Advanced timing questions

[FordGuy100]

As we all know, the more we advance our timing, the more power our IDI's create (and all diesels in general). I was working on my tractor today, a JD 7810, it has a 8.1L turbo diesel. Makes roughly 160hp. Anyways, stock, this thing runs 18.5* BTDC. This leads me to ask, why can some diesel's, especially cummins which run stupid crazy advance numbers, I've heard of 26* BTDC. What is limiting our engines to such low advanced timing?

The optimal timing is around 9.5-9.7*, but why is that? I've heard to advanced timing causes us to eat our glow plugs, correct? If this is the case, at what point (timing number), does this occur? One more question to ponder is if you are running really advanced timing, what else is effected in the motor, or is it just the glow plugs? And lastly, will our IDI's, like cummins, make more and more power as we advance the timing more and more, or is there a certain point to where we will actually loose hp/torque when we advance to far (I"m sure there is a point were all diesel's have that happen).

This leads me to a thought. I'm going to be moving down south here shortly, to Texas. Summer lows are in the 70's, I highly doubt that I will need glow plugs all that often during summer. Winter time, sure, as it will get to freezing, and we all know what kind of dogs IDI's are to start with no glow plugs and around freezing (or below that) temperatures. I could get around that, as I can just plug in my block heater, and then the rest of the day it should be fine. What if, I were to take out the glow plugs, and have somebody make some sort of special plug, or bolt, or something, that would go in place of the glow plug, and seal off the compression chamber so it will create compression. But, at the same time as doing this, it would get rid of the glow plug tip in the pre-champber, and with the really, really tight tolerances that create the rediculously high compression ratio's that we have, do you suppose that taking the glow plug tip out of the pre-chamber would in fact, probably be as effective in reducing the compression ratio as taking .060" off the top of the piston? I would loose the glow plug, but I might be able to drop compression ratio down a little bit, so I can increase the boost some. It makes you wonder if you could find something to go in place of the glow plug and yet eliminate the tip of the glow plug (as the tip is a ways farther down past where the last thread is), and free up some compression ratio.

So, if the only problem with advanced timing on an IDI is that it eats glow plugs....if one were to eliminate the glow plug, and put something in its place, while reducing the compression ratio some, could you run more advanced timing, and increase power?

I spend a lot of time in a tractor, I think a lot . Any idea's, or comments?

 

[redneckaggie]

not sure about the answer to that one but where abouts in texas will you be moving?? I really admire your train of thought on these idi's you are very methodical and have an ability to think through things that most people cant even dream about. It really makes for a wonderful read... lol

 

[FordGuy100]

I'll be moving down to Tyler, Texas

 

[redneckaggie]

if im ever over that way i will try to give you a shout

 

[RLDSL]

I'll be moving down to Tyler, Texas

You've not going to be too darn far away from here But I wouldn't plan on starting with no GPs, darn things still needed first cough of the day, even in summer, unless you want to spend a lot of money on starters and batteries.

 

[towcat]

dunno much about Tyler, but at Hamiliton, I get all four seasons with a major emphasis on the summer part. But it does drop down into the freezing marks many days in the winter.

 

[ameristar1]

When you compare the engines that you mentioned with the IDI, the thing that stands out is direct injected versus indirect injected. The combustion space that a DI motor has to work with in the cylinder is way larger than the prechamber in an IDI. And with all that room for expansion during the power stroke, the combustion process can get started sooner without necessarily damaging anything, to a point.
The other thing you asked was what gets affected. Everything gets affected! Improper combustion, whether gas or diesel places crazy stresses on everything. It's more evident with a NA IDI motor because of the compression ratio and the cam timing. And the cam timing affects the pump timing. Advancing the pump timing starts the combustion process sooner, which causes the pressure to rise sooner and whatever is the weakest link in the cylinder gets hit. That's why head gaskets blow and glow plugs get shattered, pistons crack, rods bend.
The direct injected/turbo motors have a lower compression ratio so they are not under the same stress pre boost. This allows for more timing advance because the pressure rise is not as severe as in a NA/IDI motor.
Then there are issues like piston crown/bowl design, injector design, bore size, rod length, crank angularity and a whole lot of variables that are involved too but lets just leave that alone for now.
The IH IDI and GM IDI motors were designed to do exactly what they do and not much more. The engineers did not have us in mind when they built these things, so having the extra strength, boost capacity, fuel flow capability, etc. like a Cummins wasn't even considered. If that was the case, getting more power out of these things and making it reliable wouldn't be as challenging. But it's not impossible.

