Looking to purchase a 92, why HP Difference Between 90-92 and 93-95?

[KJL]

What changes were made to the 90-92 LT-5 to generate the additional HP?

I am looking to purchase a 92 but I love the "get up and go" of my 95. The 95 has had the smog stuff removed, headers, porting chip etc. Is it possible to perk up the 92? It is a low mile car and all original so I am hesitant to mess with it. I also have Collectors addition 1996 LT-4, my guess the cars are about equal in "feel" in their stock trim?

The 92 will also be exempt from emissions inspection in another 2 years, so I could do more with it without concerns.

Are there any problems specific to 92's I should look for before purchase?

Thanks!

[efnfast]

http://www.zr1specialist.com/HAT%20Web/products/major%20engine%20upgrades.htm

[Hog]

The higher hp cars are a tad heavier. Most of the extra 30hp comes from backpressure reduction in the exhaust.

From Graham Behan(current LPE Engineer-former Lotus of GM Engineer)
Cylinder Head Differences:
The production cylinder heads for the LT5 engine were originally produced by Birmal, all engines right up to the last few of the 1995 MY were fitted with Birmal heads. The machined port matched and hand blended heads were all Birmal parts.
Originally when I returned from being Resident Engineer at Stillwater the changes for increased output for the 93 MY were intended to be increased lift and duration on the secondary cam profile from what was known as the 'B' profile to the 'RB' profile which had a further 10 degrees duration. This resulted in engines which achieved the power target but paid the price in terms of reduced low end torque, something for which the LT5 had always been criticized. Since this was now my responsibility we made a change in the design direction ie. we would stick with the same cam profiles, optimize the cam timing and devise a simple machining and hand blending operation for increased port flow. So the 1993 MY engines started to have a revised throat cutter diameter an increase in the primary and secondary ports and a simple blend at the junction of the two machine cuts. I would not really call the operation CNC porting because to me that implies some change in the fundamental port design which this operation certainly did not. Now the time frame for all of this was early 1991, Birmal advised us that they did not want to produce heads for the future model years, infact they wanted to get out of the semi-permanent mould business. So we looked for alternative sources. A.L. Dunn were selected and the tooling was transferred from Birmal. At this time because of the original production schedule and the cut back in the volume of cars produced there were sufficient Birmal heads for a large portion of the remaining engine builds. We decided that since the port core box needed refurbishment, we would take this opportunity to re-design the port so as to eliminate the need for machining and hand blending at Mercruiser. The final cast port actually flows better and more consistently than the machined part. This change was incorporated with the production fix to the right hand side chain tensioner reservoir for engines late in the 95 MY build. All A.L Dunn heads had these features incorporated. There were about 200 head sets cats by Dunns and I believe about 130 engines were fitted with them.

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxx
By Greg Van Deventer
LT5 Polishing and Performance

The fact is, the cylinder heads were the only castings to receive any "fettling" as Lotus referred to the process of removing metal from the ports with a hand grinder. They only got a very small area of the intake ports blended just above the valve seat in the short side radius on the inside wall where the bowl transitions into the runner. Yes some could have received a little more attention than others, but believe me, there wasn't enough time to get carried away, and no way to do a "special set" to go on an engine as they were picked randomly to build the engine many steps further in the process. This "hand fettling" process wasn't a huge factor in the final engines performance.
A more likely culprit of poor airflow would be core shift especially in the injector housings. Core shift in other castings could have had a part in the losses also.
Another suspect cause of variability that has already been addressed is the cam timing. The production cam timing method did have more variability than "degreeing" them in using an indicator and degree wheel.
This leads me to respond to another statement regarding the Dynomometer testing on the LT5 engine. Every LT5 was dyno tested and met the tolerances before it was shipped. The dyno sheets and tons of other data were given to the museum, in hopes it would be shared with the car owners.

