By: Carl AmundsenDate: July 20, 1998
ARC Racing, by design, will not be the first to the market place (at least not very often) with new, earth shattering ideas or products. We're not slow by any means, we just want to bring you, our customers, a well thought out product that has been thoroughly engineered and tested. We won't take an idea, make the part, then sell it to you for our testing purposes.
When we test a part, a motor is built and then run under the most undesirable conditions. We literally try to break it and, if we fail to break it, we try again.When testing the different alloys for our connecting rods, we even conducted the "Dirt Road Red Neck Test". This is done by taking rods of different designs and alloys and putting them in a vise and using a pipe to see how far they would bend before breaking, and we did break a few.
For the most part, when you buy an ARC Racing product it will be stronger, lighter and cosmetically more appealing than our competition offers and you'll be proud to own it.
We have never - and will never advertise that "this part will give you one more horsepower", or "this part will shave another seven tenths" and so on. The parts you buy from us are true racing parts and in the proper combination (with a little common sense) will make you go fast and, with a little luck added, maybe faster than everybody else.
Monday, July 20, 1998
Saturday, July 18, 1998
Rod Length Ratios
There are as many theories about rod lengths as there are any other subject that deals with racing.
As strokes get longer, rod lengths get shorter and at some point in time, this will create a problem. We don't know if we've crossed the line yet, but we're definitely leaning on it. At the same time, there's a point where rod lengths can get too long for a particular stroke and we're leaning on that line also.
Rod length ratios are calculated by dividing the rod length by the stroke.Example: a 5.000" rod length divided by a 3.000" stroke equals a 1.67 rod ratio.
For a good illustration of what increasing the rod length does for an engine, we'll use a 350 Chevy.A stock 5.7" rod divided by a stock 3.480" stroke gives us a 1.637 rod ratio.Now, put a 6.00" rod in it with the same stroke and the ratio increases to 1.724 and the engine produces more power and rpm.. This is a known fact that's been around for some 25 years.
A stock, 5 hp. Briggs & Stratton engine uses a 3.875" rod and has a 2.437" stroke which equals a 1.59 rod ratio.We know that by changing the rod to 4.475" and using the same stroke, the ratio increases to 1.863 and the engine produces more power and rpm.
The most important thing that a longer rod does is increase the dwell time of the piston when it's at top dead center (TDC) and this will make more power.The second most important thing is that it improves the leverage the piston exerts on the crank journal and this also increases power.
Another feature of using a longer rod is that it creates a much friendlier environment for the piston, cylinder and crankshaft to operate in.Consider this: The piston is moving up and down in the cylinder trying to make a crankshaft rotate in a circle. When the piston is in a down stroke, the resistance of the crankshaft is trying to push it out the front of the block and in an up stroke, with the resistance of compression, the crankshaft is trying to push it out the back of the block.Our recent test engine had a 4.225" rod with a 3.000" stroke equaling a 1.408 rod ratio and we believe we may have gone beyond the short rod ratio limit but, the engine made a bucket full of power and survived even at 9,300 rpm.
Rest assured that one day we'll reach the point of sheer stupidity.
As strokes get longer, rod lengths get shorter and at some point in time, this will create a problem. We don't know if we've crossed the line yet, but we're definitely leaning on it. At the same time, there's a point where rod lengths can get too long for a particular stroke and we're leaning on that line also.
Rod length ratios are calculated by dividing the rod length by the stroke.Example: a 5.000" rod length divided by a 3.000" stroke equals a 1.67 rod ratio.
For a good illustration of what increasing the rod length does for an engine, we'll use a 350 Chevy.A stock 5.7" rod divided by a stock 3.480" stroke gives us a 1.637 rod ratio.Now, put a 6.00" rod in it with the same stroke and the ratio increases to 1.724 and the engine produces more power and rpm.. This is a known fact that's been around for some 25 years.
A stock, 5 hp. Briggs & Stratton engine uses a 3.875" rod and has a 2.437" stroke which equals a 1.59 rod ratio.We know that by changing the rod to 4.475" and using the same stroke, the ratio increases to 1.863 and the engine produces more power and rpm.
The most important thing that a longer rod does is increase the dwell time of the piston when it's at top dead center (TDC) and this will make more power.The second most important thing is that it improves the leverage the piston exerts on the crank journal and this also increases power.
