big m block stroke
 

since you guys are talking blocks whats the biggest stroke crank you can safely put in these blocks? i forgot to mention i was looking at the 9.80 deck height blocks i dont have enoughroom for the tall decks. thanks

Excaliber,

With a Merlin II shortdeck (9.80), probably the safest is to go with a 4.25" stroke. I was thinking of going to a 4.50" stroke crank to make it a 572" engine, but I was told that it would work BUT the piston skirts would wear exsesively because of the shorter rods. It is too severe of a rod angle. I have 540's now and that's the way they will stay. If I wanted bigger cubes I would be better off starting from scratch with a tall deck block(s) and using longer rods. My .02

BTW, I don't think Merlin makes a short deck BIG M block. :(

I concur with Kaama on 4.25 for durability. Big M Block would be made by DART I believe. :)

I love this copy paste stuff!! :D :D
Material: Superior Iron Alloy
Block Height: 9.800" & 10.200"
Bore: 4.250" or 4.500" unfinished
Bore & Stroke: 4.625" x 4.750" max recommended
Main Bearing Size: Std. BBC
Main Caps: All 4-Bolt Steel or Ductile Iron
Weight: 240lb.
Largest Recommended Bore: 4.625"
Camshaft Bearing Diameter: Std. BBC
Camshaft Position: Std. BBC
Cam Drive: Std Timing chain, gear drive, or belt drive
Cylinder Wall Thickness (min): .300" @ 4.625" Bore
Deck Thickness (min): Adequate for all apps
Torque Specs/Main Caps: 1 - 5 1/2" bolts/2 - 4 1/2" splayed
Cubic Inch: 632" max recommended
Fuel Pump: Mechanical Fuel Pump provision
Freeze Plugs: Press-in cup plugs
Oil Filter: Std. oil filter location
Rear Main Seal: Std. 2-piece seal


note :Kaama speaks with knowledge and experince. I only do copy-paste to show the written information.He is more trustable..

;)

I agree with KAAMA, 4.250 is all I would go with a short deck block.

Here is some info on the Dart BIG-M BBC Iron Block,

Part# 31263344 thru 31273454
Material: Superior iron alloy
Bore: 4.250” & 4.500”
Bore & stroke: 4.625” x 4.750” max recommended
Cam bearing bore ID: 2.120”
Cam bearings: Special coated, grooved, w/3 oil holes
Cam Bearing O.S. + .010”, +.020”, +.030”
Cam bearing press: .002”
Camshaft position: Standard
Cam Drive: Std Timing chain, Gear drive or Belt drive
Cam Plug: Standard BBC 2 7/32” (2.218”) dia.
Cubic inch: 632” max recommended
Cylinder Wall Thickness: .300” min @ 4.625” bore
Deck Height: 9.800” & 10.200”
Deck Thickness: Adequate for all applications
Fuel Pump: Mechanical pump provision
Fuel Pump Pushrod: Std BBC
Freeze Plugs: Press in cup plugs
Head Gasket: Fel-Pro# 1037, 1047 or 1067
Inner Head stud: 2 slotted bosses per side
Lifter Bores: BBC .8427” - .8437”
Lifter Galley: Raised .350” for longer lifter bore
Lifter type: Roller - Gen VI (+.300 longer), Solid – Mark IV
Main bearing size: Standard BBC
Main bearing bore: 2.937” – 2.938”
Main caps: Steel Billet or Ductile Iron (sportsman) - 4 bolt, all
Main cap register: Stepped register on each side (No dowels)
Main cap press: .005”
Main cap Bolts: All 1/2”, #2, #3, #4 have splayed outer bolts
Oil system: Wet or Dry Sump - Main Priority Oiling
Oil Galley, main: Stepped , 9/16” - 1/2” - 7/16”
Oil Galley, filter-main: 5/8”
Oil Filter: Stock Oil Filter location
Oil Pan: Standard pan bolt pattern, extra bolt holes provided for strokers
Rear Main Seal: Std 2 pc seal / Fel-Pro# 2918
Rear Main thrust width: 1.622”- 1.624”
Serial Number: On main caps
Starter: Mounts in standard location
Stud holes, Head: Blind holes
Timing chain/gears: Standard
Timing Cover: Stock cover
Torque Specs: All 1/2” bolts - 105 lbs
Weight: 4.250” bore - 265 lb / 4.500” bore - 240 lb / 4.600” bore - 231 lb