From Marc Haibeck
http://zr1specialist.com/HAT%20Web/presentations/LT5%20Power%20Upgrades.pdf (http://zr1specialist.com/HAT%20Web/presentations/LT5%20Power%20Upgrades.pdf)


The LT4 car may feel similar to the 90-92, but some 1/4 mile ET's and MPHJ comparisons will illustrate the additional output of the LT5.

There are many changes as the C4/ZR-1 went forward during its production run. I have seen a list of all the improvements per year, but couldnt locate tehm in a quick search I just did. There awere some 400 changes to improve the NVH (Noise Vibration Harshness) characteristics of the C4.

[We Gone]

I don't think you can compare a modded LT5 to a stock any years. My 91 with most the mods you have on you 95 (+heads and TB) will just walk away from my 93 with chip & exhaust. I'm sure if they both had the same mods it would be an even run. Guess it shows it does not take much for the 375hp cars to match or exceed the 405 cars. I would guess a 375 with ported top end and good flowing exhaust will match hp with a 405.

[Kevin]

don't forget the later cars are carrying more weight. The lt4 isn't going to run with a lt5

[Karl]

From my readings you never know what kind of power you are getting from these engines from the factory. My '92 put down 342whp on a mustang dyno. Thats ~402 flywheel HP, way more than the 375 its rated at.

[BigJohn]

From my readings you never know what kind of power you are getting from these engines from the factory. My '92 put down 342whp on a mustang dyno. Thats ~402 flywheel HP, way more than the 375 its rated at.


Shhh, you are not supposed to tell!!!!!!!!
:confused:

[KILLSHOTS]

From my readings you never know what kind of power you are getting from these engines from the factory. My '92 put down 342whp on a mustang dyno. Thats ~402 flywheel HP, way more than the 375 its rated at.
Marc does say that most 90-92 cars actually produce 400HP.

[KJL]

Thanks for the reply's! It would seem I could easily get some decent bang for the buck by just porting top end and adding headers/exhaust. In a year I could lose the cats.

What would a low mile 1992 in excellent condition sell for? I know color combinations play into all that but on average?

[Paul Workman]

Truly, you can very easily eclipse the 93 LT5 performance, including the few 95s w/ Dunn heads, by top end porting alone. Then adding long tube headers and a free flowing exhaust and adding a tune you will be close to the same HP at the WHEELS as the 93-95s made at the crank in stock form. By the time you get to the 430 range at the wheels, the 405 "majic" is totally absorbed in the process.

The LT5 is starving for air! Give it what it wants, and be amazed at the rewards!

[edram454]

I had the pleasure of running a 1996 lt4 6 speed car for about 3/4 of a mile. It was a ridiculous race. He was there for about 2 seconds then he was gone. Once my rpms spun up I ran away from him easily. I shifted at 6500 and the my zr1 was just grinding up that lt4 car. The guy wanted to see how fast my car was compared to his since he thought they were about equal. He had headers too. No contest. A lt4 car is maybe equal to a stock c5 automatic. Maybe a stock zr1 would have made it a closer race but once you have some good mods the difference is huge like Steve (we gone) said.

ed ramos #3028

[csavaglio]

I currently own a '96 LT4 as a daily driver and a '91 ZR-1. I traded a CE LT4 on the ZR-1 when I bought it. My two current cars are stock. Being able to drive them back to back, I do have some opinions....(what's that saying...opinions are like something something....).

First, my CE, which was stock, ran 12.7 in the quarter consistently. My current one, which I owned at the same time as my CE for about 6 months, feels every bit as quick. I haven't raced the ZR-1, but judging from numbers that go thrown about, they seem to run similar or slightly slower times.

That said, the ZR-1 revs much faster and feels racier. Driving on the street, the LT4 feels like it has more grunt and keeps up about the same until about 100mph, then it's the LT5's game.

Because of the low end torque the LT4, it actually feels stronger than the LT5 in the lower revs. For me, this means that, at 55mph in 6th gear, the LT4 accelerates much quicker while the LT5 needs to be downshifted. I typically keep the LT5 in a gear lower than I would in the LT4 and shift later into 6th.

