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Old 11-15-2010, 11:40 PM
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Default gm block knowledge

heres a thread i wrote over 5 yrs ago..i know alot more now and will go threw it on my next insomia battle..but ill post it up now..an will include some lt1 and ls1 stuff later.



gm block knowledge

heres some info to help some of u out that are wondering about gm blocks and the limits..i typed this up over a year ago and there are some changes i could make to it but this will give u a good idea.

alright i'm going to drop some gm block knowledge to u again and hopefuly this one will post..if u got any ? just ask and i will answer them to the best of my knowledge.i run old school small block stuff.but alot of what know can be used with any block.

gm performance parts made an olds rocket block.this block was made for dirt track racing and other forums where u can only use a small block.the rocket block has a raised cam and takes big block cam bearing,also the pan rails are wider then a std small block chevy.the wider rails and raised cam gives u clearence to run a larger stroke cranks.the can take a 3.8 inch stroke crank with no grinding and can take a 4.125 stroke crank with grinding to clear the rods on the block.these block can also be bored to 4.180 safely and come in a 4.000 bore.they where only sold in dry sump set up u would have to machine the block for an wetsump oil system and they use a oil filter not mounted of to the side of the block not on it.they could also be bought in tall deck forum or std and has splayed mains.this block could be bought with 2.65 400 mains or 2.45 350 mains

dart now owns the casting to this block and gm no longer makes them dart makes these blocks and they are the iron eagle blocks now

the rocket block takes specail parts such as pan,timing gear,oil system,cams.

gm performance parts also makes the bowtie blocks witch there is a big block and small block version.u can get these in 2 bolt main and splayed 4 bolt main forum.these blocks are now the strongest blocks that gm makes besides the drce block witch i will talk about next.the bowtie blocks come in many deck height for both bb and sb forum.the small blocks have std cam location and std pan and std small block parts can be used on these blocks.the sb can be bought with 400 mains or 350 mains also.they can be bought in with a 4.00 bore or a 4.125 bore..the 4.00 bore can go to 4.125 max bore white the 4.125 bore can go to 4.180.the bowtie bb takes the same parts as a std big block,u can get these blocks with std deck height or tall deck height.they come in diff bore sizes as well and take std big block main stuff and can be bought in 2 bolt or 4 bolt forum.

the sb2.2 bowtie block.is un like a reg bowtie block,these come with 58mm cam bearings,2.30 283 mains,and .875 big block lifter bores and come in a 4.115 bore

the olds drce block was designed for the nhra.this block takes a specail crankshaft,oil pan,heads.non of the std big block stuff will work on these blocks beside rods and some other stuff.they come with a 4.500 bore vs the std 4.250 bore as a reg big block.


gm made all these small blocks back in the day 283,302,305,307,327,350 and 400

if u got a 283,305 or 307 block toss it.its trash has a 3.875 bore.they dont make good power when built

62-67 327 blocks had 283 main sizes.they took cranks with a 2.30 main vs the std 2.45 main on small block.also they had 2.00 rod mains vs std 2.10 mains.these blocks can take power but not as much as the block i will talk about in a bit.

u can take a early style 327 block and drop a 283 crank in it to make a 302,when doing this u have to becareful because gm 283 cranks had diff counter weights on the crank so some cranks will clear but other 283 cranks the rod will hit the block.

the std bore for all the 302,307,327 and 350 is a 4.00 bore the 400 block come with a 4.125 bore std.and the std mains size on a 4.00 block is 2.45 vs a 400 witch is a 2.65 main size.earley 327 are a 2.30

when building a 4.00 bore block up the best blocks to be used are a 68-74 block.some of these blocks came with an 010 and 020 marking under the timeing cover this standed for 10% nickel and 20% tin.if u got a block with both of them stamped on the block the and its a 4 bolt main u got the strongest std block out there.the just 010 block is stronger then the just 020 block.now u can get these blocks as a 2 bolt main or 4 bolt.i prefor to get a 2 bolt main and convert it into a splayed 4 bolt main and fill it to the freeze plugs with block filler.when this is done and u use a 010 block the can be ran up around 900hp with out failer.but a std 4 bolt main block can go to around 750hp.with the right block prep.also u got to becareful that u dont get a scaluped block this is when gm tried saveing some cash and around the mains they are indented..u dont want one of these block in an all out race setup there good to 650hp or around so.these block can go to a 4.060 bore safely


