<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by f5fstop:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by DWPC:
Frankly, I'd rather have the I5 than that 5.7 (350) cast iron dinosaur. My father's Olds had that engine. GM
really needs to take those 50-yr old push-rods out back and put 'em out of their misery. </div></BLOCKQUOTE>
The Hummer H3 will NOT have the 5.7L V8.
As for pushrod engines, yes, they are antiquated and cannot achieve much performance. I mean, just look at the LS2/LS7, only 400/505 HP (400 lb-ft/470 lb-ft torque) from those antiquated pushrod engines; damn, GM should be ashamed. (Cast iron is going out in many engines, but durability wise, it is still one of the best materials.)
Getting serious, pushrod engines tend to develop more low end torque, than overhead cam engines, in addition, if you have a very low profile front end (Corvette), pushrod is the way to go. OHC engines are lighter, create more RPM. OHV engines tend to float valves at a lower rpm due to valvetrain inertia, but that has not been a problem...let's not forget Penske winning the 500 with a pushrod engine, and the rest of the field was OHC engines.
OHC in an in-line engine tends to be less expensive, while in a V-block it tends to be a lot more expensive. In addition, displacement on demand is more expensive on OHC engines than on OHV engines. On OHV engines all you have to do is bleed oil pressure from the lifters using a simple solenoid controlled by the PCM. Displacement on demand on OHC engines requires more parts, thus more cost, which we know is pushed off on the customer.
This might be a bad comparison, but let's look at some figures:
GM pushrod engines:
4.8L-2V = 300 HP
6.0L-2V = 325 or 390 hp
Ford OHC engines:
5.4L-3V = 300 hp
6.8L-2V = 310 hp
6.9L-3V = 355 hp
There are applications for both, OHC and OHV engines. But to say OHV is antiquated, is funny. Especially since mass produced overhead cam engines have been around since 1912 (Fiat) and mass produced overhead valve engines were first produced in 1917 (Chevrolet).
The 5.3L mentioned in the article is rated about 335 lb-ft or torque at or around 4000 rpm, with 295 hp. It is a two-valve, overhead cam engine.
There are currently two versions of the 5.3L the LM7 (truck) and the LS4 (car).
And yes, the 5.7L cast-iron dinosaur is gone. </div></BLOCKQUOTE>
Since we are on the subject of this latest GM endeavor, the 2nd generation of the Displacement on Demand cylinder valve functionality is based on hydraulics, thus a quality oil viscosity should be used. Why would GM rely on oil as opposed to exhaust for this functionality? I would think that exhaust would be more reliable. If I am not mistaken, much of the diesel engine works on combustion and exhaust.
Bill