Mopar Action On-line – Tech Questions
T.J. Reome, Rochester, NY
I have a ’69 Charger R/T with a 440 six pack. The engine has been bored .030″ oversize, and has a MP .474″ lift Purple-shaft cam, electronic ignition, and other MP parts. The car is a 4-speed, with a Dana 60 rear – 3.54 gears.
My question: would the car be quicker (1/4-mile) with an automatic, because of the slow operation of the outboard carbs? I have a new Hurst Competition-Plus shifter and new linkage. I have also tried different diaphragms in the carbs. I have also installed a new clutch pressure-plate and release bearing.
I can’t seem to shift fast enough for smooth operation, even though I consider myself a very good shifter. I’ve even tried shorter shift levers for a quicker “throw”. Any comments or info would be helpful and appreciated.
You’d probably have a more consistent car with an automatic, but I doubt you’d lower you e.t.s any, if at all. Road tests back in ’69 and ’70 always reported better times for 4-gear manual cars.
I don’t think you should complain about the “slow opening” of the end carbs. After all, they’re just doing what they were designed to do, namely, prevent bogging by opening progressively to admit only as much air as the engine demands at a particular load. If you would like to experiment, though, with a faster-opening configuration, go ahead. The way to do this, though, isn’t by changing the diaphragms, it’s by changing the springs. A kit of them is readily available from Holly dealers. The stock springs are probably a-ok for automatics; if you are able to launch your 4-speed car really hard (slicks) you could conceivably find a moderate gain here.
As far as the hard or slow shifting, there are several things to look at. The first, and most obvious, is to be sure that the clutch is fully releasing, i.e., under “race” conditions (engine torqued over in the mounts) is there enough travel of the clutch fork? Is the torque shaft intact (even if it is, consider reinforcing it.) Is the firewall, pedal, or bracketry deflecting under load?
Assuming that you have the stock-type ’69 clutch setup with the 11-inch clutch, I’d seriously consider going to a 10.5″ setup. While, at first glance, this may sound a bit silly, here’s my reasoning: When you attempt a high-rev shift, what the synchronizers are trying to do is to almost instantly slow down the transmission’s main drive pinion (“input shaft”) down to the correct r.p.m. for the gear you’re about to shift into. What’s connected to this pinion? Right, the clutch disc! Think, now, of how much less flywheel effect a 10.5″ disc has than an 11-incher. It substantially reduces the synchronizer loads. For a while, back in the ’60s, I raced a 65 Valiant with a swapped-in 340. I used a 273 clutch setup, in a 9.25″ size, and it was the easiest-shifting 4-gear Mopar ever!
Other things to look at are: the condition of the synchronizers themselves, the “freeness” of the clutch disc to “float” on the aforementioned input pinion’s splines, and the shifter adjustment. If you are really serious about drag racing, the ultimate fix is to convert the transmission into an unsynchronized “crash box” by deleting the synchro’s stop rings and grinding away most of the engagement teeth. In Chrysler parlance, this is known as “slick shifting” a gearbox.
Don’t even think about driving on the street this way, though!