Cam timing, ignition timing, fuel
#11
06-26-2011, 11:11 PM
Nothing was stated about power or power ranges. I'm talking about making changes in relation to piston movement and valve opening, and how those changes affect getting fuel into the combustion chamber. I'm saying at higher rpms, advancing the valve timing to open sooner would allow more fuel/air to get into the combustion chamber than if you DIDN'T open the intake sooner.
it seems logical to me that the higher the rpm, the more advance can be utilized
At higher and higher rpm's, it's harder and harder to suck in enough fuel/air without resorting to opening the intake valve sooner and sooner
Longer opening duration and more valve lift are what is needed. At higher RPMs, you want to keep the intake valve open later in the cycle to take advantage of the momentum of the intake air charge.
Ride on
Brewster
#12
06-26-2011, 11:26 PM
Yes, I agree with the Crane info you posted. I don't think I said the powerband moves up or even stays in the same place with a 4 degree advance on the cam gear. It definitely moves down in the rpm range. In my Chevy engine the power signs on quicker and signs off quicker...ideal for a big, heavy 4X4 that almost never sees 5000 rpm.
Am I missing something?
Am I missing something?
That along with an aftermarket cam that has more advance contributes to increased performance.
Advancing the cam timing on an engine usually produces more power because the cylinder fills with a larger volume of intake charge (air & fuel)
I also built up a 383 chevy for my 73 4x4 and used components for low and mid range torque enhancement.
Ride on
Brewster
#13
06-26-2011, 11:58 PM
Lots of focus on the intake, but what about the poor, neglected exhaust valve? Lets not forget that the exhaust valve is playing a role with expediting the intake charge, at least for engines that have any amount of valve overlap.
As the piston is near the top of the exhaust stroke there is a "dead zone" of a few degrees of crankshaft travel where the piston momentarily becomes stationary, for want a better word. It is in this zone that the bulk of valve overlap will occur. The exhaust valve is just closing and the intake valve is just opening. Intake charge begins to move into the cylinder not by the pulling force of the piston but by being drawn in by the last of the exhaust gases that are rushing out of the cylinder (I think the term they used way back in A&P school was "tornadic velocity"--ages ago). Intake charge pressure, whether atmospheric or boosted is also pushing on the charge.
The more overlap you have the higher the rpm's need to be for the main operating range of the engine. That's why a "built" engine will have that loping, rumpety sound at idle (sweet!). Aircraft piston engines idle rough, too, because of their valve overlap. The power is needed in higher rpm ranges for cruise and takeoff. Both types of engine run smoothest/best at their higher rpm ranges.
For the camshaft mod on our KLX's, unneeded valve overlap for unrealistically high rpm's was tranformed into earlier intake and later exhaust openings since our engines simply don't need the amount of overlap designed into them. With Marcelino's mod we are now able to take in and exhaust the mixture in our operating range.
As the piston is near the top of the exhaust stroke there is a "dead zone" of a few degrees of crankshaft travel where the piston momentarily becomes stationary, for want a better word. It is in this zone that the bulk of valve overlap will occur. The exhaust valve is just closing and the intake valve is just opening. Intake charge begins to move into the cylinder not by the pulling force of the piston but by being drawn in by the last of the exhaust gases that are rushing out of the cylinder (I think the term they used way back in A&P school was "tornadic velocity"--ages ago). Intake charge pressure, whether atmospheric or boosted is also pushing on the charge.
The more overlap you have the higher the rpm's need to be for the main operating range of the engine. That's why a "built" engine will have that loping, rumpety sound at idle (sweet!
). Aircraft piston engines idle rough, too, because of their valve overlap. The power is needed in higher rpm ranges for cruise and takeoff. Both types of engine run smoothest/best at their higher rpm ranges.For the camshaft mod on our KLX's, unneeded valve overlap for unrealistically high rpm's was tranformed into earlier intake and later exhaust openings since our engines simply don't need the amount of overlap designed into them. With Marcelino's mod we are now able to take in and exhaust the mixture in our operating range.
#14
06-27-2011, 12:09 AM
Join Date: Sep 2009
Location: Abilene, TX
Posts: 5,050
I don't know, Brewster...maybe we just have a semantics thing going on. It seems more power "can" be made in a given engine with a given cam timing advance, but so many variables can muddy the water. If an engine has the cam advanced, and that advance is more compatible to that engine's other design elements, more power will be generated. But I agree that it will lower in the rpm range...unless the given engine was already screwed up because of bad design, bad component selection, or all of the above. Still...as I said before, the only reason I mention anything about cam timing is the compression and detonation issue. I hope it's a non-issue.
#15
06-27-2011, 12:44 AM
I was going to tag this on to Marcelino's thread, but I thought it would be better for that thread to cover the mechanical installation issues instead of a discussion about the potential effects of cam timing.
