Engine timing profiles.
05-03-2008, 04:41 PM
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Engine timing profiles.
Okay, instead of me making a new thread for every engine I time/modded, I figured I should just make one thread to put all my timing profiles for each engine under.
Here's my next engine.
TRX2.5R (stock)
Intake 63 BBDC - 126 duration
Boost 60 BBDC - 120 duration
Exhaust 79BBDC - 158 duration
Crank 40 ABDC (open) 55ATDC (close) - duration 195
Here's what I'm thinking about modding it to
Intake/boost 65 BBDC - duration 130
Exhaust 85BBDC - duration 170
Crank 40 ABDC (open) 70ATDC (close) - duration 210
What do you engine modders think?
Anyone who has modded timing on engines can post their timing profile (if they want to)
I'm looking at picking up a picco 28 and Losi 427 to mod as well, but we'll see if I get those.
Here's my next engine.
TRX2.5R (stock)
Intake 63 BBDC - 126 duration
Boost 60 BBDC - 120 duration
Exhaust 79BBDC - 158 duration
Crank 40 ABDC (open) 55ATDC (close) - duration 195
Here's what I'm thinking about modding it to
Intake/boost 65 BBDC - duration 130
Exhaust 85BBDC - duration 170
Crank 40 ABDC (open) 70ATDC (close) - duration 210
What do you engine modders think?
Anyone who has modded timing on engines can post their timing profile (if they want to)
I'm looking at picking up a picco 28 and Losi 427 to mod as well, but we'll see if I get those.
05-03-2008, 06:10 PM
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RE: Engine timing profiles.
Sorry, I do my engines only. If you want ti modded I would recommend sending it to Adam at ABmods or if you just want to know the stock timing profile its fairly easy to do it yourself.
05-03-2008, 08:02 PM
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RE: Engine timing profiles.
ORIGINAL: SAVAGEJIM
At first glance of those numbers you are shooting for, I'd say, by first intuition, that those timing profiles would make any engine perform much better that stock. By my own initial guess, that is a timing profile that most modders would shoot for in a "stage1" or maybe even a higher higher mod level to get the engine to perform more in the mid to upper RPM bandwidths.
Aside from impoving volumetric effeiciency at higher PM bandwidths (which is what increasing timing profiles generally do), another consideration to bear in mind is deciding how fast is too fast. For long stroke engines, getting the engine to turn too fast can be a bad thing since the linear piston speed in the sleeve can cause several problems (primarily friction). Lets say a big block has a particularly long stroke and it is modded with a timing profile that can get it to 40000RPM: the linear speed of the piston will be much greater at 40000RPM than a short stroke engine also turning at 40000RPM. The friction could in this case be great enough to cause the teminal max RPM of the engine to only reach about 37000 and no amount of futher duration increases can get it to ever turn faster. (Of course, affecting the engine's terminal max RPM in only one major problem. Other problems include the lubricant breaking down due to tremendous heat from the friction, the inertia of the innards of a long stroke engine can be high enough to hamper acceleration, etc.)
Though considering linear piston speed was never discussed in detail before as a concern for shooting for a desired timing profile, it is definitely one of the factors modders do take into serious consideration. That (among other reasons as well) is why they say "Depending on the engine, I will only increase the duration so much." No, I do not know what the bore and stroke of the TRX2.5 is, but given the stroke of the 2.5 is known, I can calculate what the linear piston speed will be for any RPM.
And of course, there also is the consideration of materials science and the points of failures of differnt metals. Some engines might be able to actually rev to 45000RPM with no ill effects on the parts because of their geomtry of the inner parts. Other engines will result in the conrod journals "ovalling" out and finally snapping due to the massive foces of otating so fast.
At first glance of those numbers you are shooting for, I'd say, by first intuition, that those timing profiles would make any engine perform much better that stock. By my own initial guess, that is a timing profile that most modders would shoot for in a "stage1" or maybe even a higher higher mod level to get the engine to perform more in the mid to upper RPM bandwidths.
Aside from impoving volumetric effeiciency at higher PM bandwidths (which is what increasing timing profiles generally do), another consideration to bear in mind is deciding how fast is too fast. For long stroke engines, getting the engine to turn too fast can be a bad thing since the linear piston speed in the sleeve can cause several problems (primarily friction). Lets say a big block has a particularly long stroke and it is modded with a timing profile that can get it to 40000RPM: the linear speed of the piston will be much greater at 40000RPM than a short stroke engine also turning at 40000RPM. The friction could in this case be great enough to cause the teminal max RPM of the engine to only reach about 37000 and no amount of futher duration increases can get it to ever turn faster. (Of course, affecting the engine's terminal max RPM in only one major problem. Other problems include the lubricant breaking down due to tremendous heat from the friction, the inertia of the innards of a long stroke engine can be high enough to hamper acceleration, etc.)
