1.6L Timing advance curve mod...

[burn_your_money]

Does anyone else think that there may be merit to his statement regarding the timing and emmisions?

[jtanguay]

Does anyone else think that there may be merit to his statement regarding the timing and emmisions?

by advancing the timing curve???

[Vincent Waldon]

Absolutely it is true that manufacturers have  for a long time had to balance power and drivability with emission legislation.  

A long time ago when I was a Beetle guy we clearly saw changes in carb jetting and distributor timing directly related to the legislative environment a particular model of Beetle was sold.... California was a great example of special jetting and a distributor with a *special* advance curve.

Diesel emissions of course don't follow the same math, but I can certainly believe that manufacturer still has to do tradeoffs based on emission standards.


Vince

[burn_your_money]

so then the yellow (or green, I forget) spring mod will probably net some nice clean power

[rabbitman]

Andrew, your right on the money. I checked my pump pressure and it was 10psi low. A punch and hammer work fine.....'till you get sick of tapping forever and hit just a little harder, I took mine apart like three times :roll:
After I got the pressure right it sounded like it was pinging to much so I followed hagars advice and retarded the timing as much as I could w/o it shaking. Also rigged a fuel jug up on the passenger floor so I can watch the fuel get drank, kinda depressing, so far barely 10 miles on a quart of diesel. I think I voided my pumps warranty but thats OK, they stink anyways.

[Vincent Waldon]

Hi Mark... not sure what you mean by "exhauster" ?

I know that petrol = gas, boot = trunk, and steak and kidney pie = food poisoning, but that's about it for my knowledge of British ?!! :wink:

If you mean the vacuum pump then the answer is yup.. that's where the OEM ones are driven from actually.

[gldgti]

Now, I know little about the pumps, but could the dynamic timing setting from the factory also be emissions influenced rather than performance  driven, hence there being some merit to what he said?  

good point. in my reading of numerous diesel design papers for uni i did come across many correllations between timing advance and NOx emissions.

the VW IDI is ...notorious maybe?.... for being a producer of NOx, a powerful smog creating gas.

the 1.6TD design paper even goes as far to state that in california the vw idi was given waiver from reaching emissions requirements for NOx merely because it was so good in all other areas!

i know for a fact that NOx emissions are hard to get around with IDI diesels whilst still achieving optimal timing setting for bsfc (brake specific fuel consumption).

[lyeinyoureye]

i know for a fact that NOx emissions are hard to get around with IDI diesels whilst still achieving optimal timing setting for bsfc (brake specific fuel consumption).

True, but the trade offs are definitely not proportional. A ~5% reduction in fuel efficiency is worthwhile to see a half or third of the NOx emissions IMO.

[Tintin]

I'm going to have to think about this, because I'm having a hard time grasping this.  

The feed pump is a simple rotary pump.  It is always spinning.  At low RPM's the pressure regulator isn't doing anything.  All the pressure goes straight to the pump.  Then when the RPM (and internal pressure) of the feed pump is high enough, the pressure regulator's spring is compressed enough to limit the pressure to that specific point.  Above that point the extra diesel is fed back into the intake, instead of the pump.  

Where is my logic wrong?

Yes, in part,  the regulator is effective at idle + ou -, if it's not properly adjusted, you need to back the initial timing.

Several Bosch VE pump have an electric cold start (advance timing) directly on the regulator.

With an open regulator (for test) the motor can not rev higher than 1200-1300RPM.

On another note, there are a lot of different regulator, you can make a different timing curve:

From idle at 40psi to 4000rpm at 75psi ..........
From idle at 40 psi to 4000rpm at 125 psi.........

There are a lot of combination you can make,  a low timing at low rpm is a good help to spool a big turbo,  etc...........

[CoolAirVw]

I cant get my way so I'm gonna delete my posts!

[Giles@PerformanceDiesel]

Hey  guys
being a fully trained Bosch trained tech i can give your conlusive
results on your debates

yes the pressure regualtor, regulates all the time even during cranking
and from all speeds there after.

the vane type pump is always trying to overcome the spring tension on the regulator and when you change the top plug by hitting it with the
punch you are changing the spring tension therefore changing the
pump pressure.

Giles

[Tuppence]

I'm a relatively new to the world of diesels, but I have attached a pressure gauge and photo tach to several pumps on the bench, and I can confirm what Giles just said about the regulator performing its function at all rpm.  At low/idle rpm the pressure may not be sufficient to advance the timing, but it is sufficient to make fuel flow through the orifice in the out bolt.  

Tapping the plug down with a punch results in an increase in pressure all along the rpm range, not just the 'high' pressure.

There has been mention of 'weak' vane pumps.  I'm not sure what was meant, but my experience is that if the vanes are clean and move smoothly in the impeller, they will easily develop 150 psi and good outflow.  The first pump I disassembled was rusted tight; I knew I couldn't make it any worse, so I took it apart, hammered the vanes out of the impeller with a punch, sanded the rust off with 400 grit, re-assembled, and later tested it.  Even that vane pump produced essentially the same pressure as other pumps when the same regulator was swapped into it.

What I would like to see from some of you who have dynamic diesel timing devices, (or from any source if it's available,) is a useful way to relate pressure to degrees of advance: maybe a table or graph showing the typical advance-to-pressure curve.

[jimfoo]

What I would like to see from some of you who have dynamic diesel timing devices, (or from any source if it's available,) is a useful way to relate pressure to degrees of advance: maybe a table or graph showing the typical advance-to-pressure curve.

Well, there are supposed to be at least 5 different advance springs, and on top of that, all the shims. So there is not going to be just one curve.

[Tuppence]

"five springs, shims: not just one curve"

Yeah, I knew it wouldn't be that simple; never is.  Guess I'll just have to get my own dynamic timing device; someday they'll be more affordable.  Until then I'll just have to play with the pressure issue.  Bugs me just a bit, though, that it's a process that only controls timing indirectly: if the timing advance mechanism sitting in the bottom of the pump gets some piece of crud or gunk and doesn't move properly I wouldn't even know it except if it got bad enough to impact performance/mileage to a noticeable degree, which would probably have to be more than 10%.[/quote]

[Tintin]

For those which ever seen, here a feed pump:



What I wants to say about different timing curve, look at this pic, there is different spring hardness:

**From idle at 40psi to 4000rpm at 75psi ..........
    or from idle at 40 psi to 4000rpm at 125 psi.......**



The bleed hole are also different size:



Out-Bolt are also in different size, more or less flow trough the pump and that affect the pressure, and there exist an adjustable out-Bolt:



For people more experimented, it is easy to do anything on the timing curve.