I clearanced my 396" over the weekend and I am ordering a custom ground cam.

So last night I am thinking about the combo and bam, the cam and clearancing the rotating assembly...I completely forgot about it.

I am running a Callies Dragonslayer crankshaft with a 3.875" stroke and Lunati 5.850" rods. I had to clearance the bottom of the bores and the oil pan rails to get it to clear.

So how do I go about figuring out if I need to run a small base circle cam (how small?) and will I have to do any machine shop work to the block...or can I run longer pushrods?

Any thoughts?

 

I-beam or H-beam rods? H's will give you more problems. Either way, you are going to need a .900" base circle.....maybe even a .850" to be safe.

Jason

 

This may sound simple but if you still have cam bearings in the block you could stick your old camshaft in there just to see where you stand.

 

Ditto..... check to see where you stand right now.

Base circle is also relative to the lift of the cam. More lobe lift the cam has the smaller the base circle has to be.

Bret

 

Lunati's are all I beam,no?
i third[or fourth] mocking up to check,or asking someone with similar.I seem to remember 383s needing a small base cam towards .400 lobe lift {but my memory sucks} and youve got more crank than that.



--as always, the fountain of vague recollections....time to ease up the sauce.

 

The best clearance on rods are the Eagle H-beams. We use them on these SBC stroker engines and cut the only a tiny amount on a 3.875 as they will clear a 3.750 easy with ANY cam. I don't know about the Lunatis? Other h-beams are not so good either. I won't use any of the other rods anymore because they're just simply too much trouble in a chevy.

 

Yes and the base circle is not what hits but rather the lobes and more on some than others. the "reduced" base circle deals are where they reduce the base circle even MORE than what was necessary to get the lobe height and the rest of the reduction is what pulls the nose of the cam away from the cam journal diameter and thus the rod shoulder.

Anotherwords you can easily have a .900 base circle without it even being reduced if the lobe is very big to start with. Reduced base circles are kinda gross so I try and run the right rods to avoid it in the first place.

 

That's always my though too! Run the right rods and keep the stiffness in the cams!

 

Bret,

Yes the SBC is a wonderful thing except for that damn cam location! But with a few choice parts it's not so bad. I just have a personal problem with the reduced base circle stuff although to tell you the truth they've always worked fine on milder and lower rpm stuff like hydraulic rollers etc. On say a big Solid Roller with a lot more spring pressure it's not such a good thing.

 

I had to have my cam ground on a small base circle to clear my Callies DragonSlayer 3.875 stroke/Manley Billet 6.0 inch rods combo. I believe the base circle is .875, and I had it ground on a billet core for strenght. This is a hydraulic roller that specs 242/252, .580/.580.


Nick

 

I ended up getting that small base circle cam. In hindsight, I believe the small base circle cam was not the problem because even with the cam installed, I mocked up the cam, installed straight up and the connecting rod hits on the lobe from what I can tell and only on # 6.

Fun...fun...

 

I have had a different experience with the Eagle H-beam rods, and with H-beams in general. The best (for clearance) moderate price rod I have experience with is the Lunati "Pro-Mod". Oliver billets rods ahave superb clearance, but are on the pricey side!

Rich

 

You just have to use the right rods. We don't do anything to most of our stuff and still always run full base circle rods on everything even 396s. You just got to get the right stuff! On the 396s we cut the rods back a small amount. After that they are still strong enough to run 8.00s at almost 3300 pounds.

I build these every week.

 

I ended up just clearancing the block...spins fine now and it is not even close to the cam...could have probably gotten a normal base circle and been fine.