Small Base Circle Camshafts?
Thread Starter
Melting Slicks
Joined: Jun 2000
Posts: 3,215
Likes: 6
From: Tampa Florida
Small Base Circle Camshafts?
I have two engine projects going on...one for a 407 and another for a 396, both small blocks.
My questions are on reduced (or small) base circle camshafts...
How do you know an engine requires it? What does it hit?
If the engine requires it, does this mean that you must install the cam before the crank, rods, pistons? And if so, does this mean you can't remove the cam after the engine is assembled...since even the cam bearing journals are larger than the base circle...
I understand that longer pushrods would be needed to work with this combination...
Thanks
:)
My questions are on reduced (or small) base circle camshafts...
How do you know an engine requires it? What does it hit?
If the engine requires it, does this mean that you must install the cam before the crank, rods, pistons? And if so, does this mean you can't remove the cam after the engine is assembled...since even the cam bearing journals are larger than the base circle...
I understand that longer pushrods would be needed to work with this combination...
Thanks
:)
Burning Brakes
Joined: Dec 2002
Posts: 947
Likes: 0
From: Middletown N.Y.
Re: Small Base Circle Camshafts? (No Go)
As I write this I'm remembering what I had to do to my 383. I needed a small base circle cam and found out after I had the rotating assembly in the block, obviously. Several rods would hit the cam, I don't remember exactly which ones do on a 383 but they hit. I just pulled the cam out (it's a roller hyd) and ordered the same cam but with a smaller base circle, I don't remember the exact size, It was pretty much that simple, The new cam should carefully slide in make sure you recheck for hitting and clearance that's it. I had a retro fit Hyd roller and the push rod length was supposed to be 7.250" after checking and ordering several checking pushrods the right size for me was 7.300. But you must check it, cause it will vary. Cam type and size (dur/lift) plays a big role also.Good Luck!
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Re: Small Base Circle Camshafts? (No Go)
With your 3.875 & 4 inch stroker motors I would recommend small base circle cams.
Small base circle is usually refered to any cam that has the lobe near .900 inches. My last Crane sollid roller was .930 diameter My present SR cam is 1.030 with 3.750 stroker crank and large steel 685 gram 6 inch steel rods and it runs fine.
I have always installed the cam after the bottom end.
My Crane cam because of the small base circle and .100 longer valves that come with The bigger Dart heads required .200 longer push rods. My last cam having the .100 larger base circle only required .100+ push rods.
Small base circle is usually refered to any cam that has the lobe near .900 inches. My last Crane sollid roller was .930 diameter My present SR cam is 1.030 with 3.750 stroker crank and large steel 685 gram 6 inch steel rods and it runs fine.
I have always installed the cam after the bottom end.
My Crane cam because of the small base circle and .100 longer valves that come with The bigger Dart heads required .200 longer push rods. My last cam having the .100 larger base circle only required .100+ push rods.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Re: Small Base Circle Camshafts? (No Go)
How do you know an engine requires it? What does it hit?
Thanks
:)
Thanks
:)
RACE ON!!!
[Modified by CFI-EFI, 9:33 AM 7/27/2003]
Melting Slicks
Joined: Dec 2001
Posts: 2,025
Likes: 1
From: Billings MT
Re: Small Base Circle Camshafts? (No Go)
I am using a "stroker profiled" 6.0" H-Beam rod with 7/16 cap screws in a 407 without any clearance problems. The cam is a Comp XR-288HR standard base circle. :cheers:
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Re: Small Base Circle Camshafts? (VETDRMS)
That come as no surprise to me. They are "stroker" rods, profiled to give extra clearence at the cam. They would likely be fine in a 396 (3.785" stroke) too. I'd check really closely with a 4.00" stroke. A production 5.7" Chevy 350 rod will likely interfere, even in a 3.75" stroke engine, without some grinding.
RACE ON!!!
RACE ON!!!
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Re: Small Base Circle Camshafts? (No Go)
The thing to buy from companies like Flatlanderracing is the complete racing rotating kit. They take all the guess work out of assembly. I have always done my own block grinding.
Thread Starter
Melting Slicks
Joined: Jun 2000
Posts: 3,215
Likes: 6
From: Tampa Florida
Re: Small Base Circle Camshafts? (gkull)
Thanks folks for the help.
I should have been more specific...
The 407 is using a 3.75 Scat crank and their H beam rods. I don't believe they offer the stroker profiled ones.
I would like to order Flatlander although they aren't too helpful. The prices are quite good.
I'm going with a simple 282 solid flat tappet in the 407...
:)
I should have been more specific...
The 407 is using a 3.75 Scat crank and their H beam rods. I don't believe they offer the stroker profiled ones.
I would like to order Flatlander although they aren't too helpful. The prices are quite good.
I'm going with a simple 282 solid flat tappet in the 407...
:)
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Re: Small Base Circle Camshafts? (No Go)
If I am not mistaken, the rod bolt threads into the rod fork (main rod forging) on those rods. The bolt head is on the bottom, not the top like a nut & bolt combo. If so you are likely to have plenty of clearence. Either way, get a .050" feeler guage and check it for yourself. Good luck, and...
RACE ON!!!
RACE ON!!!
Melting Slicks
Joined: Dec 2001
Posts: 2,025
Likes: 1
From: Billings MT
Re: Small Base Circle Camshafts? (No Go)
No Go I too am using the SCAT 3.75" Crank and SCAT 6" H-Beam rods. The rods are clearanced for stroker applications from SCAT. They use a 7/16" cap screw (threads into the rod [no nut]) You will however need to clearance the pan rails for the longer rods. Its easy to do with a die grinder, just install the crank, and mark out a 1" section where the rod throw will be on a 1" centerline, take ~3/16" material out, then lay the crank in and install two rods at a time, spin and check, clearance where necessary.
Good Luck :)
Travis
Good Luck :)
Travis
