Jump to content

# Motocross26

Members

1,436

1

## About Motocross26

• Rank
TT Gold Member

## Contact Methods

• AIM
bruinsboy42pj

## Profile Information

• Location
New Hampshire
1. ## The 150 project

Harris, I did a couple quick calculations on your 125 project. You will not need twice the cooling capacity to hit your goal. Based on the simulated data and assuming efficiency is pegged at 1/3, you will need a 25% cooling capacity increase. In a perfect world, BHP will increase linearly with heat generated while holding a 1/3 proportion (roughly). Example: 36 HP = 1527 BTU/min Work/Heat = 1/3 Heat = (1527 BTU/min) * 3 = 4581 BTU/min <---- Stock heat generation Repeat for 45 HP = 1908 BTU/min Heat= (1908 BTU/min) *3 =5724 BTU/min <----- New heat generation % Change = (5724 - 4581)/4581 = 25% From the limited experimental cases I've seen, roughly half of the heat generated is expelled with the exhaust gasses and half is soaked up by the coolant. So, a typical engine breaks down as such: 100% Energy in (HHV gasoline * mass flow rate) 1/3 --> Power 1/3 --> Heat out w/ exhaust gas 1/3 --> Heat out w/ coolant However, unless you want to run the engine at a significantly higher internal temperature, that 25% increase in heat will have to be compensated by a 25% increase in the cooling system's capacity. As you mentioned before, increasing the flow rate within the system will certainly increase the heat transfer rate within the water jacket. Increasing heat into the fluid in the water jacket may induce some bad mojo (boiling, pressure blow-offs). Without any data on the stock cooling system it's hard to make reasonable estimates. Perhaps a YZ250 system could be adapted to the 125? Also, this entire analysis is based on an assumption that the efficiency is increasing linearly. Does your program give you any further data such as efficiency estimates or fuel mass flow rate of the new engine? Also, I'm a little concerned about the stock YZ's internals handling the additional stress. A 25% increase in power is pretty substantial. I would be concerned about putting a rider out in race conditions with a stock transmission without an analysis of the major components under 45 HP loads. All concerns aside, I really think this is a neat project. I'll be following it for sure. Edit: I noticed you mentioned painting the radiators black for better cooling. I did a calculation on this for you as well. The most heat transfer by radiation (this is the mode of heat transfer that is affected by color) that can possibly be achieved is from an object called a "black body". If we assume the radiators are "black bodies" (they are NOT), the heat transfer from a 250 degree radiator of surface area 1 m2 to 50 degree atmosphere is roughly 57 BTU/min. This is under PERFECT black box conditions. Based on the emissivity of aluminum, a realistic high estimate would be roughly 3/4 to a 1/2 of this value. Assuming "black box" conditions, thermal radiation can only account for less than 1% of the required cooling capacity. Black paint may help SLIGHTLY, but it's not going to get you to the required cooling system performance.
2. ## Carbon fiber swingarm.

Although the MotoGP swingarm is impressive, my initial thought is that an MX swingarm is exposed to larger, more abrupt stresses than a MotoGP swingarm is. Also, the design of the MotoGP swingarm is appears to be designed to minimize large bending moments and subject the material to lateral tension and compression instead. Not to mention the swingarm is plain shorter in length. I would venture a guess that this type of design allows, in a big way, for the use of carbon fiber. If you look at the "simplistic" design of our MX swingarms, the design isn't exactly friendly to the structural material.
3. ## Carbon fiber swingarm.

This is a neat concept and on the contrary to what others have said I won't discourage you from pursuing your idea. All technological advancements were just a crazy idea at some point. KJ has made a very good point to caution you with about the "testing" process. Although it appears that carbon fiber suspension components have been used with some success, the engineering behind these (limited) production parts is vast and extensive. As junior Mechanical Engineering student, I'm cringing at the level of force analysis involved in engineering a critical suspension component such as a swingarm in a motocross application. Just preliminarily thinking about the forces involved in this part, even if you were able to design the swingarm to be strong enough to withstand the large moment around the frame-swingarm-shock connection (which is highly cyclical, further complicating the matter) and compressive force from the acceleration of the bike (also cyclical), the side-to-side forces (think swapping bike behavior) would pose an even greater challenge adding an additional fully reversed, cyclical moment. Essentially, you're talking large, cyclical stresses in all 3-dimensions. Combine that with the highly varying behavior of composite materials and you've got a nifty problem on your hands. Be careful if you chose to ride the bike, very careful. I would call a CF swingarm that's able to sustain the weight of an unmoving rider "good enough" and a job well done. Actually riding the bike in any type of setting is a completely different story. Perhaps you guys might consider a simpler part to start out with. A CF shift or brake lever? The stresses in these parts would be far easier to analyze.
4. ## Put in a new K&N Air filter and a week later my engine was destroyed

Look at the last clause in the warranty.... They don't cover off-road applications in their million mile warranty but provide a one year warranty regardless if mileage.
5. ## My new moto video! RM250 2T!!

I would love to see more quality videos like this. The film style reminds me of good, professional ski/snowboard flicks. I would definitely pay money for a full-length film like this.
6. ## 05 Yz 125, Head shake?

Getting the correct springs for you in your bike is always the best place to start with, but this may be a problem that has to do with fork packing. Try speeding up the rebound or stiffening the compression to fight this problem. Again, I highly suggest you get the correct springs in your bike regardless if this fixes the problem or not.
7. ## 2005 YZ250 jetting problem?

Did the white smoke have a very strong "burnt" smell? At first I was thinking this was a crank seal issue, but the only time I've had lingering white smoke out of my silencer after shut down was a case of a very lean main jet that allowed my bike to run hot enough to burn the silencer packing. To properly read a plug you need to do a "plug chop". Get your bike up to roughly operating temp. Then quickly change out the plug with a fresh, new one. Now do a full throttle run under load on a long straight or w/e. Stay off the pilot/needle circuit as much as possible. Reading the plug after this routine will give a much more accurate representation of your bike's running condition. Edit: If you truly are so lean that you're burning packing I'd avoid a plug chop until you've gone up a couple steps on the main jet.
8. ## Vid of me riding my 2010 yz450f

Great riding man, looks awesome! Do you know the song used in the vid by any chance?
9. ## Should I repack FMF Shorty?

Repack and fix your jetting. Your bike shouldn't be producing so much spooge that it's saturating the packing your exhaust.
10. ## Arm Pump

Try gripping with more of your ankle/calf area when standing. I'm pretty average size (5'11") and I've found that gripping with my lower legs tightly gives a much greater area to spread that contact force over. Gripping this way feels much more natural in a standing position and allows me better control of the bike for longer periods of time. I also feel much more mobile in the upper body region as my knees can pivot with the rest of my body allowing free movement of my body over the bike. When sitting, I grip with my entire lower leg including my knees as my knees naturally hug the tank in a sitting position.
11. ## Project KDX 220R - The Rebuild

Wow, great job. That media blaster does some amazing things to old parts. Which one are you using?
12. ## 2010 AmPro Yamaha Team photos

Ohlins suspension?
13. ## Do you roll it or rip it? Throttle Response ??

I agree with this. The clutch offers more control of power to the wheel than the throttle does, especially on smaller bore two-strokes. In reality, I probably use 85% clutch, 15% throttle to control power.
14. ## Short YZ125 Vid

Your son looks pretty talented. I hope he keeps it up.
15. ## Short YZ125 Vid

I thought the same thing after watching myself. I should be getting my suspension revalved and rebuilt over the winter which should help a lot.
×