5.0 Mustang & Super FordsHow To Engine
MSD Programmable Digital-7 Ignition - Uncle Tester
We Watch The Lightbulb Go Off As Uncle Robin Lawrence Straps His Nine-Second Real Street Combo On The Dyno
If you've ever met Uncle Robin, you know he likes to stir the pot a bit. We're still trying to figure out how he gets any work done while trolling the Internet message boards all day, but then again he has at least two cell phones on him for "work" purposes. After following the buildup of Robin's new Real Street combo, we thought we'd turn the interrogation lamps his way and ask him what his new combo would do-which should make for even more interesting Internet fodder.
In our last tête-à-tête with Robin Lawrence, he talked about tuning his Real Street engine on the Stuska engine dyno ("Real Appeal," Aug. '03, p. 111). He didn't go into great detail on the actual hands-on tuning as he really utilizes the engine dyno only in a developmental function. He can see things there that are impossible to check after the engine is in the car, such as fuel flow. It's also much easier to make changes while the engine is on a dyno.
But an engine dyno does have its limitations. For example, unless you have a huge dyno room, it's difficult to run the full exhaust system. Robin tells us airflow, fuel systems, and cooling systems can create subtle differences in power. With the engine in the car, using the same fuel lines, radiator, cooling fan, full exhaust, and so on as it would going down the track, final tuning can be made much easier.
Once an engine has been installed in Robin's car, his first trip is always to the chassis dyno. He runs the car on the chassis dyno before every race. "It really doesn't matter what numbers are produced," he says. "Sure, it's great for magazine articles and banter on a message board. Like a flow bench or a weight scale at the race track, it's all relative. As long as our improvements go in the right direction, we're happy." While Robin uses Don West's engine dyno, for chassis dyno tuning he usually goes to Cerra Racing or Anderson Ford Motorsport. For this article he set up time at AFM in Clinton, Illinois.
After strapping down the car and hooking up the necessary sensors, Robin warns, "If you aren't prepared for it, the first pull can be depressing." When asked why, he answered, "The two dynos load the engine in very different ways. The Stuska is a water brake and it attempts to 'clamp down' on the engine to measure the torque. On the other hand, the chassis dyno-in my opinion-more fairly represents the type of load the engine will see. The Dynojet uses a 48-inch drum to simulate a progressive resistance. It measures the time needed to spin the drum through an rpm band."
For fuel management, Robin uses EFI Systems' Programmable Management System sold by AFM. He uses the low-impedance-injector-driver option of the PMS to drive his rather large 72-pound-per-hour Seimens injectors. Robin has also opted for the DOS version of InterACQ, the PMS logging software. It provides datalogging capabilities during dyno and track testing so that all facets of a run can be checked after changes in the PMS have been made. For datalogging dyno pulls, Robin uses the Auto Meter Data Logger, also shown here. He logs with Exhaust Gas Temp probes in each header, along with intake air charge temp, boost, and engine rpm logging. He has also recently added the ability to log the EFI Systems wideband oxygen sensor into the datalogger. While the car is on the chassis dyno, he uses the Dynojet Wideband oxygen sensor, while the EFI Systems sensor comes in handy during track testing and tuning. For spark management, Robin uses the new MSD Programmable Digital-7 with boost retard.
What Did He Just Say?
OK, so we hit you with a lot of information at once. Robin is obviously a dedicated racer and takes his testing seriously. What follows is a description of the parameters he studies and how they influence performance. Yes, kids, this Real Street thing has become serious in a hurry.
For obvious reasons, Robin looks at mass airflow, fuel-injector duty cycle, boost, air/fuel ratio, and fuel pressure. Some of the more interesting stats he checks are throttle position, EGT, and battery voltage.
"You would not believe how many times we have made a pull and the throttle position didn't reach WOT (wide open throttle)," Robin says. As the PMS uses a WOT table, it is crucial that the TPS and throttle linkage are adjusted properly. It's also amazing what the EGT will tell you. Once Robin begins getting close on the tune-up, he keeps an eye on the EGT readout. Generally, a lean mixture or not enough timing will elevate the exhaust temps. As with the wideband O2 reading, exhaust temps shouldn't be the only way to look at a tune, but with other indicators it can help get you closer.
Robin says the GM MAP sensor sells for about $75. The Auto Meter sensor is calibrated and goes for about $200. It's more accurate, but as Robin said before, it's all relative. Because it's easier to log with the datalogger at the track, Robin likes to compare the numbers generated on the chassis dyno.
During a dyno pull-which is much shorter than a track pass-Robin's Real Street Mustang uses about 56-60 amps to drive all the electrical components, including the fan, the fuel pump, the fuel management, the OEM computer, and the MSD box. It's important to know if the voltage changes during the dyno pull as any fluctuation will effect how the fuel pump will run. "A low-voltage condition can kill your tune by up to 50 hp," Robin says. "Trust me-I know."
Making a Pull
After hooking up the car and veri-fying that all is ready, Robin will make an initial pull. He usually runs through the gears till reaching Fourth. At about 3,000 rpm, he hits the sample button and runs the throttle. He sets the shift light on the tach at 7,000 rpm and watches it as the engine pulls through the powerband. When the shiftlight glows, he lifts off the throttle and hits the dyno brake.
