Combustion chamber shape, squish, compression
- Thread starter StepVino
- Start date
Big B NRG
Well, this is awkward
Oke, good to hear!
The more power/hp you want from an engine that's allready running very good takes alot of time and power. Going from 4 to 10 hp is easy, but from 10 to 12 is hard time.
If you want to post pics. Upload them at: www.tinypic.com (that one works for sure) and put the link between IMG tags (Tinypic gives that IMG automaticly).
So then it would be: link [/ IMG] without the space.
Upload some pix, that makes it more understandable.
The more power/hp you want from an engine that's allready running very good takes alot of time and power. Going from 4 to 10 hp is easy, but from 10 to 12 is hard time.
If you want to post pics. Upload them at: www.tinypic.com (that one works for sure) and put the link between IMG tags (Tinypic gives that IMG automaticly).
So then it would be: link [/ IMG] without the space.
Upload some pix, that makes it more understandable.
A new header would be a nice project later on. I'm anxious
to get this pipe back together and see the effects of the
shorter head piece.
Any guesses on how much power is being lost with these
joints? There are 2 more just like it, on the way to the
divergent cone. Would it be worth cutting them, and cleaning
them all up? I was pretty happy with the pipe, before I saw
this!
I think they do it for easier setup... one piece fitted
inside another will hold together, each piece can be turned till
the whole thing fits right on jig... then weld. I don't think
extending the pipes into eachother could have any other
purpose, but to save manufacturing time at the expense
of performance.. (?).
to get this pipe back together and see the effects of the
shorter head piece.
Any guesses on how much power is being lost with these
joints? There are 2 more just like it, on the way to the
divergent cone. Would it be worth cutting them, and cleaning
them all up? I was pretty happy with the pipe, before I saw
this!
I think they do it for easier setup... one piece fitted
inside another will hold together, each piece can be turned till
the whole thing fits right on jig... then weld. I don't think
extending the pipes into eachother could have any other
purpose, but to save manufacturing time at the expense
of performance.. (?).
scootertrog
Missouri, USA
Yep, you are correct about the manufacturing process. As a mechanical designer, I have to engineer a product so a blind monkey can build it for as little as possible, lol.
Interesting, as my wife has the Next-R on her s9 and I have the RS-70 on mine. I bet both our pipes are like yours. The step inside the pipe is definately not in the best interest of performance, it has to be interfering with the return pressure waves.
scootertrog
Well, shoot... I do not have time to finish this weekend. Here's the
progress...
Header pipe with weld joints cut. First joint past flange is
already done... In hindsight this was a mistake, should have
been left unwelded for more flexility in adjustment later.
Glad Big B talked me into going all the way... The entrance into
the divergent cone is the worst one of all:
First step in removal of excess header pipe. Cut a small section out:
Grind as much of the ring off as possible, without cutting the cone material:
Use dremmel, with router bit, to cut down more into leftover welded part:
Pry out the metal ring with screwdriver:
Repeat for the other pieces. Grind off all external original weld
material, and polish with brush wheel. Should be ready for welding...?
Of course not! Turns out that with the pieces all cleaned up,
they want to fit into eachother, like they were designed to.
This is a problem, because I have already taken my 10mm out of the
first weld, after the flange. That's why it was a mistake to finish
off that first joint before everything else.
If the pieces have to be slightly inserted into eachother, the exits of
the smaller pieces need to have the edges ground off, to reduce the step:
Here it is mounted, and there's about 10mm gap. No problem to fit,
but I have already taken the 10mm I needed off, from the first weld.
If I move the exhaust pipe down to fit, the pipe will be 20mm shorter:
I'm tempted to try it 20mm shorter. If -10mm is good, then twice as
much should be twice as good
... just kidding. We'll see.
Another problem was the exhaust flange. There's a lot of play there,
and no way of knowing if it's properly lined up with the cylinder. I
might take the cylinder off, and see what can be done to help
eliminate this guess fit.
progress...
Header pipe with weld joints cut. First joint past flange is
already done... In hindsight this was a mistake, should have
been left unwelded for more flexility in adjustment later.
Glad Big B talked me into going all the way... The entrance into
the divergent cone is the worst one of all:
First step in removal of excess header pipe. Cut a small section out:
Grind as much of the ring off as possible, without cutting the cone material:
Use dremmel, with router bit, to cut down more into leftover welded part:
Pry out the metal ring with screwdriver:
Repeat for the other pieces. Grind off all external original weld
material, and polish with brush wheel. Should be ready for welding...?
Of course not! Turns out that with the pieces all cleaned up,
they want to fit into eachother, like they were designed to.
This is a problem, because I have already taken my 10mm out of the
first weld, after the flange. That's why it was a mistake to finish
off that first joint before everything else.
If the pieces have to be slightly inserted into eachother, the exits of
the smaller pieces need to have the edges ground off, to reduce the step:
Here it is mounted, and there's about 10mm gap. No problem to fit,
but I have already taken the 10mm I needed off, from the first weld.
