My stock S5 NA is detonating on hard acceleration. My question is:
Is detonating caused by:
To Lean?
To Rich?
Timing to advanced?
Timing to retraded?
The reasons those are the choice is because those are the only things I can think of. Any advice would be welcome.

 

Have you worked on the car lately? Messed with the timing? If so...

More than likely your timing is too far advanced from the baseline. Generally, on an NA at least, any detonation under WOT occuring is caused by the A/F mixture being ignited too early and the rotor hasn't made it past TDC (well, our TDC equivalent). Thus, the mixtures pressure goes so high that it violently detonates. Basically, the pressure in the chamber reaches its critical limit before the rotor is at its highest mechanical compression.

Dial your baseline timing down a tad.

If you havent messed with it, you could be running lean, or your crank angle sensor could have come loose. Is this occuring at full throttle with low or high rpm?

 

Line the pin on the front cover up in between the 2 marks instead of on the yellow one like the FSM says. Then zero your CAS and drop it back in. Timing should be almost dead on 5° Leading and 20° Trailing.

 

and make sure to run 91 octane

 

why should he run 91 octane?, its a stock s5. he shouldnt be having detonation problems in the first place.

 

Your timing is off.

I tweaked my timing a tad and on a very very very hot day on hard acceleration (or high rpms) I got detonating.

Don't run 91, or 89, run 87 no less, more is worse millage.

 

because its available for one.

2. his motor is the highest compression ratio you can get in a 13b
3. mazda reccomends it.

i can go on and on but basically higher compression engines need a less volatile fuel. higher octane is not only less volatile it also has a slower burn rate. why would anyone that wants to keep their motor together put anything other than 91+ in their rotary?

its true, but healthy motor > fuel economy

but it probably can be solved with fixing the timing issues

 

save me the speech and show me where mazda recommends 91 octane.

 

Ahh mate, please use Mr.Google more.

You're partly right, but not in the case of the rotary engine.

I ran 89 octane mostly in my old fc due to the advanced timing which prevented any possible detonation (Which I dunno why it id that one rly hot day.... maybe I had 87)

The n/a 13b in a fc is not tuned for 89, 91, or higher. It's tuned for 87 and probably slightly lower.

If you run higher octane fuel it'll not run properly due to not igniting it right with the slow burning of higher octane fuels, when I ran 91 in my n/a fc when it was stock timing it'd have little power till 6k rpm, then it'd be alil less than normal, it'd back fire more and waste gas.

Why?

It wasnt burning the fuel, anyways continue wasting your money

You can run a turbo high comp rotary engine, it needs to be tuned properly or run higher octane fuels to prevent detonation (along with a good tune) cars are often tuned for other octanes so when you take it to the track, etc.

 

lol...****, most would probably be surprised to hear that even the TII's run 87 octane stock.

 

BS, 85 or 95 it will run the same. hell they run so rich stock I've seen e85 work it's magic and that's like 100+ octane. Check your spark plugs.

 

Well there is a big yellow sticker on the inside of my gas filler door that states "92 Octane Only." So I don't know about that statement.

 

So your the one that steals those stickers from the gas station.

On a N/A car, especially a street car, it doesn't matter if you put 87 or 93 in it. Hell, if their was a 85 or a 83 pump around here, I'd probably be putting that in my car.

But on a turbo car, always 93. Do you really want to risk detonating and popping your motor over a couple cents on gas?

 

i'll third the 87... if it was making 250+ hp then, maybe you need a little more.

here is a list of stuff to check

1. timing, all the S5 na's ive had pinged in the midrange with more timing than stock...

2. plug wires, old ones crossfire, cossfire is like firing the plug way early, which is bad. in a high hp application, keeping the trailing apart from the leading wires is good practise

3. i've seen vacuum leaks cause pinging too, but on a stock ecu it wont idle

 

that was good but lets try to help him out...
any more suggestions i got nothing.

 

Detonation results when the compressed fuel-air mixture reaches a combination of temperature and pressure that causes it to spontanously ignite. The entire charge in the combustion chamber goes off at once, rather than over a period of time (as designed) as the flame front makes its way across the combustion chamber.

