Dong Fang DF 250 RTB Bobber Information

[axa]

9.0:1?

we have a winner.
your uncanny barnone.

So i must say, i didn't expect it but, indeed the CR we read for the loncin 167FMM is indeed as advertised.

So here is the rundown.
Measuring with a liquid displacement method. really there is no other feasible way:
https://drive.google.com/file/d/0B-M...it?usp=sharing

I didn't ignore the givens and actually measured the stroke at exactly 65mm and bore 67 indeed... The rest was:

Bowl 22cc = 22000ml³ (second take 22.2cc)
TDC to deck 2mm = 7051ml³
Gasket 1mm = 3526ml³
Piston dome 4cc (maybe 5cc)= -4000ml³
Stroke 65mm = 229167.404
229167+22000+7051+3526-4000:22000+7051+3526-4000
(229167.404+28577)/28577
= 9.02 CR

when i double checked a second measure of the bowl, i got the a hair over the graduated measurement line so if you call it 22.2 you get
= 8.96 CR

so it seems that the CR is indeed 9.0

BUT, It was very difficult to measure the piston with the molding clay i had on hand, it was much too hard and didnt conform to the dome and valve relief profile well, and didnt provide a deep enough void. So i estimate i may be a bit wrong on that measurement.
If the numbers are rerun for say a 5cc dome, it comes out to be quite different at 9.31, much like the advertised DF 9.2, so that is plausible as well.

Thus it will be worth while to get a softer clay and remold the piston for measurement, 0.3 is much too large a margin of error to work with. But right now i believe the number is 9.0.

So starting with 9.0, as increasing it by machining, here are the options:
Reducing the gap by 35mil yields a 25470ml³ volume for a 10.0 CR
20mil -> 9.5
50mil -> 10.5

Given confirmation on the temp, and piston dome, I will resist the urge to go straight to 10.5, 10.0 might be a more reasonable starting point...

I should note, reducing the cylinder head depth is not the only option, the cylinder itself can be reduced as there is a 2mm piston to deck height gap. Though popularhotrodding showed no power decrease for deck heights up to .125mil deep. so either or...

But despite what you may hear around these parts, going from 9.0 to 10.5 will only yield a theoretical 4.5% power increase:
http://www.popularhotrodding.com/tec...on_ratio_tech/

Unfortunately~60mph + 4.5% does not = ~80mph, not in our 3rd dimension anyway

[axa]

btw, apparently these loncin engines came with a cylinder wall cross hatch hone
https://drive.google.com/file/d/0B-M...it?usp=sharing

I didnt expect that really...
I only mention this cuz a replacement cylinder wont have it.
Its just nice to know at least the loncin factory is doing some things better than others...
which just might carry over into other areas, who knows.

[DanDaMan]

roadkill austn Is a lot of highways so im almost always on highway , when off highway indeed im in lower gears , never even touch 5th unless going over 60 mph , and hills cause me to down shift to hold 55-60

and It really dont matter how much deck u remove or turbo u add or nitrus u shoot , if u dont change gearing ,youll just pull to what u did be4 then valve float limit yourself


all I did was reverse stock air filter , and gear very tall , tall as could fit , oh and add 112 main (hair to big) to stock carb , stock otherwise

if u only ride in town and are comfortable with your rig doing 60 don't change a thing , as it will kill me off the line and probably on hills

I am not saying my rig is for everyone , My ride position has my feet straight out about 10" below my butt and the headlight/speedo act as air diverters up to mid chest level on me (would be like adding a wind screen on yours to have less drag) , and Im 165 on a heavy day

[Roadkill]

roadkill austn Is a lot of highways so im almost always on highway , when off highway indeed im in lower gears , never even touch 5th unless going over 60 mph , and hills cause me to down shift to hold 55-60

and It really dont matter how much deck u remove or turbo u add or nitrus u shoot , if u dont change gearing ,youll just pull to what u did be4 then valve float limit yourself


all I did was reverse stock air filter , and gear very tall , tall as could fit , oh and add 112 main (hair to big) to stock carb , stock otherwise

if u only ride in town and are comfortable with your rig doing 60 don't change a thing , as it will kill me off the line and probably on hills

I am not saying my rig is for everyone , My ride position has my feet straight out about 10" below my butt and the headlight/speedo act as air diverters up to mid chest level on me (would be like adding a wind screen on yours to have less drag) , and Im 165 on a heavy day

Lived in Austin for about a year and loved it. I went to the first 3 ROT rallies. Would love to retire to Bandera where maybe a little taller gearing would work for me. There are lots of good roads in the hill country for sure. That's part of why I asked about the tall gearing and hills/city riding. I lived on the I35 corridor and that traffic sux 24/7 almost from Round Rock to San Antonio. Rode a early Valk for awhile and that's the best bike I've ever oned.

