Engine redline...
Vtec 4 Life
10-03-2006, 09:58 AM
Can someone tell me what will happen to the redline of an engine if the size of the cylinder bore is increased. I know increasing the stroke lowers the redline, but nothing about what increasing the bore does. Any help will be highly appreciated. Thank you for your time.
TheSilentChamber
10-03-2006, 01:50 PM
534BC
10-04-2006, 11:35 AM
It may depend on how much of an increase. Lots of oversized piston weights are matched by the manufacturer for balance and the redline would not change. This is for stock type oversizes of 1/16 " or less.
curtis73
10-04-2006, 01:56 PM
Well there are two "redlines" to consider; there's the one where your engine makes peak power and the one where your engine may mechanically fail.
Lets say for instance your engine makes peak power around 6000. That would be the redline that the manufacturer would put on the tach. But (I'm using your VTEC as an example) that engine would physically hold together till more like 7000.
Increasing bore size may reduce the 7000 by a tiny bit if the pistons were heavier AND if their weight was a limiting factor in its mechanical ability. But careful shopping could yield pistons that were lighter and the mechanical redline wouldn't change. Either way, there's no reason to rev an enging up to 7000 if your power peaks at 6000.
Increasing bore will increase displacement and shift the power peak down a little, but not much. Even in the case of large V8s the additional displacement isn't enough to change where you'd shift for max acceleration, so the published redline on the tach will stay true if all you're doing is the pistons.
Lets say for instance your engine makes peak power around 6000. That would be the redline that the manufacturer would put on the tach. But (I'm using your VTEC as an example) that engine would physically hold together till more like 7000.
Increasing bore size may reduce the 7000 by a tiny bit if the pistons were heavier AND if their weight was a limiting factor in its mechanical ability. But careful shopping could yield pistons that were lighter and the mechanical redline wouldn't change. Either way, there's no reason to rev an enging up to 7000 if your power peaks at 6000.
Increasing bore will increase displacement and shift the power peak down a little, but not much. Even in the case of large V8s the additional displacement isn't enough to change where you'd shift for max acceleration, so the published redline on the tach will stay true if all you're doing is the pistons.
Vtec 4 Life
10-04-2006, 02:05 PM
So how does increasing the bore affect the powerband?
534BC
10-04-2006, 02:08 PM
Increasing the bore SHOULD increase the power throughout the complete range.
But really, How much of an increase in bore are you talking about? A compression change would be more significant than a redline change with a bigger bore.
But really, How much of an increase in bore are you talking about? A compression change would be more significant than a redline change with a bigger bore.
SR Racing
11-08-2006, 11:03 PM
Either way, there's no reason to rev an enging up to 7000 if your power peaks at 6000.
Increasing bore will increase displacement and shift the power peak down a little, but not much. Even in the case of large V8s the additional displacement isn't enough to change where you'd shift for max acceleration, so the published redline on the tach will stay true if all you're doing is the pistons.
Not on the street of course, but for performance, you ALWAYS go past the peak HP RPM. That is some of the valuable info you get from a dyno run..
Lets assume that your HP is the following:
4700 RPM = 270
4800 RPM = 280
4900 RPM = 290
5000 RPM = 300
5100 RPM = 310
5200 RPM = 320
5300 RPM = 330
5400 RPM = 340
5500 RPM = 350
5600 RPM = 360
5700 RPM = 350
5800 RPM = 345
5900 RPM = 340
Now assume that when you shift from 4th to 5th the engine RPM is 1000 RPM less.
If you shifted at 5600 RPM, you would be wasting the bulk of the "HP under the curve". In the example above you would shift at 5800 or even 5900 RPM.
After a dyno run, here, we always calculate the gear ranges and then determine maximum utilization of HP under the curve for the shift point. It is ALWAYS beyond the peak HP RPM point. And, unless significant mods have been done to the engine, it is almost always below the manufactures "red line" on the tach.
The "red line" the manufacturer has on the tach is independent of peak HP. It is just a recommended "do not exceed" RPM.
The balance on most modern performance engines will allow exceeding the tach "red line" RPM in most any case. However, unless significant breathing mods have been made it isn't required and shouldn't be done.
