1970 L-46 1/4 Drag Times

[Mike F.]

I took the car to the drag strip tonight and sad to say was a bit disappointed. The car is a 1970 Coupe, L-46, M-21, 3.70:1, with Chapter & Regional Top Flights. I ran the car on the strip with no modifications; it was setup the same way as I use it for daily driving and judging. (Bias-ply tires, TCS operative, etc, etc.)

The last time that I drag raced was about 20 years ago, so I am familiar with what is “supposed to happen”. Back then I had a 1989 Formula 350 A4 that ran 14:45@97mph and a 1991 Corvette Coupe A4 that ran 13:80@100mph.
Tonight’s three runs were the first time with a manual 4spd, so my launching and speed shifting is probably nothing to write home about. I have to say that either I or the car is consistently slow. Not sure what went wrong, but the 1970 sure feels stronger than the 1991 I use to have.

In the first run (15:12@94mph) I had shifted into 4^th just before crossing the line. In the second and third runs (15:11@96mph/15:10@96mph) I left the car in 3^rd , crossing the line at 6000rpm +/-.

Actual L-46 Engine dyno – 341hp/387tq (Gross)
Approx. SAE Net, 341 x .89 (-11% loss) = 303hp
Actual L-46 Chassis dyno – 244hp/305tq (RWHP)

[Bill C.]

Re: 1970 L-46 1/4 Drag Times

Reaction time at the tree.
Needs to get close to a double zero or better.

The 60' times are to slow.
I was always told that the first 60' make a huge difference in the overall 1/4 et

[Mike T.]

Re: 1970 L-46 1/4 Drag Times

Mike - With a final speed in the mid 90's I would have expected an ET more in the mid 14's. What rpm do you launch at and did you notice a lot of tire spin? You know if it's been a while since you were on the track, it could take a few more runs to get familiar with that car. I had my 66 smallblock Coupe out at Infineon Raceway back in 2008 for the first time since we bought it in '89. Here I was expected to see some decent numbers but with the 215-65 tires I had way too heavy a right foot and spun all through first gear. Still was a lot of fun though.

[Bill L.]

Re: 1970 L-46 1/4 Drag Times

I took the car to the drag strip tonight and sad to say was a bit disappointed. The car is a 1970 Coupe, L-46, M-21, 3.70:1, with Chapter & Regional Top Flights. I ran the car on the strip with no modifications; it was setup the same way as I use it for daily driving and judging. (Bias-ply tires, TCS operative, etc, etc.)

The last time that I drag raced was about 20 years ago, so I am familiar with what is “supposed to happen”. Back then I had a 1989 Formula 350 A4 that ran 14:45@97mph and a 1991 Corvette Coupe A4 that ran 13:80@100mph.
Tonight’s three runs were the first time with a manual 4spd, so my launching and speed shifting is probably nothing to write home about. I have to say that either I or the car is consistently slow. Not sure what went wrong, but the 1970 sure feels stronger than the 1991 I use to have.

In the first run (15:12@94mph) I had shifted into 4^th just before crossing the line. In the second and third runs (15:11@96mph/15:10@96mph) I left the car in 3^rd , crossing the line at 6000rpm +/-.

L-46 Engine dyno – 341hp/387tq
L-46 Chassis dyno – 244hp/305tq

Should be running mid 14s. Really good tires and perfect reaction time may get down to the low 14s. You gotta drive it like you hate it to get the best times. You know the old saying. Drive it like you stole it.

I know I could not beat on my L46 to get the best time so I am just saying Non matching numbers and it would be another story.

Bill

[Duke W.]

Re: 1970 L-46 1/4 Drag Times

The MPH is good and in line with what a production L-46 could do back in the day, but the ET is low due to the terrible 60' time, which is in line with my 2700 pound, torque-shy, two-liter Cosworth Vega that runs 17-flat at 83 MPH with an easy 2000-rev launch and granny shifting.

