mini zr-1? 4 cam 24 valve 300 hp

[BOB HDZ]

i think its a cool gm motor ! who knows we could learn something from it

[Aurora40]

Originally Posted by Paul Workman

You're playing "devils advocate" ain't cha Bob? OK...I'll play along

Isolated anecdotes aside, generally...

• the flow thru of a 4-valve design is superior to the (practical) two-valve
• OHV means less valve train weight, allowing for reduced spring tension which relates to less wear for any target peak rpm.
• The burn characteristics of the pent-roof chamber in the DOHC (e.g. LT5) allows for very fast burn rates which allows compression ratios of 11:1 on 87 octane, and higher (12:1) ratios on 93 octane. Higher compression ratio = better power and efficiency (apparently).
• Intake and exhaust cam phasing (DOHC) can be independently and dynamically controlled "on the fly" to optimize output/efficiency for any load/rpm circumstances
• Sustained high rpm operation (again due to simplicity of the valve train) favors the OHC/DOHC in actual practice (but you already know that).

So, from a cubic inch to cubic inch, or hp/volume, or a dynamic load capability point of view, it is hard to argue the virtues of a single cam, push-rod approach as being anything but a little archaic in comparison.

After the 2-valve flow has been optimized, the only door available to the daily-driver, push-rod motor to keep up the horsepower is displacement.

If I give you physical size in favor of the push-rod as a "given", I really don't have to explain further why the OHC/DOHC is a better design, do I? (Jess pullin yer tail a little, Bob )

P.

I'm not playing devil's advocate. I think what is better is whichever thing fills the particular bill. In 1990 it was cams. In 2009 it seems not to be, at least as far as Corvette is concerned.

They aren't anecdotal engines, they are two top-end engines from the same company. No other companies bother with both premium DOHC motors and premium pushrod motors to compare.

Some of the stuff you say is equally applicable to both design approaches. As soon as a 4-valve engine has been optimized, all that's left for the daily-driver cammer for more power is more displacement.

As far as compression ratios, the LSx motors have similar compression ratios for engines with similar technology. The only 12+:1 engines GM makes are ones with direct injection, a technology that can certainly be applied to a pushrod motor as well. It seems GM hasn't needed to go to that well, probably because displacement is free.

[Paul Workman]

Originally Posted by Aurora40

I'm not playing devil's advocate. I think what is better is whichever thing fills the particular bill. In 1990 it was cams. In 2009 it seems not to be, at least as far as Corvette is concerned.

If you mean "fill the bill" by providing a motor that would make hp for less money, I spoze you have a point. However, even when the LS6 arrived in '02 to match the '93-95 LT5 output, Lotus had an advanced 5.7L LT5 ready to drop in the '95 Vette making 475+ (or was it 485?). Even the LS2 at 364 cid was pegged at 400 net - significantly shy of the DOHC 350 LT5-II. Then in '06 the LS7, with the help of another 77 cid only nudged over the peak numbers for the LT5-II, but total power under the curve proves to be more like a dead heat!

Originally Posted by Aurora40

They aren't anecdotal engines, they are two top-end engines from the same company. No other companies bother with both premium DOHC motors and premium pushrod motors to compare.

When I say "isolated anecdotes aside..." I was suggesting (for the sake of our discussion) the characteristic performance of the two technologies should be compared and discussed as a group and to refrain from attempting to characterize the entire technological group by holding up an isolated example in attempt to prove or discredit either technology. That's all.

Originally Posted by Aurora40

Some of the stuff you say is equally applicable to both design approaches. As soon as a 4-valve engine has been optimized, all that's left for the daily-driver cammer for more power is more displacement.