I don't think you'll be disappointed, but, considering that most LT4's are stronger than their rated hp suggests, the gap between them at everyday speeds isn't as great as you'd think.

As far as the early/late LT5's, I think the desirability of the 405hp motor is simply the power rating and not real world. Because the later cars got a little heavier, it offsets it and, from everything I've seen, the real world performance difference between the early and late cars isn't much, if at all.

All just my humble opinions, of course and this is assuming stock, or relatively stock cars. Comparing a modded ZR-1 to a stock LT4 is apples to oranges. Years ago, I used to see an Astro van (complete with curtains in the windows) run 13's and a Chevette running 10s.....


Chris

[KJL]

Chris- Thank you very much for your thoughtful insite. I love my LT4, it too is my daily driver, the only thing that drives me crazy about it is the transmission whorling sound it makes when it is in neutral with my foot off the clutch. I can only guess it has a single mass fly wheel installed. I bet a set of headers would really wake her up.

Checking out the 92 has been put on hold, the owner was trying to do what I have been told is called a skip title, basically to avoid our ridiculous new tax law which requires the purchaser to pay the full property Tax on the car upfront instead of yearly installments. It is a way for the state to reclaim some of the lost sales tax revenue from private sales. The problem is the title is still in the previous owners name and my county requires a signed bill of sale from the current owner. That would have been a problem.

I wish there was a way to dial in on a true market value for these cars. The prices are all over the boards on these. There is a car locally for sale by a dealer, 1990 ZR1 with only 1100 miles on it for sale for 40,000. 1100 miles? really? Why would a car like that end up on a used car lot? Looks nice but not like a pristine 1K car should look. I have seen several cars over the years that looked more like 60K cars showing 12K on the odometer. Makes me wonder...

[csavaglio]

My CE made the same noise and it had the original clutch/dual mass flywheel in it. My current (dual mass when I got it and single mass now) doesn't make the noise. The single mass noise is more of a grumbling. Some describe it as rocks in a can, but I went with a heavy single mass to try to dampen it.

I think the noise you've got is the throw out bearing starting to go south. When you press the clutch pedal, you're putting pressure on the bear and the noise goes away. I used to only hear it in neutral with my foot off the clutch. That said, I drove it for a year and over 10k miles like that and it never got worse.

[KJL]

I have had it for 4 years and has not gotten any worse. The noise could also go away because once the transmission is decoupled from the engine when the clutch is engaged, everything stops turning if you are at a stand still. Could be some other component in the transmission that is making this sound when unloaded but coupled (in neutral), including the throwout bearing. My experience with throwout bearings is the opposite, they scream when that are depressed, quiet when disengaged. From what I have read about these ZF transmissions is they are very good but known to be harmlessly noisy.

[5ABI VT]

I have had it for 4 years and has not gotten any worse. The noise could also go away because once the transmission is decoupled from the engine when the clutch is engaged, everything stops turning if you are at a stand still. Could be some other component in the transmission that is making this sound when unloaded but coupled (in neutral), including the throwout bearing. My experience with throwout bearings is the opposite, they scream when that are depressed, quiet when disengaged. From what I have read about these ZF transmissions is they are very good but known to be harmlessly noisy.


Has the clutch been changed before? My bet is on the throwout bearing.

[KJL]

I don't know. not while I have owned. I doubt it. The car only had 40,000 on it when I purchased it.

[5ABI VT]

If the noise changes clutch in or out.. theres not much changing inside that bellhousing besides that bearing moving... That's what Im thinking anyways.

[Paul Workman]

I currently own a '96 LT4 as a daily driver and a '91 ZR-1. I traded a CE LT4 on the ZR-1 when I bought it. My two current cars are stock. Being able to drive them back to back, I do have some opinions....(what's that saying...opinions are like something something....).

First, my CE, which was stock, ran 12.7 in the quarter consistently. My current one, which I owned at the same time as my CE for about 6 months, feels every bit as quick. I haven't raced the ZR-1, but judging from numbers that go thrown about, they seem to run similar or slightly slower times.

