Diesel Injection Timing - What Factors Determine Timing?

[Squanderbucks]

People all over the world ask similar questions about whatever is their interest and fiddle with making it better. That is often where "new" ideas come from. Others (most of us) just say go with the book and leave it at that.
However, I suggest if you really want to play with an engine and make "improvements" to it to see what can be done to get more efficiency out of it - do it on a spare engine in your shop. don't shoot yourself in the foot and use your everyday working engine to experiment with on things critical such as injector and valve timing etc. You may learn a lot and find a new solution but if you break something along the way then you are not stuck out on a limb offshore.

[a64pilot]

It’s all a trade off. I used to road race a Suzuki GS500E, I didn’t want to put much money into the engine, but I did remove the flywheel, go to total loss ignition and put it on a dyno and adjust the ignition to max HP about 500 RPM below redline, I got significant bump in max power, but it wouldn’t idle low at all, and the timing was so advanced it was hard to start.
Of course I was running I think it was Sunoco 110 Octane race gas too, so detonation wasn’t a concern
However trying to increase power output on a small sailboat motor makes about as much sense as Nitros Oxide on a Prius.

[model 10]

I bet somebody hopped up a British taxi somehow. The Perkins 107 etc can be run from 36 to almost 50 hp. I think it's just an rpm increase. Funny thing though, many old boats I meet run their engines at like 1800 rpm, and that must be way under 36hp.

[hellosailor]

Wotname-
Were the two engines designed or built perhaps 25 year apart? One immediate consideration could be that diesel fuel standards, or emission regulations, changed during that time, and that the timing change reflects something as insignificant (mechanically) as a way to clean up the combustion gasses. Or perhaps they found that the earlier engines were having too many heat-related failures over time, and decided to cool down the combustion. (If the earlier model used solid metal valves and the later one used sodium cooled valves, that would be an example of a totally invisible engineering change to address excessive heat.)

Forgive me if it is not a marine application, but once upon a time I had a 289 Mustang. Just the less powerful Windsor block. At one point I had to have the engine serviced because the #2(?) valves had overheated, and years later I found out they had a reputation for that, the cooling passages just didn't cool the rear of the engine block enough. But in my attempts to to keep the engine properly serviced but doing better than stock, I did what everyone else did, I moved up the ignition timing as much as I could before it pinged. I vaguely recall getting it up around 40 degrees before there was any problem--and that was way way past factory spec. And yet, it still worked quite nicely.
Somewhere out there, there's an engineer who knows your timing changes. And whoever they work for, isn't going to let them answer the phone, either. Makes things harder these days, doesn't it?

[hellosailor]

"about as much sense as Nitros Oxide on a Prius."
Yeah, that really would be a stupid ghetto mod. Especially since Jay Leno has already posted the YouTube showing a Prius with a Dodge Hellcat package in it. Something like six or seven hundred horsepower, no Nitrous needed.

Winged keel, lifting foil...you know, there's potential there even for a monohull, if you can get the balance right.(G)

But if bumping the timing could match an engine's performance closer to the operating speed and load it was used at, and even give a 5% gain in fuel use? That would be worth doing. Since so many "marine" engines have been bastardized across so many boats because "that'll fit, and its cheaper" I'd expect there's a lot more than factory alternators that can be improved on.

Like a certain classic Yanmar that is always listed as a 30hp engine. Except, Yanmar themselves rate it at 24 hp continuous duty, 27 hp intermittent, and 30 hp only when the user is really high on drugs.

[a64pilot]

You want a 5% decrease in fuel consumption?
Slow down about .1 kt.
You can degree cams and “blueprint” anything, five angle valve jobs, port and polish ports
But why?
I run my 44 HP motor at about 2000 RPM and I’d guess that is less than 50% power?

[Wotname]

Originally Posted by hellosailor

Wotname-
Were the two engines designed or built perhaps 25 year apart? .........

YSE8 1974-1976
YSM8 1977-1980.

[a64pilot]

I just had a thought, we get used to the idea of what we are timing is the actual point something “fires” at because we used timing lights or statically timed magnetos and distributors, but the timing mark on a fuel injection pump does not necessarily mean that is when the injector “fires” or the injection event begins, so with different pumps, you may actually be setting the injection event to the same, even though the marks you line up or etc are many degrees different?