If I move the exhaust pipe down to fit, the pipe will be 20mm shorter:
I'm tempted to try it 20mm shorter. If -10mm is good, then twice as
much should be twice as good
... just kidding. We'll see.Another problem was the exhaust flange. There's a lot of play there,
and no way of knowing if it's properly lined up with the cylinder. I
might take the cylinder off, and see what can be done to help
eliminate this guess fit.
Aloha, the most important area/joints is the closest to the cylinder.
You can shrink the one pipe and expand the other to meet as a
butt connection.
Most important is where the flange meets the cylinder.
It is hard to find a good match with a one piece pipe.
What I do is take the cylinder off and get the pipe centered
on the exhaust port (do whatever grinding or filling in needed)
then mount the 2 flange nuts/bolts.
I take off one bolt at a time and fit and braze a tight fitting
washer so the flange/exhaust port is always in the right position.
frank
You can shrink the one pipe and expand the other to meet as a
butt connection.
Most important is where the flange meets the cylinder.
It is hard to find a good match with a one piece pipe.
What I do is take the cylinder off and get the pipe centered
on the exhaust port (do whatever grinding or filling in needed)
then mount the 2 flange nuts/bolts.
I take off one bolt at a time and fit and braze a tight fitting
washer so the flange/exhaust port is always in the right position.
frank
For street I use these EGT's. (on liquid cooled minarelli)
1: 600 C 1100 F Low and safe temp
2: 650 C 1200 F Still safe, but keep an eye on it
3: 700 C 1300 F OK but better back off a bit
4: 750 C 1382 F Hit the kill switch and full throttle
I found some engines run very cold and some very hot even though the carb mixture was right. My Malossi Replica runs 600 C whereas my old Airsal (junk I might add), ran at 700C+. If I were tuning for max power I would run that cylinder as hot and lean as I could before holing the piston as this is where the most power is.
(just Sunday reading through this thread and adding my 2 cents)
frank
1: 600 C 1100 F Low and safe temp
2: 650 C 1200 F Still safe, but keep an eye on it
3: 700 C 1300 F OK but better back off a bit
4: 750 C 1382 F Hit the kill switch and full throttle
I found some engines run very cold and some very hot even though the carb mixture was right. My Malossi Replica runs 600 C whereas my old Airsal (junk I might add), ran at 700C+. If I were tuning for max power I would run that cylinder as hot and lean as I could before holing the piston as this is where the most power is.
(just Sunday reading through this thread and adding my 2 cents)
frank
I was thinking about grinding out the exhaust and cylinder flanges,
then putting in a thin steel tube, extending a few mm into both.
It would take more time, but once done it would never be a problem
again.
Will probably go with your butt weld idea. It's was tempting to
try 20mm shorter pipe, but I just realised that 11mm of the header
was in the expansion chamber (that's how far it stuck in). Now that
is removed, even butt welding the joints will give -20mm. Sliding the
pipe pieces slightly into eachother, as in pic, would give -30mm.
Thanks for the temp readings. Will use those for calculations.
Here's an interesting discussion about exhaust gas temperatures:
http://speedtalk.com/forum/viewtopi...start=15&sid=64c954dd074b1ea3985de506f8c54e06
One guy decided to break down the exhaust components, and see what
the speed of each one is, at 1350F, then averaged them out .
It looks like the speed in AG Bell's book is too slow to use for header
pipe calculations.
then putting in a thin steel tube, extending a few mm into both.
It would take more time, but once done it would never be a problem
again.
Will probably go with your butt weld idea. It's was tempting to
try 20mm shorter pipe, but I just realised that 11mm of the header
was in the expansion chamber (that's how far it stuck in). Now that
is removed, even butt welding the joints will give -20mm. Sliding the
pipe pieces slightly into eachother, as in pic, would give -30mm.
Thanks for the temp readings. Will use those for calculations.
Here's an interesting discussion about exhaust gas temperatures:
http://speedtalk.com/forum/viewtopi...start=15&sid=64c954dd074b1ea3985de506f8c54e06
One guy decided to break down the exhaust components, and see what
the speed of each one is, at 1350F, then averaged them out
. It looks like the speed in AG Bell's book is too slow to use for header
pipe calculations.
Aloha, correct me if I'm wrong guys, but...... The rule of thumb is:
25 cm off the pipe is 600rpm plus or minus at the motor and that is 1mm
from the port height. So......
1: 1 mm higher exhaust port (on 39.2 stroke) gives 600rpm higher power band
then CUT
2: pipe shorter by 25.4mm {1 inch} for the 600rpm higher power band
frank
25 cm off the pipe is 600rpm plus or minus at the motor and that is 1mm
from the port height. So......
1: 1 mm higher exhaust port (on 39.2 stroke) gives 600rpm higher power band
then CUT
2: pipe shorter by 25.4mm {1 inch} for the 600rpm higher power band
frank
Last edited:
Big B NRG
Well, this is awkward
1 inch = 25mm (2,5 cm) btw.
You are doing a nice job StepVino! that 10mm will not make a big change on your setup. Because you do not have the high peaky revving setup.
