Engine Block Cylinder Wall Thickness

Discussion in 'Blocks' started by grumpyvette, Dec 29, 2008.

  1. grumpyvette

    grumpyvette Administrator Staff Member


    before you begin to have a engine block bored more than about .030 over size its a good idea to have the blocks bore walls sonic tested
    , bore walls are rarely if ever uniform in thickness from top to bottom or side to side, or concentric with the bore center line. and the STOCK O.E.M. production sbc block is well known to be fairly weak structually

    its common for one wall in a cylinder to be significantly thinner than the other walls
    this might sound like a unneeded extra expense but if your going to put several hundred dollars in machine work into a block you want to be fairly sure it won,t fail under stress wasting all that time and money, plus any resulting damage that might result.

    boring a BIG BLOCK CHEVY block to more than about .060 over its original intended bore diameter,or sleeving the bore ,some times its the only way to save a block, but in many cases the O.E.M. blocks are so thinly cast that you'll have bore distortion and less than ideal bore, to piston ring sealing due to the cylinder wall thickness and /or less than ideal ring sealing, once the blocks really hot. making swapping to an aftermarket DART , world products or BOWTIE block with the thicker castings and better alloy metal,a better long term option, you cant tell how thick your cylinder walls are without sonic testing them as casting flaws, core shift and years of rust can make any block walls far thinner than you might assume them to be
    let me point out a few facts, boring a cylinder takes 1/2 the bore increase off each side of the cylinder wall, and almost any big block will allow a careful machine shop to physically cut the finished bore size to be .100-.125 oversize , or a SBC .060 over bore,THAT IN NO WAY MEANS the remaining wall thickness thats left will be RIGID enough and STIFF enough to maintain a solid ring seal,or not flex and crack after repeatedly being stressed, at higher rpms and if the bore wall flexes to any significant degree it rapidly results in loss of effective compression rapid ring wear and potentially a cracked or busted cylinder wall.
    yes you can have the block sleeved, but having more than two sleeves per cylinder bank on blocks that are not factory designed to have self supported individual cylinders generally results in a weaker block.
    filling the lower coolant passages up to the level of the lower freeze plugs has a minimal effect on cooling but it reduces the UN-supported length of the cylinder walls making them stiffer.


    bores must be honed with a deck torque plate to simulate the stress of a installed cylinder head stress , the torqued bolts exert on the bore walls, the torque plate induces and duplicates that stress so that the bore walls will be pulled into the same relationship when you hone the walls concentric, rings won,t seal correctly in a non concentric bore, aftermarket blocks with thicker and stiffer castings are less prone to bore distortion
    a bit of reading here might be useful... get out a feeler gauge and look at how thick .060, .090, .120 actually is , and consider how easily a thin section of cylinder wall can flex and crack!
    when G.M. or most manufactures "RATE" a block or any other component at lets say 350 hp what they are saying is that at that level of stress it should last a very long time, they are not suggesting that if its rated at 350hp, that at 360 hp its going to fall apart, only that the expected durability life span is being reduced, generally they build in some "cushion" usually 20%-25% or more because theres always going to be manufacturing tolerances and flaws

    when you have a block magnetically or dye checked for cracks , and sonic tested for bore wall thickness, don,t forget to check lifter bores, and lifter gallery areas, and main cap webs etc. just because its not easy to access does not mean cracks can be ignored











    http://www.hotrod.com/techarticles/engi ... omparison/

    Core shift is a result of a block, cylinder head, or other engine casting shifting in its mold when the molten metal is poured in. When core shift occurs the cylinder bores, lifter bores, main bearing and cam tunnels shift from their blueprinted positions. If the shift is significant, mechanical problems can occur and some cylinder walls may be critically thin. This is especially of concern if the engine is to be used for racing applications.

    The only way to guarantee cylinder wall thickness is to have the block sonic-tested, but this can be difficult when you go to purchase a used engine.

