splayed main caps


Staff member
I was asked," whats the difference between 2,4, and a splayed bolt block"


on a normal chevy engine with 4 bolt main caps the caps look like this, notice the front cap is a two bolt main cap which is normal even on four bolt block where all the other caps have four bolts
the better machine shops pin or sleeve the main caps to prevent movement

factory OEM blocks are very thin wall casting's
the aftermarket blocks are cast of better material and made much thicker.

the answer depends on what your intending to do with that engine build and your budget.
think through your choices carefully.
chevy rates the two bolt SBC blocks at 350hp, but everyone has seen two bolt blocks built to produce 450 hp,
and stand up to that power level for short term stress.
the stock two bolt main cap block works ok up to about 400-maybe occasionally 450hp, if its only run hard occasionally.
adding splayed main caps aids the lower end rigidity, but its likely to cost you over $600 in parts and machine work costs
and might allow that original block to handle 500hp-550hp
(yeah I hear all the screams about guys who swear they build 500 hp sbc engine with two bolt main caps all the time)
theres a huge difference between hitting 6000 rpm plus occasionally vs regularly, and pushing 500 hp every once in awhile,
and running an engine hard/frequently at that power level like a dirt track cars engine! STRESS IS CUMULATIVE
if your intention is to build a daily driver , get main cap studs and use the block,
if your intention is to run the crap out of the engine added splayed main caps and spending $600 plus on caps and machine work might make sense, if your goal really exceeds 500 hp or you want a heavy use of nitrous buy a Dart or BOWTIE 4 bolt block
DART blocks are built with better quality cast iron, higher nickel alloy and have much thicker castings
keep in mind that main cap STUDS will have the entire threaded length of the main cap stud fully threaded into the block threads BEFORE the clamping force is applied and that the end extending through the main cap will have a finer thread pitch, that will allow a greater clamping force to be applied with identical torque wrench , torque loads
ARP said:
Do I need to re-torque my head bolts or studs?
If you follow the ARP installation instructions, there should be no need to do a re-torque. However, it may be necessary under certain circumstances if the gasket manufacturer’s instructions require it, particularly if a fire ring has been installed. ARP recommends not doing a re-torque on a hot engine.
Do I need lube on my bolts or studs?
We recommend using ARP Ultra-Torque lube to ensure an even, accurate clamp load and to prevent thread galling. This is particularly important for stainless steel fasteners. The lube should be used under the head of the bolt or the bearing surface of the nut and on the threads, unless a thread sealer is used.
Can I use Loctite or any thread locker instead of ARP Ultra-Torque assembly lube?
Yes, you can. Some engine builders use blue Loctite on the stud end that goes into the block. Do NOT use Loctite on the nuts for the head studs or main studs. Always ensure that the threads are clean prior to applying any lube. When using Loctite, make sure you assemble the parts before the Loctite cures. You can use Loctite instead of ARP Ultra-Torque, but do not use them together.
Do I have to use Ultra-Torque?
We spent two years developing ARP Ultra-Torque and we have come up with what we believe to be the ultimate fastener lubricant. All of our torque values are based on using Ultra-Torque. We do not provide torque values for use with any other fastener assembly lubricant (such as motor oil, moly lube, etc.) Use these other lubes at your own risk, as their use may lead to a part or engine failure, for which we are not responsible.
Do the threads of the bolts or studs going into the block need lube?
Yes. On blind holes use a small amount of ARP Ultra-Torque lube on those threads. Additionally, if the studs protrude into a water jacket, you will need to clean the threads in the block to remove all coolant and oil residue. Apply a liberal amount of ARP thread sealer or a high temperature thread sealer.
Are ARP bolts and studs re-usable?
Yes. As long as the fasteners have been installed and torqued correctly, and show no visible signs of damage, they can be re-used. If they show any signs of thread galling or corrosion, they should be replaced. In the case of rod bolts, if any of them have taken a permanent set and have stretched by .001” or longer, you should replace them immediately. See page 29 in the catalog for more detailed information on this critical measurement.
Do I install my studs into the block first?
