quote:
Originally posted by Danford1:
... I guess I want it all. Is that possible? A good middle ground cam ...
I knew you preferred a "tough" sounding idle, which is why I reiterated what my cams do. You can't have it all, but close. As we dial in more overlap to give you the idle you want, the low rpm performance diminishes. There's no avoiding that. But I may find some lobes that allow me to put a cam together that walks that line somewhere where in the middle. I have a couple of ideas. Answer these questions for me, I'll look at the lobes I have to choose from, I'll get back in a couple of days:
(1) Is your engine equipped with iron 4V heads? If not, which heads?
(2) At what rpm would you prefer the peak horsepower occurring?
quote:
Originally posted by PanteraDoug:
... do not interpret what I say as arguing against them ...
No problems Doug. I have dealt with specifying custom ground cams for people since the 1980s. I can be very clear what the cams I pen do, and let people decide if those cams perform how they want. It doesn't hurt my feelings if they don't. There are other people on the internet who will provide info that meets their needs. I understand there are differing preferences. I also admit there is some peak horsepower to be lost, I disagree that it is significant for the varying applications. This is based on experience. Street performance engines, sports car engines, road race engines require low rpm performance ... and a wide power band ... to accelerate out of corners, or pull gears to higher rpm when passing. Drag race engines do not have to do any of that. Drag racing cars can leave the line at 4000 rpm or higher, they normally wear drag slicks or street legal versions. They work best with a narrow, steep torque curve. Street cars don't leave the line at 4000 rpm unless the owner wants to attract the cops, or burn-out the clutch prematurely. Street cars are equipped with high performance street tires which are less sticky than drag slicks. Burning rubber is fun and dramatic, but when the car is burning rubber it isn't moving forward as fast as it could be, and so in terms of a street car or sports car a "peaky" torque curve isn't necessarily conducive for achieving the fastest acceleration, controllable traction is better. In my experience. A 351C with 4V heads accelerates hard enough as it is.
quote:
Originally posted by Rocky:
... how far can I (safely) let it go ...
With the car parked in the driveway, in neural, slowly rev it higher and higher, at increasing 100 rpm intervals. If the engine makes it to 7000 rpm without issue, I would call it good enough and not explore further. I have done exactly that in the past.
quote:
Originally posted by 4V & Proud:
... is this still your preferred lobe choice for the mechanical flat tappet Cobra-Pence cam ...
Well, I'm not sure. There are two specs. That's an old 7000 rpm street spec. There's also a 7000 rpm street/track spec.
I would slightly change the lobe centerlines of the spec you posted to:
112° ATDC intake lobe mathematic centerline
117° BTDC exhaust lobe mathematic centerline
Guys who wanted street-ability plus competitive road racing performance are currently using this street/track spec, and they love it:
Ford 351 Cleveland solid flat tappet street & road race cam
Grinder: Bullet Cams
Lobes:
Intake #FF280/371 (Asymmetric)
Exhaust #F292/373 (Asymmetric)
110° ATDC intake lobe mathematic centerline
115° BTDC exhaust lobe mathematic centerline
280°/292° advertised duration (286° average)
251°/263° duration at 0.050"
Indicators
29°/29° major intensity (advertised duration – duration at 0.050)
Overlap at 0.050” = 32°
Lobe separation angle = 112.5°
0.371"/0.373" lobe lift
0.022”/0.019” lash
0.642”/0.645” theoretical valve lift (1.73:1 ratio)
0.620”/0.630” net valve lift [(lobe lift x 1.730) – lash]
0.609”/0.615” factual valve lift [(lobe lift x 1.70) – lash]
EVO = 81° BBDC
IVO = 30° BTDC
Overlap = 61°
EVC = 31° ATDC
IVC = 70° ABDC
Note to Doug, take a look at this cam. Modern lobes are sometimes wonderful. This is a race cam and shall wear like a race cam, but outside of wear it does it all. This cam gives the 351C a power band like a carbureted V12 Ferrari. The engine is a little soft on the bottom, but it builds steam as rpms rise, and it revs to the moon. Peak BHP is around 7000 rpm. The engine still has the mid-range rush in acceleration that makes the 351C so dominant. But the spec is not too different than others I have posted, just the cam lobes. The charging Rhino has never charged any harder.