As yet no rum so upya bum
Of course he is. But I have no idea how he can say that the LSX motors in our factory Holden/HSV's are better than the ones in an AMG. Pirate must be hitting the rum again. Arrr.
Better in every measure except "civility".
Ima leave this here, feel free to ask questions regarding specifics. Maybe I should start another thread?
Are you comparing a modified engine to factory specs?
See above. I'm comparing GM small block two valve pushrod V8 to the Merc and BMW. No, NOT including power adders or hybrid tech. All are fielded in high performance production cars, all being of aluminum construction and none having direct injection.
* HSV / Chevy SS / Camaro SS
** BMW M3
*** Mercedes-Benz C63 AMG
Our pushrod engine offers the highest power and torque density, along with the best fuel economy. It is also the simplest, lightest, smallest and cheapest engine.
Reasons why you may not want a pushrod:
Bullshit TV shows and glossy magazine articles aside, the most common reply to that is “civility”. Have you driven a small block lately? If you have, have you also driven the other two engines? I have done all that and here’s an opinion on the civility issue…
The engines have very different characteristics, but saying that the small block is less civil than the other two is a mischaracterization. The small block is burbly down low and throaty in a throbbing baritone sort of manner when wound out. The BMW V8 quiet and smooth, but also very soft, down low. Get it past 6000 rpm and it wails with a metallic rasp of an engine note. The AMG V8 is (surprising) also rather soft below 4000 rpm, softer in fact than the previous M113 5.5 litre it replaced or the current 5.5 they put in the E550. Wind it out and it responds with vigor and a brash metallic tone from about 4500 rpm to the rev limit of 7200 rpm. Overall, the C63 has the loudest exhaust (I mean this thing is loud enough to wake your neighbors), the M3 has the finest tremble and the our SS is the least edgy and most mellow. I am sure that some of that is how the exhaust and sound insulation in the respective cars are set up, but I didn't get the impression that the pushrod engine is outdated or crude. So, there you go.
The push rod setup has A LOT to do with the noisy racket push rod motors tend to make at higher revs. Basically, valve train racket comes from valve float. In general, all valve trains "float" to a tiny degree at higher revs. Just like with suspension systems, when rebounding from a compressed state it the spring is unable to keep everything fully loaded and in contact. Higher spring rates help, but spring rates high enough to eliminate all slop will also cause excessive wear due to friction and hurt economy. A tiny amount of "float" during those small periods of time where the engine is actually reving at the upper 1/4 of its rev range does not hurt the engine.
The difference between push rod engines and OHC designs is that the actuated mass of each valve element is very high. There is the lifter, the rod, the rocker and finally the valve itself. The heavier the actuated mass the higher the impact momentum when the valve train elements floating a tiny bit at higher revs remakes contact. This creates louder noise and more notable vibrations.
On top of that, the OHV design also has more interface layers than the OHC designs. In a typical DOHC design there is one to two interface layers. With bucket tappets there is just one interface -- between the cam lobe and the tappet. In roller follower designs there is two -- cam to follower and follower to valve. In push rod designs you have four -- cam to lifter, lifter to rod, rod to rocker and finally rocker to valve. Hence, there are four locations where you'll have slop during high rev operations and a lot more noise making locations. Its like an anchor chain with five links makes more noise when you rattle it than one with three links.
The answer comes down to consumer’s perception. A car equipped with a Push Rod OHV engine is deemed outdated dinosaur by the consumer. The perceived refinement in terms of vibrations and acoustic signature also heavily favors the DOHC engines. They don’t exhibit much valve clatter at higher RPMs because their reciprocating valve train pieces are lighter, they tend to also not appear to run out of breath as easily in most cases as revs climb past 5000 rpm or so. In most cases, they are also slightly more economical because on the average DOHC designs mix fuel and air better, and have slightly lower pumping losses at cruise, than push rod designs. In the past part of the reason is that they tend to have technological content such as VVT, coil-on-spark ignitions, etc. Now so does our GM V8.
The ability to vary intake and exhaust cam separately is good for emissions control – good enough to eliminate the need for an EGR subsystem. Even though some of these are not necessarily tied to their DOHC design, they are nonetheless associated with DOHC engines because it is true that when you compare the typical DOHC engine to the typical Pushrod engine, you are more likely to find these “high-tech” features on DOHC ones. Now so does our GM V8 (well the important stuff).
Ask any professional drift team, if you are after the highest power density with respect to engine dimensions or weight, and you don’t care about perception or refinement or anything else, you’ll find it in a well engineered Push Rod engine like the LS2 or LS7. I’ll tell you this right now. A 400hp 6.0 litre Holden LS2 is probably smaller or at worst the same size as the BMW 4.0 litre DOHC V8 that goes into the M3. It is probably no heavier as well. It has better low end tractability and it is cheaper than any V8 engine built for 8,000+ rpm duty will ever be. Sure, it’ll sound and feel less refined. But, as far as performance goes it is a better solution.
Less refined but not crude:
[video=youtube_share;1w3XW9HuQoY]http://youtu.be/1w3XW9HuQoY[/video]