Another feature of using a longer rod is that it creates a much friendlier environment for the piston, cylinder and crankshaft to operate in.Consider this: The piston is moving up and down in the cylinder trying to make a crankshaft rotate in a circle. When the piston is in a down stroke, the resistance of the crankshaft is trying to push it out the front of the block and in an up stroke, with the resistance of compression, the crankshaft is trying to push it out the back of the block.Our recent test engine had a 4.225" rod with a 3.000" stroke equaling a 1.408 rod ratio and we believe we may have gone beyond the short rod ratio limit but, the engine made a bucket full of power and survived even at 9,300 rpm.
Rest assured that one day we'll reach the point of sheer stupidity.
What is Safe Peak Power RPM for an engine?
This is a question that is rarely asked before an engine blows, but always asked after the second one is in a basket.
The formula is simple: divide 22,000 by the stroke.Why 22,000 you ask ?Well, the automotive industry came up with this number after decades of engineering research using literally hundreds of stroke lengths - and we believe it's probably correct.Example: The engine we just finished testing had a 3.000" stroke so 22,000 divided by 3 equals 7,333 safe peak power rpm (which we slightly exceeded for our test).
Now that you know - just keep on truckin.
The formula is simple: divide 22,000 by the stroke.Why 22,000 you ask ?Well, the automotive industry came up with this number after decades of engineering research using literally hundreds of stroke lengths - and we believe it's probably correct.Example: The engine we just finished testing had a 3.000" stroke so 22,000 divided by 3 equals 7,333 safe peak power rpm (which we slightly exceeded for our test).
Now that you know - just keep on truckin.
The 10,000 rpm Bomb
Several times a week we get calls from people that have just exploded their engine and, for the most part, they're looking for answers as to why it happened. On occasion, they'll send us some of the parts (or the whole mess) for evaluation hoping that we can shed some light on the problem. Well - sometimes we can and sometimes we can't.
Lets take a moment to consider where it all started and where we are now.We took a 5 hp. lawnmower motor that was designed to turn a maximum of 3,600 rpm then bored, stroked, welded, ground, filed, polished, fitted, crammed, invented and generally violated the entire book on common sense and ended up with a remanufactured 10,000 rpm BOMB and all of this was done in the name of fun. Well, of course it is.
We just finished testing an engine with a .174 overbore and 3.000" stroker crank and at 9,000 rpm this is what was happening inside that engine:1. The valves were opening and closing 150 times per second.2. The crankshaft rod journal was traveling 79.8 mph in a 3" diameter circle.3. The piston & rod moved, stopped then changed direction 18,000 times per minute (300 times per second).
Think about this:The piston is at top dead center (TDC) in a momentary stop position, we've already had combustion, the piston travels down the cylinder 1.3671" reaching a top speed of 84.3 mph. while the crankshaft has rotated 75° and all of this has only taken 1/720th of a second to happen.
Another way to look at it:The piston and rod start and stop 300 times per second reaching 84.3 mph. between each cycle.
Now, we ask the $ 64,000 question:Could anything go wrong in this kind of environment ?The answer is - Everything.It's truly an engineering miracle that this (or any) engine ever gets to 9,000 rpm just once let alone sustaining it.
Lets take a moment to consider where it all started and where we are now.We took a 5 hp. lawnmower motor that was designed to turn a maximum of 3,600 rpm then bored, stroked, welded, ground, filed, polished, fitted, crammed, invented and generally violated the entire book on common sense and ended up with a remanufactured 10,000 rpm BOMB and all of this was done in the name of fun. Well, of course it is.
We just finished testing an engine with a .174 overbore and 3.000" stroker crank and at 9,000 rpm this is what was happening inside that engine:1. The valves were opening and closing 150 times per second.2. The crankshaft rod journal was traveling 79.8 mph in a 3" diameter circle.3. The piston & rod moved, stopped then changed direction 18,000 times per minute (300 times per second).
Think about this:The piston is at top dead center (TDC) in a momentary stop position, we've already had combustion, the piston travels down the cylinder 1.3671" reaching a top speed of 84.3 mph. while the crankshaft has rotated 75° and all of this has only taken 1/720th of a second to happen.
Another way to look at it:The piston and rod start and stop 300 times per second reaching 84.3 mph. between each cycle.
