downside for extra stroke
04-28-2006, 06:52 PM
#21
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Originally Posted by Ric
Pay attention to your rod/stroke ratio. A general rule I follow is a 1.6-1.8:1, with 1.7:1 being the best of both worlds number. Higher ratios will put the torque curve higher in the rpms, combining it with hp(people argue about "torque gets you going, hp wins races"... why not have both at the same time?), along with applying the power stroke in a more downward manner which saves wear and tear on your cylinder walls. Lower ratios have more leverage on the crank, giving more low-end torque at the expense of increased wear and tear on the cylinder walls.
While max piston speed is the same given the same stroke, a longer rod accelerates the piston more slowly, effectively allowing higher rpm operation. A longer rod also "squishes" the intake charge on compression, rather than "slamming" it, which can lead to detonation, or even pre-ignition. Thus, the longer rod allows for more compression and spark advance... it's even possible with lower-octane gas.
At 1.6836002208724461623412479293208:1, the factory 3.622" stroke is close to optimum rod/stroke ratio already. A 4" stroker with 6.125" rods will have a ratio of 1.53125:1... too low for my liking, but to each his own. To be in that happy median I mentioned, you'd need a rod length of 6.8".
Personally, I'd suggest a big-bore setup... possibly a 4.125" bore LS1 with stock dimension crank. You'd wind up with a 387ci Gen III that'd be happier at 6500+ rpm, and would have torque and hp in areas where you'd be more likely to use them.
While max piston speed is the same given the same stroke, a longer rod accelerates the piston more slowly, effectively allowing higher rpm operation. A longer rod also "squishes" the intake charge on compression, rather than "slamming" it, which can lead to detonation, or even pre-ignition. Thus, the longer rod allows for more compression and spark advance... it's even possible with lower-octane gas.
At 1.6836002208724461623412479293208:1, the factory 3.622" stroke is close to optimum rod/stroke ratio already. A 4" stroker with 6.125" rods will have a ratio of 1.53125:1... too low for my liking, but to each his own. To be in that happy median I mentioned, you'd need a rod length of 6.8".
Personally, I'd suggest a big-bore setup... possibly a 4.125" bore LS1 with stock dimension crank. You'd wind up with a 387ci Gen III that'd be happier at 6500+ rpm, and would have torque and hp in areas where you'd be more likely to use them.
Yeah, ha, right, that's why everyone of the engine masters 12.5 to 1 or more pump gas motors use r/s ratios that our lower then the range you specified. The shorter rod will help you run higher compression ratios everytime as the piston accelerates after top dead center much faster which limits time for detonation to occur. Further, the r/s ratio of the ls7 is around 1.51, i'm sure multi-billion dollar gm didn't do any reseach in this area
04-28-2006, 07:20 PM
#22
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Originally Posted by Ric
Pay attention to your rod/stroke ratio. A general rule I follow is a 1.6-1.8:1, with 1.7:1 being the best of both worlds number. Higher ratios will put the torque curve higher in the rpms, combining it with hp(people argue about "torque gets you going, hp wins races"... why not have both at the same time?), along with applying the power stroke in a more downward manner which saves wear and tear on your cylinder walls. Lower ratios have more leverage on the crank, giving more low-end torque at the expense of increased wear and tear on the cylinder walls.
While max piston speed is the same given the same stroke, a longer rod accelerates the piston more slowly, effectively allowing higher rpm operation. A longer rod also "squishes" the intake charge on compression, rather than "slamming" it, which can lead to detonation, or even pre-ignition. Thus, the longer rod allows for more compression and spark advance... it's even possible with lower-octane gas.
At 1.6836002208724461623412479293208:1, the factory 3.622" stroke is close to optimum rod/stroke ratio already. A 4" stroker with 6.125" rods will have a ratio of 1.53125:1... too low for my liking, but to each his own. To be in that happy median I mentioned, you'd need a rod length of 6.8".