That said, the ZR-1 revs much faster and feels racier. Driving on the street, the LT4 feels like it has more grunt and keeps up about the same until about 100mph, then it's the LT5's game.

Because of the low end torque the LT4, it actually feels stronger than the LT5 in the lower revs. For me, this means that, at 55mph in 6th gear, the LT4 accelerates much quicker while the LT5 needs to be downshifted. I typically keep the LT5 in a gear lower than I would in the LT4 and shift later into 6th.

I don't think you'll be disappointed, but, considering that most LT4's are stronger than their rated hp suggests, the gap between them at everyday speeds isn't as great as you'd think.

As far as the early/late LT5's, I think the desirability of the 405hp motor is simply the power rating and not real world. Because the later cars got a little heavier, it offsets it and, from everything I've seen, the real world performance difference between the early and late cars isn't much, if at all.

All just my humble opinions, of course and this is assuming stock, or relatively stock cars. Comparing a modded ZR-1 to a stock LT4 is apples to oranges. Years ago, I used to see an Astro van (complete with curtains in the windows) run 13's and a Chevette running 10s.....


Chris
Bench racing at its finest! :thumbsup:

Well, when you actually race your ZR-1, you'll come to appreciate the marvelous differences. Like the LS1/C5s, they too come to appreciate the DOHC arcitecture!

(This isn't me, but the scenario has played out many times.:razz:)

Link (http://www.youtube.com/watch?v=PzPPEK9Qf3M)

[Kevin]

ls1 c5's are so slow I don't even bother with them anymore. And my car is stock

[5ABI VT]

I don't feel the LT4 has more torque down low. Anyone lay a graph over either curves? I feel its the extra weight that gives it that slower feel.

[We Gone]

I also had a 96 LT4 and many times my son and I played around with them. At the time my 91 only had headers, flowmasters and chip. The LT4 had a custom tune and muffler eliminators. I will say this the LT4 did a great job up to 100mph after that the ZR-1 started to wind up and 100 to 150 I was a good quarter mile plus ahead I had to slow down for him to catch up.

[BigJohn]

ls1 c5's are so slow I don't even bother with them anymore. And my car is stock

Cool, I have a 98 C5. Do you want to race?

:dancing

[Mystic ZR-1]

Big John
Can you say Sleeper? :-D

Kevin, watch who you pick out :dancing

[edram454]

c5's are not slow. ever drive a fixed roof coupe 6 speed? very quick and light. these cars can be easily modified to make big horsepower. my c5 automatic made 525 to the wheels. no meth injection or nothing just blower and cam. stock automatics are a bit slow but great driving and cruising cars. c4 zr1 feels more like a race car and the lt5 howls. Corvettes for the most part are fast compared to other cars in general. My two favorite power plants after the l88 is the lt5 and the ls7 427. The ls7 427 505 hp 470 ftlbs torq and idles like grandma's 1968 chevy nova going to the market. No gas guzzler tax either and revs to 7k. A marvelous engine.

[secondchance]

The LT5 is starving for air! Give it what it wants, and be amazed at the rewards!

Hallelujah!!!:cheers:

[8cam]

Checking out the 92 has been put on hold, the owner was trying to do what I have been told is called a skip title, basically to avoid our ridiculous new tax law which requires the purchaser to pay the full property Tax on the car upfront instead of yearly installments. It is a way for the state to reclaim some of the lost sales tax revenue from private sales. The problem is the title is still in the previous owners name and my county requires a signed bill of sale from the current owner. That would have been a problem.

Hey a fellow Roswellian! I'm actually East Cobb, but close. The new GA is nothing but a money grab and a crime if you ask me, totally hurts enthusiasts who like to try different cars. I bought my ZR-1 last year after the law went into effect and the tax bill was something like $750. Not a huge amount of money but enough to be annoying, especially when my Ferrari tax bill is 40 bucks! Sounds like the guy never actually titled the car in his name? Yeah that's really a bad idea these days. He needs to suck it up and take care of it, and then sell the car. Since the tax ends up being paid twice (him and you), he will probably try to push the price up. You're in the drivers seat with the deal, push back.

