So I had a bit of blowby...

[XfireZ51]

I thought I would do a little documentation of a light refurb I am having Pete do on the LT5. This is another case of the "while u are there" but there were several issues I thought may need addressing.
When the motoring season started, I got things going on Roza Nero. The winter project was taken up w mostly getting ready to do the MR run for the first time.
That involved installation of a Pioneer AppRadio4 with Car Play. Came in VERY handy. During some of the shakedown runs, I noticed some blackish gray smoke going on when I would "get on it" At first I chalked it up to blowing out the carbon after a long winter sleep. Car was running pretty well, altho it was using oil w a quart every 7-800miles. It had always "used" some oil, but that it seemed to be a bit more now. And that seemed to coincide with the addition of my Air/Oil Separator. Some mentioned a bluish smoke during decel.
We headed down to Blowing Rock, NC for MR5, and the ZR ran fine. Met up w Robert DeMarco and PauL Workman in Knoxville. When we arrived in BR, Paul mentioned that something had flipped past his windscreen from the rear of my car. Left side exhaust was hanging with a hole in rear of muffler where the mounting stud used to be. We had driven roughly 1000miles in 2 days and I was down nearly 4 quarts. However, no other signs of problems w how car was running. Idled fine, cruising was good, response good. Got the muffler repaired at a local place near Blowing Rock. Pretty good guys. They liked Vettes. Hadn't really seen ZR-1s before. Bob DeMarco was a big help here staying back with us and leading us ack to the rest of the pack.
Spoke to Marc at BG about the oil consumption which he suspected was attributed to a mismatch of the Injector Housing/Cylinder Head crankcase venting restrictors. He suspected both were wide open.
Drove back thru Nashville, and aside from adding additional oil (didn't need an oil change) motor ran well and tallied 23mpg at a steady 75-80mph.
Once back in Chicago, I basically put the car out to pasture until Pete could get to it. Meantime I pulled the plugs for running a compression check and noticed #7 was sooty and black. However, compression checked to 220psi.

http://www.zr1.net/forum/showpost.php?p=263511&postcount=1

Finally, Pete has been able to get his hands on the car. Basically we started with a checklist of things to look for.

Sooty #7. Leaky Injector/Valve Guides or Seals? Or not.

Check Clutch Disk. Suspect lack of trap speed to be slipping disk

Trans Leak . Its not the rear seal

Busted Muffler Stud. Busted Motor Mount allowing over-flex of exhaust

Rod Bearings. Just in time to change. An unknown "while ur
there.."


So I hope to document our progress on this and see what results. Pete has the lower end about done.

[mike100]

As far as the trans leak goes- Mine leaked out the tail-housing, but it wasn't the lip seal...it was the metal plug in the end of the driveshaft yoke that was leaking.

[XfireZ51]

As far as the trans leak goes- Mine leaked out the tail-housing, but it wasn't the lip seal...it was the metal plug in the end of the driveshaft yoke that was leaking.

Mike,

This appears to be the middle seal in the case. There's seepage there.

[Paul Workman]

Mike,

This appears to be the middle seal in the case. There's seepage there.

Broken top ring on #7 too...was mentioned @ the FBI pizza nite two weeks ago.

Anywayz...aounds like the "Rose" is getting a new lease on life!:cheers:

[Ccmano]

Broken top ring on #7 too...was mentioned @ the FBI pizza nite two weeks ago.

Anywayz...aounds like the "Rose" is getting a new lease on life!:cheers:

That would explain the blow by. Were those the original rings?
H
:cheers:

[XfireZ51]

That would explain the blow by. Were those the original rings?
H
:cheers:

As far as I know, yes. The motor has been w me for the last 10 years.

[tnova]

The right muffler bracket broke twice on my '91. Now I'm rebuilding the engine (160k miles-oil consumption and the need for more power) and found one of the motor mounts was broken. But for your post I would not have correlated the two. Thanks.
Tnova-'91 ZR1

[XfireZ51]

The right muffler bracket broke twice on my '91. Now I'm rebuilding the engine (160k miles-oil consumption and the need for more power) and found one of the motor mounts was broken. But for your post I would not have correlated the two. Thanks.
Tnova-'91 ZR1

Yes I suspected that excessive movement of the motor was causing a flexing of the muffler sheetmetal where the muffler's rear mounting stud is attached. Ultimately, it rips the sheetmetal. The motor mount on the driver's side was cracked, and it was the corresponding muffler mount that failed.

