OHV vs. OHC?
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TECH Resident
Joined: Nov 2001
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From: Chicago, IL
OHV vs. OHC? What is it about OHV setups that inherently produce more low-end power versus an OHC valvetrain?
Example: Take 2 engines that are exactly the same except for the OHC/OHV. If both the OHC and the OHV have the same lift/duration/ramping, will the OHV engine still make more low end power? Why or why not?
Example: Take 2 engines that are exactly the same except for the OHC/OHV. If both the OHC and the OHV have the same lift/duration/ramping, will the OHV engine still make more low end power? Why or why not?
TECH Regular
Joined: Nov 2001
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From: Tullahoma TN
Re: OHV vs. OHC? No, if all specs are the same a 2 valve OHV engine and a 2 valve OHC engine will make the same torque and power at the same rpm. But you have to remember why people design OHC engines to begin with. They go to the extra cost because they want to make the valvetrain more stable at higher rpms. So obviously they wish to make their power at higher rpms than with an OHV engine. This is usually done so a smaller displacement engine can make the same peak hp as a larger OHV engine. However this peak power is at a higher rpm and the torque is not as good because usually the OHC engine is of smaller displacement. And becuase the engine and cam is designed to make power at higher rpms, low rpm torque production usually suffers.
When you start adding 4 valves per cylinder along with DOHC then you are serious about making hp at higher engine revs. This is also usually used by smaller engine displacements to make up for a lack of displacement. Again low rpm torque will suffer because the engine is usually smaller and the engine is cammed to take advantage of high rpm power production. To top it off, the 4 valves have more flow area than two, so the port velocity drops and low rpm torque and throttle response suffers as a result. But above 4,500 rpm, the DOHC engines will pull like crazy.
[ November 26, 2001: Message edited by: 2quick4u ]</p>
When you start adding 4 valves per cylinder along with DOHC then you are serious about making hp at higher engine revs. This is also usually used by smaller engine displacements to make up for a lack of displacement. Again low rpm torque will suffer because the engine is usually smaller and the engine is cammed to take advantage of high rpm power production. To top it off, the 4 valves have more flow area than two, so the port velocity drops and low rpm torque and throttle response suffers as a result. But above 4,500 rpm, the DOHC engines will pull like crazy.
[ November 26, 2001: Message edited by: 2quick4u ]</p>
