Detonation

[bnaellis]

A question regarding tuning a rotary. To avoid detonation ideally we would require the intake charge to be of a lower temperature than what is normally accustomed to rotaries. When we free up the exhaust on a rotary to something more free flowing, because the gases can escape a lot quicker this way does this in affect also make it a little less likely to detonate. I know optimally reducing the intake charge is more important for reducing detonation, I just wondered whether when freeing up the whole exhaust has the same affect but obviously in a different kind of way ??

rgds Brian

[Glenn Butcher]

Hi Brian,

Yes - a lower intake temperature (water injection can assist with this), along with the right amount of fuel can reduce intake temps.. The more fuel v's air the cooler the engine will run. For example methanol/alcohol burn colder - therefore you can make much more power.

Ultimately you need to tune your car with a Wide Band Lambda sensor (and possibly an (EGT) Exhaust Gas Temp sensor) - no question!

I think putting a larger exhaust on, will have the opposite effect of cooling down the intake temperatures I could be wrong, but as... the engine is more free to rev. then more fuel/air will be required, intake temps. go up as you are usually making more power (more heat is produced from the turbo etc.).

I don't even think that putting a larger exhaust on a standard RX-7 is a good idea unless you know it is running rich enough and not boost creeping/spiking.

Rich mixtures (11.2-11.8:1), and precise timing are very important, and will ensure a very happy, reliable engine.

[Fish]

Brian, just to add a little to what Glenn has already said.

Yes swapping for a cat free d/p will remove some heat, as when pushed hard they hold heat really badly. But as for the turbo bit, when pushing with or without a cat, they would produce the same amount of heat. Could be wrong.

By removing cat's you, your engine WILLbe leaner, thus producing more heat. Adjust the fuelling, and this can be resolved. But also adding too much fuel can have the same effect (so I have been told). But then again our rotor love fuel.

Dan