[Ccmano]

My last Z had bad motormounts at 50k miles. I'm doing new mounts on the new one when I do the headers in the next few weeks. I noticed one of the exhaust system hangers was broken last I was under the car. I suspect I will find a broken mount as well.

What are you doing with the ring issue? Might be a good time to go larger displacement if its all apart anyway. It just a matter of money....

Move here to Reno and you'll save many thousands in taxes. :thumbsup:
H

[LGAFF]

Engine ring failures(breaks) are usually caused by detonation....any thought what might be the cause? Low fuel pressure, too much timing, bad injector?

[XfireZ51]

I have datalogged my car enough to know that I don't have detonation. The top end timing doesn't induce any detonation. In researching this, I came across
this video by Hastings in piston ring failure.
https://youtu.be/3GbXxf435N4

One of the causes listed is "lugging" the motor. During some datalogging sessions, I have "lugged" the motor intentionally. Sometimes 6th gear at 900rpm
as a way of gathering readings on VE cells not typically used in normal driving.
So I'll be avoiding that in the future. Why just #7?

[LGAFF]

https://www.bing.com/videos/search?q=what+is+lugging+a+motor&&view=detail&mid=0FA3A2EEFE4C8E0D267D0FA3A2EEFE4C8E0D267D&FORM=VRDGAR

[XfireZ51]

Thanks Lee. Very interesting. I don't typically floor it in 6th and low rpm, but a a prolonged deliberate lugging of the motor could be the culprit.

[efnfast]

Well, I'll be avoiding lugging the motor a lot more. Thanks Dom.

[XfireZ51]

So a bit of an update. A couple of "while you're theres".
Replacing clutch disc and rod bearings. In the course of diagnosing the the cracked compression ring, Pete removed the rod end. He found the top portion of the bearing to be worn to the copper while the bottom end appeared to be fine. No issues w the rod journals. He surmises that this may have happened at engine initial startup. The motor came out of the 92 Aqua ZR and was a service replacement to the original motor. Pete suspects that since the service motors may have sat for some time, the top portion of the rod bearing had drained of oil, and startup of the motor without proper pre-oiling may have caused the wear.
Also, I am replacing the stock LT1 clutch disc I have been using. I have suspected that possibly the clutch could be slipping at top end after having done a series of mods that should have resulted in an increase of trap speed. Instead the trap has remained relatively flat and really isn't indicative of the power the motor is making. The disc we have removed shows signs of wear and is pretty thin. Replacing it w Centerforce sprung hub which has more "meat" to it. As you can see in the attached pics, the CF disc utilizes more of the area in the center to increase friction surface and several others like the way it works with their Fidanza FW.

[RichS]

I ran a Centerforce clutch in the GS before swapping to a auto. Drove like stock, pulled 1.5x 60's with it.

[GOLDCYLON]

So a bit of an update. A couple of "while you're theres".
Replacing clutch disc and rod bearings. In the course of diagnosing the the cracked compression ring, Pete removed the rod end. He found the top portion of the bearing to be worn to the copper while the bottom end appeared to be fine. No issues w the rod journals. He surmises that this may have happened at engine initial startup. The motor came out of the 92 Aqua ZR and was a service replacement to the original motor. Pete suspects that since the service motors may have sat for some time, the top portion of the rod bearing had drained of oil, and startup of the motor without proper pre-oiling may have caused the wear.
Also, I am replacing the stock LT1 clutch disc I have been using. I have suspected that possibly the clutch could be slipping at top end after having done a series of mods that should have resulted in an increase of trap speed. Instead the trap has remained relatively flat and really isn't indicative of the power the motor is making. The disc we have removed shows signs of wear and is pretty thin. Replacing it w Centerforce sprung hub which has more "meat" to it. As you can see in the attached pics, the CF disc utilizes more of the area in the center to increase friction surface and several others like the way it works with their Fidanza FW.

Is that the Camaro clutch disc Dom ?

[XfireZ51]

Is that the Camaro clutch disc Dom ?

The one I am replacing is a stock OEM LT1 clutch disc. So will be using the Centerforce. With 345s in back, I probably could use the clamping force.