Now, we ask the $ 64,000 question:Could anything go wrong in this kind of environment ?The answer is - Everything.It's truly an engineering miracle that this (or any) engine ever gets to 9,000 rpm just once let alone sustaining it.
Rod Length Ratios
There are as many theories about rod lengths as there are any other subject that deals with racing.
As strokes get longer, rod lengths get shorter and at some point in time, this will create a problem. We don't know if we've crossed the line yet, but we're definitely leaning on it. At the same time, there's a point where rod lengths can get too long for a particular stroke and we're leaning on that line also.
Rod length ratios are calculated by dividing the rod length by the stroke.Example: a 5.000" rod length divided by a 3.000" stroke equals a 1.67 rod ratio.
For a good illustration of what increasing the rod length does for an engine, we'll use a 350 Chevy.A stock 5.7" rod divided by a stock 3.480" stroke gives us a 1.637 rod ratio.Now, put a 6.00" rod in it with the same stroke and the ratio increases to 1.724 and the engine produces more power and rpm.. This is a known fact that's been around for some 25 years.
A stock, 5 hp. Briggs & Stratton engine uses a 3.875" rod and has a 2.437" stroke which equals a 1.59 rod ratio.We know that by changing the rod to 4.475" and using the same stroke, the ratio increases to 1.863 and the engine produces more power and rpm.
The most important thing that a longer rod does is increase the dwell time of the piston when it's at top dead center (TDC) and this will make more power.The second most important thing is that it improves the leverage the piston exerts on the crank journal and this also increases power.
Another feature of using a longer rod is that it creates a much friendlier environment for the piston, cylinder and crankshaft to operate in.Consider this: The piston is moving up and down in the cylinder trying to make a crankshaft rotate in a circle. When the piston is in a down stroke, the resistance of the crankshaft is trying to push it out the front of the block and in an up stroke, with the resistance of compression, the crankshaft is trying to push it out the back of the block.Our recent test engine had a 4.225" rod with a 3.000" stroke equaling a 1.408 rod ratio and we believe we may have gone beyond the short rod ratio limit but, the engine made a bucket full of power and survived even at 9,300 rpm.
Rest assured that one day we'll reach the point of sheer stupidity.
As strokes get longer, rod lengths get shorter and at some point in time, this will create a problem. We don't know if we've crossed the line yet, but we're definitely leaning on it. At the same time, there's a point where rod lengths can get too long for a particular stroke and we're leaning on that line also.
Rod length ratios are calculated by dividing the rod length by the stroke.Example: a 5.000" rod length divided by a 3.000" stroke equals a 1.67 rod ratio.
For a good illustration of what increasing the rod length does for an engine, we'll use a 350 Chevy.A stock 5.7" rod divided by a stock 3.480" stroke gives us a 1.637 rod ratio.Now, put a 6.00" rod in it with the same stroke and the ratio increases to 1.724 and the engine produces more power and rpm.. This is a known fact that's been around for some 25 years.
A stock, 5 hp. Briggs & Stratton engine uses a 3.875" rod and has a 2.437" stroke which equals a 1.59 rod ratio.We know that by changing the rod to 4.475" and using the same stroke, the ratio increases to 1.863 and the engine produces more power and rpm.
The most important thing that a longer rod does is increase the dwell time of the piston when it's at top dead center (TDC) and this will make more power.The second most important thing is that it improves the leverage the piston exerts on the crank journal and this also increases power.
Another feature of using a longer rod is that it creates a much friendlier environment for the piston, cylinder and crankshaft to operate in.Consider this: The piston is moving up and down in the cylinder trying to make a crankshaft rotate in a circle. When the piston is in a down stroke, the resistance of the crankshaft is trying to push it out the front of the block and in an up stroke, with the resistance of compression, the crankshaft is trying to push it out the back of the block.Our recent test engine had a 4.225" rod with a 3.000" stroke equaling a 1.408 rod ratio and we believe we may have gone beyond the short rod ratio limit but, the engine made a bucket full of power and survived even at 9,300 rpm.
Rest assured that one day we'll reach the point of sheer stupidity.
Wednesday, July 8, 1998
Discovery by Fatality
Re: Crankshaft flex and side covers
By: Lynn Cooley Date: July 8, 1998
We all are aware that a crankshaft will flex and bend. What we don’t know, or should I say didn’t know, is how much. We also didn’t know what kind of specific problems the flexing would create.
