Ignition cut/Fuel cut - bangs when shifting

Hello everyone

Probably dumb question, but at the weekend I was supporting my friend at the local hillclimb race and when some cars drove around me, I realized that I actually don't know, why some cars shoot from exhaust when shifting and others don't.

For example my car and another friend's car - both high revving N/A with seq. gearboxes and strain gauges on shift levers and mine with ign. cut dont shoot at all...never, and his banging like hell between every gear change.

Thank You

Hi Karsa,

Which ECU's are you using to control the cut strategies?

There are so many variables that determine whether a vehicle is going to have flames out of the pipes of a shift that you cannot get a definitive answer. Some, but not all of the variables that can influence this are.

- Lambda Aim (a Rich mixture has more of an opportunity to have un-burnt hydrocarbons exiting the exhaust tip, lean will tend to have the rice bubbles in the pipes)

- Level and type of cut (some ECU cut strategies are more aggressive than others)

- Fuel Film in the inlet manifold.

- Length and design of the exhaust system.

- Number of mufflers in the system.

- EGT at time of cut.

- Turbo or NA.

- Type of fuel being used.

Do you get a puff of black haze out of the exhaust when the cut activates? If so, the excess fuel is combusting in the exhaust system, rather than waiting until it is exposed to atmospheric oxygen to allow for combustion.