stroke and rod length questions
07-15-2009, 09:13 PM
#1
stroke and rod length questions
i have a few things I'm trying to figure out/ learn. one how does different bore and stroke affect a motor of the same size CI? second what does piston dwell time do and how does long/short rods affect it.
07-15-2009, 11:12 PM
#2
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A motor with a big bore short stroke will be happy reving to a higher rpm then a small bore long stroke motor, but the small bore long stroke motor may feel that it has more instetanious torque then a big bore short stroke motor especially off the line.
Mind you this has never really played out that well considering the Buick, Olds argument going back to the 60's, but put a Olds 455 in a giant rv and it does just work better. You just have to take it all the way past any logical end. Likewise put a Buick 455 in a small car like a Camaro, and you have a great car even with out fancy peformance parts. Then again a Buick Electra vs a Olds 98 there not much difference at the end of the 1/4. It will come down to who has the better running motor with the better parts.
A short rod length like the Ford 302 vs the comparabley long rod of the Chevy 302, and you can almost feel the Ford motor being snappier when you hit the throtle. In this case especially above 4000 rpm. A long rod motor will live longer "becouse of less piston rock", and generaly feel more torquey at a rpm point then a short rod motor.
I used to build lots of hot street motors from 22-28, and experimented with all kinds of stuff. Especially factory parts that I pushed past there limits, and turned into something to be proud of. But everything I described above was always seat of the pants, and what I noticed when I trolled the junk yards. Except that long rod motors live longer. Given an equal amount of motors Chevys 302 if built in a pedestrain way will generally outlast Ford 302's becouse of the reduction of piston rock.
I think its fair to say that unless to push something to the limit like a Olds 455 vs a Buick 455 you'll never get to where they technically are better. Put them in equal cars and they perform about the same 1/4 mile wise. Put them in a 15,000 pound motor home that is a rolling box, and you clearly will see the Olds 455 performs better. Like wise the Buick 455 can rev quite high on a factory crank 6000+ rpm, and generally gets great gas mileage for a big block becouse of its design.
Car Craft a few years ago built two BBC's of the same cubic inches but with different bore/stroke ratios, and the dyno proved little. To be fair they used some of the best heads and cams of the day, and niether was a restiction to output. So that will undoubtedly skew the results. I think if the did the same thing with stock heads and cams they could of seen some results, but the true test would be what is the vacome being pulled on the carb for the long stroke. That is ultimately what will give a motor like the Olds 455 the advantage off the line compared to a Buick 455.
Mind you this has never really played out that well considering the Buick, Olds argument going back to the 60's, but put a Olds 455 in a giant rv and it does just work better. You just have to take it all the way past any logical end. Likewise put a Buick 455 in a small car like a Camaro, and you have a great car even with out fancy peformance parts. Then again a Buick Electra vs a Olds 98 there not much difference at the end of the 1/4. It will come down to who has the better running motor with the better parts.
A short rod length like the Ford 302 vs the comparabley long rod of the Chevy 302, and you can almost feel the Ford motor being snappier when you hit the throtle. In this case especially above 4000 rpm. A long rod motor will live longer "becouse of less piston rock", and generaly feel more torquey at a rpm point then a short rod motor.
I used to build lots of hot street motors from 22-28, and experimented with all kinds of stuff. Especially factory parts that I pushed past there limits, and turned into something to be proud of. But everything I described above was always seat of the pants, and what I noticed when I trolled the junk yards. Except that long rod motors live longer. Given an equal amount of motors Chevys 302 if built in a pedestrain way will generally outlast Ford 302's becouse of the reduction of piston rock.
I think its fair to say that unless to push something to the limit like a Olds 455 vs a Buick 455 you'll never get to where they technically are better. Put them in equal cars and they perform about the same 1/4 mile wise. Put them in a 15,000 pound motor home that is a rolling box, and you clearly will see the Olds 455 performs better. Like wise the Buick 455 can rev quite high on a factory crank 6000+ rpm, and generally gets great gas mileage for a big block becouse of its design.
Car Craft a few years ago built two BBC's of the same cubic inches but with different bore/stroke ratios, and the dyno proved little. To be fair they used some of the best heads and cams of the day, and niether was a restiction to output. So that will undoubtedly skew the results. I think if the did the same thing with stock heads and cams they could of seen some results, but the true test would be what is the vacome being pulled on the carb for the long stroke. That is ultimately what will give a motor like the Olds 455 the advantage off the line compared to a Buick 455.
07-16-2009, 11:12 AM
#5
A motor with a big bore short stroke will be happy reving to a higher rpm then a small bore long stroke motor, but the small bore long stroke motor may feel that it has more instetanious torque then a big bore short stroke motor especially off the line.
