Both blocks are the very same casting, therefore the 4.0" bore has another 1/16" cylinder wall thickness. I would love to be able to say I have 400 cu in sbc, but for just 23 less cubic inches (377) I would gain the extra wall thickness. This would provide more wall thickness for boring when something breaks.

On the other hand with a forged Scat crankshaft (4-350-3750-6000) and their premium pro comp rods (2-ICR6000-7/16) with 7/16" ARP rod bolts, I shouldn't have anything to worry about if max RPM is 6400 and mean piston speed is 4000 fpm.

Again this is going in a T-Bucket and only weighing 1800 lbs, I should have enough power either way I go.

Any thoughts about which block???


Rick Miller

http://www.summitracing.com/parts/DRT-3 ... toview=sku


read thru this thread and its sub-links
viewtopic.php?f=51&t=47

http://www.dartheads.com/products/aitdo ... ile_id/52/

unless your going with a turbo and a great deal of boost, or a hell of a load of nitrous, ID sure go with a 4.125" bore block as theres no reason to go with the smaller bore , there casting the blocks so the minimum wall Cylinder Wall Thickness, min. ................................…… .230" @ 4.165" bore

DART Iron Small Block - Technical Notes
Deck Height ..................................................... 9.025"
Bore ..................................................... 4.00" or 4.125" unfinished
Main Bearing Size ..................................................... 350 (2.45")
Weight ..................................................... 175 lbs
Largest Recommended Bore ................................…… 4.165"
Camshaft Bearing Diameter ................................…… SBC - 2.00"
Camshaft Position ..........................................……… Standard SBC
Cylinder Wall Thickness, min. ................................…… .230" @ 4.165" bore
Deck Thickness, min ..........................................……… .675"
Torque Specs - Main Caps 1 - 5 7/16" bolts 65 ft lbs
2,3,4 outers 3/8" bolts 35 ft lbs

Dart SBC Iron Block
Part# 31161111 31161211
Material: Superior iron alloy
Bore: 4.00” or 4.125” unfinished
Bore & stroke: 4.165” x 3.750” max recommended
Cam bearing bore ID: SBC - 2.00”
Cam bearings: Special coated, grooved, w/3 oil holes
Cam Bearing O.S. + .010”, +.020”, +.030”
Cam bearing press: .002”
Cam journal OD: Standard SBC - 1.869”
Cam Plug: 2.106” dia. cup plug
Cylinder Wall Thickness: .230” min @ 4.165” bore
Deck Height: 9.025”
Deck Thickness: .675” min.
Fuel Pump: Mechanical pump provision
Fuel Pump Pushrod: Standard Length
Freeze Plugs: Press in cup plugs
Lifter Bores: SBC .8427” - .8437”
Lifters: Designed for factory 87-95 Hyd rollers, must use +.300 tall lifters if using
link bar lifters
Main bearing size: 2.450”
Main bearing bore: 2.6405”-2.6415”
Main Cap Bolts: #1-#5 7/16
#2, #3, #4 3/8” splayed
Main cap press: .005”
Main caps: Ductile Iron -
Main cap register: Deep stepped register on each side (no need for dowels)
Oil system: Wet Sump - Main Priority Oiling
Oil Pump shaft: 350 main = Stock shaft (.481” OD)
Oil Filter: Standard SBC filter, uses 2 bolt filter adapter
Oil Pan: Standard 1980-1985 SBC oil pan
Rear Main Seal 350 main - std seal
Serial No. Left front & main caps
Starter: Standard SBC
Stud holes, Head: Blind holes
Timing chain/gears Standard SBC components, will also accommodate 87-95 thrust plate
Timing Cover: Can use stock cover
Torque Specs: #1-#5 7/16” bolts - 65 ft lbs
#2,#3,#4 3/8” bolts - 35 ft lbs
Weight: 175 lbs @ 4.00” bore


http://www.carcraft.com/techarticles/cc ... index.html


Dart Machinery's Little M Sportsman Chevy Small-Block - Quick Tech
From the October, 2010 issue of Car Craft
By John McGann
Photography by John McGann

Ccrp 1010 Dart Machinerys Little M Sportman Chevy Small Block Engine
Dart's Little M Sportsman
Dart Machinery was founded in a backyard garage nearly 30 years ago by Richard Maskin. The company makes aftermarket engine blocks at a variety of price points for small and big Chevrolets and Fords. We have access to one of its Little M Sportsman Chevy small-blocks and thought we'd take the opportunity to compare it side-by-side with a production Chevy small-block at JMS Racing Engines in El Monte, California.

A. Siamesed Bores
That's JMS' block machinist Sal Alcaraz shining his flashlight down the water jacket of the production Chevy block. Look into the core plug opening-see the sliver of light between the cylinders? This block is non-Siamese: The barrels of the cylinders do not touch. All production small-blocks except for the relatively rare 400s are cast this way. The Dart block has Siamese cylinders-they touch each other in a row at the 3 o'clock and 9 o'clock positions. This makes the cylinders very rigid, which results in a better ring seal.

B. Deck Thickness
The Dart block has a deck thickness of 0.675 inch. With a production block, you'd be lucky to find one with a 0.400-inch-thick deck. You get a better head gasket seal, perfect for high-compression or power-adder applications. All the cylinder head bolts in the Dart block are blind-they don't open into the water jackets like a production block. This prevents any chance of coolant from seeping up the head bolts and eventually creeping into the cylinders.

