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Data Logging for Carb Guys - Knowledge Is Horsepower
Why data log?
How many times have you seen two racers with similar combos where one car is notably faster than the other? The difference is usually in the details. From perfecting your combo to the perfect tune, all those details can be the difference at the finish line. So how do you know if your tune and combo is truly dialed in?
The best way to know what is going on in your high performance or race engine is to datalog. By datalogging racers can review some of their engines key data after a run to see what is really going on. Recently, I had the opportunity to work with Chevelle Rob as he datalogged his 9 second nitrous powered street car and I am going to share the experience with you.
The Car
I am sure you all guessed why they call my friend Chevelle Rob. Here is his 1970 454 Chevelle. While it is not LS powered, it is carbureted just like most of our cars and that is why this test is relevant to us. Unlike the EFI guys we don’t have a complex computer running our cars; we have to create our own data.
The Data Logging Equipment
The equipment for this test was graciously supplied by Daytona Sensors. They sent us the WEGO 4 wideband. This unit not only displays the air fuel ratio, it also tracks engine RPM, throttle position and manifold pressure. And, it records this data in real time for later review. What we learned with this data was very enlightening.
The install on a wideband is really straight forward and this WEGO unit is no different. For most carb guys, the most substantial part of the install is welding in the bung for the wideband sensor.
Once the bung was installed, it was just a matter of wiring. If you want to see more about how to install the wideband, Daytona Sensors has a video on their website. Since our install is a temporary install, I won't bore you with the zip tie action.
Last edited by speedtigger; 04-10-2015 at 09:06 AM.
The reason Chevelle Rob wanted to participate in this test was all about the nitrous. Rob's streetcar is built to run on "the juice". And like most of us on a budget, frying his engine on a bad nitrous tune is not on Rob's list of things to do. Also, Rob wants to be sure his stall converter is optimum for his application and the data this testing will provide is great for sharing with his stall converter supplier.
So what does it all mean? There is a lot going on there, so let me share what we were looking at and what was important to us. I have highlighted some areas and labelled them to break it down:
As I mentioned, Rob's primary concern were the consistency and a/f ratio of his tune and the performance of his torque converter. We will start with the tune.
The Accelerator Pump Shot
The first item that I highlighted is the pump shot rich condition. Rob is a footbraker and you can see it start to lean spike when the nitrous hits, then the carburetors accelerator pumps douse the engine with a shot of gas that briefly makes the car rich, then back to the nitrous hit lean spike. This is one area Rob might choose to tweak. Would a longer lighter pump shot be beneficial? Maybe. Now that we can see what is happening, we can address it.
Nitrous Lean Spike
The second item highlighted in the tune is the nitrous hit lean spike. Rob says this is because the nitrous is under so much more pressure that it flows much faster when the solenoids open and it takes the fuel a moment to "catch up". Rob also runs a progressive on the launch to soften the hit as his car has previously produced a massive wheelstand that he is not eager to repeat. I bring this up because many progressive nitrous controllers have "fuel offset" settings that can help correct the lean spike on the hit. What must be noted here is that most guys would not even know this is happening, but the data logging that the WEGO provides illustrates this situation quite clearly.
1-2 Shift Lean Spike
The third item highlighted in the tune is a lean spike on the 1-2 shift. Many things can cause this. I suspect in this case it is the drop in RPM during the shift caused a loss of signal to the carb. This is an area that can be improved for sure.
2-3 Shift Lean Spike
As you will note, the 2-3 shift has a lean spike too, but hardly notable. Make note that rob shifted at a lower RPM on the 2-3 shift which diminished the RPM drop. This is likely part of the reason the lean spike is less substantial.
As you can see, we learned a lot about what is going on with his air fuel ratio as he goes down the track by data logging. While a regular wideband display tells your real time a/f ratio, could you imagine trying to look at that display while piloting a 9 second car? LOL Me neither. I can't wait to see this information on my car once the rear end upgrade is complete.
Last edited by speedtigger; 04-09-2015 at 05:31 PM.
Now lets look at the transmission's stall converter performance:
Stall Converter Launch Flash RPM
The first item highlighted in regards to the stall converter performance is the launch "flash" RPM. It appears that this stall converter is hitting 5400 RPM. Rob can now discuss this with his stall converter supplier and discuss what they feel is optimal.
Shift RPM Drop
The second and third highlighted areas in the RPM graph depict the RPM drop the engine experiences when the car shifts gears. This is another key area that Rob's stall converter supplier will evaluate in determining if his stall converter is optimal. In looking at the graph, it appears his RPM are dropping to about 5800-5900 RPM on each shift. I am thinking this means this converter should be able to take even more nitrous. Good thing because Rob is barely tickling this 468" engine right now.
Terminal RPM
The last item highlighted in the RPM graph is the terminal RPM or engine RPM at the finish line. His RPM is abut 6200-6300 RPM in the 1/8th mile. Rob's car would hit 7000 RPM on a quarter mile pass. This terminal RPM can be used to figure ideal gearing and torque converter slip/efficiency. All that is needed is the MPH on the time slip and a little math. Ideally we would like to know driveshaft RPM, but this particular WEGO does not have that feature, however I would not be surprised if Daytona Sensors has a solution for that.
Rob was really jacked up about acquiring this data. Being a full-time touring drag racing journalist, He knows how important this data can be for getting the most out of a combo. I am excited to datalog my car with the WEGO for myself.
Last edited by speedtigger; 04-10-2015 at 07:46 AM.
For sure. I wont have weather like this again till fall/winter. The 1/4 mile pass was at 797 feet corrected DA. My next time out should be April 24 at Bradenton.
You can address this condition by changing the HSB and emulsion package in the carburetor if the carburetor is not too big for the application. In Rob's case, I think he told me he increased the fuel pressure to his nitrous solenoid while tuning. That likely diminished the lean spike on the shift for him between the first pass and the last.
04-09-2015, 04:18 PM
Data Logging for Carb Guys - Knowledge Is Horsepower 