Under detonation the peak pressures and temperatures during the power stroke are much higher than the designer intended, and damage can result.

It is often confused with pre-ignition, in which the charge is ignited before it should be, either by mis-timed spark, or a hot-spot insie the combustion chamber. Hot spots can result from a sharp edge, ie the edge of a crater where a piece has been taken out (possibly by detonation).

Detonation/pre-ignition can result from:
sharp edges/damage inside the combustion chamber
too lean mixture (too rich provides a cooler burn and protection against detonation)
timing wrong (especially spark too early/advanced)
EGR not functioning
and a variety of others...

I have a piston in my garage from a Pontiac that destroyed itself internally due to pre-ignition/detonation.

If you look in the Chilton manual, their first recommended step for diagnosing detonation is to have the combustion chamber borescoped, looking for sharp edges/damage.

Before I went to that trouble I would try to make sure that the timing was perfect.

You also might look at the secondary injectors. If you have a partially clogged secondary, it would provide an excessively lean mixture on that rotor but only above 3800 rpm and under heavy throttle... you might consider having the injectors cleaned and or flow tested and see if the problem goes away.

Just some ideas...

 

need more info on the problem...

 

<----- that just happened to me. good info.

 

Thanks for all the great advice guys. I was chasing a idle that was sometimes steady and sometimes dropped to zero. After driving on the freeway for a while (75-80 31-3500 rpm) and pulled onto surface streets, the car would occasionaly die at a light. I grounded out the test connector and adjusted the screw on top the intake and then adjusted (advance the timing) to match the timing mark at 750 rpm. Seems it advanced the timing to far as suggested. I think the timing is to advance or the mixture is to lean. The timeing is perfect, but that is with the screw on top the manifold almost at the stop. I'll try these tips on monday....except for the 92 octane thing. Just wondering how premixing effects performance when using 92 octane plus, when I've used it in the past, I've never noticed a performance change except cleaner tailpipes and a mile more to the gallon.

 

Lol! This is what I mean. The highest octane we have around here is 91, unless I want to go buy some VP Race gas.

 

lol if your worried that much about performace just convert to E85 its much cooler for forced induction and you see hp gains.. Just good luck making one...

 

It even says it on your gas cap! My vert only has the black "unleaded only" sticker, but it was NA. That's really strange too since the owners manual (not FSM) says 87 octane for both NA and turbos. This has been confirmed by EvilAviator, Icemark and a few others that actually have a copy of the owners manual from one year or another.

Those stickers look stock too, so I wonder where the discrepancy came from. Does anyone else have one like that? I can't remember if my TII did or not.

 

I have my original owners manual and it says "Your new Mazda is designed to obtain maximum performance with Unleaded Gasoline with an octane rating of 87 or higher (average of Research Octane Number and Motor Octane Number)."

Interesting too, is says you can use Gasohol (mixture of gasoline & ethanol) if the ethanol is less than 10%.

 

that sticker is not factory mazda. i remember seeing those in the late 80's early 90's, but its probably from a porsche/mbz

 

That sticker could have been standard on one of the non-US models. The US uses a higher standard for octane ratings, so 87 PON (R+M/2) in the US is somewhere around 91 or 92 in the non-US RON standard. Therefore, the sticker would make sense if the car was originally sold in Europe or Japan, although it could just be an aftermarket sticker. More on the PON vs RON subject at the below link:
http://www.btinternet.com/~madmole/R...RONMONPON.html

In theory...
Adding oil to gasoline would decrease the octane rating and run a stock-EMS engine leaner when it operates in open loop mode. However, a correct pre-mix would not significantly lower the octane any more than the stock OMP. Also, since the stock EMS runs the engine on the rich side, a pre-mix fuel may actually run better.

In practice...
I haven't heard of any significant difference in performance, and therefore I decided that it is not worth my time to try any experiments to determine any significant difference which probably does not exist.

Unfortunately, E85 is about 30% less powerful than typical pump gas, so you would need to increase the boost in order to see any gains in performance. So far, vehicles that have been converted to E85 with no increase in boost level, compression ratio, etc., are yielding about 10-30% less power and fuel economy than they were with gasoline.