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Thread: LT4 vs LT5

  1. #1
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    Default LT4 vs LT5

    True confessions...

    Had a Red, austere, 96 with 40K miles, the LT4 and not many options. A great ride... I had it for 4 years and along came a pretty face, a 94 ZR1 with all options and 21K miles. I went for it, sold the LT4 and I must say, I've been disapointed. The ZR1/LT5 is truly an awesome machine, once it gets to 4000 RPM it will say HELLO. But gentlemen we don't dive at 4000 RPM and above most of the time, that is, we drive low end torque. And IMHO the LT4 has more drivable low end torque. After studying the LT4 I'm convinced it is one of the best bangs for the buck. Yes, I've been through the opti-spark issues and it is all fixable. The General gave us a gift in 1996.

    I have come to terms on a 96 CE with 21K on the clock, LT4, most options inc. the Z51 supension. I'm psyched. It is a new day. I'll keep the ZR1 untill I get tired of it or until someone has to have, but I believe the LT4 will be here for a long time to come. I'm back.

    Al
    1966 C180
    1994 ZR1
    1996 CE LT4

  2. #2
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    Not to start a war ... But Both are about the same up to 100 mph, it is up to the driver.. My LT5 will roast the tires at low RPMs and low speeds just by pushing the gas down. may you have some issues that need looked into.

    They should come alive at around 3K RPMs, but the secondary system will open below this based on throttle % and RPMs.

    Good luck with finding a new LT4..They are both great Vettes

    Steve

    1991 ZR-1 # 118 Quasar/Black SW Headers/Corsa-3:73 gears-Haibeck-500HP/350

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    I own a ZR1 but I've driven and tested both.
    The LT4 was the absolute high-point in the "traditional" (Gen 1/Gen 2) Small-Block V8 design and at 330 SAE net or about 380-390 at the flywheel was the most powerful production SBV8 ever.

    That said, my experience has been that in the low-end and mid-range the two engines are comparable--provided, of course, they're both running right. Another issue to consider is the ZR-1 is about 200 lbs heavier than a 96, so the weight might have some impact on this discussion, too.

    However, if the difference below 4000 rpm is that noticeable, I'd tend to think that maybe that particular LT5 might have "some issues". Perhaps cam timing is off? Or maybe you're getting some false knock retard?

    Also, Marc Haibeck in Chicago has done a lot of continuing development with LT5 calibration. One of Mark's "chips" might make a difference, too.
    Hib Halverson

  4. #4
    Member B17Crew's Avatar
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    Congrats on having fine stable of Corvettes!

    Got a call about a mint condition red ’91 Z that was coming in at a local dealer. Salesman that I had been talking to tried steering me away from the Z saying that they weren’t as lively as a LT4 down low. He suggested that I think about the kind of driving I do and consider if getting a high end screamer is really what I wanted. I haven’t put much stock in his opinion.

    In the next two to three years, I intend to purchase a ’95-’96 six-speed vert or a ’92-’94 ZR-1. Started looking at Zs this past spring and was going to unload my LT4 with the intent of using the proceeds for a pristine Z. At this point, I am keeping my LT4 and will be adding a C4 vert or a Z to keep the ’96 company.

    I worship the ZR-1, it’s my dream Corvette. Its proportions are beautiful, the aesthetic appeal of the LT5 motor is unrivaled... the finest looking engine ever dropped into the Corvette IMHO.

    Haven't had an opportunity to drive a Z as of yet to compare how it feels compared to my LT4. I’m pretty sure that roar of the LT5 at high rpms would leave a pretty big smile one my face.

    B17Crew

  5. #5
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    I AGREE WITH HIB HALVERSON NEED TO HAVE THE Z CHECKED OUT.

    STEVE

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    My ZR1 has been the shop several times looking for any issues. The symptoms were a hesitation at low rpm's and rapid throttle movement. A fix was found by reprogramming the chip to increase the timing at low rpm's - 1000 to 2000 and opening the throttle quickly. A 4 to 6 degree advance in timing at these rpm's improved the hasitation problem. I get an occasional knock if I lug it down but for the most part it responds better. It is 'engine temperature dependent' and works best when it is up to normal temps. However it does not respond as well as my LT4 did. Maybe I'm expecting too much from it. With 4 cams and the associated mass it may be what it is. Performance is good, it pulls hard to 7000 and shifts usually break the tires loose. It will not smoke the tires simply by standing on the throttle at low speeds. I'm not sure that is any measurement of performance as tire traction and road conditions come into play... I have not dynoed it or run it through the 1/4. Maybe the thing to do is get it on a dyno and look at torque and HP vs rpm. Is there any published 'normal' read-out available for the LT-5 in terms of tprgue and HP for a given RPM? Or are the variable too many to have it mean anything?
    Thanks for the input.
    Al




    Quote Originally Posted by Hib Halverson View Post
    I own a ZR1 but I've driven and tested both.
    The LT4 was the absolute high-point in the "traditional" (Gen 1/Gen 2) Small-Block V8 design and at 330 SAE net or about 380-390 at the flywheel was the most powerful production SBV8 ever.

