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Demise of the LT5 Engine

Rob

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I'm in the process of finishing up the new book by retired Corvette Chief Engineer, Dave McLellan called "Corvette From the Inside". This is one AWESOME book! He has answered A LOT of the questions I've had about the C4/C5 platforms as well as the ZR-1.

In this book, he explains in great detail why the LT5 engine was killed and why it did not make it's way into the C5 platform. He writes:

From page 233: Why the Gen III Doomed the LT5

The contrast between the Gen III [LS1/LS6 engine] and the LT5 engine is striking. The LT5 is both taller and wider, as a result of its double overhead-cam cylinder heads and its complex intake manifold. It became apparent that the next generation Corvette, if it were designed solely around the Gen III small block, could be significantly smaller and lighter than if it had to accommodate the LT5 engine.

Studies based on a large population of modern cars have given us the standard relationship between engine weight and total vehicle weight. Increasing an engine's weight by one pound means that the total car's weight will likely increase by two pounds. We estimated that taking 80 lbs out of the Corvette's engine would allow us to remove another 80 lbs from the chassis. In the case of the Gen III, reducing the engine's length would also contribute significant savings. Weight reduction of this magnitude is only possible when you're designing a car from scratch.

The planned future LT5 engine, with its even more complex valve train, would have been 205 lbs heavier than the aluminum Gen III. Thus a Corvette designed around the Gen III aluminum engine would weigh around 405 pounds less than the same car designed to use the LT5. As a result, the LT5 engine would have had to generate 55 hp more than the Gen III, simply to compensate for the heavier car. With the Gen III generating 405 net hp and the future LT5 estimated at 475 net hp, the effective power gain would have been a mere 15 horsepower. And, given an estimated $25,000 price premium for the LT5 engine, the cost of this small increment of power is astronomical.

The Corvette had reached a crossroads. We could design the C5 around the LT5 engine or we could design a smaller, lighter car that was fitted like a glove around the Gen III small block. By opting for the smaller package, we could achieve ZR-1 performance at the price of a standard Corvette. This was too important an opportunity to ignore. As we explored it further, we convinced ourselves and Chevrolet that this was the right strategy for the next generation Corvette. This, however left us with the conundrum that the far-superior Gen III might seem, to the consumer, to be low tech.

The Gen III uses computer management to control fuel and timing, providing smoothness, high power, and efficiency -- a very high-tech feature, but eariler forms of control -- such as the four-valve combustion chamber -- were what the public perceived as modern technology. We knew that the Gen III LS1 would do just fine without these older features, as they came at such a high price, in terms of size, weight, and complexity. Like the consumer, we had been accepting the notion that complexity was good. Yet, here was one case where just the opposite was occurring. The simple solution was almost as powerful, and it was smaller, lighter, cheaper, and more fuel-efficient. Whether it was considered high-tech or not, the Gen III was the better engine. So, in the end, the only logical choice was to back the Gen III small block as the Corvette's engine of the future -- even if it's roots dated back almost 50 years.

This was just one of the reasons for the demise of the engine as well as a few others, but I would be willing to bet that this was the primary reason why the LT5 engine or a direct descendent of it, did not find its way into the C5 platform.

If you have the chance to pick up this book, you won't be disappointed. I'll have a more lengthy review of the book in the coming weeks.
 

90 Corvette ZR-1

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The LT5 had the "it wasn't made here" syndrome. MerCruzer and Lotus had already made a 450 hp version that was OBDIII compliant. If the DOHC is so expensive, then why is caddy using it?
 
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Rob

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Much greater application and production numbers than the Corvette. The production cost can be spread much wider over a high production platform than it can over a lower one such as the Corvette. That's my understanding in any case.
 
V

vettepilot

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The GenIII engine and it's forefathers of the small block family are a prime example of why the KISS (Keep It Simple Stupid) principle should not be thrown out in favor of complex technology. Some prefer the complexity of the DOHC engine, and that technology is good, I'm not saying it isn't, but the simplicity of the pushrod engine coupled with it's high torque/HP at street driving RPMs makes for a more driveable ultra-high performance platform.
In my opinion, I wish the Vette group would explore the possibilities of using a stroker engine in the next generation. The 5.7 engine has almost come to it's peak with HP/TQ ratings and still meet the emmissions requirements. By going to a stroked engine, the TQ could be increased significantly, and along with that comes the performance we all desire, all that in a LS series package size and weight. Of course there is the possibility that the powertrain engineers have something really big up their sleeves, so I guess we will have to wait and see.
vettepilot
 
