[Steve C.]

I found these tidbits years ago that might provide some interest...

First, increasing the stroke greatly changes the angular relationship of the rod and cylinder. The rod is at a much sharper angle in relationship to the angle of the cylinder, generating enormous amounts of friction between the piston rings and cylinder walls, causing both friction and ring sealing problems. At lower RPM ranges this friction is easily overcome, but as RPMs increase, the friction often reaches intolerable levels. Most strokers have horrible fuel economy, and it's not just because of the extra performance equipment.

The second factor is directly related to the first. The increased rod.cylinder angularity also increases the piston velocity. That is, the piston will move up or down within the cylinder bore at a far greater rate of speed than a shorter stroke engine. Also, the piston "dwell time", that is the amount of time that the piston remains at TDC, is decreased. These factors have the effect of making the engine extremely sensitive to detonation, as well as making the engine sensitive to under-flowing heads. To illustrate, grab a bicycle tire pump sometime, and first try to operate it as quickly as you can. Then, slow down the pumping action. You will notice that it is far easier to move the pump handle slowly. Your engine is no different- slow down the piston, and the engine has less work to do. Again this condition is aggravated by high RPM conditions. The important thing to remember is that no matter how fast or slow the piston goes, the engine moves exactly the same amount of gasses during the same number of crank degrees. This situation could be improved by using the longest rods possible, which would increase the rod ratio and somewhat alleviate the angularity problem.

Here's an interesting one from Car Craft.....

"Think about rpm for a minute. That's revolutions per minute, referring to an engine's crankshaft speed. At 6,000 rpm, that's 100 revolutions per second, or one revolution every hundredth of a second. If you've got a 4.250-inch stroke, each piston is traveling 70,8333 feet per second at 6,000 rpm, which is about 48 mph, and it has to change direction twice every hundredth of a second. And you wonder why stuff breaks."

With a 4.500-inch stroke a piston will be traveling 75 feet per second at 6000 rpm.


.

[Stan Weiss]

Originally Posted by Steve C.

I found these tidbits years ago that might provide some interest...

First, increasing the stroke greatly changes the angular relationship of the rod and cylinder. The rod is at a much sharper angle in relationship to the angle of the cylinder, generating enormous amounts of friction between the piston rings and cylinder walls, causing both friction and ring sealing problems. At lower RPM ranges this friction is easily overcome, but as RPMs increase, the friction often reaches intolerable levels. Most strokers have horrible fuel economy, and it's not just because of the extra performance equipment.

The second factor is directly related to the first. The increased rod.cylinder angularity also increases the piston velocity. That is, the piston will move up or down within the cylinder bore at a far greater rate of speed than a shorter stroke engine. Also, the piston "dwell time", that is the amount of time that the piston remains at TDC, is decreased. These factors have the effect of making the engine extremely sensitive to detonation, as well as making the engine sensitive to under-flowing heads. To illustrate, grab a bicycle tire pump sometime, and first try to operate it as quickly as you can. Then, slow down the pumping action. You will notice that it is far easier to move the pump handle slowly. Your engine is no different- slow down the piston, and the engine has less work to do. Again this condition is aggravated by high RPM conditions. The important thing to remember is that no matter how fast or slow the piston goes, the engine moves exactly the same amount of gasses during the same number of crank degrees. This situation could be improved by using the longest rods possible, which would increase the rod ratio and somewhat alleviate the angularity problem.

Here's an interesting one from Car Craft.....

"Think about rpm for a minute. That's revolutions per minute, referring to an engine's crankshaft speed. At 6,000 rpm, that's 100 revolutions per second, or one revolution every hundredth of a second. If you've got a 4.250-inch stroke, each piston is traveling 70,8333 feet per second at 6,000 rpm, which is about 48 mph, and it has to change direction twice every hundredth of a second. And you wonder why stuff breaks."

With a 4.500-inch stroke a piston will be traveling 75 feet per second at 6000 rpm.


.

Steve,
Yes, increasing the stroke does increase rod angle. That is why if possible you should also increase rod length.

Stan

[srmmmm]

Originally Posted by Steve C.

I found these tidbits years ago that might provide some interest...

First, increasing the stroke greatly changes the angular relationship of the rod and cylinder. The rod is at a much sharper angle in relationship to the angle of the cylinder, generating enormous amounts of friction between the piston rings and cylinder walls, causing both friction and ring sealing problems. At lower RPM ranges this friction is easily overcome, but as RPMs increase, the friction often reaches intolerable levels. Most strokers have horrible fuel economy, and it's not just because of the extra performance equipment.

The second factor is directly related to the first. The increased rod.cylinder angularity also increases the piston velocity. That is, the piston will move up or down within the cylinder bore at a far greater rate of speed than a shorter stroke engine. Also, the piston "dwell time", that is the amount of time that the piston remains at TDC, is decreased. These factors have the effect of making the engine extremely sensitive to detonation, as well as making the engine sensitive to under-flowing heads. To illustrate, grab a bicycle tire pump sometime, and first try to operate it as quickly as you can. Then, slow down the pumping action. You will notice that it is far easier to move the pump handle slowly. Your engine is no different- slow down the piston, and the engine has less work to do. Again this condition is aggravated by high RPM conditions. The important thing to remember is that no matter how fast or slow the piston goes, the engine moves exactly the same amount of gasses during the same number of crank degrees. This situation could be improved by using the longest rods possible, which would increase the rod ratio and somewhat alleviate the angularity problem.

Here's an interesting one from Car Craft.....

"Think about rpm for a minute. That's revolutions per minute, referring to an engine's crankshaft speed. At 6,000 rpm, that's 100 revolutions per second, or one revolution every hundredth of a second. If you've got a 4.250-inch stroke, each piston is traveling 70,8333 feet per second at 6,000 rpm, which is about 48 mph, and it has to change direction twice every hundredth of a second. And you wonder why stuff breaks."

With a 4.500-inch stroke a piston will be traveling 75 feet per second at 6000 rpm.


.

These were issues I considered before doing a 350/413 stroker with a 4.25" crank. My justification included three primary points:
1) Stroke on the 455 is almost equal at 4.21";
2) Using a 6.8" rod kept the rod to stroke ratio at 1.6;
3) The weight of the 350 piston being less than larger displacement bores.

Given those parameters and the use of Johnson reduced travel lifters, in discussions with techs at Butler Performance and my contacts within the TransAm Race Series crews, concensus was that valve float would be the RPM limiting factor. The engine had no trouble spinning to 6200 rpm on Reher Morrison's dyno.

The Childress 935HP TA engine has a 3.48" stroke with rev limiters set at 9200rpm. The 525HP TA/2 Chevrolet LS3 engine is a 3.622" stroke with rev limiters set at 6800rpm.

[Jay S]

Larry Jones’s dad has a 4.75” with an aftermarket block in his 700+HP GTO. Mostly a street build, I think BES built it.

Calvin Hill might be the other 4.75 big cid drag and drive? Not sure?

4.75 in a Pontiac not common at all.

4.5 has been fairly popular in the SD455 and the 71&72 455 HO’s at one of the local shops (Willard Machine). I think Rotella’s in Omaha have at least one, mild street builds though.