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Why the LT5 was discontinued...

 
Old 04-25-2019, 02:47 PM
  #41  
Tom400CFI
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I got you now. Yep, that makes sense.
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Old 05-04-2019, 08:33 AM
  #42  
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Originally Posted by Dominic Sorresso View Post
Tom,
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.
Pure speculation that has been refuted with facts. I'll ask the same question I've never gotten an answer to...name one single machining operation the LT5 has in common with existing GM tooling of the time?

The answer is none and it was obvious from the time pencil was put to paper on the first drawing. Midgley's decision was arbitrary and capricious, even Lotus told him this engine would never go down the same line as the small block and could have any bore center they wanted.
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Old 05-04-2019, 09:38 AM
  #43  
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Originally Posted by Tom400CFI View Post
Dom....what are you talking about here? The LT4 doesn't have a "low end tq advantage", that I am aware of.
Apologies there Tom. I did mean the torque thing somewhat tongue in cheek, but I should have used the quotes to make that clear. Ur correct. The LT4 does not have a torque advantage. Go over to the C8 forum and read about how those people think that a DOHC motor has to be wound as tight as a clock spring just to start off from a red light.
Maybe the test was using the LT5 in Valet mode. 😆😆

glassslipper,

Sorry, but are u saying that Midgeley never insisted on the bore spacing or that he was just being an NIH *****?
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Old 05-04-2019, 11:27 PM
  #44  
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Originally Posted by Dominic Sorresso View Post
Go over to the C8 forum and read about how those people think that a DOHC motor has to be wound as tight as a clock spring just to start off from a red light.
I'll pass on that horse manure. The crap you read on these forums...I tell ya.

You should check out the stupid "flat plane crank" thread in C4 general or Tech.
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Old 05-05-2019, 10:05 AM
  #45  
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I still can't get over how much these things were when new.....My 91 stickered, as well as others for $ 65,600..

Heck, just a few weeks ago I saw a leftover 1LZ 2017 Z06 M7 go for $59,900 brand new....
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Old 05-06-2019, 10:33 PM
  #46  
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Originally Posted by Dominic Sorresso View Post
Tom,

I used “ “ as a way of expressing tongue in cheek.

As for trap speeds, my stock 92 ZR did 112s in the 1/4 on street tires. I don’t recall any LT anything being close to that stock.
Maybe ETs could be close, but not trap speeds. Any longer race, ie 1/2mile and adios.
Exactly. I had a 91c4zr-1 and drove a couple of lt4’s. The lt4 felt good or as good as the lt5 down low but ran out of juice up high.

Since the c4zr-1 I have had a c6z06 and now a c7z06. I miss the feel of the c4 transmission and shifter. It felt substantial compared to the c6 and c7. My favorite motor is the NA LS7. That motor felt amazing up high in the rpms—except for the dropping valves issue. The mercury marine built lt5 is and will be the most durable long lasting and unique motor of whatever has been put in a corvette.
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Old 05-06-2019, 11:16 PM
  #47  
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Originally Posted by Mr. Gizmo View Post
Exactly. I had a 91c4zr-1 and drove a couple of lt4’s. The lt4 felt good or as good as the lt5 down low but ran out of juice up high.

Since the c4zr-1 I have had a c6z06 and now a c7z06. I miss the feel of the c4 transmission and shifter. It felt substantial compared to the c6 and c7. My favorite motor is the NA LS7. That motor felt amazing up high in the rpms—except for the dropping valves issue. The mercury marine built lt5 is and will be the most durable long lasting and unique motor of whatever has been put in a corvette.
How do you like the C7Z06? I'm always pondering selling my 91Z and my 73 vert and ponying up some cash for a C7Z...

My 91 is modded with 445 to the wheels....I'm thinking if I'm lucky to get low 20's if that for the Z.......Is the C7 worth close to another 35 grand or so if I just sell the Z ?

Maybe I will go to a dealer for a test drive ..
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Old 05-06-2019, 11:40 PM
  #48  
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Originally Posted by zrc3john View Post
How do you like the C7Z06? I'm always pondering selling my 91Z and my 73 vert and ponying up some cash for a C7Z...

My 91 is modded with 445 to the wheels....I'm thinking if I'm lucky to get low 20's if that for the Z.......Is the C7 worth close to another 35 grand or so if I just sell the Z ?

Maybe I will go to a dealer for a test drive ..
The c7z is ok. Not my favorite. I liked the c6z06 the best of the bunch I have had. If I had to do it all over again I would have kept it.
I like a normally aspirated high revving motor better then the supercharged lunk of a motor in the c7z06.