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There were discussions about putting the Caddy DOHC engine in the C5, thus making the costs much lower. That had never been done before, and it was thought that the consumer would frown upon 'putting a caddy in a corvette' so the idea was dropped... I like the simple design idea anyway... how many of you open the hood when you have a problem with something, and just wished all you saw was an engine, with a fan hooked up to the waterpump, and the only pulleys are on the waterpump and alternator? basic, easy, the classic design... too bad we have to have power steering etc. these days(don't get me wrong, i love power steering!, as well as all the other power stuff)
 

FrankUrbinati

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My STS has the Northstar engine in it. The engine strongly resemble's the LT5 engine in the ZR1. And flat out haul's the bacon. IMO.. GM is going to bank on this baby. What car ? Seem's to be the question.
:w
 
A

ArtZR1991

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Thanks, Rob.

That's the explaination essentially as I had read it from other sources. And it is quite reasonable... For the unique market position the Corvette holds.

But the question still remains, what if the LT5 had been developed over many years, what could it have been?

I also agree with Frank, in that the Northstar, and the Aurora were the prime beneficiaries of the LT5 technology.

Point is, I think Corvette did the right thing abandoning the LT5 for that car, but I think a lot remains to be debated about the LT5's potential as an engine without the marketing restrictions of the Corvette (as we have traditionally defined it). That's what makes the ZR1 so valuable, in my own opinion. It's as if they asked , "what kind of Corvette could we build if we really took the gloves off?" For a brief period, we got to see it, the hopelessly misunderstood but still fantastic ZR1. Then it was back to basic business common sense.

In case anyone misunderstands, I mean all of the above in a most complementary manner. Corvette DID do the right thing. And the ZR1 will nonetheless go down in history as one of it's most exciting projects. The discontinuance of the LT5-ZR1 does not suggest in my mind any negative issues with the car as a pure car. But it was a stepchild in the Corvette family. Kinda like Zora's Grand Sports would have been. But its all history now.

Thanks for the book recommendation as well. I am crazy about that stuff.

Regards,
 

90 Corvette ZR-1

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I think we got a look at what the LT5 could have been with the Black Widdow cars. The DRM 450 and 550 horse cars. I have a friend whom owns the DRM 550 Black Widow car. That car runs like a raped ape. He is taking me for a ride once he gets his new clutch in. Also Fastlanes car is a good indication as is Norms TT 368 car. The 368's, 415, even bigger LT5's are all a great indication of what these cars could have been. Just imagine what beasts these cars would have been with the 4.0 bore spacing Lotus wanted to use....
 

rkreigh

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the Northstar, Olds, and Gen III SB LSx series all benefited greatly from the technology and lessons learned in the manufacturing of the LT5. I still believe that the quality of the LT5 is unsurpassed, but indeed weight and packaging issues as well as cost led to the obvious conclusion that the LSx would provide a much better bang for the buck, and since the engine would be used in many GM platforms, the conclusion is clear. the Vortec series is mass manufactured and the LS engine is a worthy engine in it's own right, but lacks the innovation and technical excellence and hand assembled quality that GM bestowed on the LT5. economic reasons dictated that this operation could not be sustained. many cited emissions, but really the low hoodline of the C5 and power to weight goals as Dave clearly states are the reasons.

I for one hope that the C6 is another special car. at this point "economic" reasons are dictating the technical approach. I thank Dave for having the courage to just build the best, and push the bean counters aside. His committment to excellence is to be commended.

never settle for anything less.
 
U

USA ZR1

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I only disagree with one statement that Dave made and that is the $25K pricetag. Mercruiser offered the LT5 to GM at $8K apiece if they would agree to buy 20,000 engines/year. This is the part that gets you;Mercruiser offered the LT5 for $2K an engine if GM agreed to buy 30,000/year. More than thirty thousand C5's are sold a year so read that and weep.
 
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you have to remember that C4's weren't selling like C5's, and if the LT5 could be 2 grand an engine, LT1's were probably being built for less than half of that
 
U

USA ZR1

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And your point is? We're not talking about C4's here but the engine for the new C5. What do you think GM pays for the LS1 engine as used in the Corvette? $2K,maybe?
Mercruiser could have redesigned the LT5 to take some weight off. How much does the engine in a Ferrari 360 weigh? It doesn't weigh all that much and sure isn't hurting for HP.
What killed the LT5 program was the "not invented here" syndrome. Any other reason is pure folly.
 

