Not your ordinary cam question
Thread Starter
Burning Brakes
Joined: Nov 2004
Posts: 822
Likes: 0
From: Grafton Ohio
Not your ordinary cam question
I'm in the process of doing a cam/head swap and ran into a problem (I think). I purchased a cartek cam used a while ago and was about to install it tonight but decided to measure the lobe base circle before I did. This cam has a .090 smaller base circle than the stocker I removed. Is this normal? Do I need .090 longer pushrods? Do other aftermkt. cams come with a stock base circle or are they all reduced base circle setups? I'm all ears. Should I go with this cam or should I look for something ground on a stock base circle? Jeremy. 
Race Director
Joined: Oct 2002
Posts: 16,477
Likes: 26
From: Gone
CI 6-7-8-9-10 Veteran
St. Jude Donor '03
Most high lift aftermarekt cam lobes use a smaller base circle. If they didn't, the lobe would end up bigger than the bearing bosses and you wouldn't be able to slide it in.
Stock pushrods are 7.380" long...and most people use 7.400" long with aftermarket cams to help take up some of the difference of the smaller base circle. Also remember, the rockers only "see" the radius difference (.045" in this case), not the diameter.
There is some leeway with the hydraulic lifters...but without knowing your head specs, it would be hard for anyone to advise the perfect pushrod length for you. If your heads are milled and/or using a thinner gasket, the stock length may still be fine for you..otherwise with stock head dimensions and gasket, the 7.4's should be used.
Stock pushrods are 7.380" long...and most people use 7.400" long with aftermarket cams to help take up some of the difference of the smaller base circle. Also remember, the rockers only "see" the radius difference (.045" in this case), not the diameter.
There is some leeway with the hydraulic lifters...but without knowing your head specs, it would be hard for anyone to advise the perfect pushrod length for you. If your heads are milled and/or using a thinner gasket, the stock length may still be fine for you..otherwise with stock head dimensions and gasket, the 7.4's should be used.
Last edited by Y2Kvert4me; Feb 22, 2005 at 07:57 PM.
Thread Starter
Burning Brakes
Joined: Nov 2004
Posts: 822
Likes: 0
From: Grafton Ohio
Thanks for the info. I'm using stock G.M. head gaskets (.054) and 317 casting 6.0 litre heads.
Please elaborate more on the radius vs. diameter case presented in your post as I do not fully understand.
Thanks, Jeremy.
Please elaborate more on the radius vs. diameter case presented in your post as I do not fully understand.
Thanks, Jeremy.
Safety Car
Joined: Dec 1999
Posts: 4,148
Likes: 5
From: Roxbury NJ
Originally Posted by jers98vet
I'm in the process of doing a cam/head swap and ran into a problem (I think). I purchased a cartek cam used a while ago and was about to install it tonight but decided to measure the lobe base circle before I did. This cam has a .090 smaller base circle than the stocker I removed. Is this normal? Do I need .090 longer pushrods? Do other aftermkt. cams come with a stock base circle or are they all reduced base circle setups? I'm all ears. Should I go with this cam or should I look for something ground on a stock base circle? Jeremy.
The LS1 lobes are already as big as will fit through the cam journals, so the only way to get increased lift is to reduce the base circle.
Last edited by Flareside; Feb 22, 2005 at 08:05 PM.
