| Author | Message | ||
     Redtail69 |
Hi all, First of all I'm not mechanically inclined at all so my observation might seem trivial to some of you but here goes it anyway. I seem to notice that during the early morning hours when the ambient temp is much lower(and here in the S.F. bay area it can be in the mid fifties in the early morning hours)the bike seems to pull harder after it's warmed up. I mean the thing wants to pop a wheelie at the slightest provocation. When the ambient temp is lets say in the 70s I notice some performance degradation. I know that colder air is denser than warmer air and I'm speculating that perhaps the colder air gives the bike a bit of a boost as opposed to the thinner warmer air. I'm I on the right track? And if so, what can I do to improve performance when it is warm? Thanks all. | ||
| Dbird29 |
All I know is I got a speeding ticket in the morning! Yes the bike was running great in the cool air. DBird  | ||
| Johnk3 |
red, i noticed the same... turbo/supercharge maybe? might be the only way to increase the density of the mix | ||
| Tomd |
Hi, Yep, you’re on to something. There are a few factors at work here. First, the low temps are making the air denser thus increasing the cylinder filling. The % of O2 in the intake charge is increased as a result. Second, One quality that early morning air has that warmer mid-day air does not have is moisture level. By the air temp being lower, the more moisture it will have. As the air heats, the relative humidity declines.(this is why your house gets so dry in the winter months) The additional moisture in the cool air slows the flame front slightly and allows for a "smoother" combustion event. The tendency to detonate is lowered even with the additional cylinder filling. These two factors working together combine for a real boost in engine performance. Third, the denser air has more molecules per cubic foot. These additional molecules passing over the cooling fins are able to receive additional heat as they pass by. The result of this, your engine is able to maintain it's optimum temp. One thing to note is that the additional O2 in the charge may cause lean conditions in systems that are tuned to be on the lean side of the curve when warm. But if your engine runs on the fat side when it's warm, the cold moist air will really wake it up. My 2 cents Tom | ||
| Blake |
Yes, the denser cool morning air will significantly increase actual engine power output. Some clarifications: This is real picky... Technically speaking, cooler air will not increase "cylinder filling." Cylinder fill, or volumetric efficiency (VE) is a ratio of how much intake charge the engine can draw into a combustion chamber versus how much would fill the chamber in static and ambient conditions. VE is a measure of the efficiency of the entire intake tract, combustion chamber, the cams and the exhaust scavenging mechanisms all working together to draw the air/fuel charge into the combustion chamber. It can vary significantly with engine speed (RPM). Warm air can hold more moisture than cooler air. When cool air is heated, its relative humidity decreases (thus we get dry feeling air inside house in wintertime). Relative humidity is the percentage of maximum moisture that air at a given temperature/pressure is able to hold in vapor form. Moist air is actually less dense than dryer air, so in general more humid air hurts performance from an air density point of view. Yes, more humidity helps fight detonation ( I recall the water injection system on my turbocharged '70 Chevelle SS). Humid air has a higher heat capacity than dry air, meaning it can absorb more heat without its temperature increasing as much. But temperature is a much more significant factor affecting air density than is humidity, so the cool morning air boosts the power output of our engines. It is unlikely that cooler/denser air would cause lean running problems, especially in a DDFI Buell. The DDFI systems are designed and do a great job of compensating for variations in atmoshperic conditions, not only for temperature, but also pressure as when negotiating significant changes in elevation. Not sure about cooler air providing for optimum engine temperature. Better cooling yes. But whether cooler is better is a whole other scenario.  The way all the factors work together to help an engine run well sure is neat. For instance... go up in elevation, air thins, engine cooling systems suffer (yes even liquid-cooled systems as they rely on air to cool the liquid), but the engine power output also drops and thus cooling requirments diminish. Ditto for hotter weather. I really enjoy this kind of stuff. | ||
| Buelltroll |
It's a HillBilly thang...    | ||
| Tomd |
Blake, Well I see I'm going to have to break out my ASE manuals before I go off on anymore long winded posts. :-) OK, I'll relent to the colder denser air may not increase VE but you'll have to relent that per cubic foot, denser air has more O2 molecules. Deal? :-) I think we approach the moisture content aspect from the same level but from different directions. What do you think? As far as the lean-out of the FA ratio, I was not thinking of any one application, I was simply stating a tendency I have noticed over the years. At the tracks I run cars with Holley carbs. If you have worked with them you will know that they are 2 circuit carbs. Because they are such simple devices compared to any EFI system, they compound any small changes in environmental conditions. It is not uncommon the start the day with one set of main jets, change to a smaller set at 11, then smaller jets again at 2 and then start going the other way as the day cools. Hopefully the DDFI system will keep the FA ratio in check so this wont be noticeable but you never know. Fair enough? :-) One thing I do want to point out from you post is your quote "....all working together to draw the air/fuel charge into the combustion chamber." Oh boy, my HS auto instructor would have made you prove that, just like he did when I said it once... LOL. The proper answer is always "the air charge is pushed into the engine as nature abhors a vacuum." Good riding, I'm going to break out my ASE manuals so I can be ready for the next time and ya, I live for this. Tom | ||
