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push rod vs Over head
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Posted by: themustangkid

plz dotn think im stupid for asking this but can anybody explain to me in detail y push rods have better low end respons then over head cam engines??

Posted by: GMR

9 times out of 10, over head cam engines will be of lower displacement than pushrod engines. Example: 4.6 Fords, 4.0 & 4.6 GM Northstars etc. Because of their smaller size, they rely on higher RPMs to produce the power that you would normaly get out of a bigger pushrod engine. Example: 302-351 Fords, 350-400 Chevys. So what they lack in the bottom range, they make up for in the upper. Thats why they have the over cams, chains and multiple valves per cylinder, you can rev em up high without having to worry about somthing breaking. Thats were they work the best.

Got it? Good!!

Posted by: themustangkid

thanks

Posted by: MadScientistMatt

Also, many OHC engines have larger port sizes. This often makes for better high RPM power at the expense of low end torque.

Posted by: themustangkid

makes sense, less back preasure makes for less low end power. thnax, i asked the guys in my welding class this question and no one seemed to know

Posted by: MadScientistMatt

Actually, it's not back pressure but velocity. They're easily confused, because smaller cross-sections tend to increase both velocity and pressure drop, but they are very different. A too-big exhaust pipe won't be canceled out by a muffler that might as well be a cork in the exhaust tip.

Posted by: 99FRC

Good thread...

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