? for cam experts
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
No. The small base circle is for long stroker cranks. It reduces the overall diameter of the cam so it does not hit the crank. A retro fit roller cam is for a non roller block, pre 86 blocks. You can have a small base circle retro fit or non retro fit.
Pro
Joined: Jun 2005
Posts: 725
Likes: 1
From: FL.
And A retrofit cam Means it must be used in a block thats not machined for the later OEM roller cams and lifters. OEM roller assemblies have shorter pushrods and a "spider" retainer setup for the lifters. Pictures of this spider assembly are surprisingly hard to find. But its very simple type setup.Base circle is not related directly to whether the cam is a retrofit roller or an OEM roller.
PS, Im not a cam expert but I did a 383 OEM roller block Build up a few years ago.
Last edited by 69vettester; Apr 13, 2010 at 07:35 PM.
Thread Starter
Melting Slicks
Joined: Jul 2006
Posts: 2,373
Likes: 6
From: Baltimore MD
OK,i have a non roller older block with a 383 stroker kit in it and i bought a edelbrock retrofit cam for it why does everything works great.Also if you were to buy a retrofit cam and then you bought a small base circle cam under the same cam grind ,would all the specs be the same,like the duration and lift?
Race Director
Joined: Apr 2000
Posts: 17,676
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
OK,i have a non roller older block with a 383 stroker kit in it and i bought a edelbrock retrofit cam for it why does everything works great.Also if you were to buy a retrofit cam and then you bought a small base circle cam under the same cam grind ,would all the specs be the same,like the duration and lift?
Pro
Joined: Jun 2005
Posts: 725
Likes: 1
From: FL.
OK,i have a non roller older block with a 383 stroker kit in it and i bought a edelbrock retrofit cam for it why does everything works great.Also if you were to buy a retrofit cam and then you bought a small base circle cam under the same cam grind ,would all the specs be the same,like the duration and lift?
I dont see why the same grind, retro as oem would have a different base circle dimension? But I dont know that for sure..maybe a cam expert from both schools would know for sure.
Thread Starter
Melting Slicks
Joined: Jul 2006
Posts: 2,373
Likes: 6
From: Baltimore MD
Ok Wayne heres one for ya,i just bought a small base circle cam for my engine to try out,and its the same cam as the retrofit one,its a 294D extreme energy cam,the lift numbers are the same,but the duration is different,the retrfit one is 294/300 and the small base circle cam that i bought is 293/299,i know its not much,but why is it different?and the opening and closing of the valve timing is different too,i dont get it
why are the two cams that are suppose to be the same have different numbers? do you guys know why?
why are the two cams that are suppose to be the same have different numbers? do you guys know why?
Thread Starter
Melting Slicks
Joined: Jul 2006
Posts: 2,373
Likes: 6
From: Baltimore MD
I think i know why i can run a retrofit cam in my engine with no issues,its because the stoker kit i bought was already clearanced for the cam,which i think my crank was clearanced also .
So if i am right you cant run a retrofit cam in a older non roller block unless the crank and rods are clearenced,right?
So if i am right you cant run a retrofit cam in a older non roller block unless the crank and rods are clearenced,right?
Last edited by Billysvette; Apr 13, 2010 at 08:23 PM.
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Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
I run a retro fit roller cam in mine and have stroker rods but the crank is astroker but not clearanced. This is where everything gets tricky. No matter what you have you better check clearances. Some blocks will let you run it others won't. I would not say anything will fit unless I did it myself. A lot depends on the lift and duration of the cam. Some roller have very little lift so the lobes are not very tall and will cear the crank and rods. If you have a very big lift it might hit. Check all the clearances! 
Thread Starter
Melting Slicks
Joined: Jul 2006
Posts: 2,373
Likes: 6
From: Baltimore MD
I run a retro fit roller cam in mine and have stroker rods but the crank is astroker but not clearanced. This is where everything gets tricky. No matter what you have you better check clearances. Some blocks will let you run it others won't. I would not say anything will fit unless I did it myself. A lot depends on the lift and duration of the cam. Some roller have very little lift so the lobes are not very tall and will cear the crank and rods. If you have a very big lift it might hit. Check all the clearances!
