Performance Tuning for the Tahoe

[6.2 turbo]

First thing I would do,is try a DB2 cam ring. The DS4 lobes are very small.

 

[Altec]

The start of the cam lobe should be smoothed out,when eliminating the leaf spring. I used a die grinder with about a 3/4 inch stone. I got a bit carried away,and the lobes also got fairly short and steep. So far the cam pin is holding. I might get some cam rings machined properly sometime .

Sorry to bump your thread, I was just wondering if I had read this correctly. You remove the leaf spring?

 

[6.2 turbo]

Yes,there is a little more plunger travel,with it removed.

 

[6.2 turbo]

Well I got this thing back on the road. Compression is now estimated 18-1. Power seems exactly the same,maybe a little more top end. Max boost was 42 psi. Timing seems a little retarded. Head gaskets are holding so far.

 

[turbonator]

Well I got this thing back on the road. Compression is now estimated 18-1. Power seems exactly the same,maybe a little more top end. Max boost was 42 psi. Timing seems a little retarded. Head gaskets are holding so far.

now its time for some pump mods....LOL.... still need some more fuel... which turbo are you running? still the big holset?... nice to hear its up and running... do you think the cement in the block helped to minimize the boom damage?:thumbsup: what do you run for water temp?

 

[littleboy]

Congrats on getting it running again!!

 

[6.2 turbo]

I can't get this engine over 170,even with a 180 thermostat. I also created a timing issue with the lower compression. The Mercedes nozzles made the timing a little more retarded. I set the pop pressure back down to 1600 psi. Timing still is way retarded. I advanced the pump 1/16 inch and its still retarded. I want to check charge pressure next. When the engine is warm the white smoke disappears.

 

[great white]

I'll throw out a guess:

Your spray pattern from the nozzles are too coarse as a result of the mer nozzles and maybe low pump/pop pressures.

Your white smoke is fuel impacting the precombustion chamber walls as a result of the unusually coarse spray and not burning thoroughly, resulting in a raw diesel fuel white "smoke".

Once the head and precup get up to temp, the hot metal is assisting it the vaporization of the fuel and it mixes more thoroughly with the available air charge.

Air velocities in the precup might also be a factor here, but I'm not sure if you've done any work in there or not.

Complete and total guess though...

 

[littleboy]

How do you know timing is retarded? Lower compression can make an engine seem to have retarded timing ...

 

[L98TPI]

Just a off the wall suggestion. How about setting the Merc nozzles at the pop off pressure Merc specs and see how they do? The pre chambers seem close in shape to me. :wiggle:

 

[great white]

Just a off the wall suggestion. How about setting the Merc nozzles at the pop off pressure Merc specs and see how they do? The pre chambers seem close in shape to me. :wiggle:

Dunno about that one. I think he used om606 nozzles. Here's that prechamber:

Quite ingenious really. Course spray into a chamber, pressure rises in the chamber at ignition and forces the remaining fuel through the holes similar to a modern di injector tip to further atomize it and spread the load over the piston crown. The burn pattern is very close to a di tip. Probably as close to a di idi as you can get without going all the way to di. Add to that that it is more centrally located in the head and it becomes much clearer how they get higher numbers (per liter) from the idi mercs. More of the piston crown exposed to the heat front to convert the heat energy into kinetic as opposed to ours where the piston is slammed in one spot and more of the heat escapes with the exhaust instead of being converted to kinetic energy.

I've also read that the "pearl" in the merc chambers is critical to the atomization of the fuel from the nozzle. Could be something going on there with the merc nozzle spray pattern in a 6.x style prechamber where the pearl does not exist. At first i thought the pearl was just a piece of hot metal to assist vaporization of the fuel, but i've read a couple posts where they've changed the shape of the pearl and lost power. So I'm thinking the pearl has something to do with shaping the coarse nozzle spray in the mercs, which makes me wonder if the merc nozzles might not be a good match for the 6.x engines.

The VW and BMW idi's seem to have a similar precup to ours though, might be a few possibilities there.

This is all just batting info and ideas around anyways.....I could be way off base here.

 

[6.2 turbo]

I think its mainly the compression. I ran stock injectors first,it was about the same. I'm also serious about maxing out a stock pump,so the pump needs more work regardless. Pretty much the only thing left is charge pressure,and metering valve linkage. The amount of fuel now is not that bad.

