What your saying sounds logical, however I am still a bit puzzelled as to why Yamaha didn't put the high compression pistons in as standard?

 

They may not have put high compression pistons in the Warrior but I hear they are going to re-use the Warrior engine in a streetfighter style bike a bit like the bulldog soon and they are promising a 'tuned' version of the 1700 engine in it.

 

Yanaha (and everyone else) uses lower compression for Emissions - higher compression increases NOx emissions.

 

Not to mention the requiment to run premium fuel.
Harley's recommend premium as do the victory's
both run a higher comp than our 8.3

Kyle

 

Interesting. What experiments were run to prove the theory?
When a gas is compressed it heats up. If that basic physical property didn't exist diesel engines would not run. Also, there would be no such thing as an intercooler for forced induction engines.
Engines with high compression pistons may run cooler with higher octane fuel than with lower octane fuel. But I don't agree that engines running high compression pistons and high octane fuel run cooler that engines running low compression pistons and low octane fuel.

That being said, I've seen no evidence that replacing the stock pistons with moderately higher compression pistons would increase the heat load beyond the capacity of the cooling system on the Warrior under average condidtions.

 

quote:Originally posted by Labonski

What your saying sounds logical, however I am still a bit puzzelled as to why Yamaha didn't put the high compression pistons in as standard?




its all part of the master plan. if they had installed HC pistons from the get go, than what would they sell you when their tranny needs a recall?

ROB- everything you said makes sense to me, but i still dont see where that explains why it doesnt run hotter. maybe i need to read it again, or i'm just a rock head.

 

this this is hot out of the box , I'm pretty much satisfied with it , I need a 6 gear but i can live w/o it ! i wont be getting any high comp anything !

 

I can tell you this from extensive 2 stroke egt experience. Exhaust gas temperature readings can give misleading information as to engine component temperature under certain conditions. For example, as an engine's fuel mixture is leaned the egt will start to rise. Continue to lean that same engine to the point that detonation occurs and the egt will actually fall misleading the unknowing that the engine component temperature is falling when in reality your aluminum piston is melting . Obviously like many other components,egt is at best a tool that to be effective must be used with experience

 

"Where there is smoke, there is fire" the same holds true for horsepower and heat…

HORSEPOWER=WORK=HEAT

NO, High Compression Pistons don't necessarily make more heat.

But, increased horsepower does. Anytime you do a performance mod intended to make your bike go faster you do increase the heatload. And all bikes as Modit2thmax put it have a limit it its cooling capacity. Bear in mind that Warrior is an Air Cooled Engine with very strict limits.

Lots was done to the original Road Star Engine to safely acheive performance gains. Additional cooling fins an enhanced lubrication system etc. I read that the low compression design was intened to make it rev higher & quicker.

All IMHO

 

I added 108 cylinder and high comp pistons and 4mm throttle bodies from OE. Bike has much more torque (120 at 2500 rpms) and runs fine till you get stuck in traffic. I think its overheating and getting pre-ignition sometimes when taking off. Gets a banging sound on bliping throttle when stuck in traffic.

 

CB a pinging or a clunking? It could be similar to the dreaded Road Star "knock" which seems like it affects about 50% of the R*'s. We haven't see it too much but lots of guys on the R* boards talk about it, even on stock bikes.

The info I was told of was in a sbc 350 with varying compression ratios tested, all other data was kept constant including octane, intake temperature, fuel delivery and timing. The higher compression made more power yet yeilded lower EGT. Also tested were with a given compression ratio different octane ratings of fuels where as the higher octane per a given c/r made more heat.

I'm sure there is a crossover point where the C/R offsets the higher needed octane to prevent detonation when talking about heat produced.

"Anytime you do a performance mod intended to make your bike go faster you do increase the heatload" not true, for example higher flowing heads will keep the engine cooler. Less friction/resistance equals less heat. In super sport motors you might go in and replace the bearings with ceramic or looser bearings, thus making more power and less heat too.

 

A typical engine operates in the 25 to 35 percent thermal efficiency
range. This means 65 to 75 percent of the heat energy available is lost either out the exhaust or through the emission of heat through the engine to air (or radiator in the case of water cooling).