[axa]

roadkill austn Is a lot of highways so im almost always on highway , when off highway indeed im in lower gears , never even touch 5th unless going over 60 mph , and hills cause me to down shift to hold 55-60

and It really dont matter how much deck u remove or turbo u add or nitrus u shoot , if u dont change gearing ,youll just pull to what u did be4 then valve float limit yourself


all I did was reverse stock air filter , and gear very tall , tall as could fit , oh and add 112 main (hair to big) to stock carb , stock otherwise

if u only ride in town and are comfortable with your rig doing 60 don't change a thing , as it will kill me off the line and probably on hills

I am not saying my rig is for everyone , My ride position has my feet straight out about 10" below my butt and the headlight/speedo act as air diverters up to mid chest level on me (would be like adding a wind screen on yours to have less drag) , and Im 165 on a heavy day

So by this logic just gear high enough and we can all be hitting 125...
so what you don't seem to realize is that u need to have enough power to over come resistances.
Even a rock can hit terminal velocity if u drop it off the roof...

Why don't you get your self a gps, or borrow one, post a vid of you cruising at 80, and shut everyone up...

[DanDaMan]

So by this logic just gear high enough and we can all be hitting 125...
...

no no no ive already stated I geared for 80 but valve float around 75 (the greater the motor strain the easier to valve float) , with 5th havng near no pulling power at all , but will try get a vid of me cruising over 70

[axa]

no no no ive already stated I geared for 80 but valve float around 75 (the greater the motor strain the easier to valve float) , with 5th havng near no pulling power at all , but will try get a vid of me cruising over 70

alrite... now we're down to 70, even i with higher gear ratio can get to 64 (indicated) on a decline... but that's entirely not the point...
you made the impression that you can cruise at these speeds, so ok, post that vid even just at @70. not on a decline, not with your skewed speedometer...
still then i fear we will be watching a half hour video it will take for you to reach it...

[axa]

got sort of tired of the "dont seem to realize arguments" everyone on the internet has all sorts of opinions and ideas, so i thought i would demonstrate the theory about all this.

Total power required
P(total) = P(rolling resistance) + P(wind) + P(gravity) + P(acceleration)

First Pg, gravity is eliminated as we don't care about descending a hill as I mention even a rock can hit terminal velocity, and of course these speeds are not attainable climbing, so don't even try it...

Secondly Pa, acceleration also drops for its not really a question about how long it will take dan to reach these speeds, only that it can be reached....


So then we are left with:

1 Pr Rolling resistance.

The power required to overcome rolling resistance can be described by the formula P = Crr x N x v, where

P is the power required.
Crr is the rolling resistance coefficient. define this based on the type of bike (road, mtb, cross) you used.
N is the normal force of the bike and the driver against gravity.
v is the rider velocity

As exact factors don't matter as long as they are consistent, and frankly we don't know them, we use 1.

@60mph
Pr = 1 * 1 * 60
@80mph
PR = 80

Here we can see this measure is linear vs speed, so the power required for rolling resistance alone is 33% greater for dan than others. (80-60) / 60 = .333333


2 Pw Wind resistance

The power required to overcome wind resistance (drag) can be described by the formula P = 0.5 x ρ x v3 x Cd x A, where:

P is the power required.
ρ is the density of air.
v is the rider velocity, relative to the wind.
Cd is the drag coefficient.
A is the the surface area of the rider facing the wind.

again keeping this constant for unknown factors:

@60mph
Pw = .5 * 1 * 60³ * 1 * 1 =
½ 60³ = 108000

@80mph -> 256000

Here you can speed is the factor cubed, so dans power contribution requirement is 137% greater than others. (256000/108000) / 108000
wow

Conclusion:
Without knowing all of these other coefficients I can not plug in the numbers to get the real power dan claims his higher gearing has compensated for...

But I only suggest that at highways speeds, wind is the greatest resistance to be overcome, and he has at least enough power to overcome 137% MORE of it than i do...


great hope for the argument that there is still power to be had by lifting the float ceiling. but still, who wants accelerate at a snails pace...
that's why i believe the real discussion is not about how to reduced gear ratios, but how to increase power.

[DanDaMan]

great hope for the argument that there is still power to be had by lifting the float ceiling. but still, who wants accelerate at a snails pace...
that's why i believe the real discussion is not about how to reduced gear ratios, but how to increase power.

man u seriously spamming bars thread , because I can . or claim, to be able to go 13-15 mph faster than u ?

as for power to money , best buy would be a turbo , to add nuther 2-4hp , as decking/compression ect prob add 1 or 2 for a lot more time and $$ , and those numbers might all be "to hopeful"

and the motor is nearly "square" allowing a lot more power thru out the powerband , which allows a bit more pull at lower rpms , so stretching gears made sence to me

[axa]

man u seriously spamming bars thread , because I can . or claim, to be able to go 13-15 mph faster than u ?

as for power to money , best buy would be a turbo , to add nuther 2-4hp , as decking/compression ect prob add 1 or 2 for a lot more time and $$ , and those numbers might all be "to hopeful"

and the motor is nearly "square" allowing a lot more power thru out the powerband , which allows a bit more pull at lower rpms , so stretching gears made sence to me

you would be surprised who barnone thinks is spamming this thread....
get that vid yet? im expecting to see this when you hit 80 on that desert highway...