Im wanting to run 10-12psi safely on my ls. I have 550 injectors with uberdata for tuning. What are you guys tuning your fuel curves at 10psi?
If you’ve already got the engine broken-in, and all of the turbo parts bolted on correctly, the first thing I would do is head over to a dyno shop. (Driving with NO boost.)
Buy a wideband air-fuel mixture gauge, like Horriba or AEM, etc…
While you’re on the dyno, first start with very LITTLE boost, and a safe rich air-fuel mixture. Keep close tabs on on engine speed vs. boost pressure, vs. air-fuel mixture.
Obviously, as you begin to increase boost pressure, increase the fuel injector pulse width, and fuel pressure in even, precise and proportional increments. Look for knocks and pings.
Check your EGT also, (if you’re running one), to see if your EGT increases with boost pressure, but HP does not increase. If you see your EGT skyrocket, as boost builds, but HP stays constant or drops, release WOT immediatly, because you’re on your way to detonation.
Try to keep the A-F mixture as stoich as possible, and run a little on the rich side during WOT and full boost.
(This way, if you ever get boost creep, you’ll have a safety net/cushion for the any unwanted spikes in boost pressure.)
Also, reply back here with your dyno chart and Air/fuel chart, along with your hardware list.
Happy boosting,
-Andrew
well, today we programmed the chip for 550cc injectors to run at 12psi. We also turned the rev limiter to 6800.So far so good. We turned the boost up to 15 to see what would happened and it fuel cut. It wont fuel cut at 13.5-14 so we kept it there. No detonation or ping. In a few weeks we will go to the track and she what she runs. My friend has a b18a in his hatch with the same setup and hes running 12lbs and does 12.8 in the 1/4. So im anxious to see what i’ll run. Hes car is obviously lighter but im runnin a little more boost maybe that we compensate for the weight. We will see.
Are you EFFEN kidding me? STOICH at WOT and FULL BOOST? WTF…who taught you how to tune…?
i play it safe. for my ls im going to shoot for 11.5-11.8:1 af under wot at around 10 psi
:owned:
14.7:1 + WOT boost:wtf:
Sounds pretty good. There isn’t much power differences going from 12.5:1 vs 11.5:1. The real power to be made is from playing with ignition
I apologize for the late response, but this is my understanding of how tuning should start out during your first few runs on the dyno. My understanding is that you want to start a rich and then tune towards lean, to make as much power as possible. When I said stoich, I meant stoich to begin with, and then eventually move leaner.
The complicating factor that I did not indicate in my previous post was that in designing a fuel curve, even if you know how much air is entering the cylinder at a given time, it is not necessarily clear what air/fuel mixture is optimal. Most FI tuner guys want the most maximum power possible at WOT, using the least possible fuel to accomplish this (lean best torque). But under some circumstances, it may be better to run at rich best torque (or even richer) in order to design in a safety factor to help prevent detonation with bad gas.
Also one has to think about throttle response versus efficiency at part throttle. Are you willing to sacrifice some idle quality for fuel economy? Does cam overlap dilute the idle mixture so you need a particular rich mixture for an acceptable idle? These kinds of questions complicate tuning even further.
This is a direct quote from EMS Tuning 101, by Jeff Hartman, Engine Management Systems:
“When the engine is running, ideally on a dyno, tuners adjust the engine at each breakpoint combination of speed and load, and using test equipment and a mixture trim module set ignition timing and injection pulse width to achieve low emissions best torque (lean or rich, or some combination of all three. Then they road test the vehicle and fine tune it under actual driving conditions, also fine tuning the enrichment maps….
Best power always occur when there is at least a small fuel surplus above stoichiometric because air (oxygen) is the scarce commodity in spark-ignition piston engines. The best power strategy is therefore always to make sure that there is enough fuel available so that virtually every molecule of oxygen finding its way into the engine will be able to burn fuel.” (Hartman, Engine Management Systems.)
Also, Xenocron, go back and re-read my initial post. I did not say he should run exactly 14.7:1. I said he should start rich and tune towards lean.
Assuming the engine is knock-limited and therefore does require additional surplus fuel to cool combustion via heat of vaporization effects, for best torque with optimal fuel economy at WOT, aim for a 12.2:1 air/fuel ratio midway between lean and mean best torque (12.8-12.2 AFR.)
This is MY understanding, and paraphrasing about how tuning should proceed. Simultaneously, it is not set in stone. Xenocron, I know that you know about EMS, and if I did make a mistake in my post, please point it out AND tell why it is incorrect and what another solution is. Insults wastes your time and mine.