A higher compression ratio raises the thermal efficiency by converting more of the available fuel energy into power. (A two point increase in CR will result in about 6% increase.) This results in lowering the exhaust gas temp. [A faster burning fuel (lower octane) will also increase thermal efficiency and reduce exh. gas temp, up to the point where detonation occurs.]
However, the higher CR creates higher combustion pressures and temperatures, which dissipates through the cooling system. There are lots of variables, but with optimal ignition timing and the minimum octane necessary to prevent detonation, an increase in 2 points of CR will decrease exhaust gas temp with a slight increase in engine temp. /coolant load at max power (WOT). At part throttle, the increased thermal efficiency tends to offset thermal loss through the coolant, so the engine would not run any hotter.
Conclusion: 2 points higher CR pistons will make more power without causing the engine to run beyond it's ability to stay cool.

 

CB, Do me a favor take your bike out (when its warm again) and put it under load by slightly "chugging" it along in the wrong (too high)gear, if it is detonation it'll happen then since it's under load. Blipping the throttle won't load it up enough to cause pre-ignition if it were detonating.

Most likely it's the lash in the starter gear causing this knock.

 

Are there any down sides to installing HC pistons? Like added vibration or lower MPG.I want more power but I don't want to sacrifice the relative smoothness of the bike.MPG is a little less important to me.

 

I was speaking in general terms when I said "Anytime you do a performance mod intended to make your bike go faster you do increase the heat load.”

So let me revise that statement :
Anytime you do a performance mod intended to make more HORSEPOWER, more HEAT is also generated.

Igniting fuel makes heat. Igniting more fuel makes more heat.

--------------------------------------------------------------
At the risk of getting off the topic, let me say this...

V-twin engines are pressure-driven devices that are sometimes referred to as heat pumps.
Of all the heat produced from combustion, approximately 1/3 goes out the exhaust, 1/3 is dissipated through cooling and the remaining 1/3 is used to overcome friction and produce mechanical power. These percentages make it very clear that there is plenty of room for improved thermal efficiency. But, any heat that is simply dissipated is only energy that is wasted or horsepower that goes unused. It's all about how you are able to make and use the heat/energy.
See:
http://www.peganet.net/personal_pages/ironman1/harley.html
-------------------------------------------------------------
Back to the topic...

Compression is exactly what it sounds like, the reduction of the volume of the intake mixture by a certain mechanical ratio. The ratio is dependent on the construction of the engine incorporating the bore, stroke etc. and final volume of the combustion chamber.
Standard atmospheric pressure is 14.7 psi. If the compression ratio is 8:1, the pressure in the cylinder is 8 x 14.7 psi or 117.6 psi. At a ration of 10:1 the pressure in the cylinder is 10 x 14.7 psi or 147 psi. Under that pressure, the temperature is raised considerably.
This compression creates heat -called the heat of compression.
The greater the compression the greater the heat of compression and need for fuels resistant to detonation or pre-ignition.
Compression brings fuel particles together in an engine, heating them, and giving them the opportunity to burn more rapidly. The higher the compression ratio, the higher the air temperature in the cylinder at the end of the compression stroke.

Higher compression ratios, to a point, lead to higher thermal efficiencies and better fuel economies.
The net performance gains may exceed that of the temperature increases. But I don't think High Compression Pistons are not going to make a engine run any cooler if that is what the start to this thread was suggesting.

That's my story and I'm stickin to it.

 

wgator, sorry no offense, im no rocket scientist, just automotive mechanic. but are you confusing compression with combustion?

according to mr webster:

compression:
#1 an increase in the density of something.
#2 the proses or result of becoming smaller, or pressed together.

combustion:
#1 the state of burning
#2 the combination of a combustable with a supporter of combustion producing heat, and sometimes, both lite, and heat.

therefore, heat is a by product of combustion, not compression.

higher compression = increase in density = faster ignition = less heat.

for any non believers, get a candle, lite it. now run your hand over it, fast, then slow. now which one produced more heat?

thanks, gary

ps. i've been wrong before, but i can't remember when.

