Hi all,

We have gathered all our engine bits and are ready to get it built. Does anyone on here have the technical knowledge to tell me the below pieces of information:

1) What compression ratio should I be aiming for?

2) Exactly what squish clearance I should be aiming for?
I've heard that  1.397mm (0.055") is the ideal.

3) What squish shelf length and angle is required?
Does the standard head need welding to re-shape the squish shelf I've read that the stock 11mm squish shelf should be changed to 13mm. I've also heard that the angle isn't as good as it could be.
If this is the case then what EXACTLY do I need to ask for at the machine shop.

Some engine specs:

Standard head (see photos, I think its been messed with already?)
Wiseco 86mm piston std bore size
Cylinder to be re-sleeved, skimmed and honed
V force 3 reeds
Standard carb to be bored out to 40mm
hpr or QV2 pipe in the future depending what I can get shipped to the UK
Fuel: Shell V-Power Nitro+ 99 RON

Any help would be appreciated, it's really hard getting (good/correct) info out of people regarding this topic.

Thanks Guys.

Thanks for your input; it all adds up.

I know that raising the cylinder with thicker gaskets changes the timings, I'm hoping the guy who's doing the porting will compensate for that.

Does anyone else have some informed answers?

Hi all,

We have gathered all our engine bits and are ready to get it built. Does anyone on here have the technical knowledge to tell me the below pieces of information:

1) What compression ratio should I be aiming for?

2) Exactly what squish clearance I should be aiming for?
I've heard that  1.397mm (0.055") is the ideal.

3) What squish shelf length and angle is required?
Does the standard head need welding to re-shape the squish shelf I've read that the stock 11mm squish shelf should be changed to 13mm. I've also heard that the angle isn't as good as it could be.
If this is the case then what EXACTLY do I need to ask for at the machine shop.

Some engine specs:

Standard head (see photos, I think its been messed with already?)
Wiseco 86mm piston std bore size
Cylinder to be re-sleeved, skimmed and honed
V force 3 reeds
Standard carb to be bored out to 40mm
hpr or QV2 pipe in the future depending what I can get shipped to the UK
Fuel: Shell V-Power Nitro+ 99 RON

Any help would be appreciated, it's really hard getting (good/correct) info out of people regarding this topic.

Thanks Guys.

The questions you are asking are difficult to answer because there is too many things we do not know about the rest of the engine. 

Tight piston to head clearance will produce better throttle response and peak power.  Tight piston to head clearances also requires an engine that is in perfect mechanical condition.  It also requires someone that has exceptional tuning skills to constantly monitor and make the necessary adjustments to the jetting and timing.

.055" piston to head clearance is a good number for a worn out engine and .030" to .035" for those that have a new crank, new main bearings, tight bearing pockets, exceptional tuning skills and are willing to replace the piston every few hours.

Squish band angles and widths are functions of the shape of the ignition timing curve, pipe, ports and the over-rev needed for the application.

Compression ratio is a function of the of the shape of the ignition timing curve, pipe, ports, the over-rev needed for the application, how long the throttle will be held wide open at any one time, the motored octane number, and cylinder head temperature. 

What compression ratio should we be aiming for, again bearing the above in mind.

I think he's wanting to know what type of riding will you be doing most.  Trail, dunes, etc.

Could you give me any info then Motorgeek? Seems like you're the man who can help me out.

Engine is in the shop this week 
It would be nice to go to the shop with a list of exactly what I want.

Thanks in advance.

Unfortunately, that's not an option for me. I live in the UK and it isn't financially viable to ship to and from america.

Otherwise, that's exactly what I'd be doing!

The guy building my engine has been around a while, knows his way around older 2 strokes and we know he'll do a good job. I'm sure he could build it properly without any input from me what so ever.

It would be good, however, to be able to give him information that might get me a better build.

Just need some numbers to give to the guy.

Thanks.