Random Thoughts - Part Deux [NO POLITICS] - Page 4498 - Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community

NoHaveMSG · 11-14-2019, 09:27 PM

To lower compression you would have to increase the combustion chamber volume at TDC. Since piston and rod heights are fixed the only way to increase chamber volume is to alter the stroke.

Ultramaroon · 11-14-2019, 10:47 PM

Quote:

Originally Posted by ichitaka05

Also to add... stroke changes, so not only compression ratio change, but displacement changes (bore x stroke)? So is it more (or less) than 2 liter?

Yes.

Ultramaroon · 11-14-2019, 10:53 PM

I suggest mentally picturing the system on end and consider how the cylinder bore and crankshaft axis of rotation are both fixed.

weederr33 · 11-14-2019, 11:05 PM

[ame]https://www.youtube.com/watch?v=Qffp-38_ycE[/ame]

NoHaveMSG · 11-14-2019, 11:37 PM

I'm lucky if they even put the plates on the rack and wipe down their equipment when done at my gym. The evening crowd is lazy.

Clutch Dog · 11-15-2019, 12:15 AM

Quote:

Originally Posted by NoHaveMSG

I'm lucky if they even put the plates on the rack and wipe down their equipment when done at my gym. The everyone is lazy.

fixed it

Lantanafrs2 · 11-15-2019, 12:35 AM

What is the point of variable compression ratio?

Ultramaroon · 11-15-2019, 12:39 AM

Quote:

Originally Posted by Lantanafrs2

What is the point of variable compression ratio?

Lower CR under boost. Higher when cruising with cracked throttle. CR profile is tailored to further maximize ignition advance across a wider range of operating conditions. (gamut?)

Now I'm going to go study to see if I'm in the ballpark.

Ultramaroon · 11-15-2019, 01:02 AM

Ok, yeah, I'm a smartypants.

Spuds · 11-15-2019, 01:49 AM

Quote:

Originally Posted by Lantanafrs2

What is the point of variable compression ratio?

Higher pressure results in less losses to entropy during combustion. In theory you want the highest compression you can get at all times. But the limiting factor is the tendency of gasoline/air to detonate when you compress it too quickly. By decreasing the maximum pressure, you decrease the rate of compression. Thus allowing higher rpm, advancing timing, and more fuel/air (higher boost) at higher temperatures.

Being able to tune the compression ratio gives you the best of both worlds in the same engine.

humfrz · 11-15-2019, 02:21 AM

Quote:

Originally Posted by Ultramaroon

Ok, yeah, I'm a smartypants.

- you peaked!

humfrz

EAGLE5 · 11-15-2019, 02:55 AM

Quote:

Originally Posted by Lantanafrs2

What is the point of variable compression ratio?

Marketing.
https://www.caranddriver.com/feature...-fuel-economy/

Ultramaroon · 11-15-2019, 03:25 AM

Quote:

Originally Posted by humfrz

- you peaked!

humfrz

I did about 20 years ago.

humfrz · 11-15-2019, 03:48 AM

Quote:

Originally Posted by Ultramaroon

I did about 20 years ago.

Well, seeeeeeeeeeee

humfrz

11-14-2019, 10:53 PM	#62961
Ultramaroon fabulous Join Date: Sep 2014 Drives: a 13 e8h frs Location: vantucky, wa Posts: 31,743 Thanks: 51,894 Thanked 36,345 Times in 18,834 Posts Mentioned: 1103 Post(s) Tagged: 9 Thread(s)	I suggest mentally picturing the system on end and consider how the cylinder bore and crankshaft axis of rotation are both fixed. __________________ service manuals

11-14-2019, 11:05 PM	#62962
weederr33 Airborne at your service Join Date: Sep 2014 Drives: '17 BRZ Series.Yellow Location: El Paso, Texas Posts: 6,288 Thanks: 4,513 Thanked 5,514 Times in 2,904 Posts Mentioned: 33 Post(s) Tagged: 2 Thread(s)	[ame]https://www.youtube.com/watch?v=Qffp-38_ycE[/ame] __________________ Series.Yellowbird - http://www.ft86club.com/forums/showthread.php?t=122135 MS, CSCS, TSAC-F, CPT

11-15-2019, 01:02 AM	#62967
Ultramaroon fabulous Join Date: Sep 2014 Drives: a 13 e8h frs Location: vantucky, wa Posts: 31,743 Thanks: 51,894 Thanked 36,345 Times in 18,834 Posts Mentioned: 1103 Post(s) Tagged: 9 Thread(s)	Ok, yeah, I'm a smartypants. __________________ service manuals

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11-15-2019, 12:35 AM	#62965
Lantanafrs2 Senior Member Join Date: Jan 2018 Drives: 2013 frs red Location: South Florida Posts: 3,519 Thanks: 2,520 Thanked 3,087 Times in 1,654 Posts Mentioned: 6 Post(s) Tagged: 1 Thread(s)	What is the point of variable compression ratio?

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