[Press] GM Smallblock Gets Three-Valve Head

[Rob]

People are constantly comparing the LT5 to the LS6 lately in these DOHC vs. pushrod debates.

The common comment is "The LS6 produces the same horsepower as the LT5 with a far more simple design for much cheaper!!!"

Well, I have to say that is not a fair comparison......at all. These engines are TEN YEARS apart, and they put out identical horsepower! Give the LT5 TEN YEARS of developement, and then lets see what kind of output it has! In that respect, I don't find the LS6 very impressive. In fact, a common comment that you hear is "Now if only we could get the LT5 in the Z06's body........" In the last 10 years, Corvette has not gained much ground, and arguably NONE.... Although, admittedly, the ZR-1 did set the bar pretty darn high.

Yes, the transition to DOHC will be costly--but any change is going to be at first. Once it becomes the norm, it's not going to be so "expensive". I don't think technology should stop just because Corvette guys are obviously more familiar with and only know how to fix their pushrod engines. If Corvette is going to evolve and compete on a global market, we need to be a bit broader minded and let go of some history and our childhood biases.......let history be exactly that---history. Pushrod engines are not Corvette's tradition. Corvette's tradition is CUTTING EDGE TECHNOLOGY.

I think this 3 valve design is a step in the right direction.


Brett

Actually, I think it's a pretty fair comparison. We're talking about basic engine design, not the length of time in between two different engines. Time is not that relevant in this discussion.

If the LT5 and DOHC architecture is so great, I would have to ask, why did Mosler decide to use an LS6 engine for its MT900 and didn't bother to use a DOHC engine like the Northstar?

There is no doubt that the DOHC design is a good design - I believe Ferrari is using them in their Modena models. However, if you can build a reliable, fuel efficient, low weight, simpler engine that meets emissions specifications and can very easily be modified to yield more power, why would you want to mess around with a more intricate engine with more moving parts?

Take a look at how much it costs to modify an LT5 engine to yield more power, vs. what it costs to modify an LS1/LS6 engine to do the same.

 

[Brett]

By mentioning the time difference I'm talking about how much could have been improved in that period. I think it is very relevant. Like I said, think about what the LT5 could be producing now with ten years of advancements. You're right, I wouldn't mention as we are discussing engine design, but 10 years is enough to develope an entirely new generation of the LT5 design, with less weight and more output. If only GM had had the balls to stick with it.....

I also highly disagree that it is more difficult/expensive to modify DOHC engines. The LT5 is difficult, yes, but only because it was a one-of-a-kind and limited production engine. You can't look me in the face and tell me the Import guys aren't modding our butts off! The RB26DETT in the Nissan Skyline is a DOHC 2.6 liter inline V6, and it is probably the most modable engine on the planet. In fact, the factory stats of 280+ hp of the engine don't even matter to people who know what is what, because it was DESIGNED to be modded. Japan has a factory power limitation law of 300 horsepower. So Nissan basically severely detuned a race engine that you can EASILY get to 600 horsepower with NO significant changes to the engine. Out of 2.6 liters!!! It's considered a sin to buy a Skyline and not mod it, because you're not releasing the engine's true potential.

If the LT5 and DOHC architecture is so great, I would have to ask, why did Mosler decide to use an LS6 engine for its MT900 and didn't bother to use a DOHC engine like the Northstar?

Because there's not a high output DOHC block for Mosler to buy from GM right now.



Brett

 

[Runge_Kutta]

In the hopes that the participants of this thread are
truly interested in seeking a better understanding of
design choices rather than looking for opportunities
for digs and cheap shots, here are some thoughts.

This debate about the "low-tech" GenIII engines relative
to "high-tech" DOHC engines is very old and, seems to me,
often misses the point. The first thing one does when
designing an engine with some applications in mind is
to establish objectives. For the GenII LT1, this set
of objectives is given in detail in SAE 920673

http://www.sae.org/servlets/productDetail?PROD_TYP=PAPER&PROD_CD=920673

I will not list all of it but I hope you get the flavor. There
is more in the paper an likely more that aren't even listed.