Getting a good ET is all about the launch, which is a function of traction and driver technique, and it takes a lot of practice to get it dialed in. The MPH number is indicative of average power. A lot of guys launch too aggressively and get too much wheelspin. The best launch just "hazes" the tires and is actually easier on the drivetrain.

Your reaction time is commendably good. I fact I think the 0.3241 would get a red light at some strips since it's less than 0.500.

If you haven't optimized the WOT spark advance map it could be better, so a sub 15 ET and another couple of MPH is certainly within reach.

If you want to get to the line quicker than the guy next to you, stage deep. If you want the best ET and MPH stage shallow, and I think with a little practice you can get the 60' time down to below 2.3, which will get you into the 14s.

I think the few guys that take their vintage Corvettes to the strip are usually disappointed with the performance, which may be due to the car, tires, or lack of drag racing experience or some combination of all. It's disheatening to know that a off-the-showroon V-6 mid-size sedan (like an Accord or Camry) can turn a sub-15 ET in the mid nineties.

I was browsing through the new Car and Driver at the library, yesterday and was quite taken with the new US-spec Miata - a sub six second 0-60 and sub-15 second quarter mile from the two-liter direct injection I-4 rated at 155 net HP, and it gets terrific fuel economy. The most amazing spec is that the curb weight is just over 2300 pounds.

I have to tip my hat to Mazda for sticking to the traditional sports car formula of low weight. GM has also done a great job of keeping modern Corvettes nearly as light as a well equipped sixties vintage small block, which is certainly not the case for Porsche.

BTW, great looking car. A buddy had a white/blue '70 L-46/M21/3.70 back in the day. We "tuned" it with '65 SHP/FI distributor weights/springs and different main jets and modified the Q-jet linkage to open the secondaries sooner. The carb advice actually came from an article in Corvette News! We never faced off at a drag strip, but in several highway "roll-ons" it was a dead heat between his car and my 340 HP SWC.

Maybe it would be faster with a dark blue racing stripe down the middle.

Thanks for posting the time slip.

Duke

[Duke W.]

Re: 1970 L-46 1/4 Drag Times

"Really good tires and perfect reaction time may get down to the low 14s."

Reaction time has nothing to do with ET. It's just the time from the green light to when the front tires break the light that starts the ET clock.
Take a guy in the left lane that has a 0.6 reaction time with a 14.5 ET. The right lane guy turns a 14.4, but has a 0.8 reaction time.

The left lane is the winner because he crossed the finish line first by 0.1 second.

The winner is the guy who gets to the finish line first, not the lowest ET, so reaction time is only critical in a heads-up race and is strictly a human factor, totally independent of vehicle performance.

Duke

[Bill M.]

Re: 1970 L-46 1/4 Drag Times

Perfect reaction time used to be 0.500. It is now 0.000. A red light will post as a negative reaction time.

[Stephen B.]

Re: 1970 L-46 1/4 Drag Times

Years ago, I drag raced my 1970 350/350 M21 3:55 posi car. It had a 280 comp. cam and 10.25 to 1 compression pistons, but otherwise stock. I turned 96 mph at 14.50 ET. So your times look pretty normal.

[Duke W.]

Re: 1970 L-46 1/4 Drag Times

Perfect reaction time used to be 0.500. It is now 0.000. A red light will post as a negative reaction time.

That's interesting... clearly no human being is capable of zero reaction time. The last time I ran a timed quarter-mile was when a dragstrip was set up on Terminal Island in the LA harbor area for a couple of years nearly 25 years ago. I recall they had a "pro tree", and any reaction time less than 0.500 was a red light.

One must have to anticipate the light to react in much less than half a second, so that adds another variable to the equation. I recall that launching on sight of the last yellow would give a good reaction time, but not less than half a second. Maybe now you launch at the second from last yellow...

But again, reaction time is totally independent of vehicle performance. Given two vehicles of equal performance, the driver with the best reaction time and launch technique will always win. That's the source of the old drag racing adage: You win (or lose) the race at the starting line!

Duke

[Bill L.]