Jim
Increasing bore will increase displacement and shift the power peak down a little, but not much. Even in the case of large V8s the additional displacement isn't enough to change where you'd shift for max acceleration, so the published redline on the tach will stay true if all you're doing is the pistons.
Not on the street of course, but for performance, you ALWAYS go past the peak HP RPM. That is some of the valuable info you get from a dyno run..
Lets assume that your HP is the following:
4700 RPM = 270
4800 RPM = 280
4900 RPM = 290
5000 RPM = 300
5100 RPM = 310
5200 RPM = 320
5300 RPM = 330
5400 RPM = 340
5500 RPM = 350
5600 RPM = 360
5700 RPM = 350
5800 RPM = 345
5900 RPM = 340
Now assume that when you shift from 4th to 5th the engine RPM is 1000 RPM less.
If you shifted at 5600 RPM, you would be wasting the bulk of the "HP under the curve". In the example above you would shift at 5800 or even 5900 RPM.
After a dyno run, here, we always calculate the gear ranges and then determine maximum utilization of HP under the curve for the shift point. It is ALWAYS beyond the peak HP RPM point. And, unless significant mods have been done to the engine, it is almost always below the manufactures "red line" on the tach.
The "red line" the manufacturer has on the tach is independent of peak HP. It is just a recommended "do not exceed" RPM.
The balance on most modern performance engines will allow exceeding the tach "red line" RPM in most any case. However, unless significant breathing mods have been made it isn't required and shouldn't be done.
Jim
2turboimports
11-08-2006, 11:57 PM
The transmission also needs to be taken into consideration since the accel gears spin way faster than the engine.
MishaA
11-09-2006, 12:11 AM
The transmission also needs to be taken into consideration since the accel gears spin way faster than the engine.
What do you mean by accel gears?
What do you mean by accel gears?
UncleBob
11-10-2006, 12:07 AM
What do you mean by accel gears?
what he's saying is the tranny causes the gearing ratios to change. It seems like an obtuse indirect message, but it turns out, thats what trannies are designed to do, change the final gear ratio.
Sorry. I thought that was funny.
what he's saying is the tranny causes the gearing ratios to change. It seems like an obtuse indirect message, but it turns out, thats what trannies are designed to do, change the final gear ratio.
Sorry. I thought that was funny.
GreyGoose006
11-10-2006, 02:14 AM
Now assume that when you shift from 4th to 5th the engine RPM is 1000 RPM less.
If you shifted at 5600 RPM, you would be wasting the bulk of the "HP under the curve". In the example above you would shift at 5800 or even 5900 RPM.
After a dyno run, here, we always calculate the gear ranges and then determine maximum utilization of HP under the curve for the shift point. It is ALWAYS beyond the peak HP RPM point. And, unless significant mods have been done to the engine, it is almost always below the manufactures "red line" on the tach.
The "red line" the manufacturer has on the tach is independent of peak HP. It is just a recommended "do not exceed" RPM.
good, except that most city driving happens at partial throttle, where the curve is even more different (for lack of a better word)
if you are tuning for the street, look for mods that add torque at low RPMs and shift the powerband down in RPM.
if tuning for the track, it is OK to sacrifice low end power because the only time you will use it is at the starting line.
If you shifted at 5600 RPM, you would be wasting the bulk of the "HP under the curve". In the example above you would shift at 5800 or even 5900 RPM.
After a dyno run, here, we always calculate the gear ranges and then determine maximum utilization of HP under the curve for the shift point. It is ALWAYS beyond the peak HP RPM point. And, unless significant mods have been done to the engine, it is almost always below the manufactures "red line" on the tach.
The "red line" the manufacturer has on the tach is independent of peak HP. It is just a recommended "do not exceed" RPM.
good, except that most city driving happens at partial throttle, where the curve is even more different (for lack of a better word)
if you are tuning for the street, look for mods that add torque at low RPMs and shift the powerband down in RPM.
if tuning for the track, it is OK to sacrifice low end power because the only time you will use it is at the starting line.
UncleBob
11-10-2006, 02:22 AM
that is not what he's suggesting grey. What he's saying is, to put it simply, the highest average HP per RPM range for a gear, will cause the highest acceleration for a given vehicle.
