Standard base circle for a sbc roller cam.

[Zfan]

I am curious as to what is a standard base circle size for a sbc roller cam, is there one? I have heard it's 1.10 but I measured one of mine I had lying around, it's a Comp hyd. roller XR288-HR10, it measured 1.14. My friend measured one he had and it was 1.10.

 

[grumpyvette]

I don,t think there is a STANDARD, but most standard sbc cores are in that 1.1"-1.15" range, small base circles are just as varied, in the .90-.99 range
your cams lift is the result of the lifter movement distance from the cams base circle, where the valves seated to the point where its fully up on the nose of the cam lobe where the valves at full lift.
example
lets say in this case we compare two imaginary cams
a standard cams base circle is 1.125" and
your cams running on a .900 base circle
both cams have a .560 valve lift and run with 1.5:1 rockers
so both cams will need to move the lifter .374"
that means the standard cam lobe will be 1.125"+.374" or 1.499" from the cams base to the cam lobe nose
that means the small base cam lobe will be .900"+.374" or 1.274" from the cams base to the cam lobe nose
which is significantly smaller
example

http://cranecams.com/?show=browseParts& ... e=camshaft


ALWAYS READ LINKED INFO IN THESE THREADS ON THIS WEB-SITE
have you used one of the push-rod length checker tools?

they might be a good cross check, before you order the push-rods.
it would take a bit more time but it would be cheaper in the long term.
to be sure you got it right than it would be to try to return push-rods
remember the tool works when the lifters on the cams base circle
(yes as simple as they are (PICTURE ABOVE) too use they tend to be rather accurate)
yes I use BOTH the push rod checker tools to get the quick check on length, and the adjustable length push-rods and a marker too method verify the correct length with a cross check by looking at the wear/sweep and location, on the valve tip

http://garage.grumpysperformance.co...sh-rod-length-checker-tools.13735/#post-70650

http://garage.grumpysperformance.co...rdering-correct-custom-length-pushrods.14241/

http://www.summitracing.com/search/...d-length-checkers?autoview=SKU&ibanner=SREPD5
Proform Pushrod Length Checkers 66789 SBC 3/8" rocker studs

Proform Pushrod Length Checkers 66790 SBC 7/16" rocker studs

heres a bit of useful related push rod length info (POSTED HERE) youll want to select the correct set or SETS for your shop

Big Block Chevy, Standard Length Big Block Intake 3/8" / .080" 8.275"
295-7941-8 Big Block Chevy, Standard Length Big Block Exhaust 3/8" / .080" 9.250"
295-7969-8 Big Block Chevy, Standard Big Block +.100" Long Intake 3/8" / .080" 8.375"
295-7979-8 Big Block Chevy, Standard Big Block +.100" Long Exhaust 3/8" / .080" 9.350"
295-7951-8 Big Block Chevy, Standard Length Big Block Tall Deck Intake 3/8" / .080" 8.675"
295-7961-8 Big Block Chevy, Standard Length Big Block Tall Deck Exhaust 3/8" / .080" 9.650"
295-7800 V8 396-454 Retro Fit Pushrod Set, Intake & Exhaust, 1965-Present
3/8" / .080"
3/8" / .080" 7.725 Int.
8.675 Exh

295-7913-16 Small Block Chevy, Standard Length Small Block Chevy 3/8" / .080" 7.800"
295-7984-16 Small Block Chevy, +.100" Long 3/8" / .080" 7.900"
295-7934-16 Big Block Ford, Standard Length Ford `72-'78 429-460 3/8" / .080" 8.550"
295-7951-16 Big Block Ford, Standard Length Ford `69-'71 429-460 3/8" / .080" 8.675"
295-7582-16 Oldsmobile, Std Length 455 5/16" 9.550"