In regards to what I wrote above, I’m curious, if this coincides with your tuning methods.
-Andrew
Andrew, with this, you are implying that stoich is what you need to acheive (regardless of boost level - load) and that a slightly richer than stoich mixture will give you a safety cushion in case of a spike.
Yes, of course to make optimal power you want to run as lean as possible without knocking and without melting your pistons. However, stoich is WAY to lean. most tuners at 10 psi wont go above 12.5…the more conservative ones try to lay a dead flat 12.0 line throughout boost.
I prefer the stepped, non-linear approach.
13.5 or so while crossing the threshold
13.0 from 1-3 psi
12.8 from 3-5 psi
12.5 from 5-8 psi
12.2 from 8-10 psi
11.7 - 12.0 above 10 psi
This of course on a stock map sensor. This gives you safety and power especially if you combo this with a stepped ignition retard.
Check out this write-up why your ‘more fuel cools the combustion chamber’ thoughts are a little ‘off’ as well…
Thanks for the detailed reply. I should have clarified. Regarding the richening of the AFR, here’s a direct quote from the link you gave:
If instead of the richer mixture about 10% (by mass) of water would be injected in the intake charge (0.008 kg Water/kg air), the high latent heat of the water would cool the charge by 18 degrees, about 4 times the cooling effect of the richer mixture. The added fuel for the rich mixture can’t burn because there is just not enough oxygen available. So it does not matter if fuel or water is added.
So where does the knock suppression of richer mixtures come from?
If the mixture gets ignited by the spark, a flame front spreads out from the spark plug. This burning mixture increases the pressure and temperature in the cylinder. At some time in the process the pressures and temperatures peak. The speed of the flame front is dependent on mixture density and AFR. A richer or leaner AFR than about 12-13 AFR burns slower. A denser mixture burns faster.
So with a turbo under boost the mixture density raises and results in a faster burning mixture. The closer the peak pressure is to TDC, the higher that peak pressure is, resulting in a high knock probability. Also there is less leverage on the crankshaft for the pressure to produce torque, and, therefore, less power.
Richening up the mixture results in a slower burn, moving the pressure peak later where there is more leverage, hence more torque. Also the pressure peak is lower at a later crank angle and the knock probability is reduced. The same effect can be achieved with an optimum power mixture and more ignition retard.
If we can agree that a denser AFR mixture, and a richer mixture are synonomous, then there seems to be somewhat of a contradiction in the quote above.
“A richer or leaner AFR than about 12-13 AFR burns slower. A denser mixture burns faster.”
“Richening up the mixture results in a slower burn…”
Let me know if I am misinterpreting this. (Although could a denser AFR mixture still be at 12.5:1–with increased proportions of air molecules to fuel molecules?)
From what I understand, a richer/denser AFR burns faster.
Also, as I read the article Xenocron, it seemed as if richening the AFR could actually increase knocking, because if it does increase the burn rate, and still kept at the same degree of ignition timing, peak pressure would occur BTDC. (Obviously, this seems to be the reason why ignition is retarded–to have peak pressure occur ATDC.)
If I am interpreting this correctly, your method increases fuel enrichment proportional to boost pressure. Although, I would like to see this charted with engine speed, exhaust gas temperature, octane rating, ignition retard timing, horsepower and torque. I am certain there are even more variables which effect optimum AFR, and there is no “one size fits all” set-up. Nevertheless, the chart is a good rule of thumb, with an AFR enrichment of appx. 0.2:1 – 0.5:1 increase proportional to every 2-3 psi increment increase.
In terms of 12:0:1 AFR before 1 psi, the tuners who configure in this manner, would cause the engine to most likely run too rich, and cause poor fuel economy and lose HP, because volumetric efficiency has not yet achieved 100%.
-Andrew
You seem like you’re thinking way too much into it hehe.
I cant say I spent a great deal of time reading carefully through this article, but what I ASSume he means by a denser air mixture is a mixture with more Oxygen molecules (denser in Oxygen than in fuel).
When the mixture is richer, there is less room for O2 molecules causing the burn rate to be slower.
I’m sure you’d be thinking otherwise, when you detonate an LSVtec turbo with wrong air/fuel mixtures.
-Andrew
Hehe ya fair enough, but where did ‘10lbsofboost’ go? lol
lol…i figured it out. Confusing at first. Thanks alot for the info guys. Really helped alot. im runnig 13.5lbs with no knock. I have a pretty good tuner. He read this article and explained it to me.