After M's great coverage of this cam timing mod for the KLX, I've been mulling over the possible issues before jumping into this myself. I've had some experience with advanced cam timing on my 4X4. What does a stroked 350 (383) Chevy V8 have in common with a KLX motor?...quite a bit in many of the critical elements common in most 4-stroke engines. My 383 has an adjustable camshaft timing gear which allows 4 degrees of advance. That along with an aftermarket cam that has more advance contributes to increased performance. I also have an ignition system that allows for manipulating the ignition timing while driving. With this setup I can run unleaded regular without any damage.
Now, I'm no engineer or professionally trained engine tech. I'm like most here who were just more interested than most when it comes to learning and working on our machines. It even got me a couple of very decent part time jobs for many years working at a motorcycle shop, a car dealership, and even a bicycle shop while pursuing my full time career in an unrelated field. So if anyone has any corrections or input on my comments here...jump in.
Advancing the cam timing on an engine usually produces more power because the cylinder fills with a larger volume of intake charge (air & fuel) and then compresses a little longer creating more pressure. Now, this is the ideal situation in the ideal engine I'm referring to as I understand it. Advancing the cam timing causes the intake valve to open sooner which would start the intake process sooner when drawing in the fuel/air mix. The intake valve is going to close sooner which allows the piston to compress the fuel/air for a little longer. The exhaust process is similar in that the exhaust valve opens sooner to hasten the expulsion of the combustion gases. Now, this can change a bit with some engines and designs, but it's generally why you see power increases with advanced cam timing...at least as I understand it.
Now, the potential problem here can come from the fact that compressing the intake fuel/air mix for a little longer actually can increase compression which can increase the risk of detonation/pinging in many engines. This was the case with my Chevy, and I was able to control this with an adjustable in-cab ignition timing control device hooked to my MSD ignition box. My 4X4 has a much broader range of operating use than the KLX. I tow a travel trailer, do off roading, and just tool around in it occasionally. This dramatically changes the demands on the engine. I can run a lot more ignition advance with the vehicle empty than when towing. This compares a bit to the KLX in that we wring out our motors on a more regular basis, so timing, fuel octane requirements, and compression all come into play.
If advancing the cam timing on the KLX is creating a bit more compression, there is the chance that the engine's fuel octane requirements could change too. Now, if one has an aftermarket piston that has also increased compression, it may contribute to this issue. None of these elements stand alone to help or hurt engine detonation. I don't know if the KLX will be prone to detonation with this mod, but some have asked the question...and rightfully so. Can all detonation problems be addressed with just richer jetting...not really. Timing might have to be addressed in some cases, but that usually causes a power loss at some point. Besides, the KLX's timing isn't easily manipulated.
I'm just throwing this out for discussion. I notice Marcelino has an FI engine if I read correctly. That will help some of these issues. His engine is also using a stock piston and compression. Those with big bore kits with higher compression should just be aware of the possibility of detonation. My OEM KLX300 piston and cylinder has the same compression as the KLX250S engine, so perhaps it won't be a problem. I'm not saying that this will be an issue with a higher compression KLX engine, but it's better to be aware.
After M's great coverage of this cam timing mod for the KLX, I've been mulling over the possible issues before jumping into this myself. I've had some experience with advanced cam timing on my 4X4. What does a stroked 350 (383) Chevy V8 have in common with a KLX motor?...quite a bit in many of the critical elements common in most 4-stroke engines. My 383 has an adjustable camshaft timing gear which allows 4 degrees of advance. That along with an aftermarket cam that has more advance contributes to increased performance. I also have an ignition system that allows for manipulating the ignition timing while driving. With this setup I can run unleaded regular without any damage.
Now, I'm no engineer or professionally trained engine tech. I'm like most here who were just more interested than most when it comes to learning and working on our machines. It even got me a couple of very decent part time jobs for many years working at a motorcycle shop, a car dealership, and even a bicycle shop while pursuing my full time career in an unrelated field. So if anyone has any corrections or input on my comments here...jump in.
Advancing the cam timing on an engine usually produces more power because the cylinder fills with a larger volume of intake charge (air & fuel) and then compresses a little longer creating more pressure. Now, this is the ideal situation in the ideal engine I'm referring to as I understand it. Advancing the cam timing causes the intake valve to open sooner which would start the intake process sooner when drawing in the fuel/air mix. The intake valve is going to close sooner which allows the piston to compress the fuel/air for a little longer. The exhaust process is similar in that the exhaust valve opens sooner to hasten the expulsion of the combustion gases. Now, this can change a bit with some engines and designs, but it's generally why you see power increases with advanced cam timing...at least as I understand it.