Good luck the Z is an incredible car. I've been into euros my whole driving life, and it's the first American car I've owned in more than 20 years. I love driving it hard. Other Corvette guys who have ridden with me are flat amazed at the difference, just a completely different animal from a pushrod car. Guy with a C6 at the last autocross rode with me for a run, and he talked about how different it sounded and how hard it pulled all the way to 7500, couldn't believe it. It's my kind of engine.

[Paul Workman]

Good luck the Z is an incredible car. I've been into euros my whole driving life, and it's the first American car I've owned in more than 20 years. I love driving it hard. Other Corvette guys who have ridden with me are flat amazed at the difference, just a completely different animal from a pushrod car. Guy with a C6 at the last autocross rode with me for a run, and he talked about how different it sounded and how hard it pulled all the way to 7500, couldn't believe it. It's my kind of engine.

Couldn't say it better! Nothing convinces the pushrod crowd like pairing up with a 4-CAM DOHC and having their socks blown off! :dancing The Zs always attract a crowd at the local annual 1/4 mile Corvette Shootouts after taking a thrashing from those obsolete motors...:mrgreen:

[Kevin]

c5's are not slow. ever drive a fixed roof coupe 6 speed? very quick and light. these cars can be easily modified to make big horsepower. my c5 automatic made 525 to the wheels. no meth injection or nothing just blower and cam. stock automatics are a bit slow but great driving and cruising cars. c4 zr1 feels more like a race car and the lt5 howls. Corvettes for the most part are fast compared to other cars in general. My two favorite power plants after the l88 is the lt5 and the ls7 427. The ls7 427 505 hp 470 ftlbs torq and idles like grandma's 1968 chevy nova going to the market. No gas guzzler tax either and revs to 7k. A marvelous engine.

experience tells me different. Been showing stock and lightly modded ones my tail lights since 99. Sure they can make big power modded and for a lot less but stock or near stock forget it

[Hog]

experience tells me different. Been showing stock and lightly modded ones my tail lights since 99. Sure they can make big power modded and for a lot less but stock or near stock forget it

I have the impression that the LT4 and C5 LS1 cars are on par, and the LT5 cars smoking both. All stock of course.

[5ABI VT]

From my experience the LS1 6 speed traps slighty higher than the LT4. Given that the C5 is lighter it sure lends some credibility to the LT4 being slightly underrated. Ive seen 2 LT4s trap 106-107. My friends LT4 I went to the track with with nothing but a B&B (newer restrictive system) just last year trapped 106 mph. Back when I had bolt ons on my 93 LT1 I was trapping around 111 and Stock 6 speed LS1s were slightly slower at 108-109. The only car I went up against was in 1999, and it was a stock 97 6 speed with a Borla stinger cat back and he was 109.

I guess just for comparisons sake I had Long tubes and Corsa with a haibeck chip and I was just under 118 mph. My friends LT4 car only has a chance when im not paying attention :-D

[csavaglio]

My CE LT4, which was stock, trapped between 108 and 109 consistently and, as I mentioned, usually ran 12.7. All uncorrected and actual numbers.

I never dyno'ed that car, although, from the dyno sheets I've seen of other LT4s, they seem to vary quite a bit, but usually higher than the rated hp numbers would suggest.

Personally, I think the LT4 is one of the most under rated (both by people's opinions and the hp numbers) corvette motors.

I agree 100% with WeGone. Up to 100, stock to stock, the LT4 keeps right up with the LT5. But 0-100 is the LT4's game and not the LT5's. Two very different powerplants with two very different personalities.

[Z06scentair]

c5's are not slow. ever drive a fixed roof coupe 6 speed? very quick and light. these cars can be easily modified to make big horsepower.

