Bigger turbo, less boost

[Maarten]

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...

I just left everything that I didn't know exactly the given value. Volumetric efficiency does not only rely on throttle but on a lot of other things, valve overlap is one that can bump it up, since our diesels have 0 degree overlap I don't think it will ever reach 80%.

If it is running 80%, and like fspGTD figured out that the K24 is somewhere in around the 38 trim.. I would be off the map for sure (not to mention the stock T2/K14)?

[fspGTD]

Volumetric efficiency of a 1.5lNA Diesel and a 1.6 euro GTI engine are posted here:
http://www.vwdiesel.net/phpBB/viewtopic.php?t=1106&start=8

The 1.5D hits a VE peak of 92% at 3000-4000RPM.  By 5000RPM, it drops to 84%.

Keep in the naturally aspirated diesel motor has long intake manifold runners, which probably help boost its VE in its working range, but are lacking in the 1.6lTD.

[Maarten]

Ok.. so the 1.6 and 1.9 are around 85% for the calculator

[QuickTD]

If it is running 80%, and like fspGTD figured out that the K24 is somewhere in around the 38 trim.. I would be off the map for sure (not to mention the stock T2/K14)?

Yes, the K24 would be quite far to the right at 2:1 PR (15psi) but not too bad at the stock 8-10. They are likely running close to choke at 20psi and 5000rpm. The K03, T2 and K14 would be somewhat worse. If you've ever heard the noise that a K03 makes above 15 psi and 5000rpm you would agree that it is nearing the edge of its envelope... The goals for VW were probably more related to drivability and response than ultimate power, so the stock turbo's are all a compromise in sizing. It is far more destructive to install too large of a compressor and have it surge than to run a smaller unit in choke.

 An engine with alot of overlap usually has a narrow range of peak VE but a very high peak VE. Cam overlap and very long cam timing kill VE at anything other than the "tuned" rpm. Because of this, a diesel VE curve will usually be very broad compared to a gasser but may not reach as high of a peak due to the short cam timing. Well tuned NA gas engines can achieve over 100% VE at their tuned rpm due to resonance in the manifolds providing a "supercharging" effect.

The 1.5D hits a VE peak of 92% at 3000-4000RPM. By 5000RPM, it drops to 84%.

Keep in the naturally aspirated diesel motor has long intake manifold runners, which probably help boost its VE in its working range, but are lacking in the 1.6lTD.

I think it would be safe to say the TD, without the long runner intake, operates pretty close to 80%

I should also add that attempting to size a turbo to get its peak efficiency island at full power/redline rpm will probably leave you with pretty soggy low end performance. Worse still, if you run a small enough A/R turbine housing to get the thing to spool you will be dangerously close to surging at low engine speeds. Better to have the compressor pass through the peak eff. island on its way to full power. The idea is to have the turbo spend the bulk of its time in the peak efficiency range. That won't happen if it only hits peak efficiency at full power.

[fspGTD]

Maarten - back to the original question of why the K24 turbo performance varied from one car to another... maybe one of the turbos had significant wastegate leakage that limited how much boost it was able to make?  (See my "K24 turbo disassembly" thread for more info on the wastegate valve leak test and how my K24 turbo did.)

[Maarten]

The exhaust is finally finised, I dropped in a cherrybomb to get rid of the trucknoise (most of the turbonoise is gone too )

It is far more destructive to install too large of a compressor and have it surge than to run a smaller unit in choke.

Well tuned NA gas engines can achieve over 100% VE at their tuned rpm due to resonance in the manifolds providing a "supercharging" effect.

That is clear yes... so VNT is by far the best option to go (but more difficult)

Mercedes uses that pricipal on its V6 engines too with a variable intaketraject to widen the rpmband the effect is pushing VE.

When I have some spare time later this week I'm going to plot it on the T3's 35 Trim map and look where my line is going... on the trim 40 it is very close to the surgeline at 2000-2600rpm, so that will shift a bit to the right too.

That my wastegate is leaking is an option yes... is it possible to clean it without disassembling the turbo? The I could have a testrun before and after with the wastegate screw all the way in.

[entuzijast]

I read someone said that KKK maps are rare, so i hope this my help
KKK K24:


KKK K26:


KKK K03: