Eh, what's up DOHC?

I've always wondered why GM stopped making DOHC performance engines (LT5s and future performance engines)?  I understand that 32 romping valves makes the engines prone to frequent repair and maintanence than a pushrod engine, but consider the benefits of more air flow with four valves per cylinder and an optimal location for the spark plug.  Ford can attest that producing engines with more valves permits them to still rumble with the bigger bore and stroke Chevy and Dodge motors on the market today.  The technology, research, and development went where?  In the trash?  Why haven't we heard of anything modern? Although the tried and true method of a bigger bore and stroke worked on the new ZO6, what's next?  The LT5 yielded 405hp, but much more is possible with the head flow  technology of today.  The 16 configuration was, and still is a great idea for getting a precise a/f ratio throughout the power band amd remember, this engine revs higher than the prehistoric pushrods; 72000rpm!  I hope GM tries to do something innovative for this LS series of engines that are already great power plants.  

*16 injector configuration*  

The LT5s were always plauged by problems and were overly complex for the power produced. Ultimately, it would seem that GM made the right decision in sticking with the pushrod design. Consider how long it took Ford to develop the Modular motors into a competitive piece as well as their considerable investment in initial development. Remember rpm is great but it challenges longevity. GM has already done something innovative in sticking with a pushrod design and developing cylinder head and engine management technology  to increase power and mileage and decrease emmisions.  

...But the real dilemma is...what's for the C7 ZO6!?  The supercharged engine we all saw in this past issue is probably a powerplant going in the C6.  Could Chevy do an MR like the C5  concept in the early 90's... it was twinturbo'd!  

GM still has something of a performance engine in the Northstar, which puts out 443hp in the XLR-v and 469hp in the STS-V. However, its a much more expensive design than the LS series.

The LS series also has a big advantage over a DOHC type motor in terms of weight and size. The engine that is most easily used for comparison is Ford's 4.6L DOHC V8, which is bigger, heavier, and not as powerful as an LS1.

Also, the LS7 revs to 7000 RPM

Whats next? Forced induction.  

What is Fo rd going to be able to do next with their"modern" engine?  They have already had to install a supercharger to keep up with GM's naturally aspirated engine.  Whe GM supercharges, what is left for Ford?  They can't make their engines very much larger than they already are.

You would think that with 3 or 4 valves per cylinder, the Ford engine would produce a lot more power than it does.  
The new Mustang 3 valve produces 1.07 hp per cube while GM's LS2 2 valve makes 1.1 hp per cube.  This is pretty close but look at all of the extra complexity of the Ford engine and the extra things that can go wrong.  

Look at GM 16 valve vs Ford 32 valve-
LS6 - 1.17 hp/cube  405hp 346ci
32 valve Cobra - 1.14 hp/cube 320hp 281ci

Also, the Mod motor is physically huge for only 4.6 - 5.4 liters while the LS engines have been bored and stroked to over 450 cubic inches and they will fit in anything that can handle a V8.  The Ford engine will not.  If it did, I would be installing a Cobra motor in my Maverick.  I am considering an LS1 but I just don't like half breeds.  

I read an article a few years ago on the development of the LS1.  I hope my memory is accurate -

GM was divided between people that wanted the new engine to be an overhead cam 4 valve and people that wanted the new engine to remain a traditional pushrod engine.  There was a lot of debate and heated arguments over this.

Someone came up with an idea to settle it once and for all. (Can't remember who)
They set up two Corvettes that looked identicle.  The only difference was one car had an LT1 and one had an LT5 (ZR1 32valve)

A lot of GM managers were invited to test drive each car and give their opinions of each. They were not told what engines were under the hoods.  

When everyone was finished, most if not all liked one car better.  The reason they gave is because that car had more low end power.  The bottom line - It was more fun to drive.  

That car had the LT1 engine.  The LT5 had a lot more horsepower, but is was high up in the revs.  Low and midrange torque is what makes a car fun to drive.  

