Raising Compression

[frozenveinz]

So, I was wondering what the effects would be in raising the compression ration on a HT. I understand that they come stock about 6:1. Would the engine be subject to premature failure, increased wear, etc if I were to increase compression?

Also, does 6:1 compression mean that the combustion chamber is 6 times smaller at TDC? Or 6 atm at TDC?

Would sanding some of the underside of the head off (tiny amount), increase compression noticeably? How would I go about doing this.

 

[Tohri]

https://www.treatland.tv/puch-moped-70cc-hi-compression-head-p/puch-hi-comp-head-70cc-maxi.htm Drill out the stud holes on this guy, (If you have a 66cc engine) and get the squish clearance down to .5mm or so with a combination of head and base gaskets.

Performance on these motors is easy to find, but you need to know every system and every aspect of 2 stroke tuning to get a HT running properly. Just adding compression does next to nothing.

 

[KCvale]

https://www.treatland.tv/puch-moped-70cc-hi-compression-head-p/puch-hi-comp-head-70cc-maxi.htmPerformance on these motors is easy to find, but you need to know every system and every aspect of 2 stroke tuning to get a HT running properly.
Just adding compression does next to nothing.

I agree, if you don't even have a good expansion chamber exhaust start there for about 1/2 a horse if tuned and carbed right.

One other note is if you squeeze more compression out it is going to be just that much harder to get pedal stared. The Maniac Manic high compression head I used on this build worked good and it was a jackshafted shifter so easier to start, but other than great head heat dissipation from the much larger finned head it really didn't do much.

My only point is the same as Tohri's, other than basic free/cheap stuff you should always do like port match your intake and exhaust and a better spark plug you need to spend money for the parts that make performance happen.

You don't have to go overboard like that tricked out 66cc full suspension NuVinci CVT hub shifting racer, but one thing is for sure, and expansion chamber will give you the most bang for the buck with the right one.

 

[DanielMaia]

The first effect of increasing the compression, is--> the clutch will suffer...

I put a Puch head on my 66cc, and the first think i noticed is the big increase in torque, and throttle response, but other thing was the clutch spinning on WOT, climbing a hill

Notice that the stock clutch pads are very low quality and need to be improved