4.6 block options
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ptschram said:
For a guy who likes to criticize engineers, you just wrote a whole lot of theory that really has no bearing on how things actually work.
Have you ever actually run an engine with a wideband oxygen sensor to see the real values?
The engine DOES run at 14.7:1 BECAUSE of adaptive values, oxygen sensors, and closed loop operation. Those systems are what compensates for all the variabilities you mentioned. In fact, modern fuel injection is so accurate, they have to force the system to miss the mark, swing just on either side of 14.7:1, in order to send the NOx and CO to the catalyst that they require for proper efficiency.
Talking about calibration and primary standards has no relevance to a discussion about whether or not the engine runs lean enough to cause detonation.
I wish Drew Sobota would chime in here. He would blow your theory to pieces, Rob, with real data. He's been on a dyno binge here lately testing several engine configurations with various cams, crank/rod/piston combos, and heads.
One thing is for sure, though, these engines are not running lean. Not even close.
One thing is for sure, though, these engines are not running lean. Not even close.
ptschram
Well-known member
R_Lefebvre said:
Never in this thread did detonation come into the discussion. YOU said they run at 14.7 and I stated that they ran close to 14.7 but to say that they all run at 14.7 is silly due to the huge number of variables, not the least of which is the variation in gasoline formulations as gasoline is not a finite mix of compounds, but rather anything that comes out of the cracking tower within a varying range of boiling points.
D Chapman said:
Why do you think I said they are running lean? I just said they are NOT running lean.
R_Lefebvre said:
Yes. I went through this last year. On my track car running a motorsport ECU that I programmed, Motec PLM wideband, and a high flow cat. I came in with a cruise AFR of 17:1. Works well for fuel efficiency. But, failed the sniffer. Way too much NOx. Richen it up to 14:1, NOx is zero, Hydrocarbons go through the roof. Change it to run EXACTLY 14.7:1, it's easy enough to do with a global fuel multiplier, I can adjust fuel +/-1% increments with the +/- arrows on the keyboard, so it's easy to hit exactly 14.7:1 at steady state. Both NOx and CO are lowish, but not low enough. Change it to run closed loop on the wideband, targetting 14.7:1, but with a messed up PID loop so it dithers just either side of 14.7:1 (ON PURPOSE!) and the NOx and HC are both withing spec, pass the test, get my plates.
The reason is, modern cats reduce the NOx and CO emissions of the engine to way below what is possible on even the perfect engine. But they actually need NOx and CO to do this. If the engine is a bit lean, and is sending lots of NOx, the cat can't do anything with it. It can't chemically reduce NOx into N2 + O2. If the engine is a bit rich, it's bombarded with CO. It can't change the CO to CO2, it doesn't have any oxygen. It needs both NOx and CO, so that it can change 2NO + 2CO = N2 +2CO2. It does this most efficiently when it's being hit with waves of NOx and CO. The reason for that is, cats work best when they're hot, as we all know. Sending waves of CO and NOx down the pipe gives them work to do. The chemical reaction increases the temp of the cat, and therefore, it's overall efficiency.
This is touched upon here in the section for a 3-way cat which is what we're talking about:
http://en.wikipedia.org/wiki/Catalytic_converter
And much more thoroughly here:
ftp://www.eecs.umich.edu/people/grizzle/papers/TWC98.pdf
The systems are fast enough and accurate enough to hold the A/F very close to 1.0 Lambda (~14.7), didn't used to be that way, but now it is. So now they actually have to force the system to dither a couple points either way of 14.7.
PTSchram said:
When discussing block failures and possible lean conditions, what other reason could there be? Surely you're not suggesting that if the engine is running lean, with resultant higher combustion temps but not detonation, that the cylinder walls would fail before the exhaust valves?
What other reason could lean running lead to block failure?
Who cares about what the refinery did? You fill up with a load of fuel once every 200 miles. Your ECU can adjust the fueling 4 times per second! If the gasoline you just pumped has a different energy content than the tank before, your ECU has adjusted before you're out of the gas station parking lot!
The ECU can adjust the fueling almost instantly. Variabilities in fuel chemistry, air quality, etc.... it's meaningless. The ECU is several orders of magnitude faster at adjusting fueling than the inputs change while driving your vehicle.