Spot on! Nimble in stock form is what I like to call it!

My 02z has a 408 with a YSI Trim blower, with a 2.75" pulley this car is not for the faint of heart!

HP before the blower/larger heads/cam was 532 rwhp and 502 rwt.

The car needs to be retuned after the head/cam swap last year. My buddy is on me to retune the car and get it back into action......oneday soon!

[5ABI VT]

Theres a lot of variables when it comes to track times. I only compare what ive seen at my local track and what ive run side by side. My brothers ss for the life of him couldn't crack 14.0 on street tires totally bone stock. Went to Englishtown and ran 13.4. no changes at all. Different track.. differet altitude and all the other variables etc etc.

Im not knocking the LT4 but Theres been a ton of bs about hp numbers over the years. There was one thread about how some were 370 hp even 390hp for a few %. SOrry but that is :censored: . If a 390 hp Lt4 existed.. weighing in 200 lbs less than a zr1 we would see trap speeds over 116-117 mph rivaling c5 z06s. Just not happening. Ive never seen an LT4 factory fresh run over 110 mph without some mods like headers or gears intakes etc. My 93 trapped 104 mph stock. I knew a guy who hung out with us that we went to the track with in a 96 LT4 like I mentioned earlier and he trapped 107 mph. 104-107 mph is about 30-40 hp. Right on par with GMs ratings.

I can definitely see why the LT5 may feel slower at lower speeds. It has longer runners tuned for certain rpms. at part throttle and certain rpms it only runs on half the runners. It can make for a soggy feeling engine at low speeds. GM also didn't add any gear to it. For a motor making higher torque and hp it sure could have used it. On top of that it weighs 200 lbs more. all those contribute to the slower low end feel.

[Kevin]

From my experience the LS1 6 speed traps slighty higher than the LT4. Given that the C5 is lighter it sure lends some credibility to the LT4 being slightly underrated. Ive seen 2 LT4s trap 106-107. My friends LT4 I went to the track with with nothing but a B&B (newer restrictive system) just last year trapped 106 mph. Back when I had bolt ons on my 93 LT1 I was trapping around 111 and Stock 6 speed LS1s were slightly slower at 108-109. The only car I went up against was in 1999, and it was a stock 97 6 speed with a Borla stinger cat back and he was 109.

I guess just for comparisons sake I had Long tubes and Corsa with a haibeck chip and I was just under 118 mph. My friends LT4 car only has a chance when im not paying attention :-D

I think I did 116-118mph back in 00 at the gathering in my stock 90

[We Gone]

Back to the original question, Right now I have seen some fantastic deals on 90-92 cars and would jump on them with out any thought about the HP difference. At the prices I see you will have more than enough left to put the HP even.

[KILLSHOTS]

Back to the original question, Right now I have seen some fantastic deals on 90-92 cars and would jump on them with out any thought about the HP difference. At the prices I see you will have more than enough left to put the HP even.
I agree with Steve. Marc says all it takes is headers, exhaust and a tune to get to 410-420HP. Those mods will certainly cost less than the premium you'll pay for a later car.

[Kevin]

Back to the original question, Right now I have seen some fantastic deals on 90-92 cars and would jump on them with out any thought about the HP difference. At the prices I see you will have more than enough left to put the HP even.

I like the seats/interior/ride/trans noise on the earlier ones better

[XfireZ51]

I like the seats/interior/ride/trans noise on the earlier ones better

Exactly the reason I have a 92.

[8cam]

I like the seats/interior/ride/trans noise on the earlier ones better

I love the early seats, and I like the style of the 90...which is why I have a 90.

[5ABI VT]

My favourite is the 93. Maybe one day I would consider selling mine if I could find a quasar blue 93. Anniversary year, favourite seats and dash, favourite color and the last year of it plus it's a 405hp . Ticks all my boxes. Then again I'm happy with my colour and I do have quasar already on my 93 lt1 car. All I need is early seats and eventually a dash swap