ALDA removed. Now to get more air at low RPMS?

[777funk]

I don't know much about diesel performance. When I switched to diesel it was because the longevity of these engines, not performance. But after removing my ALDA while changing my 124's Shut-off valve, I think I may be thirsty for more. I see a good amount of black smoke when I go more than half on the pedal from a stand still so obviously the engine would like more air.

Is there a way to get the turbo to spool at more like 1.5k RPMS instead of starting around 2.2k to 2.5k? I'm guessing this is a wastegate adjustment.

But is this ok for the engine? Am I going to kill anything and do I need a pyro and boost gauge for a small adjustment. Is there a rule of thumb that's considered safe?

thanks!!
Nick

[jkoebel]

Supercharger?

[Brian Carlton]

You'd need a variable nozzle turbo. Check out some of the threads on the Diesel performance forum. Lance has installed one of these and gets excellent performance at low rpm's.

[777funk]

A-ha sounds expensive! I was hoping for a screw or two to adjust. I guess there's more to it.

Oh well, a little more low RPM pep is cool with the ALDA removed. I guess that's all I get for now.

[bgkast]

Yep, get a VGT

Originally Posted by 777funk

A-ha sounds expensive! I was hoping for a screw or two to adjust. I guess there's more to it.

Right. A fixed geometry turbo will only spool as quickly as the volume of exhaust gasses can make it accelerate. The only three ways to make it spool quicker are to increase the exhaust volume put out by the engine (nitrous, supercharger, LOTS of fuel, etc), change to a smaller turbine or change to a variable geometry turbo.

[777funk]

Originally Posted by ForcedInduction

Right. A fixed geometry turbo will only spool as quickly as the volume of exhaust gasses can make it accelerate. The only three ways to make it spool quicker are to increase the exhaust volume put out by the engine (nitrous, supercharger, LOTS of fuel, etc), change to a smaller turbine or change to a variable geometry turbo.

Well if these things can go any faster, you're the one I'd ask. So thanks for the response. I suppose an intercooler would help with HP later on but probably not the immediate response on the pedal.

The one thing I notice about most other diesels (Ford's IH, Cummins in Dodges, etc) is that the immediate response is not as delayed. Not sure why this is. Even in my old GMC Suburban with the 6.2 Detroit Diesel, I feel it move when I put my foot to the pedal. Every MB diesel I've driven doesn't move much until I see the RPM's hit around 2k. It can't be just the turbo since the 6.2 engine is NA non turbo. So now I'm wondering... hmm.

But of course the 603 is way faster than the 6.2GM once the turbo kicks in. Just right off the line, not so good. I'm sure everyone who's driven MB diesels knows what I speak of. Just wondering why that is.

[Brian Carlton]

Originally Posted by 777funk

Every MB diesel I've driven doesn't move much until I see the RPM's hit around 2k.

Well, "move" is a relative term. The engine certainly builds significantly more horsepower when the turbo begins to supply more air and the ALDA supplies more fuel.

However, many of the older MB diesels are truly too slow below 2K rpm..........ridiculously so. The problem with these vehicles is one or all of the following:

1) IP timing
2) Insufficient fuel at low rpm (ALDA problem).
3) Bowden cable too loose (tightening it delays shifts).


The SD has these issues corrected and it keeps up with most traffic with about 1/4 pedal to allow it to reach 2000 rpm.

On my 617, I found that over-adjusting the ALDA would cause it to feel "flooded" at low rpm (hesitation followed by a big puff of black smoke). It was obviously over-fueling, I cured it by finding the correct ALDA adjustment (good low rpm power without the smokescreen).

[1983/300CD]

Two words: leaf blower.

(Just kidding, but there have been some crazies on Youtube.)

[777funk]

Originally Posted by Brian Carlton

Well, "move" is a relative term. The engine certainly builds significantly more horsepower when the turbo begins to supply more air and the ALDA supplies more fuel.

However, many of the older MB diesels are truly too slow below 2K rpm..........ridiculously so. The problem with these vehicles is one or all of the following:

1) IP timing
2) Insufficient fuel at low rpm (ALDA problem).
3) Bowden cable too loose (tightening it delays shifts).


