Halfcent

Think back to last domestic car that GM built that was turbo charged. The only one I can come up with was the Buick Grand National. Since then, GM has produced only supercharged forced induction cars, and a lot of them! Why is that?

I had a 2 hour long conversation yesterday with Bill Hahn about a lot of different things, but one thing was the new LNF engine. See, Bill has been quite frustrated lately with GM due to the large number of different Ecotec variants and the their different computers as well. Since 2005, there are over 10 different combinations of Ecotec engines, ECM's, and transmissions. It's kindda hard to make a turbo kit for each different type. Which brought up the LNF engine and it's soon-to-debut release in many 2008 models. Why make a turbo charged Ecotec when the supercharged LSJ already exists? Well, Bill was very interesting to listen to. Apparently, he had some rather direct contact with the LNF developers, and here is what he learned.

It all has to do with the modern catalytic converter. All of it. The history of GM using Superchargers, the current ECM designs, and now, the release of the LNF. See, a catalytic converter has to reach operating temperature before it works. Original converters took a while to reach this temp, and hence the greatest amount of pollution produced by the car was in the first several minutes after a cold start.

For you smarty people out there, you will be able to relate this Open Loop operation of the ECM, and then switching to Closed Loop after the O2 sensors reached temp.

Today, most of GM's converters reach temp with one minute. Most of the ECM's no longer even have an open loop operating mode. Emmisions controls are the best they have ever been.

But, once you stick a turbo charger in the path between the engine and the catalytic converter, your created a major hurdle to GM's years of current exhaust design. The turbo would do one thing in two different ways. First, it would be huge metal heat sink. Second, the turbine itself would also extract heat, soaking up all the heat before it ever got to the cat. This would mean back to open loop ECM programming, which GM just plain didn't want to do.

So why the LNF? Why now? Because they overcame the problem with Direct Injection. The LNF actually injects fuel during the exhaust stroke when the engine is still cold. It sends a fresh fuel air charge into the exhaust, causing it to heat up very quickly. Then, the ECM controls the direct injection to stop when operating temperature is achieved. It's actually brilliant.

Bill finished the conversation with this forecast: Imagine if the LNF is completely successful. Now take the other recent technologies of GM, like Cylinder-On-Demand power in the Impala, and build all that technology into an LS2 V-8. You now have the most fuel efficient, most powerful V-8 engine ever made.

Cool, eh?

Witt

Most GM motors already enrich during open loop to heat the O2 and cat. As a matter of fact, LSJs will actually pull timing in whats called "Cat Lightoff" when ECT is 99 degrees or below in an effort to warm the cat faster. Direct Injection shouldn't have anything to do with being able to warm the cat.

nomoreavril

this might be off topic, but that cylinder on demand thing, thats where it switches to 4 cylinders to get better gas mileage right? well what if you have an exhaust...does that make it sound like a 4 cylinder too? lol.

djt81185

Direct injection benefits are mainly more precise fuel control and atomization. Also it cools the compression charge and removes an intake restriction of the injector in the intake path. IIRC cat converters get clogged when raw fuel hits em so why would gm dump raw fuel at em...A little I can see...but not a lot.

if they really wanted cat heating theyd have stayed with superchargers as less to heat in the exhaust stream cause turbos absorb heat...lots of it.

Cliff Notes....I think cat lightoff was low on GM's priorities when they designed it. A cleaner burning, more efficient, better cooled design i think took priority. just my opinion.

Halfcent

But that is in fact exactly what it is doing. As I said, it injects fuel during the exhaust stroke, something conventional fuel injection simply can't do.
Not raw fuel. The fuel that is injected on the exhaust stroke is actually burned within the exhaust.

Jackalope

The Grand National's last year for production was 1987. The last turbod car GM produced was the 20th ann. Trans Am with the turboed 3.8 in 1989.

The GMC Typhoon was last produced in 1994 and I think the Cyclone was 1994 also.

But your right its been awhile.

