Performance Cams

[wrench459]

Originally Posted by RallyBob Usually the point of greatest interference is about 15-20° BTDC and 15-20° ATDC. As the intake valves are opening the pistons are going down the bore, as the exhaust valves are closing the pistons are coming up the bore. When both valves are open the same amount the piston is usually nowhere nearby.

Now Bob why did you bring that experimental variable compression motor that your working on into the mix?

Along with its strange cam timing events.

[Viny Charb]

This is all really good information to know for my future powertrain!!!

[gtden]

I have read this thread with much intrest and have a quick question. When using sb chev valves in place of originals what do you do about the added length of the valves as this seems to create severe angles in yhe valve train. I work in a small shop that does minor valve work and would like to upgrade the valves in my opel but am concerned about this. thanks for any help you can give.

[wrench459]

Dennis

I thought about using chevy valves..then we stumbled across some Ford
valves.

Point is don't limit yourself to just GM parts. Unless you want too.

[GTJIM]

Stock Chevy SB valves are 4.88"-4.92" long.
Stock Opel valves are spec'd at Intake 4.843" and Exhaust 5.021" (these have 'bulged' faces so actual valve seat to tip is much the same as the Intakes).

In our applications about 0.057" extra length is no big thing - especially if the new seats are located as high as possible in the chamber (seat inserts are used on the exhaust which helps here). It actually helps with higher lift cams as the rocker is positioned closer to the end of the rocker stud slot allowing more movement before contact at the other end of travel (full lift).

Also the valve/rocker stud/lifter angles are far different from SB Chevy heads so rocker geometry is quite different - Opel CIH valve gear geometry ain't SB 'Pushrod' Chevy! The valve tip with the use of Chevy valves actually move away from the rocker stud - so rocker ratio is made a bit larger by using them.

I have delved into actual CIH Opel rocker geometry after reading about 'Mid-lift' geometry with US V8s and working with Opel double roller rockers - the Opel is far different and the Chevy valves do work in them!