PERFORMANCE:
1) BSFC (Brake specific fuel consumption)
2) HP/ Vol (height x width x length)
3) HP/ Weight
4) Torque bandwidth
5) Internal friction
6) BSHC + BSNOX (Brake specific hydrocarbons and nitrogen oxides)
7) Parts count
8) Response (RPM/Sec = angular acceleration)
9) Drivability

a) Advanced technology if customer will perceive the benefit
b) Avoid gadgets an fads
c) Balanced excellence

VALUE
=====
1) Investment cost
2) Piece cost
3) Parts count
4) Compeitive comparison

a) Multifunctional components
b) Vehicle component sets
c) Minimum maintenance design
d) Easy servicability

If these are ones objectives then who cares how you achieve
them! While I am not in a position to quantify these attributes
for all of the engines out there, I would contend that the GenIII
and GenIV ( 2V ) engines are really quite impressive.

It is an all to common event in science that as researchers are
looking for ways to improve the state of the art, that they overvalue
the positive benefits of a new approach and undervalue the costs.
One can probably correctly criticize GM for being loathe to change
engine architectures. It actually put them in a position to see
just how far they could push this OHV technology when others had
prematurely abondoned it. With the advent of the 3V, single cam, GenIV
engine, I think GM will have an engine that is very tough to beat
according to the above metrics. On last thing to remember here is that
many other countries have had their legislators place limits on the
displacements of automobile engines. Legislators should NOT constrain
the engineers choices but should only constrain the results. I think
that since displacement is not controlled in the US that this may
have influenced the GenIII and GenIV choices.

 

[Brett]

Don't get me wrong, I'm not arguing against the GenIV 3 valve engine. I think it sounds great. It's going to be lighter, and all the while with more displacement and horsepower per liter. That is technological advancement in every area.

You're right about other countries having restrictions on displacement. To elaborate on that a bit, it forced them to come up with alternate ways to gain horsepower out of small displacement. In the long run, it has really helped them, as now they have light and well balanced vehicles. American technology represents the opposite approach, because we have never had those restrictions. I believe the optimal engine design is a combination, or happy medium, of both of these schools of thought.



Brett

 

[Dad]

Yes there was a high output 4 valve.

Maybe they should have sold him the Olds 4 valve after they dumped that program.

Because there's not a high output DOHC block for Mosler to buy from GM right now.

I better read up on the Corvette history, even though I've owned at least one of every generation I didn't, and still don't, look at Corvette as the cutting edge of technology. A great sports car, yes, but it don't need to be loaded down with techno-toys.

Just for fun, ever change a starter on a Corvette, or a Northstar?

 

[Brett]

That is currently being produced and has higher output than the LS6? I don't think so. The LS6 is the top engine at GM right now. That is why Mosler uses it.

I didn't, and still don't, look at Corvette as the cutting edge of technology. A great sports car, yes, but it don't need to be loaded down with techno-toys.

I find that a pretty sad outlook. Regardless of Corvette's importance in the past, times change. Corvette is a "halo" car, and halo cars lead a company these days. Corvette DOES need to be on the cutting edge of technology, or else it will die. Just because technology is new does not make it a "toy". There was a time when fuel injection, or the 350 small block, was a "techno-toy".

Just for fun, ever change a starter on a Corvette, or a Northstar?

Don't insult my intelligence. This was a great discussion of ideas and opinions until you came in and started taking little jabs.



Brett

 

[Dad]

Yes, the Olds racing engine put out more HP and RPM than the LS6. It was in limited production just as the Mosler was at the time. If Mosler got a better deal on a Ford that's what they would use.

I'm not the one that started the jabs or the questioning of anybodies intellect, remember this? –

If Corvette is going to evolve and compete on a global market, we need to be a bit broader minded and let go of some history and our childhood biases.......let history be exactly that---history.

We all learn for our childhood biases and they do stick with us just as yours are already showing. When I was 2 I didn't have an opinion, now I do, it's called experience. That's what you're going to school for, to gain knowledge and experience. It was not a jab but an expression of my history, (experience).