Re: 1970 L-46 1/4 Drag Times

"Really good tires and perfect reaction time may get down to the low 14s."

Reaction time has nothing to do with ET. It's just the time from the green light to when the front tires break the light that starts the ET clock.
Take a guy in the left lane that has a 0.6 reaction time with a 14.5 ET. The right lane guy turns a 14.4, but has a 0.8 reaction time.

The left lane is the winner because he crossed the finish line first by 0.1 second.

The winner is the guy who gets to the finish line first, not the lowest ET, so reaction time is only critical in a heads-up race and is strictly a human factor, totally independent of vehicle performance.

Duke

Oops! Too big a hurry. Perfect launch. Thanks for keeping me in line Duke.

Bill

[Bill M.]

Re: 1970 L-46 1/4 Drag Times

That's interesting... clearly no human being is capable of zero reaction time. The last time I ran a timed quarter-mile was when a dragstrip was set up on Terminal Island in the LA harbor area for a couple of years nearly 25 years ago. I recall they had a "pro tree", and any reaction time less than 0.500 was a red light.

One must have to anticipate the light to react in much less than half a second, so that adds another variable to the equation. I recall that launching on sight of the last yellow would give a good reaction time, but not less than half a second. Maybe now you launch at the second from last yellow...

But again, reaction time is totally independent of vehicle performance. Given two vehicles of equal performance, the driver with the best reaction time and launch technique will always win. That's the source of the old drag racing adage: You win (or lose) the race at the starting line!

Duke

You still go on the last yellow. I assume they used to use 0.500 as a perfect light to avoid negative numbers. It was just an added constant.

I did just see a pro race where both drivers cut a 0.000 light. The announcer said that was the first time that ever happened in the pro ranks. The pro driver reaction times are amazing (about 0.050 typical) and they seldom red light. Some of our local drivers get close to 0.100 consistently; I am not one of them....yet.

[Mark E.]

Re: 1970 L-46 1/4 Drag Times

As already said, since you own the car you were probably more gentle with the clutch and synchros than what is done to race cars or street cars when tested by magazines.

My experience is consistent with yours. I owned a 1973 L82 M20/3:55 a few years ago that was stock except for headers, AIR removed, ignition re-curved, no TCS, and its original Q-Jet tuned for the street. It ran a best of 14.9 @ 95mph with me being gentle during launch and shifts. The L82 is basically a low compression version of your engine.

What does surprise me is your L98 Vette running 13:80@100mph. I had a 1987, 240HP L98 automatic that ran a consistent 15.0 @ 90mph. Your performance is closer to '92-'96 LT1 territory.

Separate data point: In the mid-70s I had a stock 1969 GTO 400/366HP RAIII with M20, AC. I'm guessing it had gears in the 3.23 - 3.55 range. Its best was also 15.0 @ 90mph while driving conservatively with street tires. I remember trying several runs to break into the 14s with no luck.

I never thought before how closely matched these three cars (L82, L98, RAIII) were.

[Mark E.]

Re: 1970 L-46 1/4 Drag Times

If you Google "1970 Corvette Road Test" you'll find some vintage magazine articles showing:

- 1970 LT1 with 4:11 gears: 14.36 ET @ 101 mph (Motor Trend)
- 1970 LS5 Auto with 3.08 gears: 15.0 ET @ 93 mph (R&T)

So in comparison your L-46 is doing fine.

[Mike E.]

Re: 1970 L-46 1/4 Drag Times

Our memories of how fast our vintage Corvette are, is somewhat tainted when now you see a modern base 6 cylinder Camaro turning in 1/4 mile times of 14.3 @ 98 mph.


Mike

[Mike F.]

Re: 1970 L-46 1/4 Drag Times

What does surprise me is your L98 Vette running 13:80@100mph. I had a 1987, 240HP L98 automatic that ran a consistent 15.0 @ 90mph. Your performance is closer to '92-'96 LT1 territory.

Yep, it was one quick L98, 13.80 being the fastest. It was consistent in the 13.90's.