    [​IMG]Core shift example

    On engines with in-block cams, you can always take a look at the cam bearing bore. If it is noticeably offset in its machined boss, you should suspect core shift.
    the block pictured above is NOT A CHEVY, but it gives you some idea of what the block internal coolant passages and cylinder walls look like
    read this
    http://www.project33.com/Categoryarticl ... ory=Engine
    and understand its deck and cylinder wall thickness you need to verify more than core shift, its not the average cylinder wall thickness its both the MINIMUM and WHERE in the bore wall the thin section is that matters as the head bolts distort the bore, far more in some areas than in others.

    (1) yes youll need to have the block under stress with bolts, or studs and a torque plate to duplicate the stress on the bore walls , that a clamped cylinder head induces on the bore walls to get the hone done correctly





    http://www.matweb.com/search/datasheetT ... =PDEVCON05






    http://www.drillspot.com/products/31915 ... num_Liquid



    what does it mean to fill the block?


    http://www.caribbean.basf-cc.com/en/pro ... 85-Ing.pdf

    heres a cross section of a block used strictly for drag racing with about 80% of the coolant passage filled, you can fill a block up to the lower edge of the freeze plugs and add significant support with only a minimal effect on cooling as about 90% of the heats generated in the cylinders upper 2.5" of bore

    Ive also seen guys forget to install a plastic or metal tube in the lower coolant passage to allow the block to drain when they partly fill blocks to add block rigidity on thin cylinder walls, so remember to do that if your filling the block to increase cylinder wall strength up too the lower edge of the freeze plugs as forgetting thats a common new guy mistake
    watch this video, but remember , if you intend to partially fill a block to add cylinder wall rigidity, the block should be filled at least 48 hours prior to any machine work being done on the block, as the fill in the coolant passages will generally expands slightly as it sets and will change the bore dimensions slightly.
    Id also point out that a DART after market blocks significantly thicker and stiffer and made from a stronger alloy than the OEM production block casting

    on most cars used on the street your limited too filling to the bottom of the freeze plugs

    Filling a block is when you use a concrete like substance fill, that you pour into the water jacket of your motor.
    The idea is to strengthen your block from the inside.
    One of the main benefits is to control bore flexing.
    Most people do two different types of fill.
    1. Street fill-you fill up to the bottom of the lower freeze plugs.
    2. Race fill- you fill to the bottom of your water pump holes.
    All fills should be done "Before" you do your machine work.[/color]

    ok, generally you want an absolute minimum cylinder wall thickness, on a stock production block of .180 and .230 or thicker is generally considered to be ideal, anytime your bore reduces the cylinder wall thickness below .200 in my opinion, if you intend to race the engine, you should fill the block to the lower freeze plugs with a block coolant passage filler to reduce the unsupported cylinder walls tendency to flex, which reduces ring seal., and generally the semi-safe limit, with the block filled is at about .200-.180, below that, wall thickness, becomes a potential major problem and the blocks life expectancy, is usually lower,
    Id reject a block as a race engine if the upper cylinder wall thickness is under about .145" as an absolute minimum,and only go below .180 if that thin wall area is supported by block fill now Im sure youll find guys who have raced thinner cylinder wall thickness, but its pushing your luck.
    A great deal of the engines heat is produced in the cylinder heads and upper 2" of the cylinder bore, and very little comparatively in the lower engine so filling the coolant passages up to the lower edge of the freeze plugs has a minimal effect on cooling if you've got a good radiator and water pump ETC.you check this with a sonic tester AFTER FIRST verifying the TESTER accuracy on parts of the engine you can verify with a caliper.

