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Old 03-08-2008, 01:13 AM   #71
88cryan
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Re: Pushrod vs. SOHC vs. DOHC

Allright, I am going to add my two cents to this little debate. I personally think that neither engine style is better than the other, it just depends on the type of application it is going into.

Torque= The amount of work that gets done.
Horsepower= The speed at which the work gets done.

OHV PUSHROD

Characteristics:
1. Higher torque
2. Lower horsepower
3. More reciprocating mass, meaning less RPMs
4. Narrower and more compact
5. Cheaper to make
6. Slightly cheaper to maintain


OHC & DOHC

Characteristics:
1. Lower torque
2. Higher horsepower
3. Less reciprocating mass, meaning higher RPMs
4. Little more costly to maintain
5. Typically more efficient
6. More horsepower from less displacement


Q. Why do OHC/DOHC engines have more horsepower than a PUSHROD engine.
A. For several reasons: 1. They breathe better allowing more air/fuel to enter the combustion chamber, and allow the exhaust to leave faster. 2. They have less reciprocating mass allowing them to rev alot higher. 3. Efficiency equals power, variable valve timing, etc all make more power.

Q. Why do PUSHROD enignes have more torque than an OHC/DOHC?
A. The reciprocating mass that hurts their horsepower and their rev potential is the reason that they have great torque. The extra mass in the valvetrain allows the engine to "hit harder".

Q. So what applications usually have a PUSHROD engine?
A. Heavier cars, trucks, etc where the extra torque of the engine will be needed to do work ie: a 9,000 pound work truck wouldn't "shouldn't " have an OHC/DOHC enigne, to achieve the torque needed to tow, etc the engine would have to rev alot higher to do the same work that a pushrod engine could do at lower revs. The result would be a shorter engine life if it was an OHC/DOHC.

Q. What applications usually have OHC/DOHC?
A. Lightweight cars, small trucks, etc where the extra horsepower will be more beneficial than having more torque ie: If a 2,400 pound Honda Civic had a high torque pushrod engine, all that would happen when the driver took off would be a bunch of tire spin, and no go! Whereas their DOHC/OHC engines can rev to quickly to 9k RPMs without much wheelspin.

To: The other comments I've seen,

*Timing belts are supposed to be quieter, however I don't think they are.
*Timing belts should be changed at most every 100,000 miles. (Not only because they can break after that long, but they tend to stretch out causing poor performance.)
*The GM 3800 V6 is one of the best engines ever made. FACT by JD Power
*Timing chains are better (my opinion) even Nissian swtched all their cars to timing chains only! GO NISSIAN
*Torque is what throws you back in your seat.

To: beef_bourito, As far as racing goes I would think that the pushrod engine would be prefered, due to the cost, simplicity, durability, etc.
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