Patrick G

iTrader: (14)

I bet you I know what your problem is. If you are using 1.55" diameter springs and retainers along with stock rockers, the underside of the rockers are probably coming into contact with the larger diameter springs at higher rpm. I had this happen to me years ago when we used to run the larger springs (before good 1.29" springs were available). The problem totally kicked my *** because somebody at the engine shop had swapped my clearanced rockers with some stock ones.

To run stock rockers with the 1.55" diameter springs, you must clearance the underside of the rockers or you will experience valve control issues above 5000 rpm. Trust me, it happens. It's probably not the cam.

JUNK

Now u see, this is the kind of response we were looking for......I ran these heads using stock rockers w/ no issues, BUT, w/ a different cam and different length pushrods. To be honest, I personally was hoping u would jump into this thread. Worth looking into for sure.

K, u reading this? Get the car to me 1st thing AM and I will check it b4 we strap it to the dyno........if there is contact, there will be witness marks

Old SStroker

You are suggesting grinding material away on the underside of the stock steel LS rocker near the fulcrum area, correct Patrick?

No offense intended, (unless you are an engineer, which I doubt, and then offense is intended) but that is a VERY bad idea. Really bad. That is one of the highest areas of tensile stress in the very well designed rocker. It's not like extruded aluminum rockers where there is lots of material which does nothing much but add mass. The stock rocker has almost no material which isn't workling. Grinding material away in a highly stressed area just ain't the way to go, Boss.

You are some sort of cam guru to many folks here, as evidenced by JUNK's response. IMO, which is NEVER humble, you just stepped on your...ahh..."tie" with this one, PG. Your interference analysis may be correct, but your fix, if I understood it correctly, is not.

Unfortunately I was not referring to Patrick in the above quote.

I don't give a poop if KH504 and JUNK do what I initially suggested, but I really don't want them doing something to compromise the strength of their valvetrain parts.


Read this quickly guys.

Jon

Patrick G

iTrader: (14)

Jon, you're a smart guy and I always appreciate your candor and your honesty. But in this case, I'm going to have to give credit to Judson Massingill for the fix to this issue. Judson was the first one to suggest clearancing the stock rockers (when using 1.55" springs) back in '98. He did it on many sets of rockers that were (at the time) record-setting combos. With his guidance, we also did it to ours (in '99). I would consider Judson a guru on many levels and would not second guess his decision to clearance the stock rockers then or now.

Old SStroker

Glad to hear you are not taking credit...nor blame. Are you thinking of running for office?

Ever wonder why Comp recomends beehives for XFI lobes? Billy G. has an extremely good understanding of I. Newton. Probably better than anyone I've ever met.

Sometimes it's who you pick as a guru that matters. Evidently you and I don't choose the same folks.

Regards,

Jon

JUNK

If they ARE making contact, there are other ways around it. Bee-hives, or aftermarket rockers.......we are just trying to figure it out, and of everything I can come up with or hear of, this makes the most sense. I will post back here tommorow w/ my findings

Patrick G

iTrader: (14)

Not to worry Jon. Billy and I had a nice visit in December. We spoke at great length about the XFI lobes. He feels that they are one of the most stable hydraulic lobes they make for the small block cam cores and thinks they are still very good on the 55mm LS1 cores. I've seen way too many 7000+ rpm LS1 combos with a quality dual valve spring with these lobes. I don't believe the valve control issues the OP is experiencing are coming from running XFI lobes themselves. The lobes are working too well for too many people. Bad geometry, bad pushrod setup, or rocker to spring/retainer contact are much more likely culprits. The larger diameter springs totally change the problem set here.

JPH

iTrader: (2)

WTF? Start here. Just like PG and John are talking about, you rocker to spring clearance can be an issue as well and geometery. I'm sure those springs when in alittle taller then 1.80X? Start here, if this is all jacked up, buy a Comp #921-kit or what not and start over.