Mind you this has never really played out that well considering the Buick, Olds argument going back to the 60's, but put a Olds 455 in a giant rv and it does just work better. You just have to take it all the way past any logical end. Likewise put a Buick 455 in a small car like a Camaro, and you have a great car even with out fancy peformance parts. Then again a Buick Electra vs a Olds 98 there not much difference at the end of the 1/4. It will come down to who has the better running motor with the better parts.
A short rod length like the Ford 302 vs the comparabley long rod of the Chevy 302, and you can almost feel the Ford motor being snappier when you hit the throtle. In this case especially above 4000 rpm. A long rod motor will live longer "becouse of less piston rock", and generaly feel more torquey at a rpm point then a short rod motor.
I used to build lots of hot street motors from 22-28, and experimented with all kinds of stuff. Especially factory parts that I pushed past there limits, and turned into something to be proud of. But everything I described above was always seat of the pants, and what I noticed when I trolled the junk yards. Except that long rod motors live longer. Given an equal amount of motors Chevys 302 if built in a pedestrain way will generally outlast Ford 302's becouse of the reduction of piston rock.
I think its fair to say that unless to push something to the limit like a Olds 455 vs a Buick 455 you'll never get to where they technically are better. Put them in equal cars and they perform about the same 1/4 mile wise. Put them in a 15,000 pound motor home that is a rolling box, and you clearly will see the Olds 455 performs better. Like wise the Buick 455 can rev quite high on a factory crank 6000+ rpm, and generally gets great gas mileage for a big block becouse of its design.
Car Craft a few years ago built two BBC's of the same cubic inches but with different bore/stroke ratios, and the dyno proved little. To be fair they used some of the best heads and cams of the day, and niether was a restiction to output. So that will undoubtedly skew the results. I think if the did the same thing with stock heads and cams they could of seen some results, but the true test would be what is the vacome being pulled on the carb for the long stroke. That is ultimately what will give a motor like the Olds 455 the advantage off the line compared to a Buick 455.
Mind you this has never really played out that well considering the Buick, Olds argument going back to the 60's, but put a Olds 455 in a giant rv and it does just work better. You just have to take it all the way past any logical end. Likewise put a Buick 455 in a small car like a Camaro, and you have a great car even with out fancy peformance parts. Then again a Buick Electra vs a Olds 98 there not much difference at the end of the 1/4. It will come down to who has the better running motor with the better parts.
A short rod length like the Ford 302 vs the comparabley long rod of the Chevy 302, and you can almost feel the Ford motor being snappier when you hit the throtle. In this case especially above 4000 rpm. A long rod motor will live longer "becouse of less piston rock", and generaly feel more torquey at a rpm point then a short rod motor.
I used to build lots of hot street motors from 22-28, and experimented with all kinds of stuff. Especially factory parts that I pushed past there limits, and turned into something to be proud of. But everything I described above was always seat of the pants, and what I noticed when I trolled the junk yards. Except that long rod motors live longer. Given an equal amount of motors Chevys 302 if built in a pedestrain way will generally outlast Ford 302's becouse of the reduction of piston rock.
I think its fair to say that unless to push something to the limit like a Olds 455 vs a Buick 455 you'll never get to where they technically are better. Put them in equal cars and they perform about the same 1/4 mile wise. Put them in a 15,000 pound motor home that is a rolling box, and you clearly will see the Olds 455 performs better. Like wise the Buick 455 can rev quite high on a factory crank 6000+ rpm, and generally gets great gas mileage for a big block becouse of its design.
Car Craft a few years ago built two BBC's of the same cubic inches but with different bore/stroke ratios, and the dyno proved little. To be fair they used some of the best heads and cams of the day, and niether was a restiction to output. So that will undoubtedly skew the results. I think if the did the same thing with stock heads and cams they could of seen some results, but the true test would be what is the vacome being pulled on the carb for the long stroke. That is ultimately what will give a motor like the Olds 455 the advantage off the line compared to a Buick 455.
07-16-2009, 10:05 PM
#7
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I have two thought about a 4.8 crank in a 6.0 block, but I was out looking for parts for a future build. And came across a couple of low mileage 6.0's with less the 30K miles for about $1500+ depending on the accessories you want, and you can't beat that with a dead horse.
So if I keep my truck long enough becouse of children I will probily do the basic 6.0 swap, but I despartly need some gears first. My rims and tires killed any practical use of 4th gear for driving and mpg's..
So if I keep my truck long enough becouse of children I will probily do the basic 6.0 swap, but I despartly need some gears first. My rims and tires killed any practical use of 4th gear for driving and mpg's..
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07-20-2009, 11:34 AM
#9
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I heard you can use a 6.0 block and pistons with the 4.8 rod which is how they compensated for the shorter stroke. As 4.8 pistons and 5.3's are they same the rod is what compensates for the difference.
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