dougmeyer
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posted September 24, 2003 02:00 PM
Overheating and big engines
I've been seeing several comments and questions regarding overheating related to overbored/stroked engines. I detect a common misconception is at work here. Think about this;
The heat generated within the combustion chamber is directly proportional to the amount of fuel burned. The power output is proportional to the power demanded or needed to move or accelerate the motorcycle. The power needed to idle or propel the bike along at a steady state, or accelerate at any part throttle demand does not change with the size of the engine, If it takes 60 hp (a reasonable number) to drive along at 70 mph, the amount of fuel needed and burned is nearly the same within an engine family regardless of the size or ultimate hp capability of the engine. Some will suggest compression ratio is a factor. But, in fact, high compression ratios and the necessary high octane fuel actually contains and converts less rather than more heat. (Lower octane fuel contains more latent energy- more BTU's.) The reason you get more power with higher compression has to do with the expansion ratio of the burning mix, not the heat.
Most of the complaints I hear reference overheating "in traffic" or "around town". Clearly, the size of the engine has nothing to do with this.
The radiator is sized to transfer enough heat to the air to keep the engine within limits at maximum output for a period of time thought to be reasonable. At Bonneville, which is a fairly tough environment, (high outside temp, very thin air), even turbos of 300+ horsepower
stay cool for 3 minutes at full throttle.
There are two things that cause the kind of overheating y'all describe. Poor water flow due to air locks or large "bubbles" in the system and/or not enough air flow through the radiator. Engine size or peak power has NOTHING to do with it.
Just look at the size of the coolers on an 800 hp open wheel car. Not very big, but they do get the air through them.
Doug
  
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zxlnt
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posted September 24, 2003 05:49 PM
So your saying just because your bike can make 200 horsepower at redline doesn't mean it makes any more heat making 60 ponies than a 175 peak horsepower bike does when it is makning 60 ponies . Makes sense to me. Only time it should make more heat is when its making more power right?????
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frEEk
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posted September 25, 2003 12:48 AM
i'd say there are a few variables that would make a difference (new piston weight, bore/ring size, ring type, etc) but all would likely be nothing more than academic, and i'm guessing probably cancel each other out to a large extent otherwise. however i'll admit to not really thinking about it and realizing the "equal heat" fact before. thanks for the clarification doug!
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EastBayDave
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posted September 25, 2003 06:39 AM
quite interesting! Thank you Doug! 
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02' ZRX1200
00' ZX12R sold
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dougmeyer
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posted September 25, 2003 06:55 AM
Exactly right, zxlnt. frEEk, changes in the "mechanical bits" might effect internal friction a small amount and raise oil temp a very small amount but would'nt effect part throttle coolant temp at all. I forgot exactly what the "pie chart" looks like right now but I think internal friction accounts for about 20% of the total heat generated.
Doug
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addisonzx12
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posted September 25, 2003 07:15 AM
Doug makes a good point. But, having 3 different sizes of the zx12 myself(stock, 1290, 1380) I know for a fact that for each upgrade, overall the motor throws a lot more heat into the air! Now the engine/radiator can handle the heat better than I can. The temp gauge stays right at 9 o'clock as long as I remain moving, & will not get bothersome until I getted stopped for stoplights, etc. what I have noticed is once the engine gets hot it stays hot even after the temp gauge goes back down to normal. I am talking about radiant heat here all around the engine, even though the water temp is back to normal.
I think one reason for this is the engine does not have a proper oil cooler & it takes a real long time for the oil temp to come back down. I also suspect this is why the clutch plates are so sensitive to hot lapping at the dragstrip! The engine oil does not cool down quickly. The Busa is not nearly as sensitive to hot lapping as our bikes even with smaller diameter clutch plates & a similar power level.
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1bad12r
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posted September 25, 2003 08:10 AM
Thanks alot Doug, you have been very helpful. You gonna be around in Montgomery Al. next week ? I'm gonna be there and would like to stop by and talk a little about big bore kits.
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768 Ryderz
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dougmeyer
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posted September 25, 2003 08:53 AM
No, Sorry. I'm going to be at the Vulcan Riders and Owners Club RAlly in Eureka Springs Arkansas. Can't forget those Cruiser guys, you know....
