For most of us at least, when it comes to ignition systems, as long as we are getting spark in all eight cylinders and the engine isn't popping and missing, we're usually pretty happy. Maybe we'll hook up a timing light every now and then just to make sure the engine timing is still at least close where the engine builder said to put it, but that is probably about it.
Honestly, the problem with ignition systems is it can be tough to tell what effect any changes you make will have on your engine's performance. And as a result, most racers feel that their time is better served dialing in the perfect suspension set up or experimenting with spring pressures. As long as the engine is still running when the checkered flag flies, that's probably good enough as far as the ignition system goes.
Of course, we're not saying that you need to be changing the ignition advance between the hot laps and the feature. Once the ignition is operating at peak efficiency, it should be left alone. But there are some interesting things going on with the leading race engine builders when it comes to optimizing ignition systems that you can benefit from.
Recently, we had the opportunity to sit in on an R&D session at race engine builder Keith Dorton's Automotive Specialists facilities. Dorton is so serious about maximizing ignition system efficiency that he has invested in equipment that allows him to track the ignition timing in all eight cylinders individually during the course of a kind of pull. This allows him to see how the timing varies by as little as a tenth of one degree both as the rpm changes and from one cylinder to the next.
So, for example, if one cylinder is firing earlier than the rest, that cylinder can go into detonation. As a result, the engine builder may pull back on the ignition timing of the engine as a whole instead of looking at that particular cylinder. As a result, the racer misses out on potential horsepower because of a Band-Aid fix.
Another scenario happens when ignition timing fluctuates across the rpm range. When this happens, you may set your timing correctly for a particular rpm and think that you are good to go, but the timing can actually vary all throughout much of the rest of the rpm range.
Dorton's ignition timing equipment is still fairly new, and there is lots that we want to dig into and test in the future. But for now, we just wanted to take a look at how the consistency of ignition timing can vary with different types of technologies. For his own testing, Dorton had gathered a wide range of distributors from Crane as well as two different ignition boxes. The longtime engine builder has done some very extensive testing and the results should show up in his engines in the very near future, but he did allow us to share some of his most basic findings--which were still pretty advanced by our standards.
Dorton began by choosing three Crane ignitions for testing. On the high end were two of Crane's Oval Track Pro Race distributors. These units are the ones Dorton normally uses in his Pro Cup and NASCAR touring engines. They feature optical triggers which Crane says is the most accurate method currently available for routing the spark to the correct cylinders at the appropriate time. One distributor used a standard electrical wiring system while the second was fitted up with a high-end fiber-optic trigger interface which is supposed to be more accurate in a high-heat environment like a race car.
The Pro Race distributors utilize the latest in ignition technology and are proven as capable performers on the racetrack, but as such, they are also priced accordingly. Crane's Pro Race units can vary anywhere from $850 to $1,500 depending on the application and how you have one tricked out. So, for a more appropriate option for Saturday night racers we also grabbed a Pro Curve Billet unit as well. The Pro Curve Billet also features an optical trigger, but it can be purchased for less than $400.
In addition, we tested a Crane analog ignition box versus a newer digital box to see if digital technology has a real advantage or if it's all just marketing hype. And finally, Dorton also went to the trouble to test oversized distributor gears versus the standard units to see if removing some of the backlash can help improve the ignition timing pattern.
The test engine is Dorton's Circle Track Spec engine that is currently racing in a few different series. At 383 cubic inches, the engine is capable of 600 horsepower and except for a hydraulic roller cam, uses many of the same components found in most upper level Saturday night racing engines. The tests all took place over the course of a single day, and no changes were made to the engine during the tests except to swap out distributors and confirm proper timing.
Low vs. High End Distributors
It's a lie to call Crane's Pro Curve Billet distributor "low end. This is a high-quality distributor that Dorton says he has no qualms racing in many different classes. But for the purpose of our tests, this is the lower end, or more affordable distributor.