    you certainly don,t want to dump bunches of cash into a block that will likely crack if subjected to the stress of racing!
    IF your a bit under that .180 minimum, you generally strengthen the cylinder wall by filling the coolant passages in the block surrounding the cylinder wall up to the lower edge of the freeze plugs with a block filler, I prefer a slurry of about 85% steel shot of size .180" -.200", and 15%- epoxy block filler , if you use more epoxy the epoxy won,t expand at the same rate as the block when its hot, filling the lower cylinder wall coolant passage up to the lower edge of the freeze plugs has little effect on cooling,because about 90% of the heat is generated in the top 3" of the bores stroke and heads (JUST REMEMBER TO INSERT A DRAIN TUBE SO THE EPOXY DOESN,T BLOCK THE BLOCK COOLANT DRAIN PASSAGE ON EACH SIDE)
    SUMMIT SELLS G.M. BLOCKS you can use to build a 383 for $700 plus shipping , but ID suggest limiting power to about 500 hp with these
    I personally thing anything less than .145 is pushing things even WITH a partially filled coolant passage area, ask
    your self a couple questions, have you got a written quote on the required machine work? have you had the block walls sonic thickness checked, and found out what the bore walls remaining thickness will be after being bored and honed at both the top and bottom of each cylinder wall at every 90 degrees?
    how much money have you already sunk into that block in machining costs, or what it the likely cost of a line hine, bore job , maybe adding splayed man caps and having the decks trued up and how much more cash with getting the stock block prepped correctly cost, will you waste that money , what if the block cracks after you get it assembled and start running it?
    I think almost all of us start out making the same mistake of trying to get the block we already own re-machined to save costs ,not realizing in most cases its wasted effort and cash.
    if you spend roughly $1500 on a much thicker dart block you won,t be nearly as likely to have block failure related problems.
    OR you can spend a bit more and get a far stronger and thicker DART BLOCK casting for about $1550.
    yes $1550 or so is a LOT of money,and I know how difficult coming up with cash is! but this is NOT a cheap hobby and if you put $800-$1200 in an OEM block the fails and trashes the rest of your parts you hardly save any money

    http://www.summitracing.com/search/prod ... e%20Blocks


    (#4 or #2 shot, or BB size preferred) buy the 40lb bag

    http://www.ballisticproducts.com/Steel- ... info/SH04/

    there are several block fill products that are basically high strength mortar or concrete


    http://www.labsafety.com/Magnacrete-Con ... _24531183/

    is popular, for filling blocks up to the lower edge of the freeze plugs

    Ive used a slurry of steel bird shot and liquid EPOXY for my blocks

    http://www.precisionreloading.com/mm5/m ... STEEL_SHOT


    but almost everyone uses moroso concrete/grout mix as its readily available, this generally has very little effect on the cooling as most of the heat is generated in the heads and the first 2" of the upper bore of the cylinders.

    http://moroso.com/catalog/categorydispl ... Code=22008

    BTW you generally fill the coolant area BEFORE the BORE/HONE WORK


    http://raceology.com/2004/11/sonic-test ... y-how.html

    http://www.geinspectiontechnologies.com ... index.html


    http://www.popularhotrodding.com/engine ... index.html


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

    http://books.google.com/books?id=-csSm0 ... q=&f=false


    http://www.racecarmagazine.com/Articles ... .asp?ID=26

    http://raceology.com/2004/11/sonic-test ... y-how.html

    http://www.abqindustrial.net/store/soni ... -c-40.html




    This is where the aftermarket performance engine blocks generally have a huge advantage over the standard production blocks, core shift and casting thickness is generally much better controlled on the better aftermarket performance engine blocks like DART sells as an

    and yeah! at first the $1500-$3000 for a block seems absurd,
    but it comes machined if you order it that way, (EXTRA COST OPTION IN MOST CASES) and its a whole lot stronger,stiffer,thicker and less likely to self destruct under hard use than a factory block., and its NEW not something that's been sitting around rusting and being over heated for 30-40 plus years, like some sbc cores, and the dart block cylinder walls can easily be twice as thick or more than a Chevy block and made from better materials.
    here is where you, or your machine shop can screw things up on ring to bore seal, when you hone the bores,get and use block deck hone plates, during the hone process , keep in kind you want to use the same (STUDS OR BOLTS) the machine shop used and the same torque settings they used when the cylinders were honed with deck plates or the distortion of the bore and ring seal won,t be identical (exactly round)or ideal , aftermarket blocks can and usually do have significantly thicker cylinder walls, the thicker the cylinder wall the less the distortion , that effects ring seal will tend to be,under the load the bolts or studs used to fasten the heads to the block produce which will tend to distort the block