The c6z is very light and nimble and puts out stock 440 to 460 hp to the rear wheels. They are also easy to work on — water pump , starters , alternators all are easy access compared to the c4lt5 and supercharged c7z.

The c6z is the perfect amount of new tech and old school. The only issue is the potential problem with the heads. Getting an ls7 it’s mandatory to address the heads and swap the hollow titanium exhaust valves with 1 piece steel.
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Old 05-08-2019, 07:34 PM
  #49  
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Originally Posted by Dominic Sorresso View Post
glassslipper,

Sorry, but are u saying that Midgeley never insisted on the bore spacing or that he was just being an NIH *****?
I'm saying he did indeed insist on the 4.4" bore spacing and he was just being an "NIH *****". Lotus was correct, the LT5 would never go down the same line as the small block so bore spacing could be whatever the designer wanted as long as the exterior dimensions met the requirements. Imagine how many more cubic inches could be had with the bore centers 0.150" larger...
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Old 05-19-2019, 06:39 PM
  #50  
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The results surprised even the most ardent supporters of the pushrod architecture. The executives couldn’t get over how one of the Corvettes pulled from the moment they pressed on the throttle — the surge, the thrust, the torque.

In contrast, they commented on how the engine in the other ’Vette seemed to take a moment to “wind up” before pushing them back in the seat. This vehicle required more precision and planning when driving fast to keep the engine up in the RPM band where the power was.

As the day went on, executive after executive came to the same conclusion. After all had tested the vehicles, the hoods were raised. To anyone who has driven or ridden in a vehicle powered by a 300+ hp small-block Chevy V-8, it comes as no surprise that the Corvette the executives liked was powered by the Gen II pushrod V-8.

From then on, the course for GM’s V-8 powertrain was set. The world’s finest pushrod V-8 would be created to power the most profitable vehicle’s in the General Motors fleet. This was the birth of the Gen III small-block V-8.


There`s one hell of a lot of things that could have accounted for the `lag`in performance.

1. Ignorance/bias. GM execs are so used to this pushrod horseshit that they simply could be biased. I love this stupid assed attitude that DOHC is somehow `new`because these morons have taken a century to embrace it. LOTS of cars in the 20s used DOHC and 4 valves per cylinder. Not exactly new.

2. Calibration. If they didn`t calibrate the trans to work properly with the LT5, it could seem soft. This could be the case here, since the LT5 was never produced with an auto trans.

3. Combination of the first two.
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Old 05-20-2019, 03:50 PM
  #51  
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There is so much to “F**k” with in the LT5 calibration that can either make it run sharp as a tack, or lag like taffy. If you look at the stock cal for the LT5, it is sooo throttled. So the LT4 has its 330hp on tap from the start. I could keep the secondaries on an LT5 from opening until TPS% is over 50%, and so now I have a 275hp motor for practically all of my driving.
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Old 05-20-2019, 05:34 PM
  #52  
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No, the LT4 most definitely does not have 330 hp from the start. It's got ~300 lbs of tq though, and that is what you'd "feel" in this supposed test.

But, the LT5 has more tq "from the start". Even if the secondaries are closed (which they'd be anyways, "from the start"). The LT5 make more low RPM tq and therefor, this test result makes little sense to me.


....Which is why I started this thread. I RECALLED reading about this test some time ago. My recollection was that they tested two same hp engines; one a smaller DOHC the other a larger OHV engine. The Execs liked the OHV driveability/response better. -That's what I remember. Reading this account of the test, I was thinking, "That doesn't seem right at all. The LT5 make more low RPM tq...it should feel better. IDK. I guess my recollection of the test that I'd read before is off.
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Old 05-20-2019, 11:10 PM
  #53  
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Tom,

What I meant is that u can keep the LT-5 in its 275hp configuration whereas the LT4 does not have the dual personality that the C4 ZR-1 has. So by some simple manipulation of the calibration, it would be quite easy to have the LT-5 appear lethargic in any comparison “testing”.
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Old 05-20-2019, 11:56 PM
  #54  
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Ayuh. Sure. Does the LT5 make less low end tq if you change the calibration of the secondary throttle opening? That's a rhetorical question, but think about it, Dom.