After test fitting the studs in the block, it is generally easier to remove the studs, put the head gasket and head on the block and install the studs. This will reduce the possibility of damaging the upper threads of the stud and scraping the cylinder mounting holes. If the block has no alignment dowel pins, you can use the stud to align the gasket and head.
Does the chamfer on the inside diameter of the washer go up or down?
The chamfered side of the washer goes up, towards the head of the bolt. The chamfer is there to create clearance for the radius between the bolt shank and the bolt head.
Do the head studs only go in hand, or finger tight?
Yes, cylinder head studs are installed only hand tight. Other than the use of an allen wrench on the hex broached into the end of the stud (to ease installation, not to apply torque), use no tools to seat them in the block. However, it is extremely important to ensure that the studs are fully bottomed out in the hole in the block and not hung up on damaged or corroded threads in the block preventing the stud from being fully seated. This is often indicated when the stud threads extend past the deck surface.
I have heard that some people have had trouble with newly installed cylinder head studs leaking water. How do I make sure I don’t have the same problem with my new ARP head studs?
Prior to installing your new head studs, it is very important that you have clean threads on both the block and the studs. First, clean up all the threads in the block with a thread-cleaning chaser, NOT a regular tap. Thread chasers are designed so that they do not remove material from threads but merely remove debris and corrosion. Make sure you go all the way to the end of the threads in the bottom of the hole. Then clean out all the holes in the block with brake or carburetor cleaner to remove all the debris. Make sure the threads on the new studs are clean. Use a liberal amount of ARP thread sealer, high temp silicone or Loctite to ensure that there will be no air pockets that can cause leaks. Then follow the ARP instructions for installing the fasteners.
Are ARP’s torque recommendations the same as the vehicle manufacturer’s specifications?
Sometimes ARP will recommend using torque specifications that are different than the manufacturer, but not always. Our kits are engineered for specific applications, factoring in the necessary clamp load we’re trying to achieve, material type, block or head material, etc. To achieve our target clamp load, it may be necessary to use a different torque figure than what the factory calls out.
The torque/stretch number listed for my after-market connecting rod is different than what ARP calls out for the same bolt. Which specification do I use?
Refer back to the rod manufacturer and use their torque/stretch value.
What drill size do I need for my wheel studs?
To determine what drill size you need, you will need to know your axle/hub material and the wheel stud knurl diameter. If your axle/hub material is cast iron or steel, your drill size will be 0.005” smaller than the knurl diameter. If your axle/hub material is aluminum, your drill size will be 0.007” less than the knurl diameter. The Wheel Studs section in the catalog, pages 76 & 77, list the knurl diameter size.
What is the difference between ARP2000 and Custom Age 625+ studs?
ARP2000 is an alloy steel that has a tensile strength of 220,000 PSI. Custom Age is an austenitic alloy that has a tensile strength of 260-280,000 PSI, providing a greater clamping force than that of ARP 2000.
Why does L19 material require special handling?
Like most high-strength quench and temper steels, L19 requires special care to avoid hydrogen embrittlement or stress corrosion. The material is easily contaminated and subject to stress corrosion. The parts must be kept well oiled at all times and not exposed to moisture. Wearing gloves while handing L19 parts is a good precaution.
I have heard that the black oxide bolts and studs I get from ARP will eventually rust. Is this true and if it is, can it be prevented?
Yes, the bolts or studs will rust. Black oxide is a conversion coating formed by a chemical reaction with the iron in the metal to form an integral protective surface. It is NOT a permanent coating that has bonded to the surface of the fastener. The black oxide process is a short-term rust preventative only and any part exposed to the atmosphere will show signs of rust in a matter of days. Frequent application of oil to the part will increase corrosion resistance. In addition, the bolt head could be painted with black epoxy primer, followed by semi-flat paint or clear lacquer.
I was recently asked about having splayed main caps installed on a O.E.M. chevy small block, (yes when I was younger I've had it done..
we all learn from making mistakes)