    http://www.adperformance.com/index.php? ... 82_105_309

    http://www.adperformance.com/index.php? ... =69_82_106

    http://www.circletrack.com/techarticles ... index.html




    http://www.e30m3project.com/e30m3perfor ... sonic2.htm
    Last edited by a moderator: Jul 24, 2017
  2. grumpyvette

    grumpyvette Administrator Staff Member

    If your looking for a block to start with you'll generally want to look for a 4 bolt block, as they tend to be slightly stronger than the two bolt blocks,IN MANY CASES BUT NOT ALL,OBVIOUSLY 4 studs or bolts SHOULD provide greater clamping strength than two bolts or studs but the thickness of the block web area varies a great deal, and just having 4 bolts is no guarantee its stronger, unless you add splayed main caps to the two bolt blocks, but ANY production block is significantly weaker than the bowtie and DART BLOCKS available know.Ive long ago lost count of the guys that dumped weeks of work and hundreds ,sometimes THOUSANDS of dollars into converting stock engine blocks to 4 bolt main caps or splayed main caps or had the blocks decked and line honed or bored cylinders, and honed ,or sleeved and then were forced to throw all that expensive machine work in a dumpster when the block cracked under use.
    the stock blocks are designed for about 350-400hp and under 6000rpm, and while we all know guys who have built successful engine combos making a good deal more power the fact is the blocks significantly weaker than a DART AFTERMARKET block thats both a good deal thicker and has a stiffer and stronger alloy in the casting.






    most SMALL BLOCKs can be bored .030-.040, after that they tend to get rather thin in places, BIG BLOCK blocks will go .060 with no problem, some few will big block castings will go 0.100 and but you cant make a blanket statement because there are some blocks with core shift or just not enough material that are too thin to start with. if you are going to sink a lot of money in a block and machine work, and if you plan on making a lot of power you need to have the block sonic checked, and in almost every case if your goal exceeds 550 hp the DART aftermarket block is preferred as its got a much thicker casting,
    IVE HAD EXCELLENT results with standard 4 bolt blocks from the late 1968-72 time frame, we bored them to 4.310 without thinking twice, (.060 over size) IVE built engines that exceeded 650hp, with 4.25" stroker cranks and 13.7:1 compression ratios,that ran on only race gas, but those blocks are now 35-40 years old and who knows what the coolant passages and stress levels have been subjected too, the DART aftermarket and BOWTIE blocks are significantly thicker and stronger castings than any of the standard production car blocks, and machine work is expensive, if you are thinking of exceeding 600-650 hp you'll be better off buying and using a decent aftermarket block as they are significantly stronger and thicker castings , thicker decks, thicker webs thicker cylinder walls, etc, priority oil passages,etc. they are made from a better alloy and less likely to have problems
    http://www.dartheads.com/products/engin ... ig-blocks/

    http://www.adperformance.com/index.php? ... =69_82_106





    http://www.testequipmentdepot.com/reed/ ... 2a058b0ec6


    (this link below suggests a 0.125 cylinder wall thickness as a absolute minimum, on a high performance application, while 0.180, is what most shops suggest, as a safe lower limit on a race engine)
    http://books.google.com/books?id=_i_XVV ... q=&f=false

    well worth reading thru

    have the block sonic tested, if you've got any doubts and have it honed with a deck plate, as a general rule cylinder wall thickness should ideally be a minimum of .200-.250 thick, getting much thinner,due to boring it larger, allows too much distortion for proper ring seal, and yes we all know guys who get away with .180 occasionally, but remember just because something, sometimes doesn,t fail the first few dozen or even the first few hundred times, its used, doesn,t mean its operating correctly, Id suggest getting an aftermarket block if you want a larger bore, and your pushing those limits on a stock production block, simply because the decks and cylinder walls are significantly thicker and the basic casting design is stronger, and if the stock casting fails at high rpms you might loose all your components, machine work, etc, certainly making the up front higher cost of the aftermarket block looking far more reasonable if looked at in that light.

