compression ratio - Page 5 - Triumph Forum: Triumph Rat Motorcycle Forums
» Main Menu

Discussion Forums
 » Twins
 » Tiger
 » General
 » RAT

Features
 » Blogs

Motorcycle.com Links

Contribute
 » Photo

Motorcycle Forums
» Insurance
» Sponsors
» Our Partners
»ATV Reviews
»Motorcycle Games

Twins Talk Discussion of Hinckley Triumph Twin related matters and topics.

Reply
 
LinkBack Thread Tools Display Modes
Old 11-01-2012, 11:49 AM   #41 (permalink)
Senior Member
SOTP Vintage Series
Main Motorcycle: 03 T100
 
mikeinva's Avatar
 
Join Date: Mar 2007
Location: richmond va
Posts: 7,775
Quote:
Originally Posted by norton74 View Post
You're right. Raising the CR does improve thermal efficiency a little and as a result, torque and horsepower. What I haven't figured out is how fuel consumption goes down. At a given engine speed, the amount of fuel being burned with each combustion cycle would have to be pretty much constant. The only way you could burn less fuel is for the air fuel mixture to become leaner. Running lean presents a whole new set of problems so let's assume that the air fuel ratio stays constant no matter what the CR is. I guess that it's time to hit the books.
if you inprove thermal efficency you burn less full to make same amount of power.And its not like its just alittle.But i give up you know everything there is no need for any of us to tell you anything.
__________________
Why do I feel young on my bike
mikeinva is offline   Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
Old 11-01-2012, 11:55 AM   #42 (permalink)
Senior Member
SOTP Vintage Series
Main Motorcycle: 03 T100
 
mikeinva's Avatar
 
Join Date: Mar 2007
Location: richmond va
Posts: 7,775
Quote:
Originally Posted by JustPete View Post
Norton74, in simple terms raising the compression can result in more power using less fuel. In reality it's more then that, keeping ALL things the same and raising just the compression will most likely result in knock, lowered performance and MPG along with a lunched engine.This topic can go long and deep so I think if you research thermal efficiency of an internal combustion engine you will get the information you're seeking. BOL Pete
That is true but as long as you dont rase it to much on these motors you wont have any knock.I have run them up to 11.5 to 1 on 93 octane pump gas on the street for many miles.If you took a other wise stock motor you could prob run 10.5to1 on reg gas because stock bikes the timing is way slow to start with.These bikes are way under tuned to pass epa reg.
__________________
Why do I feel young on my bike
mikeinva is offline   Reply With Quote Quick reply to this message
Old 11-01-2012, 12:18 PM   #43 (permalink)
Senior Member
Formula Extreme
Main Motorcycle: 2012 T100
 
norton74's Avatar
 
Join Date: Jun 2012
Location: Stockbridge, MI
Posts: 731
Other Motorcycle: 2013 Rocket 3 Touring
Extra Motorcycle: '73 Ducati GT750
Quote:
Originally Posted by mikeinva View Post
if you inprove thermal efficency you burn less full to make same amount of power.And its not like its just alittle.But i give up you know everything there is no need for any of us to tell you anything.
Sorry, I didn't mean to put you out of sorts. I was simply asking a question that hasn't been answered.

The question is moot to me as I don't intend to change the CR of my bike and I doubt that anyone riding a motorcycle is going to change the CR of his bike just to improve (debatable) his mpg.

This discussion is quickly sounding like a debate over how many angels can dance on the head of a pin.
norton74 is online now   Reply With Quote Quick reply to this message
Old 11-01-2012, 01:26 PM   #44 (permalink)
Senior Member
SuperSport
Main Motorcycle: 2012 base bonneville
 
Join Date: Jun 2012
Location: coal township pa USA
Posts: 1,051
Other Motorcycle: 2013 victory hammer
although a totally different animal look at diesel torque at low rpms, WOW!! their high compression leading to hi cylinder pressure is one of many reasons for it
rodhotter is offline   Reply With Quote Quick reply to this message
Old 11-02-2012, 06:24 AM   #45 (permalink)
Senior Member
Powerbike
Main Motorcycle: 2009 Thruxton
 
Join Date: Feb 2009
Location: Johannesburg, South Africa
Posts: 329
Quote:
Originally Posted by norton74 View Post
What I haven't figured out is how fuel consumption goes down. At a given engine speed, the amount of fuel being burned with each combustion cycle would have to be pretty much constant. The only way you could burn less fuel is for the air fuel mixture to become leaner.
Norton, the reason you get stuck on this is because you assume an engine has a fixed volumetric efficiency, which it doesn't. The cylinders of a NA internal combustion engine do not fill completely to the swept displacement, usually not even at WOT. Air is springy, a little bit can stretch to fill the cylinders, but it's still just a little bit of air carrying an equivalent little bit of fuel. Think of the throttle as a way of controlling volumetric efficiency by restricting the air going into an engine, and it that way it controls the power. If you are only using 5% of an engine's power at a given RPM, it's because you've decreased the volumetric efficiency to about 5% of maximum by using the throttle. The throttle butterflies are nothing more than variable air restrictors, they control power by controlling volumetric efficiency.

