Thread: mark iv bore & stroke

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Hey just found and joined this site. Looks like tons of help. I have a mark iv block I am starting to build for a mud bogging blazes. How big can I safely bore and stroke my 2 bolt for max tq. No spray to be used. Hope to make about 650 tq with 600hp. Any help will be appreciated.

Originally Posted by blueblazes

Hey just found and joined this site. Looks like tons of help. I have a mark iv block I am starting to build for a mud bogging blazes. How big can I safely bore and stroke my 2 bolt for max tq. No spray to be used. Hope to make about 650 tq with 600hp. Any help will be appreciated.

Pat McCarthy is the resident big block guru. If he doesn't see this thread, send him a PM.

Hey while your at it throw me some insight while answering his question. What is the gen IV, V, VI and whatever else there are. I assumed the IV was the first series of early big blocks.

Originally Posted by blueblazes

Hey just found and joined this site. Looks like tons of help. I have a mark iv block I am starting to build for a mud bogging blazes. How big can I safely bore and stroke my 2 bolt for max tq. No spray to be used. Hope to make about 650 tq with 600hp. Any help will be appreciated.

You can easily go .060,.090 or more with sonic testing.
You can swing a 4.25 stroke which will give you 489/496 depending on your bore size.

i have gone to 100 over with sonic check back over 20 years ago bad idea .i did a 512 cid 4.320 bore and 4.375 crank thats as far is i would push a stock block i think he tells every one it a 396 .if you are looking for more cid it is better i think to add some stroke and keep it cool on the bore then you have one more bore job to go if some thing goes bad

Originally Posted by erik erikson

You can easily go .060,.090 or more with sonic testing.
You can swing a 4.25 stroke which will give you 489/496 depending on your bore size.

Thanks Erik, I didn't mean to leave you out...

I've run and have bored many to 4.375 but generally limit it to 4.350 so have another size to go to if needed.

my old 100 over is still out there it now close to 4.360 hone out so many time yes back when you could not get cheap steel 4.250 cranks low dollar builds with TRW piston and some went to 125 . i had mine bore to 100 over used the old TRW had diamond sonic check it and had the pistons tapper turned sent down 4 bocks till i felt good with one to bore alot of guys just look at the walls tru the freeze plug holes to see how thick the block was some used a arc welding rod for a go no go i had one sonic check i would of not of bore past 060.i have done my share of big block i reach my fingers thru the water ports on the deck and feel the walls tells you some thing but for a 100+ bore still should have it sonic check less your going to fill it with block rock.i had one customer just did not want to throw out the block was at 4.375 told him no warranty and a set of custom pistons it was cheaper for him to get another block .i just cant see going thru the money for the sonic check to get the cid and have to worry about the walls flexing . if you have a block thats big now and you do not want to find a nother block then get it sonic check and go from there

Thanks for all the great info.I found a dart 572 block w/ eagle forged assembly for a good price. Think I will go with it for max tq. for my mudder. Will I have any problems finding accessories -oil pan,what heads for max tq? I have very little knowledge of bb so much help is needed.

This combo is listed on racingjunk.com. Does anyone know of these folks? It looks like a good deal. I need lots of tq.to move my blazer on 44" tires thru deep mudpits. Will have to use mild cam as I have to pull 16" vac at 1000. Want something durable and doable on med budget. Any ideas?

Originally Posted by blueblazes

Thanks for all the great info.I found a dart 572 block w/ eagle forged assembly for a good price. Think I will go with it for max tq. for my mudder. Will I have any problems finding accessories -oil pan,what heads for max tq? I have very little knowledge of bb so much help is needed.

i have built engine for sand drags trucks and mud pit s .the engine could be a 4.500 bore and 4.500 stroke and would be a tall deck