Big Block Chevy's

[gcarter]

What is the difference between a Mark IV and Gen V 454 blocks????:confused:

[Cuda]

The only I can remember is the Mark V doesn't have a boss for a fuel pump I think. I had just seen a post about the different generations on Oso, and apparently nobody knows.

[BUIZILLA]

my 454 HO is a Gen VI and HAS a fuel pump provision, there IS a Gen V without fuel pump provision. There is a Gen VI that has a fuel pump provision, and one piece rear seal, block part #12550307, thats what mine is. The pic in the GMPP book for my engine is wrong, it shows a non fuel pump pic, but in reality it DOES have a fuel pump mount setup and is a one piece rear seal.

[gcarter]

So could I assume a Mark IV has a two piece seal???
I want to be an informed consumer!! :wink:

[gcarter]

Based on what Jim said above, should I just assume any configuration is possible?

[BUIZILLA]

Based on what Jim said above, should I just assume any configuration is possible?

I wouldn't assume that at all..

what EXACTLY is your question, and what EXACTLY are you trying to determine here??

[ITTLFLI]

Mark IV (not gen...why, I'm not sure) have a 2 peice rear seal. Now...there are adaptors that one could use to run a 1 pc crank in 2 pc MarkIV motor :bonk:

[handfulz28]

I hear a lot of times that for whatever reason, accessories don't always transfer between the different blocks. Maybe the mounting bolt holes in block/heads are different.
But the biggest difference is the fuel pump provision. For whatever reason, the short-lived Gen V blocks use that funky raw water pump-mounted fuel pump.
Somewhere in there they also changed cooling passages. I think it goes that you can use Mark IV heads on newer blocks, but not the other way around.
Then I think Gen VI they started using roller cams so there's a bunch of changes to the front cover, etc.

[oldandtired]

If you are talking about assembled and running engines, the only difference that matters is the fuel pump. If you are talking about building an engine, then there are differences as mentioned in other posts.

Rene

[RedDog]

The attached is extracted from Dennis Moore's BBC Marine Performance book.

[BigGrizzly]

I have a question,. Moore refers to a 454 with two bolt mains. I have never seen a 454 with 2 bolt mains and I don't know anyone that has seen one. I someone has actually seen one please let me know.

[MOP]

Some of the older BB 396's + 427's were 2 bolt, link below to a torque chart.

http://www.boxwrench.net/specs/chevy_bb.htm

[ITTLFLI]

My father has some

Look here also. They came in some trucks and motorhomes.

http://www.mortec.com/bbc.htm

[Rodger]

BigGrizzly
My original 454/330 HP in the 78 F22 is a 2 bolt main. Was your original 454 in the Crit a 370 HP since it is a four bolt main? I re-used the original block when I built the turbo engine but I converted it to 4 bolt mains. I have also seen other 2 bolt 454's at swap meets.
Now you know of one person who has seen a 2 bolt main 454.

[BigGrizzly]

My original 1981 Criterion engine I still have and it is a Merc 330 with 4 bolt mains and flat tappits.

[Rodger]

Grizz,
I guess something changed in the 454's during the three years between yours and mine... or possibly they slipped me a "mickey". I think mine is the norm back in it's era though. A couple of fellows that build marine engines were not at all surprized by the 2 bolt mains in the 70's. I know though that 370 HP and more had 4 bolt blocks.

[Pismo]

So changes include water passages, oil passages, one piece rear main seal, timing cover bolts, fuel pump, roller setup. Great book, I wish I could find one to buy.

[BigGrizzly]

I just have never seen one. Hear they exist. Even the chart shows some generations with both. I gave seen the 427 and 396 2 bolt main just never the others.