What is a double overhead cam?

Question

I never had a car with one until recently, so naturally I don't know what they are. People keep oohing and awing at it but all I see is a mazda 626 2.5 liter engine, nothing major.

IMy car is a 1994 ford probe, but like it was said ford and mazda share parts. If you unscrew the ford logo it says mazda right under it. Also 1994 was the last year for the Probe, so it had the least amount of glitches since it was improved on every year for 5 years. My red line is almost non-existant and I can 100 miles per hour and still get around 25 MPG in the proccess.

Answer 1

Cam: a mechanical "axle" with portrusions that controls your cylinder's exhaust and injection.

Overhead cam: instead of putting the cam "inside" the engine, the cam is moved "above" the engine to make it simpler and lighter, away from the heat. This usually allows the engine to achieve higher revolutions (and thus, more power)

Dual overhead cam: instead of one cam handling all cylinders, two separate cams share the work, allowing even higher revolutions (and more power!)

DOHC engines produce a lot of power for their time. My '96 Ford Contour had one of the most advanced American engines of its time, a DOHC Duratec 2.5L V6. It produces 170 HP, an impressive displacement to HP ratio in its days. Its redline is 6750 RPM, almost unheard of in a V6.

It's beaten later by Acura Integras getting 180-190 HP from their 2.2L (or was that 2.0?) DOHC I-4's.

As Mazda shares a lot of mechanicals with Ford, your engine could be cousin to my Ford Duratec engine! :)

Answer 2

Old engines didn't have overhead camshafts. Newer ones do because if you have overhead cams (camshafts positioned above the cylinders at the top of the engine) it allows for a more efficient arrangement of intake and exhaust valves. Double overhead cams allow for even more valves and more precise synchronization of the ignition of the fuel in the cylinders. All things being equal, a motor with 4 valves per cylinder ( made possible by overhead cams ) will perform much better and more efficiently than the same motor with single overhead cams or no overhead cams at all. for example, a 450 cc honda engine with double overhead cams will perform as good as a 750cc engine without overhead cams, and still get better gas mileage. You would need a simple diagram of a motor to see the arrangement of the different types of cams vs no cams to really appreciate the difference.

Answer 3

Most modern engines use a camshaft to open and close the exhaust and intake valves. A single camshaft is good enough, but two is what you find on higher-performance engines. Overhead means that the camshaft or camshafts are on top of the cylinder head pressing down directly on the valves. Normal V8 or V6 engines have one camshaft that operates pushrods and rockers that open and close the valves. Go to this site: http://auto.howstuffworks.com/camshaft.htm
You'll get much more information than you will from the morons on this board.

Answer 4

There are 2 cams in each head. Like in cobras, there Dohc and a V8, so it has 2 heads and each head has 2 cams for a total of 4 cams. In a mazda, I'm sure it only has 1 head, therefore it has 2 cams.

Answer 5

A double overhead camshaft (also called double overhead cam, dual overhead cam or twincam) valvetrain layout is characterized by two camshafts being located within the cylinder head, where there are separate camshafts for inlet and exhaust valves.

http://en.wikipedia.org/wiki/DOHC#Double_overhead_camshafts

Answer 6

Simply means that your vehicle has two camshafts opening and closing valves instead of one...makes the vehicle a bit more efficient...and a bit more expensive to fix if you ever have engine problems