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Timing retard to combat knock

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Hey guys,

I have another question/issue I'd like addressed by an experienced tuner.

Where I live, the best fuel we get at the pumps is 95 RON.....for the guys in the states that's like you guy's middle grade fuel.

Consider these two scenarios, one car is a naturally aspirated engine with significantly high compression ratio....north of 11:1. The other car is boosted and is running relatively high boost in the region 20-25psi.

Is it right in saying both of these cars can be tuned safely on "shitty fuel" like what I have in my country ,once we retard the ignition timing is retarded sufficiently on both engines so that knock is not occurring?

As experienced tuners, is there anything detrimental in taking this approach and running very retarded ignition so that both engines above do not encounter any knock? Taking it one step futher, would be it viable using this approach to tune the NA above under even shittier fuel say 92 RON as well as say tuning the turbo car by just upping boost and retarding timing as much as you can to try to stay away from knock? Or is this something not advisable and if so why?

Hi Chris,

From what you're saying both engines are both knock limited, the easiest ways of dealing with this are you tune as your describing, retarding the timing until you reach a safe ignition level where knock does not occur or you could 'dope your fuel' by adding octane boosters or alcohols such as ethanol or methanol but this would add an extra element to the tune.

Hi Chris,

Basically what I'm asking is if it is ok and acceptable to have the mindset that regardless of how knock limited the engine may be that we as the tuner can "make anything work" by simply retarding timing advance values until we see no knock? Is there a point as a professional tuner you would say to the customer, hey the setup you have really needs better fuel and I won't tune it unless you get that better fuel?

Here in Trinidad tuners have the mindset that they are magicians on the laptop and can run any engine safely regardless of fuel octane quality. I want to know this sort of approach is acceptable.

One thing you should be aware of especialy on a turbo engine.

If you run more boost than the engine really can take without knocking and you retard timing alot to "fix" this, you might end up with high EGT.

This might be "ok" on a road going car that isnt doing long highway pulls all the time and such, but on a car that is pushed alot and at long intervals (like a track car) you might end up with burnt valves or burnt turbine on the turbo because of the late ignition.

Thanks a lot for that kickerzx, so basically this is the main concern then, elevated EGT's on both the NA and the boosted. How do you know when is too much retard? 5 degrees btdc? 4? 3? is there any range to look for?

As kickerzx mentioned, one thing to watch out for is when you go to retarded in the timing you will generate really high EGT's, which will also raise water temps and combustion temps etc.

One of the things I see a lot and try to explain to people when running on poor quality fuel (and don't/can't change) is that sometimes if you reduce boost (or even sometimes compression ratio) you will end up with the same result, but safer. I have seen this many times.

Lets say at 20psi you have 7 degrees peak and make 300kw, you now go up to 22psi although due to the fuel the engine knocks. You need to remove more timing and say end up around 3 degrees. Gone up 2 psi although down 5 degrees, engine will most likely make around 300kw. So why go up in boost? All you do is increase water temp, increase cylinder temp and pressure and generate higher EGT's. The other down side to this is higher EGT's will start generating more boost. So you maybe running 22psi although after a long pull on the road and a gear change I could almost guarantee it will be 23psi, or at least spike to.

On a boosted car if I start getting down to around 2-4 degrees BTDC on boost I will stop, Tell the customer their fuel cannot cope with the pressure. Either we change fuel, boost levels or engine design to help reduce possibility of knock.

Same applies for a high comp N/A, most good N/A engines will take 28-34 degrees peak. If you're down around 16 or way off where it should be, then I would stop, talk to the customer and give them my opinion on what needs to be done and then ask how they would like to proceed.

I tend to stay away from octane boosters here in NZ as we have found them to be incredibly inconsistent and dangerous. Although as Chris250 mentioned, mixing with Ethanol and making like an E10 would help massively. Just means you need to buy a drum or containers of E100 and mix as you go.

What he said. :)

If any more Chris`es join this thread it will be ridiculous...

Lol haha on the Chris's what a coincidence.

Chris Wall thanks a lot for the response bro, got a much better understanding and picture of it all now.

Can you by chance say or give an estimate as to what the maximum amount of boost you would tune an engine to on 95 Ron fuel? I know theres gonna be many factors involved and every engine is different....let's just say a popular engine like the 4g63 or 4b11.

Similarly, would you ever even attempt to tune a relatively high compression na or low boost engine on 92 Ron?


In gonna say +1 on that suggestion!

I'll just add my 2c to what Chris (Wall) mentions:

With a turbocharged engine it's normally pretty clear where it's 'happy' place is. I always start at the wastegate boost level (minimum) and build up the tune and boost from there. On pump gas you'll frequently get to the point where you start increasing the boost but need to pull timing significantly to prevent knock. At this point you find that the power pretty much plateaus and you go around in circles adding boost, removing timing and creating more heat and stress. It's sensible to reduce the boost to the point where the power started to plateau - You'll get the same power with less stress and heat.

As an aside, on our local pump fuel which is rated as 98, I most often find that this happy place ends up being somewhere in the vicinity of 1.5 bar or 22 psi. Not a rule to live by but surprisingly common.

Hi Andre,

Thanks for the response, basically reinforced what Chris Wall has said.

I see you gave a sort of line in the sand with 22psi on you guy's 98 RON fuel. This is what was confusing me all along.....tuners here in Trinidad are running 22-25psi on engines on our questionable 95 RON fuel.....most are not using quality audio however so the engines are most probably knocking yet still showing increase in power at the wheels?

Its a scenario I wonder about a lot, guys here are doing this and basically getting away with it for the most part....I don't hear about engines falling to pieces on a regular basis. Makes me wonder as someone who's learn't to do things the right way from you guys Andre, how do you compete with this.....its a sad truth but tuner's are rated here based on the amount of power you get out of an engine....customers think there is some form of black magic involved and that certain tuners can magically get more power for them.

Making sense from what you are saying Andre, the sort of line in the sand for our fuel here would obviously be below 22psi max boost....but then there are many guys running evo's doing as much as 26psi on our fuel, its a tough predicament really for a new tuner trying to break through.


I can see how it can be quite confusing etc although to expand on what Andre said about the boost levels. I have found the same and that around 22psi on our 98 is what most engines will run happily before having to pull out lots of timing.

However, I wouldn't call this a line in the sand. There is no definite number and as I mentioned in my earlier post things like engine design make a massive difference. For example the Mitsubishi EVO 4G63 on 98 will take around 22psi (as mentioned) and be happy around there. Although the later model 4B11 will take around 25psi on the same fuel, that is basically down to engine design.

Last week I tuned a 2.3L Stroked 4g63 we built, this runs 98 fuel and slightly lower compression ratio (around 8.3:1) and pushes 29psi safely.

Compression ratio and cam design will make a massive difference.

I have had cars on 95 pushing 23-26psi and still taking a good amount of timing, sometimes you need to run them a tad richer to help add in cooling the charge.

So the line in the sand is quite broad. There is no black magic in tuning, you just need to learn how to read an engine and give it what it wants and being able to get good numbers from fuel like 95 is not impossible, just not as good as better fuels.

I think you've summed it all up well Chris Wall. Thanks so much for the insight, I have a much better understanding now.

I think you've summed it all up well Chris Wall. Thanks so much for the insight, I have a much better understanding now.

No worries at all Chris, happy to help.

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