while theres zero doubt the addition of properly installed splayed main caps helps crank retention and helps bearing life, most machine shops charge $500-$800 to add the splayed main caps and line hone the block and deck honing the bores and other almost mandatory machine work is always going to add several hundred to almost an additional $700-$1200,
and your still working with a block that will rarely accept a .060 over bore and still have reasonably thick bore walls and structural rigidity....
yes it works, splayed cams are an option...
its also in the long term pissing money down a rat hole!
especially when you compare the total cash outlay,
of purchasing a stronger and thicker higher strength block up front,
compared to the cost of modifying the O.E.M. block,
and what you eventually have too work with at the end of either choice you've made.

heres a few related threads you really should read through











CNC blocks said:
On the SHP blocks
Since the Dart SHP and SHP Pro blocks have come out it not really worth dealing with an OEM block that can only be bored maybe .060 over.
once we get the block from DART,
I chamfer around the main housing bores

Chamfer the freeze plug and rear cam plug hole

Tap oil galley holes deeper

I line hone the to at least the middle spec or some shops/engine builder have me line hone to the high limit, When adding studs I do see the housing bores tighten up.

Blocks are deck to the customers desired dimension

Bored if needed

Plate honed using the same hardware and gaskets to be used in the end build.

Lifter bores are checked for size and honed as needed, Most customers do a lifter bore up grade to .904 lifter and I must have the lifters for fit to the bores.

On 3.875 stroke crank I do have to add a little more clearance to the pan rails.

So far out of a couple hundred SHP block no known failures.

Like with any new block all blocks have to be check for size.
Click to expand...


aftermarket blocks like dart have significantly thicker bore walls, main cap webs, decks, can be ordered with splayed and billet main caps


look closely at ARP main studs have one end with course threads matching the O.E.M. block threads and the outer end with finner pitch threads, that use a harden washer and 12 point flange nuts


on a two bolt block all the caps look like the front cap like this block below

racing blocks have SPLAYED 4 bolt main caps like this





http://www.superchevy.com/technical/eng ... main_caps/






http://www.superchevy.com/technical/eng ... main_caps/


I found these really rather good photos posted on the internet, of some of the machine work required for a well built engine
which are even stronger

BTW you can CONVERT standard two bolt blocks to SPLAYED 4 bolt with a KIT and a MACHINE SHOP to REFIT AND HONE THE MAIN CAPS
theres MILLIONS of guys running 350 two bolt blocks with few problems, if your block has only two bolt caps you have two options, you can add ARP studs if you want to increase the caps holding strength about 30%-50% or you can convert that two bolt block to splayed 4 bolt caps if your really concerned , but unless your over about 450hp I would not be even slightly worried , if your using a standard sbc 4 bolt block with ARP bolts or studs


typical two bolt cast crank 350


ARP ,two bolt main cap STUDS will work ok at the 400hp-450hp level, but are not ideal.
but heres some splayed caps, if your interested,
be aware that your going to spend between $400-$550 in most machine shops by the time you figure on the $200 for the caps themselves and added to the machine work expense, to get them correctly installed on a 2 bolt block,in your case its more than likely wasted money,because by the time you buy a 2 bolt block, pay for the machine work required too add splayed man caps and have the block decked , bored, bores honed and line honed the cost can frequently be close to the cost of a DART BLOCK with its much thicker and more rigid casting, but if you feel better knowing they are there...... well all I can say is I bite the bullet and get them installed simply because with everyone's plans changing over time and a shot of nitrous as a future option in most high performance engines they add a good deal of strength, but in the long haul the DART BLOCKS A BETTER VALUE
this is a great example of project cost creep, yes you'll more than likely NEVER use the extra strength, on most common engine builds used on the street as most of those engines true hp level unless nitrous or a supercharger is being used fall in that 450hp and under range.,and yes its more than likely wasted money,if you already have a 4 bolt block with ARP fasteners. but many of us just look at it and say, hell, its a good investment in the bottom end strength... and Ill feel better knowing their there!, the money would be better spent in almost every case on better quality rods in most cases simply because rods and rod bolts fail far more often than caps do! its insane in most cases to go to the expense of splayed caps on the block if your still running stock connecting rods, invest in good quality (H) style rods with 7/16" ARP rod bolts and a STEEL CRANK before worrying about SPLAYED MAIN CAPS