    the stock OEM components are rated by chevy, to with stand 350-400hp and 5700rpm-6000rpm,obviously we all know guys that have pushed their components to exceed those limits, but stress is cumulative, and the harder you push or the more frequently you push past those limits the more likely you are to experience component failures
    look at the rated hp

    http://www.sallee-chevrolet.com/ChevyBa ... 05123.html

    the DART SHP Chevy Small Blocks are significantly stronger castings in the stressed areas and are rated UP TOO 600hp, the little m blocks are even stronger

    http://www.dartheads.com/products/shp-c ... locks.html

    http://www.dartheads.com/products/engin ... locks.html

    it would make very little sense to build an engine thats intended to produce over about 500-550 hp on a STOCK PRODUCTION Chevy block simply because the main caps will walk or the lifter bores will crack or the cylinder walls will begin to flex ETC. at some point, and that point will be noticeably lower in the power curve than an aftermarket block , thats been properly machined, Ive got splayed 4 bolt main caps and use all ARP hardware in my block and Im still reluctant to push it much past those limits, because I see the results far to often in my shop, when guys insist on spinning the nearly stock engines to 7k plus or dropping a 150-200hp worth of nitrous,or use of stock bolts on an engine without the proper mixture and ignition controls and all forged components.


    a reasonably common result of boring the block walls too thin to support the rings, especially without partly filled water jackets on an OEM block bored more than .060 oversize, or if you fail to sonic test the block wall thickness, but keep in mind a rod letting go, a failed rod bolt or a piston destroyed by detonation could result in similar damage

    an example of a sonic test on a stock block bores .060 over bore


    notice several areas, A-E where the block walls less than .100 thick


    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

    theres hundreds of ways to destroy an engine, but a common route is trying to compress solid objects in the combustion chamber,where theres not nearly enough clearance,or having the valve train bind up due to clearance issues or reveing the engine above its valve control limitations.
    failure to keep the pistons from hitting the valves, bending valves, ,over reveing the valve train and having un-controlled valve movement, or having chunks of piston,that detonation can break loose, being compressed against the heads,can result in the cracked cylinders, and bent rods like the pictures below show

    the crank or block can have the correct bearing clearance but still be slightly bent or the block may be warped and result in the bearing wear , keep in mind main bearing caps can crack or be improperly machined, this is FAR less common on DART AFTERMARKET BLOCKS
    I think the 400 SBC 4 bolt blocks have a bad reputation that's probably not fully deserved , the rumor is that the web area of the block is weaker and the outer bolts further weaken the block, but I think its more a case of the extra bolts don,t significantly add to the block rigidity .
    the 350 and 400 SBC OEM production blocks were designed to handle 350-400hp max,and when pushed well past that stress level its just logical that they occasionally fail.
    if a two bolt block fails the normal response seems to be that
    'we should have installed the angled aftermarket main caps'
    if a four bolt block fails the normal response seems to be that
    'we should have installed the angled aftermarket main caps, because the damn four bolt blocks weaker'
    the truth is that by the time your making 500hp neither block with stock main caps keeps the main caps from moving under full loads and adding the splayed main caps while helpful is not a cure, its a band-aid at best, the aftermarket DART block has much thicker castings in the block web area and better and stronger alloys used.

    http://webtools.delmarlearning.com/samp ... _ch139.pdf


    Neither plastigage or a full set of micrometers or other ways of checking crank to bearing clearances will detect a bad align bore or a crankshaft with runout.