C. Cylinders
You can get a Dart Little M Sportsman block in either 4.00- (350) or 4.125-inch (400) bore sizes. However, you can bore the Dart blocks out to a maximum 4.185 inches. That's bigger than you could ever dare go with a production block. The deck height is 9.025 inches-the same as a production, as are nearly all the other dimensions of this Little M. You have a choice of either standard 350 main bearing journal sizes, which are 2.450 inches, or the slightly bigger journals of a 400 at 2.650 inches. The rear main seal for all Little M Sportsman blocks is the early two-piece design.

D. Crankcase Clearance
A production 400 engine came with a 3.75-inch stroke, and that crankshaft is what guys use to build 383s out of a 350 block. The maximum stroke Dart recommends is 3.875 inches. Combine that with a maximum 4.185-inch bore, and you will have a 426.4ci engine. Better call it a 427, though.

E. Main Caps
Most small-blocks came with two-bolt main caps from the factory. You don't need a lot of clamping force in a 175hp Malibu engine. The Little M also has four-bolt main caps, but notice that the outer bolts are situated at an angle rather than straight like the production caps. This splayed bolt design is superior because it spreads the clamp load over a much wider surface than the straight cap design. The caps themselves are made with ductile iron rather than the cast-iron alloy used at the factory. It is stronger and less resistant to fatigue and cracking than the factory material.

Oiling
One of the biggest improvements over a stock block is Dart's oiling system. Dart's block deviates from the production block by sending filtered oil from the pump to the main bearings first. After building pressure at the mains, oil goes to the cam bearings and lifters, then on to the cylinder heads through the push-rods. This priority main oiling system differs from a production block that sends oil to the cam bearings first before the main bearings. Priority main oiling is better because the crankshaft is subjected to much greater forces than a camshaft. There are additional bosses cast into the lifter valley that can be drilled for a dry-sump scavenging.

Which One to Buy?
Dart's tech guys told us sales are split right down the middle for 4.00- or 4.185-inch blocks. Since the price for either bore size is the same, we wondered why anyone would buy a 4.00-inch-bore block when the 4.125-inch block costs the same. Some racing classes limit bore size to 4.00 inches, some guys have a bad block but good 4-inch internals, and some guys just want a 4.00-inch-bore block to build a 327 or 350 to match the badges on their fenders. Otherwise, buy the 4.125-inch Little M Sportsman and build yourself a big small-block.

Can you elaborate a little more on this. It seems to me that if something breaks and goes thru the cylinder, then it could easily put a very deep gouge in the wall. It seems that you think that any cylinder wall gouge could be easily removed without boring too far. I know anything is possible and you cannot guarantee that nothing bad will happen, I'm just wanting more discussion about why you don't seemed to be concerned.

Thanks!


Rick Miller

a block with a larger bore diam. generally un-shrouds valves and allows the ports to flow slightly better.

every inch of displacement your engine gains tend to potentially add at least 1-1.5 horsepower and 1-1.5 more foot pound of torque to your engines power curve

With a bore size a shade under 4 inches, this Dart block has over 400-thousandths wall thickness on the minor thrust side (arrow) of the bore, and nearly 500-thousandths on the major thrust side.

READ THESE THREADS
viewtopic.php?f=51&t=47

http://www.popularhotrodding.com/tech/0 ... index.html

viewtopic.php?f=51&t=2229

viewtopic.php?f=51&t=2692

viewtopic.php?f=51&t=125

cylinder damage normally falls in three basic category,s

expected bore wear,
which varies with the engines age,and mileage and stress levels,intended use, and the quality of lubrication, a simple minor hone and re ring job and installing the original pistons can usually suffice.bore wear is cosmetic or very minor

here a thick cylinder wall adds rigidity and it helps a good deal and the after market blocks are made from better quality casting metal and thicker so they tend to flex less

minor damage , or distortion under load
which varies with the engines components used,and mileage and stress levels, heat and the quality of lubrication, and frequently can be corrected with a minor bore increase or re-bore, because the bore wear or damage exceeds a .001 depth,bore damage from a busted ring, detonation, or other causes frequently falls in this realm
here a thick cylinder wall adds rigidity and it helps a good deal,your aftermarket blocks thicker walls tend to distort measurably less under bolt clamp loads and the bores tend to stay closer to 100% round and the after market blocks are made from better better quality casting metal and thicker so they tend to flex less
a DART block with a 4.165 bore will be thicker and much more rigid than most stock OEM 400 blocks were in the original bore size



major damage
cracked bores, busted cylinder walls etc. usually the block requires re-sleeve work, or its beyond repair, and that is usually the result of a busted valve, piston or rod and it won,t matter a great deal about your original wall thickness, if a rod comes loose at 6000rpm






sleeving the bore,some times its the only way to save a block, but your very unlikely to need this type of work on a well assembled DART or AFTERMARKET BLOCK, all these examples were bored to under .100 thick
short answer is that unless your dealing with a major component failure the thicker aftermarket blocks and better metal tend to flex less and distort less, but if a crank snaps or a rod comes off a crank or a pistons destroyed by hitting a valve or detonation, its not going to matter much in the final resulting damage,(although in some cases, the thicker aftermarket casting will be easier to re-sleeve)

That's exactly what I was looking for, just your thought process for going with the larger bore SHP block. Now I understand the WHY in your suggestion to go with the 4.125" bore.

I guess what Clint Eastwood said, kinda applies here....."How luck do you feel?"

Thanks again!!!


Rick Miller