Most qualified mechanic to appraise a C4 ZR1?

[Llewelyn]

Hi all

I’ve had my ZR1 advertised for a week or so - had load of interest but the same story from most buyers… Nervousness that it has been off the road for many years essentially.

I feel that although people enjoy my videos there is a general assumption that my car is, how do I put this, probably not running well and a bit patched together basically. I had a comment from a club member at a show recently too;

"Got your ZR1 running properly yet?"
"Err - It's running very well thank you"
"Really?! I highly doubt it"

I was slightly erked and haven't forgotten that comment.... I shouldn't need to justify anything but I will.

While it could benefit from some paintwork this irritates me because I know for a fact it is mechanically as strong as any other C4 ZR1. Not just the engine but the drivetrain, suspension, brakes, electrics. And had probably had way more work than the majority of them have, certainly in recent times.

I plan to put it on a dyno to demonstrate the power.

What I’d also like to do is get an inspection report from the most well qualified C4 ZR1 experienced mechanic in the country. Any idea who that might be so I can reach out to them? (Preferably one within reasonable reach of Nottingham)

Any advice appreciated!

Llewelyn

 

[CaptainK]

Sorry I don't know of any mechanics etc, but I look forward to the Dyno Episode being on Youtube. Your ZR1 looks very nice and I'd like to own it, but alas I don't have space for it, and the missus would kill me.

 

[Llewelyn]

Sorry I don't know of any mechanics etc, but I look forward to the Dyno Episode being on Youtube. Your ZR1 looks very nice and I'd like to own it, but alas I don't have space for it, and the missus would kill me.

Thanks! The dyno vid will happen once I can get it booked in

 

[Chevrolet]

What I’d also like to do is get an inspection report from the most well qualified C4 ZR1 experienced mechanic in the country. Any idea who that might be so I can reach out to them? (Preferably one within reasonable reach of Nottingham)

How about Parts USA Manchester way? They are a GM authorised Vette repair and service company and have a great reputation. Neil there is ex Bauer Millett Manchester, who were the sole GM authorised UK Vette dealer for many years until closing in 2015(ish).

Parts USA - Authorised Parts, Service & Repair for your American Vehicle

Parts USA - General Motors Authorised Repairer. Cadillac, Camaro, Corvette, Hummer parts supplied within the UK and internationally. Manufacturer backed maintenance, repair and bodywork carried out. All American cars and trucks catered for.

www.partsusa.co.uk

 

[Roscobbc]

Keith at Eurovettes (when he's back in the UK) has been dealing with C4's for years - also has good knowledge of special C4's (Callaways) and presumably Zr1's?

 

[Llewelyn]

@Chevrolet @Roscobbc both good choices, it would ideally need to go on a ramp and be test driven etc by whoever looks at it!

 

[teamzr1]

FYI
Back in 1998 I put on a Corvette chassis dyno day
Results are from a NON load bearing dyno and is rearwheel output
Several were C4 ZR-1s we owned

Keep in mind early years ZR-1s had 375 HP, where 93-95 had 405 at flywheel
but due to the waxers bitching about tranny gear rattle at idle, the 405 version had less torque than the 375 HP did

The ZF tranny was designed for maximum torque output and the lashing (spacing) between tranny gears was real close
that was than causes the rattle at idle where GM had more spacing in-between gears to remove that rattle
but at a loss of torque output

 

[Llewelyn]

VERY interesting results! And also your comments about the gear spacing - I didn't know that!

Mine is booked in for monday so I will post the results here (and film it)

 

[teamzr1]

Be nice if you reported was the chassis dyno used was load bearing or not, was calibrated and
takes into account for a correct D/A as to weather and elevation

Also, a secret
At the time I worked for GM engineering and worked with Tim Holland of Lotus who was the LT5 program manager
He was pissed that GM was dumping the ZR-1s so he had the 95 LT5s with different ECM tunes
He sent me an ECM E-prom to test with me 94 ZR-1 and hence the output was higher and people
would say GM must have hacked on mine as my racing numbers were better than other stock ZR-1s

Good book on the LT-5

 

[Llewelyn]

I'll have to get a copy of that Interesting re the ECM tunes too!

