Is there anyway to avoid getting a "dog"?

[Brett]

It seems like I often hear about varying horsepower in the ZR-1 and the LT4. Some perform much better than they are supposed to, and others are much worse.

Is there anyway to avoid purchasing a dog, short of actually taking it to the dyno?



Brett

[Vettelt193]

I have read a few things about the varying HP in cars... GM actually said it is normal for a 5% variance in power from what they advertise. (I am not sure if it is +- 5%, or +-2.5%, but i have a feeling it is +-5%)

When it comes to purchasing, it is really luck of the draw as far as I know.

[JT ZR-Won]

I've driven a couple different ZR-1's before so it would be easy to tell if one of them wasn't performing as well as another.....but honestly, I haven't been in one that didn't haul ***

It is very hard to tell the difference between 5-10 horsepower.

Jay

[Brett]

Thanks. It was kind of one of those questions I new the answer too, but it's just so frustrating to think about.

By the way, JT, that is a beautiful ZR-1 you have there. I love the pre-1991 nose. It looks sharper to me. And I like the maroon red better than the torch red. It's more subtle, and you can see the lines of the car better. If I had my choice at any King out there, it would be hard to beat yours!



Brett

[BadZr1]

If it gets your adenialin flowing it's NOT a dog................

[SurfnSun]

you could always dyno test before you buy.

[vettl83]

Brett my advice would be to take a ZR-1 guy with you to check it out. They have a few little quirks once in awhile that aren't serious, but may seem like it if your not familar with the LT5. 84 CF 91 ZR-1

[JT ZR-Won]

Originally posted by Brett
By the way, JT, that is a beautiful ZR-1 you have there. I love the pre-1991 nose. It looks sharper to me. And I like the maroon red better than the torch red. It's more subtle, and you can see the lines of the car better. If I had my choice at any King out there, it would be hard to beat yours!

Thanks for the kind words Brett. Actually, mine is the bright red color. Just the time of day it was when I snapped the picture makes its appear a little darker

Jay

Brett:

As I've stated before, the HP numbers in the LT5 do vary, and sometimes more than the legally allowed variation from the advertised HP rating. Each and every LT5 was dyno tested at Mercury Marine. Those dyno tests (if they haven't been destroyed by now) were not released to the public. The difference in HP is somewhat curious since the basic engineering of the engines were the same. However, remember that these engines were hand built. Sometimes hand built engines are more susceptible to different HP output. Internal friction causes a loss of HP, and the easier everything spins, the more HP you will see on the dyno and feel on the street. There are a number of factors which could cause the HP difference, but my gut feeling is that it is just attributable to the assembly process and perhaps the delivery and installation of some better machined parts. All-in-all, if you've never driven a ZR1, it would be hard for you to tell the difference. If you've driven quite a few (as I have been lucky enough to do), you will be able to tell the difference. Good luck.

[Ol Blue]

Brett and Legalfish
There are several thoughts about the differences in LT-5 power. One that I've heard that the first 500 built are stronger than those built later. Perhaps something to do with move precise cam timing as I understand it is very critical to the LT-5.

I've also heard the engineers talk of the + - 5% horsepower at a ZR-1 seminar at the Corvette Museum. Rumor has it that they didn't want to release the dyno-sheets because some cars came out under the advertised HP rating. GM may have had a point there because one disgruntled (apparently slow) ZR-1 owner was quite a pain in the A.. about it during the presentation.

The dyno-sheets do not have the serial number of the car on them, only the engine number. The National Corvette Museum has boxes of them, and I've heard that they plan on selling copies to owners, but they can't seem to find the time to organize the records. Many ZR-1 owners are champing at the bit, to no avail. Hopefully the records will not get lost/misplaced before the NCM can get to them.
Ol Blue
http://www.knology.net/~corvettes/63vett.jpg

PS Oh, my son has a 90 ZR-1 and insists that many of the slower ZR-1's ar that way simply because they aren't driven hard enough to keep the secondary throttle bodies and injectors working properly. Soooo, every time you drive one, get 'em open, and keep 'em open!!!

Ol Blue:

I don't think there is any question that the dyno sheets weren't released by GM due to the varying figues. Back then, that seemed to be the unspoken truth. It seems to still hold true today.

As far as the cam timing is concerned, they may be some truth to that, but remember that changing the timing to any significant degree could also effect the emissions - something GM certainly didn't want to do.

The secondary injectors argument is interesting, but I don't think it is applicable to the engines that were running on the dynos at Mercury. Again, I think it had to do with assembly, better machined parts (heads, intakes, etc.), and less internal friction. Just my 2 cents.

[Ol Blue]

legalfish
Yes, I agree that the secondary operations wouldn't have much if anything to do with factory dyno-runs. However, for ZR-1's on the road today the lack of use can be a factor. My sons car had been babied until we brought it home from North Dakota and it progressively ran better (faster) as we made the trip back to Indiana. Could have been due to secondaries coming into use more often, could have been the computer learning more, or maybe it just felt faster due the euphoria of owning his dream car...

The vacuum canisters that are under the plenum can go bad as well as minor leaks in hose fittings. I understand that many of the vacuum canisters were put on incorrectly at the factory, which put the linkage in a slight bind. When my son took his plenum off, his were incorrect. I'm not sure if that prevented them from opening all the way though.

I agree that in any engine assembly there will be some that run better than others, with no easily determined reason. Even NASCAR engine builders seem to find that one engine may run better than others.
Ol Blue
http://www.knology.net/~corvettes/63vett.jpg

[rkreigh]

we've seen engines pick up 7-15 HP on the dyno just by clearing their throats. as the carbon builds up, the secondaries can become a bit stickey.

as the secondary injectors aren't used as often then can be more prone to clog.

my zr1s get the secondaries exercised often enough that this hasn't become a problem. but many of the zr1s I have owned got stronger (and emissions cleaner!!) as I owned them longer and made sure they were driven with gusto more often.

[BA ZR WON]

Hello!

It's mostly cam timing that causes the performance variance engine to engine. This issue has been covered many times by the people who were instrumental in the LT5s development. Re: bad maching processes causing performance variations: The LT5 was assembled to very exact standards, no production engine from GM ever has, or more than likely ever will be, assembled like that again.

Most LT5s produced less than the advertised power(375 or 405, depending on the year) when on the dyno at Mercruiser. Engines take some run in time before they start producing max power. This is one of the contributing factors to GM Legal not allowing the dyno sheets to be distributed(or so the story goes).

Re: running them hard to keep peak power, it's a fact. Even the owners manual says to occasionally open the car up or it will start to run poorly. It does warn that the LT5 will make a lot of noise under full power so do it in a secluded place! As my Dad(Ol Blue) used to say about his '63, "You rev it up to 5K in first gear every 3rd stop to make sure it stays cleaned out." Did I get that right Dad???

Brian A.
90 ZR-1

Just don't be in a hurry, take your time and look, look, look. I looked for 6 months before I bought my car from Paul Smith. It hasn't given me a lick of trouble.
Good Luck.
Joel