Now, the potential problem here can come from the fact that compressing the intake fuel/air mix for a little longer actually can increase compression which can increase the risk of detonation/pinging in many engines. This was the case with my Chevy, and I was able to control this with an adjustable in-cab ignition timing control device hooked to my MSD ignition box. My 4X4 has a much broader range of operating use than the KLX. I tow a travel trailer, do off roading, and just tool around in it occasionally. This dramatically changes the demands on the engine. I can run a lot more ignition advance with the vehicle empty than when towing. This compares a bit to the KLX in that we wring out our motors on a more regular basis, so timing, fuel octane requirements, and compression all come into play.
If advancing the cam timing on the KLX is creating a bit more compression, there is the chance that the engine's fuel octane requirements could change too. Now, if one has an aftermarket piston that has also increased compression, it may contribute to this issue. None of these elements stand alone to help or hurt engine detonation. I don't know if the KLX will be prone to detonation with this mod, but some have asked the question...and rightfully so. Can all detonation problems be addressed with just richer jetting...not really. Timing might have to be addressed in some cases, but that usually causes a power loss at some point. Besides, the KLX's timing isn't easily manipulated.
I'm just throwing this out for discussion. I notice Marcelino has an FI engine if I read correctly. That will help some of these issues. His engine is also using a stock piston and compression. Those with big bore kits with higher compression should just be aware of the possibility of detonation. My OEM KLX300 piston and cylinder has the same compression as the KLX250S engine, so perhaps it won't be a problem. I'm not saying that this will be an issue with a higher compression KLX engine, but it's better to be aware.
#16
06-27-2011, 12:58 AM
Engine knock, maybe? Might be gasoline octane. For all that's been done to your engine it may very well need the highest octane you can find.
#18
06-27-2011, 01:58 AM
Join Date: Jan 2008
Location: SW Ontario, Canada
Posts: 869
I think what we've done with Marcelino's mod is to advance the intake cam timing by 10 or so degrees but retard the exhaust cam by an equivalent amount.
Marcelino's original issue is that the stock cam timing is set for an upper rpm range that is literally not possible with our KLX250's as set up. Therefore he took away valve overlap for an unachievable top end and gave us some increase in volumetric efficiency in the lower and mid ranges.
Marcelino's original issue is that the stock cam timing is set for an upper rpm range that is literally not possible with our KLX250's as set up. Therefore he took away valve overlap for an unachievable top end and gave us some increase in volumetric efficiency in the lower and mid ranges.
#19
06-27-2011, 02:12 AM
If I may add something to this, I did notice what I'm now realizing was a pinging noise. I stopped off at a gas station do take all of my keys off of the keychain because I at first thought it was the keys clanking against the triple clamp. I then thought I was throwing rocks off my brand new tires into the motor. Neither was the case, as I still heard the noise watching closely to make sure it wasn't rocks hitting the engine. This noise occurred maybe once every 2 miles or so and was a set of like 4 or 5 pings. Not loud pings or anything, but definitely a pinging noise. I did a few test runs and noticed that the pinging only occured cruising in 6th gear between 35-40mph at about 4-5k RPMS. For anyone that hasn't been following, I have an older 06 klx 250s with the BB 351 kit. This is just my experience and I have done a lot of stuff at once, so take it with a grain of salt what I just said.
The new motor is not balanced the same, and alot of stuff will vibrate (harmonics) that didn't before. everytime i heard it i would let off the gas, and it went away of course. Don't be surprised if you have the same issue. Also, you took a bunch of stuff off the bike that was kind of settled in. Don't get paranoid, just think it all through, and take your time diagnosing your issues one at a time.
Just like your oil leak, turns out it was a pretty simple thing and nothing to get excited over. Ride the bike a while before you report more things that are most likely simple fixes. Soon you will be as good of a mechanic as the friend who assisted you!!!!
#20
06-27-2011, 02:56 AM
I'll give this a try.
Jhoffy, I had a similar noise. turns out it was the right gas tank plastic vibrating.
The new motor is not balanced the same, and alot of stuff will vibrate (harmonics) that didn't before. everytime i heard it i would let off the gas, and it went away of course. Don't be surprised if you have the same issue. Also, you took a bunch of stuff off the bike that was kind of settled in. Don't get paranoid, just think it all through, and take your time diagnosing your issues one at a time.
Just like your oil leak, turns out it was a pretty simple thing and nothing to get excited over. Ride the bike a while before you report more things that are most likely simple fixes. Soon you will be as good of a mechanic as the friend who assisted you!!!!
The new motor is not balanced the same, and alot of stuff will vibrate (harmonics) that didn't before. everytime i heard it i would let off the gas, and it went away of course. Don't be surprised if you have the same issue. Also, you took a bunch of stuff off the bike that was kind of settled in. Don't get paranoid, just think it all through, and take your time diagnosing your issues one at a time.
Just like your oil leak, turns out it was a pretty simple thing and nothing to get excited over. Ride the bike a while before you report more things that are most likely simple fixes. Soon you will be as good of a mechanic as the friend who assisted you!!!!