Bigger turbo, less boost

[Maarten]

The Garrett T2 (~1.2bar boost) on my 1.9 AAZ broke down last week so I swapped it for a KKK K24 with a 70mm downpipe, I didn't change anything on the injectionpumpsettings. The K24 ran only 0.6 bar with the wastegate disconnected  :? but performance was comparable with the T2 ~1.2bar.

After the first testruns I screwed the spring under the LDA all the way down and gave it some more fuel, now I hit 1.0 bar and a lot more torque.

Can someone explain why the bigger turbo produces less boost but gives about the same performance and at 0.2bar lest boost (compared to the small turbo) a lot more torque?

[A2TD]

Efficiencies between the 2 turbos are different. I havn't looked at the 2 maps but I'll bet the Volumetric efficiency on the KK is greater than the Garrett, hence the KK can move more usable air into the engine at a lower pressure.

[Maarten]

I thought it would be something like that but I lack some turbo-knowledge

A friend runs the same turbo on a 1.6TD JR engine, when he disables the wastegate he hits 1.5-1.7bar, that is cause by the 1.6 engine consuming less air, thus the intakepressue raises much faster than in my engine?

The KKK K24 is OEM from a 1.6TD, do you have a flowmap for that turbo?

[Cheesetoast]

ok, let me confirm, the turbo from the 1.6 gives you more power, all gains no losses?? i was going to do this upgrade and my mechanic talked me out of it because he claimed i would lose power on the low end of my 93 td.

[Maarten]

The turbo has a bit more lag but the flow it produces is massive compared to the T2/K14, and it pulls much longer due to the less restrictive exhaust turbine.

If you use the standard downpipe I think you'll have more lag and less results.. so if you go with the K24, get a bigger downpipe too  :!:

[Maarten]

When do you know it's time for a TDI gearbox with 100m flanges and a sportclutch? When the inner CV joint on the driverside brakes in half and the clutch can't handle the torque when accelerating in 3rd/4rd/5th gear  :roll:

A friend runs the same turbo on a 1.6TD JR engine, when he disables the wastegate he hits 1.5-1.7bar, that is cause by the 1.6 engine consuming less air, thus the intakepressue raises much faster than in my engine?

Was I thinking right overhere?

Garrett maps are all over the palce but few KKK's so a flowmap for the OEM K24 is very appriciated

[fspGTD]

I have not seen a compressor map for the 1.6lTD K24, only the 1.6lTD Garrett.  But based on comparing the specs of the two compressors, I'd expect the compressor maps would be very similar and both would develop roughly the same pressure ratios.  The KKK might flow a small bit more due to it's slightly larger inducer bore.

For a given boost pressure, the efficiency of the turbo will only impact airflow through the motor as much as different pre-turbine backpressures aid the scavenging of the cylinder (which on our high-CR, low overlap motors wouldn't be very much.)  The more efficient turbo however would run with lower pre-turbine backpressure, which could give better performance due to better engine efficiency.  In this case we should also expect to see improved engine effiency (better fuel economy), and reduced EGTs (because less pressure = less temperature.)

It's hard to put a finger on the exact for different boost pressures in the two different motors, but the differing displacements could have an impact.  Certainly differing fuel injection quantities could make a difference.  More fuel burnt = more energy to develop boost.

[deepmud]

how does your low rpm performance feel? I have been considering larger turbos to get the effiency up for highway performance (I have a 1.9td)but worry about the loss of low rpm torque - right now I get 10-12 psi at 1400-1500rpm.

[Otis2]

Deepmud,  what gear are you in, and what speed are you travelling, when you get 10 - 12 psi at 1400 - 1500 rpm?  

I have the same engine (mounted in a heavy Vanagon Westy) and I don't see 10 to 12 psi until about 2500 or more rpm in third gear.  Van is laid up right now, and I can't remember what 2nd gear gives me, but it sure the heck is not 12 psi at 1400 rpm!!!

[deepmud]

In each gear
Mostly first, low range - I have the 1.9td adapted to the Samurai drivetrain - or did, before I tore it all out last year - it's bolted to a Toyota W56 4x4 now, nearly ready for the road again after a major "remodel"

I did do the "bleed" mod to the controller, and the Smog power mods, so my max boost is now about 13 psi, and when I get on the road with the new intercooler, I will shoot for about 18.

thread pirate off

[Maarten]

I have not seen a compressor map for the 1.6lTD K24, only the 1.6lTD Garrett.  But based on comparing the specs of the two compressors, I'd expect the compressor maps would be very similar and both would develop roughly the same pressure ratios.  The KKK might flow a small bit more due to it's slightly larger inducer bore.

Do you perhaps know the trim? On the 40 and 45 The boost is in the middle island from about 3500rpm till redline:

Turbocalculator

I don't have a tacho yet so I can't really tell when the boost is coming but I can tell you it is pretty fast, a bit slower then with the Garrett T2 but it flows much more, you can feel it  :wink:

[QuickTD]

I don't think the T3 garret turbo from the 1.6TD is any conventional trim. I have both 40 and 45 trim T3's and they are huge in comparison to the 1.6TD turbo.

[fspGTD]

Using the measurements and formulas from this page: http://www.vwdiesel.net/phpBB/viewtopic.php?t=1841&start=15, I figure the trim is 35 for the Garrett 1.6lTD turbo, and it is 38 for the KKK 1.6lTD turbo.

Here is the compressor map for the Garrett 1.6lTD turbo:
http://www.vwdiesel.net/phpBB/viewtopic.php?t=1576&start=8

[Maarten]

thnx  

Gonna try to plot my flow onto that map

I started to weld my 60mm exhaust: the toiletbowl, short bend, straight pipe till the fueltank, 2 bends and then it goes straight in the direction of the hole in my rollpan (have to finish that part tomorrow)

The sound dissapoints me a tid bit, it sounds like a big truck atm... the whiste is more constant and even the revving down of the turbo between gears is very noticable (sounds like a BOV but then lower). Boost goes up even faster and tops just over 1.1 bar while I turned the fuel down a bit to save my driveshafts and clutch  :roll:

[QuickTD]

On the 40 and 45 The boost is in the middle island from about 3500rpm till redline:

Actually, you're calculations used 67% as the volumetric efficiency. A diesel with its unthrottled intake would likely do better, closer to 80% I would think. This pushes the the curve to the right somewhat. In reality the T3 45 trim would be a bit small for a 1.9 diesel running 15psi. I'll let you know how the non-theoretical portion of this T3 sizing exercise goes...