502 MK IV Block

[88sport240]

Who has one laying around? Short block needing a rebuild???? I want it!!!!

[88sport240]

Nevermind apparently I am a moron and they do not exist....

[speedfreek1]

you may want to post on mwbp I know there are a few bare blocks floating around in there..

[$hooter]

MK4 blocks are 396, 402, 427 & 454


Gen 5 & 6 blocks are 454 and 502

[70ss]

GM produced Mark IV 502's from 89-93 and everyone I have ever seen in a boat was a bowtie. I have a friend with a couple he said he'd sell for the right price as they have been hot tanked, sonic tested, bored .030, decked and aligned. He said somewhere near $1750 each.

[$hooter]

GM produced Mark IV 502's from 89-93 and everyone I have ever seen in a boat was a bowtie. I have a friend with a couple he said he'd sell for the right price as they have been hot tanked, sonic tested, bored .030, decked and aligned. He said somewhere near $1750 each.

Hmmmmmmmmmmmmmmmm...dont recall ever seeing one of those puppies...but whoever has those blocks...they are waaaaaaaaaaaaaaaayyyyyy to high on the price. You can get a brand new Dart or Merlin for the same or slightly cheaper.

[70ss]

HMMM....get a new one for the same money, spend more $ to have it machined only to go out of round when it gets some heat put in it for the first time and have more in it than you thought and lose HP at the same time. What makes a new block worth more money than a freshwater seasoned block with no damage?

I'm sure he'd consider reasonable offers as he's moved on to tall decks.

[$hooter]

The blocks that I get...for less money...are ready to go...light hone and fill the holes. As for going out of round after it gets warm...awwwww...no offense but you have been reading too many I wanna be a motor builder books. Any block after time will go out of round, but not from just getting warm on a new block. The blocks that you stated are .030 bored...so using that logic...since this is a new bore, that means that they will also get out of round after they get warm since there has not been a piston run in the new bore...right??


Dart and Werlin "cook" their blocks after the machining has been done, but a motor should never be bored until you have the pistons that are going into it, then you can size each hole for the piston going into that holeand you should also use a torque plate before you start any bore procedure (this PREVENTS the out of round problem). Thats how you do it to make big HP numbers. Boring a block and then stuffing pistons in it is not the way to do it as you will never get good numbers from a motor that is done that way because the pistons are always slightly different resulting in a tight fit and loose fit pistons in the block.

[70ss]

Minimal offense taken.....new boring has no effect on the metallurgical stabilization of a block that has repeated cycles of natural heating and cooling. FYI...I haven't read any wanna be book other than torque specs and sequences.

The blocks will need a final hone for piston fit and they were done with a torqueplate.

You are right, stuff them in and scuff them up.

Do you suppose my pump gas 383 with iron heads that flow 320 cfm at .550 lift makes any HP?

[$hooter]

Your 383 should make some decent power...how much...no idea. I am not a mouse guy...strickly rat.


I have never had one of my motors have a problem with egg-shaping cylinders using a Dart or Merlin block that was new...either in boats or cars...after a lengthy period of use...yes...but never new. Maybe I am lucky but when I asked one of my friends that same thing this afternoon, he just looked at me and said ...WHAT...where the Hell did that come from?? I asked him if they have ever had a motor brought back or a complaint about it...the answer was no. Who is this guy...the wizard of wizard...David Reher...the guy that owns Reher & Morrison who use to run a Pro Stock Cobalt in NHRA.

[70ss]

620 @ 7400 -

And the person who does my machining has a 427 Mopar that runs upper 8's on 10" tires with no wheelie bars on strictly gas and does cylinder heads for lots of people that put their "Known" names on them.

Anyway - to each their own. If you or anyone else is interested make an offer and I'll pass it along.

[88sport240]

Wow guys....cool argument or maybe just interesting exchange...anyway good info too! I do think that would be to much money for a used block. I was thinking high end for a 502 used would be like $800......maybe I am wrong.

70ss...my buddie has a 350 bowtie now .060 so what is that like 360 cu/in??? Anyway, small blocks can make power. It Dynoed 682hp @ 9000 rpm!!! It is in a 63 chevy II with a 400 fogger on it. Nasty car. Never ran the bottle yet though. I am not sure but I believe it is a high 9 second car.

[88sport240]

OH YEAH...70SS............Where do you get all of that power from the small block. My buddy's is 13:1 and .660 lift.

[70ss]

They are iron Dart Sportsmans that flow enough air to support 9000 rpms but the package is not clearanced to run enough cam to get there. Limiter set at 7600. 11:1 compression. Callies crank, Oliver rods, Crane custom cam, Jesel Rocker and Belt system - you know, way too much in a small block, but is lots of fun to spool up.

If you can find a ready to go Mark IV Bowtie 502 for $800 you should probably grab it quick.

Off to the pond.