Exhaust temperature / boost pressure

[DieselMonkey]

I posted a question a few weeks back, confused as to why my wastegate wasnt operating even at high engine revs while sitting stationary.

Can someone clear this up for me once and for all.....

Basically, i would have thought that the total volume of exhaust gas exiting the cylinders and entering the turbine housing would have been the same with the engine 'loaded' or unloaded, simply due to the same amount of fuel being used to produce the same number of revs.

In short, does loading of the engine increase exhaust gas temperatures to a greater point of expansion, which is necessary for the wastegate to operate ?

If a TD engine is sitting stationary... would a boost pressure gauge show little to no boost pressure if the engine was unloaded and fuelled up (even to red line) ?

Any info. much appreciated. Regards. DM

[QuickTD]

Here's where you've got it wrong...

Basically, i would have thought that the total volume of exhaust gas exiting the cylinders and entering the turbine housing would have been the same with the engine 'loaded' or unloaded, simply due to the same amount of fuel being used to produce the same number of revs.

The amount of fuel injected does NOT directly relate to engine RPM. The amount of fuel is used to rev the engine to redline under load is FAR greater than that used to rev it to redline unloaded. Think about it, with no load on the engine the only force that must be overcome is the internal friction of the engine itself. This will require only slightly more fuel than idling. Pushing the vehicle requires far more power and therefore more fuel. This in turn creates a much larger volume and higher temperature exhaust stream.

[Mark(The Miser)UK]

My '88 Quantum/Passat Estate will start to show boost if revved above 2000 rpm. It only takes partial depression of foot.
Revs then climb presumably up to red line region except I raise foot to mere 'tickling' of pedal to decrease revs. My turbo happens to only reach 8 or 9 psi when flooring it up a steep hill; whilst my spare '87 'Hatchback' will happily boost over 10psi on the flat...
My Estate does 48mpg imp round town and 60mpg imp on a run at 70mph.... :twisted:

[Patrick]

Question is, how much will these engines take without problems? (melting pistons/valves, etc. The only thing I ever had gauges on was a 1981 Kenworth with a big cam I 855 ci cummins. Was supposed to produce 400 hp at 155psi rail pressure with about 15 lbs of boost. Overfueled (but still clean burning) It would put up about 23-25 lbs boost (depending on ambient air temp)with a rail pressure of about 200 psi. Exhaust temp (about 4" past turbo) would stay below 900 if the revs were high enough (2000 rpm on an engine the factory ran at 2100) to get enough air through the engine to cool it . Let the revs drop,(1600 rpm or less) and the engine would still really pull well (and burn clean) but the pyrometer would climb like crazy if you let it. Cost me a couple ov valves until I got more careful! :oops: I found some links for car size pyros and boost guages, but I don't know what these engines (1.6TD) will take. I'm assuming 800 past the turbo is pretty well the limit for exhaust, but what about boost?

[andy2]

With my K24 the pre and post temps read around 275-300 degrees different

[lord_verminaard]

I've heard of people running 1300 degrees or so (pre-turbo) before you get into problems. I know some of the TDI people have run it that high.   Also, didnt someone a while back mount a 1.6TD on a stand and hit it with as much boost as they could get just to see what it did?  Something like 100 psi of boost or so before it melted the prechambers.   :shock:

[andy2]

I hit 1450 pre turbo once or twice a week and have been doing so for a good year now, this along with 20+psi boost and my engine seems to be holding up ok,It still starts at -20 without a block heater and doesnt really have anymore blowby than before I powered it up :twisted:

[QuickTD]

I hit 1400-1450 pre-turbo regularly, so far so good. Still using a K03 turbo (the original, BTW). Motor has 250000km on it, starts instantly @-20ºC and uses no oil.

[Patrick]

Now we're getting somewhere! probably safe at 1000 post turbo and 20 lbs boost? 30 lbs would be nice!

I just looked at a 91 Jetta with a 1.9 in it, runs nice. Going to think about it for a few days, but I think I'm going to buy it. Now I need some guages and some parts out of my spare 1.6TD pump..................

[QuickTD]

I would say that you would be very safe at 1000 post turbo. 20 psi of boost has been proven pretty reliable with K24 and Garret turbo's. The K03 on the 1.9 might be a bit iffy, I have heard of some misfortune... Therabbitree just posted elsewhere that composition head gaskets can be a problem @ 35psi boost, can't say I'm terribly surprised.   Steel 1.9TD gaskets might allow more boost, but the TDI crowd has reported connecting rod bending problems beyond 35 psi. I'm not sure if the 1.6/1.9TD rods would be stronger or not. I would be inclined to think not, so explore at your own peril...

[andy2]

just thought I'd ad some info about the k24, I reciently plugged the accuator line on mine in hopes of finding its max boost and It went up to 23-24psi and the dropped back to 20-21 :? .So then I took the line off the wastegate itself leaving the wastegates inlet vented and boost spiked at 27 and held at 26 steady. So this proves that the wastegate starts to open via exhaust backpressure at 23-24 psi and is probably fully open at 27 psi,Dr diesel got the same max boost(27psi),I'm running mine at 24psi with a boost controller and I've found it impossible to control the wastegate between 24-27 psi this due to the wastegate opening unassisted.If someone were to weld or hold the wastegate closed the k24 would go 30+psi I would think,not that I would want to go that high anyways but I just thought you guys would find this interesting :wink: