Late model engines overfueling at WOT

[Brian P]

The catalytic converter's job is to consume unburned hydrocarbons in the exhaust stream. An over rich mixture will make the converters glow red hot and they have been known to catch stuff on fire.

It can only do so if there is oxygen to go along with the hydrocarbons.

[midnightbluS10]

My Premium spec fuel '97 3800SC* Park Avenue (*with undersize driven pulley) would ping lightly at part throttle for a short time if I tanked up with mid-grade but would then switch to its low octane spark table and go quiet. It and all US-certified road vehicles were/are mandated to run frequent function tests while being driven, including checking the knock sensor(s) by briefly advancing the spark until knock is detected. Each such test would re-establish the degrees of knock margin and allow an immediate return to the more aggressive spark table.
I'm very confident that twenty years on cars are much smarter.
Also, many vehicles are calibrated to go rich after 'X' seconds of WOT to keep converter temps down.

Reminds me of my old 95 Blazer. It had the same type of thing. The manual stated that it required 87 octane minimum and running premium 93 octane fuel would result in premium performance. I haven't seen it in anything since then.

[pamotorman]

GM would like to see only high test sold as it would help with the EPA MPG and emissions

[peejay]

I understand the engine management fattening the fuel/air mixture as a safeguard when the engine is pulling hard....But to the point of visible black smoke ?

Not necessarily smoke, but soot is common.

Keep the cat cool with lower EGTs and no leftover oxygen to react in the catalyst.

[4vpc]

As intake temps rise the ECU richens the mix to stave off det'. Is this news?

[Truckedup]

As intake temps rise the ECU richens the mix to stave off det'. Is this news?

No but smoke is news...

[modok]

I see a lot of folks around here on the more major roads pulling away from the lights at WOT or near, and rarely is there smoke.

[user-23911]

But they've all got smoke when you look up the tail pipe.

[ptuomov]

http://f10.m5post.com/forums/showthread.php?t=588858

Dethrottling the engine offers advantages not only in the form of outstanding response, but also for consumption?

Yes, the engine of the new BMW M5 fulfils nearly all map ranges without fuel enrichment, and therefore higher fuel consumption. All in all, the measures I have described, together with other steps, lead to a huge reduction in consumption during approval procedures and as experienced by customers. This serves to extend above all the range – a benefit that our customers have wished emphatically in the past. Today, our engineers can travel from Garching to the Nürburgring on a single tank of fuel. Earlier, this was just a pipe dream.

We sometimes hear that turbo engines are preferred because they are easier to build. Is that true?

No, at least not our engines, not by a long chalk. High speed aspirated engines are subjected to high mechanical forces, and I need charge changing that works not only at the highest speeds, but also with adequate efficiency in normal driving mode.

Furthermore, the turbo engine must fulfil high thermal requirements. The V8 engine of the BMW M5 can run with exhaust temperatures up to 1050 °C. The higher the possible temperatures, the better: I don’t need to enrich the mixture – and raise fuel consumption – for cooling the engine, and high temperatures are good for the response. These temperatures, though, must be mastered and controlled. The engine block of about 200 kg measures at least 110–115 °C, and the temperatures of the exhaust manifolds and turbochargers can be as high as 1000 °C.

These must be contained and controlled both in the moving car and after the engine has been switched off. On top, the engine can provide a great deal of power at low speeds too (as I said before: about twice as much as the old V10), so considerably more heat can accumulate there as well. For most cars, this is scarcely of any significance because the full power output is brought to bear only very rarely, if ever. Yet the BMW M5 is a sports car, and this power is demanded, especially on the race track.

[DaveMcLain]

The catalytic converter's job is to consume unburned hydrocarbons in the exhaust stream. An over rich mixture will make the converters glow red hot and they have been known to catch stuff on fire.

It can only do so if there is oxygen to go along with the hydrocarbons.

I see that makes sense.

[n2xlr8n]

The factory programmed USDM Subaru turbo engines are typically found to be in the 10.2-10.5:1 AFR range...pig rich, but no black smoke.

Look at any late model Hyundai Veloster tailpipe- one can clearly see they are pig rich.

It's the new Black

[Zmechanic]

GM computers run an octane test at startup. It does not stay retarded until tuned again. Why in the hell would any fool put low octane gas in a Corvette?? What would be the point? Save two dollars on a fill up?

There are endless threads online about people pondering if they can put low octane gas in cars that call for premium. Ask the average corvette owner if they know the C/R of the engine in it off the top of their head or what the octane rating actually affects. Fools are everywhere.

[vwchuck]

11.0 is nothing some older turbo cars run 10.0 from the factory. You have to realize that there is a deviation in the entire fuel management system of at least +- 7-8%. On the rich side of stoichiometric 8% is one AFR. So the factory will tune to 11AFR in the rare case you have a car with the tolerance stack up that give you -8%. Then you are still safe.
It really isn't worth the potential destruction for a measly 10hp leaning it out that one AFR. Only a fool would give up reliability for 10hp. Plus in the case of a turbo car just turn the boost up.

[DaveMcLain]

The factory programmed USDM Subaru turbo engines are typically found to be in the 10.2-10.5:1 AFR range...pig rich, but no black smoke.

Look at any late model Hyundai Veloster tailpipe- one can clearly see they are pig rich.

It's the new Black

I'm not convinced that just looking into the pipe and seeing it look black means that its rich at all when running on unleaded. A properly jetted engine will make surfaces exposed to the exhaust either white or black, no in between. Where the surfaces are cooler, black, hotter white. Look into the exhaust port, I bet it has walls that are black yet the valve itself will be white or maybe have a very slight tan tint. The header pipe will be black up by the head where its cooled but then turn white as it gets farther away from the cooling system. Tail pipes and end of the collectors, black.

[Truckedup]

On my 03 Chevy truck ,4.8 , driving around without a load the inside the tail pipe looks clean and wiping a finger leaves just the slightest trace of black...Pulling a trailer on the highway for a distance the inside of the tail pipe is a lot more black......I use leaded race fuel in my track bikes, the inside of the pipes is off white gray just like the old days of leaded fuels...