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Old 07-12-2007, 04:39 PM   #1
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Join Date: Sep 2004
Location: Charles County, Maryland
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Car: 89 TA, 79Z28, 88K1500 TPI swapped
Engine: 350 HSR, 350TPI
Transmission: 700R4 w/ Raptor 5X 9.5" converter
Axle/Gears: 3.73 8.5" ring 10 bolt

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What is "standard" cam base circle dimension, vs. "small" base circle? (roller!)

Hi guys, I have a custom roller cam that I bought on this board a little while ago, that is 0.495/0.530" lift, 220/230, 114 LSA, roller. It looks like a small base circle cam that was ground for a 383 (the guy listed it for 383 application when I bought it). The base circles on the intake and exhaust lobes measured slightly differently- 1.15 vs. around 1.175. Is this really a "small" base circle?

I grabbed a stock LT1 roller cam to measure, and the base circle measured around 1.25", for comparison. Keep in mind I am just using a digital caliper to get as close to measuring base circle as I can.

Will I have to get custom pushrods for this 0.10" difference in base circle from stock, or is that a small enough difference that it won't mess up my valve train geometry bad enough to worry about it? Can anyone tell me what the STOCK L98 pushrod length is? I'll look-see if Summit sells a +0.100 pushrod just for fun.
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Old 07-12-2007, 04:43 PM   #2
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Car: 1984 Z28 Hardtop / 1988 IROC T-top
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Re: What is "standard" cam base circle dimension, vs. "small" base circle? (roller!)

The normal base circle on a cam is slightly smaller than the cam bearing diameter minus the lobe lift.
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Old 07-12-2007, 06:21 PM   #3
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Location: Charles County, Maryland
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Car: 89 TA, 79Z28, 88K1500 TPI swapped
Engine: 350 HSR, 350TPI
Transmission: 700R4 w/ Raptor 5X 9.5" converter
Axle/Gears: 3.73 8.5" ring 10 bolt

Classifieds Rating: (8)
Re: What is "standard" cam base circle dimension, vs. "small" base circle? (roller!)

Oh -- oops. In that case my .495/.530 cam may be a normal base circle, since it is not that much smaller than the .445/.455 cam base circle. A "small base circle" cam must have almost no base circle, above what the center of the cam stick is, since the 1.150/1.175 base circles are barely sticking out past the cam stick.
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Old 07-12-2007, 06:21 PM
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