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Why the LT5 was discontinued...

 
Old 05-21-2019, 01:39 PM
  #61  
Dominic Sorresso
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Originally Posted by Tom400CFI View Post
Dom, is your tuning stock?



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.


.
Tom,

If the Valet Key is set to Full Power and I tromp the accelerator from a standing start, the secondaries come on after the .3sec delay I referred to.
I get your point and we both agree that the LT5 makes more torque. I have been trying to support ur contention that perhaps the test was rigged and suggested a few ways it could have been.

Last edited by Dominic Sorresso; 05-21-2019 at 01:42 PM.
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Old 05-26-2019, 10:58 AM
  #62  
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Originally Posted by Dominic Sorresso View Post
Tom,

If the Valet Key is set to Full Power and I tromp the accelerator from a standing start, the secondaries come on after the .3sec delay I referred to.
I get your point and we both agree that the LT5 makes more torque. I have been trying to support ur contention that perhaps the test was rigged and suggested a few ways it could have been.
the LT4 is a strong engine and under rated. Lt4 cars typically turn very competative times until you get pretty high up top

dyno both and the torq curves are right on top of each other, and the LT5 only runs away above 5500 or so with a much broader power band and pulls hard up top.

the LT4 is not far off there either. The LT5 is NOT cheap or ez to mod, but oh so worth it in terms of feel, durability and yes torq

secondaries operate off an algorithm based on load and do not just snap open at 3k. Secondaries do add a small smidge of low end torq but only below 2k

the LT5 gets to 2k quick enough (like when I let out the clutch) and removing the secondaries doesn't "kill" low end torq like most people think

to the contrary, I picked up about 10 hp and 10 ft lbs of torq in the midrange.

All that being said, the "opening rate" of .3 seconds seems about right looking at the relatively slow operation of the vacuum canisters.

Lots of manufacturers (like GM Ford Honda, ect...) used "mult tract" intakes to create a broader flatter torq curve.

with the relatively small port size of the LT5 heads, I don't feel they are necessary and are largely an "emissions" mod to keep port velocity and swirl high a low rpms.

for performance, they crutch a problem the LT5 DOES NOT have (responsiveness, and low end torq)

the small port size and high velocity tuned port intake with the long runners is the biggest factor in helping build low rpm torq

the 350 engines (including the old 85 tuned port) all make pretty similar low end torq. if you dyno the rear wheel torq on stock cars, the dyno torq curves lay on top of each other below around 3500 rpms

torq is more a function of displacment and especially stroke. Compared to the "pre LS" engines, the lt5 has a slighly smaller bore and slightly longer stroke so low end torq production is not an issue.

take a look as the LS1 and later LS motors and you see those similar bore stroke combos show up as the approx 3.66 stroke and 3.9 bore seems to be a very good combo

Lt5 ponies will ALWAYS be more pricey than HP from similar pushrod engines. More parts ain't cheaper.

Last edited by Rkreigh; 05-26-2019 at 10:58 AM.
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Old 05-26-2019, 12:27 PM
  #63  
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Ron,

Just a clarification. Secondary injector turn on is 3 TENTHS of a second, not 3 seconds in the stock cal.
Also, secondary activation IS based on RPM v TPS% not MAP. In the lower rpms it takes something like 88%
TPS until 2000rpm where it drops to 50% and so on.
Finally, torque and hp numbers can be “somewhat similar” BUT they occur is VERY different. No LT anything has a tirque peaking at ~5300rpm kr a hp peak in the 6k+ range. Not only that, but watch what happens to those curves after peaking. On pushrods, the curve sinks like a stone. Not so w DOHC where drop off is much more gradual.
Those of us w LT-5s have a certain love for DIY. But of course that also means we don’t have the luxury if the aftermarket supporting us w less expensive mods. Having said that there’s a satisfaction of how well ur car performance based on ur own handiwork or that of the ZR community.

Last edited by Dominic Sorresso; 05-26-2019 at 12:37 PM.
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Old 05-26-2019, 02:47 PM
  #64  
Tom400CFI
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Since this thread is sufficiently pooched, I'll just throw this in,

There are plenty of LTAnythings that make horsepower Peak over 6,000 RPM. None are stock, however. But then, neither does an LT5. I don't even own a ZR-1 and I know that the horsepower Peak is at 5800 RPM.
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Old 05-26-2019, 03:59 PM
  #65  
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Yeah this thread has dragged on...All good insight I must say...Then again there's my motto, mod whatever corvette motor ya got, who cares about stock....
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Old 05-27-2019, 02:29 PM
  #66  
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Which engine is this:


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Old 05-27-2019, 05:20 PM
  #67  
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Originally Posted by RUBYREDSLIPPERZR1 View Post
Which engine is this:

That's an LT-5
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Old 05-27-2019, 05:33 PM
  #68  
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Thanks! I was informed that it is "discolored" but know very little about them. Is there a physical # or identifier on the engine (& where) that will tell me if it is the original one that belongs with the car itself? Appreciate any help.
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Old 05-27-2019, 05:40 PM
  #69  
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Originally Posted by RUBYREDSLIPPERZR1 View Post
Thanks! I was informed that it is "discolored" but know very little about them. Is there a physical # or identifier on the engine (& where) that will tell me if it is the original one that belongs with the car itself? Appreciate any help.
Over time a lot of them get discolored...Don't know for sure where the identifier # on the engine is....All though I really have not seen one where it wasn't the original engine...

The engine option back in the day was almost as much as the car ( which to me was crazy ) ....Never the less these motors are pretty rare to come by....Never really seen a C4 ZR-1 with a different engine in it.....

You do though in fact come across standard C-4's with motor swaps but never a ZR-1
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Old 05-28-2019, 06:30 AM
  #70  
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Originally Posted by RUBYREDSLIPPERZR1 View Post
Thanks! I was informed that it is "discolored" but know very little about them. Is there a physical # or identifier on the engine (& where) that will tell me if it is the original one that belongs with the car itself? Appreciate any help.
the paint on the LT5 can easily discolor when not cleaned properly. This example looks like the paint on the cam cover is scratched up for some reason.
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Old 05-28-2019, 11:48 AM
  #71  
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