Rev Matching and Valvetrain
Joined: Mar 2001
Posts: 37,305
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Your valves have no idea why they are being sped up, or slowed down. They won't know weather you are pumping the throttle in neutral, to impress yourself, or passers by, or are going back a gear or 2, into a hairpin.
Asking them to speed up a bit by the odd mismatched gear change, or blipping in neutral will have no detrimental effect on them.
They won't even be able to tell your mechanic of your poor driving, as you won't have caused a problem.
Your diff & clutch, on the other hand won't like it too much. Minor miss matching they will take in their stride. If however, like acquaintance of mine, you do fast take-offs by moving your clutch foot sideways, off the clutch pedal, at high revs, they will soon be telling your mechanic of your driving habits, as he replaces them.
Asking them to speed up a bit by the odd mismatched gear change, or blipping in neutral will have no detrimental effect on them.
They won't even be able to tell your mechanic of your poor driving, as you won't have caused a problem.
Your diff & clutch, on the other hand won't like it too much. Minor miss matching they will take in their stride. If however, like acquaintance of mine, you do fast take-offs by moving your clutch foot sideways, off the clutch pedal, at high revs, they will soon be telling your mechanic of your driving habits, as he replaces them.
However, I have a theory (pure conjecture) that I've held a belief about for some time now. We've been hearing about valve spring retainers cracking and valves dropping, etc over the past many years with regard to S2000s. Now, I have absolutely no proof of what I'm about to say but with some elementary knowledge in physics, I can visualized that it's not only a mechanical over-rev that can damage retainers, but the "rate" at which the rpm is forced to rise, that may cause undue stress to retainers (and other rotating engine parts). When a mis-shift occurs, like on an accidental high rpm downshift or downshifting 2 gears instead, and then dropping the clutch, the engine revs are forced to accelerate unnaturally rapidly. This also happens when you downshift and just "drop" the clutch (no blipping) at medium rpm as well. This can create extreme forces and inertia to act upon moving parts. This would not be a dis-similar action to giving a car a push by another car to get it unstuck from the snow or mud. It's one thing to nudge up against it and give it a gradual push. It's a whole other story if you took a run at it to push it. That sudden acceleration from a stop (or slower speed) can be quite detrimental because it's providing a physical force that the various parts and components weren't designed for. These same laws of physics should apply to the valve train and other bits and pieces of the drive train.
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Joined: Oct 2012
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Originally Posted by Old racer' timestamp='1354969199' post='22197646
Your valves have no idea why they are being sped up, or slowed down. They won't know weather you are pumping the throttle in neutral, to impress yourself, or passers by, or are going back a gear or 2, into a hairpin.
Asking them to speed up a bit by the odd mismatched gear change, or blipping in neutral will have no detrimental effect on them.
They won't even be able to tell your mechanic of your poor driving, as you won't have caused a problem.
Your diff & clutch, on the other hand won't like it too much. Minor miss matching they will take in their stride. If however, like acquaintance of mine, you do fast take-offs by moving your clutch foot sideways, off the clutch pedal, at high revs, they will soon be telling your mechanic of your driving habits, as he replaces them.
Asking them to speed up a bit by the odd mismatched gear change, or blipping in neutral will have no detrimental effect on them.
They won't even be able to tell your mechanic of your poor driving, as you won't have caused a problem.
Your diff & clutch, on the other hand won't like it too much. Minor miss matching they will take in their stride. If however, like acquaintance of mine, you do fast take-offs by moving your clutch foot sideways, off the clutch pedal, at high revs, they will soon be telling your mechanic of your driving habits, as he replaces them.
However, I have a theory (pure conjecture) that I've held a belief about for some time now. We've been hearing about valve spring retainers cracking and valves dropping, etc over the past many years with regard to S2000s. Now, I have absolutely no proof of what I'm about to say but with some elementary knowledge in physics, I can visualized that it's not only a mechanical over-rev that can damage retainers, but the "rate" at which the rpm is forced to rise, that may cause undue stress to retainers (and other rotating engine parts). When a mis-shift occurs, like on an accidental high rpm downshift or downshifting 2 gears instead, and then dropping the clutch, the engine revs are forced to accelerate unnaturally rapidly. This also happens when you downshift and just "drop" the clutch (no blipping) at medium rpm as well. This can create extreme forces and inertia to act upon moving parts. This would not be a dis-similar action to giving a car a push by another car to get it unstuck from the snow or mud. It's one thing to nudge up against it and give it a gradual push. It's a whole other story if you took a run at it to push it. That sudden acceleration from a stop (or slower speed) can be quite detrimental because it's providing a physical force that the various parts and components weren't designed for. These same laws of physics should apply to the valve train and other bits and pieces of the drive train.
