built b20 piston to valve clearence question

[joe.teg]

hey guys

im in the process of building a hi comp b20 motor, its going to be running 12.8:1 compression etc. Im thinking of running brian crower stage 3 cams in it. The specs are as follows:
Adv @ 0.50in
260°/254°
220°/220°
220°/220°
Lift (inch)
.496"/.496"
.443"/.443"
.428"/.428"
Lift (mm)
12.60/12.60
11.25/11.25
10.88/10.88

Any information you guys can provide me would be greatly appreciated im just worried that i wont have enough valve clearence etc.

Thanks guys :)
Joe

[joe.teg]

help anyone????

[TODA AU]

What pistons? Std valve size? how much has the head & block been decked?
If nothing sillyis going on, & if the cams are timed right, you should have no issues

[anjin]

Going to depend on the piston profile, and how much your head and block lose when being surfaced. It will be specific to your build. The only way to find out is to 'clay' your head. When doing this just use the inner springs on one cylinder - no need to go the full assembly. And use a small nut in the rocker arms to make sure vtec is engaged; or measure the clearance on the non-vtec lobe and subtract the difference to the vtec lobe - call it two mm. You may have to do some work in the valve pockets. For example, with todo spec B cams, stanard pistons and 18 thou head surfacing, the exhaust had 4.5mm clearance as measured this way.

If you are looking at adjusting the cam timing much, then you could also assemble the block with one piston out, put on the head and adjust the lash, and then look up the bore to see how close the intake and exhaust valves come as you more the cam gears around.

Its all fun fun fun with high comp engine builds!

[joe.teg]

What pistons? Std valve size? how much has the head & block been decked?
If nothing sillyis going on, & if the cams are timed right, you should have no issues

Theyre CP flat top pistons and im currently tossing up between keeping the standard valve size or going 0.5mm bigger. Any ideas their adrian??

Yeah i was under the impression that i would have to use plaster guage and dummy fit the head and measure the clearence, does anyone know what my minimum clearence can be??

Thanks
Joe :)

[tinkerbell]

flat top pistons? will you be able to get to 12.8:1 CR?

i checked my p2v clearances on mine and they were both over 0.060" with VTEC engaged and cams gears degreed in (and +/- 5 degrees) with std valves and SC7121 pistons with head milled to the ****...