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When folks install their new Sniper 4150, Super Sniper 4150, or Sniper XFlow on their high-horsepower engine, usually there are two reactions. First, “Wow, does this deliver some amazing power!” Then, about the time they get in to a situation where a deft touch of throttle is required, “Wow, I need a way to manage that power!”
At 800 and 900 CFM for the Sniper / Super Sniper and XFlow (respectively), these throttle bodies can really be a handful at throttle tip-in, particularly when the situation calls for one to behave themselves. If the car has a naturally stiff throttle pedal that just makes the situation that much more challenging. That’s why folks who install the progressive link that we offer almost universally have the same response: “Why in the world didn’t Holley deliver the Sniper with that in the first place?”
In a few cases, however, progressive link users find they get a little rich bog when they tip into the throttle with the progressive link installed. Fixing that is easy and I’m going to show you how.
When you learn how the Sniper manages acceleration enrichment it is not surprising that you might get a little rich bog when you add the progressive link. The acceleration enrichment that is calculated based on the throttle position is expecting four barrels of air to be dumped into the manifold. But with your progressive link installed it is only going to dump two barrels of air in until such point that the secondaries are added.
Have a look at the default AE vs TPS table for the Sniper, shown below. You can find this only by using the Sniper Software. AE vs TPS is not tunable using the handheld. If you download your configuration from your ECU either to the SD card or directly to the software (if you are using a CAN-to-USB adapter cable) then click on the fuel injector icon (at the top nav bar), then Acceleration Enrichment (on the left window), then AE Correction vs TPS (at the top-right of the main window) you’ll see this:
As you see above, the Sniper is going to dump in a maximum amount of fuel at zero TPS, begins to remove acceleration enrichment at 60 percent TPS, and then removes all acceleration enrichment correction at 100% TPS. Perfect—if you have the original synchronous linkage.
Now that you are bringing the secondaries in later you will need the same amount of acceleration enrichment but you need it applied at a different rate. Instead of bringing in all the fuel at zero TPS, you will initially bring in half the fuel, and taper it off at the same rate as the original graph above. Now you’re going to bring the other half of the fuel in at the secondary tip-in point, but you need to taper it off more rapidly so that you’re still at zero percent correction at 100% TPS.
The example above is a good starting point if you have the fixed progressive linkage. Depending on your specific installation, those usually come in between 45% and 50%. If you have the adjustable progressive linkage, you’ll need to change the chart above to match your particular secondary tip-in point. Save the configuration file with a new name, upload it to your Sniper ECU, and enjoy the improved throttle response.
In my experience, you don’t have to worry about getting this too dead-on. For 90% of the users if you’re within a few degrees TPS and a few percent AE correction either way it’s going to be fine. Of course, a geek like me creates a spreadsheet that lets me calculate this for customers based on their specific tip-in point. And if you’re that into it you’ll also want to datalog the tip-in event just above and below the tip-in and try to fine tune this.
(Note: The Sniper progressive link does not work on the Sniper Stealth throttle bodies or any of the two-barrel Sniper variants. If that’s you then we recommend that you try the throttle lever extension instead.)
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