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400 Small Block swap

R

rpounds

Guest
I am considering a swap in my '75 from a 350 to a 400 small block. I have an opportunity to pick up a 400 on the cheap (free), that I can take my time building up and stabbing at a later date.

Question . . . are the motor mounts in the same location for a 350 and a 400? Everything else should line up fine, but I have been told the mounts are different.

Any help would be appreciated.

Ron
 

Jack

Well-known member
Joined
Dec 27, 2000
Messages
1,825
Location
Florence, SC (Timmonsville SC)
Corvette
71 War Bonnet Yellow VERT 71 BH Blue CPE (SOLD)
Chevy 400 small block mount bosses on block are in same position as Chevy 350 bosses ... simply use the same configuration motor mounts as in vette now. If it's a Pontiac 400 I wouldn't expect the same. Get the sbc 400, take your time, then enjoy! BTW, a 2-bolt main 400 (once fitted with aftermarket 4-bolt main caps) is stronger than a factory 4-bolt main 400. G'luck!
JACK:gap
 
R

rpounds

Guest
Thank you. You have confirmed my thoughts.

I have heard that the 400 2 bolt main with studs and converted to 4 bolt with splayed caps are the way to go.

Thanks for the info.

Ron
 
D

Dave L.

Guest
You will also need a 400 harmonic balancer and flywheel as the small block 400's are externally balanced.
 
R

rpounds

Guest
Burglar,

Thanks. That much I was aware of. Also, the 400 has the center two cylinders on each bank 'siamesed' which means that I have to use heads that have been drilled for steam holes.

Here's a question about the Harmonic Balancer . . . '75 Vettes use a small diameter damper in order to clear the front frame cross member. Do you know what the stock diameter damper is on a 400 small block and will it clear the cross member?

Thanks again,

Ron
 
D

Dave L.

Guest
GM part# 6272225. 8 inch. don't know the answer to your clearance question.

Dave
 
Joined
Jan 1, 2002
Messages
7,246
Location
Washington, Michigan
Corvette
'67 Marina Blue Convertible
You shouldn't have a clearance problem - Vettes back to '63 used the 8" balancer on SHP small-block engines, and all frames from '65 up have clearance at the front crossmember for the big-block balancer, which is located further forward than the small-block balancer.
 
R

rpounds

Guest
Thanks guys. This is all very good information. I live in Southern California and the engine is in Oregon. It belongs to the father of a friend of mine. I can have it for nothing more than the shipping costs. I have a few mixed feelings I guess about the swap, but the engine that's in the car is not original anyway. So I figure I can pick up some low end by rebuilding the 400 and sticking it in there in place of the current 350.

Thanks again for this information . . . now I have to go make that phone call . . .

Ron
 

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