 

[teamzr1]

Here is the secret E-prom tunes Tim sent me to test on street and track
I used that tune as baseline when I tuned customer's ZR-1s
You can see his address in the UK and me at the GM tech center in Warren, Mi
I still have this one of a kind ZR-1 E-prom and tune it has
.

 

[Chevrolet]

Keith at Eurovettes (when he's back in the UK has been dealing with C4's for years - also has good knowledge of special C4's (Callaways) and presumably Zr1's?

Definitely. And back in the day, Keith rescued a ZR 1 mule off the scrap heap and brought it back to life:

 

[Llewelyn]

We've had the car on the dyno - Video link below but the headline results are

Power key on - Circa 335hp at the crank
Power key off - Circa 210hp at the crank

So in conclusion it's healthy although not making stock power - there is the subjective element of the dyno, calibration, traction etc. Also we are running a haibeck chip which was gifted to us but we don't know if it could be causing a problem due to it not being for a 91 car (would this make a difference? @teamzr1 ). I also have a Doug Rippie chip so I might go back and do 3x runs - Stock, DRM and Haibeck to compare the differences.

 

[teamzr1]

Those numbers are not correct
My understanding of the English language on that video coming out of a small computer speaker is limited
Best is to post those dyno results so we can analyze the results

I believe they stated this was a load bearing dyno and if so

1. Did they calibrate the dyno with the ZR1 on the dyno ?
2. did they assure that dyno had a weather station and made sure it was reporting the correct weather and elevation
so that a corrected D/A was factored into the results
3. For correct run they needed to be using a 1:1 gear ratio and for that tranny is fourth gear
4. All N/A engines, max torque crossing HP is 5,250 RPMs, did they push engine beyond that RPM ?
5. With Valet key ON, power does not really come on greater than 3000 RPMs so if they dyno pull to higher RPMs
then maximum horsepower would not be seen
6. Was rearwheels tire pressures be set correctly for dyno pulls and if not then some wheel spin and lose of performance numbers
7. best numbers would be less gas in the tank as to weight
8. the manual tranny for ZR-1 and drivetain has a 10% loss of performance to rearwheels

9. Best would have been during the pulls is using an OBD1 scanner in record mode and then analyzed that data as to the BLMs, INTs, AFR, timing and engine knock as I suspect the tune was not best

Design of 1991 ZR-1 as to GM Specs



5 C4 ZR-1s ( 375, 405 HP and couple ECM tuned and 1 with custom CAMs

 

[Llewelyn]

Thanks for the reply! I’m not an expert on dynos but here are the results:

 

[teamzr1]

The numbers are not right and if using that to sell the ZR-1, the value would be lower

Possible the dyno was not calibration fully for that ZR-1 as to its weight with driver in it
Load bearing dyno should be calibrated each time it is used with another vehicle and check that the correct weather and elevation inserted before the pulls.

Or results show the outside temp but not showing the dew point or pressure, or elevation, which would cause those lower numbers
Not sure why it shows final gearing as it does as I posted above show have been using 4th gear which is a 1 to 1 ratio

It those times for the run shown were only about 14 seconds, would not be long enough for the secondaries and other 8 fuel injectors along with WOT timing to fully engage
MPH listed at 122 MPH is not a full run, the number is too low, I ran higher speeds in at a drag strip of quarter mile

But even their flywheel numbers are too low for GM did a lot of testing of LT5 and in fact the 375/370 flywheel hp/tq would be correct

I crunched your numbers shown below, and you can see the stock flywheel numbers they got are not normal
Possible as added issue is the ECM tune
If you have the stock memcal with GM calibration in E-prom is swap that in at the dyno and do a good compare

IF you do not have GM one and cannot get one
I am helping another UK C4 owner who is a member of your club, Steven Smith, who is doing engine mods
and I'm helping with doing the custom tuning
I could email him a stock 1991 LT5 GM calibration and Steven bought a EPROM burner and some new EPROMs and could burn the GM tune into a new EPROM which has to be a 27C256 K
You would not to send him a PM on this forum

........................................ Dyno Results .................................................... Drivetrain rearwheel loss reported
Plus shows what stock flywheel is to what they reported in their results, way too low as to normal GM flywheel numbers