What is too much compression?

130psi is the max I recommend for these engines.
look for a head with at least a 7cc volume.
 
130psi is the max I recommend for these engines.
look for a head with at least a 7cc volume.
Well would the head i suggested be too much in the long run? I could not find specifics like the cc's and the amount of compression added.
 
The ones above it are available at mz Miami right now for $45.00 and if left stock are closer to 8 cc the rse one has alot less cooling area and might be better suited to short high speed runs it closer to 6cc!
 
jag some of us have run much higher compression with no adverse affect when set up properly!And some of the heads available now offer good tunability with ample cooling to help off set the higher temps generated by high compression and sustained higher rpm's
 
over 130psi means a shorter bearing life of crank and rod bearings.
it also means too high engine heat, although some of the aftermarket heads do have more surface area for cooling.
it also means more blowby which is already too much because the ring end gap stock is already too much.
it also means detonation if the jetting is too lean or the timing is too advanced. yes, the stock timing is too advanced for high compression. the higher you make the compression the more retarded you need to make the timing.
 
agree with the above - these motors are made with chinese materials that are just not up to usual standards - they are a good utility motor, but trying to get more power is risking a blown motor

that said, the GF's bike is at 165psi cold, and runs in the mid 40s with 44T sprocket - stock head, but ported to the max with shaved barrel - she doesn't really care if it blows up
 
I am using one of those heads, somewhere i had a post of the exact volume but I cannot remember now.
full

The head works well. No tendency to over heat and gives great torque.
It is not a high speed head, an extra 5mph can be had with less squish and compression.
As Crassius mentions, the compression does take its toll on many things such as wristpin bearings and plating.
More power = less life.

Your compression can be adjusted to a degree by adjusting base gaskets and head gasket thickness.
The gap between piston and head can be anywhere from 0.020" to 0.060" which will make a significant difference in compression.

Steve
 
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