Personally, I'd suggest a big-bore setup... possibly a 4.125" bore LS1 with stock dimension crank. You'd wind up with a 387ci Gen III that'd be happier at 6500+ rpm, and would have torque and hp in areas where you'd be more likely to use them.
While max piston speed is the same given the same stroke, a longer rod accelerates the piston more slowly, effectively allowing higher rpm operation. A longer rod also "squishes" the intake charge on compression, rather than "slamming" it, which can lead to detonation, or even pre-ignition. Thus, the longer rod allows for more compression and spark advance... it's even possible with lower-octane gas.
At 1.6836002208724461623412479293208:1, the factory 3.622" stroke is close to optimum rod/stroke ratio already. A 4" stroker with 6.125" rods will have a ratio of 1.53125:1... too low for my liking, but to each his own. To be in that happy median I mentioned, you'd need a rod length of 6.8".
Personally, I'd suggest a big-bore setup... possibly a 4.125" bore LS1 with stock dimension crank. You'd wind up with a 387ci Gen III that'd be happier at 6500+ rpm, and would have torque and hp in areas where you'd be more likely to use them.
One well known engine builder made a comment I liked:
"The optimum rod ratio for a V8 is 8 rods to 1 crankshaft."
04-29-2006, 02:17 AM
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Yeah... somebody beat you to the punch. Truth is, there's unlimited ways to get the same end result, and I could care less what some hard-line race mechanic has to say about my way of thinking. Maybe someone could show me something that I don't know of, and I'll change my mind?
And it also comes up much faster as well, creating hot spots in the combustion chamber which can lead to detonation... let's just agree to disagree on this one aiight?
I'd hope they did their homework on the LS7, considering the Z06's $65,000+ price tag. Stronger alloy metals help keep such engines reliable... they'd be even more so with longer rods, but then cars nowadays are made to wear out. Wouldn't want a customer to NOT have to buy another car, would they?
The shorter rod will help you run higher compression ratios everytime as the piston accelerates after top dead center much faster which limits time for detonation to occur.
Further, the r/s ratio of the ls7 is around 1.51, i'm sure multi-billion dollar gm didn't do any reseach in this area
04-29-2006, 08:40 AM
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Originally Posted by Ric
Yeah... somebody beat you to the punch. Truth is, there's unlimited ways to get the same end result, and I could care less what some hard-line race mechanic has to say about my way of thinking. Maybe someone could show me something that I don't know of, and I'll change my mind?
And it also comes up much faster as well, creating hot spots in the combustion chamber which can lead to detonation... let's just agree to disagree on this one aiight?
I'd hope they did their homework on the LS7, considering the Z06's $65,000+ price tag. Stronger alloy metals help keep such engines reliable... they'd be even more so with longer rods, but then cars nowadays are made to wear out. Wouldn't want a customer to NOT have to buy another car, would they?
And it also comes up much faster as well, creating hot spots in the combustion chamber which can lead to detonation... let's just agree to disagree on this one aiight?
I'd hope they did their homework on the LS7, considering the Z06's $65,000+ price tag. Stronger alloy metals help keep such engines reliable... they'd be even more so with longer rods, but then cars nowadays are made to wear out. Wouldn't want a customer to NOT have to buy another car, would they?
04-29-2006, 10:23 AM
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You know? That does make more sense to me, now. I've wondered about the quench area and how rod length would affect hot spots. I still have to believe that, with almost no piston skirts, short rod setups are still a bad brew as far as longevity goes... not questioning the LS1's reliability, believe me. But I do think longer rods would have made it possible for it to run almost forever. Or it could just be that it's Saturday morning, I've got a good night's sleep for once this week, and things are a little clearer to me right now.
I never intended to inply that the ol' 454 would outlast the LS7... if it was a better engine, I believe GM wouldn't have dropped it. Also, to keep peace and harmony here
... don't think I was referring to you as some hard-line race mechanic, aiight? There are plenty of them around here that try to tell me they know "that new 350 motor" inside and out, so I just nod my head and walk off in the middle of their spurt of "wisdom".