Witt

However pulling timing accomplishes the same thing on a port injected setup, which is whats implemented into GM vehicles now.

The easiest thing to do to reduce open loop emissions isn't to fuel the cat (which will kill its life anyway) but rather place a pre cat on the manifold. Subies do this and even non turbos like Toyota/Scion do as well.

Witt

That will kill a cat in no time. If you tune a car too rich, you'll see these effects immediatly, not to mention burning a valve.

Edit: I don't mean to discredit anyone, but what he seems to be saying really doesn't make much sense to me.

shabodah

The Mitsu's use pre-cats and cat's as well. However, due to the drop in wideband sensor pricing, I'd say that would be the easiest way to get into closed loop.

Halfcent

I fear I don't have any of the specifics on how reliable of a set up it is. But I know the idea is directly related to there being a turbo charger in the path first before reaching the cat. However, I do know it has nothing to do with being rich. The F/A ratio for engine combustion would be completely separate. The compression and combustion stages would use up the first charge. Then the injector fires a new fuel charge post-combustion.
I completely forgot about those trucks. Nice.

shabodah

I don't see the need to use the cylinders injectors to do this. With an injector than can withstand combustion temperatures, you'd be able to have just one, basically anywhere in the exhaust piping. Not that I see it as being worth it. New Emissions rules are way out of hand.

Edit: I do believe the last year you could get a 2.0L turbo Sunbird was 1990.

joeworkstoohard

the fifth injector concept was last used effectively on the bosch k-jetronic lambda systems of the late70s early 80s... let it die man, let it die.

meanwhile, i'll go downstairs and play with mine.

shabodah

It was use for and only for emissions purposes?

joeworkstoohard

in a way, yes. CIS injection uses the pressure of the fuel to fire the injectors, in other words, they're constantly spraying.

in order to help get the car to start without damage, there was a fifth injector upstream in the intake that would fire under start up. a heat sensor would tell it when to turn off. so, when you started the car, it would spray for a few seconds to get the car to turn over THEN the normal injectors would take over...

weird, but actually a pretty reliable system.

shabodah

I've read about that, that's more along the lines of the choke on a carb than what I'm suggesting.

Witt

I don't know much about cat efficiency temps or anything, but I do know tuning when it comes to EGT temps. I'm still conviced the quickest way to light a cat (or increase EGT) turbo or not, is to simply pull timing. Thats why this isn't really making sense to me, more so that GM already has been doing this for cat light off(see attached pic). Its a more controlled way of delaying burning fuel, rather than let it burn uncontrolled in the cat and destroy components.
Attachment 1104

shabodah

Witt- I, too, think it'd make more sense to do like they've done on other engines, and move the cat closer to the engine, and maybe even use materials in the exhaust that have better heat transfer properties.

srt-killer

Why can't they use a turbo and no cat. I understand the wole emisions thing but how can subaru do this. The 06 WRX comes cat less. They don't seem to have a problem. And on top of that runing cat less would free up alot of HP.

That Cobalt LT Guy

I dont think you know what your talking about, you dont burn a valve by runing rich you brun them up runing lean.

That Cobalt LT Guy

How about this put the cat infront of the turbo.

Witt

It was my understanding that some subies have catless uppipes only, and have an air injection system instead. They all still have a cat downstream from the turbo I believe.

Pyros777

iTrader: (4)

Everybody always forgets about the poor old 2.0 turbo sunbird. lol

Witt

ROFL, I don't think you understand what increases EGT temps. A burnt valve is from EGT temps exceeding 1600 degrees and not being able to heatsink those temps. Lean mixtures, retarded timing, and still burning fuel in the exhaust caused by overly rich mixtures will all burn a valve.

Edit: Poorly designed cams have also been known to burn a valve as they can't cool enough by seating against the head for enough time.

BACK2GM

There's a reason for that

That Cobalt LT Guy

WTF oh well I guess im guess im too old school give me a carborator and a screw driver.