Compression Ratio vs MPH

Don Whitmore · 04-26-2009, 01:55 PM

Two super-stock motors make similar horsepower. They are similar in displacement. One motor has a higher compression ratio, but is limited somehow so that it makes similar horsepower as the other motor, which has a lower compression ratio.

Install both motors in the same super-stock car. Will they MPH the same?

D. Whitmore

Joe Abbazia · 04-26-2009, 04:30 PM

The mph should be the same if the horsepower is the.However when the air gets bad i would like to have the comp. motor.

Don Whitmore · 04-27-2009, 12:29 PM

Wow...392 views and only 1 reply? Or, is the answer that easy and I'm missing it?

Jeff Lee · 04-27-2009, 02:23 PM

I would say there are no more responses because Joe is correct. HP is a function of MPH. If nothing else changes (like aerodynamics or weight) then the MPH will be the same. I also agree with Joe that I would rather have the compression with bad air.

Mike Taylor 3601 · 04-28-2009, 06:38 AM

I agree only thing I may add is higher comp. engine usaully makes a little more torque also if that was only change. Mike Taylor3601

tgriffith · 04-28-2009, 06:58 AM

I asked a motor guy that question,,,,,,,he claimed impossible to answer,,,,,,,for the motor that has higher compression to have same HP,,,your going to have differences in other places that reduces HP,,such as cam,,,that alone may bring down rpm curve so that it wouldnt MPH faster

he tends to think that the higher compression,,,the easier to get it up in rpm...on the other hand,,,once the motor is turning higher rpm,,lower compression will have less resistence,,,

he tends to think that your answer is YES more compression would make higher mph,,,,,reason for this is that most motors like a reduction of timing at higher RPM,,,if Im not mistaken,,,once your retard your timing , doesnt that fire the cylinder closer to the top, thus having more compression???,,,,I think cylinder pressure would be higher at 28 degrees VS 36 degrees...or am I thinking about this backwards??

04-26-2009, 01:55 PM	#1
Don Whitmore Member Join Date: Aug 2004 Location: Central Illinois Posts: 140 Likes: 0 Liked 0 Times in 0 Posts	Compression Ratio vs MPH Two super-stock motors make similar horsepower. They are similar in displacement. One motor has a higher compression ratio, but is limited somehow so that it makes similar horsepower as the other motor, which has a lower compression ratio. Install both motors in the same super-stock car. Will they MPH the same? D. Whitmore

04-26-2009, 04:30 PM	#2
Joe Abbazia Junior Member Join Date: Aug 2005 Location: USA Posts: 66 Likes: 0 Liked 19 Times in 4 Posts	Re: Compression Ratio vs MPH The mph should be the same if the horsepower is the.However when the air gets bad i would like to have the comp. motor.

04-27-2009, 12:29 PM	#3
Don Whitmore Member Join Date: Aug 2004 Location: Central Illinois Posts: 140 Likes: 0 Liked 0 Times in 0 Posts	Re: Compression Ratio vs MPH Wow...392 views and only 1 reply? Or, is the answer that easy and I'm missing it?

04-27-2009, 02:23 PM	#4
Jeff Lee VIP Member Join Date: Jul 2007 Location: Anthem, Arizona Posts: 2,766 Likes: 0 Liked 3 Times in 3 Posts	Re: Compression Ratio vs MPH I would say there are no more responses because Joe is correct. HP is a function of MPH. If nothing else changes (like aerodynamics or weight) then the MPH will be the same. I also agree with Joe that I would rather have the compression with bad air. __________________ Jeff Lee 7494 D/S '70 AMX

04-28-2009, 06:38 AM	#5
Mike Taylor 3601 VIP Member Join Date: Oct 2008 Location: Somerset,Ky Posts: 1,372 Likes: 358 Liked 308 Times in 103 Posts	Re: Compression Ratio vs MPH I agree only thing I may add is higher comp. engine usaully makes a little more torque also if that was only change. Mike Taylor3601

04-28-2009, 06:58 AM	#6
tgriffith Member Join Date: May 2002 Posts: 187 Likes: 0 Liked 0 Times in 0 Posts	Re: Compression Ratio vs MPH I asked a motor guy that question,,,,,,,he claimed impossible to answer,,,,,,,for the motor that has higher compression to have same HP,,,your going to have differences in other places that reduces HP,,such as cam,,,that alone may bring down rpm curve so that it wouldnt MPH faster he tends to think that the higher compression,,,the easier to get it up in rpm...on the other hand,,,once the motor is turning higher rpm,,lower compression will have less resistence,,, he tends to think that your answer is YES more compression would make higher mph,,,,,reason for this is that most motors like a reduction of timing at higher RPM,,,if Im not mistaken,,,once your retard your timing , doesnt that fire the cylinder closer to the top, thus having more compression???,,,,I think cylinder pressure would be higher at 28 degrees VS 36 degrees...or am I thinking about this backwards??