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Why the LT5 was discontinued...

 
Old 04-22-2019, 12:16 AM
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Tom400CFI
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Default Why the LT5 was discontinued...

I know all the reasons that have been discussed over the decades, but found THIS article the other day and something struck me as odd about it. Scroll down to just below the pic of the LT1 to the heading, "Thumbs Up For The Gen III".

I've read this same story before. I can't for the life of me, remember where. I looked in "Corvette from the Inside", and "The Heart of the Beast"...couldn't find it in either. I wonder where in the hell I read this story before??....

Anyway. MY recollection of the story was the blind comparison was done w/a smaller displacement, DOHC engine of similar hp to a larger displacement OHV motor. GM brass like the feel of the larger motor. In this article, they're claiming the test was done w/an LT4/auto vs. an LT5/auto, and GM execs liked the feel of the LT4/auto.

NFW. The LT5 has way more low end tq than the LT4, more midrange tq...more tq everywhere. It also has fantastic throttle response -just as good as the LT4. Can anyone shed more light on this "story"...and perhaps where I had read it previously? I don't think the story is portrayed correctly in the article linked above.
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Old 04-22-2019, 02:01 AM
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I’ve always read the LT5 wouldn’t fit in the new C5.
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Old 04-22-2019, 09:22 AM
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Yep. It wouldn't....or they'd have had to make the C5 bigger and heavier.

But I'm really trying to find the source of that story about the blind demo. I know I've read it elsewhere, and I was SURE it was in "Corvette from the Inside"....but now I can't find it.
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Old 04-22-2019, 09:41 AM
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Tom,

The LT-5 program was cancelled in 1991. If u recall, the C5 Corvette was not a given, It was very much in doubt whether there would even be another generation Corvette after the C4. Also, the LT-5 engine management borrowed heavily from the L98. Basically, the ECM is an L98 ECM w a daughter board. The programming is very much L98 but for Speed Density and added code to handle some of the unique features, ie port throttles, of the LT-5. The new generation LT-5 was going to require its own engine management, and for the volume of the motor, which was not going to be used in other GM vehicles like ahem, trucks, the ROI wasn’t there. Finally, GM continued to suffer from NIH, and the Powertrain guys never forgave McLellan for “going off the reservation” in sourcing the LT-5. That’s why the myth of the LT-4 being practically as good as the LT-5 was put out. We know that’s total baloney. I think some of those people still suffer from that delusion, just look at the C8 discussion about whether to retain a pushrod motor in an ME platform.
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Old 04-22-2019, 12:23 PM
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Old 04-22-2019, 01:10 PM
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While we’re on the subject of discontinuation, Dave gave Roy Migley a big nod in Heart of The Beast, but I remember page 26 of the book they recall he was not having the bore spacing be different than a traditional SBC. Lotus tried to explain that would hold back the promised 400 hp, but Migley didn’t care and was happy with 385.

Even later in the book I believe he rags on the Lotus guys because the engine couldn’t go up a hill at 55 mph in top gear. They tried to explain with it being DOHC the torque band wouldn’t be as compatible with a low speed top gear hill climb like an L98 would. There were a few other parts in the book like this but he seemed more an antagonist to the project than a committed team player.

I kind of got got the impression he wanted the project to flop.
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Old 04-22-2019, 02:03 PM
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Thanks for that Dom....I've read all that before. That's not really what I was looking for though. I'm looking for the story about the blind test. I have a hard time believing that it was done w/an LT5 and didn't produce the same "feel" as an LT4. That doesn't make sense.


Originally Posted by 1985 Corvette View Post
Dave gave Roy Migley a big nod in Heart of The Beast,

I kind of got got the impression he wanted the project to flop.
I agree. From all my readings about Roy Migley, my take away was basically, "What a dick." There was a REALLY good discussion about the 4.4" bore center decision several years ago....read it HERE if interested. It's a lot of speculation about why Roy made that call...but good points made on both sides of the conversation. Roy commenting that the LT5 wouldn't climb a hill in high gear or whatever is dumb; the LT5 makes more tq at every/all RPM than the L98...so assuming they're geared the same, the LT5 should be able to climb any hill the L98 can, in the same gear.
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Old 04-22-2019, 05:07 PM
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Originally Posted by Tom400CFI View Post
Thanks for that Dom....I've read all that before. That's not really what I was looking for though. I'm looking for the story about the blind test. I have a hard time believing that it was done w/an LT5 and didn't produce the same "feel" as an LT4. That doesn't make sense.

