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Discussion Starter #1 (Edited)
So...other than ordering a cam, installing it, and measuring rod clearance...then returning it if it isn't right, is there any way to tell if I need a small base circle cam?

400 block, .030 over = 406
4.155 bore
3.75 stroke internal balance 4340 Eagle crank
6" Eagle ESP H-beam rods
-20cc 5019H3 Wiseco pro-tru forged pistons

I'm thinking about a Comp XE274 or XE284, or a Voodoo 103 or 104.

I called Comp's help line, the tech said "We can't tell you if it's going to clear, *you* need to tell *us* if you need a small base circle cam."

Is there a downside to using a small base circle cam? Maybe I should just go that way in the first place...
 

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With that combo I will almost garanty you will need a small base cam, They say that those rods are ground for stroker clearance, but in my 406 some had enough clearance and some didnt, cylinder 2 in my engine only had.025, and the minimum is .050, my machine shop guy said we could just grind the rod a little, but everything was already balanced so I decided to go the small base circle route instead.
Comp ground it for 200 bucks, not that much more than the regular base circle version.

Mike
 

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I've never liked them, have always just ground away the necessary to get the clearance. It always seemed to me that if you are opening the valve say .550'' with a smaller base circle and the same ratio rocker , that you would have to be moving the lifter up the ramp at a greater velocity and therefore increasing the probability of valve float and increased frictional losses, but maybe that doesn't happen, don't know, just don't like the way they look.
 

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I have a 406 with a standard size cam. And, yes I had clearance issues. My cam has .510/.533 lift. I'm using reconditioned 350, 5.7in long rods. Yours are defiantly better :) and IMO, will probably offer better clearance.

My suggestion: Get the cam of you choice. Assemble the engine - crank/rods/pistons (less rings), and cam of course, and rotate the bottom end - slowly, by hand. See what happens, and let us know!

The downside to a small base circle cam, is 'surface speed'. Any mechanist knows this term. The smaller the dia, the faster the surface speed. The faster the surface speed, the more heat produced, and things can quickly wear out. I'm sure one of our moderators can chime in here, and explain better than I.
 

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I'm sure it would not be an issue in this situation but I have heard that under high spring pressures small base circle cams are prone to deflection and possible breakage...I'm sure I read that on here...hmmm...it must be true cause this is the internet after all:rolleyes: :) ;)
 

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69NovaSS said:
I'm sure it would not be an issue in this situation but I have heard that under high spring pressures small base circle cams are prone to deflection and possible breakage...I'm sure I read that on here...hmmm...it must be true cause this is the internet after all:rolleyes: :) ;)
What would be better? Grind the snot out of the rods/bolts or get a small base-circle cam :confused: Do H-beam rods give ya more clearance than I-beam rods?



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DriveWFO said:
What would be better? Grind the snot out of the rods/bolts or get a small base-circle cam :confused: Do H-beam rods give ya more clearance than I-beam rods?

I wasnt saying they were a bad thing..just that I have read that on this site that they can deflect under high spring pressures...I guess if I was going to build an all out roller cam large cube small block I would get an aftermarket block with raised camshaft journals......that way I have use a regular (stronger) cam and still have the long stroke too....without having to gring the rods or block for clearance....sorta a have your cake and eat it too situation...

You can get rods that are supposedly clearanced for stroker cranks...they might be the way to go....I'm sure you would still want to check the cam clearance even with them as you wouldnt want to find out the hard way you didnt have enough:eek:
 

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I just knocked a little off of the corner of the boss where the top of the stud was... if that makes any sense. I found that 1 and 3 had problems, so I ground all of them like that, and didn't have a problem when I checked clearances.

ohyeah, mock it up without the rings... that way you can accuratly feel when the cam and rod collide!
 

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Patman

Wanted to thank you for your posts - I've been following your build and it has helped me out.

My 406 has 6" I beams so the're not the same, but for what its worth - the standard base cam- Comp Cam 286H with a 490 lift worked for me. Finished installing my rockers last night.

Is it possible to use a smaller lift cam and 1.6 ratios with the same results?
 
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