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
Can't really answer that but those numbers are so close you would never know any difference between the two. Are the numbers at .050 the same. The advertised duration is something I never look at because they all are measured differently. The .050 numbers tell more about the cam.
Thread Starter
Melting Slicks
Joined: Jul 2006
Posts: 2,373
Likes: 6
From: Baltimore MD
Can't really answer that but those numbers are so close you would never know any difference between the two. Are the numbers at .050 the same. The advertised duration is something I never look at because they all are measured differently. The .050 numbers tell more about the cam.
why different numbers on advertised duration then.The other numbers are different though,opening and closing valve timing.dont know if that matters.
Team Owner
Joined: Apr 1999
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
The duration @.050 gives a closer comparison number. When I look at cam lobes the .200 lift duration numbers really tell the true ramp speed.
Look up some cams and you will see the .050 could be the same, but the .200 might be very different.
Whenever you change base circle size you have to change the length of the push rod the same amount.
Thread Starter
Melting Slicks
Joined: Jul 2006
Posts: 2,373
Likes: 6
From: Baltimore MD
Advertized duration numbers are pulled out of a hat for marketing. One company might measure @.004 lift another .007.................
The duration @.050 gives a closer comparison number. When I look at cam lobes the .200 lift duration numbers really tell the true ramp speed.
Look up some cams and you will see the .050 could be the same, but the .200 might be very different.
Whenever you change base circle size you have to change the length of the push rod the same amount.
The duration @.050 gives a closer comparison number. When I look at cam lobes the .200 lift duration numbers really tell the true ramp speed.
Look up some cams and you will see the .050 could be the same, but the .200 might be very different.
Whenever you change base circle size you have to change the length of the push rod the same amount.
Last edited by Billysvette; Apr 14, 2010 at 02:59 PM.
Drifting
Joined: Aug 2005
Posts: 1,682
Likes: 3
From: League City TX
When the base circle of the cam is reduced, the lifter will sit further down in the bore when it is riding on the cam's base circle.
Since that will put the lifter further away from the rocker, a longer pushrod is needed to compensate.
Since that will put the lifter further away from the rocker, a longer pushrod is needed to compensate.
Thread Starter
Melting Slicks
Joined: Jul 2006
Posts: 2,373
Likes: 6
From: Baltimore MD
But wait its the same lift and duration as the other cam how can you go with longer pushrods if they are the same?
Le Mans Master
Joined: Nov 2008
Posts: 5,691
Likes: 12
From: columbus oh
Are you saying if i change over to a small base circle cam i will have to change pushrods ? Why? I already changed when i put in the retro hydraulic roller in my engine,wouldnt it be the same length pushrods for a small circle base cam?the lift and everything should be the same i would think?
Thread Starter
Melting Slicks
Joined: Jul 2006
Posts: 2,373
Likes: 6
From: Baltimore MD
I understand how to do pushrods,what im not getting is why i might have to,i will check when i put cam in,but,the two cams a retro fit and a small base circle cam with same specs,i would think have to use the same pushrods because the lift has to be the same ,right,and if i change pushrods that changes the geometry of things.600 lift on a retro as to be the same as sm base circle.if you were to measure from the center,right?
My brain is frying here
The only thing that would be different is when the valve is closed ,on the sm base cam pushrod will go deeper ,right
My brain is frying here
The only thing that would be different is when the valve is closed ,on the sm base cam pushrod will go deeper ,right
Last edited by Billysvette; Apr 14, 2010 at 05:35 PM.
Le Mans Master
Joined: Nov 2008
Posts: 5,691
Likes: 12
From: columbus oh
I understand how to do pushrods,what im not getting is why i might have to,i will check when i put cam in,but,the two cams a retro fit and a small base circle cam with same specs,i would think have to use the same pushrods because the lift has to be the same ,right,and if i change pushrods that changes the geometry of things.600 lift on a retro as to be the same as sm base circle.if you were to measure from the center,right?
My brain is frying here
The only thing that would be different is when the valve is closed ,on the sm base cam pushrod will go deeper ,right
My brain is frying here
The only thing that would be different is when the valve is closed ,on the sm base cam pushrod will go deeper ,right