It is easy enough for us to tell you to send your engine back to the builder when it is not running quite right. But that’s not always an option. Of course, there will be times when you absolutely need to send the motor back to the engine builder— catastrophic failure or anything remotely close would probably be one of those times. However, when it comes to tuning the engine at the beginning of the season, or freshening it up midseason, Circle Track is here to help.
This month’s Tech Focus is obviously about engine timing, jetting, rebuilding, and tuning. Circle Track spoke to several engine experts across the country to see what they had to say about engine tuning. We received so many great ideas that we had to narrow it down to the top 15.
Our first four tips are from engine- builder Dannie Cox. Cox is owner and operator of Cox Race Engines out of Ramseur, North Carolina, and has 25 years of experience building engines for short track cars, as well as drag and street performance. With his engines, he has racked up multiple track championships, including one Hooters Pro Cup Championship.
1 Most Saturday night short track engines are equipped with some type of Holley-brand carburetor. Whether it is a two-barrel or a four-barrel, both will need the same attention. In my experience, I have found that racing fuel will make the gasket between the metering block and the carburetor housing swell enough to change the fuel curve the engine sees. That is why you want to replace it and the bowl gasket with new ones.
The first thing you want to do is remove the four bowl screws. This will allow you to remove both the bowl and the metering block. While you have the bowl removed, it is wise to replace the power valve with a new one of the same number. This can be done with a 1-inch wrench.
Blowing through the holes in the metering block with compressed air is always a good idea too. When I have done this, the drivers always say that it really helps the throttle response.
2 Many Saturday night Street Stock cars are required to run stock-appearing valvesprings. These valves come from companies such as K-Motion, Comp Cams, Crower, and Isky and are 1¼ inches in diameter, 110 pounds, with a seat pressure of 250 pounds over the nose, depending on the lift. Heat by high rpm or water temperature is by far the major downfall of these valvesprings. If the engine has been run hot or at high rpm, the springs should be changed at midseason.
To change the valvesprings, remove all of the spark plugs and valve covers, as well as all of the rocker arms. Shoot compressed air into one cylinder at a time. Here at the shop, we use KD’s tool #912 which costs less than $20, to remove the keepers, then the springs. This may sound like a lot of trouble, however, keep in mind with today’s aggressive cams and the maximum amount of spring pressure you are running with a 1¼-inch new spring, you’re probably over-running the valvetrain at around 6,400 rpm.
3 Midseason is also a good time to check the distributor. To do this, you want to put the engine at top-dead center and place a mark for the distributor housing down to the intake. Be sure to make a mental note of the direction of the rotor button for reinstallation. Then you want to remove the distributor and inspect the gear for excessive wear. Next, look carefully at the roll pin that holds the gear. What you want to look for is lost motion, or any wear around the pin.
Moving to the top of the distributor, you want to check for shaft wear or lost motion. Again, be sure to inspect the cap and rotor button for cracks or wear. Once you have inspected these components, remove the rotor button. Next you’ll want to check your weights and springs for excessive wear. If there is any rust, lubricate them with light oil. Be careful to check the weights at maximum extension to be sure that the stop is not worn. If it is worn, it will allow the weights to sling upward. This can lead to an increase in total timing and break rotor buttons. Be sure to replace any parts as needed, reinstall the distributor, and set the timing. (See “Setting Engine Timing”)
4 Many times, an overlooked part on an average Saturday night race car is the battery and charging system. You want to be sure to always check the water level and connections, as well as the general appearance of the battery externally.
Some race cars that run short features, such as 25 to 30 laps, can get by without an alternator. I personally do not recommend this. The argument here is of the additional weight and horsepower loss when you run with an alternator. In my experience, I have seen that a car running without an alternator at less than 12 volts is hurting the power too. If you’re still in doubt, check your battery voltage immediately after the race—always make sure that the engine is grounded to the frame.
Billy Smith of RPM Engine Development in Tempe, Arizona, contributed our next set of tips. RPM Engine Development specializes in oval track, sprint car, and Indy Racing League engines. Stevie Smith, of the World of Outlaws, along with SCRA and USAC driver J.J. Yeley, and Jacques Lazier of the IRL all run RPM engines.
