downside of advancing timing??

[kevcruiser]

Good day gents........I'm curious if you could weigh in to the downside of advancing pump timing. My old cruiser (hdj80) had the timing advanced before I had the pump redone and was excellent to drive. Lots of power and very good mileage. I've just done the shaft seal on my wife's Delica and upon re-assembly accidentally advanced the timing on her van. It has way more power but the fluffy load rattle makes me wonder. I've heard that over advanced timing can be hard on BEB's?? Is this true and/or are there other concerns????
Thanks in "advance"..........(get it??)

 

[Dougal]

More advanced timing means:
More black smoke.
Higher cylinder pressures meaning more noise and more vibration.
Higher NOx emissions
Better efficiency
Usually better power.

 

[gifu]

I advanced the timing on my 1HZ+T by about 1mm. I saw an EGT drop of about 250F (preturbo).

 

[Dougal]

Not to mention more advanced timing gives less boost and delayed boost due to cooler exhaust. More retarded spools the turbo sooner.

 

[Tapage]

I advanced the timing on my 1HZ+T by about 1mm. I saw an EGT drop of about 250F (preturbo).

I did that in my 1HD-T and got the opposite .. maybe due to the amount of diesel that I have set in my IP ..

 

[Dougal]

I did that in my 1HD-T and got the opposite .. maybe due to the amount of diesel that I have set in my IP ..

Maybe due to less boost.

 

[Tapage]

Maybe due to less boost.

I'm pushing 14PSI .. but hey that's just my experience ..

 

[canucksafari]

On the NA TD4.2, Twinnotter600 took it from the factory .74 to .82. He also upped the injector nozzel breaking pressure to 1850 PSI. He says it has given him better fuel economy and performance. I guess the only way to say for sure would be to test it before and after on a dyno. He did up a set of injectors for me at 1850 PSI. If i can get my hands on a timing gauge with the right fitting, I might try pushing the timing up to .82.

 

[gerg]

What does .82 mean exactly? Is that a measurement in mm or something? I am use to timing being expressed in degrees BTDC.

 

[twinotter600]

On the NA TD4.2, Twinnotter600 took it from the factory .74 to .82. He also upped the injector nozzel breaking pressure to 1850 PSI. He says it has given him better fuel economy and performance. I guess the only way to say for sure would be to test it before and after on a dyno. He did up a set of injectors for me at 1850 PSI. If i can get my hands on a timing gauge with the right fitting, I might try pushing the timing up to .82.

I first advanced the timing on a non turbo TD42 from factory 0.74 to 0.82. The rig went way better with no perceptible increase in noise. John you had a ride in it near the Ottawa airport. Some time later I rebuilt the injectors on my '94 factory turbo TD42T, upped the cracking pressure to 1850 and advanced the timing from 0.4x (can't remember). I also used nozzles from a TD42Ti which are 121 degrees instead of 113 degrees. The cracking pressure for these nozzles (TD42Ti) is about 1850 instead of 1630 ish.

The timing values mentioned are cam disk lift from a VE pump measured through the back of the pump head.

As I understand this tech, the timing is set slightly retarded for emissions.

 

[Dougal]

What does .82 mean exactly? Is that a measurement in mm or something? I am use to timing being expressed in degrees BTDC.

Yes a plunger measurement. Spill timing to know degrees BTDC is the way to really know, but even I don't bother with that. I just keep adjusting till I've got the right tradeoff between all the variables. Which on my Isuzu was right where the factory alignment marks were.

 

[canucksafari]

The rig went way better with no perceptible increase in noise. John you had a ride in it near the Ottawa airport.

And you will remember I thought I was in your turbo rig it hauled @ss so well! ... and no black smoke.

 

[diby 2000]

Thread dig!

I just keep adjusting till I've got the right tradeoff between all the variables. Which on my Isuzu was right where the factory alignment marks were.

Are these variables;
Spool rate
EGT
Noise
Ecconomy

Are there others to look for?
Can you tell the combustion temps/pressures or NOX production?

 

[gerg]

peak cylinder pressure tools are available but are not a coomon tool for any shop. Not sure where you would get that. Only reasonable way to tell if your timing is optimal is to dyno tune it. Adjust timing and dyno...adjust timing and dyno... repeat over and over for an hour till your where you like it.

 

[diby 2000]

peak cylinder pressure tools are available but are not a coomon tool for any shop. Not sure where you would get that. Only reasonable way to tell if your timing is optimal is to dyno tune it. Adjust timing and dyno...adjust timing and dyno... repeat over and over for an hour till your where you like it.

So is it power and torque your looking for?
Along with EGTs and above variables.

 

[gerg]

So I personally wouldn't tune timing for egts, id use boost to control that. Id be looking for what timing gives me peak torque a few hundred rpms before my cruise rpm but that is my personal preference. Fuel gives you the power you want, boost controls your egts and timing determines at what rpm your torque peaks. That's the way I do it. Course if you have an aneroid your fuel is limited by your boost so it would be more complicated in that regard, especially at low rpms.

I believe that peak cylinder pressure device is to determine if your peak pressures are beyond your design limits. Lowering compression is a good way to lower peak pressures, timing can also do that but you can loose upper rpm power by retarding. When I ported my 3B head I intentionally removed in cylinder material to lower my compression ratio to give my engine longevity. When the temps are really low, like -15c, it is more glow dependent for the first minute, but I feel its a fair trade off.