Sorry to hi-jack the thread, all. Just realized that.
I never intended to inply that the ol' 454 would outlast the LS7... if it was a better engine, I believe GM wouldn't have dropped it. Also, to keep peace and harmony here
... don't think I was referring to you as some hard-line race mechanic, aiight? There are plenty of them around here that try to tell me they know "that new 350 motor" inside and out, so I just nod my head and walk off in the middle of their spurt of "wisdom".Sorry to hi-jack the thread, all. Just realized that.
04-29-2006, 11:05 AM
#26
I do not know about you guys, but I always like to try and pull my engine down every winter. I will inspect and repaire it as needed. I come from the school of thought that the longer the rod, the better, to a point. You don't want to have a 5lb rod in the thing.
04-29-2006, 11:09 AM
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Originally Posted by Ric
You know? That does make more sense to me, now. I've wondered about the quench area and how rod length would affect hot spots. I still have to believe that, with almost no piston skirts, short rod setups are still a bad brew as far as longevity goes... not questioning the LS1's reliability, believe me. But I do think longer rods would have made it possible for it to run almost forever. Or it could just be that it's Saturday morning, I've got a good night's sleep for once this week, and things are a little clearer to me right now.
I never intended to inply that the ol' 454 would outlast the LS7... if it was a better engine, I believe GM wouldn't have dropped it. Also, to keep peace and harmony here ... don't think I was referring to you as some hard-line race mechanic, aiight? There are plenty of them around here that try to tell me they know "that new 350 motor" inside and out, so I just nod my head and walk off in the middle of their spurt of "wisdom".
Sorry to hi-jack the thread, all. Just realized that.
I never intended to inply that the ol' 454 would outlast the LS7... if it was a better engine, I believe GM wouldn't have dropped it. Also, to keep peace and harmony here
... don't think I was referring to you as some hard-line race mechanic, aiight? There are plenty of them around here that try to tell me they know "that new 350 motor" inside and out, so I just nod my head and walk off in the middle of their spurt of "wisdom".Sorry to hi-jack the thread, all. Just realized that.
04-29-2006, 02:58 PM
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Cool beans, bro.
And Tex, you're right... 5-lb rods would suck.
One of the downsides to my Mopar is its 6.768" rods. Boat anchors. If I could only afford a set of BME alumnumnum rods.
And Tex, you're right... 5-lb rods would suck.
One of the downsides to my Mopar is its 6.768" rods. Boat anchors. If I could only afford a set of BME alumnumnum rods.
04-29-2006, 05:12 PM
#29
Forget the aluminuim ones bro. We just finished a 440 mopar that had 6pack rods in it. Man those things are huge and heavy! He even had a set of TRW forged pistons on them! I am suprised the thing would even rev up. We put some light weight Ross Pistons with some Scat Rods in it. I do not remember the weight loss do to this, but when the assemble was ballances, the ballencer had to make some serious cuts on the crank do to the extreme weight loss. Very nice peice now.
04-29-2006, 05:45 PM
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The trend with pump gas motors has once again shifted back to the smaller bore/longer stroke method. Big bore will, more often than not, make more power than big stroke. But the crappy gas we have nowadays is dictating the switch back to the strokers. All that bore may be great for improving the flow of the air/fuel mixture into the cylinder but it sucks when it comes to keeping detonation at bay. Look at the buildups of the masters' engines. Lotsa stroke and smaller bores.
If your run race gas then stay with the big bore method. You'll make more power and have less wear and tear on the motor.
If your run race gas then stay with the big bore method. You'll make more power and have less wear and tear on the motor.
04-30-2006, 12:25 PM
#32
FormerVendor
It's a very well known fact with the SAE that shorter rod ratios REDUCE detonation sensitivity. The reason people ran such short rods and long strokes in engine masters among other reasons was that this style of engine is more efficient and has less detonation sensitivity not more!
Extreme long term wear might be slightly more on a steady state highly loaded engine like an 18 wheeler but the rod ratio changes people are talking about don't seem to add up to squat in reality. I am sure Chevy's new bad rod ratio LS7 will last just as long as ever.