Far beit from me to discount cid: there's no replacement for displacement, as they say. But, my point was that due to the relative limited ability for 2-valve designs to breathe, the 2-valve push-rod has to revert to higher lift and longer duration and give up driveability in turn to get the same output a 4-valve config gets w/o a loping idle or loss of driveability and emissions problems! And, usually, loping cams tend to skew their performance upward on the rpm band at the expense of grunt on the low end. That is to say as output climbs from a 2-valve, single cam motor there is much more of a shift away from the flatter torque characteristics of the 4-valve design (apparently).

But, to your point, eventually as output demand grows, even a 4-valve configuration eventually has to go to volume increase to get the power. However, I'd love to see the dyno output comparision of Bob G's 427 LT5 vs. an LS7 and see which design makes the better use of the cubic inches...just for grins!

Originally Posted by Aurora40

As far as compression ratios, the LSx motors have similar compression ratios for engines with similar technology. The only 12+:1 engines GM makes are ones with direct injection, a technology that can certainly be applied to a pushrod motor as well. It seems GM hasn't needed to go to that well, probably because displacement is free.

In view of the new economy standards coming, I'm not sure displacement is free in the future, due to inherent limitations of the 2-valve/push-rod config - which gets to the heart of my point: It is obvious that state-of-the-art small displacement, high-revving DOHC motors with direct injection and variable, independent (intake-exhaust) cam phasing are capable of whopping performance that was only achievable in the past with big cube thumpers of the past, and then only w/in a limited rpm range! And, I can remember building and driving some big cube thumpers, but none of them would hold a candle to the performance of my LT5...before I did the P&P!

I think I understand the bigger pieces of why GM stopped development on the LT5 in favor of the LS motors. But, in view of the changing requirements and technology, it (to me) was a reversion rather than an advance to take the direction for the Corvette that GM did...Just IMO.

Time will tell, but my crystal ball says we are seeing the "last hoorah" for that old approach (in the Corvette, at least), unless there is a change in future requirements. It kinda reminds me of epitome of piston engine design for aircraft: The fuel injected, 4-row, 28 cylinder radial, air cooled engine, replete with multi-stage supercharger and intercooler just couldn't compare to the performance of the turbo prop technology.

And so it is with the 2-valve, single cam, push-rod design too, methinks. Competition for maybe even more than 505 hp from engines that get over 36 mpg will drive the last nail in our beloved big cid 2-valve push-rod thumpers. They'll live on in trucks and heavy equipment, I recon, but I will not be surprised to see them gone from the next generation of the Corvette...assuming there will be one??

P.

[LGNDLT5]

[quote=tomtom72;76365]I was watching one of the episodes of that Ultimate Factory series over the weekend and almost fell over when they showed the new base V6 for the camaro.

*Just got my '10 "LLT-V6" Camaro, absolute screamer! Not as quick as my '91 Z but that is just a few mods away. This motor seems to respond well to basics exhaust iat relocation etc. But the best will come after the ECM software access gets solved. Just a few basics on this V6: Forged crankshaft, 6 bolt mains, Direct injection, polymer coated pistons, etc.*


Watching them build the motor; I thought I saw some genetic connections to our LT5's.

*No real LT5 heritage that I am aware of. Actually, this engine was developed by Holden and produces in the 380+ hp range with a tweaked "open" engine management computer. Check out the CAMARO5 forum you would be amazed.**

Made me think what would direct injection do for an LT5?
Good Question.

[bb62]

Paul,

I think you are overlooking a key set of variables in why the LS series of OHV engines were selected and have been countinues over the past two Corvette generations.

1. Vehicle aerodynamics - a lower profile engine (i.e. LS versus LT5) were a lower profile allowing for significantly better aero characteristics. This in turn leads to better fuel economy.
2. Manufacturing - far easier decking in the vehicle assembly process.
3. Power density - HP per weight of the engine and HP per package size of the engine. The weight savings also affected overall vehicle weight the potential effect on acceleration.
4. Cost - self explanatory in the case of the LT5. But Chevrolet did put a lot of cost into the LS (from a design standpoint). But with the ability to amortize the cost over many more units (trucks included) the variable costs could be contained fairly well.

