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Yes you are correct they are only generating so much power but no matter what if you build a motor with high compression you need more fuel and therefore more heat. A high power motor is going to always produce more heat and use more fuel unless you gear it to do ridiculously low rpms. Think about it by the volume of air the motor is pumping per mile. High performance machines will pump more per mile at the same rpm then a low performance motor of the same displacement and more air means you have to have more fuel.
 

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Not to nit-pik, but at cruising speed, both are probably producing less than 10 hp to keep you moving along.
I want to nit-pik. What do you mean by 'cruising'? If it's something like 100Km/h in top gear I'm guessing the motor is doing about 4000 RPM. 10 HP at 4000 RPM means the engine is only making 14 ft/lb of torque. Sorry dude, you can't escape the maths.

Cheers
 

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Discussion Starter · #24 ·
Engines with the same displacement at the same rpm have the same airflow irrespective of differences in their compression ratios.
 

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Wrong. Displacement is only a small function of compression. Intake and exhaust efficiency are a huge part of it. Take the 675 motor for example. It's rated at 12.65:1. However when running the overall efficiency of the motor causes actual cylinder compression to be around 14:1. A motor with less compression and therefore needs less efficiency in intake and exhaust will not flow as much air for the same rpm even with the same displacement.
 

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Discussion Starter · #26 · (Edited)
Wrong. Displacement is only a small function of compression. Intake and exhaust efficiency are a huge part of it. Take the 675 motor for example. It's rated at 12.65:1. However when running the overall efficiency of the motor causes actual cylinder compression to be around 14:1. A motor with less compression and therefore needs less efficiency in intake and exhaust will not flow as much air for the same rpm even with the same displacement.
Displacement is by definition the function of compression ratio - it is a measure of the maximum combustion chamber volume (displacement) of an engine vs the minimum combustion chamber volume (displacement) of the engine.

While it is true that volumetric efficiency (VE) will affect actual air flow as opposed to theorectical air flow, amongst most factory intakes and exhaust the VE of normally aspirated engines are not statistically different. Compression ratio does not atler VE at all. Intake and exhaust design primarily decide VE.

Could or would someone design a better intake and exhaust flow for an engine that is going to have a higher compression, sure. But there is no cause (higher compression ratio) and effect (higher volumetric efficiency).

Let me restate:

Normally aspirated engines with the same displacement and the same volumetric efficiency at the same rpm have the same airflow irrespective of differences in their compression ratios.

Higher compression ratios benefit thermal efficiency and increase mechanical advantage - but it is not a determinent of volumetric efficiency.

To the original point, yes a higher compression engine is making more power and will be hotter than a comparable lower compression engine. And yes an engine with better intake and exhaust will have better volumetric efficiency and flow more air than an engine with a lower volumentric efficiency. But compression ratio is not a contributing factor towards volumetric efficiency in a normally aspirated four stroke engine.
 

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Interesting discussion and way above my pay grade. But whatever the displacement differences between the Bonnie and the Tiger 800 may or may not make, the Tiger is considerably hotter on the rider in hot weather than is the Bonnie. Today was another scorcher here and I chose to ride the Bonnie - again.
 

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Discussion Starter · #28 · (Edited)
Yeah was out today and not as bad as last week. And the components weren't as hot either. My friend's 2008 Bonnie was much less hot to ride though.

One thing I noticed as a difference is that during last week's highway ride when traffic cleared I was riding rather fast and up towards 6,000 rpm hoping to cool myself off. It was no cooler than running slower though. Today's open road riding was between 3,000 and 4,000 rpm and even during longer areas of slow traffic and stop lights it wasn't nearly as hot.

I think a large part of my problem last week is that I was getting no benefit from the higher speed and was likely just making more heat and soaking more heat into the frame than if I had kept the rpms lower. So my increased rpms definitely was flowing more air, more fuel and more heat.

So my initial problem that caused posting of this thread was likely double user error: improper gear (only denim jeans) and improper use (running higher rpms unnecessarily). I think on days over 90* I am going to avoid sustained rpms over 4,000.
 

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Doesn't compression affect pulse width and therefore efficiency? Not to mention higher compression motors typically have direct intakes and more efficient air boxes. So it may be true that directly and on a bench the higher compression motor shows similar volume but in the bike and running down the road it does move higher volumes.
 