http://www.dartheads.com/products/engin ... all-blocks



http://www.milodon.com/instructions/mai ... d-bolt.pdf

http://www.vhrpartsandaccessories.com/s ... let/Detail
HERE the STUDS that should be used to replace the stock main cap bolts, they ate far stronger, ... don,t forget a good MILODON windage screen and a high volume oil pan, they are very important to insuring long engine life at high rpm levels

0945400 – PRW Billet Steel Main Girdle
PRICE: $ 169.50

These kits contain main cap studs and the block must be line honed with the girdle in place.

#2---Main Bearing Stud Girdles 04/23/2007


Main bearing girdles were first used on supercharged Small Block Chevy's in the early 60's. When the heavy-duty 4 bolt blocks became available they disappeared. The 5.0 Ford started splitting down the middle about 10 years ago and the main bearing girdles again made their appearance. All of the new power producing parts such as strokers, high flow heads, manifolds, and camshafts available today severely over stress the stock Mopar blocks. The 'good' cross-bolted factory Big Blocks and the 4-bolt 340 blocks are in limited supply at best, or nonexistent. This leaves you with 2 options: our main girdles or - "that can't be good" - Bubba!


The beauty of these kits is that you can use the original main caps, which will only require line-honing. This drastically reduces the cost of the job and gives better support than other methods to boot - a true win-win situation.

The main bearing girdles are used to tie the main bearing caps and bulkheads together, thereby stiffening the block lower-end and increasing crankshaft support. Our stud girdle is designed to reduce fore and aft and lateral block movement (that means front-to-rear and side-to-side for the chatters). We are not trying to prevent bending of the block with the girdle. The thickness of the girdle has very little to do with its strength. Its strength lies in its width rather than its thickness. For the vertical strength (thickness) to be a factor, the plate would need to be 1.5" to 2" thick and have the caps as an integral part of the girdle. Many newer OEM engines are made this way and that is a good design, which cannot be duplicated with a flat plate. In addition, if the plate is too thick, it makes oil pan removal more difficult in the chassis.

When the engine is running, especially under highly loaded conditions, the crankshaft is being twisted back and forth trying to move the main caps and bulkheads along with it. This crankshaft twisting is the reason for needing the harmonic damper. When the power output (twisting) becomes great enough the main caps will move "walk" against the block causing fretting (micro-welding). If this continues long or hard enough, the caps and/or main bulkhead can crack. Worst-case scenario: the block will split up through the cam bores.


Our girdles provide additional support points below the crankshaft and tie all the caps together substantially reducing any possibility of flexing or twisting. Testing (pre and post girdle) has shown power increases in engines with severe twisting (binding) situations and longer component life with the girdle installed.

The small block kit can be bolted on with no machine work required. There is also an option of machining the caps for increased clamping area. Instructions for both applications are included. The big block girdle ties the main studs into the pan studs and block skirt area, too, and there is no machine work required.

All kits are complete with studs, shims, spacers and nuts and, as always, our real world, easy-to-follow instructions. The kits are supplied with studs for their superior clamping ability. When installing studs, the block must be line honed, unless it was previously line honed with studs. Using longer studs will not have an effect.

