Valve clearances
 

We are running 3.0 case, 100mm JE High Dome pistons with valve reliefs, GT3 Crank, SC spec rods 131mm long.

Cams are Elgin, spec is 5.6mm lap.


at 11 deg BTDC Exhaust valve is 1.55 clearance

At 11 deg ATDC Intake is run in and never hits piston.

This is a race only engine.

Question is, 1, can I advance cams a bit with all the rockers in to get the exhaust a bit more room, or 2, is 1.5 acceptable?

TIA

What kind of rpm will you turn? and do you have aftermarket springs on it? 1.55 mm is close, but I have seen it work. 306/288 profile?

int=320 duration exh=304 106 valve centerlines 5.6mm lift at lap. CMW race springs..

We limit RPM to 7600..

Did you clay the valve to piston clearance? Does the valve touch the piston at an angle or relatively flat?

John,

We did not clay the dome/Head interfaces.

I only ran the valves in after the build. This engine was run in the past, we added a new GT3 crank and R+R rods. Heads and pistons have been used in the past.

Can I advance the cams without removing the rockers? We are at exactly 5.6mm on both banks, would 6.0 get me the clearance gains needed to help me sleep at night? ;)

6.0mm will work. How did you check the v-p ?

I have heard of people backing off the rockers to move cam timing, but I don't know for sure. Good question for Henry at Supertec.

If you mean the valve pockets V-P, they were checked on the last build of this engine, nothing changed in the heads or Pistons, so I figured the geometry would/should be the same with regards to valve into pockets..

I figure I can try to back off all rockers and gain the .4mm advancement, and recheck..

Ok, Timed both cams to 5.85mm, and now we have 1.75mm on the exhaust.. All buttoned up and waiting for the body to get back from paint. Should have it on the dyno beginning of Spring. As long as I don't miss a downshift, it should be ok..

7600

John,
It was much easier setting the advance with the other rockers in, the added resistance was an aid.

Good deal.