Though considering linear piston speed was never discussed in detail before as a concern for shooting for a desired timing profile, it is definitely one of the factors modders do take into serious consideration. That (among other reasons as well) is why they say "Depending on the engine, I will only increase the duration so much." No, I do not know what the bore and stroke of the TRX2.5 is, but given the stroke of the 2.5 is known, I can calculate what the linear piston speed will be for any RPM.
And of course, there also is the consideration of materials science and the points of failures of differnt metals. Some engines might be able to actually rev to 45000RPM with no ill effects on the parts because of their geomtry of the inner parts. Other engines will result in the conrod journals "ovalling" out and finally snapping due to the massive foces of otating so fast.
05-03-2008, 08:35 PM
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RE: Engine timing profiles.
Does that mean you like my timing profile I'm going to use?
I think the TRX 2.5R has a bore and stroke of 14.7mm (I know the bore and stroke are the same)
I think the TRX 2.5R has a bore and stroke of 14.7mm (I know the bore and stroke are the same)
05-03-2008, 09:14 PM
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RE: Engine timing profiles.
First off, I know nothing about timing on a 2 stroke or where the power lies. Second, I'm no expert on anything. A long rod is better than a short rod for a few reasons. 1, the acceleration/decelleration forces of the piston are less with a long rod. 2, the side loading of the piston is less meaing less friction to overcome or protect against. 3, the dwell at TDC is greater allowing for a more complete combustion of the fuel charge. There is a conrod/stroke ratio that is important and I think I remember the number as 1.6:1 which means as the conrod length gets closer to the stroke mechanical forces start mounting up in a hurry. Used to be piston speed needed to be kept under 4 feet per second or severe damage could set in. I'm not sure of the ft/sec but that mostly was because of metalurgical standards in the 1960's. Notice I said long rod and not stroke. Another way of looking at it, for a given bore and stroke a longer conrod will be able to rev higher and last longer. All of this information is older than jbcomp so it may not stand today but mechanical advantages and "guidelines" don't change much, metal and lube quality can but math formulas seldom do. This is not meant to flame anyone or disagree, just food for thought.
05-03-2008, 09:23 PM
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RE: Engine timing profiles.
You can EASILY over time and engine and lose power AND most importantly power band. The combustion chamber has alot to do with this as well. I have seen too much timing KILL and engines power and power band 1st hand here on my dyno. SO I suggest more mild timing alterations and ease your way into it.
05-03-2008, 09:24 PM
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RE: Engine timing profiles.
ORIGINAL: Grits
All of this information is older than jbcomp so it may not stand today but mechanical advantages and "guidelines" don't change much, metal and lube quality can but math formulas seldom do. This is not meant to flame anyone or disagree, just food for thought.
All of this information is older than jbcomp so it may not stand today but mechanical advantages and "guidelines" don't change much, metal and lube quality can but math formulas seldom do. This is not meant to flame anyone or disagree, just food for thought.
ORIGINAL: Colt4g63
You can EASILY over time and engine and lose power AND most importantly power band. The combustion chamber has alot to do with this as well. I have seen too much timing KILL and engines power and power band 1st hand here on my dyno. SO I suggest more mild timing alterations and ease your way into it.
You can EASILY over time and engine and lose power AND most importantly power band. The combustion chamber has alot to do with this as well. I have seen too much timing KILL and engines power and power band 1st hand here on my dyno. SO I suggest more mild timing alterations and ease your way into it.
05-03-2008, 09:48 PM
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RE: Engine timing profiles.
You're down to 45* of crankcase compression timing on your modded motor, down from 65* - I don't know how that relates to the really wicked engines, but I know that too little crankcase compression time means bad things.
You've also increased the exhaust-transfer port offset to 20* from 16*. Adam, would I be right in thinking that for a higher performance motor you'd want to decrease this offset by opening the transfer/boost ports by a greater amount than you open the exhaust port? Or is the exhaust port more important for the high speed motor?
JB, this is an awesome idea. I tried to get this kind of thing going in another thread, but maybe because I'm a newbie on here I'm not going to get alot of response. The only one that got added to my thread was for the Dynamite Mach 28, with 120* boost port, 124* transfer port, 166* exhaust port, and intake port duration of 48ABDC to 50ATDC for 182* total.
You've also increased the exhaust-transfer port offset to 20* from 16*. Adam, would I be right in thinking that for a higher performance motor you'd want to decrease this offset by opening the transfer/boost ports by a greater amount than you open the exhaust port? Or is the exhaust port more important for the high speed motor?
