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     Rick_A |
I think it's pretty much been established as a fact that on Buell twins the rear cylinder runs hotter than the front. A former shop owner told me today that the rear cylinder on a Harley runs cooler, and the jetting is set for the front cylinder. His view is that the turbulent airflow off the front tire cools the front cylinder poorly and the fins straighten the airflow to the rear. Sounds like a load of old timer myth to me. Whatdoyathink? | |||||||||||||||||||||||||||
| Timbo |
FWIW, I have heard that the rear cylinder runs cooler because it runs slightly richer. Not sure if I go along with it, but as I was told the rear gets more fuel due to the forward motion of the bike. The thinking being, it's easier for the fuel to get into the rear than it is to the front. Again, not sure how acurate that is and I've never seen any data to back it up, but have heard it more than once. It would seem hard to believe that the front runs hotter, being in cooler more direct air, but I've heard it discussed before in shops with the "rear is actually cooler" being the word from the guys who know the most. Again, not sure if I agree. All I know is they work and I LIKE 'EM! Timbo | |||||||||||||||||||||||||||
| Roc |
Seems like the rear would be cooler and it ought like an easy check with a temperature gun. | |||||||||||||||||||||||||||
| Ftd |
Doug from Headquarters (porting shop in Canada) has discussed this previously on: http://clubs.yahoo.com/clubs/harleydavidsonperformance I wish I could remember the specifics but has to do with the basic design of the HD engine and the number of degrees spent by front/rear cylinders producing power??? Make any sense to the more knowledgeable engine guys out there?? | |||||||||||||||||||||||||||
| Mikej |
Get in your car with the windows up, and take two passengers, each with a squirt gun. A station wagon, van, or pickup with a shell on back works best for this test. Drive down the freeway at a fast rate of speed, with the windows up and the air conditioner and heater fans off. Have one passenger in the front of the car/truck/van/Hummer, have the other passenger in the rear. Have the front passenger squirt the rear passenger in the face with the squirt gun and see how long it takes for the water to travel from the squirt gun barrel to his/her face. Have the rear passenger do the same exercise to the front passenger and record the results. You will find, than in an enclosed airspace without outside air resistance, and without acceleration being factored in, that both shooters will be all wet, most likely just like the comment that the rear cylinder gets more fuel than the front cylinder due to the motion of the bike.  The air flow patterns of the air coming into the air filter and funneling through the carb venturi and then splitting off into each intake pathway will be what determines fuel flow to each cylinder. Bike speed will affect that due to air pressure and wind flow, but once it gets into the venturi it is somewhat straightened out and then you're playing with bubble bursts as each intake valve opens up. That venturi flow is constantly getting constipated due to both intake valves being closed, then one opening, then the other opening, then both being closed again. That venturi flow is doing a major dance routine, remember the discussion here recently about the gas fogging seen by some outside of the intake venturi.?. You can get thermal tape or thermal probes to measure cylinder temps. Go for a ride, have the shop ready to measure temps, pull in, shut down the engine, and have them measure both temps after a ride. Depending on how your bike is set up, and the speed you rode at, and the prevailing wind conditions (no Wyoming 70mph cross winds), you should see a hotter rear cylinder. At least that's my non-mathematical backyard understanding of the issue. I wish that one guy recently hadn't disappeared. There was a good thermal discussion started, but I think there was some mutual misunderstandings by both sides of the discussion, but it was leading to some interesting stuff. People just needed to seek clarification instead of attacking misassumptions with misconclusions and misunderstandings, and so on and so forth. My take on that discussion is that the exhaust side of the cylinder ran hotter than the intake side of the cylinder. 'nuff said, gotta go, bye. Now go get wet and test the theory.  | |||||||||||||||||||||||||||
| Blake |