 

[L98TPI]

Dunno about that one. I think he used om606 nozzles. Here's that prechamber:....

I shall consider my self spanked. at:

I was looking at the top and thinking they were like some I have had in my hand years ago out of a tractor. Way different. They also make me wonder why GM didn't go this way also. Humm you reckon the 6.X nozzles spray into the walls of the cup like where the spray goes after it hits the pill/perl?

 

[6.2 turbo]

The spray hits the glow plug,on a 6.5 .

 

[L98TPI]

The spray hits the glow plug,on a 6.5 .

Yep. I bet the back splash from the jet hitting the pill/perl is the spray that gets to the Merc 606's glow plug. They seem to start fine in the cold despite the glow plug being over to one side. (The sister has two MB diesels and the nephew has one)

I'm wondering what the Olds diesel's pre chamber looks like. I have seen a cutaway in the past IIRC is like the 6.X's.

 

[great white]

The turbulence in the prechamber is the primary mechanism to break the fuel droplets from the nozzle spray into smaller droplets, thus exposing greater surface area to the available O2.

The heat in the precup is also a factor in vapourizing fuel that makes it to the wall. Too coarse a spray probably would see too much impact the wall and quench the heat from the precombustion chamber wall, much like a gasser using fuel to cool the intake valve as it passes through. That's a guess though...

The fuel that hits the glow plug in a 6.x is for starting purposes, although the tip probably imparts some added turbulence to the flow.

The pearl in the mercedes cup could be to induce more swirl in the airflow vice a direct effect on nozzle spray. Seems to make sense. But I won't claim to be an expert on that though.

Heck, I won't claim to be an expert on any of this.

"spanking" was not my intent either...

 

[L98TPI]

The fuel that hits the glow plug in a 6.x is for starting purposes, although the tip probably imparts some added turbulence to the flow. The pearl in the Mercedes cup could be to induce more swirl in the airflow vice a direct effect on nozzle spray. Seems to make sense. But I won't claim to be an expert on that though.

Sooo the glow plug tip is the pill/pearl in our engines. If you look into the bore you see the glow plug blocking a direct shot to the cup hole.


The other side, cracks everywhere all the white marks.

 

[great white]

Sooo the glow plug tip is the pill/pearl in our engines. If you look into the bore you see the glow plug blocking a direct shot to the cup hole.
View attachment 31625

The other side, cracks everywhere all the white marks.
View attachment 31624

I don't think I would go as far as to say the glow tip in the 6.x chamber is the same as the pearl in the merc chamber.

I'm sure the pearl has more to do with swirl/turbulent flow than starting.

The 6.x tip is out there to expose it to the fuel on start. Although it probably does make a marginal contribution to turbulence as the air rushes in to the chamber via the huge hole offered in the 6.x design.

The 6.x rushes in to the chamber from one side and sets up a rotating motion as it swirls around the bowl shaped chamber. This is what beats the snot out of the nozzle coarse spray and exposes more surface area of the fuel to O2. The heat retained in the chamber also aids in vaporization of the fuel. The same design that makes our engines run so hot when worked hard (chamber in head) also aids in cleaner burning....catch 22.

The merc is forced through the smaller holes in the tip and, I would assume, tumbles even more around the pearl. This turbulence from both the nozzles and the pearl is what likely beats the heck out of the nozzle's coarse spray. The pearl may also introduce heat which further assists vaporization. The main benefit of the merc chamber I see is the central location and promise of high speed fuel/air action on the piston as it is reminiscent of a modern di tip with several fuel jets from the tip (and a more central location acting on the piston crown).

of course,'as I said before, I could be way off base on all of this...

Anyways:

/hijack

 

[6.2 turbo]

I made a special fitting ,and checked charge pressure. 50 psi at idle and 110 psi at 4500 rpms. I would like to see 100 psi or more at a much lower rpm. I also discovered that the cold advance/housing pressure changes more than timing. I jumped the solenoid to positive,the timing went up slightly. It would idle fine but at part throttle it would surge majorly,and would randomly go wild. The only thing I can think of,is that housing psi keeps the plungers from over traveling at light load ? Or it could have something to do with air bubbles ?

 

[6.2 turbo]

I modified the metering valve and linkage,also modified the charge regulator. Charge pressure is now 100 psi at idle and 125 psi just above idle. I need to limit the internal advance,it has too much now. I got the timing to retard enough,by adjusting the allen screw,but it wastes charge psi,down to 110.