That's probably it. Mummert did the heads. I left it to his discretion.



Lawrenceville, GA

All this talk about raising rocker shafts makes me wonder, is there a market for taller than stock rocker stands? Iron or aluminum?

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

Frank/Rebop

Bristol, In ( by Elkhart) 

Frank:

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"

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)

Another chink in the armor of "Common Knowledge"! John runs a lot of lift in the Hurricane also, although not that much. His top end speeds seem to bear out what you're saying. You both have better heads than my "stockers" also.

    Some day we'll have to talk you into a blown engine dyno thrash.

Frank/Rebop

Bristol, In ( by Elkhart) 

If higher stands were readily available that I could mill to the height needed, I'd buy them. Don't know that it is a big market, though.


Lawrenceville, GA

Ted, your experience confirms what I have been wondering about for years. Excess lift (lift greater than max flow point) should produce greater flow for an intake cycle. Max flow occurs, stays steady for a bit and then declines as the valve closes. More flow under the curve as we are dealing with a truncated wave whose max value is defined by the head, not the valve opening. A valve lift equal th the point of max airflow yeilds a flow pattern where airflow just reaches a peak and then declines with the valve closing. This peak may not even be max flow as shown by the flowbench due to the inertia of the air.

Nice job of compensating for the increased duration of the cam, something not often done thus masking any potential benefits.

Just as an aside I know truck pullers are running lifts in excess of 1 inch, using roller cams of course. This is an example of trying to maximize air flow by increasing duration at maximum airflow.

Hopefully related, & relevent; does anyone know the thickness of the oil deflectors that were under the rocker stands on early y blocks?

.038"

John - "The Hoosier Hurricane"

And I found some that are as thick as 0.044”.  Thickness likely varied simply due to run of the mill manufacturing variances.

Lorena, Texas (South of Waco)