Making the complete exhaust smooth, will gain you power. You want to keep the exhaust temp between 600 - 650 C (1100 - 1200 F). That's where the combustion is optimal. Going hotter and your piston will melt.
Going colder, your engine won't be runing up to specs.
You are doing a nice job StepVino! that 10mm will not make a big change on your setup. Because you do not have the high peaky revving setup.
Making the complete exhaust smooth, will gain you power. You want to keep the exhaust temp between 600 - 650 C (1100 - 1200 F). That's where the combustion is optimal. Going hotter and your piston will melt.
Going colder, your engine won't be runing up to specs.
Big B, I was doing this on the assumption that it's the pipe's
dimensions that are holding the engine back.. not allowing it
to rev up to where the porting is?
More power is good, but I am hoping for higher revs too.
I guess it's a subtle point, more power will make it rev higher...
but I was hoping for a good contribution from the shorter header
length as well.
dimensions that are holding the engine back.. not allowing it
to rev up to where the porting is?
More power is good
, but I am hoping for higher revs too.I guess it's a subtle point, more power will make it rev higher...
but I was hoping for a good contribution from the shorter header
length as well.
Big B, I was doing this on the assumption that it's the pipe's
dimensions that are holding the engine back.. not allowing it
to rev up to where the porting is?
More power is good
I guess it's a subtle point, more power will make it rev higher...
but I was hoping for a good contribution from the shorter header
length as well.
The pipe has to be matched to the cylinder and work together and they will work at the optimum rpm. You should get the most HP there and then you need to tune your transmission to use this power (overrange, gearup, wider belt. etc). The goal is not to force more rpm's but get a match.
frank
I think I understand that.. and I don't mean that sarcastically,
but quite literally. Anyways.. yes transmission should be tuned
to max torque, for best acceleration... pipe should be tuned
to engine's power band. However... right now I'm going for
max speed, not fastest acceleration.
Assumption is that motor is capable of higher rpm... but pipe
does not have the correct length for that rpm. I know max rpm
is not where max power is... but if you are only looking for
top speed, wouldn't you just use the pipe to boost the engine's
power at the higher rpms?..Without regard to where engine's max
power is?
but quite literally. Anyways.. yes transmission should be tuned
to max torque, for best acceleration... pipe should be tuned
to engine's power band. However... right now I'm going for
max speed, not fastest acceleration.
Assumption is that motor is capable of higher rpm... but pipe
does not have the correct length for that rpm. I know max rpm
is not where max power is... but if you are only looking for
top speed, wouldn't you just use the pipe to boost the engine's
power at the higher rpms?..Without regard to where engine's max
power is?
Aloha, Well you want to be on the top of the power curve and adjust your transmission to hold the RPMs exactly there from 0-70 mph. Then you will get your highest speed. You will not be able to pull a top speed if you are overrevving on the backside of the curve, unless you are going downhill. I am writing this in a rush so it may not address the topic exactly.
frank
frank
I think I might be starting to see your point
There is more power available at lower rpm... at the top
of the power curve. If I were to put an upgear on it, then
I could go faster there, than on the other (tail end) of the curve,
at higher rpm, but without upgear? Something tells me that
it's a zero sum... rpm x torque will be the same, so might not
go any faster. Just a feeling though...
I think, but I'm not 100% sure, that the belt has finished it's travel
by ~10k+ rpm. So don't think transmission tweeking (belt part) alone
would do it.
There is more power available at lower rpm... at the top
of the power curve. If I were to put an upgear on it, then
I could go faster there, than on the other (tail end) of the curve,
at higher rpm, but without upgear? Something tells me that
it's a zero sum... rpm x torque will be the same, so might not
go any faster. Just a feeling though...
I think, but I'm not 100% sure, that the belt has finished it's travel
by ~10k+ rpm. So don't think transmission tweeking (belt part) alone
would do it.
I think I might be starting to see your point
There is more power available at lower rpm... at the top
of the power curve. If I were to put an upgear on it, then
I could go faster there, than on the other (tail end) of the curve,
at higher rpm, but without upgear? Something tells me that
it's a zero sum... rpm x torque will be the same, so might not
go any faster. Just a feeling though...
I think, but I'm not 100% sure, that the belt has finished it's travel
by ~10k+ rpm. So don't think transmission tweeking (belt part) alone
would do it.
Aloha, maybe I can explain it a bit better.... I tune by first finding the rpm that makes the most power (top of the power curve). If you have a dyno then it is easy or u may need to block your pulley so your CVT doesn't function properly and you can go through the RPM range and see the sweet spot.
Then I set my weights in the pulley to keep that "sweet-spot" rpm constant. (trick is to find a pulley-vario that will do this. Most stock ones are junk)
If at top speed your rpm increases significantly, probably you have "run out of Pulley" and you need to look at other options (having the pulley close tighter, wider belt, bigger pulley, etc). It is NOT good to overrev to get more speed, and it will be hard to do so because of lack of power. If you overrev and have done all u can to the vario pully-rear pulley ,etc then you need to fit a Malossi or Metrakit primary gear. frank