According to the article, this was the point when it was decided to stay with a 16 valve pushrod engine.
GM definitley made the best choice.

Note -
When Chrysler decided to build their new engine, they had the luxury to look at what GM and Ford did.  They could study the good points and bad points of each engine.
They must have decided that GM made the best choice since their Hemi is almost a carbon copy of an LS1. I wish they would have designed it so the heads would be interchangable with GM.  Wouldn't it be neat to bolt on a set of Hemi heads on your LS1?  

You can have 4 valves per cylinder in pushrod engines like the 6.2 liter GMC sierra denali engine.  

The 6.2 Denali engine has 2 valves per cylinder.  Where did you hear it had four?  

I guess the reason GM quit on DOHC engines is because they don't know how to make them. I can see the firestorm brewing already, so let me explain a few things:

DOHC engines are not by nature heavier or lacking in broad-powerbans: just the LT5. I drive now and then a 2007 BMW 550i: it makes 360hp at 6300rpm and 360 foot pounds at only 3400 RPM. And the engine is only 4.8 liters. So its basically as powerful as a L76 engine with a little less torque. Imagine if they moved the displacement out to 6 Liters: it'd be making 450hp and still running on pump gas! Thats 50 hp more than an LS2, which needs cam and head modifications to make that power and then you lose some daily street comforts.

I've built a few small-block LS engines before, two LS1s, an old-school 427, and a 327 smallblock, as well as three import motors like the 4.8 Liter in the 550i, a Honda K20Z3, and the RB26DETT.

And I can say without a doubt that all the import motors I have built were lighter in the end than any small-block I've ever worked on. DOHC designs just don't add the weight GM engineers say it does. At most maybe its a few pounds, nothing that isn't made up for with the airflow it provides.

I know some of you point to Ford's 4.6 L as an example of how DOHC is not that good. Do take into consideration that an 03 Cobra had 390 horses on that engine and it was ONLY 4.6 Liters. Compare that to General Motors 6 Liter LS2 which has only ten more horses. Meaning that the LS2 gets 66hp per liter, where as the Cobra engine got 84hp per liter. Given that, had the Ford engine been 6 liters, it would've made 508 hp! Thats the most common problem I see with the thinking here: rather than talk about how many horses per liter the engine makes, we talk about pure power.

And I know for a fact DOHC engines can be torquey: just drive a 550i, go schedule a test drive sometime. A lot of comparisons are done to the LS7, but that is brand new technology with a lot of Euro-influence like the dry-sump oiling system. Ford has not yet tried to remake the old 4.6 DOHC, so until they do with new technology I don't think we can do a comparison. Also, we always should keep in mind that added displacement just adds to fuel consumption as well, not just horsepower. If someone can get 500 hp out of a 5 liter or 500 hp out of a 7 liter, which one is using less fuel?

Now I don't want any of you to get me wrong: I like General Motors small blocks, thats why I'm here. I'm also researching how I can modify the crap out of the L76 engine once the G8 drops in 2008 (too bad I'll have to wait to next fall for the manual transmission).

But all this badmouthing of imports and their motors I think is why so many people left GM in the first place. The small cars of the late seventies-till-now from foreign automakers have been hailed as fun to drive for a long time, why haven't we picked up on that? If these cars had horrible torque numbers and torque was solely what makes a car fun to drive, then why does everyone who drives an import eventually call them "fun to drive?" Because they really are.

Now that thats said, I think GM should reconsider DOHC designs. Its true that a 7 liter OHV makes more power than a 4.8 L DOHC. But if we have a 7 Liter DOHC done right next to a 7 Liter OHV, which one will produce more torque and power? The DOHC. The fact that the LT5 has to be one of the worst engines from GM ever does not invalidate that (I watched an uncle try and work on his once, how the *** can one engine have so many oil problems?).

That and its pure, well known science that more airflow means more power.  

