Tuning for water injection: fuel, ignition, and EGT

[Boostingawd]

Originally Posted by b_boy

Now one thing I've notice in the various "calculators" I've browsed is that more power can be had with lower AFR than 12.5. While this is the fuel ratio of optimal power per gram of fuel, it may not in practice be the AFR of best power. So, I question the assertion that 12.5 AFR should necessarily be the starting goal for best power.

I would think that a safe AFR would be based on the amount of meth injected. Not to sure how a mixture of water and meth would play into effect since I have only run meth. Stoich for gasoline and meth are different. With that in mind more meth means a richer AFR. Well at least this is what I see on my car, the only problem I have is that I am spraying the same amount of meth at all boost levels, since it is a single stage injection that turns on at 20psi. It does seem to have a bit of lag down low and maybe it would be smart to run a leaner mixture at lower RPMs to help with spoolup. It is something I have been thinking about but ran out of time last year since my car is not driven in the winter.

When it get nice out I am going to attempt to run one more jet and hopefully 3-4 more pounds of boost.

Victor

97 GSX, 32 psi with 1.0 & 0.8mm jets @ 100psi with 93 octane, roughly 12.8GPH.

[Airspeed]

Hello,

First of all, this is a great post!

For me, this graph below has been very informative with regard where to tune for.



regards,
Walter

[Wayne in NZ]

Wow Guys, I feel so much more smarterer.

What a read.
Way too much for me to absorb it all.
But my general gist of it all is:

50/50 water methanol mix is best "all round" ratio.

Tune car for max power at best air/fuel ratio without knock with no injection (12.5/1)

Add injection and then reduce fuel to bring air/fuel ratio back to optimum

Advance timing to gain more power to just before knock

For more power after that either add more fuel or injectant

Have I got that right?

I am off now to soak my head in a bucket of ice water for an hour or so. LOL

[RICE RACING]

First few pages in this thread are gold, roll back 2004. Where are these people now?

Anyway I can tell you in a practical testing environment allot of what is discussed as theory or quoted from 80 year old tests does hold true in a real modern high speed internal combustion engine.

WI does indeed take a fair bit (no scrap that ! allot of) knowledge and testing to extract the most from this quite complex science. From personal experience there is much to be said for testing testing then testing some more~! I know the years of work I have done has gained me so much knowledge in this subject and so much of it is hard earned, brain frying stuff, its a stressful job some days, as you are doing things no one else (or very little) can achieve, cause its hard, it takes time, money, analytical ability and a certain level of relevant education to have a hope to repeat what many great engineers found since way back to the 1880's (yes first tests on WI!)......

I love the topic and the science, its my most enjoyable area of research for the above listed reasons and many more once you get aligned with the great resources Richard has collated here and many other valuable members have linked or posted of their own testing you too can be on the very rare bandwagon of capable people who don't need "power in a can" to look great Lets face it, anyone can open their wallet or extend a bank loan to pay for race fuel or some other rubbish that eats injectors or fuel system parts, but very few men can actually say that they have fast and reliable and mega powered cars running just normal gasoline/petrol............... that is priceless, just like this forum and the science that is water injection

[rotrex]

It depends. Given a high octane base fuel, enough water meth, effectve nozzle location and a well designed combustion chamber/piston/squish etc. you might hit MBT before any knock occurs. If you plainly map to the knock limit, you might seriously overload your engine.
Most engines today run a rather high compression ratio and often hit knock before MBT.
My strategy (supercharger) was always to start with reasonable low timing, get the AFR you want and then increase timing step by step and feel if power increases. If either power does not increase anymore or knock occurs, you have hit the limit.
On a dyno, you can see rather small changes. The butt dyno works well enough for street use. If you do not feel any increase anymore, it is not relevant anyhow.
In terms of amount of spray, I found with my latest direct port nozzle location right before the fuel injectors on the top side that the more flow I dailed in the more extra power I was able to extract after adding timing. When I improved squish I found no more improvement past a certain amount of spray despite a increased compression ratio. I seems I am no longer knock limited. :-)

[beetos]

Thank you Rotrex, that makes sense. I think the J&S safegaurd, if calibrated correctly will alert well before serious knock occurs and it can pull out up to 2degrees per engine cycle on a specific cylinder, up to 20degrees. I think this unit keeps me well away from serious knock, but always better to be safe than broke....those 930 engines are not cheap to do properly!

