SRX porting, head volume, etc.

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ModMMax

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My new to me SRX has been ported. As stated in an earlier thread, my compression is at 90# at 7500 ft. Engine is apart so I can't test it at 1800 ft. Crewchief (thanks crewchief) and my guru dealer buddy confirmed that ported engines may show less compression because of a reduced distance from the head to the closest port, in this case the exhaust port. I have no way of knowing how much it has been raised because I did not own the engine in stock form. Ported it measures 31 mm from the top of the cylinder to the top of the exhaust port. Transfer ports have been opened up a lttle. I tried to get photos but they are blurry. Heads do not look cut, measuring 35.2 mm from the bolt hole bolster to the head surface.

I have to make a decision. If I have my heads custom cut, what volume should they be for use at 7-10k riding? I would like to be able to use premium fuel and use a premiem/c-11 blend for the occasional ride here at 1800 ft.
 

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MPI's catalogue recommends reducing the stock SRX 26cc head volume to 21cc for use at 10k ft. Does anyone have an opinion about whether 21 is the max safe reduction?
 
Whats important here is not just the cranking compression but rather what the squish clearance, squish angle and then head volume is. You need some basic measurements before anyone could give you any pertant information as to what to do. You need to start with a squish check, easily done with lead solder bent in a 90 degree angle, make sure you can feel the smooth side of the bore while inserted thru the sp. plug hole. this is placed on top of the wrist pin, from left to right on top of the pin so the piston can not rock back and forth contaminating your measurement. Roll the engine over by hand , grasping the primary works well and let the piston squish the solder aginst the head, remove and check with calipers as to your findings.
 
Thanks mr viper. I can't check the squish until I get it back together. If it helps, I know the pistons are stock and I'm pretty sure the heads have not been touched.
 
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