Mike, The exhaust side of the head may run hotter, that would not surprise me since the intake is cooled by the cool air/fuel charge and the exhaust side is heated by the hot combustion gasses. However, the data presented by Notsip shows as expected that the intake sides of the cylinders (the insides of the "V" ) run considerably hotter than the outer/exhaust sides. This is as we would expect do to exposure to airflow and radiative heat environment. Not only does the V arrangement shelter the intakes side surfaces of the cylinders from airflow, but the radiative heat exchanged between the two closely spaced inner cylinder surfaces is significant. It is a shame Notsip failed to follow through on his word to provide pertinent information to support his assertions and to clarify the data he presented. I was really looking forward to that.  My diagram below reflects the data Notsip provided, though he did initially challenge it indicating that in his mind I had incorrectly interpreted it. I posted the following and never got a response... Notsip, My diagram reflects the data you provided, unless you are contending that the "thrust" side of the cylinders is the front instead of the rear. That would be incorrect. Here's how I understand it...  Thrust side is where piston is "thrust" against cylinder wall due to kick load imparted by connecting rod. Notsip's Temperature Data
 Questions notsip failed as yet to answer. 1. Is that data for aluminum or iron cylinders? 2. Do you have data for the other? 3. What were the conditions under which the temperatures were produced? 4. What kind of performance (peak RWHP @ rpm) did the engine produce on the dyno? 5. What comprised the engine, stock or high performance parts, bore, stroke...? 6. Was this a dyno simulation or an actual on the road/track test? 7. What engine lubricant was used? | |||||||||||||||||||||||||||
| Blake |
Rick, Ask your misinformed source to explain how fins oriented 45o to the ambient airflow can act to "straighten the airflow to the rear." He may have a point on a big bagger Harley with the mongo huge front fender, but I'd still be skeptical. I mean if the airflow is disturbed for the front, how does it magically reform immediately behind it? Makes no sense at all to me. Also, if the front cylinder's fins are "straightening the airflow" then they must be exposed to airflow. Too easy. No math required. Go set him straight. | |||||||||||||||||||||||||||
| Mikej |
Yep, that's the discussion, got muddy fast. Guess I'd want to see it measured in person as I still think the exhaust side should run hotter due to the heat sinking of the header pipe vs the cooling of the intake flow. Not arguing, just curious and stubborn. | |||||||||||||||||||||||||||
| Socal |
A couple thousand miles ago, my S1 started sputtering, popping and puking. At the same time, I noticed, when I warmed up the motorcycle, the header pipe from the front cylinder would glow red almost instantly after I started it up, while the pipe coming from the rear cylinder did not glow at all. It only did this for a couple days, as I rebuilt the carb and tuned the bike up and the glowing header pipe went away. I know this is different from the topic slightly in that the question is more towards the fact of which cylinder runs hotter under normal running conditions, but it might shed some light on . . . ? As far as the fins and cooling air flow: do they still sell those little smoke bombs we used to use for our science fair volcanoes in school? If so, grab a couple of those and a regular fan. Place the smoke bombs in a bowl or something in front of the motorcycle, and place the fan aiming towards the front of the motorcycle, with the smoke bombs in front of the fan. Light the smoke bombs and turn on the fan and there ya go - instant wind tunnel and aerodynamic testing facility! ![:]](http://www.badweatherbikers.com/buell/clipart/proud.gif) Rock and Roll. | |||||||||||||||||||||||||||
| Ftd |
As I understand it the front cylinder is the hotter one do to the fact that the front cylinder "works" harder. Has to do with the HD engine design and the fact that the rear cylinder only has to move the crank 45 deg to the front cylinder and then the front has to power it back around 315 deg to the rear. http://www.mecc.unipd.it/~cos/DINAMOTO/twin%20motors/twin.html | |||||||||||||||||||||||||||
| Rick_A |
I've never heard some of these theories. Some one has to have a temp sensor, pyrometer, or at least a thermometer! If Notsip's data is correct, seems a cooling fan pointed towards the "V" would go far. Blake, I pointed out some flaws in his theory today...he admitted he may be wrong in regard to Buells, but maintains that Harley's are that way. If it was true, then why would temp sensors and knock sensors always be on the rear? | |||||||||||||||||||||||||||
