[Cliff R]

I've had quite a few of these engines on the dyno and at the track using HR set-ups. With "standard" weight valvetrain parts and PLENTY of spring pressure they start to experience valve train stability issues around 5800 rpm's. Adding more spring pressure (shimmed the springs .030") had zero effect on this the last time we were on the dyno with one of these engines.

My last 455 engine would literally tear your head off to exactly 5800rpm's, then just quit revving, like you hit a rev limiter. The same engine on the dyno spiked the graph pretty hard at exactly the same rpm's.

My new engine is very similar, although it has more cam and head flow, it will rev right past 5800rpm's and shows no signs of quitting to at least 6400rpm's. It uses the "tight lash" set-up, HIPPO solid rollers lashed at .005" on a HR camshaft.

A few things to consider with my comments. For the 455 engines using HR set-ups, we don't typically choose camshafts for them that will make peak power beyond 5800rpm's anyhow, so using a HR set-up is not an issue right to start with.

For any engine with enough head flow and camshaft to make peak power past 6000rpm's, I wouldn't even look at a HR set-up for it, even with ultra light retainers and beehive springs. Not saying it can't be done, woln't work correctly, or anything else. As mentioned earlier, you are well into solid roller territory at that point, so why use anything less?

I also do not trust the HR lifters we've been getting. Early versions were HORRIBLE, having too much plunger travel and they didn't have the internals right in them. The engine we just finished up a few days ago had short travel HR lifters from Howards. Most likely they are Morel lifters, but I have no way to confirm that. They also had a pretty stiff spring in the plunger assemblies, so may fair pretty well at high rpms.

Even with all that said, P-Dude has been running high rpm HR set-ups for quite a few years with great success. I'm sure Ken has science out what lobe profiles, springs, retainers and other valvetrain components will work with HR set-ups at high rpm's. Instead of playing on that playground I went to the "hybrid" set-ups here, with zero issues to date with any of them. The only downside of that deal is that you are going to have to check valve lash on occasion, so there is some maintenance involved......Cliff