Gary,
I have opportunity to purchase an earlier model bowtie block. This one does not have splayed mains, but does have blind head bolt holes. It's new, never used or machined and I can get it for close to the same price as a new 502 block. Which is better and why? Is there any difference in the metallurgy of the bowtie vs 502, cylinder and deck thickness, etc.? Thanks in advance for all your help.

TTT

Not knowing specifically which Bowtie block we're talking about, I'm guessing that we're talking about a Mark IV Bowtie with 2 piece rear main seal. If so, it's a very good block. There have been some improvements over the years, one piece main seal, priority main oiling, bosses in the valley for roller lifter retainer. I think your decision on which block to use has to be predicated on your end goal. If you're building a street engine, or race engine up to 1500 horsepower, I'd go with the Gen 6 502. Over 1500 hp, I'd look at a Gen 6 Bowtie. If we're talking an 800 hp street engine any would do. The Mark IV Bowtie, if it is a 454 block, would be a good one to buy and resell to someone who wants to build a 427 because it will accept the 396/427 crank. Those blocks are getting a little hard to come by.
Metallurgy is the same, the Bowties have more bore range, and a thicker deck.

Bowtie block has higher nickel content and is "CNC". It also has a reinforced deck and no water passages between adjacet cyl. Hope this helps. In a nut shell a bowtie block can handle more HP!!! :D

All cast iron big block blocks are machined on the same equipement, all are CNC today. All are honed at the same facility. This occurred when they went out of regular production for trucks a few years ago.The nickel content is added for machinability, I believe they are the same today.They are all poured at the same facility as well.

This one has straight main bolts/studs, rough bore to 4.49xx and the head bolt holes are blind. I had an earlier version that was a lot like this except that the head bolt holes went into water. This one should end up in the neighborhood of 925 - 950hp when built, so this block should do nicely. I'll be using a 2-piece rear main crank, so it will be a drop-in. I have one of the late model CNC blocks as well and am tempted to frame it and mount it on the wall - it's some kinda nice, much better finish look than Dart or Merlin. Thanks for your help!

AFAIK, all early tall and short deck Mk IV Bow Tie blocks came with semi finished 4.25 bores. Even the earlier Mk V Bow Ties had semi finished 4.25 bores, but later Mk V Bow Ties were available CNC machined.

Regarless, as you mentioned: blind bolt holes, good for up to 4.560 bore, 4.25 stroke. The cylinder walls are much thicker than a standard production Mk V or VI block, with thicker decks and reinforced main bearing bolt bosses.

John

I read the specs on the www.sallee-chevrolet.com (http://www.sallee-chevrolet.com) website and they say the gen 6 502(NOT BOWTIE) block is only safe for 700hp and can only be bored .030 over (4.50).

Jeff, that is the official answer. The reality is something very different.We've used the Gen 6 502 blocks at well over 1000 hp.

Gary

Gary,
GMPP catalog PP no. 9, 1997 version, listed a Bow Tie block #12370833, which is a MKIV short deck, 2 pc. rear seal, with a bore range to 4.560.

This block was also listed in catalog no. 11 (1999), but is not listed in catalog no. 15 (2003).

My contacts at GMPP and GM racing told me that this block has not been produced (as of last Spring), but that it would be available later this year. Can you tell me if this block is available yet? I was hoping to stay with the 2 piece seal. Thanks.

PN 25534362 Gen 6 standard deck Bowtie with two piece rear main. Replaces the 12370833. Also available as PN 25534363 with one piece rear main. Both have roller cam provisions, priority main oiling, 16 degree splayed caps, mechanical fuel pump boss, and as delivered bore of 4.494.4.60 bore range, 4.50 stroke clearance and no jacket between the bores.

Gary,

Please send me an e-mail at home and price one of the PN 25534362 blocks when you get a chance.

And does it have the Z-bar bosses like the Mark IV blocks??

pdq67

pdq,

The www.gmpartsdirect.com (http://www.gmpartsdirect.com) price is $1785 and shows the list price @ $2550.

Gary,

Thanks for the clarification. Is it only able to go .030 over bore?