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The difference between Pre 86 chevy 350 and post 86 350's

55K views 12 replies 10 participants last post by  DoubleVision 
#1 ·
I am in the process of getting my dad's car for free. Its a 85 monte carlo. I want to switch motors from a 4.3 v-6 to a 350. I have multiple pre 86 350 blocks and a 89' 350 with fuel injection. The fuel injeted one is in a van and still works I don't know which motor to start with and find myself short of money. what is the difference between the motors and which one can I get the most bang for the buck:confused:
 
#2 ·
Pre 86 had a two peace rear main seal,perimiter bolt valve covers and the standard intake bolt pattern.
Post 86 had a one peace rear main seal which fits in a big adaprter thingy,which also requires a special oil pan.Centerbolt valve covers.And altered intake bolts in the center.
Another thing is the flexlate bolt pattern is differant from the pre86s and I believe the same might go for the balancer.
I would use a pre 86 block and if ya have several look for one with 010 under the timing cover.Thats spossa mean high nickel.
 
#3 ·
78 got it right, However, keep in mind the 87 and up blocks that came in passenger cars had hydraulic roller cams, the truck line kept the flat tappet cams. the late 80`s blocks were a bit thin on the castings, but they`ll live just fine in a mild street application. I would use the post 86 with the 1 piece rear main seal, as they can go there full service limit with no leaks, the older 2 piece rear seal block usually has a leak within 50,000 miles.
 
#4 ·
damn, deja vu!

I'm in the process of getting my dad's '84 Grand Prix for free, and switching out the 5.0L (305) for a 350.

Personally, I'd go with a pre '86 block. While you have it out I'd replace the gasket set and replace the oil pan gasket/rear main seal/timing cover seal. If you get MRG-5884 from Summit Racing it includes all the oil pan seals.

I choose the pre '86 block because switching in the fuel injected motor could be more costly and harded to do than switching in a carburated motor. I'm on a strict budget, so I choose a standalone (non computer controlled) engine so I don't have to worry about compatibility (just pull the bulb on the engine warning light :) ). That way I can just pull the computer (engine is the only thing it controls).
 
#5 ·
Hello,
I think the 010 on the blocks is part of the casting number on the back of the block also, the last 3 digits. It used to just signify a fully machined main web. Some are 2 bolt some 4 i think its the same casting just machined differently. I don't know about nickel content on these blocks as far as numbers, i have never seen consistency in the same casting numbers (I use an Ames hardness tester).

I have the found the hardest blocks in general, to be out of police, taxi, and 40 series and up trucks. Most of these blocks can be identified by the machinig around the lifter bores. Its hard to explain but you will see the difference if you see one. I wish i knew enough about computers or i would give you a pic.

Thanks
Jeff
 
#7 ·
All the parts on the post 86 blocks interchange, heads, and etc. the only difference is roller cam in passenger cars, slotted center intake bolt pattern which is easily done with a drill to a older intake, reverse rotation water pump which can be interchanged with the older pump, oil dip stick on passengers side which is also no problem, external balanced flywheel / flexplate. you could put older heads on the post 86 block and never know the difference.
 
#12 ·
TBI on a 1979 350 block?

I'm planning to install a 350 in a 91 S-15 Jimmy that currently has a 4.3 with TBI. I have a 1979 350 block. I'd like to put an Edelbrock Performer package on it. The package has a TBI intake, heads, cam and lifters. Can this package be installed on the 1979 block or should I get a 1986 or newer block?
 
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