I just got my hands on a 454 motor,about a mid 90's,has a fuel pump boss,a different type timing cover,one piece rear main seal,peanut port heads(of course),different looking rocker arm nuts.Is it a 5 or 6 Gen??
Im told it's a Gen 6 and can use older style heads?
Are they worth rebuilding for a mild perf.car?
The motor was in a Sprint trk that had gotten hot,and was running at the time of removal about 3 months ago.
Thanks
Rick

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66 300 Deluxe 350/330hp
71 350 malibu (project car)
72 Elcam 402SS
78 Malibu Classic (daily driver)

If it has a roller cam, it is a GEN VI.

Red Label

im running a gen 6.block the timing cover $80.00and oil pan $300.00 both run rubber seals, cam is different all by itself, will not fit in mark5 or4 stuff but mark 4s 5s heads will fit on 6 stuff http://www.chevelles.com/forum/smile.gif

this has a flat tappit cam,but has the area's in the block for a roller set up!
It was a replacement engine put in about 96.

Will the block # help ID if it's a V or VI?
Rick

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66 300 Deluxe 350/330hp
71 350 malibu (project car)
72 Elcam 402SS
78 Malibu Classic (daily driver)

I just went out and got the # off the block,#12550313.I noticed it say's Gen V on the push rod guild plates,soooo I guess I answered my own ??.I was under the impression it was a VI and could use the old style heads.Bummer http://www.chevelles.com/forum/frown.gif
Rick

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66 300 Deluxe 350/330hp
71 350 malibu (project car)
72 Elcam 402SS
78 Malibu Classic (daily driver)

The GEN 6 with roller cam was first listed in the Chevy HP parts book in mid 97. One note that may help is GEN 5 front covers are sheetmetal and GEN 6 are plastic, 6 bolt covers.

Red Label

What's the pro's and con's of the Gen V motors?
Will the Gen IV heads fit on the V?
Any difference in the cams?
Are they worth spending $$ on?
Rick

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66 300 Deluxe 350/330hp
71 350 malibu (project car)
72 Elcam 402SS
78 Malibu Classic (daily driver)

Let me put it this way. By all accounts the Gen 6 was actually known as the "Mark Fix" on the inside because the Gen 5 was such a disaster.

So much for modern engineering.

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Once you have made up your mind, facts are but a mere annoyance.

the casting # is for a Gen 5 crate motor or a Gen 6 4.25" bare block 1991 and up according to the chart on MotTec's web site. hope this help's, it mean's it could be a Gen 5 or 6..hehehehehe http://www.chevelles.com/forum/smile.gif

The fuel pump boss is a good sign since production installed Mk V had no boss. Supposedly some service replacement motors "bowtie" versions were modified to accept mark 4 heads and mechanical fuel pumps. What is the casting date code??

The mark 5 is actually a pretty tough motor with 4 bolt mains improved oil pan etc. The GMPP aluminum oval port heads and Edelbrock heads both will fit a mark 5 block when using a mark 5 head gasket. Any production head 65-90 will not fit due to differences in the cooling passages.

The gen VI has better interchangability but uses a unique cam. Any truck mark 5 or 6 oil pan will not fit a Chevelle GMPP or Moroso ? sells the right pan, dont know the part#

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Frank W
Forgotten Chevelles Rule
74 Laguna S-3 454 soon, 350 sooner 3.42 Posi
Homepagehttp://www.chevellepages.com/folingo
Club Page clubs.hemmings.com/bearingburners (http://clubs.hemmings.com/bearingburners)

[This message has been edited by 73Malibu (edited 01-29-2001).]

If the engine has a flat tappet cam AND bosses in the lifter valley for the roller lifter retainer, then it is a very late production Gen V engine built with a Gen VI block. We did that for about 6 months, before putting roller cams in everything and calling them Gen VI. What you have is a Gen VI block. It should have 6 bolt holes in the timing cover, roller lifter retainer bosses in the valley and a flat tappet cam. Confused....good that must have been our intent.

Hope this helps.

So Gary that means that motor will accept older mark IV heads since it is a Mark VI block ?? We love this stuff, factory special block nobody knows about it, makes 1000 hp http://www.chevelles.com/forum/biggrin.gif

I am looking at a 454 block with an Dec 90 date code, which would mean 91 model year or first year of Mark V production. I was able to determine the engine had a fuel pump boss and two piece rear seal, so apparently another changeover mutant..

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Frank W
Forgotten Chevelles Rule
74 Laguna S-3 454 soon, 350 sooner 3.42 Posi
Homepagehttp://www.chevellepages.com/folingo
Club Page clubs.hemmings.com/bearingburners (http://clubs.hemmings.com/bearingburners)

So,if this a Gen VI block,how is the cam different?
It has a metal timing cover with 6 bolts.
Being a GenVI means that I should be able to use older IV heads but will need a special cam??? http://www.chevelles.com/forum/confused.gif
Are the cams for these VI's alot more $$ than any other cam for a BB??
Rick

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66 300 Deluxe 350/330hp
71 350 malibu (project car)
72 Elcam 402SS
78 Malibu Classic (daily driver)

The Gen VI block you have will accept all Gen VI parts and will accept Mark IV heads.

Thanks Gary, http://www.chevelles.com/forum/biggrin.gif
So when I go looking for a cam for this beast I need to tell them it's a VI block?
Looking in Comps catalog they only show rollers for it.IS that all Im going to be able to use in?The one in it is a flat tappet type BUT was that only from "the General"??

As a rule,what goes bad with these motors when they are run HOT?Do the heads crack easily like the SB's? Excessive wear to the cylinders,pistons,etc.?

Sorry for so many ??'s Just don't need to throw good $$ away if possible. http://www.chevelles.com/forum/biggrin.gif

Rick

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66 300 Deluxe 350/330hp
71 350 malibu (project car)
72 Elcam 402SS
78 Malibu Classic (daily driver)

I would put a roller cam in it, but you can use an earlier flat tappet if you want. Flat tappet would need to be Gen V style cam.

Run hot, check the deck for warpage and check the cylinder walls for out-of-round. Check the heads for warpage and valve guide wear.