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Discussion Starter · #30 · (Edited)
Are you referring to injector pulse width? Yes compression ratio would alter the needed injector pulse width, unless the fuel pressure were increased relative to the change in compression pressures. Although I suspect I may be misinterpretting what you are referring to. And absolutely overall engine efficiency and performance and heat is increased with compression increases. Although higher compression ratios are usually fueled richer to prevent detonation and offer some evaporative cooling in cylinder - but likely not enough to overcome the additional thermal efficiency of the combustion process itself.

I absolutely agree that when engineers design an engine for higher compression they would be well adviced to put additional work and engineering into the intake and exhaust areas to compliment and support the higher compression, but I believe it is those items that are a much more direct cause for higher VE's.

I also saw you reworded the original post that caused my off topic response (in a thread I originated no less...) and likely I wouldn't have responded if it was originally worded that way.

Overall your point was accurate and on point, the relatively higher performance of the engine would tend to generate higher levels of heat being handled by the cooling system and transferred to the air flow coming off the radiator. I was likely being overly anal nitpicking my views on a point unrelated to the larger picture.

After today I think I resolved 75% of my original issue - for myself I now won't ride with the engine over 4,000 rpm for extended periods (i.e. highway cruising) if the ambient is over 90*. Well we will see how that works in the long run at least my intent will be to keep it at or below 4,000 rpm. :D
 

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No I'm talking about intake and exhaust pulse width which affect volumetric efficiency.

Glad to know you are seeing some sort of improvement. Do understand that the temps do go down as the bike breaks in.

You must have read my post right after I posted it as I rarely edit my posts unless I just posted it. I have a bad habit of posting then proof reading. I know I should proof read first but well this isn't my job so I hope people can understand if I make mistakes.
 

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Discussion Starter · #32 · (Edited)
I have a bad habit of posting then proof reading.
I do the same and often get caught changing my views.

I can definitely see the effect that the added power from higher CR would have on the exhaust pulse, which could likely bleed over some to the intake pulse through scavenging. Enough for me to reconsider my view as expressed earlier. Though I suspect that the effect would be nonlinear and much greater for large differences in CR than small. Say 8:1 vs 12:1 as opposed to 10:1 vs 12:1.
 

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Last weekend riding on highways Saturday and Sunday 3 hours each day the XC was very hot to ride. Amibents were 97*. The XC ran fine and the coolant temperature was stable and 2/3 so no issues there.

The engine and of course the cat throws off a lot of heat but also the heat sink into the frame is really bad. The frame and the body plastic just above it at the knee got really hot. To the point that I had minor burns around my knees through my jeans.

Any thoughts on if wrapping the exhaust manifold and pipes (not the cat itself) would help reduce some of the heat thrown off the engine and the heat sinking? For the cat any thoughts on whether additional heat shielding could help?
Burns too!!! Even if I don't let my knees hug the tank. Sure I can wear jeans, but it's still flipping hot! This can't be right?
 

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It's a very rare day that I would get on my bike without leather pants, leather motorcycle boots, perforated leather jacket and my Held leather (kangaroo) gloves. No burns ever, and as long as I keep moving I don't overheat.

Of course I realize that in New England it's not too often we're over 95ºF (35º C) like it can be down south. When it gets too hot to wear that stuff, I get in the car and turn on the A/C. :D
 

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Burns too!!! Even if I don't let my knees hug the tank. Sure I can wear jeans, but it's still flipping hot! This can't be right?
Please tell me you weren't riding your motorcycle wearing shorts...flip flops too perhaps? You are straddling an engine and it will produce heat...I don't care what type of motorcycle you are riding. Even wearing jeans on a hot day you will feel the heat coming off the engine. Yes, Tigers are known to throw off a good amount of heat but seriously...wear proper riding gear.

If you are looking for any empathy/sympathy you certainly won't get it from me because you chose to ride a motorcycle not wearing proper gear. I have ridden across Death Valley with temp's approaching 120 degrees F and yes it was hot but I didn't suffer any ill effects because of the heat being thrown off from my Tiger. Why you might ask? Because I wearing proper riding gear...it's as simple as that.

Bob
 

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All bikes will "cook the boys" when the right conditions are met...typically...wicked hot temps...stop and go traffic, asphalt etc.
Every bike I've owned, always seems to be "the worst ever" when those conditions are met.
But seriously...I can't decide if my 1950 HD panhead, or my 1993 Honda ST100 were the worst.
 

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Has anyone tried a different coolant (different than the Triumph coolant)? I am wondering if a high performance coolant might keep the engine temperature lower? Just a thought.
 
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