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Discussion Starter · #1 ·
Let's pretend that with cold air intakes, and/or performance exhaust systems, that the air/fuel ratio leans out - perhaps even leaner than ideal. How would I trick the car into running richer?
 

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Interesting, I know with my GM projects that putting headers on them typically made the fuel/air ratio go a bit rich. I have been reading up on Speed Density systems and I still have a lot to read. If there are some ideas like that in the reading, I will post them.

Todd
 

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Perhaps you could replace the air intake temp sensor with a high resistance resistor? Though this would also retard the timing.
 

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marlinspike said:
Perhaps you could replace the air intake temp sensor with a high resistance resistor? Though this would also retard the timing.
why would it retard timing. Isn't timing a leard fuction via the knock sensor?

anyway take a look at this mixture control
 

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I could be wrong, but I thought that on these newer cars air intake temp sensors control both mixture and timing. Guess not. I'm a bit confused by that mixture control write up. Why would tricking it into thinking it's cooler make it richer? Shouldn't it do the opposite? I understand colder = more O2, but I know from my own tuning on my mechanical injection car that when it gets colder I dial in lean for more power.

Edited to add: just realized, we are talking about different types of timing. I'm talking about injection timing.
 

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Why would you want it richer? They already are pig rich. Leaner is faster, but more dangerous as detonation(pinging) can be fatal.
 

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We all are going to need to know how to get the computer to respond to mods we do(those who mod, that is). Without the ability to move the PCMs targets around, we are going to run into some serious problems with aftermarket parts.

If we fake the IAT into thinking it is much hotter than it really is, it will start dumping extra fuel to richen the PCM up(know this from my drive through Yuma in 122 degree heat, MPG dropped dramatically even going to lower speed). However, the PCM will also pull timing a certain amount and then it will listen for knock. If it hears knock, it will pull more timing, but it will put it back if the knock goes away.

Right now, the only way I think it could be done is to have a set of injectors made that flow "x%" more than the stock injectors. This is a costly route for us, though, as injectors come in various sizes already that problem won't support a small change in flow. We could also try to figure out how to bump the fuel pressure. Fuel injectors are rated at something like 31psi of fuel pressure. If you run 50psi of pressure, the effective flow rate of the injector goes up. I can't find fuel pressure info on our SRT8s, so I will have to see if we have a schraeder(sp??) port on the fuel rail. If so, I have a fuel gauge I can stick on it. The next problem would be figuring out how to bump that pressure small amounts.

Edit: Okay, our fuel rail is bare. No test port. Our fuel system is a returnless system, so there is no easy way to boost the fuel pressure. I am going to have to crawl under the car to see if the fuel pressure regulator is internal to the pump(bad news, as then we have to pull the pump/regulator system to make any changes) or an external split right outside the tank(possible, but I doubt it). When GM went to returnless fuel systems, some of the hard core guys built simple return lines in after the line exited from the tank. The put a regulator in place and simple return line that just went back in the tank.

Todd
 

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It may be possible to use and external pump and regulator system to boost the stock pressure. Most of this would mount down along the fuel line somewhere on the frame. You would most likely still have to drop the tank and plumb in a return line.

Until somebody gets us specific tuning ability for the DCX cars, we are really looking at a bit of work, IMO, to get the air/fuel ratio shifted one way or the other.
 

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marlinspike said:
Bugszrt, it's cause he's got aftermarket headers on.
My brother just got headers on his charger. He is going to the dyno and will have the A/F charted. I believe headers will make a speed density system run a little leaner but from what I've seen these cars need to be leaned out some.

I will post the before headers and after headers A/F readings.
 

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Speaking of getting the 6.1 flowing, musn't Hennessey have been able to mess with the computer in order for his 392 stroker to work? Is he holding out on us on the computer front?
 

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JMatt said:
Let's pretend that with cold air intakes, and/or performance exhaust systems, that the air/fuel ratio leans out - perhaps even leaner than ideal. How would I trick the car into running richer?
What A/F ratio do you consider the onset of problematic, and what A/F are you aiming to achieve?

Zilla
 

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marlinspike said:
Speaking of getting the 6.1 flowing, musn't Hennessey have been able to mess with the computer in order for his 392 stroker to work? Is he holding out on us on the computer front?
It is possible that Hennessey has ways to work the PCM, but I am skeptical on that. All the tuners I have contacted and the info I have read points to a very difficult PCM. However, it is also very possible that very few enthusiats have come onboard with DCX products to really push the aftermarket. LT1 edit was kind of the starting point for GM tuning as we see it today and my understanding is that a couple of skilled computer guys got involved with F-bodies and started looking at the code. It just kind of exploded from there. Maybe some skilled computer boys/girls will get into the LX platform soon and want some mods :D

Todd
 

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Discussion Starter · #15 ·
Is leaner than 13.5:1 too lean? I'm thinking 12:1 could produce some power gains. Now that all that extra air is flowing, I'm curious about getting some gas flowing to match.
 

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the stock fuel system is fine up to 450 rw hp. if some of you guys want to re-invent a new wheel and put it on your pogo stick then thats cool too. most fuel injectors are rated at 3 bar or 43.5 psi.
 

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Every motor is different but leaner than 13:1 (before cat) can be problematic on a street car. Too many variables ... bad gas ... different loads ... changing weather.

BTW - Programaramma (company) has some new Mopar flash tech coming soon so expect a Mopar HEMI truck predator soon and maybe a few other applications to boot. I just became a Chipmaster Revolution user/tuner myself. Fun stuff :)
 

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14.7:1 is stoichiometric so how can leaner than 13:1 be problematic? Besides, leaner gives you more upper end as long as you are still burning all the O2. This engine is what 10.5:1 compression? I don't think you'll gain anything going from 13.5:1 to 12:1, maybe down low but you'd lose enough to more than counter that up top. Max power is typically around 13.7:1, leaner if you have the octane to support it.
 

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John Hennessey said:
most fuel injectors are rated at 3 bar or 43.5 psi.
Is that all? I have a mechanical injection car that runs at 45psi, I would have thought by now they'd be much higher pressure, especially in these high hp engines.
 

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marlinspike said:
14.7:1 is stoichiometric so how can leaner than 13:1 be problematic? Besides, leaner gives you more upper end as long as you are still burning all the O2. This engine is what 10.5:1 compression? I don't think you'll gain anything going from 13.5:1 to 12:1, maybe down low but you'd lose enough to more than counter that up top. Max power is typically around 13.7:1, leaner if you have the octane to support it.
I am speaking of WOT operation and as you admit yourself "leaner if you have the octane to support it." I have to run FTP 3 bag sim tests and do specific grav tests on pump gas and I will tell you that OCTANE fluctuates nearly a whole point from tank to tank or brand to brand for the same "91" octane fuel. CA fuel sucks to say the least. If you are talking engine dynos and constant load 13.7 is not a bad number to achieve BUT we are talking street cars where they are exposed to non-spec fuel, four passenger loads 15% inclines and sudden changing load conditions (spinning tires @ 4500-6000 then getting traction.) A street vehicle tuned @ 13.7 for WOT is careless tuning when what you are trading is 5-6 HP for substanitally higher risk to detonation. Race cars are an entirely different game-controlled environment, controlled fuel, purpose built car.

Is that all? I have a mechanical injection car that runs at 45psi, I would have thought by now they'd be much higher pressure, especially in these high hp engines.
What he said was injectors are RATED at 3 bar not that it was the pressure most cars run at. All my recent cars (GM) run 52-65 psi depending on whether they have bypassing fuel systems or static pressure. My carbed Nova is a standard 12-15 psi.
 
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