JB, this is an awesome idea. I tried to get this kind of thing going in another thread, but maybe because I'm a newbie on here I'm not going to get alot of response. The only one that got added to my thread was for the Dynamite Mach 28, with 120* boost port, 124* transfer port, 166* exhaust port, and intake port duration of 48ABDC to 50ATDC for 182* total.
05-03-2008, 10:08 PM
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RE: Engine timing profiles.
ORIGINAL: ugly duck
You're down to 45* of crankcase compression timing on your modded motor, down from 65* - I don't know how that relates to the really wicked engines, but I know that too little crankcase compression time means bad things.
You've also increased the exhaust-transfer port offset to 20* from 16*. Adam, would I be right in thinking that for a higher performance motor you'd want to decrease this offset by opening the transfer/boost ports by a greater amount than you open the exhaust port? Or is the exhaust port more important for the high speed motor?
JB, this is an awesome idea. I tried to get this kind of thing going in another thread, but maybe because I'm a newbie on here I'm not going to get alot of response. The only one that got added to my thread was for the Dynamite Mach 28, with 120* boost port, 124* transfer port, 166* exhaust port, and intake port duration of 48ABDC to 50ATDC for 182* total.
You're down to 45* of crankcase compression timing on your modded motor, down from 65* - I don't know how that relates to the really wicked engines, but I know that too little crankcase compression time means bad things.
You've also increased the exhaust-transfer port offset to 20* from 16*. Adam, would I be right in thinking that for a higher performance motor you'd want to decrease this offset by opening the transfer/boost ports by a greater amount than you open the exhaust port? Or is the exhaust port more important for the high speed motor?
JB, this is an awesome idea. I tried to get this kind of thing going in another thread, but maybe because I'm a newbie on here I'm not going to get alot of response. The only one that got added to my thread was for the Dynamite Mach 28, with 120* boost port, 124* transfer port, 166* exhaust port, and intake port duration of 48ABDC to 50ATDC for 182* total.
Oh man, I forgot to time the SPI, well I'll have to do that tomorrow. I think the SPI is suppose to be around 70-80 degrees of duration. lsurber was the guy I was talking to about the SPI when I was first doing it, but now I think he left RCU, I haven't seen him post in a awhile.
I'm not sure if I'm going to cut the crank that far or not, I still have not got a carbide cutter for the dremel (even though I've been planning on it for months now)
Tomorrow I'll probably start cutting away at it, hopefully it still runs or my Maxx with be with out an engine for a little while.
05-03-2008, 10:15 PM
#12
RE: Engine timing profiles.
You may get away with the longer exhaust timing but you'll lose low down power for acceleration. IMO the crank closing timing is far too radical though and I'd tend to leave it as it is because it's got quite a good closing as is. Engines only work with high exhaust timing if they use a proper tuned pipe and from what I've seen a car exhaust system is far from being tuned. They're more like a muffler with maybe a slight bit of resonance at some point.
Here's an example of the timing for an engine that's designed for one purpose and one purpose only. Flat out running developing the maximum possible power with a full length tuned pipe. This is an OS 40PS Pylon racing engine.
Transfer opens 64 BBDC
Boost opens 63 BBDC
Exhaust opens 91 BBDC
Inlet opens 38 ABDC
Inlet closes 64 ATDC
But powerwise what's it like? Well with an open exhaust (no muffler, no pipe) it's totally gutless. Peak HP is 1.4 @ 20,000 with a nice smooth HP curve. But put a full length tuned pipe on to take advantage of that high exhaust and things get a bit different. Basically it can't run between 16,000 and 23,000 revs...it's either one or the other. Meaning it's either off the pipe or on the pipe. At 16K it's developing just under .8HP but at 23K it's developing 2.6HP and doesn't reach a peak until 26,000 where it's putting out 3.14HP. A car engine set up like this would be completely undriveable. Slow to accelerate out of a corner (gutless) then suddenly having 3 times the power with no control in between.
What this is all supposed to show is that there's a point of overkill when changing timings. You can make a gain in one area but have terrible losses in other areas. If model cars had oval track racing then you could get away with wild timings and a proper pipe but not on twisty tracks.
On the point of rod/stroke ratios as grits said, the higher the ratio the better. This OS has a ratio of 1.94 which is excellent but it's something that can't really be changed on our engines.
Here's an example of the timing for an engine that's designed for one purpose and one purpose only. Flat out running developing the maximum possible power with a full length tuned pipe. This is an OS 40PS Pylon racing engine.