Obviously the .875" journal crank could flex more than the 1.000" journal crank but there is not as much difference as you might think.
As a lot of you already know, we have been conducting tests on our new .875" stroker rods. This has been ongoing for about 6 months and we've tried several engineering designs along with different alloys and finally arrived at the ultimate design and alloy. Now let the serious testing begin.
We have a dynamometer but felt that real testing is accomplished on our adult fitted Jr. Dragster and a custom built Kart.
Our first test engine was built using a Raptor block, .140" overbore, 4.225" ARC stroker rod with .875" bearing, 3.000" forged stroker crankshaft, ARC head, ARC flywheel and ARC billet side cover.
This engine assembly was carefully balanced by us.
Now, to be fair and honest, our goal from the get go was to break the rod. We really abused this engine. Our RPM limit was 9000, but we did hit 9300 a couple of times.
The first problem was a high RPM miss and then coil failure. The clearance between the flywheel and the coil was set at .020. When the flywheel rubs the coil the first thing that happens is an interruption of the magnetic field and the coil misfires. The next thing is that friction creates heat and fries the coil.
The flywheel was checked and was running true and the coil was not slipping on its mount. We finally had to set the air gap on the coil at .030 to keep it from contacting the flywheel. This seemed strange and, little did we know, our next lesson would teach us a lot.
About 10 more minutes on the Kart and we blew that sucker all to pieces. The only parts that survived were the carburetor and the ARC cylinder head. The ARC stroker rod looked like it had been through a war but survived - unbroken.
The crankshaft had broken straight down at the radius of the rod journal. This is exactly were it would and should break if the crankshaft bends and flexes. Incidentally this crankshaft is one of, if not the best on the market.
The first symptom of this flex problem was the high speed miss and then the coil failure. By examining where the flywheel had rubbed the coil the hardest, we determined that most of the flex occurs at BDC (bottom dead center). The second place was just after combustion or TDC (top dead center), both of which really make sense.
Think about it - cylinder pressure is at its highest just after combustion and when the piston reaches the bottom, there is no resistance to cushion the abrupt change in direction of the reciprocating weight. As the piston travels upward, it has compression to offer resistance in one stroke and exhaust gases to offer some shock absorption on the next.
On the same note, have you ever wondered why additional deck clearance is needed the more you increase engine RPM? Most engine builders think of rod stretch the same as you do in automotive.
In a Briggs application, crankshaft flex is the main problem. In fact, we checked every rod we had tested and didn't find any permanent stretch.
Our next test engine was built using a BlockZilla block, .174" overbore, 4.225" ARC stroker rod with .875" bearing, 3.000" forged stroker crankshaft, the new ARC BlockZilla head, ARC flywheel and a billet side cover (no name mentioned). The ARC side cover was still working its way through engineering.
With the air gap set at .030" between the coil and the flywheel, we ran the engine very hard for 10 minutes, stopped and immediately tore it down. The temperature of the crankshaft got our attention real fast. After 45 minutes the crank was still to hot to handle (have you ever bent a piece of wire back and forth and felt the temperature just before it broke?). We felt that if we had run it any longer, we would have broken another crankshaft.
One other problem that showed itself on the billet side cover (no name mentioned) was that the 0-ring seal had scuffed and chaffed itself almost into nonexistence along the top of the cover. Along the bottom and up each side seemed to be OK (remember, this was only a 10 minute run).
THE PROBLEM
Ball bearings, by nature, have a certain degree of self-alignment built in. The inside dimension between the 2 ball bearings in the block is 3 ½ inches. It's not hard to flex the shaft .020" in one direction and still have a free spinning shaft. This translates to at least .040" total flex in the shaft and could probably go to as high as .050" and still free spin.
To add insult to injury, the manufacturer of the forged cranks we tested leaves entirely to much clearance on the slip fit bearing area on the shaft. This dimension should be .9995" not .998". This sloppy fit can allow another .015" flex and still free spin. Remember this lesson if you ever have to slip fit a bearing on a stock Briggs crankshaft.
To summarize all of this, it's no wonder the flywheel rubbed the coil and that the crankshaft broke.
