N00b Question
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Topic: N00b Question
Posted By: Uncle Rudder
Subject: N00b Question
Date Posted: 28 February 2009 at 7:58pm
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Could one you car-smart guys please explain to me why running lean (<12AFR) can cause an engine to turn into a 700 lbs paper weight? I suspect it has has to do with the fuel thats being injected cooling the engine, however, I know some tuners who run turbo's tune extra rich to cool intake temps, but it is my understanding that this does work slightly but you lose power in the process?
God-dang, seems the more I learn about cars the more confused I get.
EDIT: I might as well ask this question since I already made the thread. It seems that there is a lot of controversey if a lightweight flywheel gives you added WHP. I understand the basic concept behind a lightweight flywheel and less rotational mass. I hear all this talk about "useable horsepower" which is where I get confused. Lets assume you put your car on the dyno before and after flyweight installation, will you increase your numbers, or just rev up faster?
Thanks. ------------- 
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Replies:
Posted By: merc
Date Posted: 28 February 2009 at 8:01pm
| i never got into AFRs but i think your on the right track about it burning hotter when its lean. probably the heat and pressure burns up the rings. |
Posted By: TinMan
Date Posted: 28 February 2009 at 8:15pm
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The more air in the fuel air mixture the more volatile it becomes.
A lean mixture burns much faster for less time.
When the mixture is lean like that, preignition or ping happens.
The fuel mixture is ignited by the compression and cylinder temperature
rather than the spark.
That creates pressure in the cylinder before the piston travels past the top. TDC.
Heat and pressure can crack pistons, break rings, melt pistons, break crankshafts
and so on.
Modern engines with knock sensors control the problem. Tuners on the other
hand block knock sensing to avoid misreading of the sensor. If a knock sensor
senses a knock/ping it will retard the timing while enriching the fuel mixture.
Bad for performance.
Hope that helps.
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Posted By: tallen702
Date Posted: 28 February 2009 at 9:56pm
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Dang, Tin Man beat me to it.
Most modern direct fuel injected engines have an ECU that will alter the mix from lean to rich and everywhere in between based on the necessities of the engine. As TM pointed out, pre-ignition can occur in ultra-lean mixtures which essentially throws the timing to hell and will keep the engine from running properly if at all. More an more modern vehicles are coming with ECUs that are increasingly hard to crack and mess around with the timing. You can put a turbo on a Mazda 6 V6 for instance, but you'll only get a marginal increase in BHP and WHP due to the fact that the timing and mixture settings can't be "tuned" due to the encrypted ECU. Now, for your more popular tuners, you can get after-market ECUs to replace the OEM ECU, but you're running the risk of messing with the timing and fuel richness to the point where you'll royally eff-up the engine. As for the lightweight flywheel, you decrease the curb weight of the vehicle AND increase wheel torque though not necessarily WHP. The flywheel is what keeps the engine turning when you aren't actually feeding it gas. Using a lightweight flywheel is great for engines with a broad power-band and close gear ratio as you'll get the benefits of the reduced weight, however, the smaller the power-band on your car, the faster you have to shift otherwise your revs will drop below the shift point and the flywheel's lack of mass becomes counter productive. Flywheels rely on their mass to keep them spinning. To make them lighter you remove mass which means that it won't spin as long which can cause a drop in revs which will cause you to stall if you don't shift quickly enough. No problem on straightaways, but in cornering, it can be a biiiiiig issue. ------------- <Removed overly wide sig. Tsk, you know better.> |
Posted By: TinMan
Date Posted: 28 February 2009 at 10:17pm
| ^^^ new found respect for Tallen's auto knowledge. |
Posted By: Lightningbolt
Date Posted: 28 February 2009 at 10:32pm
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In worse case scenario a lean condition could warrant a visit from Mr. Squeeky. You will damage a motor. If this is happening something like "man this thing is running better than it ever has" will probably be going thru your head right before it smokes. Guys with turbos have to richen the fuel/air mixture(less air to more fuel) to compensate for a performance enhancement as drastic as a turbo. The more power the more fuel required to cool things down. It's under heavy debate how well and to what extent stock electronic fuel systems handle modification.
While in most cases an actual rich condition will equal less performance as well as worse fuel efficiency the aguement can be made that a rich condition can improve a hole-shot by increasing the torque number. If you could successfully achieve this you'd eventually want to lean the mixture out when the weight of the car becomes "hidden" by virtue of forward motion. Once the car gets rolling it doesn't require as much torque to move it forward so you want an "ideal" mixture to take advantage of h.p.
In most cases you want your motor to run somewhere between rich and lean. I'm not aware of a term that actually describes the area between lean and rich. It's case-by-case where some motors may like a mixture closer to rich while others may like a slightly leaner mixture. A general rule of thumb is the larger displacement motors like or can handle more fuel.
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Posted By: new jersey
Date Posted: 01 March 2009 at 4:35pm
| I like carbs, myself. |