Then, of course, we paired it against Crane's top-of-the-line distributors. Interestingly, it did quite well, as you can see in the chart titled Distributor Comparison below. The timing was set at 36 degrees BTDC with the engine at 5,000 rpm, and the dyno pulls were from 4,000 to 8,000 rpm. Compared to either of the Pro Race distributors, the Pro Curve Billet had the most variation of timing. The lowest mark we had was 30.4 degrees and the highest was 37.4, so the timing varied across the pull by as much as 7 degrees from the highest to the lowest, but the average timing was 34.288 degrees. So, overall, this distributor lost a little timing.
In comparison, the Pro Race distributors performed almost identically. The standard electrical wiring unit had an average of 35.85 while the fiber-optic Pro Race showed an average timing mark of 36.217. We also charted the percentage each distributor was off from the 36-degree target, and while the standard Pro Race shows up a little better in that regard, we suggest you don't put too much into it. The difference is tenths of one percent, which is negligible.
So while the Pro Curve Billet expectedly didn't hold the ignition timing across all eight cylinders as precisely as the Pro Race units, we don't think this shows the Pro Curve unit isn't a quality race piece. On the dyno, the power curves were practically identical. But Dorton cautioned us to remember that these are identical conditions with brand-new distributors. Racing doesn't take place in a dyno room. And Dorton says that for professional racers he trusts the ultra-high construction quality of the Pro Race distributors to hold their high tolerances despite heat, vibration, shocks, and general abuse that they will see in a race car over a season or more of racing.
Distributor Gear Size
One of the variables that almost always involved in the ignition is the "slack in the system. How much play is in the timing chain or belt? The amount of backlash in between the cam and distributor gears also adds a certain amount of slack or play in the timing. Some backlash is necessary to keep the gears from grinding themselves apart, but just how much is optimal?
To find out, Dorton tested a variety of different sizes of distributor gears. Check out the chart titled Distributor Gear comparison on this page. This is unusual and a step many engine builders aren't willing to take the time to make. But Dorton says in the right situations, adjusting the amount of backlash in the gear mesh by swapping out an oversized cam gear can be helpful to both an engine's health and performance.
Although Dorton tested with a variety of gear sizes in a variety of different situations, we're posting the results from just two: a standard distributor gear and one that is 0.020-inch oversized (the largest Dorton tried). When testing with an oversized distributor gear, you do need to make sure you still have some free play or backlash between the gears to ensure they don't grind themselves up. Also, check for backlash every 90 degrees to make sure you don't miss a high spot that could wind up damaging the distributor and possibly the entire engine.
Our test subject is the standard Pro Race distributor. The variance didn't change much, which seems to be a function of the distributor or ignition box, but the timing didn't drop as much which makes sense considering we took away some free play in the gears. This seemed to be a consistent result no matter which distributor we tested.
Analog vs. Digital
After testing several distributors and swapping out lots of brass gears, we took a look at the ignition boxes for a change. See the results on this page. The baseline is Crane's HI-6N high-output multi spark box that's approved for NASCAR use. The box is a proven winner, and lots of top race teams swear by it. But that's an old-school analog box, so we're testing it against the next generation, Crane's HI-6R fully digital race ignition.
Honestly, we're not sure what to make of this test. We didn't catch it before we pulled the engine off the dyno, so we didn't have an opportunity to back it up with some more testing (yet). But the digital box seemed to be high throughout the pull. Dorton set the timing at 36 degrees at 5,000 rpm, but during the pull we show the ignition timing for the number one cylinder at 37.3 degrees BTDC at 5,000 rpm. The mostly likely answer is the distributor moved a bit while tightening the hold-down.
The reason why we haven't thrown out this test is the digital box shows remarkable consistency throughout the rpm range despite the timing being set too high. On all the other tests we had a variance from the high to low marks of at least 4.5 degrees. But for the HI-6R box the variance was just 2.5 degrees. And while the percentage change from the target of 36 degrees is high at 5.39 percent, if you compare the 37.941 degree average timing compared to the real timing of 37.3 degrees we saw in the number one cylinder during the test, that makes the percentage change just 1.71 percent. This one definitely deserves to be looked into further, which you can be we will. Stay tuned.