| Court |
You can go the your ASE manuals, but I'll save you some time. With several (yes, I know there are actually more than that) variables in play, just go to your Cessna Pilot's Operating Manual and find the Density Altitude chart. Any helicopter pilots (or fixed wing who have tried to take off on a hot humid day - my personal lesson came at Johnson County Executive over gross with shotguns headed to go peasant hunting). Along the same lines, and sans even a peek at a book, I can tell you that a Piper Saratoga feels like mush on a hot, humid day and like a T-38 on a cold winters night. I used to like to make zooming noises...emulate the sound of high performance fighter jets as I took off. That all ended the day I left the comm radio in transmit and got a reply from a roomful of laughing controllers in Olathe. Court - Varrrrrrrrrrrrrrrrrrrrrroooooooommmmm! | ||
| Craigster |
Ahhh Blake.... We agree agin! A cubic foot of air laden with more water than a second cubic foot of air cannot hold as much oxygen. Hence less potential power even at optimum air-fuel ratio and especially worse if they system cannot compensate and as a result now runs even more rich AFR. Water is my enemy......Unless were talking about forced induction. I agree with Tom on the vacuum thing. I work in semiconductor and I view almost all things regarding pressure/vacuum from the molecular side. Most of my applications live in the 3x10e-7 Torr ragne. 14.7 psia of pressure is pushing that air into the engine! Just as in my applications all the molecules are trying to zoom around at random bouncing off what ever is intheir path 'til they find free space. | ||
| Kowpow225 |
Badweatherphysicists | ||
| Blake |
Court, "with shotguns headed to go peasant hunting." I've always suspected that you had some kind of deep-seated aristocratic tendencies, but this is a real shock and frankly a bit disturbing. I mean, some of my family are peasants. Tom, Craig, Fun stuff for sure... Reminds me of lesson one in rudimentary engineering... "You can't push on a rope." I agree, the precisely accurate technical description would be that the intake charge is pushed into the combustion chamber. | ||
| Blake |
FYI: Lesson two in rudimentary engineering?... •••• don't flow up-hill. | ||
| Steveshakeshaft |
....and could I offer as lesson #3? "If it looks right, it usually is"! Steve www.shs-consulting.co.uk | ||
| Court |
Blake: That was an ugly evening......the ONLY time I'd ever lifted a butt cheek thinking the runway lighting was coming through the floor. Then I get to chattering, on a clear as a bell night at 8,500 ASL and kinda forget to navigate. Ended up wandering all over looking for Concordia, KS. Worse yet....two days later, coming home, the ceiling was about 800' AGL and I ended up doing something that emulated a combat "under the radar" run for a couple hundred miles. Had a guy in the back scouring sectionals for "potential TV towers". I am not threat to the peasants OR the pHeasant and once said "I ruined an otherwise perfectly good hunting trip by accidently killing a poor bird I shot at". | ||
| Xring |
Peasant hunting...  Most sensitive-to-temperature engine I ever owned was a turbo Shelby Daytona. That thing would scream on cold days. I kept an A/F ratio gauge in the dash, which was very enlightening for tuning in engine mods and noting changes due to weather and altitude. Some of the guys I used to drag race with (on a track, of course) used to ice their intakes before each run. Haven't notice that much difference on cool days in my XB9...but then I don't run it that hard. I'm living for lean angle these days. Good luck, Bill | ||
| Redtail69 |
So is there some kind of supercharger that one can install on the bike to counter the loss of air temp related performance reduction? | ||
| Blake |
Sure, a small turbo-charger. | ||
| Kowpow225 |
With an intercooler. | ||
| Diablobrian |
I almost gave my computer a pepsi shower after the "peasant hunting" bit. As long as we are splitting hairs.....14.7 psig is only applicable at sea level. if you are above sea level count on less "push". I am also surprised no one has mentioned the affect barometric pressure plays in air density. Just more fuel for the fire.  I also love this stuff. | ||
| Blake |
Atmospheric pressure doesn't vary much outside of significant changes in elevation. All else being equal, folks not running turbos or superchargers up at mile high elevations suffer around a 15% hit in power loss compared to running closer to sea level. | ||
| Blake |
Almost forgot... | ||
| Court |
>>>Protect the peasants! Indeed and there is not better protection than arming me with a shotgun. I'm still laughing about this typo. I think it's funnier in that I was flying out of JoCoExec which, about that era, was the 3rd wealthiest county in the US. I still laugh when New Yorkers ask "what was it like growing up on the prairie"? I always respond that I am adjusting to NYC and not having an elevator in the house. Protect the peasants! Court | ||
| Rek |
 Protect peasants by coming to Montana and chasing grouse instead! Rob |
