On Labor Day I drove a local Corvette buddy's '66 L-36 Convertible that has a fresh set of Avon CR6ZZ tires that I recommended to him to replace the slimy bias ply repro tires. The car has a Regional Top Flight, and he doesn't plan to take it any further. He also has a '67 L-71 Coupe that won a Duntov at the 2018 national convention.
Although I have been recommending these tires for some time, this if the first time I actually drove a C2 with a set. All I can say is WOW! WOW! WOW! It's like driving on fly paper. Even the owner, who I have always accused of driving like an old lady, was driving it very aggressive because the tires are so confidence inspiring.
Then when I took my turn I think I scared the hell out of him weaving between lanes to pass traffic going up a hill with sweeping curves at 15-20 MPH over the speed limit.
Just eyeballing the wheel alignment I think there's more to gain, but right now we're working on the spark advance map.
He complained about variation in idle speed - sometimes 600 and sometimes over 1000. The first thing I checked was the VAC that may be original and it was only semi functional, so we swapped it out with a new B26. Then when I went to check the centrifugal advance is was only 20 degrees instead of the OE 30. I was suspicious that the weights were non-OE, and clearly someone has been inside the distributor doing naughty things. I knew an amateur had been messing with it because there was grease on the centrifugal advance mechanism. NO! NO! NO! GM didn't use any grease and neither should we. At least there was not a whole lot there. Some I've seen looked like it was applied with a soup ladle.
So we cleaned the grease and wiped everything down with WD-40 to provide corrosion resistance.
Next thing I did to try to get close to the 36-40 total WOT range recommended in the GM Power Manuals by advancing the initial from about 4 to 11-12. But then we ran into a "trailer hitching" problem due to what is likely excess advance at low speed light load. He wanted to install the old VAC, but I said no way because it was way out of speed and a boat anchor. Further I said we had to pull and disassemble the distributor to find what atrocities had been committed and either repair the parts or get used serviceable OE parts to get back to something close to the OE spark advance map, and then see how quickly we can get 30-32 degrees centrifugal in since OE is a lazy 5000.
Don't worry buddy, we'll get it dialed in. With optimal alignment and spark advance map this car with be AWESOME and capable of embarrassing modern sports cars.
The Avons are size 205/70R15 rather than 215/70 and are mounted on OE KOs. The reason for the 205s has to do with the actual dimensions of these tire may not conform with Tire and Rim Assc. standards. Of course, they're manufactured in the UK, so...never mind.
The Avon spec sheet lists the inflated OD of the 205/70 at 26.6" but only 0.1" more for the 215/70, but the section width is higher, as it should be and the tread width is listed at a whopping 7.56" versus 6.61" for the 205/70. My own measurement was more like 6.0", but it can be tough to discern what the limit of the tread with are on many tires due to the shape of the shoulders.
A quick clearance check indicated over an inch on all but the right rear witch was barely a finger width away from the fender lips, so the 215s may have been a problem.
These tires have a very smooth sidewalls and you have to get down low to read all the manufacturers and regulation required data. That makes it easy to add a sidewall treatment. On '64 Coupe owner on the CF has raised with letter "Goodyear" appliques and they are mounted on American Torq-Thrust wheels... very period cool.
Duke
Although I have been recommending these tires for some time, this if the first time I actually drove a C2 with a set. All I can say is WOW! WOW! WOW! It's like driving on fly paper. Even the owner, who I have always accused of driving like an old lady, was driving it very aggressive because the tires are so confidence inspiring.
Then when I took my turn I think I scared the hell out of him weaving between lanes to pass traffic going up a hill with sweeping curves at 15-20 MPH over the speed limit.
Just eyeballing the wheel alignment I think there's more to gain, but right now we're working on the spark advance map.
He complained about variation in idle speed - sometimes 600 and sometimes over 1000. The first thing I checked was the VAC that may be original and it was only semi functional, so we swapped it out with a new B26. Then when I went to check the centrifugal advance is was only 20 degrees instead of the OE 30. I was suspicious that the weights were non-OE, and clearly someone has been inside the distributor doing naughty things. I knew an amateur had been messing with it because there was grease on the centrifugal advance mechanism. NO! NO! NO! GM didn't use any grease and neither should we. At least there was not a whole lot there. Some I've seen looked like it was applied with a soup ladle.
So we cleaned the grease and wiped everything down with WD-40 to provide corrosion resistance.
Next thing I did to try to get close to the 36-40 total WOT range recommended in the GM Power Manuals by advancing the initial from about 4 to 11-12. But then we ran into a "trailer hitching" problem due to what is likely excess advance at low speed light load. He wanted to install the old VAC, but I said no way because it was way out of speed and a boat anchor. Further I said we had to pull and disassemble the distributor to find what atrocities had been committed and either repair the parts or get used serviceable OE parts to get back to something close to the OE spark advance map, and then see how quickly we can get 30-32 degrees centrifugal in since OE is a lazy 5000.
Don't worry buddy, we'll get it dialed in. With optimal alignment and spark advance map this car with be AWESOME and capable of embarrassing modern sports cars.
The Avons are size 205/70R15 rather than 215/70 and are mounted on OE KOs. The reason for the 205s has to do with the actual dimensions of these tire may not conform with Tire and Rim Assc. standards. Of course, they're manufactured in the UK, so...never mind.
The Avon spec sheet lists the inflated OD of the 205/70 at 26.6" but only 0.1" more for the 215/70, but the section width is higher, as it should be and the tread width is listed at a whopping 7.56" versus 6.61" for the 205/70. My own measurement was more like 6.0", but it can be tough to discern what the limit of the tread with are on many tires due to the shape of the shoulders.
A quick clearance check indicated over an inch on all but the right rear witch was barely a finger width away from the fender lips, so the 215s may have been a problem.
These tires have a very smooth sidewalls and you have to get down low to read all the manufacturers and regulation required data. That makes it easy to add a sidewall treatment. On '64 Coupe owner on the CF has raised with letter "Goodyear" appliques and they are mounted on American Torq-Thrust wheels... very period cool.
Duke
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