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Tell me about Turbos on 4.2's

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I just bought another Gq  oiler that comes complete with a snail. 

​It's not inter cooled and I was wondering if this makes any difference to the output you can wring out of them or has any other benefits besides the obvious.  I'm not sure about fitting an IC but I will be fitting Water injection which probably has a better cooling effect on the intake charge. 

Being a turbo I can easily rig the WI to a pressure switch and trigger it that way. I'll also be looking for a possible location for a substantial water tank.

If I do go the IC route, does anyone know what the best size is and what sort of thickness or specification is needed?
I'm thinking and IC, air con condenser and the radiator is a lot of coolers to be putting at the front. 
On boost up a hill, the radiator may be getting warmed up rather than cooled off!


I don't know what actual turbo the thing has, but is there a general safe boot pressure and EGT for the things?

I'm not after max output but I would like to have it healthy and safe. I'm hoping even a conservative level of tune should be a big Improvement on the old NA Girl. 

Any general advise and insight would be appreciated. 


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Where does one start?

The general idea about inter-cooling is lower temp of incoming air from the compressor side to gain extra air/oxygen in to the combustion due to increase in the density of the colder air. This also has an effect on power output but more importantly on the fuel consumption and that's where inter-cooling counts.

There are several factors when considering inter-cooling and those are;

1.Pressure drop and restriction across the cooler and piping

2. Thermal efficiency of the cooler being able to cool the air efficiently.

So with those in mind you'll need to polish your knowledge on thermodynamics and airflow physics.

Choosing the right inter-cooling depends on several factor but alternative methods are;

Water to air being easier but less effective (engine coolant temperature is a limiting factor consider 80°-90°C.

More high end unit would employ different cooling fluid than engine coolant.

Air to air being reasonably effective consider best/better designed units can lower the temperature to about 10° - 15° C

above the ambient temperature.

Than you'll need to consider the TMIC (Top Mounted Intercooler) and FMIC (Front Mounted Inter-cooler) where of course there are trade offs between each type.

I'd of course go for FMIC being the most effective however it is the most difficult to get right even if you buy of the shelve unit and hopes are whoever designed it has done the home work right.

There are several commercial alternatives available for TD42 but knowing your attitudes you'll probably try something yourself.

Here is a link to get you started --> Intercooling


Edited by Rumcajs
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There are several commercial alternatives available for TD42 but knowing your attitudes you'll probably try something yourself.

Here is a link to get you started --> Intercooling



Geez, I'm that predictable 'eh?    :D 


Thanks for the link, Very informative. 

I have also read that on a lot of  Diesels the factory IC works more as a heat sink than a constant cooler.  There isn't enough time for the IC to cool the boost to the outside air, the thermal mass of the IC sinks the heat for the boost event. When on boost a long time such as climbing up a hill, then obviously the IC effectiveness falls off markedly.

I also read about Water sprays on the coolers which are effective but WI is more effective still. 

It seems to be quite a science with a lot of trade offs in space and weight and application as to what you want to do as far as vehicle use.

What are the generally accepted Numbers for this engine as far as max ( safe) boost and EGT?

Would 15 PSi and 600oC be right?

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Thanks for that. 

Next is to get some gauges to see where the thing is going. 
I'm keen to see how the water injection works with EGT's. 
I have read very conflicting reports so I'm keen to see what I find. 

One thing I do know is that when I was towing my trailer with my NA Diesel and I had the water running nearly full time, the engine temps were a LOT lower than without the water.  Could just be due to cooler intake air temps which I tend to think is the likely case but I'll do some checking and see!

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  • 5 weeks later...

I'll also be looking into this for similar reasons.  Finding an affordable 200PSI water pump has got me looking for alternative methods.  I'd rather use/try WI rather than IC as I need the de-coking primarily.  Lower intake temps are a bonus.


I think the  high pressure pumps for WI are a complete and utter crock to make more money from people that believe the Hype. 

Water will break up very effectively in an airstream all on it's own.  I have poured water down the Inlet of my cars Dozens of times to clean them out and you can plainly see how the water breaks up from a smooth stream into a spray as soon as it goes in the throat of the inlet manifold. 

I reckon you couldn't get water to enter a cylinder in a steam unless you put a lot of effort into it. 


The super fine spray is also a creation of the Petrol performance guys imagination. 

They want the water to be vaporised by the time it hits the Cylinders mainly for detonation control.   For De coking in a diesel, what you need is droplets going into the cylinder so they change state in the energetic " explosion" that will greatly aid in the removal of any buildup. 

I have read research where they concluded that this " Cavitation" was sufficient to remove carbon deposits but not energetic enough to erode Pistons or metal in the cylinders. 


I am just going to shoot the water down the intake elbow through a bit of flattened copper pipe to fan it out a bit and let the heat, flow and pressure break it up from there. A mate has had this sort of injector for a few years now and his system works perfectly. Normally on my NA's I use a plastic garden spray nozzle but it won't be practical to mount on the turbo system. 

I am not going to do it pre turbo because that will vaporise the water before it gets to the Cylinders which is not what I want. If I did want pre- turbo, I'd just use a garden nozzle pre air cleaner which has been tested to provide pure water vapor as it evaporates off.  

the reports I have read and the tests I have done myself show there is no degradation of the paper element. 

I tested mine and then left the element in the weather for weeks. It was good as new. 

In any case, you can get the Sureflow type pumps on ebay that do 160PSI pretty cheap. The one I have is 70 PSI rated at 3.8 gal per min but the flow is nothing like that even at 0 pressure.  No matter, I only want 300 Ml min. I was happy for a 35 PSI model but this one came up cheap so I grabbed it.

More than what I'll need. 


