Table of Contents

11.9 Deceleration Popping

What is it?

Deceleration “Popping” is caused by fuel burning when it enters the exhaust or header. It is important to remember that fuel can only burn when combined with air and heat. We can not remove enough heat from the header to make a difference, so when discussing decel pop the focus must be on air and fuel.

Why is it a problem?

A moderate amount of Deceleration pop is not “bad” or “wrong”. A properly calibrated ECU/Engine pairing will have decel popping, but you may not notice it until you remove the parts than have been muffling and absorbing the noise. For example, aptly named “Mufflers”. OR you may magnify the severity of the popping by removing or adding parts that increase the favorable conditions of popping. Ie removing Baffles or adding short exhausts with a high chance of reversion.

So it's not “wrong”, it is just... not attractive and, when we spend so much time and money on our really attractive exhaust “upgrades”, we want it to sound attractive too. This is important to say because it is important for your customer to hear. It puts everything in perspective. We don’t want it as a crutch so we can be lazy about making it sound attractive. Rather, we want people to understand that, if we “fix” this noise, we are actually applying our knowledge of these engines to deliver sexy results beyond right and wrong. ...and there is always a chance we can't hide the noise completely.

Going forward with “fixing” this issue, we must understand that we are not going to TUNE the decel pop out. We are going to push the ECU off calibration in the decel ranges to manipulate elements (fuel or pressure) that may serve to muffle, stifle, or hide the popping. This is why AUTOMAPPING doesn’t always eliminate the issue. Automapping gets the ECU in sync with the engine it is controlling. Decel pop fixes are, essentially, a set of desyncing actions.

A quick word about the Decel Enleanment table. This totally sounds like it would offer a solution, right? It doesn’t really. This table works by adding to the target AFR during Decel. This means that it leans out the mixture, at most, 2 afr/15%. Decel pop is usually resolved by adding fuel and in amounts 15-30%.