    But there are some simple ways to check both.

    http://www.herboldracing.com/2010/02/19 ... ank-runout

    Here are a set of main bearings that 400 miles o them and you can see there was an alignment issues the rear main bearing is missing but was in good shape.

    if you check you'll find that stud girdle use does little or nothing for the individual main cap strength but it does marginally increase main cap stability and block flex.
    now the potential difference is probably not worth the expense, in that your generally spending cash that would be better used in the purchase of the stronger aftermarket block casting from a known source like DART.
    look through the links and read the sub links
    the billet splayed main caps on the aftermarket block is the stronger route, but Id bet 90% of the guys building their first engine think they will save money using the O.E.M. block they already own.....well, until... they add up all the machine work costs and price of parts like aftermarket splayed caps, ARP main studs ,the labor costs from the machine shop, etc. but by that time the machine shop owner is smiling all the way to the bank, and youve just figured out the true cost of that cheaper O.E.M BLOCK
    failure to check for cracks or use of a O.E.M. block at power levels its not designed for can and frequently does result in engine failure, most O.E.M. SBC blocks are rated at no more than 400hp, we all know guys pushing them to 500hp but much beyond that its a crap shoot and the blocks eventually going to flex and fail.
    Last edited by a moderator: Jul 10, 2017
  3. grumpyvette

    grumpyvette Administrator Staff Member

    • Siamesed Extra-Thick Cylinder Walls: Resists cracking and improves ring seal (minimum .300'' thick with 4.625'' bore).
    • Scalloped Outer Water Jacket Walls: Improves coolant flow around the cylinder barrels to equalize temperatures.
    • Four-Bolt Main Bearing Caps: In steel or ductile iron have splayed outer bolts for extra strength.
    • Crankshaft Tunnel: Has clearance for a 4.500'' stroke crank with steel rods without grinding.
    • True ''Priority Main'' Oil System: Lubricates the main bearings before the lifters.
    • Oil Filter Pad: Drilled and tapped for an external oil pump.
    • Rear Four-Bolt Cap: Uses standard oil pump and two-piece seal - no adapter required!
    • Lifter Valley Head Stud Bosses: Prevent blown head gaskets between head bolts.
    • External Block Machining: Reduces weight without sacrificing strength.
    • Simplified Install : Fuel pump boss, clutch linkage mounts and side & front motor mounts simplfy installation on any chassis.
    • Dual Oil Pan Bolt Patterns: Fits standard and notched oil pans.
    • Bellhousing Flange and Rear Main Bearing: Reinforced with ribs to resist cracks.
    • Note: Does not include cam bearings, freeze plugs, or dowels

    Racing Articles
    Sonic Testing - What, Why, How
    by Don Terrill ©2004

    In the racing world a sonic tester is used to measure the thickness of metal in areas that can t be accessed for direct measurement, the most common being cylinder walls and roll bar tubing. For this article I m going to focus on the engine block s cylinder walls.

    Relative to the induction system, there isn t much power to be had in the short block, but one of the most important areas is ring seal. The interaction between the rings and the cylinder wall is critical. Rings can handle some irregularity, but there is no question, the better the cylinder wall, the better the power.

    How a sonic tester works:

    Just like a bat or a radar gun, the sonic tester sends out a sound wave and then calculates the thickness of the metal by measuring the time for the reflected wave to return.

    Calibration is the key to accurate readings. For the best results you should find two pieces of like material (cast iron), one thinner than typically readings and on thicker, to use as standards. You need to be able to physically measure these pieces and then compare them with the tester to make adjustments. You can try to find areas on the block for calibration or take a sledge to a blown up block and make your own. I was “lucky” enough to have a customer forget to put antifreeze in his block over the winter, which supplied me with the perfect donor block.