    That said, my experience has been that in the low-end and mid-range the two engines are comparable--provided, of course, they're both running right. Another issue to consider is the ZR-1 is about 200 lbs heavier than a 96, so the weight might have some impact on this discussion, too.

    However, if the difference below 4000 rpm is that noticeable, I'd tend to think that maybe that particular LT5 might have "some issues". Perhaps cam timing is off? Or maybe you're getting some false knock retard?

    Also, Marc Haibeck in Chicago has done a lot of continuing development with LT5 calibration. One of Mark's "chips" might make a difference, too.

  7. #7
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    Check out this site..

    http://www.zr1netregistry.com/

    My 91 with a Marc Haibeck Chip & catback puts out 339.01 RWHP 346.05 Torque has about 44K miles on it..

  8. #8
    Member Aurora40's Avatar
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    Quote Originally Posted by AlHewitt View Post
    My ZR1 has been the shop several times looking for any issues. The symptoms were a hesitation at low rpm's and rapid throttle movement. A fix was found by reprogramming the chip to increase the timing at low rpm's - 1000 to 2000 and opening the throttle quickly. A 4 to 6 degree advance in timing at these rpm's improved the hasitation problem. I get an occasional knock if I lug it down but for the most part it responds better. It is 'engine temperature dependent' and works best when it is up to normal temps. However it does not respond as well as my LT4 did. Maybe I'm expecting too much from it. With 4 cams and the associated mass it may be what it is. Performance is good, it pulls hard to 7000 and shifts usually break the tires loose. It will not smoke the tires simply by standing on the throttle at low speeds. I'm not sure that is any measurement of performance as tire traction and road conditions come into play... I have not dynoed it or run it through the 1/4. Maybe the thing to do is get it on a dyno and look at torque and HP vs rpm. Is there any published 'normal' read-out available for the LT-5 in terms of tprgue and HP for a given RPM? Or are the variable too many to have it mean anything?
    Thanks for the input.
    Al
    The LT5 has a very healthy low end. 300+ lb-ft of torque from 1000 rpm to 6000 rpm. If you can't break the tires loose stomping on it in first, something is wrong with it, or maybe you drive around on DR's or slicks? Coupled with what you described as low-throttle hesitation, it really sounds like something is wrong.

    FWIW, I don't think a tune on a stock car is the appropriate way to address a drivability issue. Certainly a tune can be beneficial, but only to improve things on an already well-running car. If something is wrong, it needs to be fixed, not tuned around.


    I see you are in Seattle, WA, you may want to give Jeff a shout: http://www.pnwzr1.com/

  9. #9
    Member Aurora40's Avatar
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    Also, if you aren't hitting 4,000+ rpm very often, you aren't doing it right...

  10. #10
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    Jeff Flint has done the work on my car, Jeff has joined up with Tom in Vancouver, WA and together they have the LT5 place to go. Having said that Jeff has a highly modified 90 ZR1. I've driven it and the throttle response on it is much more crisp than mine. Jeff had a great road rally a couple of months ago and my ZR1 would run with the pack. My point is the HP is there it just seems to come at higher RPM's than does the LT4. I'm not going to shoot my ZR1 just pointing out to the LT4 folks that IMHO the LT4 is a better driver than MY ZR1. Like I said I'd like to run it on a dyno.
    BTW ha any one on this list ran their LT4 on a dyno and id so what HP and torque are you seeing?
    Thanks
    Al

    Quote Originally Posted by Aurora40 View Post
    The LT5 has a very healthy low end. 300+ lb-ft of torque from 1000 rpm to 6000 rpm. If you can't break the tires loose stomping on it in first, something is wrong with it, or maybe you drive around on DR's or slicks? Coupled with what you described as low-throttle hesitation, it really sounds like something is wrong.

    FWIW, I don't think a tune on a stock car is the appropriate way to address a drivability issue. Certainly a tune can be beneficial, but only to improve things on an already well-running car. If something is wrong, it needs to be fixed, not tuned around.


