Hitchcocks Forum

Hi, my bullet 350,test 2007,ride with open exahust,sb air filter,standard mikarb with 27.5pilot and 105 main...I have possibilities to put in high compression piston: what do you think about? Possible increase power? Or better with standard piston ? Thank you....

I have found on the Redditch 350 a higher compression piston gives the motor a bit more punch. It doesn't really improve top speed (not on it's own, anyway!) but makes the power delivery sharper.

REgards, Mark

Standard enfield pistons are made of melted down rupees mixed with elephant dung. Then half sawn through in an attempt to supply more oil to the bore. As such, they have a tendancy for the crown to collapse after a time trapping the rings in the lands and leading to a loss of compression, light scoring of the bore and burning of oil. (Rather than totally ripping the piston in half like a 500 can). If/how quickly this happens depends on how hard you ride it.



Our hosts "higher" compression piston is similar to a standard one, just more domed (Note "higher" rather than "high"). It is also a fair bit cheaper than a standard one so I use them, I don't think the quality is much better and I didn't really notice a huge difference in power output over a standard one.



I'm not aware of a "high" compression piston for the 350 models? What are you proposing to fit?



The forged piston available from our hosts claims to give a similar compression to the "Higher" compression ones. This is made of real metal in a controlled engineering process and is not half sawn through. As such you could well consider one these to be a good investment. I am moving towards fitting one to my 350. I personally treat Indian pistons as a service item and change them at every de-coke. My current one is getting close to this point as evidenced by the fact I no longer need to use the decompressor to get it over TDC without the clutch slipping.



As ever, the more you tune an engine, the closer you take it to catastrophic failure. That said, bumping the compression from 7.25:1 to 8:1 isn't exactly going to be squealing the rear tyre away from the lights.

You can fit a Meteor Minor Sports piston to give about 9 to 1. I also shorten the barrels by around 2mm, eo get 10 to 1. Standard cams will work well with this, but retarding the inlet will boost top end power, at the cost of a tiny amount of bottom end power. The standard conrod, bottom end etc will be well up to taking these modifications, on top of these, my 350 still has the standard valves, springs and rockers. I ported the head and added a 389 Monobloc carb and it goes very well.

Hi everybody ... the piston that I would like to mount is the number 17459 of the hitchcocks catalog. do you think it could be dangerous for the engine? can it cause overheating or breakage? I would like to change it also because the standard piston seems too ovalized ..

You should be totally fine with that. I use one in my 350 which has a very similar state of tune to yours. I find they do eventaually start to collpase/go oval but only after tens of thousands of miles of unsympathetic thrashing.