head clearance
 

I am running a Picco red dot 12 engine with 30% Byron fuel in a 1/10th sedan. What should I be running for head clearance with this setup? I am currently at about 30 thousandths clearance but the engine seems to be a little weak for power. Any suggestions for this problem? thanks.

Head Clearance For Picco based .12 engines

The “real head clearance” of Picco engines, when the piston is at Top Dead Center at sea level, can be calculated as follows:
Real head clearance = Thickness of head shims + 0.05mm*
* (that‘s due to the internal construction of the engine and the compression of the head shims, when the cooling head is mounted)

You may want to adjust the shims depending on nitro-content (see table) or track layout. Large tracks may require an extra 0.10mm shim to reach higher top speed and improved fuel consumption, but this will decrease acceleration slightly.

Nitro content: 16% 20% 25% 30%
Real head clearance: 0.45mm / 0.45mm / 0.55mm / 0.65mm
Head shims: 0.40mm / 0.40mm / 0.50mm / 0.60mm

Generally on a .12 engine 0.10mm will change the compression ratio about 3/4to 1 point.

AFM

Does this head clearance apply to all brands or is there brand specific clearances? I ask because I am wondering about a Rossi 353 '08.

Thanks

different brands will have different default head clearance (without shims).
however, should be the same if based on the same parent brand.
nova & nova-based, picco & picco-based...but i don't think 100% of them follows.

Thanks everyone for the help!

I know the LRP Engine (picco based) follows the same calculations as mentioned above.

On a .12 engine It's advisable not going 0.10mm over or under 0.46mm, so that is 0.36mm or 0.56mm of total head clearance at sea level, with the lower number suitable for 16% nitro and the higher number for 30%.

Generally on a .12 engine 0.10mm will change the compression ratio about 3/4to 1 point..

One last comment. never assume that the head shim that is on the engine is the actual head clearance. In some cases you will find that the engine actually has 0.20mm to 0.15mm without any head shim. For example if an engine has a tolerance of 0.20mm without one, and the factory installs a 0.30mm shim, it gives the engine 0.50mm stock head clearance.
When in doubt measure the head button register and the piston to the top of the liner at top dead center and subtract, to determine proper shim. This is the only way to really know.

AFM

Always use some solder to squish between piston and head to messure that as the real clearance.

thanks pal