The SD has these issues corrected and it keeps up with most traffic with about 1/4 pedal to allow it to reach 2000 rpm.

I've owned 4 MB diesels and all of them were less pedal responsive than other diesels. The 300d I'm driving now is decent but still doesn't compete anywhere near the others at the first touch of the pedal. This is just something I've noticed driving many different diesels. Most of them are quicker (ie jerkier when you hit the pedal). I can floor my 300d and not break the tires on blacktop. It goes very nicely and will jerk your head back after 2k which is in about 1-2 seconds or so. But not remotely a launch from a stop. This is probably better for the car but just curious why this could be.

Brian, your points are valid but I don't think a problem with my car.
1. The IP was recently timed by the MB dealer (very good 60 year old MB diesel mechanic)
2. No ALDA on this one so I'm sure that's not the problem
3. Transmission shifts pretty late if I floor it. Probably around 4-4.5kRPMs.

But I still notice the launch thing. I don't think it's a tuning issue. I'm getting more than enough fuel.

I still think it's a Mercedes thing. Every other diesel I've driven has more immediate (jerky) pedal response. But I wonder why this is.

See the picture of what I interpret a typical 0-60 time as in a Mercedes 300d turbo with a 603. Notice the slow ramp of 1-2 seconds to 10mph or so. It's a cool feeling when the turbo kicks in but different than other diesels. I'm wondering why?

[Brian Carlton]

Originally Posted by 777funk

Brian, your points are valid but I don't think a problem with my car.
1. The IP was recently timed by the MB dealer (very good 60 year old MB diesel mechanic)
2. No ALDA on this one so I'm sure that's not the problem
3. Transmission shifts pretty late if I floor it. Probably around 4-4.5kRPMs.

But I still notice the launch thing. I don't think it's a tuning issue. I'm getting more than enough fuel.

I still think it's a Mercedes thing. Every other diesel I've driven has more immediate (jerky) pedal response. But I wonder why this is.

See the picture of what I interpret a typical 0-60 time as in a Mercedes 300d turbo with a 603. Notice the slow ramp of 1-2 seconds to 10mph or so. It's a cool feeling when the turbo kicks in but different than other diesels. I'm wondering why?

Yep, you've got the best you can achieve.

You're expectations are a bit high for a vehicle that has 123hp at 4400 rpm.............and, probably about 40 hp at 2000 rpm. You'll never get the launch that you seek with 40hp...........just isn't physically possible to move a 3500 lb. mass forward at any significant velocity.

[777funk]

Yeah you're right about that Brian with the launch factor. I figured that there probably wasn't much that I could do. But I still wonder why there's a quicker response with other diesels even low power engines like the old 6.2 in GM vehicles.

It seems like the curve is more linear with other vehicles. actually it is probably the inverse in the 6.2 lol! It looks like it's going to go somewhere when you first step on it and then drops of quite a bit unlike the Mercedes.

[rcounts]

Could part of it be the gearing, in addition to the low HP numbers at low RPM?

Seems to me like maybe these cars were initially intended for the Autobahn. Not so great off the line, but once they get wound up they have lots of pep, AND get substantially better mileage.

Both the "slow off the line" feel AND the difference between city vs. highway mileage seem to be a bit more exaggerated in these cars than in most others. Seems like they really were built to get out there and RUN - not so much to do the stop-n-go...

[Brian Carlton]

Originally Posted by 777funk

Yeah you're right about that Brian with the launch factor. I figured that there probably wasn't much that I could do. But I still wonder why there's a quicker response with other diesels even low power engines like the old 6.2 in GM vehicles.

It seems like the curve is more linear with other vehicles. actually it is probably the inverse in the 6.2 lol! It looks like it's going to go somewhere when you first step on it and then drops of quite a bit unlike the Mercedes.

Take 6.2L without a turbocharger..........a fairly slow turning engine........with quite a bit of torque due to it's size...........and it feels terrific off the line. Unfortunately, due to the low rpm's and lack of airflow, it can't make any horsepower despite it's bulk and you don't feel any additional thrust as the rpm's come up.

Take a turbocharged engine..........one half this size.........which makes most of it's power above 2200 rpm via the use of the turbo..........and the launch is a bit slow but the power increase is significant when the revs come up.

They are just two very different engines............