*****Standard length. Because of the variable rocker arm geometry of the Opel (sliding tip), a longer valve will reduce valve lift, so in this case going to a longer valve will reduce performance and cause erratic wear. Valve lash is adjusted the same, no problems.Bob, What length Chevy valves do you use, and do you have any problems with adjusting valve lash?
*****The ports are virtually identical, but the 1.5 has smaller valves than the 1.9. So proportionately, the 1.5 should improve more. However, nothing is ever that easy I'm afraid. The 1.5 head will require more unshrouding when larger valves are used due to the smaller chambers. Ultimately, the 1.5 head will not flow as much air as the 1.9 head because of this fact, all other factors being equal.-Does a 1.5 head respond better or worse to the larger valves than a 1.9?
*****I highly recommend this for the exhaust seats.-Do I need to install hardened valve seats when I modify the heads for larger valves?
*****The 1975 head has flame-hardened seats. They are not press-in inserts. Because of this, and the material used for the head casting, this head is horrible, they crack VERY badly. The coolant passages are no better in this head, and the valve sizes are the same size and material, although there is some dispute about the larger intake valves (1.65) being installed on some 1975 heads. I've never seen any, but others have. It was probably a mid-year change if this is the case.-I always thought the 75 head with hardened seats, better cooling passages, and stainless valves was one of the best cheap heads, but it it really any better?
*****I did some light research on the 1.1, but never pursued it. Not enough interest to warrant a full-blown performance evaluation IMO. And the stock 3-bearing crank is really the limiting factor anyway for power. But, I did discover that you could use valves from the European 1.6 litre OHC engine in the 1.1 head. They're larger in diameter, but the stem diameter and length is the same as the 1.1 head.Do you have any similar tricks for a 1.1 litre head? Thanks