 

Compressing air will increase the temperature... higher compression=higher temp. But the real increase in temp comes not from compressing the air more, but rather from a bigger "bang" of combustion created by more molecules of air and fuel squeezed together by the higher compression.

The faster burn of the mixture doesn't produce less heat, it applies more of the heat to the power stroke (higher thermal efficiency)because the piston is still near the top. Slower burn means the piston has moved further down on it's stroke, so the combustion heat/pressure does less mechanical work, and that extra remaining heat goes out the exhaust pipe and through the cyl walls.

 

quote:Originally posted by bkrintraining



ps. i've been wrong before, but i can't remember when.
Hehe, 02/05/2004 : 3:05:41 PM to be exact. Sorry couldn't resist that one.

Compressing a gas will make it hotter. Releasing a compressed gas will make it colder.

For a real-world example, look at the air compressor in your shop. Feel the tank as the it fills with compressed air. There is no combustion going on, but the air gets hotter. Now take the hose and blow air onto your hand. The air feels cooler.

 

I think that we need the myth busters from TV to answer this one. Any body have a diesel car? They run at high compression and don't produce much heat, in the winter sometimes you have to cut off the air cooling the engine just to get the temp up, just an observation. Because the HC pistons are more efficient more heat is transfered into power leaving less as thermal heat going out as exhaust or absorbed into the cylinders.

This is fun. I just thought I'd add my .02 worth. All of these theories sound good to me.

 

im sorry, i just dont understand? how does heat push anything? are we talking about steam engines?
the pressure created by explosion, from ignition of compressed, air, and fuel. pushes the piston through its stroke, not heat.
heat is mearly a by product of combustion proces
you guys seem to be thinking of gas in terms of refrigeration, and heating.
i understand what you are saying, but the amount of increase of heat from raised compression is of set by faster burn resulting in more efficient burn, and less heat. the major sourse of heat in the internal combustion engine, is created by combustion, and friction, not compression. my point was, if you had a puddle of gasoline, and a puddle of kerosene, and lit both at the same time, gas would burn faster. the more that air, and fuel, are compressed the faster they burn, meaning that, your MAJOR sorce of heat is shortened, in length of burn time. meaning, less heat.
gunny, heat is heat, hiher compresion creates more horsepower because of a bigger bang, from more volitile fuel, air mixture, not heat.

 

almost forgot, i respect all your opinions, and mean no offense. i just love to argue. thats why i say im very rarely wrong, but been known to happen, i just cant remember when, ha ha.
seriously, if i am wrong, i would like to understand why.
i understand freon, when it changes from gas to solid, and solid to gas, (by compression), heat, and cooling result.
thankyou for listening, gary

 

Agreed, I think the discussion got a little side-tracked regarding the elevated temps on the compression stroke due to higher compression ratio. It really wouldn't amount to much. However, the higher compression equates to higher combustion efficiency resulting in more energy being released. The more energy you release, the more heat you produce. Or is it the other way around?

 

i agree, but, i believe it's more heat. just in a shorter duration, resulting in slightly cooler running overall.

however, i must contradict myself, if you then adjust air fuel ratio to compensate for higher compression, arent you back where you started?

 

What about the increase in air flow by using a BAK and a free flowing exhaust? Doesn't this increased air flow help with the cooling process no matter what internal motor mods we make? If the HC pistons because of efficiency lower the heat produced, and if used with BAK and free exhaust then the motor should run a lot cooler than stock right?

 

finallyfree, ya, you would think, but then again, you have to add more fuel to maintain proper air/fuel ratio. (thinking outloud), i was trying to remember science class, memory long as, so i may be wrong, but when the fuel, and air enter the cylander, compression causes them to combine. the more compression, the better they combine, (atomize fuel molecules?), therefore the better they burn, the less fuel required to achieve proper combustion, therefore, less heat?
the only thing i know for sure is: a more efficiant motor runs cooler. hc pistons make your motor run more efficient. hey rob, how about some help?