    Where to test:

    Major thrust â Located opposite the rotation of the motor. Facing the front of the engine, if it turns clockwise, the major thrust is the left side of each bank (V8). This is the location of the largest loads and thus it would be nice to see the thickest cylinder walls.
    Minor thrust â Located opposite the major thrust and on the same side as the rotation of the motor - Typically the right side of both banks.
    Front and back of block â This would be the front of the front cylinders and rear of the rear cylinders. Most manufacturers put a good amount of material in these areas, probably because they had the room.
    Between cylinders â This is typically the thinnest section of the cylinder because of closeness of adjacent cylinders and the need to allow room for coolant. I ve actually seen blocks run with less than .100 on the pin sides.

    What s a good thrust side thickness? .300+
    What s ok? Over .250
    What s bad? Under .200 on a thrust or under .100 on a pin side â I d call this a nightmare

    What can go wrong? Egg shaped cylinder walls and worse, a cracked cylinder wall. A good way to know how good a block is without a sonic tester is to see how out of round the cylinders get after a season of racing, good blocks will take next to nothing to clean up, bad ones may take .002+ every season.


    Grouting the block - Filling a block with grout is no replacement for having a good block. Grout can be helpful, but for other reasons that I will discuss in a future article.
    Sleeving the block - There are so many things that can go wrong with sleeving a block that it s not worth the risk in my opinion.
    Offset boring â Offsetting the boring bar away from thin spots may help a fuzz, but unless you re doing a large overbore you just can t make enough difference.
    A better block â In the end this is the only true fix, with a few more pounds on the nose of the car being the only negative.
    Last edited by a moderator: Mar 1, 2017
  4. grumpyvette

    grumpyvette Administrator Staff Member

    just for grins IM posting this info to try to show why you don,t want to use a OEM 400 block thats been improperly machined.
    a great deal many more problems can be avoided entirely, if you take the time to think things through and do a bit of research into what works and what tends to fail, than you'll generally find by rushing into a project with the stock OEM engine block and waving your check book under the nose of the local machine shop owner!
    Start by getting the block carefully cleaned and the block wall thickness sonic tested, then dye test for cracks , the last thing you want is to spend hundreds of dollars on a block thats already cracked or so thin in places its sure to crack under stress, or one that has bore walls so thin they flex and cause ring seal issues.
    yes testing and inspections, and cleaning cost money, but its better to find problems early then after you spend hundreds of additional dollars on a junk block.
    in this case a guy on a different site posted pictures of what the result was when he used a stock OEM 400 block that had been bored .060 over size and honed without deck plated during the hone process.
    this guy put hundreds of dollars into block machine work , and while tightening the head bolts he heard a (POP SOUND) and the torque changed, inspection showed the bolt tension caused the thin block casting that was bored .060 over size to crack.
    you could easily pay $400-$800 for a clean 400 block, and add another $500-$1200 in machine work, think about that, then think about the far stronger DART block cost, and its far less likely to have similar problems

    the answer, to what machine work and parts you'll need and what main cap design is best for your application, will of course depend on what you intend to DO- WITH THE COMPLETED engine , yes a common upgrade is to use the stock main caps and ARP main studs, they can be used but the difference in tension may require the block gets line honed to maintain the correct crank bearing alignment compared to the factory main cap bolts ,and this generally works ok up to the 450-475 hp level, and yes there's stronger billet aftermarket main caps, splayed main caps and main cap girdles that can be used to increase the blocks strength and rigidity, but the aftermarket blocks use thicker castings of a sightly better design making them significantly stronger and a splaid main cap is structurally a stronger design.
    Most OEM production SBC blocks are factory rated for under 400 hp use, we all know people that have pushed the limits to 450-500 hp but theres a huge difference, in stress, levels a block sees, between the malt shop hero who got his car dyno tested at 475 hp who spends 97% of his time cruising around to impress his buddies with the cars lumpy idle, and racing once every few months , and some guys racing a stock car, for several 50 lap races at 6500 rpm every Saturday night, in what you can reasonably expect from the main cap durability and main cap stability because stress is CUMULATIVE !
    you can get away with amazing amounts of abuse SHORT TERM, that will EVENTUALLY cause major parts , durability issues & failures