You're stuck back in the carburetor world where you have to pull your carb and change jets to change your fueling.
The EFI systems are so fucking fast now, the only thing stopping them from being faster is the transport time between exhaust port and the downstream oxygen sensor. It takes some amount of time for the exhaust gas to actually reach the sensor so the computer can measure it, and adjust fueling.
But the latest systems even have THAT conquered with calculated transport times so accurate that the computer can resolve exhaust pulses coming from individual cylinders, and develop a fuel correction factor for every INDIVIDUAL cylinder!
"This lean pulse came from cylinder #3, so I'll add 1% more fuel to just that one"
Have you ever actually driven a truck and watched the Short Term Fuel Trims? They change once per second, and probably faster than that but once per second is the polling time of the OBD reader you're using. The STFT's have an authority of +/- 25%, and can go from one end to another in seconds if required. The composition of fuel and air do NOT change anywhere near that fast.
Result? Engines cruise at EXACTLY 14.7:1, +/- what the engineers CHOSE to make them dither at.
The only exception to this, is worn O2 sensors giving an inaccurate reading.
Ok, well the way that read, seemed like you were attributing the lean thing to me.
So what theory is it I have that Drew Sobota would blow to pieces? That EPA certified engines cruise at 14.7:1?
So what theory is it I have that Drew Sobota would blow to pieces? That EPA certified engines cruise at 14.7:1?
ptschram
Well-known member
The 14.7:1 number is a theoretical calculated ratio that only applies for the standard fuel, standard atmosphere, at STP.
As the fuel composition changes, the ratios will change.
This is general chemistry stuff, basic RedOx.
As the fuel composition changes, the ratios will change.
This is general chemistry stuff, basic RedOx.
Ok, from that angle, technically correct. However, it's still pretty irrelevant to the discussion.
My Motec PLM doesn't measure AFR. It measures lambda. Lambda is absolute. You program it to tell it what to display based on what fuel you're using. In this case, Lambda 1.0=14.7. It's just a numerical representation that people are more used to seeing than 1.0.
The Pectel PLM also deals in Lambda, not AFR.
The 14.7 reference is just that, a reference, that people understand, to say that the truck runs at stoich, 1.0 Lambda. If I had said the truck runs at Lambda 1.0, who would know what I meant? You're one of the few who know enough to pick nits about it, you're also smart enough to know what I meant, and that this discussion is irrelevant to the OP.
The truck doesn't run lean.
My Motec PLM doesn't measure AFR. It measures lambda. Lambda is absolute. You program it to tell it what to display based on what fuel you're using. In this case, Lambda 1.0=14.7. It's just a numerical representation that people are more used to seeing than 1.0.
The Pectel PLM also deals in Lambda, not AFR.
The 14.7 reference is just that, a reference, that people understand, to say that the truck runs at stoich, 1.0 Lambda. If I had said the truck runs at Lambda 1.0, who would know what I meant? You're one of the few who know enough to pick nits about it, you're also smart enough to know what I meant, and that this discussion is irrelevant to the OP.
The truck doesn't run lean.
I don't know if this adds to the discussion about engine blocks or not but folks on the forum have shared with me that my 4.6 with the 4.0 pistons had to run lean and that the ECU was setting the timing back so much to keep it from pinging that my pistons and valves would burn up - failure was just waiting to happen - - none of that is true.
The Dyno runs we made were on a stock 4.0 Gems and my 4.6 high compression engine. The 4.0 was in a Defender and the 4.6 is in a Disco. The dyno used a 4 probe sniffer in the tail pipe to measure air fuel mixture. Both trucks were running rich. If I can remember, as I do not have the print outs from the runs, the numbers were in the high 14's to mid 15 air fuel mixture. This ratio did move around at different RPMs but never went lean. The bottom line from both these GEMS trucks at the tailpipe was that they were rich all the way through the rpm spectrum until the speed sensor cut it out - way rich on on initial full throttle if I can remember like 16 or so - - neither engine ever leaned out to the point where it would be considered anything but rich. Neither of these truck need to pass emissions so I cannot say if they would fail or pass. I also cannot say they never saw 14.7 at some time during the run but the tuning guy running the dyno felt the easy path to more horsepower for both trucks would be to lean the tune on the ECU with a chip as they ran so rich in his opinion it was taking away from the horsepower. FYI the timing advance on the stock 4.0 GEMS was maxed at 50 degrees by about 3200 rpm the 4.6 engine with the 4.0 pistons and 10:9 to one compression maxed timing at 46 degrees @ about 3800 rpms. End results as fact you do loose 4 degree of timing running a 4.6 crank 4.6 rods and 4.0 pistons but if you run D&D's timing gear you can get that back and the thing still runs rich and doesn't ping with high test. I do not believe you cannot burn a piston or valve running as rich as these trucks ran.
