May be a stupid question but have the 350 engine blocks changed over the years? By this i mean have they gotten any larger or smaller in overall size from an 1985 350 to a 1990 350? Or were the only things that changed the heads and the fuel system? I'm asking this because I'm curious to know if a 1985 350cid is the same in overall size as a 1990 350cid and if there is the same "leg room" for headers between the two. I don't know if these questions make any sense so please let me know if they don't and maybe i can clerify..

Thanks

 

Externally, the SBC block has had the same external dimensions since 1955.

 

But internally... I currently have a 91 305 TPI and want to start building a 350 TPI for my Procharger... I can get a seasoned 350 block from a machine shop that's has been gone over, cleaned, checked, etc... for about $650...

I saw on jegs they had brand new GM blocks for $750... I thought, well, for $100, I can get a new one that starts out @ 350 and hasn't been bored / honed / 100+k miles on it, etc... good choice...

http://www.jegs.com/i/GM+Performance...05123/10002/-1

I know that in 86 or 87, something changed, they went from 2 piece rear main seal to 1, and what else...??

I had thought the above motor was the newer one (I have a 91 TPI and want to keep it like that with upgraded base, runners and ported plenum)... But then I came across this block...

http://www.jegs.com/i/GM+Performance...62516/10002/-1

It's almsot twice as much!

There is also an older 350 with 2 piece main seal, for $700

http://www.jegs.com/i/GM+Performance...66034/10002/-1

I'm just curious... I need the more expensive one to keep my TPI, since I have a 91, would you guys get the $1200 block or get a "seasoned" freshly machined used one for half that?

Raf

 

The 350 blocks have changed over the years in the following ways:

Original 350 - 2-piece rear main seal, dipstick on driver's side, flat tappet cam.

1980 - dipstick moved to passenger side (affected the block and oil pan).

1986 - one-piece rear main seal (affected the block, crank, & oil pan as well as the seal itself).

1987 - roller lifters introduced. Affected the block, cam, timing set.

1992 - LT1 with reverse coolant flow introduced (Vettes - 1993 for f-bodies). This is a Gen II block, and shouldn't be considered for anything but a Gen II build.

1997 - LS1 introduced (Vettes - 1998 for f-bodies). This is a Gen III engine, completely different from the traditional SBC. It's actually 346 cubic inches, but is called a 5.7 liter, just like the 350 SBC.

There are a bunch of other changes from 1955 if you want to talk about SBC's in general. But, since the question was about 350's, we'll let it go at that.

 

There are even more internal differences in the Gen 1 blocks. You were asking about external differences to know if headers would still fit etc. Since so many parts are interchangeable between those gen 1 years, external parts all fit in the same locations. You could have an old 283, 1970's 350 or late 80's 350 under the hood and the same headers will fit on all of them in the same location. The only issue may be the location of the dipstick.

The "new block" from Jegs or any other block supplier will still need to be bored and honed. New blocks are sold with the cylinders undersized so the machine shop can bore and finish hone the cylinders to fit the pistons used. Cast, hypereutectic and forged pistons need different tolerances. Any reputable machine shop won't bore a block without having the pistons. They also need to know the type of rings that will be used to know what type of finish to put on the cylinder walls with the hone.

 

It's good to know so much information about the engine itself. I was more concerned with the externalities of the engine, not so much the internal components and changes that have been made throughout the years. The reason I was asking is becuase the engine I have in the car is five years older than the car itself and the headers that are on there have been giving me problems (the one on the passenger side rubs the frame). If the external dimensions of the 350 changed between the years I was thinking that this could be the problem, but now i'm thinking that the guy who did this horrible job of an engine swap just didn't know jack about what he was doing. I think he put headers on there that were cheap and aren't a good fit for the car. Or I have something going on with the way the engine is mounted

 

Sagging original rubber engine mounts often cause problems.

So do cheap headers.