Wow! When it rains it pours! There are more people making big block main bearing stud girdles everyday. Some of them are partial kits with no instructions and no one to call for help and others are very elaborate and could easily be considered overkill.
What we are all dealing with is a stock block that has many weak areas. The main cap and bulkhead areas are ones that show up first and can be strengthened by using our main bearing stud girdle kit. When we developed our girdle we were seeing cap walk when the horsepower reached the 600HP area. The longer stroke engines only exacerbate this situation. (For you "chatters" exacerbate means "to make the situation worse".)
Our goal was to have a system that would allow the stock blocks to live at 907HP, for obvious reasons. We have customers who have exceeded this goal by 10% or more. Therefore we our confident that our system is more than adequate when dealing with a stock block. We do not suggest or recommend using other than stock main caps. We do not feel the extra expense and machine work is worth it. Ours, and our customer's success with our design has proven this point. The caps are not the problem.
The stock blocks have other weak areas that cannot be addressed by making the main caps & girdle any different than what we offer. There also seems to be a misunderstanding by some girdle suppliers as to exactly how our kit is designed. Just because they claim that their kit is exactly like ours don't be fooled! They aren't.
We use clamping bolts on the main caps AND the girdle. (see photo below)


Next we use selected shim packs between the main cap nut and the girdle. Then a second nut is used to clamp the girdle to the stud. We do not stack up washers to fill the space between the main cap the girdle. When using our system there is no distortion of the girdle.
What about attaching the #5 main cap to the girdle? This looks like it would be easy to do.... that is until you try to put the oil pan on. There is not room unless you want to play "Jesse James" (of Monster Garage fame) on your pan and even then it is a very tight fit. We looked into putting a smaller stud, like the oil pan studs, in the #5 cap but knew our customers would see that as a ploy to "claim" that we had clamped to the rear studs when in fact it would have been a less than sincere effort. And even then you must ask yourself if it is really worth the extra work if the girdles support strength is already exceeding 907HP...which it is. You can put lipstick on a pig but it is still a pig.
If the prototype of our current design had not been successful at the original designed goal of 907HP we had a "Plan B" to strengthen and stiffen the bottom end of the block even more. Since this was not needed we didn't pursue it. Just as a point of interest... these stiffening techniques did not have anything to do with the main caps themselves or making the girdles any thicker!
Be warned when others try to copy or modify our original design, they don't give you everything. One of the strengths of our kit is is in the fact that we are clamping the cap to the block with one nut and the girdle to the cap with another nut. We are not relying on one nut to try and hold it all together. Others cannot do this because they do not have access to our custom made ARP main studs. Remember, ours are running at over 907HP with stock caps and no sign of cap walk. This is the best complete kit at the best price. Some of the others may be smooth talkers but they are poor copycats.

Here is the instructions for your PRW: http://www.jegs.com/i/PRW/228/09350...MIgefpm7P51wIV3bfACh1teASgEAQYAyABEgLo7fD_BwE

You have probably seen this article before: https://www.jalopyjournal.com/forum/threads/small-journal-chevy-main-girdle.381686/
the better machine shops, will suggest you have the option too pin or sleeve the main caps to help prevent main cap movement


PRW Billet Steel Main Stud Girdle, Chevy 454, 1045 Billet Steel Girdle, including PRW steel studs, nuts & washers

PRW Billet Steel Main Girdles are engineered to help eliminate the block flex and cap walk that occurs as a result of stress while under extreme loads, including nitrous oxide power bursts in high performance engines. PRW main girdles are manufactured from premium quality 1045 billet steel. These kits include high quality steel studs, spacers and nuts. (limited machining may be required for proper fitment).
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Staff member
Grumpyvette: I had asked you before about the strength of a 2 bolt versus 4 bolt main SBC blocks especially those with 1 piece rear main seal. I have also spotted girdles for 2 bolt blocks and valley girdles also. Please see http://www.horsepowersales.net and evaluate and comment please about using these valley girdles and crankshaft main cap girdles concerning strenghening the block. Your thoughts please.