Extreme long term wear might be slightly more on a steady state highly loaded engine like an 18 wheeler but the rod ratio changes people are talking about don't seem to add up to squat in reality. I am sure Chevy's new bad rod ratio LS7 will last just as long as ever.
04-30-2006, 12:33 PM
#33
FormerVendor
Also destroking an engine and then running it in a higher rpm band to make the power back always results in less engine life not more even though you have made the rod stroke ratio "better." Anotherwords with any given bore more stroke will give you the same or more power at a lower rpm and this is why people use and sell these cranks.
Ever wonder why no one sells a 3.000 LS1 crank or why Eagle can't sell many of the chevy or Ford cranks in that range? NO one on their right mind will buy them since people want power not rpm of some arbitrary level. What a crank does is increase the piston speed and throughput and therefore the potential power at any given rpm. Why limit the airflow of the engine?
A bigger crank is essentially a power adder and that's the reason displacement is always limited in racing. Large engines are faster than small engines heads up whether people like it or not. Also with the heads available in this day and age the bigger stuff will still pull almost as high anyway. In fact the little stuff can't spin high enough to use decent heads nowadays.
Ever wonder why no one sells a 3.000 LS1 crank or why Eagle can't sell many of the chevy or Ford cranks in that range? NO one on their right mind will buy them since people want power not rpm of some arbitrary level. What a crank does is increase the piston speed and throughput and therefore the potential power at any given rpm. Why limit the airflow of the engine?
A bigger crank is essentially a power adder and that's the reason displacement is always limited in racing. Large engines are faster than small engines heads up whether people like it or not. Also with the heads available in this day and age the bigger stuff will still pull almost as high anyway. In fact the little stuff can't spin high enough to use decent heads nowadays.
04-30-2006, 12:45 PM
#34
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Originally Posted by Ric
Personally, I'd suggest a big-bore setup... possibly a 4.125" bore LS1 with stock dimension crank. You'd wind up with a 387ci Gen III that'd be happier at 6500+ rpm, and would have torque and hp in areas where you'd be more likely to use them.
04-30-2006, 01:42 PM
#35
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Originally Posted by niphilli
Thats the motor I wish GM would build. Basically an LS7 with a 3.62 stroke
The new "428" (LS7) would be my preference.How about an LS7 with a 3.27 (83mm) stroke from the 4.8L LR4 engine for ~350 cubes? Oh, maybe they already did that for the first CTSV-R.
How about an LS1 with basically stock bore and a ~3.18 stroke for a 5.0L? Think Daytona Prototype. Even with a mandated 7100 rev limit, that's only about 3760 ft/min. piston speed. To use a 3.00 crank they'd have to go past the max alowed bore or sacrifice about 17 cubes and maybe 25+ hp. They could go smaller bore and more stroke, but I don't recall anyone doing that.
04-30-2006, 03:09 PM
#37
More bore > More stroke, IMO.
As mentioned, more stroke moves engine parts faster, and thus creates more stress on the engine's internals. Increasing stroke is usually cheaper than increasing bore. Increasing bore means you have to take the block out of the car and have it machined to exact tolerances, or get it sleeved, or just get a new block. When increasing stroke, all you basically need is a new crank.
As mentioned, more stroke moves engine parts faster, and thus creates more stress on the engine's internals. Increasing stroke is usually cheaper than increasing bore. Increasing bore means you have to take the block out of the car and have it machined to exact tolerances, or get it sleeved, or just get a new block. When increasing stroke, all you basically need is a new crank.
04-30-2006, 05:36 PM
#38
My 2¢.
If breathing is your limit, the bore limit is the size of the valves you can fit in. This will dominate where there are no rev or intake restrictions: F1, NASCAR, etc.
Most current engines seem to be in the 87+/-4mm range. I believe, and have no evidence to substantiate, that this reflects the shape of the combustion chamber for optimal combustion. While a high flow, a dominate topic on LS1Tech, can help you have mixture to burn, how well and when you burn it is also important. A well known author frequently comments on engines that consume less air after a modification but produce more power.