The reason I ask if you had ever changed a starter on the Northstar wasn't to insult your intelligent. It was to point out what had happened to the serviceability of an engine when it developed to the present day Northstar. Just so you don't have to look it up, it's under the intake manifold. I was at the Auto show in Chicago when they unveiled the Northstar, couldn't wait to get one, had them for about 10 years. Cost a ton to maintain, no power, average gas mileage, but they were smooth. Went back to driving a Corvette because I like to feel a kick in the seat of the pants once in a while. Ordered a 1997 as soon as I drove one. It took so long it was a '98 when I got it. It has been nearly flawless and it has no techno-toys. That's the way I like them, you can get yours the way you like them.

 

[Brett]

It doesn't sound like this Olds engine was in high enough production for Mosler to use it. I've never even heard of it. Where can I read about it? Remember, I made that comment in regards to Rob's comment (did Mosler choose OHV over DOHC). Your comment that Mosler would have gone through Ford had they given them a better deal appears to further disprove that.

I also do not see how the comment you quoted puts down or questions anyone's intellect. It was certainly not intended that way.

All I meant by that statment was that at some point or another, all engines were "techtoys", so it does not do a disservice or ruin Corvette's history to change from OHV to DOHC, or to this new 3 valve for that matter, or whatever! Whatever works best.



Brett

 

[motorman]

i posted several months ago that the corvette will be 3 valve because the new 2004 ford trucks have 3 valve heads and since the corvette engine is truck engine based GM is not going to have ford trucks have a advantage. if GM would use a DOHC engine in the corvette they would need a dry sump engine to get it to fit under the hood because the a DOHC is much taller. older BMWs used the horizonal short push rod in their 4 valve pushrod engines

 

[sscam69]

There is nothing new about a DOHC engine.

It is still an internal combustion engine and still only puts ~33% of the burnt fuel to good use. It is just a different configuration, thats it nothing more.

I would figure people would be calling the rotoray engine in the RX-7's/8's new technology but if you look in the history books these things have been dreamed up since the early 1900's.

They are bringing about these changes for several reason. I am willing to put money on emissions and fuel economy.

 

[Dad]

Loosely speaking the DOHC V8 Olds was based on the Northstar design, just smaller and lighter. It did win it's share of races, why they droped it I have no idea. Except GM droped Olds, or did they?

http://irlinsider.adnetweb.com/1101OldsFinal.htm

They have a very nice rendering of it here -

http://www.precision-illustration.com/Drag_Engines_3.html

3.5 liter, 650 HP at 11,000 RPM was their target, not sure what they got.

Mosler would have to get a super, super deal to go Ford, they are all ex GM people on his team.

Don't get me wrong, if a third valve will eat the snakes, bring it on.

 

[Dave63]

My 2cents based on having owned a 5 spd DOHC Lumina Z34, an auto STS Northstar, and a whole bunch of auto and manual pushrod GM v8s:
The DOHC v6 Lumina 5 was very fast, but nearly undrivable at low speeds due to lack of torque. The Northstar is a wonderful, smooth, powerful engine, but many are massive oil users. My 3 present pushrod GM engines (Suburban 5.7, GTP Gran Prix, and MN6 C-5) get good gas mileage, use no Mobil 1 between changes (even the Burb with 148k miles), and the two cars will dust off 98% of the "exotic, high tech, modern, up to date" ricer cammers, while still being repairable and reliable. The truck will out-tow all the cammer trucks (Oh yeah, now I remember, there aren't any.) Why not stay with pushrods? Sprint Cars dyno over 850hp with pushrods, NASCAR stockers turn 9k with pushrods- whats the problem?

 

[LongTimer]

There is NOTHING low-tech about the Gen IV engines. They may, in fact, be higher tech than most DOHC engines and take up less space while making more torque (torque is a generality).

 

[BigRed]

I loved the line " A special jig will hold the parts together!"

ROFL GM