Looking to do a few mods on my TDic

[Aidan]

Having put about 5k miles on my recently aquired 95 940 wagon, (current milage 112k) and determined that it is a damn good engine (no blow back at all from the oil filler, no oil or water used in 5k miles, compressions are spot on) I'm in the mood for doing a couple of mods to get a bit more power from the engine, I'm not going drag racing but would like to get more of the engine's potential. I do drive pretty hard a lot of the time so I want to restrict it to whatever would be a safe maximum without having to fit a steel head gasket or replacing the head bolts with studs. I'm looking at 4 main area's, 1, doing the little trick with shimmimg the pump governer springs, 2, up the fuel screw a little bit (not too much, I dont want it smoking like a Missisipi paddle boat), 3, up the turbo burst, it has the factory intercooler so from what I've read I can safely go to about 15 on the boost???, and 4, I'd like to get the turbo to start boosting (spooling?) at lower revs. I'm also thinking of some of the smaller mods like the egr valve and the wastegate valve. The first 3 mods are well covered on here but mod 4 doesn't seem to be. Is it possible to get the factory turbo to boost at lower revs?, at the moment it starts to boost a little over 3,100 rpm, I would like to get it down nearer 2,500 or lower if possible so any idea's on how to do that would be very welcome. The car is dealer maintained from new, has full service history and was very well looked after and never thrashed by the previous owner, I know the guy and can verify it was never overheated so it's a good sound solid engine. I'm running full synthetic 15/40 engine oil and will be flushing the autobox shortly, changing the filter and using full synth auto fluid. A new cambelt, injector pump belt,water pump and idler's etc were fitted 21k miles ago, I know there good for about 80k but I'll probably put a new belt on anyway just to be certain as due to the low milage the belt is 5 years old. In the future I plan to fit a taller axle to give it longer legs in the gears and get the revs down a bit for highway cruising. Any thoughts, recommendations, or comments on what I'm planning are very welcome, especially regarding what order to do the mods as I'll be doing it over a period of time, I was thinking governer spring first, then up the boost, next up the fuel screw and finally get the turbo to start boosting at lower revs, seems a logical way to proceed to me, what do you guys think? thanks guys,
Aidan.

[Jason]

I would stick with the 15lbs or so limit on boost, I wouldn't bother taking the pump apart to shim the gov at this performance level however. Turn in the main fuel screw, also grind the fuel pin and adjust the star wheel down in the AFC housing slightly for a little more low speed fueling. You also need to look at the condition of your turbo, and check for intake and exhaust leaks. The stock turbo is tiny (.36 A/R exhaust housing) and should spool instantly almost. If your not making boost untill 3k rpms, somthing is leaking boost out, exhaust is leaking out before it gets to the turbo, or your turbo's compressor impeller is junk. The stock turbo should be spooling or starting to make boost by 1500 to 1800 rpm and easily make full stock boost by around 2000 rpm. My big T3/T4 can make 20lbs of boost at 2500 rpm, and full boost by 3000, and this is with a much larger stange III .63 A/R housing. For you to have that lazy of a spool up something isn't right, I would look into that first.

Jason

[Jason]

Also don't loose too much sleep over the actual boost level, its more the fueling that makes a difference. You can install an inline waste gate adjuster and make it push 15lbs of boost with stock fueling but have no improvment in performance. Turn the fuel up untill the 15lbs doesn't clean up all the smoke, and then back off the fuel screw untill it just has maybe a light haze at full throttle and boost, then you are using all the fuel your injecting, and utilizing the 15lbs of boost. If you did a different intercooler, I wouldn't hesitate to push up to 20lbs of boost. I ran 25lbs for a year and a half before my head gasket let go (stock gasket with bolts) and it was a ROUGH year and a half. More conservative fueling and about 20lbs of boost would net you a nice increase in power.

Jason

[Aidan]

Thanks Jason, thats an interesting point you mention about the turbo. I dont have a boost gauge fitted, (although I will be fitting one) I'm going purely by how the car performs, if I accellerate at full throttle, it'll pull quite strong up to 3,100 rpm and then it's like your hit up the back by a truck, it really slams you into the seat hard and pulls like the Devil so I'm just assuming thats the point when the turbo starts boosting. There is definately no exhaust leaks anywhere on the system or at the turbo, or on any part of the induction so perhaps the impeller is worn or similar. I would have thought, as you say, a turbo that small should spin up a lot quicker. I'll have a look at the turbo and see what it's like inside. Thanks for the tip, much appreciated. BTW, what is the stock boost for this engine, am I right in thinking somewhere around 4 or 5 psi?