[XfireZ51]

Below is a view of the top compression ring from #7. Also, motor is starting to go back together. Before Pete started, we discussed cc'ing the heads just to make sure we had all uniform chambers. Pete verified that they were uniform
40cc chambers. We did this on the suggestion of Marc H. Wanted to check if there was some other explanation for compression being overall somewhat lower on the driver's v passenger side banks. However, the FSM states compression should not vary greater than 15% from low to high cylinders. We're ok there (210 v 245). And FSM states that high end of adequate compression is 200psi. So we are over that by a significant number.

[WARP TEN]

Below is a view of the top compression ring from #7. Also, motor is starting to go back together. Before Pete started, we discussed cc'ing the heads just to make sure we had all uniform chambers. Pete verified that they were uniform
40cc chambers. We did this on the suggestion of Marc H. Wanted to check if there was some other explanation for compression being overall somewhat lower on the driver's v passenger side banks. However, the FSM states compression should not vary greater than 15% from low to high cylinders. We're ok there (210 v 245). And FSM states that high end of adequate compression is 200psi. So we are over that by a significant number.



Did the little pieces of the ring stay in the groove or did you have to go fishing in the oil for them?--Bob

[Jagdpanzer]

Dom,
How did the cylinder wall look?


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[XfireZ51]

Did the little pieces of the ring stay in the groove or did you have to go fishing in the oil for them?--Bob

Bob,

Fortunately, the ring pieces all stayed within the ring groove. No damage was done to the cylinder bore. U can still see the xhatch pattern on the Nikasil.

[Dynomite]

I was skeered to ask how the Sleeve looked and if all the pieces stayed on the piston ;)

All I can say is "good for you" :thumbsup:
The Piston Groove may need a bit of inspection also :handshak:

[XfireZ51]

Latest Update. Cylinder heads are on w cam covers now bolted in and cams timed. So motor is about ready to get dropped back into engine bay. Attached are pics of busted motor mount on drivers side. I suspect its been either like this or in some degree of damage for sometime. My driver's side exhaust would twist and I have had now 2 mufflers w metal fatigue in the area of the hanger.
Hopefully, this will remedy the situation.
Briefly what appears to have happened is that metal retainer which limits the amount of movement of the mount, basically spread out and so no longer limited the travel of thentop of the mount. And due to that, the mount essentially was ripped in half and failed along a horizontal line around the circumference of the mount.
BTW, the replacement is the same part# as the LT1/LT4 mount.

[ssrszz4]

Kind of like a loose cannon!!

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[XfireZ51]

Dr. Greekenstein sent a pic of his latest implant. He also sent me comparison that shows the quality of his work. We have PRE and POST valve job leakdown numbers. This is part of Pete's "quality control". Significant improvement in 4 of the 8 cylinders.

B/A

1. 6-5%
3. 10-4
5. 8-4
7. 5-5* This is the cylinder w broken compression ring

2. 8-4%
4. 20-3
6. 12-4
8. 2-2

[tpepmeie]

Wth was wrong with cyl #4? That's a terrible before number?


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[XfireZ51]

Wth was wrong with cyl #4? That's a terrible before number?


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That would be a question for Dr. Pete. Interesting that u have adjacent cylinders
w the worse #s.
Interestingly, the same can be said for the driver's side bank as well, albeit not to the extent of the passenger side.
I would also say that these were heads I had purchased from a previous LT5
enthusiast. These heads were ported and massaged by GVD sometime in the late 90's or early 2000. So the porting job had been done on the basis that they
knew about then rather than the current state of porting.

[XfireZ51]

Went to Dr. Greekenstein's lab this afternoon, and the motor etc was all buttoned up. Some minor details to attend to but powertrain and drivetrain is ready to go. So we started it up. I'll be checking the tune right away to see if any of the mods have shifted the fueling requirements.
Pretty certain there will be some changes but it should be a matter of tweaking to optimize.

It sounds healthy.

https://youtu.be/3HZhzi-uoSw

[Ccmano]

Nice.. I'm jealous you have both Pete and Al so near by. It will have to be on the job training for me at some point.
H
:cheers:

[XfireZ51]

Nice.. I'm jealous you have both Pete and Al so near by. It will have to be on the job training for me at some point.
H
:cheers:

Could be cheaper/faster shipping it back here. These guys along w Marc have forgotten more than I'll ever know. Which allows me to just turn the key and motor off. ;)

[Ccmano]

Could be cheaper/faster shipping it back here. These guys along w Marc have forgotten more than I'll ever know. Which allows me to just turn the key and motor off. ;)

... and open the check book.
H
:cheers:

[XfireZ51]

... and open the check book.
H
:cheers:

Do it once and do it right.

