TECH: Cams for Stock Street Motors

I prefer cams with a small (lower) Overlap Number in stock stroke street engines.  Overlap is a period of time where both intake and exhaust valves are open.  You can figure the overlap number by adding as follows:

Example:  14/34  41/12  Overlap is 14 + 12 = 26
Example:  36/40  45/36  Overlap is 36 + 36 = 72

The "26" camshaft should give you less hesitation, less flat spots, less babble out the pipes at lower rpms - a Torque Cam.
However, It may kickstart a bit harder, and it won't like higher compression (9:0 of higher) it might ping?

The "72" camshaft may babble out the pipes at low to mid range, have a flat spot at lower rpms, and
require mufflers to perform properly.
However, It will kick easier, likes higher compression.  Power cam. Strokers !

I also like cams that the fractions of intake and exhaust are the same numbers "diagonally" - they seem to perform better . . . that's just my experience. 

Example: 16  36
               36  16

So . . . try a cam with a Low Overlap Number, with numbers the same diagonally, Valve lift .450 or under for stock spring installed heights and seat pressure.  You don't want any bigger(stronger) valve springs then necessary.  It just adds unwanted pressure and wear to valve components, pushrods, tappets, rollers, valve stems, cam bearings, etc.  It also takes extra horsepower to open those heavy springs ! 
 

6 comments:

Chayse said...

The last paragraph is what MOST Harley engine builders don't consider for street bikes. The new Metric stuff uses titanium for a reason....and so do I!

Noot said...

So true, but we don't believe in the metric system on this blog - we just drive tractors.

Chayse said...

Where do MOST of your replacement parts come from!!!!:)

Bastard said...

Interesting......My favorite cam for a Shovelhead was
the Andrews C, although the #6 was also excellent.. Yeah,
I prefer a stroked engine.. The 88" shovel with a C cam
was in a FX bike with the wide ratio gear box and 24/48
rear gearing...Great in town and great power two up with
gear out on the road..

I'm currently doing a 1928 JD..Have you seen the cam profile
on one of these? It looks pretty radical...No wonder those
old JD's ran so good.....

Noot said...

All that valve train "snicka click" sounds from those steep ramps ! Like a big solid in a 283 ! I just got that Andrews #1 in my panhead, and there's a little more valve train noise, not a lot, but it's a good sound . . . mechanical. Up the street and back, it's more responsive after a few carb adjustments. Idles smoother and I can make it run quieter out the pipes if I want. Try it good this weekend hopefully.

PS. Chayse, You've got a point there - hard to find USA parts for a lot of stuff, I like to fix the OEM H-D parts, or good used when I can.

Jeff Hawbaker said...

Chayse is a smart kid