 

[Agnem]

The correct 8.5 BTDC setting using the pulse method was decided upon, because it was my understanding that at the factory, each engine was put on a test stand, and dyno tested. As part of the setup, the pumps are bolted on static timed, but then IH had some kind of rig that would hold the IP firmly in position, while it could be rotated with the engine running! This is true dynamic timing in that the pump is set in order to produce the engines advertised HP rating. Now the interesting thing of course, is that the advertised HP is different depending on the engine application, and that HP is produced based on pump calibration. However, the timing recommendation is the same across the entire engine family. So the question becomes, is there really a timing value that is better, or was that just the "middle of the road" setting that was decided upon based on the range of IP's that would be used with this engine? Of course we know about the glow plug problem, and yea your right. If you get rid of the glow plugs, you solve that problem. But what other undiscovered problems may lie beyond that?

 

[Diesel JD]

Yeah down here I still need my glow plugs even in the summer, for the first start and everyone after that if it has sat more than 5-6 hours. Not that it won't go it will in these temps but it's just not pretty.

 

[DeepRoots]

damn internationals.... I still can't figure out how to use my snapon M3558 timing meter on this thing

 

[FordGuy100]

Ok, thanks for everyones input.

Now as far as not starting with glow plugs, that would be on the person who would embark on this endevour. If I were to do it, I probably would only have it through summer max, maybe just pop the glow plugs out and put the plugs in for a day or two so I can put down a little more hp for certain events. I would not run it during winter, I would set timing back to normal, and put glow plugs back in. Shouldnt take more than 3 hours to swap back.

Now, as stated above, there are many weak links, but honestly, how much timing are you going to have to run to bend a rod, it makes one wonder. Blowing head gaskets would be one thing, but effectivly, I would be lowering compression, even if it was just to 20.5:1, it would still reduce it.

I'm not talking crazy advance numbers. I'm thinking along the lines of 10-12*. Does anybody know what our trucks run at when the cold idle advance is on? Its got to be a couple degree's, and the truck is definatly more peppy. If we can run with that much timing while warming up, I would think it would be fine to run around all day, though maybe things might go wrong as the engine warms up.

Mel, I think it was just the safe place where the trucks were quiet, made decent power and had good fuel economy. As others have found out, when running the pump dry and it searches for fuel and advances timing like no tommorow, we get a huge increase in power. Same thing with the cold idle, it makes it feel like we pick up 10-20hp...or maybe thats just me.

 

[RLDSL]

The thing with advance on an IDI engine is more isn't always gooder
You get to a point, and it isn't too darn far over spec and your fuel mileage will go in the toilet and your engine will sound like it is going to self destruct. most high compression Pre chamber injected engines cannot take too darn much extra advance or bad things start happening in a hurry.
Think about it real hard what you are doing when you are timing the injection point . You are trying to get the fuel to go in at a point when the piston is coming up to just before the top so as it is hitting the top the fuel in the swiril port fires off sending the flame out into the main combustion chamber exactly when the piston hits the top of it's stroke so all the energy of the expansion is spent pushing the piston down.
Now if you advance the timing too darn far is search of something, what ends up happening is the the flame from the pre chamber ends up entering the main combustion chamber too darn soon and it in essence wants to turn the stinking engine backwards..., but MR starter has already set the flywheel in motion the other direction, so you get this horrible knocking and shaking as the engine tries to tear itself apart. Not a pretty situation.

It'll be great having you in the neighborhood, but I sure don't want to have to be making an emergency rescue run for an engine rebuild right off the bat

 

[FordGuy100]

I see. I'm just thinking about timing around the cold idle. Maybe some dyno numbers to back it up. Who knows .

And how close will I be? It would be nice to have some IDI guys close to me out there, or at least Texas/S.E. US close (where 6 hour drive is close ).

 

[FordGuy100]

Engine parameter: TIMING is:
RETARDED ( - ) ADVANCED ( + )
EXHAUST TEMP: increases decreases
CYLINDER PRESSURE: decreases increases
INTAKE MANIFOLD PRESSURE
(BELOW P-TORQUE) WASTEGATED: increases decreases
BSFC (brake specific fuel consumption): increases decreases
NOX (oxides of nitrogen): decreases increases
HEAT REJECTION: increases decreases
HYDROCARBONS (HC): increases decreases
BLACK SMOKE: 1000RPM: increases decreases
BLACK SMOKE: PEAK TORQUE: decreases increases
BLACK SMOKE: RATED: increases decreases
WHITE SMOKE: < 1000RPM: increases decreases
WHITE SMOKE: > 1000RPM: increases decreases

 

[RLDSL]

And how close will I be? It would be nice to have some IDI guys close to me out there, or at least Texas/S.E. US close (where 6 hour drive is close ).

Bingo! You get out this way and we start thinking half day driven is *close* . Heck, My sister is *close* and she's about 2 hours on the other side of where you will be I'm about smack dab in the middle of Arkansas.

The thing about that nifty little cold advance kick in the pants is , now, I cant remember about the ford manual, but most diesel manuals with an automatic cold advance will state very clearly to drive with a light foot till the thing warms up enough to kick down .They get very specific about that for a reason.