pegleg (6/23/2009)

---

Ted, how come so much lift? thought the ports stopped gaining flow at least .100" before that?

Frank.  I’ve heard the same thing about Y heads over the years but I don’t put a lot of credence in flow numbers by themselves.  With the Isky 505-T camshaft, I was running 0.537” lift and ran a best of 9.76.  Upped the lift with another cam to 0.595” and have run a best of a 9.60 quarter mile et at one track and 9.61 at three other tracks.  These are all at leaving the line at 4500 rpms.

But it wasn’t as simple as just increasing the lobe lift at the camshaft.  The duration was increased from 254° at 0.050” to 263° at 0.050” but this was so I could get a cam profile that was happy with the more aggressive lift.  Both cams were ground on the same 108° lobe centers and both installed at 2° advance as measured with no load on the valve train.  The valves and springs were also changed to accommodate the higher lift and the rocker arm geometry readjusted to get it back where it belonged.  Using the rocker stands from the 302/332 LYB engines simplifies geometry adjustments as they are considerably taller to begin with and give ample room to make geometry adjustments without the use of shims.  As an FYI, the LYB rocker stands if turned upside down puts the rocker shafts at the stock Y height.

To compensate for the loss of lowend with the increased duration, the heads were milled an additional 0.015” each which increased the static compression ratio from 12½:1 to 13.0:1.  This kept cranking compression at the same 210 psi with both cams and in turn kept the 60’ and eighth mile times the same instead of losing some et in the early stretch which otherwise would have had the engine only making up part of the et loss on the big end.  This essentially  made for an even greater reduction in et than would have been observed otherwise.  I think that was the short explanation.

Lorena, Texas (South of Waco)

John already has taller stands available.  One side is stock height, turn them over and raise the shafts .050.  He sent me a set to try on Gordon's engine, but it didn't require taller stands because the valves were stock length.

John - "The Hoosier Hurricane"

     Ted, how come so much lift? thought the ports stopped gaining flow at least .100" before that?

Frank/Rebop

Bristol, In ( by Elkhart) 

Charlie.  Non-stock valves?  Anytime longer than stock valves are substituted for the originals, the rocker shafts do need to be adjusted so that they are appropriately higher.  The stands on my roadster engine place the shafts ~¼” higher than stock simply due to longer valves which in turn were required by the valve springs which in turn were required by the 0.600” lift at the valve.  The dominoe effect was is in full force here in that one thing led to another and another and……  The point being that each change required another and ended up being a cascading effect.

As far as pushrod clearance issues in the heads go, they actually diminish as the rocker shafts are raised.  Not raising the shafts while going with longer than stock valves will tend to aggravate any existing pushrod clearance problems but by the same token, lengthening the pushrod will also tend to improve the situation by lieu of moving the adjuster more outboard or closer to the intake manifold.  I’ve found that these clearance issues when present are typically at the inside bottom of the pushrod hole at the deck surface of the head so I just try to remember to simply grind in these areas while the heads are disassembled and being worked on.

Lorena, Texas (South of Waco)