The Dyno runs we made were on a stock 4.0 Gems and my 4.6 high compression engine. The 4.0 was in a Defender and the 4.6 is in a Disco. The dyno used a 4 probe sniffer in the tail pipe to measure air fuel mixture. Both trucks were running rich. If I can remember, as I do not have the print outs from the runs, the numbers were in the high 14's to mid 15 air fuel mixture. This ratio did move around at different RPMs but never went lean. The bottom line from both these GEMS trucks at the tailpipe was that they were rich all the way through the rpm spectrum until the speed sensor cut it out - way rich on on initial full throttle if I can remember like 16 or so - - neither engine ever leaned out to the point where it would be considered anything but rich. Neither of these truck need to pass emissions so I cannot say if they would fail or pass. I also cannot say they never saw 14.7 at some time during the run but the tuning guy running the dyno felt the easy path to more horsepower for both trucks would be to lean the tune on the ECU with a chip as they ran so rich in his opinion it was taking away from the horsepower. FYI the timing advance on the stock 4.0 GEMS was maxed at 50 degrees by about 3200 rpm the 4.6 engine with the 4.0 pistons and 10:9 to one compression maxed timing at 46 degrees @ about 3800 rpms. End results as fact you do loose 4 degree of timing running a 4.6 crank 4.6 rods and 4.0 pistons but if you run D&D's timing gear you can get that back and the thing still runs rich and doesn't ping with high test. I do not believe you cannot burn a piston or valve running as rich as these trucks ran.
R_Lefebvre said:
Can I say that the Lambda is the measurement, number, or reference base on the stuff comes out of the exhaust. If the lambda is =1 and you are using gasoline, the afr will be = 14.7. BUT if you are using some other fuel, let say ethanol, it will still try to reach lambda=1, but this lambda=1 will present the AFR of ethanol.
I will try to get actual numbers from dyno pulls but whatever the numbers were both the trucks were described as running rich on dyno not lean.
ptschram
Well-known member
Ppaulred96 said:
I have a box full of broken pistons with bits burned away. I don't know if it was because of running lean or superchargers, but they do burn bits away.
Years ago, I had a truck come to me with a worn out fuel pump, throwing all manner of codes for lean conditions. That one didn't burn any holes in the pistons, but I've got a bunch of 4.0 and 4.6 pistons with holes in them and bits missing.
I don't think I've ever seen a Lucas truck burn pistons-yet.
Ppaulred96 said:
wouldn't surprise me, if it was a continuous pull the pcm would not be in its cruise setting, but in a mode that emulates a carberator power valve. But the wideband at the tailpipe on a vechile with cats still shouldn't be trusted.
ptschram
Well-known member
FB111 said:
Could be.
One of them was horribly overheated and driven with no coolant in the block. There are pieces missing from the block deck even
As to what leads to this, I'm unsure as I wasn't present when the failures happened.
Both of the supercharged engines I've torn down had missing pieces of pistons, this could certainly be due to lean conditions as the set-ups I dealt with were known for poor distribution of the incoming air/fuel charge to the front and rear cylinders. The next one I build will have baffles in the intake and a much taller blower mount to increase the volume of the intake plenum.
ptschram
Well-known member
robertf said:
Good point. At the end of the tailpipe, the exhaust has already been scoured for the combustion by-products we'd be looking at to determine stoichiometery.
On an engine dyno, it wouldn't be an issue, but on the vehicle, I'd hope they'd be sampling at the oxygen sensor ports.