Scryer, I for one totally agree with what you've said. It has long been my dream for GM to get serious about over head cams. I feel my GM engines waste so much HP/TRQ by pumping all that oil to keep 16 lifters pumped up and working; as well as slinging all that weight back and forth starting and stopping and then pumping oil all the way up those long old pushrods that are working back and forth just the same . The way I see it with an overhead cam we could utilize some of the roller rocker technology that has come out in last couple of years to run those rockers directly off a rotating cam/cams  turned by a cogged timing belt that doesn't stop and start. I'm no physics major but I can see this much.  There is a man named Airis (sp?) that builds hemi- heads that will fit my 7.4L ; I want to get a set and and build a craddle for the top of the heads so I can at least attempt a single OHC ; I would be doing away with the lifters and pushrods where I feel so much energy is lost.
 * My real hope is that somebody will come out with a set of solenoids that will bolt in place of the valve-springs/retainers/rockers and operate my valves through the computer. That way I can design any kind of cam action I want and not sling any weight  at all !!! I could even program my valves to work like 5 different cams all in one motion and power band !
 Do you think anything like that will ever happen ?!?  

My two cents:  First of all, DOHC makes for a larger engine footprint in anything with more than 4 cylinders.  Compare a 7 liter OHV with a 4.6L DOHC, and they're about the same size.

Secondly, GM being one of the largest (if not THE largest) automaker in the world, it has to succumb to what pays the bills....consumer perception.

The wear and tear factor actually heavily favors the OHV design, along with the fact that liter for liter, the OHV is substantially lighter than a DOHC when built using the same materials.  The OHV is also a simpler design.

People can talk about DOHC being "high-tech" all they want...but the fact of the matter is, all the high-tech gadgetry that is typically associated with DOHC engines has more to do with marketing and manufacturer choice rather than valvetrain design.

Lastly (at least for this post)is low RPM power vs. high RPM power.  Think of your average daily drive, whether it be to work, shopping, whatever....

....How many times are you over 6000 RPM?  The vast majority (not all) of DOHC engines don't really come alive until over 5000 RPM, and can tickle 8-10K RPM in manufacturer tune.  Conversely, the OHV design specifically targets low end power, which is where 90% of consumers spend 90% of their time....under 5000 RPM.  

Ford originally intended the Romeo or mod motor for FWD applications which were transverse thus it had to be shorter thus limiting the bore centers. Even with the siamese or Grand Am block and the biggest stroker it can only yield 5.4 liters although in Roush-Yates GT 3 spec with stroker  would be in the neighborhood of 600 hp with about 435 lbs fully  dressed but it is 30 inches wide  and don't think about the cost.By comparison the 3 valve GT 4.6 is 420 lbs. fully dressed with 300/300 hp/tq.
On the basis of power density (the exterior cubic volume and weight) the  LS 7 beats either one hands down but has limitations in port layout and valve train inertia as compared with an OHC. You  pays your money and takes your choice.
You always wondered  why GM stopped making DOHC performance engines. You have to lay off the Rip Van Winkle pills. I certainly count the 2008 Caddy CTS V6 3.6 direct injection engine as a performance engine. With 304 hp and 273 tq with 26 hwy mpg I  call that performance. I haven't seen any numbers yet on external engine size or hp and torque  curves but it doesn't take a great deal of imagination to see the possiblity of 2 more cylinders being grafted on and having this engine replace the long in tooth Northstar which in its highest output in the XLR makes  325 hp from 4.6 liters. By simple mathmatical extrapolation the new V8 would make 406 hp and 364 lbs of tq. Bore it .060 over and you would be just short of 5 liters and around 415 hp or very close to the 425  of an SRT 8. The Caddy ,however, would carry about 200 lbs less and with the FE3 supension package and shorter wheelbase outhandle the Mopar  as well. I also suspect that with some type of variable displacement the 26 mpg figure could be retained.
Can you say happy Mopar hunting boys and girls? Finally an existential questioon. Is it more fun to beat  the Mopar on the track or at the gas pump?