If city driving = highest HP at lowest RPM possible, then everyone would be driving diesels.
There is a wide variety of vehicles and engines to chose from on the market. I don't like low-reving engines personally. There is disadvantages with any configuration. Low reving = low HP/L. Can't have your cake and eat it too.
If city driving = highest HP at lowest RPM possible, then everyone would be driving diesels.
There is a wide variety of vehicles and engines to chose from on the market. I don't like low-reving engines personally. There is disadvantages with any configuration. Low reving = low HP/L. Can't have your cake and eat it too.
sracing
11-12-2006, 08:35 PM
"The curve is different"? There is no real curve for a part throttle HP run. It's a non-sensical point.
And since the thread was regarding "red-line" or performance shift points, city driving is not at issue. And, I clearly pointed out that this was for performance.
If you are tuning for the street, strip or road course, or oval. You tune for HP at the RPM you will be operating at. This "tuning" is building the engine, gear ratios and tire sizes to keep the engine in the max HP RPM as long as you can. If you are tuning for economy, none of this thread makes much sense.:grinyes:
good, except that most city driving happens at partial throttle, where the curve is even more different (for lack of a better word)
if you are tuning for the street, look for mods that add torque at low RPMs and shift the powerband down in RPM.
if tuning for the track, it is OK to sacrifice low end power because the only time you will use it is at the starting line.
And since the thread was regarding "red-line" or performance shift points, city driving is not at issue. And, I clearly pointed out that this was for performance.
If you are tuning for the street, strip or road course, or oval. You tune for HP at the RPM you will be operating at. This "tuning" is building the engine, gear ratios and tire sizes to keep the engine in the max HP RPM as long as you can. If you are tuning for economy, none of this thread makes much sense.:grinyes:
good, except that most city driving happens at partial throttle, where the curve is even more different (for lack of a better word)
if you are tuning for the street, look for mods that add torque at low RPMs and shift the powerband down in RPM.
if tuning for the track, it is OK to sacrifice low end power because the only time you will use it is at the starting line.
MishaA
11-12-2006, 09:05 PM
"The curve is different"? There is no real curve for a part throttle HP run. It's a non-sensical point.
And since the thread was regarding "red-line" or performance shift points, city driving is not at issue. And, I clearly pointed out that this was for performance.
If you are tuning for the street, strip or road course, or oval. You tune for HP at the RPM you will be operating at. This "tuning" is building the engine, gear ratios and tire sizes to keep the engine in the max HP RPM as long as you can. If you are tuning for economy, none of this thread makes much sense.:grinyes:
All makes sense except for the partial throttle curves. If you never saw one, it does not mean they do not exist. I'd been drawing quite a few of those when worked for the industry...
And since the thread was regarding "red-line" or performance shift points, city driving is not at issue. And, I clearly pointed out that this was for performance.
If you are tuning for the street, strip or road course, or oval. You tune for HP at the RPM you will be operating at. This "tuning" is building the engine, gear ratios and tire sizes to keep the engine in the max HP RPM as long as you can. If you are tuning for economy, none of this thread makes much sense.:grinyes:
All makes sense except for the partial throttle curves. If you never saw one, it does not mean they do not exist. I'd been drawing quite a few of those when worked for the industry...
GreyGoose006
11-12-2006, 09:21 PM
sorry, thats what i thought you were talking about...
i like diesels for the simple fact that they are more efficient.
i like high revving engines better otherwise.
does hp/liter really matter?
torque is a lot better in real world driving.
thats just my opinion tho. ;-]
i like diesels for the simple fact that they are more efficient.
i like high revving engines better otherwise.
does hp/liter really matter?
torque is a lot better in real world driving.
thats just my opinion tho. ;-]
Steel
11-12-2006, 09:44 PM
that is not what he's suggesting grey. What he's saying is, to put it simply, the highest average HP per RPM range for a gear, will cause the highest acceleration for a given vehicle.
If city driving = highest HP at lowest RPM possible, then everyone would be driving diesels.
