The center of the pushrod to the center of the pivot point.The center of the valve stem to the center of the pivot point.If you're tempted by a stroker engine, you can find more info.The rocker arm ratio is the relationship between the 2 halves of the rocker arm. It's also a lot easier to get 250hp from 4.6L than it is from 4.0. With the added displacement, the engine will produce more torque and make highway driving even more enjoyable. With the crank from the Jeep 258 engine and a 0.030" overbore, you can increase displacement to 4.6L. You could go further than a mere stock rebuild and build a stroker engine out of your 4.0. Mopar Performance have 1.6 ratio roller rockers for the 4.0 but they're so ridiculously expensive to make these a complete waste of time. It IS possible to adapt 1.7 roller rockers for the Big Block Chevy to the 4.0 but it's an involved process and the HP gains are probably too small for this to be worthwhile. Unfortunately there aren't any higher ratio (1.7) roller rockers available specifically for the 4.0. Thanks Patrick! The stock rocker arms are indeed 1.6 ratio and since the stock 4.0 cam has a lobe lift of 0.265", the valve lift is 0.424". Any and all tips you can give will be greatly appreciated. However, I want to retain the normal drivability and use mid grade gasoline. In short, I would like to give the old XJ a bit more get-up-and-go. Since the rest of the valve train including the camshaft will be replaced I think it is only reasonable to replace the rocker arms as well. What I do not know is the ratio of the OEM units. I want to replace the OEM rocker arms with some after market ones. Most (80% +) of my driving is on the highway with the occasional trip to a wheeling park. I looked at one of your posts on this forum regarding engine upgrade to give about 250 HP. Despite this, I still get up to 20 MPG on the highway at 75 MPH. To date it has only the usual symptoms of the typical 4.0 namely piston slap and valve clatter. I am planning to rebuild my aging 4.0L, which has in the excess of 240,000 miles. The article on increasing the power of the old 4.0 is most timely for me. I read your post on this forum and I am very impressed by the wealth of knowledge you possess regarding the XJ.
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