[Blue Flame Restorations]

Car is in good hands. Glad to see you getting it rebuilt.

[XfireZ51]

Have gotten the keys back from Pete so now I get the chance to drive around a bit, and do some datalogging. Anytime I do any kind of modification to the motor or drivetrain, I check the fueling calibration to tune the operation for as optimum as I can. You would be surprised how mods like flywheels, rear axles, injector changes affect the tune. I'm not speaking of something that's "good enough", its about a tune that is specific to the motor and the modification state it is in at the moment.

As an illustration, I had modified the tune to the motor prior to heading to MR5.
I suspect the broken ring had already occurred although the motor gave no indication of a problem idling or cruising. Even MPG was good at 23-24. We drove over 2300miles in 10days, and aside from the oil consumption, the motor never hiccuped.
I have attached pics of the changes to the fueling tables made after my initial logging session yesterday. Its rich pretty much all over the operating range.
The tables are of the new calibration so the negative numbers are fuel being removed compared to the previous cal.
Its important to get this part of the fueling correct before ever taking it to the dyno for WOT tuning. One depends on the other. And part throttle really can't be done on a dyno. Maybe an engine dyno, but even the OEMs do their fine tuning after logging lots of miles over many different types of environments and roads. I'll take it out again today to confirm the changes and update. Its an iterative process. Rinse and repeat.

[Ccmano]

Are you using TunercatPro to datalog?
H
:cheers:

[XfireZ51]

Are you using TunercatPro to datalog?
H
:cheers:

No. Not sure that Tcat even offers a datalogger. TunerPro does and there's also a version for use on an Android tablet which I also have connecting to ALDL via Bluetooth. But I have been using EASE(Personal) diagnostics for the last 15 years. I may switch over to TPRT logging because of the simplicity of the tablet logging.

[XfireZ51]

Did some more datalogging today w initial revision of calibration. Noticeably smoother. Acceleration responsive to the smallest change in throttle position.
To illustrate the difference between the initial tune and the new one I just created, attached are pics showing the changes to the same VE table and
how much change was needed for each revision. The 9.18 table is the most recent revision which I will datalog next. You can see how the table got "cleaned up" quite a bit with first revision. You will never get to all zeros, but the recommended delta to the VE will be insignificant. You'll see a seesawing of the VE% between one revision and the next. And that's how u know you are as close as you'll get on this aspect of the tune.

[XfireZ51]

Update: Recheck of Compression #s after rehab.

1 220#
3. 222
5. 221
7. 220

2. 232
4. 230
6. 234
8. 242

Thanks Pete.

[tpepmeie]

The bank-to-bank comparison is interesting. Cam timing?


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[XfireZ51]

The bank-to-bank comparison is interesting. Cam timing?


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Todd, I don't have an explanation. I know Pete does a great job in setting up the
cams. However, the L v R relationship between banks is consistent w how it was
prior to the engine work. Pete cc'd the heads, and chambers were all 40cc. However, the left bank certainly benefitted from the rehab.
Not sure if there is a correlation, but the right side also has a tendency to run somewhat richer than the left.
Pete also has observed that #8 on LT5s also has a tendency to have the highest compression #s.

[Pete]

Dom,
Yes your right can not tune drivability on the dyno, dyno is only good for WOT.
Even on Dyno i always play it safe dont need blowing up a motor, i only take risks with my Z take it to the limit.:-D

I like some people think they are tuners cause they took a reputable shops chip and tuned in another 4 RWHP and all they did was add 2 degrees of timing so now they are expert tuners what a crock of ****.
I get more power by putting 2 less gallons of gas LMAO.

Best way to tune a camed motor is to have the car in person.

Pete

[Pete]

The bank-to-bank comparison is interesting. Cam timing?


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Todd if you look at Doms previous #'s a couple of his left bank cylinders were just as high as the right bank.
Previously his left bank was weaker then the right bank now both banks have increased a little.

As Dom mentioned i have noticed #8 cylinders most always have higher #'s.
I dont know why will research it some more.

Pete