There is a wide variety of vehicles and engines to chose from on the market. I don't like low-reving engines personally. There is disadvantages with any configuration. Low reving = low HP/L. Can't have your cake and eat it too.
That's why everyone drives diesels in Europe. It's better for city type driving because of the torque low down. Remember, people buy horsepower but drive torque. I like low revvers (except for 7's), because i hate having to wind out a motor to get anywhere, its annoying. I wish i had a VW diesel, those are soo easy to drive its great. It's easy to forget that they only make 90 horsepower when you have 155 torques at your disposal.
If city driving = highest HP at lowest RPM possible, then everyone would be driving diesels.
There is a wide variety of vehicles and engines to chose from on the market. I don't like low-reving engines personally. There is disadvantages with any configuration. Low reving = low HP/L. Can't have your cake and eat it too.
That's why everyone drives diesels in Europe. It's better for city type driving because of the torque low down. Remember, people buy horsepower but drive torque. I like low revvers (except for 7's), because i hate having to wind out a motor to get anywhere, its annoying. I wish i had a VW diesel, those are soo easy to drive its great. It's easy to forget that they only make 90 horsepower when you have 155 torques at your disposal.
UncleBob
11-12-2006, 11:43 PM
people buy horsepower but drive torque.
only people that don't comprehend the relationship of hp and torque anyway.
Didn't we already hash this out somewhere else?
Europeans like diesels because of their efficiency first, due to the high fuel costs there IMO. Something that will catch on real quick in the US if gas prices continue to rise.
only people that don't comprehend the relationship of hp and torque anyway.
Didn't we already hash this out somewhere else?
Europeans like diesels because of their efficiency first, due to the high fuel costs there IMO. Something that will catch on real quick in the US if gas prices continue to rise.
Steel
11-13-2006, 12:07 AM
AND the fact that they're easier to drive because they have all the low end torque. Torquey cars FEEL fast because of the same lowend torque. That's why V8's FEEL faster than rotaries, even if the rotary is faster.
example. RX-8 vs thunderbird supercoupe (not a v8, but i digress). RX-8 = 238hp, 159tq. SC = 200hp, 318tq. Guess which one feels faster off the line? Guess which one you have to wind out to eleventybillion RPM to get anywhere? Guess which one wins in a race?
In my racecar, i want a high-revvin, screamin' snortin' powerhouse.
In my DD, i want a slow turning, quiet, torquer.
example. RX-8 vs thunderbird supercoupe (not a v8, but i digress). RX-8 = 238hp, 159tq. SC = 200hp, 318tq. Guess which one feels faster off the line? Guess which one you have to wind out to eleventybillion RPM to get anywhere? Guess which one wins in a race?
In my racecar, i want a high-revvin, screamin' snortin' powerhouse.
In my DD, i want a slow turning, quiet, torquer.
UncleBob
11-13-2006, 12:34 AM
Well, as long as you feel like you're accelerating quickly, thats all that matters I guess :D
My daily driver is a 9 second 1/4 mile turbo'd motorcycle. And it rev's to 11.5K rpm's. Its horrible. It feels really really slow due to the redline.
Not.
My daily driver is a 9 second 1/4 mile turbo'd motorcycle. And it rev's to 11.5K rpm's. Its horrible. It feels really really slow due to the redline.
Not.
2.2 Straight six
11-13-2006, 05:47 AM
That's why everyone drives diesels in Europe. It's better for city type driving because of the torque low down. Remember, people buy horsepower but drive torque.
No, people over here drive them becasuse they have such good fuel economy, and no one has anything against them. unlike the US where it seems you get some stick from other people for driving a diesel car.
don't go thinking everyone here has diesels, they're more commen but there are still more petrol cars on the roads. i think germany/france/spain probably have the most diesels on the road, in UK there are plenty of them, but there are far more petrol cars around.
No, people over here drive them becasuse they have such good fuel economy, and no one has anything against them. unlike the US where it seems you get some stick from other people for driving a diesel car.
don't go thinking everyone here has diesels, they're more commen but there are still more petrol cars on the roads. i think germany/france/spain probably have the most diesels on the road, in UK there are plenty of them, but there are far more petrol cars around.