5 One of the first things you want to do is create an accurate baseline tuning setup before you begin any performance tuning. This includes ignition timing, jetting, fuel pressure, and valve lash setting. By doing this, you always have something to go back to if problems arise and you’re not sure what they are.
Along with the baseline setup, you want to make any performance tuning changes at a similar track and under similar conditions that you made your baseline setup. For example, if you created your baseline setup at 1,100 feet of elevation on an 80 degree day with 20 percent humidity, you don’t want to make any major tuning changes for performance at a 6,000-foot elevation track on a 50 degree day with 90 percent humidity and expect the same results.
6 For performance tuning you should have the proper distributor wrench, accurate timing light, vacuum gauge, stop watch, fuel-pressure gauge, spare jets and power valves (if using a carburetor), spark plug reader, fresh spark plugs, and the necessary hand tools. The necessary hand tools would include items such as: a plug wrench, screwdrivers, wrenches, and a pair of heat resistant gloves—among other needed tools.
7 Always remember to set up your spark plug wrench at the shop or garage before you get to the track. If the car is equipped with headers, there is nothing worse than fighting a spark plug socket/wrench that barely fits over the spark plugs and can only be turned 1/8 of a turn at a time.
8 If you are fine-tuning to the point where you are reading the spark plugs, it can only be done accurately by installing a fresh set after the engine has already been warmed up. The best way to go about doing this is to warm the engine first, and then change to a clean set of plugs. After you have changed the plugs, go out and run about three laps. You want to make sure that you shut the engine off clean—meaning shut if off on the back or front straightaway—not in the turn. Once you have done that, pull the plugs and read them. (See “Setting Engine Timing” for more information on plug reading.)
9 If you have an engine that runs on methanol, and you think the engine water temperature is running too cold, never lean the engine out to increase the water temperature. I have seen quite a few new drivers do this and it has always led to burned plugs, valves, and pistons. Many new drivers believe that if the engine is running too cold, then it must be too rich. This is not always the case.
10 Do not go too far astray from the cam manufacturer specs on the valve lash settings. Tighten or loosen them on a mechanical or roller cam only—not with a hydraulic cam—and only a few thousandths at a time. This usually makes a bigger difference than most realize.
11 A good way to check if your cam is too small is to install higher-ratio rocker arms. This is also a cheap way to make the engine think it is running a bigger cam. The best way to go about doing this is to try one side at a time—meaning do the rockers first and then go to the exhaust.
If the engine responds well to the rocker arm ratio change, you may want to try a slightly larger cam on the next rebuild. Be sure to call your cam manufacturer and inform them of the testing you have done, and they can help you make the best selection.
12 Always begin the season with fresh parts—carburetor, engine components, fuel system, and ignition system. Everything should be fresh and ready to go by the first race of the season. Having fresh parts in the beginning of the season saves you from having to send components out to be rebuilt midseason when you do not have the time to have it done properly.
James Lyle of Lyle Speed Automotive Center in Maysville, Georgia, has come up with a midseason check list and tune-up that will help keep your racer running right the whole season.
13 During the midseason, you want to be sure to do an engine compression check; making sure the engine cylinder pressures are all about equal in reading.
14 Check your valvespring pressure. You want to make sure the spring pressure is still within 15 percent of installation pressure, and that you do not have more than 10 percent separation form spring to spring. If you have more than 10 percent separation in the springs, replace them with springs of the correct installed height.
If the spring pressure is correct when you check it, re-adjust the valves to cam specifications. Be sure to check that the valve setting is not too loose or too tight. Either instance could lead to engine failure. If you do find the valve setting is too loose or tight, find out what the cause is.
Once you’ve completed the task, replace the valve cover, remember not to overtighten the bolts, and do not use any silicone as gasket sealer on the gasket surface.
15 When you are checking your distributor components for wear, also check all spark wires for hot spots and cracks in the insulation. Replace these as needed. You also want to replace your spark plugs with plugs of the correct heat range and spark gap.
Other Tips to Remember
• Only change one thing at a time.
• Tune your engine from your own experiences. What other guys are doing is not necessarily what is correct for your car.
• Don’t try any major performance tuning during the race. There is never enough time. Performance tuning and creating a baseline should be done during the off season or a practice session.
