Point/Counterpoint: DOHC v OHV

[XfireZ51]

Originally Posted by Paul Workman

That would be interesting... But, IIRC, the MM DOHC heads were a "work in progress"; that is to say that VVT and DI was not yet accommodated. Do you (or anyone) have some "fill-in" info in that regard?

Well but the LS9 didn't have either. The heads were designed to work w the LS architecture not the LT, at least not yet. MMR showed them at SEMA on an LS block. Its worth an inquiry. I'm sure they ain't cheap but neither would a LT-5 swap be. On the other hand, we know the LS block fits and works w the PCM.

[edram454]

Originally Posted by 5ABI VT

I have owned a few german cars, VW and a BMW. I sold them because like you mentioned.. they require a fair bit of $$ for maintenance. Im a DIY kind of guy so none of my cars has ever seen a dealer or shoppe (fingers crossed) for the last 15 or so years and hopefully never will. Turning rotors is a fraud in the auto industry in my opinion. it should never be done. $2300 sounds like a lot but if it were me and priced out accordingly I probably could have picked up a used brembo kit or retrofit from another vehicle for the car for that amount scavenging the forums for those cars. Of course I will admit that I do appreciate the level of refinement they provide, its just not in my income range to be able to just drop one off at a dealer and say service it. I have yet to drive anything american that compares to even my e46 M3 in terms of refinement. Even my passat wagon.. puts my ctsv to absolute shame in terms of design, engineering and refinement. But I chose to buy a ctsv because its a pickup truck drivetrain in a 4 door chassis and its cheap to maintain and modify/upgrade when repairs are needed and is a more diy friendly vehicle.


If I had a LOT of money.. I would buy a blue c6 ZR1, paint the roof and b- pillar blue, lower it on coilovers and add some HREs. I would pull the LS9 and sell it to someone looking to do a restomod, and I would plop a fully built no expense spared LT5 in there. i would also enlarge the window on the hood for obvious reasons

You are right about the refinement of the euro cars and high end asian cars. they put alot more money in those cars but it tends to price out a lot of people who would like to own one but cant afford it. The Corvette is relatively affordable to middle income Americans. It is not to hard to save a little and buy one and be in the hobby. It is only recently that a Corvette has sported a real nice interior with the c7. It is a semi-high quality interior instead of the low quality it has put in virtually all other Corvettes. the Corvette constantly gets ripped by reviewers on the cheap seats and interiors and I have to agree. For that, thank God for the c7. I think a blue zr1 c6 is a fantastic car. An absolute gem that really hauls azz. I would love one of those cars and if I had room, which I dont, I would try to acquire one. You are right about the brembo brake kit for that audi but I was out of town so I just had the car picked up by the mechanic and paid for the work. I eventually gave her that car in the divorce that way i got rid of problems in one swoop. by the way, I love your youtube video and the sounds you car makes. It made me call corsa and order and corsa system for my car. It is being installed and I would be happy if it sounded like yours. I dont have gears or the fidanza flywheel but I do have agressive porting with long tube headers, no cats and custom chip so it should sound similar. I drive around with my back window slightly propped open with a corvette gadgetman latch just so I can hear that sound really loud. I also liked your shifter so I went out and bought a hurst shifter with custom shifter ball in black. All your mods are great so keep up the good work.

ed ramos #3028

[XfireZ51]

An article that's very much "on point" with our discussion here. Be worth following it. Coyote v LS3.

http://www.enginelabs.com/engine-tec...gine-shootout/

[KILLSHOTS]