So, if a bike is making more power due to more compression and hence better burn efficiency, you will be using less throttle under the same conditions. In other words, you will be letting less air into the engine, and because the air/fuel ratio remains unchanged, you are also letting less fuel in.
Grubscrew is offline   Reply With Quote Quick reply to this message
Old 11-02-2012, 07:02 AM   #46 (permalink)
Senior Member
Formula Extreme
Main Motorcycle: 2012 T100
 
norton74's Avatar
 
Join Date: Jun 2012
Location: Stockbridge, MI
Posts: 731
Other Motorcycle: 2013 Rocket 3 Touring
Extra Motorcycle: '73 Ducati GT750
Quote:
Originally Posted by Grubscrew View Post
Norton, the reason you get stuck on this is because you assume an engine has a fixed volumetric efficiency, which it doesn't. The cylinders of a NA internal combustion engine do not fill completely to the swept displacement, usually not even at WOT. Air is springy, a little bit can stretch to fill the cylinders, but it's still just a little bit of air carrying an equivalent little bit of fuel. Think of the throttle as a way of controlling volumetric efficiency by restricting the air going into an engine, and it that way it controls the power. If you are only using 5% of an engine's power at a given RPM, it's because you've decreased the volumetric efficiency to about 5% of maximum by using the throttle. The throttle butterflies are nothing more than variable air restrictors, they control power by controlling volumetric efficiency.

So, if a bike is making more power due to more compression and hence better burn efficiency, you will be using less throttle under the same conditions. In other words, you will be letting less air into the engine, and because the air/fuel ratio remains unchanged, you are also letting less fuel in.
Yours is an explaination that makes sense to me. Thanks

Still, few will go to the expense and bother of increasing the CR just to get a small increase in mpg. The more likely scenario is that a range of changes are performed to increase power and; ultimately, decreasing mpg.
norton74 is online now   Reply With Quote Quick reply to this message
Old 11-02-2012, 06:57 PM   #47 (permalink)
Senior Member
SOTP Vintage Series
Main Motorcycle: 03 T100
 
mikeinva's Avatar
 
Join Date: Mar 2007
Location: richmond va
Posts: 7,775
Quote:
Originally Posted by Grubscrew View Post
Norton, the reason you get stuck on this is because you assume an engine has a fixed volumetric efficiency, which it doesn't. The cylinders of a NA internal combustion engine do not fill completely to the swept displacement, usually not even at WOT. Air is springy, a little bit can stretch to fill the cylinders, but it's still just a little bit of air carrying an equivalent little bit of fuel. Think of the throttle as a way of controlling volumetric efficiency by restricting the air going into an engine, and it that way it controls the power. If you are only using 5% of an engine's power at a given RPM, it's because you've decreased the volumetric efficiency to about 5% of maximum by using the throttle. The throttle butterflies are nothing more than variable air restrictors, they control power by controlling volumetric efficiency.

So, if a bike is making more power due to more compression and hence better burn efficiency, you will be using less throttle under the same conditions. In other words, you will be letting less air into the engine, and because the air/fuel ratio remains unchanged, you are also letting less fuel in.
lol can you beleave it for once we both agree.
__________________
Why do I feel young on my bike
mikeinva is offline   Reply With Quote Quick reply to this message
Old 11-02-2012, 07:10 PM   #48 (permalink)
Senior Member
SOTP Vintage Series
Main Motorcycle: 03 T100
 
mikeinva's Avatar
 
Join Date: Mar 2007
Location: richmond va
Posts: 7,775
As far as doing mods hurting gas milage(on these bikes)If they are tuned right the only 2 things that can hurt milage are the bigger cams (not talking 813 class cams) and 2 useing the right hand more ,that is hard not to do when you have power because it feels so good.Even going to the big bore stroker motor does not kill mpg much.I get upper 40s mpg on the 1087 with full race cams .I got around 50 stock.the 1087 makes 2 x the hp of a stock bike and around 50% more torque.going a steady 65 mph on the open road you barely have the throttle open on the 1087.It does not slow down on hills as much as a stock bike does so you dont have to open the throttle to keep the same 65mph speed.
__________________
Why do I feel young on my bike
mikeinva is offline   Reply With Quote Quick reply to this message
Old 11-04-2012, 06:17 PM   #49 (permalink)
Senior Member
Formula Extreme
Main Motorcycle: 2012 T100
 