I agree. From all my readings about Roy Migley, my take away was basically, "What a dick." There was a REALLY good discussion about the 4.4" bore center decision several years ago....read it HERE if interested. It's a lot of speculation about why Roy made that call...but good points made on both sides of the conversation. Roy commenting that the LT5 wouldn't climb a hill in high gear or whatever is dumb; the LT5 makes more tq at every/all RPM than the L98...so assuming they're geared the same, the LT5 should be able to climb any hill the L98 can, in the same gear.
Tom,

I do not have what you are looking for, but some comments as I have seen (and sometimes coordinated) these types of drives myself when I was with Ford's powertrain group:

1. It is unlikely that GM would have developed a new calibration for the LT5 given the use of an automatic transmission. The calibration for an automatic transmission can be distinctly different than with a manual. If an LT1 calibration was used off the shelf, it would likely not have been reoriented to the torque curve of the LT5 given the time to develop an updated calibration.
2. The cam timing itself was developed for a particular application and while the LT4 was also developed for manuals, it is very likely that the rpm range of operation was not equivalent in the two applications.
3. Some of our studies showed that the biggest indicators of comparative performance feel was the accelerator pedal angle traveled relative to the percentage of throttle opening. If there was anything that could have been easily manipulated (given the NIH syndrome of the LT5) it is this.
4. Which LT5 application was selected for the study? 375HP or 405HP? And given that the engine tested was a 1996 pre-production LT4 engine, why didn't GM consider the upgraded 450HP LT5 that Lotus and Mercury Marine had been developing that also would have been available? Did GM bother to check to see what would be possible with the LT5 by 1997?
5. While all executives like to have ride and drive tests (we often had Jackie Stewart at our testing in the late 80s early 90s), there are dangers in comparing "feel" between engines. It was common knowledge that big blocks "felt" slower than small blocks because of how the power kicked in with small blocks and how smooth the torque curves were with big block. Drivers simply didn't know how fast they were traveling. The same was true comparing different types of sports cars like Corvettes versus Porsche 911s. The 911s always felt slower, even though they were not slower.

The point I am making is that GM powertrain could have made anything happen with these ride and drives - especially if they had reason to want to make the LT5 look bad. I saw much of the same NIH at Ford when there were investigations of vehicle applications comparing the Ford Modular engine, the Jaguar AJ architecture, and the Yamaha narrow angle V8s that we studied.

Last edited by bb62; 04-22-2019 at 05:15 PM.
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Old 04-22-2019, 07:02 PM
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Tom,

One reason I didn’t discuss the “blind test” is that I never heard that story. I’ve gone to The Gathering for 10 years, and listened to any number of members of the C4 LT-5 team including visiting w Dave McLellan several times. That never came up.
Purportedly, Midgeley’s insistence on the SBC bore spacing was based on the eventuality that the LT-5 cylinder heads and block would be processed by existing GM tooling. If the LT-5 was going to ultimately find a home in other GM vehicles beyond the Corvette, GM would need a way to produce many more units than what Stillwater could produce.
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Old 04-23-2019, 10:06 AM
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Originally Posted by Dominic Sorresso View Post
Tom,

One reason I didn’t discuss the “blind test” is that I never heard that story.
I hear you. That's what I'm looking for though...where I read that originally. The test is actually referenced by Dave, in CFTI, in the pages where he's talking about the future of the SBC, "Making the SBC modern", I beleive the chapter is called. I SWORE the description of the blind test was in that book...in that chapter. But all that's in there is a single sentence where he references the blind test w/in a larger list of reasons why the LT5 didn't continue.

Originally Posted by Dominic Sorresso View Post
Purportedly, Midgeley’s insistence on the SBC bore spacing was based on the eventuality that the LT-5 cylinder heads and block would be processed by existing GM tooling. If the LT-5 was going to ultimately find a home in other GM vehicles beyond the Corvette, GM would need a way to produce many more units than what Stillwater could produce.
Yep. If you review the thread linked above, that aspect was covered. Counterpoints were also made -that had a lot of validity.
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Old 04-23-2019, 03:52 PM
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Bottom line is the LT-5 was too damn awesome and would have hurt the LS series engines feelings....
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Old 04-23-2019, 11:46 PM
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Originally Posted by Tom400CFI View Post
found THIS article the other day
Very interesting read.

