| "Old Fashioned" Push Rod VS. "High Tech" Over Head Cam |
| This is a mere misconception, that Pushrod valve operation is older than Over Head Cam, and becasue its "older" its inferior. This misconception most likely develops from American Cars using Pushrods throughout the 60's and 70's in their muscle cars. Now more and more automakers Use Dual Over Head Cam (DOHC) or Single Over head Cam (SOHC) in their vehicles. Including Honda, so therefore it must be absolutley superior to anything else. Below is a Picture of a 4 cylinder using durning the 1920's in Model T's. So well before the era of big block, push rod muscle cars, DOHC was used in American cars. Might I add that during this time a Japaneese car was an oxymoron. |
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| 1920's DOHC 16 valve 4 cylinder |
| Notice the engine above has 16 valves with divides out to 4 valves per Cylinder. This is the next reason why DOHC has been dubbed "high tech" becasue pushrod engines only use 2 valves per cylinder. More valves = more breathing which is better, right? In some instances perhaps but the majority of the time a 2 valve per cylinder pushord engine can breathe just as well. How is this you ask? Although DOHC may have twice as many valves per cylinder, the valves are much smaller than the two large valves used in a pushrod aplication. Below is a Bseries Vtec cylinder head which uses 4 valves per cylinder and a Corvette cylinder head which has two large valves. |
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| Corvette Cylinder Head (LS1) |
| Honda Cylinder Head (B-Serries) |
| The Final reason why Pushrod layouts are labeled inferior to DOHC is because they "Can't rev as high". Again this isnt necesarily true. The method of valve operation is almost irrelevant to how fast a motor can rev. Instead factors such as how balanced the engine is and the size of the pistons play a greater role. It is easier and requires less energy to move smaller pistons. This is why in prodution cars small engines from about 2.5L or less redline at about 7-8,000 rpms and larger motors, a 4.6L or 5.7L typically redline at 5-6,000 rpms. This is not to say that a large motor can't rev as high or higher than a small one. Nascar Uses 350ci (5.7L) Naturally aspirted Pushrod engines that will rev upwards of 11,000rpm. Many DOHC enthusiasts claim that it is superior because it is used in F1 cars which rev to 16,000rpm. However their redline is higher but the motor is almost half the size of a Nascar motor. Seeing that a Nascar motor is almost twice the size of an f1 motor, if it reved half as high (about 8,000) it would be just as much of an achivement, however for its size the Nascar 350ci acheives more revs than the F1. Ultimately DOHC will rev higher than a Pushrod layout, but I just wanted to show that impressive engine speeds can be obtained from both. (Also i am by no means comparing the preformance of a F1 car and Nascar) |