Originally Posted by northiam
My combo is:
238 cam @.050
Runs 12.9ET with flat 2sec 60’s on part throttle launch due to lack of traction.
Question: Would changing from 3.5 to 3.9 or so improve my ET? Or would I lose top end speed and run out of revs? I change at 6000rpm.
Would tyres or gears be the better investment?
The best thing for your combination would be a 1.60 sixty-foot time. You need to improve traction first and foremost if you're looking to improve your ET. Add a pair of Caltracs or SOMETHING to get it under control. You'll be really, really
glad that you did. You can easily drop that ET down to the mid to lower 12s with improved traction.
Once you make more traction than your engine can overpower, then start thinking about gear combinations that will increase your launch (lower your sixty). Good traction may require different tires, perhaps even slicks. When you start breaking parts, it is time to go on a diet (car and, at least in my case, driver!).
Lose 100# in the car. The preferred way is re/moving weight from in front of the COG (center of gravity) point. Lower unsprung weight wherever possible. If relocating weight, move it behind the rear axle or directly over the rear axle if possible.
Be sure to make your safety checks along the way to ensure that you're safe, eg: driveshaft loop, SFI-rated axles...and then borrow a set of slicks from a mate and have a blast down the track.
If you're short of funds, play around with your launch so that your tires do not slip at all as you're accelerating away. Use less and less throttle until traction is on that precarious edge of going away. At that point, you can't accelerate any quicker. If your tires are slipping "now," you could be accelerating more quickly with proper driving of it so that there is no traction loss.
If you still can not gain traction, change to a higher gear ratio (lower numerical value). Try moving from a 3.50 to a 3.23 or a 3.00. You'll get better fuel economy and perhaps not overpower the tires so easily. If you can afford a gear change, you can afford Caltracs (assuming you have leaf springs). Caltracs really work and will help your car hook. I ran 11.02 in a 2950# car with Caltracs, adjustable Rancho shocks and BFG drag radials. The car did have a full cage and subframe connectors.