70mm stroke into a cc calculator I'm only coming up with 850 cc's. Not that the size really matters, only how it preforms but why call it a 858 when its not.

Someone straighten me out if I'm wrong here.

 

[rmscustom]

Just a guess but do you need to add the head volume to?

 

[The Fourth Wolf]

Why call the stock motor an 800 when it's really a 795?

 

[polarisfornow]

Because all the sled makers have an "800 class" sled. It makes brand comparisons easier.

Sent from my MB886 using Tapatalk

 

[byeatts]

Am I missing something? if I enter the bore size by 70mm stroke into a cc calculator I'm only coming up with 850 cc's. Not that the size really matters, only how it preforms but why call it a 858 when its not.

Someone straighten me out if I'm wrong here.

just a game, Some measure the bore size, some measure the piston size

 

[Going West]

just a game, Some measure the bore size, some measure the piston size

If you go on piston size its even smaller only 848cc then. I just found it a little surprising being that 858 seems very specific, I just assumed that it was exactly 858cc's

 

[shabs]

858 ...It just sounds way more badass?

 

[damx]

Well is the PAR 910 a 910cc? Carls chcle a 900cc? Bikeman 860cc? Or they all just round up to sound good?

 

[moly may]

Doesnt make alot of sense when you really think about it. What it is is what it should be but hey gives us something to talk about

 

[mountainhorse]

Where are you seeing the bore size of the RKT pistons?


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[Going West]

Where are you seeing the bore size of the RKT pistons?


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Measured on the kit I bought

 

[mountainhorse]

Well... what do they measures..

Thx












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[Going West]

Bore was right around 87.9mm

 

[trackvs2wheels]

Just a guess...but maybe a slight difference in how/what was measured by different people??

I know when I measure my dingaling it's around 10"...but when my wife measures it's only about 8"

 

[diggerdown]

Bore x stroke x head volume. Different head, different volume.

 

[Ol* Geezer]

Head volume should have nothing to do with engine size, only compression ratio.

 

[Laundryboy]

Head volume should have nothing to do with engine size, only compression ratio.

Ha ha, I think rather than go to the trouble of a big bore I'll just install a big thick head gasket for the same effect.

 

[POLZIN]

Just a guess...but maybe a slight difference in how/what was measured by different people??

I know when I measure my dingaling it's around 10"...but when my wife measures it's only about 8"

I think you measure like a ski resort measures new snow ! actual x 2

 

[sled_guy]

Measure the cylinder bore, not the piston size.

sled_guy

 

[Zak.V]

volume bdc - volume tdc = Displacement

Head volume is constant, therefore cancels out.

from wiki:

pi/4*(bore^2)*stroke*2 cylinders = Total Displacement.


(Bore diameter is used instead of piston since the ring+piston is assumed to perfectly seal to the cylinder. Note that vertical gap between ring and piston top is constant and therefore also cancels out.)

Math is what it is