C3 Frame conversion from big block to small
Race Director
Joined: Mar 2003
Posts: 11,608
Likes: 780
From: Eustis ( Area 51 Bat Cave ) Fl
Depends on the frame year 68 to 72 swap easy o, bb or sb, 68 has a few little things different nothing epic,
My factory 69 sb car auto has the frame from a 68 4 speed car, we did add the rear frame kick up reinforcement that early 68 lack,
A bb frame itself isnt different to sb
My factory 69 sb car auto has the frame from a 68 4 speed car, we did add the rear frame kick up reinforcement that early 68 lack,
A bb frame itself isnt different to sb
Melting Slicks
Joined: Jul 2010
Posts: 3,176
Likes: 633
From: perth western australia
so the replacement frame is from a similar year corvette , namely 68,69,70,71,72,?
the BB and the SB use exactly the same mounting points and bell housings ,so any early vette frame will accept a BB or SB.
If its a 73 or 74 the frame starts to get different as in regards to mounting the "new " bumper type
the only thing I would be concerned with is the measurements of the replacement frame , if its from those 5 first years , no one pulls apart these cars for no reason ,so its more than likely it was involved in an accident so it could be bent .
the BB and the SB use exactly the same mounting points and bell housings ,so any early vette frame will accept a BB or SB.
If its a 73 or 74 the frame starts to get different as in regards to mounting the "new " bumper type
the only thing I would be concerned with is the measurements of the replacement frame , if its from those 5 first years , no one pulls apart these cars for no reason ,so its more than likely it was involved in an accident so it could be bent .
Last edited by bazza77; Sep 23, 2017 at 07:59 PM.
Melting Slicks
Joined: Jul 2010
Posts: 3,176
Likes: 633
From: perth western australia
Thread Starter
7th Gear
Joined: Sep 2017
Posts: 7
Likes: 1
so the replacement frame is from a similar year corvette , namely 68,69,70,71,72,?
the BB and the SB use exactly the same mounting points and bell housings ,so any early vette frame will accept a BB or SB.
If its a 73 or 74 the frame starts to get different as in regards to mounting the "new " bumper type
the only thing I would be concerned with is the measurements of the replacement frame , no one pulls apart these cars for no reason ,so its more than likely it was involved in an accident so it could be bent .
the BB and the SB use exactly the same mounting points and bell housings ,so any early vette frame will accept a BB or SB.
If its a 73 or 74 the frame starts to get different as in regards to mounting the "new " bumper type
the only thing I would be concerned with is the measurements of the replacement frame , no one pulls apart these cars for no reason ,so its more than likely it was involved in an accident so it could be bent .
Melting Slicks
Joined: Jul 2010
Posts: 3,176
Likes: 633
From: perth western australia
Just a thought , if your frame is rusted too badly ,how's the birdcage ?
Thread Starter
7th Gear
Joined: Sep 2017
Posts: 7
Likes: 1
I have read , from someone on this board who knows more about the history around these cars than I ever will , that GM sold the 74 frame as a service replacement for the early C3 , Also I have had a 74 frame here (parts car) and the bare rear is not to far from the early frame , I think there's a tab that needs to be cut off. More than likely holes drilled but definitely do-able !
Just a thought , if your frame is rusted too badly ,how's the birdcage ?
Just a thought , if your frame is rusted too badly ,how's the birdcage ?
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
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
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
Drifting
Joined: Jul 2002
Posts: 1,995
Likes: 110
From: Garland Texas
A 74 frame is a modified 69-73 frame. And it can be easily un-modified. The four mounting holes for the front bumper will have to be re-drilled along with changing the two welded nuts on each side. The frame horns themselves are exactly the same as the 71. Check for cracks around the front spring pockets and lower a-arm mounts.
Mike
Mike