[Steve C.]

Butlers suggested 255 degree hydraulic roller lobe on the intake would only have .558" lift with a 1.5 rocker ratio, and .613" with a 1.65 ratio. Not suggesting that it has to but that's not going to fully take advantage of a .700" lift cylinder head.


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[Steve C.]

Comps Xtreme Marine High Lift hydraulic rollers have 0.3800" lobe lift. With Harland Sharp 1.65 rocker arms that measure closer to about 1.684 ratio it would have 0.639" valve lift. Some have suggested the measure closer to 1.7 ratio.


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[Lee]

If the ONLY target is HP, then there are half-dozen ways (more, actually) to design a cam that will hit that goal. But they will perform VERY differently at other aspects. Some will have plenty of vacuum for power brakes, others nearly none. Some will peak the HP and then barely drop for several hundred RPM past - while others will peak then drop like a rock. There can be huge differences in TQ as well, even though peak HP is the same.

I've designed LS7 (modern) cams that were under 240 @ .050", but put nearly 600 to the wheels. They also had killer mid-range and pulled HARD from a roll. Although they made very good peak HP, they were designed for best average HP over the powerband typically used.

The downside to Pontiac HR cores, is that they don't typically have as much "meat" on the lobes, and that limits the design parameters. Some of the LS designs I've had ground are not even possible on the current Pontiac HR cores. The LS having a larger core to begin with also helps. A few hours ago I delivered a 235/272 @ .050" LS HR cam, for a turbo motor - no way I could get those specs with any of the current Pontiac cores.

But you DO need to provide a fair amount of data, for the cam designer to really get the cam tailored to you needs & goals.

[Lee]

Originally Posted by Steve C.

Comps Xtreme Marine High Lift hydraulic rollers have 0.3800" lobe lift. With Harland Sharp 1.65 rocker arms that measure closer to about 1.684 ratio it would have 0.639" valve lift. Some have suggested the measure closer to 1.7 ratio.


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1.71 on the ones I've measured, and I've had others tell me that they measured 1.72 on their engine (different geometry and such can swing the numbers a bit either way).

I recently measured the new CompCam 1.65's, and they were actually about 1.72.

I also measured the "1.7" Crower aluminum rollers, and they were a bit over 1.68.

[pastry_chef]

Originally Posted by slowbird

Highly doubt you'll ever get too much valve area in a Pontiac unless someone designs a 4valve head

Example, a situation the owner wants the engine to make peak HP at target RPM range. Extending valve area more than needed will move HP RPM out of target.

Huge importance in the speed of sound!.

Yes, as we know bore is limiting to max valve diameter and hurts the max effort.

[Steve C.]

I used the 1.684 ratio on the HS rockers because that was the ratio on a set Ken Crocie measured on a build. I've seen stated it all over the map.


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[pastry_chef]

Originally Posted by Steve C.

I've seen stated it all over the map.

Vizard tested many different rocker brands, the ratios will also fluctuate through the range of rocker sweep.

[Steve C.]

Related, interesting article....

Rocker-Arm Comparo
What’s in a Number? More Than You Think


https://www.hotrod.com/articles/hrdp...r-arm-comparo/


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[Jay S]

It appears FTI may have used the valve diameters to set the cam E/I split on the cam. 13* @.050” more duration on the exhaust is plenty on a round port unless their is something really restrictive that has not been discussed. If you want to power to be flat up top past the power peak like what Lee mentioned, that FTI cam will do that.

Butler is using a cam profile design for marine applications. It is designed to be easy on valve terrain, has .372 lobe lift.

It appears FTI and Butler are both recommending using marine grinds. Not totally sure on the FTI, looks like it might be a extreme marine HR.

I have a Bullet .3823 HR grind with 1.65s, similar profile to the comp marines HR’s. I think Bullet has a .405” lift HR profile that is similar to the .3823”.. For the street I like running solid rollers with pin oiling on those HR profiles when the lift is up above .6”. Lash runs about .010” with a 1.65, slightly less than tight lash solid roller (.014-.018). More power, durable, very infrequent lash checks, no worries about collapsed lifters. The tighter lash is easier on the rollers. Above those lifts I switch to a solid roller lifter and solid roller profile. But when I can I will use a big rocker ratio (1.7+) on those HR/SR hybrids.

I usually work with Tim at Bullet, most of my engines run custom cams from them or compcams.

[70GS455]

Originally Posted by Lee

1.71 on the ones I've measured, and I've had others tell me that they measured 1.72 on their engine (different geometry and such can swing the numbers a bit either way).

I recently measured the new CompCam 1.65's, and they were actually about 1.72.

I also measured the "1.7" Crower aluminum rollers, and they were a bit over 1.68.

Will depend on how you measure them. I measured some 1.6's that turned out to be 1.65 with light checking springs. With the actual valve springs, they measured just over 1.6, due to deflection

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