norton74's Avatar
 
Join Date: Jun 2012
Location: Stockbridge, MI
Posts: 731
Other Motorcycle: 2013 Rocket 3 Touring
Extra Motorcycle: '73 Ducati GT750
Quote:
Originally Posted by mikeinva View Post
As far as doing mods hurting gas milage(on these bikes)If they are tuned right the only 2 things that can hurt milage are the bigger cams (not talking 813 class cams) and 2 useing the right hand more ,that is hard not to do when you have power because it feels so good.Even going to the big bore stroker motor does not kill mpg much.I get upper 40s mpg on the 1087 with full race cams .I got around 50 stock.the 1087 makes 2 x the hp of a stock bike and around 50% more torque.going a steady 65 mph on the open road you barely have the throttle open on the 1087.It does not slow down on hills as much as a stock bike does so you dont have to open the throttle to keep the same 65mph speed.
You just said that your mileage was better with the stock configuration than when you modified it.

Do you have to use premium fuel? If you do, then your cost of operation is higher.

The average tourer would rather get better mileage and use less expensive fuel. If you are racing, then mileage is rarely of much concern.
norton74 is online now   Reply With Quote Quick reply to this message
Old 11-04-2012, 06:34 PM   #50 (permalink)
Lifetime Premium
Site Supporter
Supernova
Main Motorcycle: '08 Triumph Bonneville
 
leftarmlogan's Avatar
 
Join Date: Nov 2007
Location: Denver? Pittsburgh? Where am I?
Posts: 20,019
Other Motorcycle: '65 Ducati 350 Sebring
Quote:
Originally Posted by norton74 View Post
You just said that your mileage was better with the stock configuration than when you modified it.
That's really splitting hairs, no?

If Mike got 50 mpg average on a bone-stock bike and now gets "upper 40s" (let's say 47-49 mpg average) while getting twice the bhp and 50% more torque, I'd say that's pretty good.

I get about 50 mpg out of my very mildly modded Bonneville. If I could have power like a 1087 and only lose one-to-three, even five-to-seven, mpg I'd be bouncing off the walls.
__________________
This post does not subscribe to the international plan

"It's a great day for hockey" - "Badger" Bob Johnson

I should really update this: http://cundalini.blogspot.com/

Last edited by leftarmlogan; 11-04-2012 at 06:37 PM.
leftarmlogan is online now   Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Triumph Forum: Triumph Rat Motorcycle Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter your valid email address, that can receive an automated confirmation message. Otherwise, you won't be able to gain full access.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Compression ratio difference? maydaymike Twins Technical Talk 8 05-09-2011 01:32 PM
Compression ratio bias Classic, Vintage & Veteran 12 05-12-2009 01:24 AM
Compression ratio, CR heronhead Hinckley Classic Triples 1 04-12-2008 07:55 PM
Compression ratio okiecityflash Classic, Vintage & Veteran 8 05-30-2006 07:11 PM
possible compression ratio deception???? Maintenance & Workshop Talk 2 09-16-2004 06:26 AM

Powered by vBadvanced CMPS v3.2.2

All times are GMT -4. The time now is 12:02 PM.



Motorcycle News, Videos and Reviews
Honda Grom Forum Harley Davidson Forum Honda 600RR Kawasaki Forum Yamaha R6 Forum Yamaha FZ-09 Forum
1199 Panigale Forum Roadglide Forum Honda CBR1000 Forum Vulcan Forum Yamaha R1 Forum Yamaha R3 Forum
Ducati Monster Forum Harley Forums Honda CBR250R Forum ZX10R Forum Star Raider Forum Yamaha Viking Forum
Suzuki GSXR Forum V-Rod Forums Honda Shadow Forum Kawasaki Motorcycle Forum Star Warrior Forum KTM Duke 390 Forum
SV650 Forum BMW S1000RR Forum Honda Fury Forum Kawasaki Versys Forum Drag Racing Forum Ducati 899 Panigale Forum
Suzuki V-Strom BMW K1600 Triumph Forum Victory Forums Sportbikes BMW NineT Forum
Volusia Forum BMW F800 Forum Triumph 675 Forum MV Agusta Forum HD Street Forum Suzuki GW250 Forum
Yamaha Motorcycles Victory Gunner Forum Honda Vultus Forum HD LiveWire Forum

Garage Plus vBulletin Plugins by Drive Thru Online, Inc.

Search Engine Optimization by vBSEO 3.6.0