Gen 5 vs. 6
 

I want to build a blower motor and I am trying to figure out the EXACT diffrence between a gen 5 and 6 block. Dose any one know. I am not really looking for options, just facts on this one. Thanks

The blocks are similar. Gen VI came factory with a roller cam. The front cover is also different. If you go to a performance cam the factory roller lifters will most likley need replacing anyway. I have heard the threads for the acessories are a different size.

When did the switchfrom gen 5 to gen 6 blocks. wasnt it about 1996 - 1997 ish?

The gen 6 casting is thicker and stronger in general. Gen 5's were from 1994-1995 but I wouldn't be suprised if a few made there way into 1996 boats. The timing cover is a dead givaway.

gen6 has a better oiling system

The Gen VI was often referred to as the 'Gen Fix.' There were numerous oiling problems with the Gen V that stemmed from the re-routing of some of the oil gallery inputs from the Mk IV that they royally screwed up in the Gen V, which came out about 1991/2, the Gen VI came out shortly after (1996) to address these problems.

Cast front timing cover, cast rocker covers, heads deleted the bypass flow cooling ports down the centre, re-shaping of the forward and rear head cooling ports (which is why Gen VI heads aren't compatible with Mk IV). They also added the 1 piece rear main seal which means the Mk IV pans don't fit either. The oil filter pad is different and there are oil gallery output ports adjacent to the oil filter mount and an additional tapped hole for an oil pressure switch or oil temp sender just up from the filter.

The Gen VI didn't come with a mechanical fuel pump provision and you cannot modify it for one without serious work, though why you would want to is beyond me! That having been said, the very first blocks made, some did have a mech pump drive. Mercruiser ran the combo water pump with a provision for the mech fuel pump to be driven from the shaft, though I personally don't think water and fuel go well together.

The Gen VI Vortec heads have D shaped exhaust ports to increase the flow and alleiviate turbulence along the bottom of the port, but as yet, no aftermarket manufacturers make an exhaust which takes advantage of this. The new port design is now reflected on World, AFR, Dart and Merlin heads as well so it must work.

There are other differences, the balancer is different and came stock with timing marked in degress on the balancer, the flywheel was slightly different and again different between the 454 and 502 Gen VI motors. (the 502 balancer and flywheel have cast on counterweights to balance the heavier rotating assembly.)

The front of the block is slightly different by way of the mounts for things line up, but the Gen VI uses a slightly larger bolt for mounting brackets. The Mk IV water pump bracket doesn't fit (or does with modification) and neither does the alternator tensioner arm (again, does if modified).
All these things I learned the hard way. I now have a whole pile of junk Mk IV brackets and a good set of modified ones on the motor. Trust me, take you time and look to make sure you get Gen VI gear first!

Good Luck! :drink:

My gen VI ZZ502 came with the provision to mount the mechanical fuel pump. I was very suprised.

You are one of the lucky ones then! It's nice to have the option isn't it?

Gen 5 didn't have the fuel pump provision.
Gen 6 did.
Gen 5 didn't have the provision for the z bar ball stud for std. transmissions on cars and trucks, Gen 6 did.

Short story, That is way the Gen V was only made two years.
My advise if you have the option go to the Gen VI or Mark IV.