    look closely the red arrow shows the threads were repaired with a heli-coil thread insert, while thats not necessarily a huge problem the CRACK that goes thru the STEAM HOLE (GREEN ARROW) IS POTENTIALLY A MAJOR ISSUE

    notice that the piston rings don,t show contact wear on the cylinder walls ,adjacent to the bolt holes (LOOK IN THE RED BOXES) where the bolts tension pulls the cylinder walls outward, this could be compensated for if the block was honed with deck plates in place but the cause is extremely thin and flexible cylinder walls, the correct route is use of the far stronger and thicker casting used in the DART aftermarket block

    Ive got zero doubt that adding main cap girdle adds rigidity, You can certainly make a great deal of horse power, but the rpm level stress goes up rapidly past 6000 rpm, and Id point out that the block casting design is the key to strength, in many designs, EXAMPLE, an olds blocks main web strength is not noted as nearly as strong as some of the other engines, so no matter what you do your stock casting is not going to be as strong as a good aftermarket block, like a DART,splayed 4 bolt main on a chevy big block, or a cross bolted block like some fords, hemis and LS1-LS7 engines so Id still recommend staying under 6000rpm, and last time I checked theres no OLDS ARP,connecting rods with 200,000psi rated 7/16" rod bolts, think thru your component selection with the intended rpm range in mind, theres no reason to spin some engines to higher rpms that the designs made to safely operate at.

    before you dump a $1000 dollars or more into machine work on any block have the bore walls thickness checked and the block MAG TESTED for FLAWS & CRACKS , failure to spend the time and money required to do so can cost you a great deal of wasted time and money!
    mag check for cracks in the block


    look closely youll see the lack of basic olds main web thickness, to anchor the main cap studs is a potential problem

    have your block carefully sonic tested , read the links , you can get away with rather tin bore walls in less stressed areas , but if you find any place under about .o90 I would not put any more cash into the block (personally Id want thicker) if you intend to seriously thrash the engine, stress is cumulative, like bending a steel coat hanger over 90 degrees then back strait, the first couple times it handles the stress, but repeat the process over and over and at some point the wire just breaks off

    and remember the bore wall is subjected to hundreds of PSI of cylinder pressure 50-70 times a second,

    if we calculate that 700 psi at peak cylinder pressure a 302, 327, 350, 383 has about a 4" bore so roughly 12.6 square inches of piston surface , over 8800 ft lbs of force on the crank and thats not counting inertial loads

    an example of a sonic test on a stock block bores .060 over bore


    notice several areas, A-E where the block walls less than .100 thick












    http://www.hastingsmfg.com/ServiceTips/ ... ishing.htm




    JUST COMPARE TO A mopar wedge FULL SKIRT girdle that uses all the oil pan bolts in the BLOCK

    the better machine shops pin or sleeve the main caps to prevent movement










    Last edited by a moderator: Feb 25, 2017
  5. grumpyvette

    grumpyvette Administrator Staff Member

    Indycars posted this great info

    http://www.hotrod.com/techarticles/engi ... omparison/

    If you look at the Chevy block on page 2, this is remarkably close to my experience. I bored a
    350 in² SBC .060", which is .030" on a side. My thinnest wall was .064" on cylinder #4.

    If the Chevy block in the Hot Rod (Page 2) article was bored .060" over, it's thinnest cylinder
    would be .062".

    Wish I would have known these facts before I spent $200 on boring a block I'm not going to use
    for a performance application.


  6. grumpyvette

    grumpyvette Administrator Staff Member

  7. Grumpy

    Grumpy The Grumpy Grease Monkey Staff Member

Share This Page