    I see you are in Seattle, WA, you may want to give Jeff a shout: http://www.pnwzr1.com/

  11. #11
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    Quote Originally Posted by Aurora40 View Post
    (snip)
    I see you are in Seattle, WA, you may want to give Jeff a shout: http://www.pnwzr1.com/

    If you're in the Pacific Northwest, I recommend Jeff Flint's shop. He's a very knowlegible LT5 technician.
    Hib Halverson

  12. #12
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    Default lt4 dyno results

    Quote Originally Posted by AlHewitt View Post
    Jeff Flint has done the work on my car, Jeff has joined up with Tom in Vancouver, WA and together they have the LT5 place to go. Having said that Jeff has a highly modified 90 ZR1. I've driven it and the throttle response on it is much more crisp than mine. Jeff had a great road rally a couple of months ago and my ZR1 would run with the pack. My point is the HP is there it just seems to come at higher RPM's than does the LT4. I'm not going to shoot my ZR1 just pointing out to the LT4 folks that IMHO the LT4 is a better driver than MY ZR1. Like I said I'd like to run it on a dyno.
    BTW ha any one on this list ran their LT4 on a dyno and id so what HP and torque are you seeing?
    Thanks
    Al

    My LT4 generated 307.4 rwhp and 311.5 lb-ft in the best of 2 dyno runs on a dynojet. The only modification at the time was a b&b tri flo catback 3" system.

  13. #13
    LT4 vs LT5 tobijohn's Avatar
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    Quote Originally Posted by LT4 DRIVER View Post
    My LT4 generated 307.4 rwhp and 311.5 lb-ft in the best of 2 dyno runs on a dynojet. The only modification at the time was a b&b tri flo catback 3" system.
    FWIW, mine stock did 291 rwhp and 310 lb-ft on a Mustang dyno with something breaking up the HP curve over 4800 rpm. Temps were in the low nineties, humidity in the low eighties...

  14. #14
    simbadb
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    Quote Originally Posted by AlHewitt View Post
    True confessions...

    Had a Red, austere, 96 with 40K miles, the LT4 and not many options. A great ride... I had it for 4 years and along came a pretty face, a 94 ZR1 with all options and 21K miles. I went for it, sold the LT4 and I must say, I've been disapointed. The ZR1/LT5 is truly an awesome machine, once it gets to 4000 RPM it will say HELLO. But gentlemen we don't dive at 4000 RPM and above most of the time, that is, we drive low end torque. And IMHO the LT4 has more drivable low end torque. After studying the LT4 I'm convinced it is one of the best bangs for the buck. Yes, I've been through the opti-spark issues and it is all fixable. The General gave us a gift in 1996.

    I have come to terms on a 96 CE with 21K on the clock, LT4, most options inc. the Z51 supension. I'm psyched. It is a new day. I'll keep the ZR1 untill I get tired of it or until someone has to have, but I believe the LT4 will be here for a long time to come. I'm back.

    Al
    1966 C180
    1994 ZR1
    1996 CE LT4
    ________________________________________________________________

    The performance figures and specifications listed below were compiled by Forum Member, Stan A (Stan Adelman) of Auto Performance Test Lab located in Atlanta, Georgia. The Corvette Action Center would like to thank Stan for allowing us to post his Performance Review Data here.
    Regarding the stock LT4 horsepower numbers, Stan explains:
    The LT4 really can vary in Horsepower and torque. Like I said, the average one on the street comes in between 350hp to 360hp. We have tested over 125 LT4 units since 1996 and found that less than 25% of the units come in under 345hp. About 15% come in between 360hp and 375hp. About 10% range between 375hp and 385hp. 2% have been found to hit the very low 390hp range. This is all stock from Bowling Green. Keep in mind that the torque also increases too. One unit came in on the dyno at 392hp/426lbs-ft torque @5850rpm. Very rare but still present out there. This is why there have been reports of LT4s running with or past ZR1-LT5 cars over the years. Basically, the LT4 will out run the LS1 in 75% of all cases.
    http://corvetteactioncenter.com/spec...96/96perf.html

  15. #15
    Member LT4man's Avatar
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    The LT5 engine is a multi-valve overhead cam design.

    The LT4 engine is a two valve cam in block design.

    In my over 35 years of experience in the automotive mechanical repair industry, I have yet to see a normally aspirated overhead cam engine put out tons of torque at low RPMs.

    I am impressed with the LT5. I will have one in the future. But, someone would have to throw a whole bunch of cash at me to let go of my LT4! My LT4 SCREAMS and the throttle is instantaneous.

    JMHO!

    SAVE THE
    An attendee at all the CruiseFests including the one which never happened.


    Autosig (Shadow) A

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