when building a 4.125 bore or 400 block.these blocks came in 2 bolt and 4 bolt main setup just like above.the 010 an 020 thing goes for these 2 and the scaluped mains also.these block have weaker main webbings so when fully built with splayed main caps and filled i wont run them past 800hp with these blocks.they also got nickel added to the blocks the 509 and 511 have the most.these numbers are the block numbers.so the best one to use would be a 509,010,020 block converted to splayed 4 bolt mains.your probley wondering what a splayed main is.seeing how i said it so much now.this is when the outter 2 bolts go into the block at an angle instead of just up and down.also these blocks can be bores to a 4.165 bore safely after that u may hit the water jacket.

now remember when using these blocks in n/a,n2o,blower or turbo they all put diff amount of stress on the blocks..all the hp levels i said are in n/a forum

i know theres now lsx stuff sorry about that..i dont know enough about them to do a tech thing for the blocks.

info about the 8.20 deck height and 8.700 deck height blocks

GM/Performance Parts introduced a "short deck" smallblock block (PN-24502650) in 1997 for racers wanting to build a short stroke motor. The block deck height is 8.200". The siamesed cylinder bores are 3.894" and this CNC prepared block can be bored to 4.190". It has splayed steel main caps on #2-4 and the crank journal diameters are 2.300" to fit the early style small journal cranks. It uses the two piece rear main seals, but can use the late model one-piece oil pan gasket. A big block style water pump is used. The cam bore has been raised .391" compared to a production smallblock and the cam journals are 2.25" in diameter to fit roller cam bearings. The "short deck" Bowtie smallblock uses the Oldsmobile Aurora bellhousing pattern. Gen.I style heads will bolt to the block, but you'll need an aftermarket custom intake.

GM/Performance Parts has introduced a "medium deck" smallblock bare block (PN-12480050) in the 2001 model year for racers wanting to build a NHRA Pro Stock Truck smallblock motor. The deck height is 8.700" and can be decked to 8.500". Bores are 3.900" and max bore is 4.190". The "medium" deck height block uses the standard Chevy bellhousing pattern and has 2.300" main bearing diameters and uses a 2.25" cam bearing. The crank centerline to cam centerline is 4.953" and GMPPP recommends a Jesel timing belt for this application. The block is delivered without the head bolt holes or the lifter bores drilled.
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Old 11-16-2010, 02:41 PM
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Again Great Write up. its stuck.
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Old 11-16-2010, 05:28 PM
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alright remember i said i would ad to this so heres a very fast up date.

Hp limit for a gen 1 350 block is 1000hp for turbo and 850-900hp for juice..this is fully preped race blocks though..filled with splayed main caps in the center and front caps splayed or changed to 4 bolt.On the turbo motor he started pulling head studs out the block..Mike fratina who ran nmca street race is who made the turbo power..< lil note with all the block work an such done you are at the same price of getting a used bowtie block

Hp limit for a gen 2 sbc turbo is around 1400hp an n2o is around 1k..these are the max but no one has cracked a block yet so they are still climbing really..same as above for block work.filled and splayed caps with the front cap turned to 4 bolt or splayed..this is a must because you will beat the crap out of the front bearings if not.

^biggest crank that can fit in these block is a 4.00 stroke yes you heard me right..you will have to do a short fill to make sure when grinding you do now run into a water jacket when clearancing the block for that size stroke..also you will really want to run a 5.85 rod in a block with 4" or 3.875 stroke to not put the piston pin in the oil ring and to have a better ring stack.

400 sbc blocks are good from 700-900hp also but these are ticking bombs..core shift is a huge problem with these blocks along with the mains..you could get 200 runs at that hp level or 1 run..you are def better off just going bowtie,rocket,dart or merlin at this point..same thing as the above 2 blocks to at strength.
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