Unfortunately, I think, it’s “on pointâ€� in more ways than one. IMHO, this article is not a good argument for a DOHC platform. First, they had to handicap it by starting with a truck engine for the Coyote, because a truly-comparable Mustang engine is far too expensive to be built vs. the LS3. That’s red flag #1. Then, they acknowledge that the Camaro’s (and Corvette’s) pushrod LS3 produces more power in stock form than the Mustang’s DOHC Coyote in stock form, so they handicap it again by throwing a HP per liter parameter into their testing criteria to save the Coyote’s bacon. Ouch, that’s red flag #2. Does anyone who’s being truly objective really care about HP per liter, as opposed to just the amount of power produced? HP per liter, in a case like this, is nothing more than a BS qualifier, an excuse, vis-Ã*-vis, “Well, maybe my Mustang only has 420HP but it’s NOT FAIR, because your Camaro has more cubic inches!â€� And just as an aside, the smaller displacement Coyote is a MUCH larger and somewhat heavier engine than the LS3, which begins to shine a light on the potential packaging limitations of a modern DOHC layout. This is important, because if GM designs a Corvette around such a large and heavy engine, then it also needs to consider how that car's dynamics may suffer, especially in this age of rapidly rising CAFE standards, thanks to the greenies.

Please understand that, as I’ve said before, I love the LT5…wouldn’t have owned a Z unless that was fully true. But it seems to me that we’re generally falling into 2 camps here: those who really want GM to move back toward DOHC power for the Corvette, and those who believe that it’s generally not currently viable from a cost perspective. Regardless the final dyno numbers, I think that the entire premise of this particular article does a better job of validating the latter group’s argument.

[mike100]

The Coyote is only 430 lbs if I recall correctly. It is certainly not the cheapest way to make an 11 second street toy, but there are a couple of useful advantages that I consider:

1) True dual cam VVT. The powerband from 300 cubic inches is really amazing and you don't have to always shift to keep it above 4000 rpms like you do on an LS engine when you get caught on the dull part of the low rpm power curve.
2) no surge of massive torque to blow off the rear tires as with large displacements. I find that this type of engine easier to drive a car at its limits than a big inch one.
3) There are sometimes intangible properties like an engines willing to change speed and rev although with the coyotes borrowed long stroke from the modular engines, the advantage might be for the LS. Just like diesels- they might have 800 lb/ft of torque, but they are locomotive slow to rev up. My mustang is geared so much lower than my vettes- it certainly seems faster to rev out- the 5.0 engine takes it in stride and seems balanced better. (maybe not better than the LT5, but certainly than the LS3).

conclusion: the transmission might be the more important discussion, but true variable valve timing raises the area under the curve for torque so that coupled with close ratio gearing is really hard to beat.

[XfireZ51]

The article was not cited in order to score points for the OHC motor. It was put there as a source of greater objectivity than may be displayed on this forum, and that includes me. I am interested in seeing what they come up with.
What would be a really interesting "comparo" would be taking an LSsomething and dropping the MMR DOHC LS heads on it. Same block, but different valvetrain architecture and even same induction. THAT would make for a very interesting test.

[Paul Workman]

In a pure scientific (DOHC v OHV) discussion, when making comparisons of examples with varying degrees of critical variables, there has to be some mollification of differences - especially in something as critical as displacement. Another example is comparing a NASCAR motor to one designed to me emissions and perform equally well in city type stop and go traffic with the AC turned on as it does at WOT.

Originally Posted by KILLSHOTS

[FONT=&quot]Unfortunately, I think, it’s “on point� in more ways than one. IMHO, this article is not a good argument for a DOHC platform. First, they had to handicap it by starting with a truck engine for the Coyote, because a truly-comparable Mustang engine is far too expensive to be built vs. the LS3. That’s red flag #1.

Irrelevant to architecture analysis (DOHC v OHV)

Originally Posted by KILLSHOTS

[FONT=&quot]Then, they acknowledge that the Camaro’s (and Corvette’s) pushrod LS3 produces more power in stock form than the Mustang’s DOHC Coyote in stock form, so they handicap it again by throwing a HP per liter parameter into their testing criteria to save the Coyote’s bacon. Ouch, that’s red flag #2. Does anyone who’s being truly objective really care about HP per liter, as opposed to just the amount of power produced? HP per liter, in a case like this, is nothing more than a BS qualifier...*

"Does anyone who’s being truly objective..." really think displacement is irrelevant??

I agree that you're spot on when considering power/$$ and marketing. I mean after all, about 1/3 of ZR-1 owners admit to never pushing their LT5s beyond Gen-I SBC capabilities. The LT5's characteristics are pretty much moot if limited to 5500 or 6000 rpm.