Rob

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Clint,

I'm not sure I agree. The LT5 Engine would have had to have been completely redesigned from the ground up in order to match that of Ferrari's 360 Modena Engine which is 3.6L, 40 valve/cylinder, dry-sump lubricated engine, and still only puts out 400 horsepower.

Specifications from Ferrari's site:

No. of cylinders 90° V8

Bore & stroke 85x79 mm
3.34x3.11in.

Unit displacement 448.2 cc
27.36 cu. in.

Displacement 3,586 cc
218.84 cu. in.

Maximum power 294 kW (400 bhp) @ 8,500 rpm

Maximum torque 373 Nm (275.6 lbs/ft) @ 4,750 rpm
 
U

USA ZR1

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Of course it would have to be redesigned,Rob. I was just using that engine for an example. Only 390hp out of 3.6 liters? What would a new design 6.0 liter LT5 produce? I'm sure 475hp would be a conservative number.
My point to all the above discussion was that if GM canned the LT5 program when the engine was offered to them at $2K each in quantity,some of the other reasons given don't wash.
At least that's I've heard in private conversations with some GM and Mercruiser people. The real truth may never be revealed.
Clint
 
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USA ZR1 said:
And your point is? We're not talking about C4's here but the engine for the new C5. What do you think GM pays for the LS1 engine as used in the Corvette? $2K,maybe?
Mercruiser could have redesigned the LT5 to take some weight off. How much does the engine in a Ferrari 360 weigh? It doesn't weigh all that much and sure isn't hurting for HP.
What killed the LT5 program was the "not invented here" syndrome. Any other reason is pure folly.

My point was this... if mercruiser could sell the LT5 for 2 grand to chevrolet, this means a couple of things: I am sure merc wasn't losing money at the 2 grand number, so, if merc can build the very complex LT5 for 2 grand, the much less complex LT1, built in house, should be able to be built for half that. Same goes for the LS1 and LS6.

Why would GM go for more expensive, more complex etc., if they can get what they want in the cheaper, simpler package? how much weight does the LT5 stand to lose?? it is already all aluminum...
-Honestly I seriously doubt GM wants a 475 HP engine... You must realize that the average Corvette buyer is much less experienced with horsepower than the average Ferrari buyer. GM doesn't make a Corvette that will destroy a Viper because the liability of making a car that fast, for such a low cost is very high. What GM likes to do is make a Vette that is excellent... then leave plenty of room for aftermarket improvement... this gets the liability off of them, meanwhile, the aftermarket always makes viper/porsche/ferrari killing Corvettes to defend the Corvette name.

-Is ZR1 king of the hill? Sure it is... but if you really want to go fast, I think simple is better... less stuff to break, less money, less weight... I am with Reeves on this one... the ZR1's are overweight pigs... especially when you compare them to Callaway TT's or Z06's
 

90 Corvette ZR-1

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Right with the TT's that need $15,000 rebuilds cause they can't handle the power that is being put out and puke up rods thus cracking the block, or the rubber fuel lines that run right next to the cherry red turbos.
 

Rob

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Vettelt193 said:


-Is ZR1 king of the hill? Sure it is... but if you really want to go fast, I think simple is better... less stuff to break, less money, less weight... I am with Reeves on this one... the ZR1's are overweight pigs... especially when you compare them to Callaway TT's or Z06's

Well, now I have to disagree with this. The 1990 Callaway TT weighed in at approximately 3,403 lbs and made 390hp.

The 1990 ZR-1 weighs in at 3,460lbs and produced 375 hp.

That's a difference of 57 lbs and 15 horsepower. I don't call that an "overweight pig". Just my opinion.

References:

Callaway Twin Turbos: http://corvetteactioncenter.com/specs/callaway/index.html

ZR-1: http://corvetteactioncenter.com/specs/zr1/index.html
 

90 Corvette ZR-1

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Rob:

Its only 5 hp. The LT5 made 385, not 375. It was under rated 10 hp.
 

Rob

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That's news to me? Where did you read that? I haven't seen that in any documentation. Based upon what I've heard from people that have run stock dyno runs, the engines vary quite a bit and can make approximately 5% less than or more than 375 hp at the crank.
 

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