I'm not clear if how much the additional movement near TDC improves detonation tolerance. There is theory. Is there also empirical evidence?
A higher rod/stroke ratio will reduce side loading on a piston. As engine speeds and piston thrust goes up, this can be increasingly important. How important? Better minds than mine will have to comment. Note that Hondas and a host of other modern cars have short rods and long strokes. And there are commonly modifed by lengthening the stroke. 3.7" strokes with 5.4" rods at 9-10k rpm and 100-200 hp/cylinder. Add Supras (5.59" rod) in that group.
If breathing is your limit, the bore limit is the size of the valves you can fit in. This will dominate where there are no rev or intake restrictions: F1, NASCAR, etc.
Most current engines seem to be in the 87+/-4mm range. I believe, and have no evidence to substantiate, that this reflects the shape of the combustion chamber for optimal combustion. While a high flow, a dominate topic on LS1Tech, can help you have mixture to burn, how well and when you burn it is also important. A well known author frequently comments on engines that consume less air after a modification but produce more power.
I'm not clear if how much the additional movement near TDC improves detonation tolerance. There is theory. Is there also empirical evidence?
A higher rod/stroke ratio will reduce side loading on a piston. As engine speeds and piston thrust goes up, this can be increasingly important. How important? Better minds than mine will have to comment. Note that Hondas and a host of other modern cars have short rods and long strokes. And there are commonly modifed by lengthening the stroke. 3.7" strokes with 5.4" rods at 9-10k rpm and 100-200 hp/cylinder. Add Supras (5.59" rod) in that group.
04-30-2006, 05:48 PM
#39
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Personally, I'd rather have a bigger bore and a smaller stroke.
Shorter stroke means the pistons have less distance to travel to complete a cycle, yielding higher RPM's. Obviously, with higher RPM's you are going to have higher HP.
This is why I believe that Turbo Supras can push out such insance HP with such smaller engines. Their strokes are so much shorter than LSx engines, so they can achieve higher RPM's and then throw on the fact that they are bullet-proof = a lot of HP.
Shorter stroke means the pistons have less distance to travel to complete a cycle, yielding higher RPM's. Obviously, with higher RPM's you are going to have higher HP.
This is why I believe that Turbo Supras can push out such insance HP with such smaller engines. Their strokes are so much shorter than LSx engines, so they can achieve higher RPM's and then throw on the fact that they are bullet-proof = a lot of HP.
04-30-2006, 10:53 PM
#40
FormerVendor
Originally Posted by Louie83
Personally, I'd rather have a bigger bore and a smaller stroke.
Shorter stroke means the pistons have less distance to travel to complete a cycle, yielding higher RPM's. Obviously, with higher RPM's you are going to have higher HP.
This is why I believe that Turbo Supras can push out such insance HP with such smaller engines. Their strokes are so much shorter than LSx engines, so they can achieve higher RPM's and then throw on the fact that they are bullet-proof = a lot of HP.
Shorter stroke means the pistons have less distance to travel to complete a cycle, yielding higher RPM's. Obviously, with higher RPM's you are going to have higher HP.
This is why I believe that Turbo Supras can push out such insance HP with such smaller engines. Their strokes are so much shorter than LSx engines, so they can achieve higher RPM's and then throw on the fact that they are bullet-proof = a lot of HP.
You don't have more power when you make an engine smaller and then try and turn it more rpm. That's why we have displacement limits in racing. The bigger engines are always faster whether they turn lower rpm or the same.
Maximum displacement limits are in effect in ALL forms of racing. There is no racing where you can run as large an engine as you might want but yet not less than some lower limit on displacement. With the thousands of santioning bodies out there and tons of smart people this should give almost anyone a clue.
Now as far as the Supra well they are a joke when you look at them in anything other than turbo form. You put a big turbo on a big stroke american engine and that Supra is history.