THE SOLUTION
Since the ARC BlockZilla side cover was still in the engineering stage, we added a second ball bearing to it and held them in place with 3 recessed button head screws. This created the first DUAL BEARING SIDE COVER.
After installing our new duplex bearing side cover on the same BlockZilla block with .018 clearance between the coil and the flywheel, we had no problems. The engine was run hard for 20 minutes then disassembled and with a shorter cool down period, the crankshaft was noticeably cooler. This was a huge improvement even though the crankshaft had the sloppy slip fit on the bearings.
One other plus over the (no name mentioned) side cover that we tested, is that the ARC BlockZilla side cover is truly light weight, and the ribbing supports on the outside of the cover and, more importantly, the outer perimeter ribbing reduce flex.
Our 0-ring seal showed just a slight sign of scuffing.
The testing was so successful, we decided to use this same technology on our Raptor side covers, and they will be available by the time you read this.
You should see a longer life of the Raptor blocks as well.
The primary reason for all of this testing was to see if our new stroker rod design would live, and IT DID. Both sizes are now in production and available.
See our "Product Showcase" for details of these and other new products.
SPECIAL NOTE:
We try very hard to keep our prices competitive, so look closely at what is furnished with this new ARC side cover design :)
By: Lynn Cooley Date: July 8, 1998
We all are aware that a crankshaft will flex and bend. What we don’t know, or should I say didn’t know, is how much. We also didn’t know what kind of specific problems the flexing would create.
Obviously the .875" journal crank could flex more than the 1.000" journal crank but there is not as much difference as you might think.
As a lot of you already know, we have been conducting tests on our new .875" stroker rods. This has been ongoing for about 6 months and we've tried several engineering designs along with different alloys and finally arrived at the ultimate design and alloy. Now let the serious testing begin.
We have a dynamometer but felt that real testing is accomplished on our adult fitted Jr. Dragster and a custom built Kart.
Our first test engine was built using a Raptor block, .140" overbore, 4.225" ARC stroker rod with .875" bearing, 3.000" forged stroker crankshaft, ARC head, ARC flywheel and ARC billet side cover.
This engine assembly was carefully balanced by us.
Now, to be fair and honest, our goal from the get go was to break the rod. We really abused this engine. Our RPM limit was 9000, but we did hit 9300 a couple of times.
The first problem was a high RPM miss and then coil failure. The clearance between the flywheel and the coil was set at .020. When the flywheel rubs the coil the first thing that happens is an interruption of the magnetic field and the coil misfires. The next thing is that friction creates heat and fries the coil.
The flywheel was checked and was running true and the coil was not slipping on its mount. We finally had to set the air gap on the coil at .030 to keep it from contacting the flywheel. This seemed strange and, little did we know, our next lesson would teach us a lot.
About 10 more minutes on the Kart and we blew that sucker all to pieces. The only parts that survived were the carburetor and the ARC cylinder head. The ARC stroker rod looked like it had been through a war but survived - unbroken.
The crankshaft had broken straight down at the radius of the rod journal. This is exactly were it would and should break if the crankshaft bends and flexes. Incidentally this crankshaft is one of, if not the best on the market.
The first symptom of this flex problem was the high speed miss and then the coil failure. By examining where the flywheel had rubbed the coil the hardest, we determined that most of the flex occurs at BDC (bottom dead center). The second place was just after combustion or TDC (top dead center), both of which really make sense.
Think about it - cylinder pressure is at its highest just after combustion and when the piston reaches the bottom, there is no resistance to cushion the abrupt change in direction of the reciprocating weight. As the piston travels upward, it has compression to offer resistance in one stroke and exhaust gases to offer some shock absorption on the next.
On the same note, have you ever wondered why additional deck clearance is needed the more you increase engine RPM? Most engine builders think of rod stretch the same as you do in automotive.
In a Briggs application, crankshaft flex is the main problem. In fact, we checked every rod we had tested and didn't find any permanent stretch.
Our next test engine was built using a BlockZilla block, .174" overbore, 4.225" ARC stroker rod with .875" bearing, 3.000" forged stroker crankshaft, the new ARC BlockZilla head, ARC flywheel and a billet side cover (no name mentioned). The ARC side cover was still working its way through engineering.