Doug
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entropy
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posted September 25, 2003 10:12 AM
 Edited By: entropy on 25 Sep 2003 11:12
I understand exactly what Doug is saying, and fer putting around, maintaining a constant speed, no vigorous accel, the diff between an OEM and a big in motor(big hp), both w/same same CR ought to be negligible. Same hp to perform same work
BUT! If you take yer 1361 and accel vigorously it will pull higher g's, more work, more temp incr. Sure the hp blasts are short, but the 12 doesn't throw heat well.
Like addison, I understand the theory, but I KNOW my 1427 heats up more after a pass. Yes that's extreme, not related too closelt to "spirited street ridiing, but i think its indicative.
That said, I run water + water wetter, and I get ALL the air out of my system, and my 1427 DOES NOT OVERHEAT when the fan is running.
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dougmeyer
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posted September 25, 2003 10:59 AM
Entropy,
Sure it heats up more and quicker at full throttle. That's in keeping with the premise I cited. More power = more fuel burned = more heat. But, it doesn't OVER-heat. That's the point.
Doug
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addisonzx12
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posted September 25, 2003 01:16 PM
I agree with Doug. The engine won't overheat, but it is not very comfortable for the rider sitting on the bike! Definitely the only negative about going big bore! I think that is the problem everyone is referring to(rider felt heat on the seat, I know all about it), not the bike actually overheating. I wish there was a fix for that! For now, I just ride another bike when the temp is above 80-85ish.
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ra12r
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posted September 25, 2003 05:16 PM
I am not sure that the bikes won't overheat. I have seen zx12's overheat and steaming in stop and go traffic(overflows boiling). My bike will go from 9 to 11 oclock in just minutes once it ever gets to 11 oclock if i am stopped at a long light or in SOME stop and go traffic while just riding around. In these conditions the bike is simply ideling and not reving, but that temp gauge moves up in regular intervals. I personally have never risk letting my bike go higher than 11 oclock before just pulling over or jumping lanes to get moving. But, the fan comes on right after 10 oclock, but that DOES NOT stop the temp from continuing to rise if the bike is ideling or moving slowly.
I am on my 3rd engine configuration. The first two stock and 1270 acted basically the same. My billet however is DEFINITELY different as far as heating characteristics go and as far as the personality of the motor sensitivety to temperature change. NO ONE should read Doug post and assume that you can "comfortably" cruise around town with a billet block!!! YOU CAN NOT!!! It can be done, because i do it about everyweekend, but the bike is VERY temperamental! It is harder to start when hot.....please reread,,,,,It is HARDER to start when hot!
Now, this is with the same 60hp require to move the frame around. All things are not equal even though intellectually they should be equal. Riding around at 60hp the bike will run at cooler with a billet, but as soon as you stop the temp changes faster up and down. This block will jump from 11 to 9 oclock in a 1/4 of time that my stock motor would cool down. But it will also jump right back up to 11 oclock just as fast.
Entropy, how did you make sure that you got all the air out of your system?
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dougmeyer
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posted September 25, 2003 06:27 PM
ra,
Something else is going on. It isn't the fact that it's a block carved from billet unless the flow through that block is restricted somehow or not as great as the stock system. Runaway temp can only mean that the heat is not being shed to the air, either because the coolant isn't moving, or because the air isn't. I've seen it result from something as simple as too many bent fins on the rad.
I'm not doubting that what you say is happening isn't, but the why is another story entirely. No need to take my word for it, though. It's simple physics.
Hot starting is another issue with other causes.
Doug
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entropy
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posted September 25, 2003 11:35 PM
quote:
...Entropy, how did you make sure that you got all the air out of your system?
from another topic:
i have a 1427, use water wetter & distilled water. No problems with over heating, BUT gotta be careful to remove trapped air bubbles from the coolant system.
My method for removing air is to have the bike on a rear stand, idling, pour in the coolant slowly as the bike starts to warm up, when full of coolant & no more bubbles coming to the filler opening, temp guage at 8pm; cap it. Then idling and lite blipping let the system heat up and pressurize, temp guage at 9pm.
Still running, I disconnect the fan connector and let the temp get up to 11pm, but NOT into red. At this point the coolant is HOT and is expanding into the overflow bottle.
I then reconnect the fan connector and even put an external fan on it and the temp comes down quickly to 9m and I shut the bike off. 30 min later, when cool, an inch or so of the coolant has been sucked from the bottle back into the engine/rad, and air bubbles are GONE. Sometimes it takes 2 cycles to get all the air. 
