SoCal Jet Boats

Tech Talk => Engine Mechanical / Electrical => Topic started by: beerjet on December 02, 2008, 11:35:58 PM

Title: Mark IV vs Gen 6
Post by: beerjet on December 02, 2008, 11:35:58 PM

What are the diffrences ? No Mechanical fuel pump , bigger bore , machined for roller cam , 6 bolt chain cover vs 10 bolt .

Are the oil pan rails the same ? Prices on alot of these bolt on parts seem to be about the same price yet alot of people talk about how worthless the Gen 5 was thus the birth of the Gen 6 . Am I missing anything else ?

-beerjet-

Title: Re: Mark IV vs Gen 6
Post by: Oldsquirt on December 03, 2008, 12:30:08 AM

Probably the best thing to do to try and make sense of all the differences is to go to a Chevy dealer and pick up a copy of the latest "Performance Parts" catalog. That way you get pictures to go with the descriptions.

The Gen VI 454 has the same bore and stroke as the Mark IV 454.The larger bore is only on the 502.

In general, the Mark IV pans will not work on a "production" Gen VI. This due in the most part to the Gen VI having a one-piece rear main seal which results in a differently shaped rear main cap. Timing cover design is also different, although the early covers will fit by just drilling and tapping a few holes.

Current Gen VI 454 blocks have a fuel pump pad. This was required when the last of the Mark IV 454 blocks were used up and GM still needed a "service replacement block" to take care of all 454 replacement needs. Originally the fuel pump pad was eliminated when the change to fuel injection was made. Saved money on machining and eliminated a potential source of warranty claims for oil leaks from a block-off plate and gasket.

When you start getting into the various levels of "performance" blocks, things get a little more complicated........

Title: Re: Mark IV vs Gen 6
Post by: beerjet on December 03, 2008, 12:42:54 AM

Quote from: Oldsquirt on December 03, 2008, 12:30:08 AM

Probably the best thing to do to try and make sense of all the differences is to go to a Chevy dealer and pick up a copy of the latest "Performance Parts" catalog. That way you get pictures to go with the descriptions.

The Gen VI 454 has the same bore and stroke as the Mark IV 454.The larger bore is only on the 502.

In general, the Mark IV pans will not work on a "production" Gen VI. This due in the most part to the Gen VI having a one-piece rear main seal which results in a differently shaped rear main cap. Timing cover design is also different, although the early covers will fit by just drilling and tapping a few holes.

Current Gen VI 454 blocks have a fuel pump pad. This was required when the last of the Mark IV 454 blocks were used up and GM still needed a "service replacement block" to take care of all 454 replacement needs. Originally the fuel pump pad was eliminated when the change to fuel injection was made. Saved money on machining and eliminated a potential source of warranty claims for oil leaks from a block-off plate and gasket.

When you start getting into the various levels of "performance" blocks, things get a little more complicated........

So early Gen 6 wont have a fuel pump boss but the early ones will ???

-beerjet-

Title: Re: Mark IV vs Gen 6
Post by: crewchief22 on December 03, 2008, 05:54:27 AM

There is some information on the GM Performance Parts site. 

http://www.gmperformanceparts.com/Parts/showcase.jsp

If GM closes maybe we can get some good "close out" pricing  ;D      (j/k)

Title: Re: Mark IV vs Gen 6
Post by: Oldsquirt on December 03, 2008, 10:55:41 AM

Quote from: beerjet on December 03, 2008, 12:42:54 AM

So early Gen 6 wont have a fuel pump boss but the early ones will ???

-beerjet-

To the best of my knowledge, only the "service replacement" Gen VI blocks are machined for a fuel pump. They were available at least as early as 1999 for the 427/454 according to my GMPP catalogs.
This does not mean that any of the "production" engines installed on the assembly line ever had that machined fuel pump pad, nor does it mean that they didn't. A GM parts guy could more accurately answer that question.

BTW, "service replacement" means the part in question was intended for use in the repair industry for original parts that were no longer available(as in the MarkIV block) or where the manufacturer decided to use one part to cover a wider range of original part numbers. As a mechanic, I see this all the time.