[Jason]

Stock boost is 8 to 10 psi. It may be spooling up slowly up to the 3k rpm point, or the start wheel under the AFC housing is up pretty tight and its taking the full boost to push the diaphram on top of the pump down to allow that little extra bit of fuel. I would do the boost gauge first to see where your at, if your getting the boost down low but it doesn't really pull untill higher rpms, the air is there, the fuel is not. Adjusting the afc housing and grinding that pin will help with that, along with turning in the main fuel screw. Make sure you read up on doing that, and do it with the engine running. Also have the idle screw loose so you can back it off and keep your idle as you adjust the main screw in. At the level your trying for, I would expect about a turn in or so will add the power your looking for, but every pump is different, it will be guess and test.

Jason

[Aidan]

thats great Jason, thanks, I'll get a gauge sorted out first then and see whats happening with the boost, not much point doing the other stuff until I have a better idea of what the turbo is doing.

[Aidan]

Ok, just rigged up a gauge, I used my Sun Electric pressure gauge from my gas engine diagnostic/tune up kit because I know it's very accurate, and at 4 inch diameter, it's nice and easy to read while driving. I tee'd it into the small pipe that runs from the inlet manifold to the top of the pump. Not much happens free reving in neutral until the revs get up high but obviously it's not under load so I wouldn't expect much boost at lower revs. Once driving however (it's auto) the boost shoots up as soon as you touch the throttle, even the slightest pressure on the throttle gives an instantainous increase in pressure which rises very smoothly and rapidly. Being auto I cant "hold it" in gear but on half throttle in 2nd I can easily get minimum 10 psi boost before 3,000rpm, in fact it's probably pushing a good bit over 10 psi, my gauge only reads to 10 psi and the pressure builds up so quick you can actually hear the needle "dink" as it hits the stop. On a kick down to 2nd at 25 mph, it goes from about 1.4 psi to 10 psi in 0.9 of a second (using a calibrated digital timer) Climbing a steep hill in second I can easily get 10 psi at around 2,700 rpm on lightish throttle so It looks like the turbo is working just fine. Your probably spot on regarding the fuel pin/star wheel aspect as the power really comes on with a bang above 3,100 rpm, and I would also suspect it's running weak/lean anyway (if their the right terms to use for a diesel) as apart from a very slight puff of light greyish smoke when starting there is no smoke whatsoever from the exhaust even at full power, the tailpipe itself is exceptionally clean for a diesel (the exhaust is about 5 years old) no sooty or oily deposits at all, it's more like a gas engine exhaust. At night you can normally see smoke showing up in the headlights of the car behind, with mine there's no smoke at all showing up, all you can see is what I would call a "heat haze" effect, a kind of visual shimmering, but certainly no smoke, so it looks like the engine could easily handle some more fuel.

[Jason]

If its slaming your gauge, you may want to get one that reads higher and see what its doing. Your waste gate may be bad (mine was when I bought my car) and it ran like crap. High drive pressure since it doesn't open up, and rather than the waste gate controll boost, the dump valve would just open in front of the manifold and blow boost out there. Total crap as far as performance is concerned.

Jason

[Aidan]

yep, I was thinking I could use a higher reading gauge to see just how high the boost is getting. this being my first diesel, and indeed my first turbo, I confess to not having much knowledge of waste gates, I believe there function is to relieve excess boost pressure but I dont know how to test them or what pressure they should open at (I assume the waste gate is that device with a diagphram and lever that sits between the turbo housing and the exhaust manifold???). Naturally I cant be certain but my instincts tell me that side of things is ok, as apart from the bang in acceleration at 3,100 rpm, and a slight drop in acceleration at 4,600 rpm upwards, overall the engine drives very well indeed and the way I drive it (very hard) after 3 months I'm sure something would have gone bang by now if there was an excess boost problem. I'll see if I can get another gauge and see where we're at as it's definately pushing a lot more than stock boost. Thanks for your help on this Jason, it really is appreciated.

[Jason]

You are correct, the waste gate controlls boost. However if its bad and doesn't open, you can over spool the turbo which creates high charge temps and high drive pressures, along with sky high EGTs. I'm not familiar with the factory intercooled setup, I don't know if you have a boost dump valve built into your manifold or not. My car had a dump valve that would open at around 11 or 12 lbs of boost and relieve manifold pressure back into the intake before the turbo. The boost readings wouldn't get high, however the turbo was screaming fast enough to make 30lbs of boost and with the waste gate staying closed, the drive pressure was super high and at upper RPMs the engine couldn't breath... A higher reading boost gauge would be a good idea.

Jason