From there, it's straight to the numbers. "The first thing we look at is the horsepower graph," Robin says. "If laid over a previous run, we can look at the improvement or decline in power. We also look at the air/fuel ratio. The most important thing is to keep the A/F in a safe yet powerful area. On our Real Street engine we see an A/F between 11:1 and 12:1. It depends on the conditions. We have found that leaning the engine down has little improvement on power. It only helps to find the limit of your head gaskets.
"We then look at the InterACQ. We look to see that the PMS was 'WOT' during the run. We also look at the duty cycle. On our car we are in the conservative 75 percent range. Any more than 100 percent and you have a problem with the injectors going static. You've lost the ability to control the fuel at those points. We also look at the mass air meter numbers. Are they smooth? We look for as smooth a chart as we can get on the mass air meter. The Pro-M 80mm mass air meter does a great job for us. Our graphs are within 2 hp of each other when using this meter."
After looking at the horsepower and torque numbers, Robin then grabs one of his five laptops and plugs it into the Auto Meter Data Logger. This item is not legal for use in Real Street competition, but as you can see Robin makes great use of it for between race testing. While it's not an inexpensive piece, its benefits to analyzing a race program are exponential. Robin began using this system in Factory Stock, so it's safe to say dataloggers aren't just in the realm of Pro 5.0 race teams.
Robin begins by going straight for the exhaust-gas temperature readings. If these are too hot, engine damage could be imminent. If they're too cold, power will be lacking. He prefers to see the EGTs in the 1,200-degree range on a short dyno pull, but he has seen as high as 1,400 at the end of a full-on dragstrip pass. Again, these are relative numbers, as Robin prefers to tune for the best power, not the most attractive numbers.
"We start to tune conservatively-too much fuel and too little timing," Robin says. "It's safer that way. As we get the A/F close, we start to increase the amount of timing. If everything is good, then we usually see a drop in the EGTs and an increase in power. It's easy to get lost in a tune. I've had many people tell me about a combination with gobs of timing. Too much fuel can cover that up. While the combination may be fast, it would ultimately be better with less timing and a decent A/F ratio."
As you know, a tune-up can vary greatly based on the combination. Robin is an unabashed supporter of the Vortech supercharger system. He runs the V-2SQ S-Trim legal in the class. So, naturally, shortly after making sure the EGTs and air/fuel ratio is safe, he takes a look at the boost numbers. "Generally, we see boost in the 16-17 pound range at 7,100 rpm," he says. "That's in the Midwest with a 'normal' barometer. Look for a little more closer to sea level. The intake air temp is good for comparing run to run. We make every attempt to cool the engine exactly the same between runs. This number on the dyno is generally in the 240-260-degree range." An erratic boost curve will indicate the belt is slipping, and that's a bad thing.
Naturally, you have to feed the savage blower beast with lots of fuel to match that boost. Blower cars typically need to run a bit on the rich side to fend off detonation. As such, Robin keeps a careful eye on the fuel pressure. "We run an Aeromotive Eliminator fuel pump," he says. "We have the pressure sensor for the datalogger at the Y before the fuel rails. Normally, most people sense pressure after the rails at the regulator. I wanted to study what the batch fire injectors were doing at high rpm. With this setup, I'm able to verify that the pressure is increasing along with the boost, and with that we don't have any worries about too low a fuel pressure under boost."
No matter how well your engine was built or how well you've selected the pieces for your combination, tuning is everything. While Robin uses the powerful PMS to tune his combination, he primarily uses it to run the fuel side of the equation. At 4,000 rpm, the PMS takes over and ignores the factory computer, forcing the will of its program on the combination. The reason Robin only taps into the fuel controls is he also uses the powerful MSD Programmable Digital-7 with boost timing retard to run the timing end of things-mainly because he can retard individual cylinders to fend off detonation on those better-flowing cylinders. Real Streeters run unmodified intakes, and they all have a slight variance in airflow from cylinder to cylinder.
"With the ability to monitor EGTs," Robin says, "one can dabble with individual cylinder timing. One never knows if more or less timing on certain cylinders will make more power unless you test it on the dyno as we have. The Digital-7 has other functions related to track testing that we will talk about in the next article [In an upcoming issue...-Ed.], where we tune my combination at the track. In the past, we have used a timing curve dependent on engine rpm only. With the new 7535, we're able to utilize a boost retard function across the RPM band. This should lead to cleaner burnouts and staging. It will also allow us to pull out more timing at peak torque, which is where cylinder pressure is the greatest. We then add in a degree or two at the top end. Again, only experimentation will tell. In Real Street, we found that timing is what takes out head gaskets. It may run like Jack the Bear for a pass or two, but [the head gaskets] will let you down if you try and go rounds that way.I run conservative, and unlike others in the class, I have only 7/16-inch head bolts and two-bolt mains."
|Dyno & Data|
|Dyno Pull 1|
|Dynojet Auto Meter Data Logger|
|Fuel||EGT 1||EGT 2||Air/Fuel||Boost||Intake Air|
|Dyno & Data|
|Dyno Pull 1|
|Dynojet Auto Meter Data Logger|
|Fuel||EGT 1||EGT 2||Air/Fuel||Boost||Intake Air|
As you can see, Robin Real Streeter makes consistent power from pull to pull. Here we'e laid the Dynojet numbers next to the Auto Meter Data Facts log so you can see how the various parameters Robin studies influence the performance of his combination. The really scary thing is Robin now has his engine pulling all the way to 7,500 rpm.