For our testing we went to the Lakeland Drag Strip to make some shake-down passes. We're fortunate here in Florida to have several area drag strips at our disposal for racing and testing. every week a drag strip in the United States shuts down permanently, and only half as many new tracks open. If we don't support our local tracks we may eventually be forced to pay $750 a day for dyno time to tune our engines instead of the $12 it cost us to make as many passes as we wanted on a Thursday night at our local track. we encourage our readers to head to their local drag strip and have some fun. Believe it or not, drag racing, not sitting in a parking lot with lawn chairs, is what these cars were designed to do.
On our first pass down Lakeland's eighth-mile we wanted to seat the clutches and bands in our fresh transmission and make sure everything felt good and worked correctly, so we limited our right foot's travel to about one-third throttle. The resulting 6.90-second elapsed time had us encouraged that this combination had potential to achieve our goal of low nines in the quarter. With everything working correctly, we made a full throttle, just over half-track pass that resulted in a 6.26-second elapsed time and a stout 1.32-second wheelstanding 60 foot time. Back in the pits we pulled a spark plug and saw that it was nearly snow white, so a jetting change was in order. When jetting we step up or down in increments of two until we are close, then fine-tune by making jetting changes of one size at a time. With 92 jets in both primary and secondary metering blocks, we made our first full pass running a 6.04-second elapsed time at 114 mph. Technically, this equates to a 9.48-second quarter-mile, so we did reach our goal, but we knew we had more in it. By richening the jetting further, the car responded with quicker elapsed times and higher mph until stabilizing at an e.t. of 6.00 at 115.5 mph with 97 jets in both ends of our King Demon. We then bumped the ignition timing up four degrees to 40-degrees total advance and ran our quickest elapsed time of our test night at 5.98 seconds at 116.8 mph! This equates to a quarter-mile e.t. of 9.38 seconds, putting us solidly in the low nines. Always remember that weather changes will change the power your engine makes. Cooler temperatures and higher barometric pressure will improve the output of your engine; weather needs to be tracked and considered when tuning. Our weather stayed consistent throughout our test session, so we were sure our improvements were due to our tuning changes and not improving atmospheric conditions. Our test time was running out for the night, but we were comfortable our tune-up was now much closer than when we started, and reading the spark plugs verified that our mixture was now in the safe zone of enrichment, so we decided to call it a night.
Unless you have a provision...
Unless you have a provision for an oxygen sensor or other means to determine air/fuel ratio, taking plug readings prior to making jet changes is your best bet. After a half pass showed snow white plugs indicating our mixture was on the lean side, we installed number 92 jets front and rear to continue with our tuning.
It's important to note that...
It's important to note that since our application is drag racing only and will only see wide-open throttle operation, the power valve provisions of our King Demon carburetor have been blocked off as shown here. This will necessitate larger main jetting to give our engine the correct fuel/air ratio. For our baseline, we chose number 90 jets and will read the plugs and time slips to make adjustments.
Each time we richened the...
Each time we richened the mixture by increasing jet size, we saw an improvement in e.t. and mph. The e.t. on a timeslip tells how well the car is working, but the mph is a direct relation to horsepower, so we pay more attention to mph when jetting our carburetor. When we reached our performance plateau at number 97 jets, we stopped jetting and moved on to other areas of tuning.