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Originally Posted by Michael_S
I know this is a little off topic - I hope no one minds.
The 3.5L DOHC 250 horsepower V6 is already in production in the Cadillac CTS and the SRX, and it was announced for the Buick Lacrosse, if I recall correctly. On the other hand, the new Pontiac G6 will have as an optional engine a 3.9L pushrod 245 horsepower V6 as an option. Most existing GM sedans with V6 engines use either the 3.4L or the 3.8L pushrod.
The Cadillac Deville, Seville, SRX, and XLR all use the 4.6L DOHC NorthStar V8. The Corvette and GTO use 5.7L pushrod LS1 and LS6 V8s. if I recall correctly most GM pickups, SUV, and vans with V8 engines use pushrods too.
I don't understand why GM uses both kind of valve systems for their V engines. From what little I know of car engines, you have to use an overhead cam for an inline engine like the I4s in the economy cars or the big I6s in the base level GM SUVs. So obviously if GM wants to use that type of engine an SOHC or DOHC is the only choice. But why make two different types for everything else?
I used to be a big fan of DOHC over pushrod, but not any more. DOHC gives more power per cubic inch of cylinder displacement, but since the valvetrain and such takes up more space, the pushrods tend to make more horsepower per pound of total engine mass. That's better both for keeping vehicle weight down and fitting larger engines into smaller engine bays (like the LS6 in the Cadillac CTS-V).
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GM uses both because they don't feel like spending the money to develope new engines, not to mention that pushrod engines are cheaper to manufacture.
The weight difference between DOHC and pushrod is not a huge deal. If it was, most of the exotics would be fucked, because they ONLY use DOHC technology.
Yeah, i forgot the CTS just for the new global 3.5L V6. not a bad motor at all. Competes with the imports at least.
I am not quite sure why the vette keeps it current motor design. I tend to think it is for two reasons.... the first... GM is scared after the LT5 in the ZR-1 back in the early to mid 90's. It was cost prohibitive for them to keep producing the car (the motor almost doubled the price of the car). But, rumors say the next Z06 (or Z07) will have 3V per cylinder, but still remain a pushrod motor. There are aftermarket heads available for pushrod motors that give is 4V per cylinder, but they are pricey. The only real advantage that DOHC has over pushrod is the extra valves, which CAN be added to a pushrod motor, as I have stated previously. Ah well... I'm done for now.