I'm going to trigger the WI with a pressure switch at 4 psi which is as low as I can get it. I'd prefer it to come on at 2 PSI so I'll keep a look out for a suitable switch I can substitute. IF I find something to trigger the water at that pressure, I'll back the flow off to around 100Ml/ min and compensate with the extra time the system will be spraying. 

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I'd keep the boost slightly lower around 12-14 psi for longevity and EGT 500° C max. Conservative values could be even lower as the goal is not max power. Cheers


I have put a Grandfather clock size  Pressure gauge on the thing to measure Boost and It's showing 7 psi. I saw a label on the wastegate actuator the other day that says 7.5 PSI so it gels pretty well. 

​I'm in 2 minds about turning up the boost and if there will be any benefit.

What I really want is low end boost as it makes the 7 PSI at about 2250 rpm. I usually find that changing gear around 2000 around town is fine in the traffic.


 I took the thing up the county the other day and was really pleased with it. I got on the freeway and put it in 5th and didn't change gears again till I got to the other end. It had no trouble on any of the hills through the central coast or anywhere else and the biggest problem was keeping one eye on the speedo so as to not creep over the limit. 

For me, thats a totally new experience from any other diesel I have owned. 

I would like a taller diff in the thing though to drop it to about 2500 rpm rather than the 3000 it sits on at 120. Just seems to be revving needlessly for that speed.  Wasn't as economical as I hoped for either and I'm sure dropping the revs would help that too. 

I noticed that I'm getting about 1.5-2 PSI boost at 100-120 on the flat. From there it will go straight to full boost as soon as you touch the throttle. 

I'm not really chasing the top end power which is why I'm not sure if putting on a boost controller and tweaking it up to 10 PSI will do me any good. 

The fuel at the bottom end is already to rich and without the IP having a compensator, turning the fuel down as I need to is going to take the top end out of the thing as well. I guess when I'm doing the highway runs I could turn the fuel up again but it's a bit of a pain on the patrols unlike the ease of access  on the wifes car. 

A mate of Mine had a truck that he turned the Boost up on and swore he got better performance without touching the fuel and the thing ran very clean before hand. I'm of the opinion that turning up boost without turning up fuel will be detrimental if anything but I guess it's something I'll have to test myself. 

Is there a consensus of opinion on changing the boost? 

Would I be better to put on an adjustable boost controller that modifies the signal pressure to the actuator or just get the pressure actuator I want given that it will be conservative anyway?

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Experimenting a little with it shouldn't cause too much pain.


If the waste gate actuator has adjustable rod than see if changing the adjustment will give a bit extra boost because indeed that could make the whole thing more responsive at the lower end and with a bit of extra air coming in should theoretically fix your black smoke too.


The turbo waste gates are usually progressive beasts that is they start to bleed the pressure slightly earlier(depends on type of turbo) during the spool up so you could delay that and have just a little extra (read quicker spool up) while using max pressure limiter to control max boost so something more manageable.

Worth trying for sure if you are after a quicker response


I'm not exactly sure what your setup is and what effects the increase in boost pressure or spool up rate it will have but you could technically if it is possible have quicker spool up at lower revs yet keep the boost same  or marginally higher.


Question is: Have such conservative boost values been set to protect the engine or the turbo or both?



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  • 5 months later...

I have a northside 4x4 water cooled intercooler and upgraded Garret turbo on my GU ute. 137rwkw @13.5 boost. Super impressed with the performance. Full boost 1900 rpm and basically flat to 2800rpm, no turbo lag. Just did 9000k loaded near 4T, mostly dirt. Pulled like a train and I love driving it.

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Just saw this topic has come to light again. 

I have been running the Turbo Troll at 11 PSI after purchasing one of those little boost controller things. Best $40 ever spent!
The thing spools up SOOOO much quicker now and transformed the thing. It's so much better off the lights and a real torque monster down low. 
THE Boost controller seems to have done as advertised and stopped a lot of the wastegate creep down low. 
I dialed the thing up to 20 Psi for a couple of trips round the block but it didn't make much difference. There is enough air at 11 Psi to burn all the fuel I want to put in it so anything else is just hot air and stress for nothing. 

I still can't back the fuel out of the bottom enough without killing the rest of the rev range badly so it's something I have to watch.  I'll keep blending with 5% ULP and hope that helps with combustion as I'm sure it does. 

I put a water injection on in my traditional way, windshield washer pump through a garden micro  nozzle and am spraying into the airbox. Some hits the filter, some goes straight through to the turblow. I have been keeping an eye on the blades for the parroted erosion but unsurprisingly, no sign of it so far. Biggest surprise has been it hasn't even washed off the oily crap that the PVC vent was dumping in there before I pulled that stupid idea out. I was wondering if a little tiny bit of washing liquid may help shift that and any other crud further down the line without building up somewhere else. 

The water makes a big difference to the way the thing goes.  I'm running about 400Ml/min to keep the effects of Veg build up at bay seeing I can't really clean the thing up at low revs with the non compensated pump. The water makes a difference far more than I would have expected, especially when this engine is so grunty to start with.   You can tell when the water runs out because the edge to the torque just falls right off.  I noticed the water made it harder to drive smoothly because any little indiscretion with the clutch or throttle is greatly magnified when the squirt is running. ATM I have it coming on at 3 PSi because the thing will boost to 2 PSI just on the flat at 100 kmh. In that way the water is great because as soon as you touch the throttle the water and boost are there together. I had the water coming on at just 1 PSI and to my surprise, the engine didn't mind it at all.  Just goes through a LOT of water when it's pretty much on all the time. 



So far I haven't tried this one with meth. It will be interesting because maybe it will allow the veg to be backed off and the difference made up with the WI which will help keep the engine clean. I might go get 10 L of E85 tomorrow and wash the petrol out and see how it goes. 

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