That's actually a really interesting theory you have there haha. I want to clarify that I do rev-match at low rpms especially when traffic congestion gets heavier here in socal. I'm just afraid that if at mid-range rpms (5500-6500 or so) if one doesn't blip the throttle enough the stress on the engine to meet road speed would harm components of the drivetrain and/or valvetrain. I have an 2002 AP1 and I'm looking to upgrade to dual valve springs for safety and peace of mind.
Joined: Apr 2011
Posts: 305
Likes: 51
From: South East Queensland Oz.
I'm an old racer, so old, that in the early 60s I was racing improved production sports cars, mostly a Morgan +4 against the Triumphs, Healeys MGs Jags, with the odd Porsche, Daimler SP250, Volvo & Sunbeam around as well.
I was continually amazed how these things held together with some of the driving. Many would arrive at a corner at over 6000 RPM in top, [quite high for 60s engineering other than the Honda S600], & go straight back a gear, or even 2, as soon as they started braking. You could hear the valve bounce over the scream of pain from the exhaust as they pulled almost Honda revs. I have always, since then, avoided over revving on the overrun. I believe this is much more damaging than similar revs on power, as there is no gas to compress or push out, to help slow the pistons at top dead centre.
Yes they broke a lot of engines, mostly failed big end bearings , with broken con rods & pistons popular, but dropped valves were rare. Conrod straight at Bathurst was so named for the number of con-rods that came out the side of the block, particularly in the braking area.
So I'm saying, be careful when changing down, that you don't over rev your engine, there is no rev limiter to help you there, as there is when accelerating, & it is not only valve gear that suffers.
I was continually amazed how these things held together with some of the driving. Many would arrive at a corner at over 6000 RPM in top, [quite high for 60s engineering other than the Honda S600], & go straight back a gear, or even 2, as soon as they started braking. You could hear the valve bounce over the scream of pain from the exhaust as they pulled almost Honda revs. I have always, since then, avoided over revving on the overrun. I believe this is much more damaging than similar revs on power, as there is no gas to compress or push out, to help slow the pistons at top dead centre.
Yes they broke a lot of engines, mostly failed big end bearings , with broken con rods & pistons popular, but dropped valves were rare. Conrod straight at Bathurst was so named for the number of con-rods that came out the side of the block, particularly in the braking area.
So I'm saying, be careful when changing down, that you don't over rev your engine, there is no rev limiter to help you there, as there is when accelerating, & it is not only valve gear that suffers.
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Joined: May 2009
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From: Indiana
1. You're always in gear, meaning you can always get back on the gas if needed to avoid a collision
2. You aren't forced to downshift just before, during, or right after exiting a turn to get back on the gas, avoiding a possible loss of traction situation if you drive like an idiot
3. When racing you will have your best times by proper heel-toe downshifting while braking
Also, you're not always coming to a complete stop, so rev-matching is the only way to do it. Otherwise you're putting your car into the lower gear after having braked down to whatever RPM that will always be >1000 RPM idle speed so the engine will be forced to jump up another 1-2k RPM instantly. This doesn't *necessarily* hurt anything but it feels crappy for the people in the car and it puts undue strain on all moving parts, however little that may be.
Joined: Mar 2001
Posts: 37,305
Likes: 18
Originally Posted by JayC07' timestamp='1355042312' post='22198861
Why dont you just coast it... u wont have to worry about doing any damage other than ur brake pads
1. You're always in gear, meaning you can always get back on the gas if needed to avoid a collision
2. You aren't forced to downshift just before, during, or right after exiting a turn to get back on the gas, avoiding a possible loss of traction situation if you drive like an idiot
3. When racing you will have your best times by proper heel-toe downshifting while braking
Also, you're not always coming to a complete stop, so rev-matching is the only way to do it. Otherwise you're putting your car into the lower gear after having braked down to whatever RPM that will always be >1000 RPM idle speed so the engine will be forced to jump up another 1-2k RPM instantly. This doesn't *necessarily* hurt anything but it feels crappy for the people in the car and it puts undue strain on all moving parts, however little that may be.
5. The use of "coasting" to a stop will result in more threads popping up in future about ..... "My car dies or vibrates like crazy and nearly dies when coming to a stop. Please HELP!"
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I agree. Coasting doesn't help at all unless you want to get in an accident. Don't get me wrong there are instances where coasting is fine, such as coasting to a complete stop because of a stop sign.