Transfer opens 64 BBDC
Boost opens 63 BBDC
Exhaust opens 91 BBDC
Inlet opens 38 ABDC
Inlet closes 64 ATDC
But powerwise what's it like? Well with an open exhaust (no muffler, no pipe) it's totally gutless. Peak HP is 1.4 @ 20,000 with a nice smooth HP curve. But put a full length tuned pipe on to take advantage of that high exhaust and things get a bit different. Basically it can't run between 16,000 and 23,000 revs...it's either one or the other. Meaning it's either off the pipe or on the pipe. At 16K it's developing just under .8HP but at 23K it's developing 2.6HP and doesn't reach a peak until 26,000 where it's putting out 3.14HP. A car engine set up like this would be completely undriveable. Slow to accelerate out of a corner (gutless) then suddenly having 3 times the power with no control in between.
What this is all supposed to show is that there's a point of overkill when changing timings. You can make a gain in one area but have terrible losses in other areas. If model cars had oval track racing then you could get away with wild timings and a proper pipe but not on twisty tracks.
On the point of rod/stroke ratios as grits said, the higher the ratio the better. This OS has a ratio of 1.94 which is excellent but it's something that can't really be changed on our engines.
05-03-2008, 10:23 PM
#13
RE: Engine timing profiles.
ORIGINAL: JB COMP
Oh man, I forgot to time the SPI, well I'll have to do that tomorrow. I think the SPI is suppose to be around 70-80 degrees of duration.
Oh man, I forgot to time the SPI, well I'll have to do that tomorrow. I think the SPI is suppose to be around 70-80 degrees of duration.
.If by SPI you mean sub piston induction...the duration should be anywhere from zero to -360 degrees
. In other words none!
05-04-2008, 07:29 AM
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RE: Engine timing profiles.
ORIGINAL: JB COMP
Well, that could be because I'm not asking them to tell me what to set it or how to do it
Well, that could be because I'm not asking them to tell me what to set it or how to do it
05-04-2008, 11:06 AM
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RE: Engine timing profiles.
ORIGINAL: downunder
Oops, a couple of posts came while I was typing that last one .
If by SPI you mean sub piston induction...the duration should be anywhere from zero to -360 degrees. In other words none!
ORIGINAL: JB COMP
Oh man, I forgot to time the SPI, well I'll have to do that tomorrow. I think the SPI is suppose to be around 70-80 degrees of duration.
Oh man, I forgot to time the SPI, well I'll have to do that tomorrow. I think the SPI is suppose to be around 70-80 degrees of duration.
.If by SPI you mean sub piston induction...the duration should be anywhere from zero to -360 degrees
. In other words none!
ORIGINAL: Grits
one post not too long ago was refering to a project for high school?
How do you know how old I am? (but yes I'm sure it is)
one post not too long ago was refering to a project for high school?
That was a while back, but I guess I did say that[&:]
ORIGINAL: ugly duck
Gee, thanks. I thought my thread was pretty clear, in that I was asking for stock timing information and wasn't asking for anything special.
ORIGINAL: JB COMP
Well, that could be because I'm not asking them to tell me what to set it or how to do it
Well, that could be because I'm not asking them to tell me what to set it or how to do it
05-04-2008, 12:34 PM
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RE: Engine timing profiles.
Again since I don't know anything about 2 strokes, maybe do a little searching and find 2 different engines of nearly identical displacements but with different conrod lengths and mod them the same and compare the power. I see short rod engine as having more velocity in the air through the engine, maybe, and the long rod engine making more rpm? I don't know but that might be a path to take for modding research. Again, I really don't know about 2 strokes and with 4 strokes one gets into valve timing, duration and overlap and lobe separation and on and on...I enjoy just running them for fun but it would be interesting to see what you wind up learning. Have at it and good luck!
05-04-2008, 12:37 PM
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RE: Engine timing profiles.
I'm not modded my engines to get max power (I'm not that good) All I'm looking for is more power then stock with a little better run times, and being able to say I'm running a modded engine
05-04-2008, 12:39 PM
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RE: Engine timing profiles.
ORIGINAL: JB COMP
Oh, well as I time/mod my engines I'll be posting them here[8D]
Oh, well as I time/mod my engines I'll be posting them here[8D]
05-04-2008, 02:03 PM
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RE: Engine timing profiles.
ORIGINAL: ugly duck
In that case, I'll be watching this space. I don't dig all the cloak and dagger stuff when it's really supposed to be a DIY hobby, so if you're willing to share your stuff, I totally appreciate your efforts and I'm sure I'm not alone.
