Petrol head thread!!!

[Dark Lightning]

Aw, shucks, I'm nobody. I will say though, that thermal wrapping of the exhaust may provide some HP, as the cooling of the pipes reduces extraction. Are the pipes long enough for that to have an effect? A youtube rabbithole may be in Billy's future.

[billy rubin]

i have not forgotten

Then there is tire traction to be reckoned with. If all else is delivering and there is some drive tire slippage........... you get the idea. Fat rear tire, maybe even a slick might be appropriate. At 100 plus MPH the chain is working pretty hard and it is transmitting a huge lot of force. If the chain stretches even a little bit, it will, then the rollers and the sprocket may not fit perfectly and ...............well there are too damned many things to think of and work on.

the tire slip isnt an issue for me on pavement. on the salt it would be serious, but i dont have the horsepower to slip the tire at speed, even the little 2.5-inch racing slicks ive run. the larger machines lose as much as 10 percent of their wheel rpm on the salt in slip.

on chains, i generally run a brand new chain every meet, mostly because my machine eats an ordinary chain in about 200 miles. i have found some better quality chains that last longer, bnut its hard to get 530 chains without O-rings, and there isnt clearance to run an O-ring chain.

[billy rubin]

The number plate encloses the top of the rear wheel.......Maybe lowering the rear end of the plate to allow air pressure to escape the top of the wheel...Just brainstorming here...

i may take them off entirely, and just stick the numbers on the side of the engine. i was using them to hide some of the whirling spokes from the wind, but maybe thats a bad idea

Your pipes are really short. That is typical of high rev engines. A bunch of hot air comes out of the pipes.. Is there any way to utilize that tiny bit of thrust? or maybe deflecting the flow away from the rear wheel.....just grasping at straws in the wind....

ive tested pipes from 40 inches down to 32, in two inch increments. mine are 1-5/8 by 34 inches, measuirng around the curve. two inches either way loses 4 mph on top. i have a set of traditional triumpgh TT pipes-- 1-3/4 inches by 52? that desihn was the hot ticket for years in flat track, and are similar to mine except they are longer and bigger ID. i ran 1-5/8 based on a tuners recommendation, and the length i got by testing. i may weld up a set that tucks in closer in front of the engine, but that will have to be in the later fall. as is, they exitoutboard and blow straight back on my feet.

That blunt ended, both ends, fuel tank annoys me. Sure, it is adequate for fuel enclosure but that is not the sum of its usefulness or its harm.

Could some sort of configured pad on the top of the top frame bar, be configured to clean up the air on some of the other bits and pieces nearby.... the ones below the pad. Or on or near your belly. Surely a pad could be within the rules.

i know you hate that tank. so does my son, who thinks the whole thing is really ugly, in a steampunk manner. but directly behind the tanks is me, and im way bigger and a worse shape than the tanks. i suspect that just allowing the aircushion in front to form a dynamic blund end will be enough. what i would really like to do is try to clean up the drag behind me. changing the wheels will help alleviate side friction from the low pressure zones on each side of the spoked wheels, but there's nothing at the end to cxlose up the slipstream except my fat ass. ive tought about trying a kamm tail, and i can make one easily, but i really dont want an aero aid if i can help it. the most id like to do there is close up the business in just behind the carburetter bell mouths with a piece opf flexible plastic. it would also keep the carbs from eating dirt thrown up from underneath.


the rules in modified dont allow anything ahead of the rider that assists air flow or looks like it might assist airflow. i can put on a round headlight, but then i have to use stock mounts. thats the most thats allowed. i cant even put aerofoil rear edges on my fork legs, which actually might help

The problem with cleaning up small airflow parts,is that improving one thing may cause an increase of drag on an adjacent thing. All that on a naked bike will surely need a lot of head scratching.

Keep thinking. Apologies; I will probably continue to interfere with your thought processes. Maybe DL will weigh in here. He is a physics guy who knows a lot of stuff, including aerodynamics.

   

drag is weird. if you look at the old information

ill post some of them

things that are aerodynamic at once speed are not sao at another. viscosity effects and so on. it isnt even barely intuitive. i cant afford a wind tunnel, but ive thought about taping yarn all over my leathers and then riding down the practice course with my kids filming alongside to see where the year goes laminar. but theres only so much io have time for.

[MarcusA]

I feel the need for speed.
- Tom Cruise, Top Gun

[billy rubin]

Aw, shucks, I'm nobody. I will say though, that thermal wrapping of the exhaust may provide some HP, as the cooling of the pipes reduces extraction. Are the pipes long enough for that to have an effect? A youtube rabbithole may be in Billy's future.

exhaust is hard for me to understand. i have zero faith in computer models of exhaust tuning, because i done ever see where the constants come from or why they justify holding certain variables like EGT or MAP constant.

i rejet when the temperture or air density changes. how can i hope to understand what do with a pipe when the sun goes behind a cloud?

the old six cylinder hondas that mike hailwood raced at the isle of man would run strong when in the sunshine, then collapse in a fit of misfiring when he ran a stretch in the shade under the trees, because the air was denser there.

i dont even run megaphones on the pipes, not because they wouldnt stretch out the power band but because my needs are so narrow a straight cut off gives me what im looking for while making it easy to test.

but im very interested in anything you suggest. time is th egatekeeper, though. i worked nearly 15 hours today hauling garbage, and got in at 8 pm and told my boss not to expect me tomorrow. so ill have some time for a little while

[Icarus]

  Your engine transmits force through the clutch, gearing, and chains. Force is diminished by the ratio of sprocket radius versus wheel and tire radius.  We arrive at some unit of force at the contact patch. (patch force)... We lose some significant force, between the crankshaft and the rear wheel.  All that intermediate mechanism saps some of the Juice.