I'd love to hear what the real story was also.
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Old 04-24-2019, 05:37 AM
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Originally Posted by 81c3 View Post
Bottom line is the LT-5 was too damn awesome and would have hurt the LS series engines feelings....
prettiest girl at the dance to be sure. Dave M. explained it best, the engineers finally met Lt5 performance levels and were able to make decent alum engines in house

the lt5 raised the quality bar and the new ls6 finally met hp, emissions, and performance targets with much lighter and smaller engines for the low hood line of the c5

the lt5 weighs quite a bit more and the z06 would have to make 430+ hp if the weight was added. At the end of the day the cheaper combo was much easier to build in volume and service which helps the GM bottom line

as far as "star power" just look at the new SB4 and I rest my case A nice fat NA 750 hp that can retrofit on a standard ls block

that is what GM had in mind for the LT5 program (bolt on 4 valve heads to freshen up the old SB chevy) and Lotus convinced them that an integrated approach and new block would be needed to meet the goals for durability and refinement in addition to the HP

I have both "platforms" and can tell you the Lsx motors are no slouch, but don't have anywhere near the panache of the LT5

at over 600 hp on the street, I'll take the overall driving characteristics and especially the upper rpm charge of the LT5 over the LSX

However, the LSX does open up some doors for forced induction that have seduced me on that front to scratch my turbo itch without costing quite as much.
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Old 04-24-2019, 08:47 AM
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When I bought my ZR-1, was looking at C5 Z06 as well. The ZR-1 felt more substantial and the Z06 a bit more “go-karty”.
What really persuaded me was seeing the ZRs that Pete and Al had here in Chicagoland doing 11.0s and mid 10’s respectively while retaining the ability to idle smoothly at 875-950rpm. And be quite streetable. The motor doesn’t give any sign of its horsepower away. Whether 375 or 700hp, it looks exactly the same. I like sleepers like that.
My current ZR is in the 460rwhp range from a 5.7L stock block. Just love it when it climbs the rpms.
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Old 04-24-2019, 09:57 AM
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Originally Posted by bb62 View Post
Tom,

I do not have what you are looking for, but some comments as I have seen (and sometimes coordinated) these types of drives myself when I was with Ford's powertrain group:

1. It is unlikely that GM would have developed a new calibration for the LT5 given the use of an automatic transmission. The calibration for an automatic transmission can be distinctly different than with a manual. If an LT1 calibration was used off the shelf, it would likely not have been reoriented to the torque curve of the LT5 given the time to develop an updated calibration.
2. The cam timing itself was developed for a particular application and while the LT4 was also developed for manuals, it is very likely that the rpm range of operation was not equivalent in the two applications.
3. Some of our studies showed that the biggest indicators of comparative performance feel was the accelerator pedal angle traveled relative to the percentage of throttle opening. If there was anything that could have been easily manipulated (given the NIH syndrome of the LT5) it is this.
4. Which LT5 application was selected for the study? 375HP or 405HP? And given that the engine tested was a 1996 pre-production LT4 engine, why didn't GM consider the upgraded 450HP LT5 that Lotus and Mercury Marine had been developing that also would have been available? Did GM bother to check to see what would be possible with the LT5 by 1997?
5. While all executives like to have ride and drive tests (we often had Jackie Stewart at our testing in the late 80s early 90s), there are dangers in comparing "feel" between engines. It was common knowledge that big blocks "felt" slower than small blocks because of how the power kicked in with small blocks and how smooth the torque curves were with big block. Drivers simply didn't know how fast they were traveling. The same was true comparing different types of sports cars like Corvettes versus Porsche 911s. The 911s always felt slower, even though they were not slower.

The point I am making is that GM powertrain could have made anything happen with these ride and drives - especially if they had reason to want to make the LT5 look bad. I saw much of the same NIH at Ford when there were investigations of vehicle applications comparing the Ford Modular engine, the Jaguar AJ architecture, and the Yamaha narrow angle V8s that we studied.
This test was over before it began. The methodology used assured the LT-4 car would outshine the LT-5. The actual drives simply confirmed what the test developer knew form the outset.
Hooking up a stock LT-5 to an automatic prevents the motor from performing at it's best.
BB62 is spot on.
That test was about as rigged as the Car and Driver "GTO vs Ferrari GTO" test of 1964.
The winner of the LT/4/5 test was the gent who defined how it was to be conducted.

