Quote:
Originally Posted by thePill
There are mnay things wrong with a pushrod engine, the main one being the pushrods themselves. Pushrods rob major amounts of horsepower due to design and add a lot of stress on a single cam. With an OHC, it allows the more delicate camshaft to make direct contact with the rocker arms. This eliminates valve float at high RPMs and allows the engine to spin more freely. Most race OHVs can spin up to 10,000rpm, a race OHC can spin up to 20,000rpm. I understand that a 3 valve OHV can be done, but you are adding more pushrods in the engine and a single pushrod can be responsible for 2-8 horsepower per rod (RPM depending) so naturally, a larger displacement is always needed.
Another big issue with a 2 valve, and in most cases all valve configurations (but more so in a small head OHV) is valve shrouding. This is when your only intake/exhaust valve is in close proximity to the chamber wall. This restricts airflow from sometimes 50% of the valve opening, on an OHC engine, heads are naturally larger so chambers can be designed around this problem and... there are additional valves to aid airflow. DOHC cams are hollow and easy to swap out compared to the old cam in block design. With a timing suppression tool, you can literally change 4 cams in a 1/4 of the time it takes to swap out a OHV cam. There are a lot of additional measures you have to take to get a cam out of the block....
If GM would have stuck with the Northstar, it would have been a fantastic engine and for some reason, Team Corvette took offense to the LT5 since it was built overseas. Besides, if OHVs were really that good, they would have stuck with them across the board...
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False, as you know overseas have taxes on displacement, thus inherently favors OHC.
Also the ability to rev to 20000 rpm is pointless for real work applications. Another thing is you can increase displacement without increasing the size of the motor with ohv, so you don't have to rev to the moon to get performance out of it, so your point is moot. The northstar is a good motor, but nothing compared to the LS2 at the time. Heck the LS3 is a better motor than Ford's 5.0, more power, more torque, less weight and bullet proof durable. IMVHO in N.A. applications a well designed OHV V8 > DOHC V8.