[rotrex]

I use a J&S, too. 20 deg is too harsh unless you have a very slow burning combustion chamber design, e.g 60ies to 70ies Hemi heads etc. 10 deg worked best.
With the J&S serious knock is well captured. You can still hear it and also feel it from the power loss of the pulled timing under boost. I usually use it to point me to the map spots that need some correction. I had a pump issue once with the priming pump controller of my Aquamist 2c not working properly anymore and the J&S had some serious work to do as WI essentially failed. The engine spit blue flames from the exhaust with serious misfires as the J&S pulled 10 deg on all cylinders. That was a nice light show on the gauge. But nothing else happend.
As I am converting to an other engine I have sold my current engine and J&S last week.
The J&S is not as smooth as a fully tuned factory knock control system, but it does its job to indicate knock and provide some monentary correction. For street tuning, it is very very nice to have.
I would not "run" on it as in dail in full timing and the J&S does the rest.
I still can recommend it. It is 1000% better than having no means of interventing on highly strung forced induction engines.

[beetos]

Completely agree. I will only use the J&S in the 10degree total / 1 degree per knock event mode, and never really lean on it heavily to pull timing under normal conditions, but it's nice to know it will be very aggressive in pulling timing if it has to, and also seeing the gauge go nuts gives plenty of knock warning.

[arthurtoo]

I'm running an aquamist HSF-2 kit for my JDM 2006 Subaru STI. injecting only water at 42% IDC onwards. car runs great!

but i realized that there is a very very minor knock during initial injection and it's persistent throughout my logs. should this be of a concern or is there anyway to totally eliminate this?

thanks.

[RICE RACING]

Originally Posted by arthurtoo

I'm running an aquamist HSF-2 kit for my JDM 2006 Subaru STI. injecting only water at 42% IDC onwards. car runs great!

but i realized that there is a very very minor knock during initial injection and it's persistent throughout my logs. should this be of a concern or is there anyway to totally eliminate this?

thanks.

Knock has to be one of the most mis understood terms in the after market performance world.
Typically when an engine is raised in power its vibration recorded through the acceleration sensors will go up (knock sensor), the shape and amplitude of these traces and the zero cross over point can be literally traced within a couple of CA to an in cylinder pressure transducer!, so its a very accurate representation of what is happening inside the combustion chamber.

As the BMEP goes up the 'knock' goes up, this all has to be defined in the ECU you chose to run, some do this better than others, some work, most don't! I would say so far that in all the ECU I have used (not owned or paid by anyone but out of my own pocket!) there is only ONE ECU that you can buy that does this properly and its made by Life Racing in the UK, all the others I would not piss on personally. Why does it work??? they build their own engines that race in LMP1, they are running on knock limit all the time, and they just work as intended, unlike the spec sheet racers with glossy web pages and blogs etc.

Now having got that out of the way and back onto your question.
You need to know what is normal what is not in your own engine, or otherwise the severity of the events, this is easy to define with nothing more than an acceleration sensor and some experience and the correct electronics that have a history of management in the real world at the peak of competition, if your own stuff you run does not meet these then its hard to honestly rely on the information you are being presented with. And note if someone tells you to use audible knock tools then put them in the *fuck head basket* never ever to be consulted with ever again!

Knock has to be quantified and acted upon within one engine cycle, you need to know what it is, if its normal, and where its heading (towards pre igntion) and countered at all costs, the importance of this varies with heat release or potential energy in the chamber IE: the more power it makes the more critical it becomes, some engine types when stressed will fail catastrophically and instantly when moderate levels of knock are exceeded.

Final note, some knock is good! generally the closer any engine runs to destruction the better its performance will be! so its not uncommon with Life Racing electronics to run the engine on the verge of this point all of the time to extract the most power and highest efficiency. Water Injected cars will allow you to run closer to this point without then quickly leading to pre igntion, this is no one really talks about, but is one of the key things that WI allows (not higher ratios of meth than 50% cause that will lead to far inferior performance FYI). So its a long reply but is normal to have light levels of 'knock' and its a healthy by product of an optimized engine. If you levels are right I cant say obviously as that information is not at hand and not validated.