the first thing ID point out is that the chevy small blocks are far less prone to cracking from flexing than the ford small blocks and that anytime you exceed about 550-600hp your much better advised to use an aftermarket DART BLOCK with its much thicker cylinder walls, main webs ,and block endwalls, before spending hundreds of dollars on machine work, but the chevy block will stand up to a good deal more abuse than the sbf generally will if its correctly machined, read thru the links, JOBYs turbo build on a STOCK short block lasted for quite awhile under higher loads
Id bet 90% of the guys building a SBC based engine never give the basic block or foundation strength a second thought UNTIL they find out thru part failure that the basic OEM blocks are just not meant to be rigid and solid enough to allow you to build an engine that exceeds about 500hp without expecting it to eventually have major problems.
The reason so many people get away with using stock OEM blocks is BOTH that darn few SBC engines that people claim make 500 or more horse power actually do, and many that do are seldom run in the rpm range where they make that power level for more than a couple seconds, at a time. you really see the way the stock OEM block casting flexes in applications like stock car racing , where the stress is prolonged and the main caps tend to be subjected to more repeated and higher stress.










lets put it thisway, Ive built over 175-200 engines in 39 years and Ive never seen a block crack thru the lifter gallery unless it was the result of a rotating assembly grenading and that was usually at over 6000rpm, with obsurd levels of nitrous used, chevys crack cylinder walls, main caps, main cap webs, and decks on occasions but even the stock chevy blocks take alot more abuse than stock sbf seem to from what Ive seen

cleaning up the threaded holes is mandatory if you want consistent clamp loads










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


PS, what does that lifter valley brace really do that the correctly bolted in place chevy intake maninifold not do, IE, it prevents the cylinder banks from easily flexing thru the lifter gallery



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Staff member
I was recently asked if adding SPLAYED 4 bolt main caps

to a O.E.M. 2 bolt block,


was a good worth while upgrade, this is one area where experience teaches you a few things
the short answer is that the route you take depends on both your budget and GOALS for the engine.

adding splayed main caps to a standard 2 bolt O.E.M. block does significantly strengthen the clamp loads holding the crank in place with those main caps, if your main caps on the block move under high stress loads the bearings take an exceptional beating , tend to loose oil pressure and cooling and eventually will fail but your still anchoring the main caps to a significantly WEAKER and thinner block casting made from weaker cast iron alloy and main block web area compared to an aftermarket block like DART sells.
main caps with inner sleeved main cap bolts tend to have much reduced main cap movement under stress.
a O.E.M. SBC block will frequently have cylinder walls that are less than .100 thick with a .030 over bore while a dart block will still have a .250 cylinder wall thickness with the same bore size
the cost of adding main caps will vary a great deal in machine costs but main caps alone cost about $160-$270 , mandatory main studs and splayed side bolts add an additional $150 or so, then the machine work can easily add $350 or more, so your looking at a cost of about $750--$850 in most cases, and your still dealing with a thin cylinder wall casting and weak main block webs.
don,t forget that when ordering main cap studs you'll want the ARP main studs DESIGNED to mount a windage screen with the stepped extensions that allow you to adjust the windage screen to be 1/8" from the rotating assembly arc.
yes IM well aware we all know some guy, some place, whos been pulling well in excess of 550hp while using a O.E.M block, and yes that's been done all the time, but stress is cumulative, and pulling 550-600hp a couple times on a dyno for bragging rights or racing once or twice a year is not nearly the same thing, as lets say an engine thats used almost weekly at the strip, or a guy whos using a 150 shot of giggle gas (NITROUS) on his 400hp street engine or a circle track car where the average rpm levels and duration of stress is far longer, if you talk to those guys youll see far more main cap fretting, bearing wear, and bearing problems...its not like a block will always fail if subjected to 550hp, its that its on borrowed time, because it was designed to handle 350-400hp and yes there a safety margin in strength built in, but time stress and casting variations WILL eventually detect the flaws, thru component failures that are far less likely to occur with the stronger block castings
keep in mind both the main caps base and the area in the block must be machine precisely parallel , and there is a slight interference fit into a slight recess in the block on most engines to help prevent the caps moving once tightened into place by the main cap bolts or main cap studs. on some performance engines its fairly common for a hollow sleeve,s inserted 1/2 its short length, into the block and 1/2 its length into a shallow recess into the main caps, too fit into matching recesses around the main cap studs , this locates and prevents lateral movement of the main caps





