tsnobaddays

Member
Feb 11, 2008
39
0
I have a questions about the '08 MX dirt bikes like Honda, Kaw., Suz., and Yam. I did some research and all but the Honda have 13.5:1 compression stock. The Honda has 12.9:1 compression does this make a huge differ. in power or does Honda just have it setup this way for reliability. One more quetions is I saw a cover that goes on the Honda that allows you to change the oil filter without having to drain the coolant ,so do you have to drain the coolant to replace the oil filter.

Any answer would be great cause the Honda is a canidate for me thanx
 

mox69

Member
Mar 26, 2007
236
0
Those ratios are "static compression." This would be the correct ratio if the valves never opened. The "dynamic compress" (or actual compression) will be lower, and will change based upon the cam profile (valve overlap, cam timing). It is also probably slightly different for every manufacturer.


So to answer your question, no don't worry about it, the number is fairly useless as is.
 

Rich Rohrich

Moderator / BioHazard
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Jul 27, 1999
22,838
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mox69 said:
The "dynamic compress" (or actual compression) will be lower, and will change based upon the cam profile (valve overlap, cam timing).

Dynamic compression is based on the Intake Valve Close (IVC) timing. Overlap has no influence on it.
 

tsnobaddays

Member
Feb 11, 2008
39
0
Wonder why Motosports advertise a cover from Pro Circuit called Oil Filter Cover description is -Allows oil & oil filter changes without draining engine coolant.
-Made of aluminum and anodized in Red and Brown

They sell them for Honda CRF250R 04-05
KXF250 04-07
RMZ50 04-06
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
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Merrillville,Indiana
I looked through all kinds of bs at that site! Talk about after my wallet, wow! I have changed oil a couple of times on the honda 250 and 450. You can do it without draining the coolant. That would really suck! Really, I lost track of how many things that claimed to do something, NOT! But the bling, now that is another story.
 

mkelly04

Member
Jul 27, 2007
196
0
tsnobaddays said:
Wonder why Motosports advertise a cover from Pro Circuit called Oil Filter Cover description is -Allows oil & oil filter changes without draining engine coolant.
-Made of aluminum and anodized in Red and Brown

They sell them for Honda CRF250R 04-05
KXF250 04-07
RMZ50 04-06


As far as I know the only bikes that required you to drain the water to change the oil filter were the kx250f and rmz250 04-06.

I think motosports is mistaken.
 

wileyE

Member
Jul 6, 2003
51
0
You can sometimes reach a point fast with the 250f's that more compression will not gain you anything, even lose. Pumping losses and the way the piston (built to raise compression) shrouds the chamber are the culprits.

Efficient combustion makes power, not compression.
 
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