Larger Cam Base Circles
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Larger Cam Base Circles

  1. #1
    Senior Member Ahsumtoy's Avatar
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    Default Larger Cam Base Circles

    I'm considering purchasing a new aluminum race block. All of the block mfgs offer larger cam bearing base circles as an option. What are the pro's & con's?
    Last edited by Ahsumtoy; 03-14-2009 at 10:02 AM.

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    Just another Wannabe Wannabe's Avatar
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    Pros; Less cam flex with large spring pressures. Also, roller cam bearing options.
    Cons; Huge price increase. Complete custom cams. Harder to throw another cam in on the dyno to see changes. Interchangable parts for whatever reason.

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    Senior Member wagspe208's Avatar
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    Quote Originally Posted by Wannabe View Post
    Pros; Less cam flex with large spring pressures. Also, roller cam bearing options.
    Cons; Huge price increase. Complete custom cams. Harder to throw another cam in on the dyno to see changes. Interchangable parts for whatever reason.
    Yes....don't forget lead time on getting those custom cams ground. Not as bad as custom piston vs shelf piston, but it happens.
    Wags

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    Spiral out MikeF's Avatar
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    What are you gonna do w/ your useless old aluminum block that you're taking out?

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    Unless you plan on having one inch lift and 1200lbs of open spring pressure use a standard journal size.Those big cores were developed for cam flex and to get huge lobe lift.They come in 55mm and 60mm diameters.

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    In my opinion, saying you have to be going to 1.00" lift to take advantage of a larger core is off a bit!
    With the trend toward bigger engines, bigger lifts and higher spring pressures, I believe the advantages of a larger core come way before that point.
    If starting from scratch, and planning on going to anything over a .450-.475 lobe at any time, I would definitely go to a larger core, and the biggest diameter lifters I could afford. This will make the system more stable, and open up areas such as larger push rods and faster cam rates. But through the process there are things that will be different. Most of them were mentioned above (cams can cost more and be harder to get ect.) but another is lifter location. When going to a bigger core (and accompanied larger base circle), it instantly means that the lifter while on the base circle will now be at a taller height in the bore. Couple this with the greater lobe lift you'll prolly be running (with out it and greater spring pressure the advantages to the larger core lessen) and now you need to make sure the lifter bore/sleeve is modified properly so the upper end will get proper oiling, and the oiling holes in the lifter don't come out the top of the bore at max lift.
    This "new" aluminum block is going in a jet boat? This means that you are pretty serious about performance so I think it would be a wise choice to go to both the bigger journal bore and larger/keyed lifters if it's in the budget (again, aluminum block for a jet boat, I think the budget is fairly decent! ). If not, just don't get carried away with lobe lift/spring pressure and it will be fine.

  9. #7
    steelcomp was here
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    Not to mention you'll be able to run slightly shorter pushrods, and that can never hurt.
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    gn7
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    Although I have no numbers for a BBC sized cam, the small block with a .420 lobe and approx 800# springs can deflect the rear of the cam +/- 2* (4* crank) depending on which side of the lobe the lifter is on. Alot of the spark scatter that use to be blamed on the oil pump is really from cam flex. Have to imagine that a certain amount still accures in the BBC even with the larger core size.



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    Pros Reduced camshaft flex in high rpm and/or high spring load applications

    Cons Price

    Cam core diamterers and roller lifter diameters when made larger are found to stablize the valvetrain in a given application.
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  12. #10
    cfm
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    Quote Originally Posted by Warp Speed View Post
    When going to a bigger core (and accompanied larger base circle), it instantly means that the lifter while on the base circle will now be at a taller height in the bore......
    IMHO - this is a huge advantage.

    Edited due to run-a-way typing on the phone. Still a quickie, but hopefully less generics and clearer typing. LOL.

    Because of it's design, a roller cam lifter has significant side loading. Designing the cam for faster lifter acceleration will cause higher side load. Using a larger base circle will reduce this side load. Also, as mentioned, a larger roller will also reduce this side load. As a note: flat tappet cams/lifters really don't have much of this side loading.

    Also, many cams reduce base circle to increase lift. Not just because of fitment issues, but for ease of machining / cam core specs / etc. Example: Crane states they reduce the base circle on their BBC .359" (.610" lift w/1.7) + higher HR lobes - they are unclear if they do this on the next smaller lobe .345" lobe (.587" with 1.7) or smaller. A reduced base circle let's the lifter drop further down the bore. This can leave more of the lifter unsupported and cause even more side loading issues as the lifter can '****' more. A longer lifter can help alleviate some possible issues by this. A longer lifter adds weight that we don't always want to add. Not all blocks have longer lifter bores, so boring the lifter bores larger and installing larger diameter roller can reduce side load issues. Lifter size/length and bore size/length is all about supporting the lifter. Again, A larger core cam (larger base circle) would and does help alleviate this side loading big time.