But, $$ wise, the ZR-1 was X2 the price of the base Corvette when new, and pretty much the same is true today, except for some NCRS garage queens that push that to X3 perhaps. So, for some, and that includes all of us, $$ isn't the deciding factor, but rather determines how long one (like me) has to wait to be able to afford one!

And, one could question my saying so, but the "FBI" has taken home the team trophy for the fastest aggregate of 3 cars at a local Corvette drag race shootout event, 3 out of the last 4 years, plus the first year when we won but didn't register for trophies. [I] I dunno... But, it might be a clue? (And there's no more scoffing from C5 or C6 owners when a "lowly C4" with a ZR-1 badge on it comes to the line against one of their LSx bretheren...

So, the burning question is, what would be possible if GM did build contemporary DOHC V8? I'm w/ Dom: what does the LSx do with a set of MMR DOHC heads on it?? And, why are so many manufactures moving to the DOHC architecture w/ VVT and DI in spite of the drawbacks??

[KILLSHOTS]

Originally Posted by Paul Workman

In a pure scientific (DOHC v OHV) discussion, when making comparisons of examples with varying degrees of critical variables, there has to be some mollification of differences - especially in something as critical as displacement. Another example is comparing a NASCAR motor to one designed to me emissions and perform equally well in city type stop and go traffic with the AC turned on as it does at WOT.



Irrelevant to architecture analysis (DOHC v OHV)



"Does anyone who’s being truly objective..." really think displacement is irrelevant??

I agree that you're spot on when considering power/$$ and marketing. I mean after all, about 1/3 of ZR-1 owners admit to never pushing their LT5s beyond Gen-I SBC capabilities. The LT5's characteristics are pretty much moot if limited to 5500 or 6000 rpm.

But, $$ wise, the ZR-1 was X2 the price of the base Corvette when new, and pretty much the same is true today, except for some NCRS garage queens that push that to X3 perhaps. So, for some, and that includes all of us, $$ isn't the deciding factor, but rather determines how long one (like me) has to wait to be able to afford one!

And, one could question my saying so, but the "FBI" has taken home the team trophy for the fastest aggregate of 3 cars at a local Corvette drag race shootout event, 3 out of the last 4 years, plus the first year when we won but didn't register for trophies. [I] I dunno... But, it might be a clue? (And there's no more scoffing from C5 or C6 owners when a "lowly C4" with a ZR-1 badge on it comes to the line against one of their LSx bretheren...

So, the burning question is, what would be possible if GM did build contemporary DOHC V8? I'm w/ Dom: what does the LSx do with a set of MMR DOHC heads on it?? And, why are so many manufactures moving to the DOHC architecture w/ VVT and DI in spite of the drawbacks??

I understand the hypotheticals and don't necessarily disagree. My point is that GM has no incentive to produce another DOHC Corvette today. Sure, it would be really cool if they did. But it makes no financial sense and isn't necessary, considering the fact that the car is a world-class performer in all areas with a cheaper pushrod engine.

[Johnny5]

wow, reading only the first few pages and cracking up I have to add that I have a 91 Zr1 and my brother has a 2004 Z06 so i have experienced both DOHC and OHV engines/layouts. The z06 has more down low torque, more of a throw you back in your seat at low or any rpms where our LT5s have to rev up to get that adrenaline feel. His engine is hundreds of lbs less and way cheaper to build, maintain etc. Given our cars were KING until the C5 z06 came out. the z06 is faster and handles better but the LT5 has more potential. I have ported plenum/IH catback and a tune and I was neck and neck with the stock c5 z06 but he eats me up in the twisties. At the end of the day I love my car more bc of its rarity, group of people, car guys that actually know what a zr1 is, no blind spots, and I **** on my bro every chance i get by saying i can take my top off.....plus his girlfriend likes my car more lol. Long live the KING

[XfireZ51]

Your interior doesn't look like it was vacuum formed out of sheet plastic either.
Again, match up to his 405hp, then run beyond the 1/8 mile. See what happens.