With the air gap set at .030" between the coil and the flywheel, we ran the engine very hard for 10 minutes, stopped and immediately tore it down. The temperature of the crankshaft got our attention real fast. After 45 minutes the crank was still to hot to handle (have you ever bent a piece of wire back and forth and felt the temperature just before it broke?). We felt that if we had run it any longer, we would have broken another crankshaft.
One other problem that showed itself on the billet side cover (no name mentioned) was that the 0-ring seal had scuffed and chaffed itself almost into nonexistence along the top of the cover. Along the bottom and up each side seemed to be OK (remember, this was only a 10 minute run).
THE PROBLEM
Ball bearings, by nature, have a certain degree of self-alignment built in. The inside dimension between the 2 ball bearings in the block is 3 ½ inches. It's not hard to flex the shaft .020" in one direction and still have a free spinning shaft. This translates to at least .040" total flex in the shaft and could probably go to as high as .050" and still free spin.
To add insult to injury, the manufacturer of the forged cranks we tested leaves entirely to much clearance on the slip fit bearing area on the shaft. This dimension should be .9995" not .998". This sloppy fit can allow another .015" flex and still free spin. Remember this lesson if you ever have to slip fit a bearing on a stock Briggs crankshaft.
To summarize all of this, it's no wonder the flywheel rubbed the coil and that the crankshaft broke.
THE SOLUTION
Since the ARC BlockZilla side cover was still in the engineering stage, we added a second ball bearing to it and held them in place with 3 recessed button head screws. This created the first DUAL BEARING SIDE COVER.
After installing our new duplex bearing side cover on the same BlockZilla block with .018 clearance between the coil and the flywheel, we had no problems. The engine was run hard for 20 minutes then disassembled and with a shorter cool down period, the crankshaft was noticeably cooler. This was a huge improvement even though the crankshaft had the sloppy slip fit on the bearings.
One other plus over the (no name mentioned) side cover that we tested, is that the ARC BlockZilla side cover is truly light weight, and the ribbing supports on the outside of the cover and, more importantly, the outer perimeter ribbing reduce flex.
Our 0-ring seal showed just a slight sign of scuffing.
The testing was so successful, we decided to use this same technology on our Raptor side covers, and they will be available by the time you read this.
You should see a longer life of the Raptor blocks as well.
The primary reason for all of this testing was to see if our new stroker rod design would live, and IT DID. Both sizes are now in production and available.
See our "Product Showcase" for details of these and other new products.
SPECIAL NOTE:
We try very hard to keep our prices competitive, so look closely at what is furnished with this new ARC side cover design :)
Thursday, July 2, 1998
Remove 400 lbs. from your crankshaft!
How - you ask ? With an ARC billet connecting rod.Compared to some connecting rods that are on the market today, the ARC rod produces 400 lbs. less centrifugal force (on the crank journal end) at 9000 rpm.That's a lot of unnecessary pressure on the rod, rod bolts, bearings and crankshaft.
Have you ever wondered why additional clearance is needed in the air gap between the coil and flywheel and piston to head clearance on a high rpm race engine ? Crankshaft flex !The less weight the crank rod journal "feels" the less flexing, fatigue, wear and breakage you'll encounter.
How can a part be lighter, smaller and stronger ?After numerous hours of research into the physical properties, force, inertia, elasticity and extensive dyno pulls of connecting rods, we found that attention to details such as shape, type of material, size and weight are extremely important to the structural integrity of a connecting rod.
Just one more plus of the ARC billet connecting rod is that when it's used with most Briggs & Stratton crankshafts, the engine is better balanced. This is very important for the Kart classes that don't allow modifications to the crankshaft :)
Have you ever wondered why additional clearance is needed in the air gap between the coil and flywheel and piston to head clearance on a high rpm race engine ? Crankshaft flex !The less weight the crank rod journal "feels" the less flexing, fatigue, wear and breakage you'll encounter.
How can a part be lighter, smaller and stronger ?After numerous hours of research into the physical properties, force, inertia, elasticity and extensive dyno pulls of connecting rods, we found that attention to details such as shape, type of material, size and weight are extremely important to the structural integrity of a connecting rod.
Just one more plus of the ARC billet connecting rod is that when it's used with most Briggs & Stratton crankshafts, the engine is better balanced. This is very important for the Kart classes that don't allow modifications to the crankshaft :)
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