| Jprovo |
I have always heard that the front cylinder runs hotter due to oil splash/slinging. The engine rotates clockwise when looking from the cam side, and is kinda makes sense that the rear cylinder would get more oil splash/slinging than the rear cylinder. I have access to a digital temperature gage and thermocouple probes, but the Sportster's not running. On my Buell, the front cylinder is definitely hottter... but I ride a Blast!!! James | |||||||||||||||||||||||||||
| Sportsman |
This is good stuff! OK, if the diagrams are representative, the center of the V is seriously hotter than either exhaust side, maybe that's why X1's came with the air scoop aimed there. I'd always thought it was for the back head. The "thrust" side of the rear cylinder shows only a 12 degree difference from the nonthrust front side so thrust seems negligable. but WOW, the V section or intake side needs help. XB's have a fan there don't they? | |||||||||||||||||||||||||||
| Blake |
Mike, The cylinder heads are one thing; the cylinders are another. There is an insulating gasket between them. | |||||||||||||||||||||||||||
| Xb9 |
I've also been told by a very knowledgeable tech at Thiel's Wheels in Upper Sandusky, Ohio the same theory as Ftd describes. Thiel's has built some pretty impressive drag bikes and engines, and they know their stuff. Makes a lot of sense to me, that the front cylinder does most of the "work", thereby producing the most heat. Keep in mind that "producing the most heat"(BTU's) does not take into consideration differences in each cylinder's air flow for cooling that heat. The deficiency in cooling air flow on the rear cylinder MAY cause the rear cylinder to actually have a higher RUNNING temperature than the front cylinder, even though the front cylinder creates more heat. Thoughts? | |||||||||||||||||||||||||||
| Blake |
Sportsman, Though he never did answer, I would bet that Notsip's data is for iron cylinders on a hot rod bike that was being run HARD on a dyno. James, I disagree, I think your rear cylinder definitely runs hotter. FTD, The front cylinder does not fire 45o after the rear cylinder as you seem to think. It fires 360o+45o=405o after the rear cylinder. So if your theory were true, the rear cylinder would be doing more work. No matter, the flywheel and drivetrain inertia mitigates that effect keeping engine speed fairly consistent throughout each revolution. It is a bogus theory. Socal, Your fan and smoke idea is interesting, but would be probably not yield valid results applicable to a bike traveling through a constant/steady airstream. You would be surprised at the turbulence coming from the exhaust side of a fan. At a minimum you would need a set of louvers to straighten the airstream. here's a link that shows how to build a homemade wind tunnel. | |||||||||||||||||||||||||||
| Blake |
A "very knowledgeable tech".  How many of those same "very knowledgeable techs" used to warn us about how synthetic oil would ruin our engines. Sorry, that theory just doesn't hold water. | |||||||||||||||||||||||||||
| Xb9 |
They use redline, and recommended the same to me. I don't personally claim to know the answer, but I would think the engine builder for this team (the knowledgeable tech) knows what he's talking about. 1999 AHDRA National champions 2000 AHDRA National Pro Stock champions 2001 AHDRA Eastern Pro Stock champions #2 2001 AHDRA National Pro Stock | |||||||||||||||||||||||||||
| Rick_A |
...but it's too slippery!... anyway...the XB cooling fan is behind the rear cylinder. Ftd's link is pretty cool. It's nice seeing those forces at work there illustrated. | |||||||||||||||||||||||||||
| Ftd |
"Harley front cylinders DO run hotter because they work harder. Front cylinders fire and then the rear fires 305 crankshaft degrees later taking advantage of crankshaft momentum. The front cylinder has to wait another 405 crankshaft degrees to fire again. The front does more work and that is all there is to it. Try moving a set of bicycle pedals around like that and see which leg wears out first." FYIW This opinion is by Doug Coffey, owner of Head-Quarters. http://www.head-quarters.com/ | |||||||||||||||||||||||||||
| Blake |
Your friend may be knowledgeable about high performance dragster engines. That doesn't necessarily translate to street bike engines. The front cylinder on a V-twin dragster engine with the front cylinder's intake on the rear of the head will run leaner than the rear cylinder with its intake on the front of its cylinder head. The significant acceleration of a dragster tends to push the air/fuel charge aftwards. I don't know if your friend's dragster uses such a configuration, but if so, that may explain where he derives such an impression. For the same reason, high powered IL4 engines use downdraft carburetors to keep from going lean under hard acceleration. If you are not accelerating, there is no such effect. | |||||||||||||||||||||||||||
