C4 406 SBC swap question
Thread Starter
Navigator
Joined: Jul 2021
Posts: 9
Likes: 1
C4 406 SBC swap question
I have a question for those who have installed a SBC 400 in a C4. I have an 87 convertible that I plan on swapping a mild performance 406 into. This is an externally balanced motor with the larger harmonic balancer and 168 tooth flex plate. Are there any mods required to the crossmember to get the larger harmonic balancer to work? I know the 700R4 dust cover will need to be modded with the larger flex plate. Any help would be appreciated. Trying to cover all the bases before I yank the old L98.
Team Owner
Joined: Oct 2004
Posts: 81,241
Likes: 3,063
From: altered state
St. Jude Donor '05
Ought to get an answer pretty quickly here lots of traffic.
What else are you gonna do to the 400? Came too close to installing one in an 89 I had but a ZR-1 found me.
Wish I did it...they make so much torque!
What else are you gonna do to the 400? Came too close to installing one in an 89 I had but a ZR-1 found me.
Wish I did it...they make so much torque!
Thread Starter
Navigator
Joined: Jul 2021
Posts: 9
Likes: 1
The 406 has 5.7 rods with speed pro Hyper 10:5 to 1 pistons. A Lunati 262/268 cam with 1.5 roller rockers. Skip White NKB 200 aluminum angle plug heads in 64cc. SLP big mouth intake with ported SLP runners and 58mm throttle body. Ported stock L98 headers with a free flowing "catless" exhaust. Car does have a dana 36 with a 3:55 ratio. Motor is all built now I'm worried about the 400's harmonic balancer? I think I'll be ok?
Thread Starter
Navigator
Joined: Jul 2021
Posts: 9
Likes: 1
Thanks, I just bought a assault racing 6.75" 400 sbc dampner. I never knew until today they made it! That solves that issue. In regards to the headers, does anybody have any experience with ones that fit well?
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
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
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
Team Owner
Joined: Sep 2001
Posts: 62,171
Likes: 1,735
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
Team Owner
Joined: Oct 2004
Posts: 81,241
Likes: 3,063
From: altered state
St. Jude Donor '05
Have a brand new set of 1-3/4" shorties, custom made if you dont want longtubes. Not gonna be using them
Asking cost, 5 bones plus ship
Longtubes get the best results though esp if youre going to be running dual exhaust
Asking cost, 5 bones plus ship
Longtubes get the best results though esp if youre going to be running dual exhaust
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Well that's a good question. I was using a flywheel (stick shift).
It turns out that they DO MAKE 'EM
It turns out that they DO MAKE 'EM
Team Owner
Joined: Oct 2004
Posts: 81,241
Likes: 3,063
From: altered state
St. Jude Donor '05
TCI, nice. Figured at least Pioneer would make them
400 is a killer choice imo for a low rpm tall geared c4. Improve the intake, exhaust it will roast rubber at any time.
DId CFI-EFI ever get his in or was it a 350 still?
If I Could afford another C4 thats the route Id certainly go. Good heads, small cam and make it sleepy (quiet)
400 is a killer choice imo for a low rpm tall geared c4. Improve the intake, exhaust it will roast rubber at any time.
DId CFI-EFI ever get his in or was it a 350 still?
If I Could afford another C4 thats the route Id certainly go. Good heads, small cam and make it sleepy (quiet)
Race Director
Joined: Apr 2003
Posts: 17,700
Likes: 1,667
From: moraga ca
I am running ARH stepped 1 3/4" to 1 7/8" headers on my 406. They are worth 1.5 tenths over Hooker 1 3/4" headers in the quarter. With the bigger cubes, better heads and breathing, I would look at a miniram for your car. My motor is internally balanced so I can run a normal sized, neutral balanced balancer and flexplate.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
And it's going in my '92.....some day..... 
Drifting
Joined: Jan 2005
Posts: 1,354
Likes: 325
From: San Antonio Tx
When I installed the 350 vortec motor form a 96 truck into my 86, the 8 " balancer that came on that motor hit the crossmember before it was fully lowered into position. I replaced it with 6.75" from Summit Racing and I still can barely get a finger between the balancer and the crossmember. I would think your 87 would be the same as my 86. Things changed in that area in 88. I thought about notching the crossmember but with the front spring in there I decided not to go that route. Changing the damper was much easier.
