Apples and Oranges ;-)

[67HEAVEN]

You may have wondered about the 1/4 mile times for those midyear big-blocks, and why the Special High Performance and the Heavy-Duty engines ran anywhere between 13.5 and 12.8 second 1/4s.

Given their potential, perhaps you've thought, "Shouldn't those times be a bit better?". Well, haven't you?

Consider:

1965-67 factory tire size: 7.75 x 15"
1965-67 factory tire design: bias ply (non-radial) sort of like a rubber band
1965-67 factory tread width: 4.7" for Firestone Deluxe Champion

2013 factory Z06 tire size: P325/30ZR19 (rears)
2013 factory tire design: Z-rated high speed, sticky high-performance tire
2013 factory tread width: 12.8"

Not only are the new tires sticky radials, they're 2.75 times as wide as the '65-'67 tires.

According to TireRack.com, here's the 1960s Euro-metric size equivalent to North America's 7.75 x 15.....195/82R15. YIKES!

So, with all that in mind, how about we install some 7.75 x 15's on a new Z06 and see how it does?

Okay, I'm done until the next snow storm.

 

[CCO]

Quite right Bob -- those small skins must have held them back big time.

Good point. Keep up the "cabin fever" ..... Lots of food for thought comin from your cabin.

C.

 

[Case75]

Have you ever put 67HEAVEN up against the clock Bob with the tires you have on it now? Be interesting to know what it does now.

 

[Keith Tedford]

By '69, there were actually four problems which were easily fixed. First there were the little F70 bias ply tires, then for emissions there was the very slow advance curve with retarded timing and a way lean condition on the primary side of the carb. The 4346 Holley on our COPO Chevelle had #68 primary jets when #72 or #73 were more in the ball park for performance. The advance curve wasn't fully in until up around 5K rpm. It all added up to a pretty lazy engine. The exhaust system wasn't the greatest either. With our Chevelle, headers, jetting and the advance curved properly made a huge difference. At first the F70s were actually not bad traction. After getting things working right, I immediately had to go looking for the biggest rubber I could find and they didn't work very well either. There weren't a lot of decent street tires in 1969. Still, these cars probably wouldn't do much better than mid 12s without a better cam. You have to remember that this is 50 year old technology and these cars can still work pretty well. There would be something seriously wrong if the manufacturers hadn't learned a lot in all those years. A friend has a stock looking '69 Chevelle except that it has a very healthy 496 stroker motor under the hood. He easily showed tail lights to a newer Z06 427 Corvette. It never pays to get cocky. You never know what your are dealing with. I guess it has always been that way.
This was my car not long after getting the tuning done and the bigger tires.

 

[buckhorn76]

weight transfer and suspension modifications would also affect 1/4 mi times, the big block cars with all their torque were prone to squatting on the launch. even a spring wedge on the right rear and 90/10 shocks up front would make you run quicker. i'm talking solid axle cars obviously.

 

[67HEAVEN]

Have you ever put 67HEAVEN up against the clock Bob with the tires you have on it now? Be interesting to know what it does now.

Case75,

No I haven't. Without half-shaft loops, it's a sure way to come home on a flatbed.

With a modified 502, a 5-speed Richmond and completely upgraded suspension, it wouldn't be a test relevant to the discussion anyway.

 

[Riley P]

I've always wondered what the old tires were equivalent to in today's tires and had that exact thought as well. I would love it if someone put an old style bias ply tires on a new Corvette then saw what it could do in the 1/4.

 

[buckhorn76]

you would never find rims that would work.

 

[Riley P]

Yes, good point. You would have to remove the discs and calipers.....

 

[67HEAVEN]

Yes, good point. You would have to remove the discs and calipers.....

Wouldn't matter. It wouldn't get going fast enough to be a worry without rear brakes.