That said, and also acknowledging my love of the ZR-1, I have always said a C-4 LT-4 car is simply one of the finest "around - town " drivers of it's day. That engine / trans combo, just always seems to be in the sweet spot and is fun to drive.
That is until max POWER is summoned. At that point, your longing for the LT-5 will become clear.

I once beat a 426 hemi with a worked 389 Pontiac...………….. after I made him spend 45 minutes driving to 5 places to race.
By the time we ran, his car was so loaded up it was over before it began.

If you cheat well, you will likely win.
The designer of the test knew that very well.
Marty
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Old 04-24-2019, 10:08 AM
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Originally Posted by DRM500RUBYZR-1 View Post
This test was over before it began. The methodology used assured the LT-4 car would outshine the LT-5.
Where did you glean that from? That is the relevant question of this thread. Where did you read that? I'm trying to find out where I originally read that story.....

I can't see how an auto would hurt a 375 lb ft engine more than it would hurt a 340 lb ft engine. The only "unfair" comparison would be if the put a 3.73 gear in the "LT4 car (or was it an LS1?), and then a 3.07 gear in the LT5 car....or mis-matched ratios like that.
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Old 04-24-2019, 10:23 AM
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Marty,

Very interesting. If true, it clearly demonstrated the NIH mentality pervasive at Powertrain.
Think about this. There were some at GM willing to tell the nearly 7000 owners of the C4 ZR-1 that GM had just shafted them for an additional $30k on a motor that was not any better than a warmed over SBC.
Great customer loyalty.
I think who ever set this “test” up certainly didn’t want to try it up against the 3rd Gen LT-5 Lotus was proposing given that the cam phasing for that motor would have eliminated any “low end torque” advantage an LT4 would have.
I say all this and still must recall that at the time, the Vette was on the corporate ropes. So did some people do what they thought they needed to do to save the car from the green eye shade people? No doubt, as documented by McLellan and others that their love for the Vette is unquestionable. Maybe Barra is one if thise people along w Reuss.
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Old 04-24-2019, 10:28 AM
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Originally Posted by Tom400CFI View Post
Where did you glean that from? That is the relevant question of this thread. Where did you read that? I'm trying to find out where I originally read that story.....

I can't see how an auto would hurt a 375 lb ft engine more than it would hurt a 340 lb ft engine. The only "unfair" comparison would be if the put a 3.73 gear in the "LT4 car (or was it an LS1?), and then a 3.07 gear in the LT5 car....or mis-matched ratios like that.
I "gleaned" it from 23 year of owning and driving a ZR-1.
That beautiful LT-5 motor would overmatch an 80's automatic in every situation other than foot to the floor.
That trans simply was not designed to work with an engine that enjoys high revs.
It was also not like the C-7 computer controlled trans that would have handled the situation far more skillfully.
Part of the ZR-1 driving fun is knowing where to be when you want a particular outcome.

I am sure the designer of that test would not have wanted his or her name in bright lights.
He knew the jig would be up at some point.
"Rigged"
Marty
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Old 04-24-2019, 10:31 AM
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Originally Posted by Dominic Sorresso View Post
I think who ever set this “test” up certainly didn’t want to try it up against the 3rd Gen LT-5 Lotus was proposing given that the cam phasing for that motor would have eliminated any “low end torque” advantage an LT4 would have.
Dom....what are you talking about here? The LT4 doesn't have a "low end tq advantage", that I am aware of.
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Old 04-24-2019, 10:34 AM
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Originally Posted by DRM500RUBYZR-1 View Post
I "gleaned" it from 23 year of owning and driving a ZR-1.
That beautiful LT-5 motor would overmatch an 80's automatic in every situation other than foot to the floor.
That trans simply was not designed to work with an engine that enjoys high revs.
OK, got it. So that was all "made up". Thanks for the honest clarification.

FYI, The 700R4 has worked just fine, behind more than a few engines that "enjoy high revs". Not that that matters when we're talking about low end tq and throttle response in this "blind test".
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