The article said that... "Both were fully integrated for their specific powerplants to give a real-world experience to the executives."
As for being biased toward Pushrod engines, I don't recall that being the case back then. The article agrees, saying: "At the time, the automotive business was ferociously arguing the merits of building complex, seemingly high-tech dual overhead cam (DOHC) engines, as opposed to simple, seemingly low-tech pushrod engines. "
^THAT^, I recall.
So, there is that.
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Old 05-21-2019, 10:23 AM
  #55  
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Originally Posted by DRM500RUBYZR-1 View Post
Dom,
Well said!
Imagine that.
You mean General Motors had their own "deep state" or swamp.
I am so shocked!
First thing you learn in business, is don't mess with another's rice bowl.
Perhaps that "Lotus Business" peed a few folks off?
Revenge was sweet.
Marty
Marty,

Its my understanding that if u visit GM Powertrain you won’t find an LT-5 displayed along w other GM powerplants.
They never took ownership of it. Never acknowledged it.
What I don’t understand is now that Cadillac is positioned to be the leader for GM into “electrification”, what are they doing developing the Blackwing series of DOHC motors?
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Old 05-21-2019, 11:12 AM
  #56  
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Tom,

If u re-read my comment, I never said anything about torque. I said I can manipulate the calibration to make the motor feel lethargic. I can affect tip-in response. Even w the valet key on FULL POWER, u can manipulate how much throttle would be needed for that to engage.

“The results surprised even the most ardent supporters of the pushrod architecture. The executives couldn’t get over how one of the Corvettes pulled from the moment they pressed on the throttle — the surge, the thrust, the torque.

In contrast, they commented on how the engine in the other ’Vette seemed to take a moment to “wind up” before pushing them back in the seat. This vehicle required more precision and planning when driving fast to keep the engine up in the RPM band where the power was.”


That “takes a moment to ‘wind up’ “ is due to the delay of .3sec. for the secondaries to kick in. That’s what’s in the cal. Feels like “turbo lag”. Anybody that drives a stock LT-5 will experience this. There’s no indication in the accounting of this test as to how much throttle was used for comparison purposes. Was it uniform among all the drivers? Did some jump on it while others accelerated slowly? However, w a stock LT-5 they would have all hit the point, w Valet in Full Power, where they would feel a delay once the secondaries were triggered, whereas the LT4 would not have exhibited that same delay.


I think we are actually in violent agreement here that the SOTP RESULTS are not indicative of what the numbers would suggest.
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Old 05-21-2019, 11:28 AM
  #57  
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Isn't it all academic now ? Motors that followed the LT-5 made more HP and torque with a vast majority having the aftermarket parts to make even more power....

Yes, you can build up an LT-5,but from what I have been seeing with 391ci 415 ci you need some pretty deep pockets...

ZR-1 gives a great bang for the buck today and are rare which does set it apart from other cars.....
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Old 05-21-2019, 11:33 AM
  #58  
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You're totally missing the point Dom. When you start out from a stop, the secondaries are out of the picture, no matter how you "tune it". They don't open unitl ~3k RPM, right? Takes WAY more than .3 to get to 3k.

You're right though, that we are totally in agreement that the SOTP results of the test don't make any sense. Not to me. If the test were a 4.0L DOHC 330hp vs. a 5.7L OHV 330hp...then yeah, the results would totally make (some) sense. I thought that is what the test actually was. But this article is saying it was a 375tq, 5.7L engine vs. a 340tq 5.7L engine...so the results don't make sense to this guy. Add to that my limited but actual driving experiences in ZR-1's and they seemed just as punchy and responsive (down low, in the middle and up high) as any LTx engine.

Weird results....or story. I'm guessing there are some missing pieces to the story.
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Old 05-21-2019, 11:57 AM
  #59  
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Tom,

Secondary activation is based on RPM v TPS%. Its a table not a single point. Mine come on right off idle for instance.

Last edited by Dominic Sorresso; 05-21-2019 at 12:03 PM.
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Old 05-21-2019, 12:56 PM
  #60  
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Dom, is your tuning stock?


Originally Posted by Dominic Sorresso View Post
Tom,

Secondary activation is based on RPM v TPS%. Its a table not a single point. Mine come on right off idle for instance.
Dom....NO stock LT5 opens the secondaries right off idle...do they? No, they don't. They TYPICALLY come on ABOUT 3000 RPM or so. I understand that it is a function of RPM and TPS...but I was trying to save typing above, and keep the post simple. I thought that you'd be able to comprehend that.

The point being, I think that we can assume that, if "Both were fully integrated for their specific powerplants to give a real-world experience to the executives." then in this test, the LT5 should be making ABOUT the same tq from idle to ABOUT 3k as any stock LT5...and that is more tq than the LT4 makes at the same RPM's. That was my point. Hopefully that was clear and detailed enough, this time.


.

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