| Sportsman |
Reguardless of iron barrels, built or not, if the front cylinder works harder but cools better, the v portion is takeing the heat. Since oil coolers are a normal add on, and racers add oil volume to aid cooling, wouldn't it make sense to cram some air between there? After seeing that diagram, I've been staring at my bike trying to reengineer a air scoop below or incorporating the intake. What won't ram in could help cool. Thoughts? and anybody got a old GTO hood? Even though those guys really know their stuff, Big time drag bikes don't even have cooling fins so I don't think they're really a good source for practical application. | |||||||||||||||||||||||||||
| Rick_A |
As far as which cylinder does more work...I could see it either way...seems to me they'd both do the same amount of work. Our twins are basically a little chunk of an aircraft radial engine. Which cylinder(s) in a radial do more work??...and again...why are engine temp and anti-knock safety devices always on the rear?...jetting/EFI (oxygen sensors) are almost always based on the rear cylinder as well. If the front cylinder was the more critical to tune, it would make sense that all this would be based on it instead. Drag racing seems to be a far cry from streetbikes or even roadracing bikes for that matter. | |||||||||||||||||||||||||||
| Bomber |
Er, didn't the factory start putting a thermocouple or other temp-sensing thingie on S and M series tubers? I believe it was hooked up to the ignition, or perhaps that fan thingie . . . and wasn't the sensor and fan dealing with the rear jug? | |||||||||||||||||||||||||||
| Hootowl |
Sportsman, Buell makes a fan for tubers that blows on the manifold area from the left side of the bike. It is stock on Japan-bound Buells. | |||||||||||||||||||||||||||
| Torqd |
when I stick pistons it is ALWAYS the rear... | |||||||||||||||||||||||||||
| Vincy666 |
Off the subject a little bit but has to do with heat. I have an X1. I've just installed the Force intake and have removed the stock airbox and the left side air scoop to have a more balanced look. I have noticed though, when I'm riding hard, my right thigh gets alwfully warm. Never experienced that before with the scoop and airbox in place. Anyone else experience this? Should I be concerned? After following along on this thread I'm thinking about putting my body panels back on! On another note, does anyone know what happenned to that company Streetwise? I was thinking about getting their left scoop body panel but it looks like they are no longer around. Thanks. | |||||||||||||||||||||||||||
| Rick_A |
Vincy...that's normal. What I think happens is that the covers and airbox shroud your legs from the heat. You're probably getting better airflow overall...but more of that heated air is now getting to you. I basically did the same to my S1...removed all covers from around the engine, put on a smaller aircleaner, and cut a good portion of the front of the tailsection down. My right leg gets a bit roasted in traffic on hot days (I have to be careful 'cause my right leg can now tuck in enough to actually touch the rear head and header)...but I see it as just hot air that's flowing off my engine more efficiently. Seems to me the scoop wouldn't have been necessary if Buell didn't decide to cover the rear cylinder for styling purposes. | |||||||||||||||||||||||||||
| Notsip |
The temperatures of the cylinders are: Front Cylinder: Front(Minor Side)Top: 365 deg. Middle: 380 deg. Bottom: 325 deg. Rear (Major Side) Top: 185 deg. Middle: 184 deg. Bottom: 182 deg. Rear Cylinder: Front (Minor Side)Top: 197 deg. Middle: 196 deg. Bottom: 191 deg. Rear (Major Side) Top: 440 deg. Middle: 445 deg. Bottom: 431 deg. The temperature probes were placed deep in the cylinder fins up tight against the cylinder. Measured at this point there was minimal difference between Aluminum and Cast. As the probes were moved outward toward the tip of the fins the temperature decreased on the Aluminum fin, but the core temperature stays relatively the same. | |||||||||||||||||||||||||||
| Blake |
Well look who's back. We thought you shipped off to Kuwait or something. Are you planning as promised to answer our questions? Here's another one... What do you mean by "minor side" and "major side"? |
