Engine balance experts…….
Thread Starter
Race Director
Joined: Mar 2018
Posts: 10,851
Likes: 2,253
From: Golden Colorado
Engine balance experts…….
……jump in here.
Todays subject is internal balanced Chevrolet engines.
Question, is there a difference between a 350 sbc manual trans flywheel and a 402/427 bbc manual flywheel of the same clutch size, as far as rotating assembly neutral balance?
Goal is to use a 350 flywheel on a 402.
Thanks in advance.
Todays subject is internal balanced Chevrolet engines.
Question, is there a difference between a 350 sbc manual trans flywheel and a 402/427 bbc manual flywheel of the same clutch size, as far as rotating assembly neutral balance?
Goal is to use a 350 flywheel on a 402.
Thanks in advance.
Safety Car
Joined: Mar 2009
Posts: 4,191
Likes: 951
From: Corpus Christi, TX
On all 2 piece rear main seal engines, theyre all interchangeable EXCEPT 400 small block and 454 big block flywheels/flex plates. Those two have counterweights bc those engines cam from the factory externally balanced.
Race Director
Joined: Mar 2001
Posts: 14,643
Likes: 4,691
From: Mustang OK
2026 Corvette of the Year Finalist - Modified
2025 c1 of the Year - Modified Winner
2024 C1 of the Year Finalist - Modified
2023 C1 of the Year Finalist - Modified
2015 C1 of the Year Finalist
As an added comment, ALLLLLLLLLLLLLLLLLLLLLLLLLLLL 55-85 FIRST generation small blocks, W-motors, BBs (with 2-piece rear main seal) HAVE EXACTLY THE SAME BOLT PATTERN AT THE REAR OF THE CRANK. Thus, ALLLLLLLLLLLLLLLL flywheels for these engines are a PHYSICAL bolt-on swap.
Also, as mentioned, EXCEPT for the SB400 and 454, ALLLLLLLLLLLLLLLLLLLLLL flywheels (153 teeth and 168 teeth) are ONLY NEUTRAL BALANCE.
As pointed out above, the SB400 and 454 (and variations such as 383SB or 468-496BB) use a 168 teeth flywheel with ADDED WEIGHT on one side. They are commonly referred to as EXternal balance flywheels.
Below is a comparison of a neutral balance and an external balance flywheel. The external balance 454 flywheel id moderately common, but an external balance flywheel for a SB400 is ULTRA rare. Sooooooooooo, when building a SB400, I either use a 454 flywheel and have my machinist balance it as needed, OR, use a neutral balance flywheel and have it balanced as needed simply by having metal removed to achieve the necessary EXternal balance (second picture).
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
5 Best & 5 Worst Corvette Daily Drivers
Joe Kucinski
The Headlights of Every Corvette Generation Explained
Joe Kucinski
5 Best & 5 Most Overrated Corvette Track Packages of All Time!
Joe Kucinski
Every 2027 Corvette Engine Explained
Joe Kucinski
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Verdad Gallardo
10 Ugly Corvettes That We Still Kinda Love
Joe Kucinski
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
Burning Brakes
Joined: Dec 2010
Posts: 1,224
Likes: 361
From: Southington CT
There is some incorrect info in the post above. Aftermarket 383, 400/406 and 454/496 on up can be internal/neutral balanced. Most high quality forged crankshafts for these combinations can be ordered as neutral/internally balanced. I know this because I have built all of the engine combinations I listed above and they were all neutral balanced. You might want to qualify your post as being limited to GM factory produced applications only with a disclaimer that aftermarket applications will vary depending on how the engine was built.
Race Director
Joined: Mar 2001
Posts: 14,643
Likes: 4,691
From: Mustang OK
2026 Corvette of the Year Finalist - Modified
2025 c1 of the Year - Modified Winner
2024 C1 of the Year Finalist - Modified
2023 C1 of the Year Finalist - Modified
2015 C1 of the Year Finalist
There is some incorrect info in the post above. Aftermarket 383, 400/406 and 454/496 on up can be internal/neutral balanced. Most high quality forged crankshafts for these combinations can be ordered as neutral/internally balanced. I know this because I have built all of the engine combinations I listed above and they were all neutral balanced. You might want to qualify your post as being limited to GM factory produced applications only with a disclaimer that aftermarket applications will vary depending on how the engine was built.