SAFETY MOMENT!!!!!!!
Last Sun I was heat cycling the bike as above. Temp ga was at 11pm and I leaned over to snap the rad fan connector together, and WHOOSH! A rad hose connector explosively let go on the l side and drenched my chiken legs in V HOT coolant/steam. Of course I was wearing shorts... I'm a dumbass... A red legged, oozing, peeling, limping, dumbass...  But hey, that's why God gave us emergency rooms and Vicodan
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psycho1122
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posted September 26, 2003 06:24 AM
I would like to add one factor to this "big engine-overheating" issue......
I have noticed that these big engine's w/ high compression DO NOT like running lean. If you have tuned w/ a DJ250, you could be too lean. Lean combustion chamber is a hot and not very smooth running one!
It was very interesting to watch my 1270 smooth out and generate ton's of torque (112 ft. lbs.) as we added fuel. Not only that we could watch the temp go down as well, even at idle w/ no airflow!
Even on trackday's w/ my 12 (out here in Phoenix) we have had 105+ temps' and I never have had it go above the 9 O'clock position. Pull it in after a session and sometimes the fan won't even come on!
Keep in mind that even w/ 13.8-1 compression, I run pump 91 octane w/ no problems. Proper A/F=Cool Combustion.
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dougmeyer
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posted September 26, 2003 06:25 AM
Edited By: dougmeyer on 26 Sep 2003 07:27
The bleeeding process can be especially difficult on a bike with a lower-in-the-front stance. You may have noticed at the races that when running the Turbo ZRX we had to very carefully bleed the bike by running it with the front end up on a 6" block and then we would lean it to the left repeatedly while running to put the filler at the highest point. Without attention to that process it would absolutely overheat. Bleeding is one of those things that is often overlooked and underappreciated. When I worked on the Can Am and F-5000 cars, we had a series of -3 lines from the tops of both the coolers to the header tank (which was always the highest point) to continuously purge air out to the top. It takes very little air to form a blockage to the coolant flow, especially in an engine like the 12 with small passages.
Right on, Psycho.
Doug
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ra12r
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posted September 26, 2003 07:10 AM
Doug, Well, i am certainly open to ALL solutions to normallize the heat components. I will recheck my radiator for bent fins. The block is a billet block by SBM. My observations are that differences between SBM and Muzzy's block is almost none. So, are you saying that you that you have not experienced the heat swings with the billet block?
When i fill my engine with coolant, i always do so with the motor running and slowly filling. Then i let it heat up through some cycle and recheck the level. I hope i don't have a pockets, but how can you know for sure?
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dougmeyer
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posted September 26, 2003 08:28 AM
ra,
Depending on the "vintage" of your block, the differences can be substantial. Up until recently when I think he may have changed his design, our design was completely different than his.
Heat "swings" sure, depending on your system and thermostat. But as I said above, not OVERheating (see some comments by Kcadby, entropy, etc.). The stock pump and radiator is plenty capable of keeping the system within limits.
As far as knowing if you've got it bled, that's a tough one. Iguess you can only try some of the gyrations we and ohers have done. Raise the front end up as much as you can, roll the bike side to side, etc. Also we keep a close watch on the actual amount of coolant going in from dry. That is, until we're sure of how the system works (I'm talking custom system race bikes here) we use a graduated container to be sure all the coolant the system is capable of holding is going in.
Doug
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EastBayDave
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posted September 26, 2003 01:08 PM
I'd be curious what the exact amount of fluid into the stock ZX12R block would be considered "maximum" w/all the air bubbles completely gone...?
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Enjoy the ride!
02' ZRX1200
00' ZX12R sold
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dougmeyer
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posted September 26, 2003 01:13 PM
Edited By: dougmeyer on 26 Sep 2003 14:15
Here's a starter- If your system is well bled and working well, measure how much comes OUT next time you drain it. Then make sure that amount goes back IN everytime you fill it from dry.
Oh yeah, and the book says a Stock system holds 3.6L including a 1/2 full reserve tank.
Doug
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psycho1122
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posted September 29, 2003 07:38 AM
Right on Doug.. 
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EastBayDave
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posted September 29, 2003 01:54 PM
Thanks Doug....
Brain fart...go pick up the manual......doh!
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Enjoy the ride!
02' ZRX1200
00' ZX12R sold
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