now if your only going to try to strengthen the block and reduce main cam movement at the 450hp-500hp level that most street sbc engines see only occasionally because you spend 99% of your time well below peak rpm levels this is a worth while addition to block strength, but if you going to add a heavy nitrous shot, a turbo or supercharger that adds significant cylinder pressures its basically throwing $700 plus in the dumpster in my opinion, that $700 PLUS would be FAR BETTER SPENT on a significant part of the price on a good aftermarket block, especially if you consider the other extra machine work thats more than likely required like boring, honing, decking, lifter bore indexing etc. if your truthful with yourself and actually do check all the factors and machine work costs its usually actually LESS expensive in the long run to buy the aftermarket performance block if your power goals exceed about 550HP from a SBC






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.
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.
















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Staff member


Pro-Gram Engineering has had the pleasure of serving the automotive community for 22 years and is proud to claim the title of the world's largest and best manufacturer of aftermarket main bearing caps. Dedicating ourselves to the principle of "quality, not quantity, is our #1 product" enables us to provide a superior part in design, manufacture and material. These principles have allowed us to provide parts to all facets of the automotive performance industry including NASCAR's Nextel, Busch and Craftsman series, NHRA Drag Racing, NTPA Tractor Pullers, Offshore and Drag Boat Racing as well as industrial and military applications.

Quality, as defined by Webster, is "the degree of excellence of a thing"; Pro-Gram Engineering strives to maintain an excellent quality in our materials and production methods.

Material: With the influx of lesser quality goods and materials to the US, Pro-Gram Engineering solely uses materials certified as produced in the US. This allows us to guarantee the quality of the materials used in our parts, which are critical in any performance application.
Equipment: The machinery and equipment used to manufacture our products is continually being maintained and upgraded to ensure the highest precision available.
Location: Pro-Gram Engineering manufactures all of it's goods here in the US. Our manufacturing facility is located in Barberton, OH, which allows us to have direct influence on our product quality and manufacturing methods.
Personnel: Pro-Gram Engineering proudly employs highly skilled men and women from the surrounding communities. The combined machining and manufacturing experience at our, and your, disposal is in excess of half a century. While already highly skilled and competent, Pro-Gram engineering's employees are continually trained in new manufacturing methods and techniques as well as CAD design and software. Pro-Gram Engineering's technical support team of Ken and Dan Anderson have been working and serving the automotive racing industry as father and son for 13 years while Ken has served the automotive community at large for over 43 years.

Along with Pro-Gram Engineering's own product line, we proudly offer other high quality parts from a select group of manufacturers including Diamond Racing, Oliver Racing and ARP to name but a few. These parts, and manufacturers, are known for the quality and consistency that we expect and require of ourselves.

Pro-Gram Engineering's dedication to quality has given us the privilege of supplying some of the world's best race teams and engine builders. It is an honor to continue working with MOPAR Performance, Bill Davis Racing, Rousch Yates Racing, Arrington Racing, Coughlin Bros. Racing, the Butler Performance Group and M&W Engine Service of Australia as well as numerous aftermarket engine manufacturers.


In any application where your tightening a nut on a stud , such as on the outer threaded ends of main cap studs or head bolt studs, youll want to use a lube on the threads that gives consistent torque reading from your torque wrench indicating the correct bolt or stud TENSION, oil and MOLY assembly lube and various thread sealants do not always do that,the end in the blocks course threads have thread sealant, the fine threads on the outer end require a totally different lubricant


Staff member
"I was told that a two bolt BBC can be converted to a four bolt while still retaining the stock two bolt caps. This is accomplished by counter boring the stock cap where the additional bolt would go on a standard 4 bolt block and then drilling and tapping the block to accept the additional fastener.
This would be a way to add some additional clamping strength to the main caps without the added expense of having to buy and fit aftermarket caps.