[Aurora40]

Originally Posted by LGNDLT5

*No real LT5 heritage that I am aware of. Actually, this engine was developed by Holden and produces in the 380+ hp range with a tweaked "open" engine management computer. Check out the CAMARO5 forum you would be amazed.**

Made me think what would direct injection do for an LT5?
Good Question.

Are you talking about the corporate 3.6L engine? I do not believe it was developed by Holden at all, it is a product of GM Powertrain. The engine was first developed for Cadillac for the CTS and STS.

I don't believe Holden has ever made any noteworthy engines. The GM corporate (Buick) V6 and (Chevy) V8 have been godsends to their product lineups.

I guess one thing that relates somewhat to the LT5 is the way the V6 has grown product-wise. Initially it was a fairly expensive engine, and an extra cost option on the CTS. Somewhat like the LT5 it was costly and not widely available. But as time went on, the engine has grown, presumably the cost has come down, and now the V6 is available in all sorts of cars, from the Camaro and STS down to Saturns and G6's. Maybe if they'd stuck with the LT5, the price would have started to come down, and it would have been used more widespread.

Though I suppose the Northstar paints an opposite possible fate, where the engine may have been so cutting edge that the company would just sit on their laurels and not update it, until it was obsolete and faded away...

[Paul Workman]

Originally Posted by bb62

Paul,

I think you are overlooking a key set of variables in why the LS series of OHV engines were selected and have been countinues over the past two Corvette generations.

1. Vehicle aerodynamics - a lower profile engine (i.e. LS versus LT5) were a lower profile allowing for significantly better aero characteristics. This in turn leads to better fuel economy.
2. Manufacturing - far easier decking in the vehicle assembly process.
3. Power density - HP per weight of the engine and HP per package size of the engine. The weight savings also affected overall vehicle weight the potential effect on acceleration.
4. Cost - self explanatory in the case of the LT5. But Chevrolet did put a lot of cost into the LS (from a design standpoint). But with the ability to amortize the cost over many more units (trucks included) the variable costs could be contained fairly well.

Um yeah, and I would add a healthy dose of "not invented here" to the mix as well. Bottom line is...well...the bottom line (of course!). I believe pushing the push-rod was only temporarily expedient. If fuel economy AND hp is to be pushed farther, then the virtues of DOHC are going to outweigh their relative complexity and slight weight disadvantages. Case in point: The 350 cid LT5, fully ported and using an exhaust dimensions of similar size, is making the same hp as the 427 LS7 - and that is on LT5's STOCK cams. And, taking a peek at the potential, we only have to look as far as the variable valve timing being used by Mercedes Benz to get enormous performance from less than 300 cid. And, look at how much performance those little ricers are getting from minuscule displacement (non-pushrod) motors as another "elephant in the room". (Hell, I drive a 5.4L (330 cid) SOHC, 24V Ford F150 that makes 1 hp/cid and a pile of torque with less displacement than my previous LT1 Vette. There is a pattern in here somewhere, methinks!)

Who knows what the sports car will evolve to, including future Corvettes. But, if there is to be a future for the Corvette, I am willing to move a big portion of my chips from the pushrod square onto the DOHC square.

FWIW,

P.

[bb62]

Originally Posted by Paul Workman

Who knows what the sports car will evolve to, including future Corvettes. But, if there is to be a future for the Corvette, I am willing to move a big portion of my chips from the pushrod square onto the DOHC square.

FWIW,

P.

Paul,

The only problem preventing the scenario you mentioned above is the investment required to re-engineer and retool their existing lines. The Corvette shares much of the tooling with their truck brethren and the investment would not likely be there without some ability to amortize it over a broad spectrum of vehicles. The Corvette would not likely drive a new architecture again. The LT5 is precisely the experience that would tell them a Corvette only architecture is not the way to go - at least in the near term future.