Way back in time I worked for Food Machinery Corporation (FMC division of Link Belt)  We made food Machinery but also giant fans to use in citrus groves when the temperature dropped below freezing.

The fan had a right angle gear boxes at the bottom and top of the fan pedestal. The gear boxes were operated for days on end with polishing compound inside the gear box. The gears were polished to a fare thee well before the machine was delivered to the customer. The average net gain in efficiency was astounding at more than ten percent. Quieter and longer lasting too.

Consider opposing forces. The engine delivers some potential force to the tire patch. The drag factor is an opposing force. The tire patch pushes you forward, the drag force pushes backward. When drag overwhelms the tire's traction capacity there will be slippage. There is a threshold of force vs traction. If you cross that threshold then the tire is slipping. The question is....at what velocity does aero drag exceed traction?

To identify the possible slippage, within less than a minute after the run, take the tire temperatures at the edges and at the middle of the tire patch. That will give you a clue about how the tire is contacting the ground when at speed. Also use a marker, such as a white out pen, to put several sideways stripes across the contact surface of the tire. After a run the condition of the stripes will give you some information.

You can get a tire temp gauge fairly cheap from one of the auto race parts suppliers. Worst case scenario; the driven tire is dangerously hot and may blow out and cause you to meet Jesus before you are ready.

The pipes are an important element that affects engine output. I suspect that you already know that a pulse travels down the pipe and when it meets an opening, the end of the pipe, a reverse pulse is generated that may reach all the way back to the exhaust valve. Given the correct length for a particular RPM the pulse wave can aid exhaust extraction and suck in some more fresh air/fuel during overlap period. Interestingly, the difference in area of the 1.625 pipes and the 1.75 pipes is about 16 percent. That implies that the exhaust pulse will be slower in the larger pipes and also implies that the larger ones should be shorter. (that Italian guy,Bernoulli, gets involved here.)

If the exhaust blows on your feet it is probably operating in a seriously turbulent zone or even a positive pressure zone...we are dealing with small plus or minus factors all over the whole machine and rider.  If we could identify enough of the little things, and fix them, I wonder whether that matters enough to care about. Yeah! I am pretty sure that the sum of a lot of tiny negative things makes a much bigger negative.

[Tank]

Looks like you're on a serious diet Billy if you want that world record. And you'll have to ditch the leathers for latex and/or Lycra! Or hire a low cross section midget?

[billy rubin]

ive fallen down at 115 mph, some 46 years ago

im still here, a bit creaky

that 51-year old motorcycle goes 118 today.

[Dark Lightning]

ive fallen down at 115 mph, some 46 years ago

im still here, a bit creaky

that 51-year old motorcycle goes 118 today.

I was doing about 45, I guess, when I slid off the road in '72. I was only 20 at the time, thus immortal, so far. Falling off at 115 is not good business; glad that you survived.

[billy rubin]

there was nothing for me to hit-- just a speed wobble on a sttaight road and a long slide

i mostly dont do the ton on the public roads anymore

[Icarus]

Today's newspaper has an article about a local motorcycle rider who is now dead. He was going fast on a twisty road and lost it. Fell away from the bike into oncoming lane. He slid under an approaching Nissan pickup truck.

Going too fast on a 900 pound Harley that handles like a barge is ill advised.

[billy rubin]

those things are not designed to go fast.

i dont understand the people who think they are some sort of high performance machine.

like driving a farmall C50 to the drag strip. sure, it will go there.

but why?

[Dark Lightning]

I'm lucky that I slid off the road instead of into oncoming traffic. Simple matter of which way the road turned, TBH...and it was a mountain road with little traffic.

[billy rubin]

raced on maine

2500 miles there and back

the elwctronic ignition worked fine on the bench but wouldnt pull more than 6000 rpm, so it maxed out 105mph.

that record i set at 135 sure looks far away

rejetted. nothing

changed from straight gasoline to oxygenated, And rejetted. nada

changed plug gaps from 028 to 025. nada y pues nada.

nothing i could do would get the bike over 6000 rpm.

so it was slow. but the boy rode it to 100, which i found funny. he wasnt expecting it to accelerate the way it does.

"it almost threw me off."

"yes."

i was pkanning on putting the magneto back but i have a friend in oz who is building me an ignition. s all i have to do is get a rotor made

[Tank]

I bet that bugged the fuck out of you!