Has anyone ever seen this done? "



http://www.harborfreight.com/cpi/ctaf/d ... mber=90124


its usually standard practice to lightly stamp the outward facing rods and rod caps and main journal caps with the cylinder number or location they will be or are located in and a matched stamped number on the oil pan rail of the block, its also useful to stamp the main caps on one edge and a matched stamped number on the oil pan rail of the block, indicating which direction each main cap faces and its location during the original DIS-assembly process or first engine assembly to prevent potential screw-ups during later builds or refresh builds.
just make the stamped number clearly readable but not deeply stamped as you don,t want to induce potential stress risers that might weaken the connecting rods


OEM main caps on most blocks are cast iron and have a tendency to fracture under lower stress loads than machined steel splayed main caps,that have outer bolts anchored in the blocks thicker outer section, this can be an important consideration if you intend to use nitrous or push an engine well in excess of 4000fpm in piston speeds


you can see the modified two bolt caps above
are not nearly as well anchored to the block as correctly modified splayed main caps below

thats NOT a BILLET or solid steel main cap, Id bet theres little too no effective strength added as the outer bolt clamping on that limited amount of a cast part can,t exert much clamp force before distorting the cast main cap or perhaps causing it to crack under load,
even 4 bolt main cap cast caps are not super strong

Id bet you would gain more if limited to the original cast main caps just using ARP main cap studs
drilling extra holes in the block web in that area is not usually beneficial

on some engines they have main cap girdles available

milodon sells replacement splayed main caps, for under $250, the splayed outer bolts would add significantly more strength and any time you are swapping to 4 bolt main caps on a two bolt block your very likely to need the block line honed as the extra bolts change the way the clamp forces distort the main webs in the block


STOCK OEM 4 bolt 454 blocks are not all that expensive
and a 2 bolt block with ARP main studs can support a surprising amount of hp, I don,t think its financially worth the effort to convert a 2 bolt block rather than swapping to ARP studs or a 4 bolt block, the conversion machine work and splayed main caps are likely to make selling a current block and purchasing a factory 4 bolt block a better option





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Staff member
CNC BLOCKS N/E;3556266 said:
I have been asked about the installation of splayed caps many times over the years. First of all this proceedure can be done in a Bridgeport, knee mill, CNC machine ETC.

I use flat bottom caps with 10 degree angle outer bolts because with the 10 degree outter bolts you should not get into the water jackets. I have had many calls about outter bolt holes getting into the water jackets only to find out its because of the 18 or 22 degree outter bolt holes.

Alot of classes out there are restricted to run OEM blocks and most racers like the weight savings of the OEM block and 383's we are now seeing over 500 plus HP and with the added stroke its best to go to a splayed center cap, Its always best to sonic test the cylinders for thickness before spending time and money on cap work.

Caps I prefer are caps from http://www.cipcoindustries.com/ or http://pro-gram.com/ Price on cipco caps are right at 160.00 a set Programs are right at 210.00 a set.

First process is to cut the register either with an end mill or I use a 2.5 shell mill on 2 bolt blocks the register has to be only cut appox. .120 deep measure of the pan and on 4 bolt blocks the register have to be cut appox. .140 deep. I like to see a .003 press fit


Next step is using a 1/2 in end mill at a 10 degree angle is to mill a flat spot.


Next is to center drill


Next drill holes using a the letter U drill appox. .800 deep


Next would be taping with a spiral tap seems to work best.


Line boring can be done with a line boring machine or I use the PLB-100 which seems to very fast and accurate, I cut the housing bores close to size.


Once line boring is complete the caps are taken off and cut appox. .0025 to .003 off the bottom then then reinstalled and aligned honed to the last .001 caps are loosened retorqued to check for size and hone to size.


Finish product


Note: On the Cipco caps they are OEM height and you can use an ARP bolt kit and on the Porgram caps they are appox. .200 taller and would require a stud kit.

Hope this thread answers most questions about cap installation.