    Side loading is still large with a roller no matter what you do, but the issue here is to reduce it as much as possible, not only for power, but in many circumstances, because of dependability/reliability / carnage possibilities.

    I recently saw pics of some destroyed SR lifters, that where going further down in the lifter bore than they where designed to do. The lifters 'cocked' in the bores and where 'jamming' against the lifter bore. No, these didn't last too many hrs.
    Last edited by cfm; 03-17-2009 at 05:31 AM.

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    gn7
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    Quote Originally Posted by cfm View Post
    IMHO - this is a huge advantage.

    As the lifter 'falls' out of the bore farther, less of the body is supported and thus get's jammed into the side of the lifter bore when it is being raised. I believe this is where a lot of the cam flex comes about. Spring psi's too - sure, but mechanical interference can create more of an issue.
    Remember, to get more lobe lift from a core, the grinder has to remove material from the base circle. Most think the cam is 'ground bigger' but it's actually ground 'smaller' to gain more lift. Thus, the lifter 'falls' further down in the lifter bore. Thus reason for some blocks having taller lifter bores and people using taller lifters - ie: more support for lifter body as it goes thru it's travel.
    CFM, are you drinking? Cam grinders only grind the base smaller when they need to for rod clearence, or it's a regrind of existing cam, or the required lobe profile excedes that which can clear the cam bearing. (I.E. approx .420 on a SBC) I have BBC cams ranging from .350 to .450 lobe, and they all have the same base size. The reason for the taller lifter boss isn't so the lifter can drop further and still be stable, it's for taller OEM hyd rollers.



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    Senior Member MACHINEHEAD1's Avatar
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    I had to use a tall body lifter on my aftermarket Aluminum DART SBC. This took full advantage of the availible surface area. It had a BBC core also. Only run 190/540 open to 6200. Overkill is OK for the Baja 1000! BTW got the custom Comp grind with the big core in 4 days! Not a problem these days. I have also seen many cams that have been ground into the base circle for the big lift stuff. Lobe lift needs to be off set by core Dia. to keep fromm getting into the meat of the core.

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    gn7
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    Quote Originally Posted by cfm View Post
    IMHO - this is a huge advantage.

    Edited due to run-a-way typing on the phone. Still a quickie, but hopefully less generics and clearer typing. LOL.

    Because of it's design, a roller cam lifter has significant side loading. Designing the cam for faster lifter acceleration will cause higher side load. Using a larger base circle will reduce this side load. Also, as mentioned, a larger roller will also reduce this side load. As a note: flat tappet cams/lifters really don't have much of this side loading.

    Also, many cams reduce base circle to increase lift. Not just because of fitment issues, but for ease of machining / cam core specs / etc. Example: Crane states they reduce the base circle on their BBC .359" (.610" lift w/1.7) + higher HR lobes - they are unclear if they do this on the next smaller lobe .345" lobe (.587" with 1.7) or smaller. A reduced base circle let's the lifter drop further down the bore. This can leave more of the lifter unsupported and cause even more side loading issues as the lifter can '****' more. A longer lifter can help alleviate some possible issues by this. A longer lifter adds weight that we don't always want to add. Not all blocks have longer lifter bores, so boring the lifter bores larger and installing larger diameter roller can reduce side load issues. Lifter size/length and bore size/length is all about supporting the lifter. Again, A larger core cam (larger base circle) would and does help alleviate this side loading big time.

    Side loading is still large with a roller no matter what you do, but the issue here is to reduce it as much as possible, not only for power, but in many circumstances, because of dependability/reliability / carnage possibilities.

    I recently saw pics of some destroyed SR lifters, that where going further down in the lifter bore than they where designed to do. The lifters 'cocked' in the bores and where 'jamming' against the lifter bore. No, these didn't last too many hrs.
    Well now a new trick! When you get caught with your head up your ass, just edit your entire post! and make it longer winded while your at it. Longer lifters in a standard block, where the stock length lifters don't drop lower that than top of the lifter bores is of no help. The lifter can only be supported by the length of the lifter bore. Any amount of the lifter body above the bore is just weight.



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    Last edited by gn7; 03-17-2009 at 06:56 AM.

  16. #14
    cfm
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    No new tricks. You quoted what I first typed. No biggie. I read your reply, looked at mine that you quoted, and saw what i wrote was no good. it happens. Brain farts / finger farts / and distractions. No, I wasn't drinking but it sure looked like it, actually looked more like I was trippin. LOL.

    I put in there that I edited it. I was being numb/dumb/ or all the above. Figured I'd put a little better info then my last attempt vs leaving that in
    there.

    Yes - I wrote like a Dumbass ! LOL. LOL.

    From you -
    Longer lifters in a standard block, where the stock length lifters don't drop lower that than top of the lifter bores is of no help. The lifter can only be supported by the length of the lifter bore. Any amount of the lifter body above the bore is just weight.
    I agree, and would like to add much better written (quicker to the point) then I usually can write. And obviously I had that problem above. I had different scenarios in my head that I couldn't explain exactly.

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