ORIGINAL: JB COMP
Oh, well as I time/mod my engines I'll be posting them here[8D]
Oh, well as I time/mod my engines I'll be posting them here[8D]
) But I'm slow on getting around to modding engines, and my 15 year old bank account can't take me buying too many engines.
05-04-2008, 05:44 PM
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RE: Engine timing profiles.
Okay, I'm done modding this engine, I did not go as far on the crank (probably only 205 duration)
The red arrows point (kind of) to where the timing has been altered
I re shaped the crank a little (since this is a engine I had modded before)
LMK what ya'll think.
The red arrows point (kind of) to where the timing has been altered
I re shaped the crank a little (since this is a engine I had modded before)
LMK what ya'll think.
05-04-2008, 07:26 PM
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RE: Engine timing profiles.
ugly duck
Here's the timing profile for my Hyper 21 8-port (I did not mod this engine)
Intake 67BBDC - 134 duration
Boost 67BBDC - 134 duration
Exhaust 88BBDC - 174 duration
Crank 197 duration (not sure of the open and close) I think its 40 ABDC open - 57 ATDC close
Here's the timing profile for my Hyper 21 8-port (I did not mod this engine)
Intake 67BBDC - 134 duration
Boost 67BBDC - 134 duration
Exhaust 88BBDC - 174 duration
Crank 197 duration (not sure of the open and close) I think its 40 ABDC open - 57 ATDC close
05-04-2008, 11:51 PM
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RE: Engine timing profiles.
Sweet, thanks for the numbers, Jon. I'll trade you for some of my own. I just timed my poor ol' VX-18 and the numbers are predictably soft:
Crank opens 43 ABDC and closes 52 ATDC for 189* duration
Boost 53 BBDC for 106* duration
Transfer 57 BBDC for 114* duration
Exhaust 77 for 154* duration
The construction of this engine is equally predictably ... quaint. Still great pinch, so no excuse NOT to port it. Not sure what I'll do yet but I'll probably try and correct some of the deficiencies while I'm at it.
Your porting hand looks pretty steady. Personally, I'd shape the fang so that the trailing edge lines up with the arc of the transfer port, like the attachment below. Would probably ramp the jet off the curve a bit stronger than just the fang alone. I'd also give more slope to the lower side of the boost port (though from the side view it looks like you've got a goodly slope on there), and I'm not sure about the three fangs on the boost port but I've seen it done that way on a few examples. The inlet to the crank still looks a bit abrupt, but it might be the photo. I'm still a newb in modifying these engines but I've ported a few cylinder heads... like that means anything.
Crank opens 43 ABDC and closes 52 ATDC for 189* duration
Boost 53 BBDC for 106* duration
Transfer 57 BBDC for 114* duration
Exhaust 77 for 154* duration
The construction of this engine is equally predictably ... quaint. Still great pinch, so no excuse NOT to port it. Not sure what I'll do yet but I'll probably try and correct some of the deficiencies while I'm at it.
Your porting hand looks pretty steady. Personally, I'd shape the fang so that the trailing edge lines up with the arc of the transfer port, like the attachment below. Would probably ramp the jet off the curve a bit stronger than just the fang alone. I'd also give more slope to the lower side of the boost port (though from the side view it looks like you've got a goodly slope on there), and I'm not sure about the three fangs on the boost port but I've seen it done that way on a few examples. The inlet to the crank still looks a bit abrupt, but it might be the photo. I'm still a newb in modifying these engines but I've ported a few cylinder heads... like that means anything.
05-05-2008, 08:39 AM
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RE: Engine timing profiles.
Okay, the other side is closer to what you where talking about. Like i said it was an engine I had already ported I just took off a little more here and there on it. There's no © on the picture, I was messing around in Photoshop and I stuck it in there
Like I said before about the crank I don't have a carbide cutter yet so I was doing all the crank work with a stone bit that's used to sharpen chain saws with. (and the tip of it is getting thin)
Like I said before about the crank I don't have a carbide cutter yet so I was doing all the crank work with a stone bit that's used to sharpen chain saws with. (and the tip of it is getting thin)
05-05-2008, 09:24 AM
#25
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RE: Engine timing profiles.
ORIGINAL: JB COMP
Okay, I'm done modding this engine, I did not go as far on the crank (probably only 205 duration)
The red arrows point (kind of) to where the timing has been altered
I re shaped the crank a little (since this is a engine I had modded before)
LMK what ya'll think.
Okay, I'm done modding this engine, I did not go as far on the crank (probably only 205 duration)
The red arrows point (kind of) to where the timing has been altered
I re shaped the crank a little (since this is a engine I had modded before)
LMK what ya'll think.
you need to de-chrome the whole port... just cutting the edhe like that will alter the intake angle of the motor.....