UncleBob
11-13-2006, 01:48 PM
I would be curious what the ratio is. In the US, the number of cars with diesel engines is nearly non-existant. The VW TDI is the only recent car that is selling well.
About the only place you see diesels are large american pickup trucks, I would guess around 25% of them are diesel. 6000-7000 pound trucks getting 18-20 mpg. Thats almost as good as my crappy little 4 banger ranger truck.
About the only place you see diesels are large american pickup trucks, I would guess around 25% of them are diesel. 6000-7000 pound trucks getting 18-20 mpg. Thats almost as good as my crappy little 4 banger ranger truck.
Steel
11-14-2006, 09:05 AM
Well, as long as you feel like you're accelerating quickly, thats all that matters I guess :D
My daily driver is a 9 second 1/4 mile turbo'd motorcycle. And it rev's to 11.5K rpm's. Its horrible. It feels really really slow due to the redline.
Not.
Sarcasm is not needed, especially when you're comparing a 300 pound bike to a 3300 pound car. Obviously torque is not a huge factor for bikes. Even then, torqier bikes (v-twins) *feel* faster than high revving bikes (4 cylinders). And guess what, the V-twins are easier to drive than the 16k revvers. Simple truth.
*edit* and that's the reason that a good portion of RX-8 owners were dissappointed with the performance of the car. Sure it had 238 hp, but it certainly didnt feel like that. It would constantly push you back in your seat, but 'neck-snapping' torque describes it not.
My daily driver is a 9 second 1/4 mile turbo'd motorcycle. And it rev's to 11.5K rpm's. Its horrible. It feels really really slow due to the redline.
Not.
Sarcasm is not needed, especially when you're comparing a 300 pound bike to a 3300 pound car. Obviously torque is not a huge factor for bikes. Even then, torqier bikes (v-twins) *feel* faster than high revving bikes (4 cylinders). And guess what, the V-twins are easier to drive than the 16k revvers. Simple truth.
*edit* and that's the reason that a good portion of RX-8 owners were dissappointed with the performance of the car. Sure it had 238 hp, but it certainly didnt feel like that. It would constantly push you back in your seat, but 'neck-snapping' torque describes it not.
Steel
11-14-2006, 09:08 AM
I would be curious what the ratio is. In the US, the number of cars with diesel engines is nearly non-existant. The VW TDI is the only recent car that is selling well.
About the only place you see diesels are large american pickup trucks, I would guess around 25% of them are diesel. 6000-7000 pound trucks getting 18-20 mpg. Thats almost as good as my crappy little 4 banger ranger truck.
http://www.dieselnet.com/news/2004/12bosch.php
About the only place you see diesels are large american pickup trucks, I would guess around 25% of them are diesel. 6000-7000 pound trucks getting 18-20 mpg. Thats almost as good as my crappy little 4 banger ranger truck.
http://www.dieselnet.com/news/2004/12bosch.php
UncleBob
11-14-2006, 01:14 PM
I think what you're "feeling" moreso is the power curve. Turbo diesels have a very abrupt power hit when the turbo spools, where as your example, the RX7 didn't have any "curve" worth mentioning since it was dead flat.
Due to diesels low reving engine, the gearing is greatly raised (lowered numerically) which counteracts applying the extra ft/lb's to the rear wheel. As far as your run-of-the-mill diesel, I've yet to drive one that did anything for me. Thats just me I guess.
I'm not trying to argue that more torque doesn't feel faster. If you take any vehicle and double its torque, it will feel way faster. That is obvious.
Due to diesels low reving engine, the gearing is greatly raised (lowered numerically) which counteracts applying the extra ft/lb's to the rear wheel. As far as your run-of-the-mill diesel, I've yet to drive one that did anything for me. Thats just me I guess.
I'm not trying to argue that more torque doesn't feel faster. If you take any vehicle and double its torque, it will feel way faster. That is obvious.
Steel
11-14-2006, 07:12 PM
WEll i tell you, i was impressed when i was in the VW on the highway. Got stuck behind a truck at 55mph. To pass him, i just got in the left lane and pushed to go pedal, no downshifting silliness. I was also impressed with its hill-climbing ability. 30-35mph in 4th gear up a fairly steep hill is no sweat.
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