Cam base circle question

[David]

I recently purchased a 421 SBC with Bowtie block. It has Lunati 3.875 stroke crank and Oliver billet 6" rods. I am going to run a smallish street solid roller around 250-260 at .050. My question is, can I run a standard base circle cam with this combo? I have a set of Erson lifters with horizontial spring loaded link bar. I am pretty sure they will not work if the cam is on small base circle. I can machine the block some to clear if needed.

[Ed]

It's not block clearence that stops you from running a std base circle cam. Its rod clearence to the cam lobes. I have used the lunati spring loaded horizontial bar lifters with a .890" for a few years now with no problem. With that combo you will need a maximun of a .900" BC. Most cam companies can grind what you want just call them.
Why such a small cam in a 421" ?
ED

[David]

Are you running the Bowtie block? It has a very tall lifter bore that usually requires tall lifter bodies or machining to clear some lifters. Mine has already been notched for link bar type lifters. THe pad linking the lifter bore pairs can be machined down to allow the horizontal links to fall farther down to reach small base circle cams. This is the machining that I feel I will have to do if I run a small base circle. THis motor is for my street car to run on pump gas. I need to run power brakes and am looking for a decent idle quality. I will be running a set of Fast Burn heads that I ported myself. Have them over 280cfm right now and still improving on them. The 210cc intake runner will likely limit rpm, but should work well with the small cam. Any suggestions on cam will be appreciated, particularly LSA. Thanks

[bigjimzlll]

Have ground on a billet core...some street rollers aren't

[85Iroc]

I have a small base circle Lunati cam for sale in the classifieds with 255/263 dur. @ .050 It's on a 109 LSA with .626/.626 lift.
Not sure about using power brakes & idle quality with it though, or any cam with that much duration unless the lobes are spread quite a bit. It idled pretty good in my 355.

[David]

Thanks for the heads up on the cam. It is perfect for what I want to do except that my block has roller cam bearings. It uses a slightly larger cam journal.

[85Iroc]

I hear ya. That's why I'm selling it, my bowtie block has roller cam bearings as well.

[David]

I have a line on a Isky solid roller that is brand new. It was ordered for roller cam bearings by mistake. It is 256/264 @.050 with .650/640 lift w1.5 rockers. Ground on 106LSA and .960 base circle. I would buy it if it were ground on a 109 or 110LSA. Let me know if you are interested.

[85Iroc]

hmmmm. Do you know if the .960 base circle will work with 3.75 stroke & h-beams? That might be too much of a cam for a street truck. Do they make different size roller cam bearings? I've seen some people say 50mm, some say 55mm & 58mm. Are there that many sizes? I'm not sure what mine are.

[David]

I am in the same boat as you....more questions than answers. I usually try to do all the leg work for my projects, but I have decided to let the machine shop I use handle these things since they have experience with them. THis is the first big inch small block or aftermarket block deal I have done. I think they plan to try some cams in the block with the bottom end together and check clearance on the cam. Once they determine what base circle I can use, I will order the cam. I talked to Oliver, who makes the rods I have and they cannot tell me for sure about the clearance. He did say that he had run standard base circle with 3.75 stroke with these rods. THe 3.875 is not a huge difference, but who knows. I don't want to order a cam and it not work.