Compression Ratio Change vs. Oil Temp

Chris Hill · 03-28-2007, 01:55 PM

Just curious if anyone has experience with this.

If you were to increase compression ratio only, would water and oil temperatures increase or decrease?

Chris Hill
Spec 125 Light

SSDiv6 · 03-28-2007, 03:59 PM

Chris, there are other factors involved such as how many points of compression is increased, cylinder head material and cooling system efficiency.

Chris Hill · 03-28-2007, 04:29 PM

I realize the answer is not straight forward. I just didn't know if someone might have experienced this.

A fine example of my question would be chaning from a dish 305 to a flat top, or vice versa. I think they are the same except for dish volume, and thus compression ratio.

Chris Hill
Spec 125 Light

Don Whitmore · 03-28-2007, 08:10 PM

Chris,
An engine's inlet charge mixture is modeled as an ideal gas. If no other changes are made, increasing the compression ratio (compressing) will theoretically increase the inlet charge mixture temperature. It may be hard to see/measure the difference, but it will.

That said, the change doesn't have to increase other fluid temps as cooling system etc. modifications can be made to compensate.

D. Whitmore

Adger Smith · 03-30-2007, 01:26 AM

Chris,
In your example the higher compression engine would have cooler chamber & most likely cooler ex temps if tuned correctly. It could also have cooler oil temps, but there are a bunch of things that can change oil temps. Esp. piston design.

Adger Smith

03-28-2007, 01:55 PM	#1
Chris Hill Senior Member Join Date: Jan 2002 Posts: 654 Likes: 8 Liked 244 Times in 26 Posts	Compression Ratio Change vs. Oil Temp Just curious if anyone has experience with this. If you were to increase compression ratio only, would water and oil temperatures increase or decrease? Chris Hill Spec 125 Light __________________ Chris Hill https://ihmusedparts.com

03-28-2007, 04:29 PM	#3
Chris Hill Senior Member Join Date: Jan 2002 Posts: 654 Likes: 8 Liked 244 Times in 26 Posts	I realize the answer is not straight forward. I just didn't know if someone might have experienced this. A fine example of my question would be chaning from a dish 305 to a flat top, or vice versa. I think they are the same except for dish volume, and thus compression ratio. Chris Hill Spec 125 Light __________________ Chris Hill https://ihmusedparts.com

03-30-2007, 01:26 AM	#5
Adger Smith VIP Member Join Date: Dec 2001 Location: Texarkana Ark/TX Posts: 2,419 Likes: 518 Liked 783 Times in 294 Posts	Chris, In your example the higher compression engine would have cooler chamber & most likely cooler ex temps if tuned correctly. It could also have cooler oil temps, but there are a bunch of things that can change oil temps. Esp. piston design. Adger Smith __________________ Adger Smith (Former SS)

03-28-2007, 03:59 PM	#2
SSDiv6 VIP Member Join Date: Feb 2003 Location: Glendale, Arizona Posts: 2,999 Likes: 693 Liked 1,470 Times in 550 Posts	Chris, there are other factors involved such as how many points of compression is increased, cylinder head material and cooling system efficiency.

03-28-2007, 08:10 PM	#4
Don Whitmore Member Join Date: Aug 2004 Location: Central Illinois Posts: 140 Likes: 0 Liked 0 Times in 0 Posts	Chris, An engine's inlet charge mixture is modeled as an ideal gas. If no other changes are made, increasing the compression ratio (compressing) will theoretically increase the inlet charge mixture temperature. It may be hard to see/measure the difference, but it will. That said, the change doesn't have to increase other fluid temps as cooling system etc. modifications can be made to compensate. D. Whitmore