Distributor Comparison
Timing set at 36 degrees at 5,000 rpm - Dyno Pull from 4,000 to 8,000 rpm
Low High Variance Average % Change Crane Pro Curve Billet 30.4 37.4 7 34.288 4.99 Crane Pro Race 32.7 37.2 4.5 35.85 0.42 Crane Pro Race Optical 34 39 5.1 36.217 0.6
Distributor Gear Comparison
Timing set at 36 degrees at 5,000 rpm - Dyno Pull from 4,000 to 8,000 rpm
Low High Variance Average % Change Standard Brass Gear 32.7 37.2 4.5 35.85 0.42 Brass Gear +0.020 Inch Oversize 33.6 38.7 5.1 36.196 0.54
Analog vs Digital Ignition Comparison
Timing set at 36 degrees at 5,000 rpm • Dyno Pull from 4,000 to 8,000 rpm
Low High Variance Average % Change Race Pro w/ HI-6N (Analog) 32.7 37.2 4.5 35.85 0.42 Race Pro w/ HI-6R (Digital) 36.2 38.7 2.5 37.941 5.39
Crane Pro Curve Billet Distributor Test
Engine Configuration: V-8 - Cylinder Configuration: V-8
Cylinder Ordering: Left Bank - 1 - 3 - 5 - 7 - Right Bank - 2 - 4 - 6 - 8
Firing Order: 1 - 8 - 4 - 3 - 6 - 5 - 7 - 2
Cylinder Rotation: 0.0 - 90.0 - 180.0 - 270.0 - 360.0 - 450.0 - 540.0 - 630.0
Cylinder #1 Timing: 36.0
RPM Cyl #1 Cyl #8 Cyl #4 Cyl #3 Cyl #6 4,000 35 36 35.4 35.2 35.4 4,100 36.1 37.1 36.3 35.6 35.7 4,200 35.6 37.1 36.6 35.6 35.6 4,300 33.5 35.6 35.5 34.7 34.6 4,400 33.4 34.4 34.2 33.8 33.5 4,500 34.1 34.4 33.4 33.1 32.8 4,600 35 35 33.5 33.3 33.2 4,700 34.7 35.4 34.2 34.1 33.8 4,800 34.4 35.5 34.5 34.5 34.4 4,900 34.6 35.4 34.6 34.4 34 5,000 34.8 35.4 34.7 34.1 33.7 5,100 34.7 35.4 34.7 33.7 33.8 5,200 35.3 35.3 34.3 33.5 34.4 5,300 35.4 35.2 34.4 33.6 34.4 5,400 34.8 35.8 34.4 33.5 35 5,500 34.7 35.8 34.7 33.7 34.8 5,600 34.7 35.1 34.5 34 34.5 5,700 35.1 34.4 34.4 33.6 34.5 5,800 36 34.1 34.8 33.3 34.9 5,900 35.5 34 35.1 33 34.6 6,000 35.8 33.5 35.4 33 34.6 6,100 37 32.9 36 33.3 34.8 6,200 37 32.2 36 33 34.3 6,300 37.3 32.2 36.2 33 34.2 6,400 37.7 31.8 36.7 32.9 34.3 6,500 36.3 31.6 37.8 32.1 34.7 6,600 33.9 32.7 37 31.2 35.8 6,700 32.5 34.9 34.6 32.3 36.6 6,800 31.9 35.3 33.9 33 36.2 6,900 30.7 35.8 33 33.2 36.1 7,000 31 35.5 33 33.3 35 7,100 33 34.9 33.8 33.6 33.8 7,200 33 35 33.7 33.8 33.8 7,300 32.6 34.8 33.1 33.7 33.5 7,400 32.4 35 32.9 33.3 33.7 7,500 31.7 34.3 33.1 32.6 33.5 7,600 31.1 33.7 33.4 32.2 33.1 7,700 31.1 33.9 33.6 32 33 7,800 31.3 34.2 33.4 31.8 33.2 7,900 31.5 34.1 33.4 31.9 33.2 8,000 31.6 34.2 34 31.7 33.5