Meaning say for instance you set the marks on one engine at 28 BTC and it “fires” at 10 BTC, next engine, same pump because the timing marks are different requires you to set the pump up at a different number, to achieve injection at 10 BTC.

Potato head manufacturing, same pump, different motors, just like injectors, set up for engine X and it cracks at one pressure, set up for a different engine, different cracking pressure, higher pressure could be used to narrow the injection pulse, or decrease amount of fuel injected, making same parts applicable for different engines, delay the injection event by requiring higher pressure, means you need different timing to have injection event occur at the same time.

This is all theory.

[model 10]

Originally Posted by a64pilot

I just had a thought, we get used to the idea of what we are timing is the actual point something “fires”at because we used timing lights or statically times magnetos and distributors, but the timing mark on a fuel injection pump does not necessarily mean that is when the injector “fires” or the injection event begins, so with different pumps, you may actually be setting the injection event to the same, even though the marks you line up or etc are many degrees different?

I tried to say that several days ago.

[a64pilot]

Originally Posted by Ecos

I tried to say that several days ago.

Sorry, I guess it didn’t click in my brain, or maybe did but took awhile?

[Oceanride007]

Last time I worked on ships as a Marine Engineer, I noticed that the out of phase diagrams indicated about 10-15Deg retarded timing of what similar sized engines than a generation before. And rigid enforcement, that they could not be altered.
Difference is the dreaded Nitrogen oxide. And Environment legislation.

They are formed during the high temp and pressures that occur at TDC. Retarding the timing decreases the contamination.
Cetane number of the fuel, which is a measure of the speed of the flame front. (Octane rating in Petrol Engines) is a most significant determinate in timing delay, I wouldn't think that would change much in distillate but it does in Heavy Fuel Oil. Dilation in pipes is a good reason to get genuine spares, short versus long distance between pump and injector, trust the manufacturer.

[Compass790]

Good question Wotname. Afaik the cams are the same & I have both. Yes the same thought occurred to me about why timing is so different. After reading all the posts I'm staying with stock setting. Interesting Atolls real world test didn't show any noticeable difference & I noticed the same when YSM8 was out 8o but still put it to stock setting.

[Wotname]

Originally Posted by Compass790

Good question Wotname. Afaik the cams are the same & I have both. Yes the same thought occurred to me about why timing is so different. After reading all the posts I'm staying with stock setting. Interesting Atolls real world test didn't show any noticeable difference & I noticed the same when YSM8 was out 8o but still put it to stock setting.

Compass, are you referring to the valve cam lobes or the bolt on injector pump actuating cam lobe?

[Wotname]

Originally Posted by atoll

when i rebuilt my YSB 8 i tried very hard to set it up at 12 degrees,but found it ran fine no matter what combination of shims i put in.

probably the best test would be to run it under load with multiple shims at about 20 degrees then remove shims untill the exhaust runs with less smoke as a sign of less unburnt fuel and better combustion so as to find the sweet spot,bench testing is not really going show optimum combustion angle when under no load.

Good to know!

Which injection pump does the YSB have? The YSE Yanmar one (simpler one) or the Bosch YSM one?

[Wotname]

Originally Posted by Squanderbucks

People all over the world ask similar questions about whatever is their interest and fiddle with making it better. That is often where "new" ideas come from. Others (most of us) just say go with the book and leave it at that.
However, I suggest if you really want to play with an engine and make "improvements" to it to see what can be done to get more efficiency out of it - do it on a spare engine in your shop. don't shoot yourself in the foot and use your everyday working engine to experiment with on things critical such as injector and valve timing etc. You may learn a lot and find a new solution but if you break something along the way then you are not stuck out on a limb offshore.

Good post and FWIW, I don't plan to experiment and will stick with the book numbers but nevertheless, I still keen to understand why such a difference exists.

One thing for sure after reading the replies, I'm no longer going to stress about getting within a degree or two. It's hard enough getting it even close to a couple of degrees. I should note, the YSE manual calls for 8 to 12 degrees and the flywheel mark is 10 degrees. I am erring towards the 10 to 12 area