wastegate bleed for a 98 TDI

[TDI Power]

As this is my first post, I would like to say I love this forum, I red so much stuff and learned so many things about my car I never dreamed of!
Some of you guys sound like you are actually the TDI engine engineers.

There is one thing though I seem to be confused about. I believe my car has the GT15 turbo
and in order to get a boost I have to use the bleed system. Some people say to bleed the line going from the intake manifold to the ECU, and some say to bleed a line from the compressor to the regulator valve -N75- where actually there are two lines. One is red and one is blue, which one to use?
Which way is better? Will they give me different results? Is the Dawes controller a good bleed?
Also, I am not exactly too sure where to place a boost meter if I am bleeding. Wont the meter give me a false reading?
If someone could help me out in detail I would appreciate it. Thanx!

------------------
98 Jetta TDI

 

[Peter Cheuk]

Welcome aboard, TDI Power!

I suggest that you get a boost gauge before playing with the boost level any.

I have my boost gauge hooked up to the line to the ECU. I tapped it into the line near the brake booster. I cut the line near the ECU for the bleed. I played with the configuration again two nights ago and the car now gets to about 20PSI under heavy load. I feel that this is the best way to bleed the system since bleeding the line to the wastegate might throw a code. I noticed last night that under light throttle applications the wastegate still operates normally (the sound of the turbo changes from a whistle to a whoosh).

I had analysed the Dawes device and concluded that it shouldn't work on our cars (I, too, have a '98 Jetta-see my car in the Member's rides section, Jetta, MeanGreenTDi). It will probably throw a code before any meaningful boost can be made, though I haven't actually used one to confirm this. Same goes with bleeding the other lines that you mention (again, I haven't confirmed this).

[This message has been edited by Peter Cheuk (edited December 10, 1999).]

 

[TDI Power]

Peter, that was a wild ride with your mean machine. Like the way you ran the STOP sign!LOL. Also no visible smoke going up that hill...nice.

The way I understad this, your boost gauge and bleed valve are on the same line to the ECU. The valve is closer to the ECU in order for the gauge to give actual turbo boost pressure. Am I correct?

 

[GoFaster]

I did the "wastegate bleed" trick with my Passat (same engine as yours), and found that it's worthwhile. Not a huge difference, but what do you expect for $4.29!!

I've had it installed for about a week now, I had it installed before but experienced some set-up problems. Those are now fixed, and the engine pulls noticeably stronger above 2500 rpm or so.

If your car is otherwise stock (like mine, and unlike Peter's!) you might not be able to get boost readings as high as Peter does. Honestly, I don't really want to run boost too much higher than stock, because I tow a trailer with my car, and the last thing I need is a blown head gasket or a hole punched through a piston because of the engine running continuously high boost while slogging up a hill. Like Peter said, this is not something to be messed with unless you have a boost gauge.

Right now, I'm getting 17 psi peak and 14 - 15 psi sustained, which is right about where I want it. Stock, it peaks at 15 and drops to 12.

If you do a search for "bleed" you'll get more info on how to do it,

Brian
'96 Passat TDI

 

[TDI Power]

Brian,

You mentioned a price of $4.29...just curious what did you use as a bleed valve and in which line did you place it in.
Also where is your gauge hooked up to?

Thanx!

 

[Birdman]

I have a 96 Passat Tdi with the Witt Chip. Last week i installed the bleed valve just before the waste gate. I can now get 24 LBs of boost. Every once in a while the car will go into limp home mode when it,s still cold and i get into it. Other then that it shows no codes runs strong.
I think exhaust change will help now.

 

[GoFaster]

All the connections are made at the small hose which comes out of the intake pipe (top/rear of engine) and goes back along the firewall (eventually leading to the ECU).

The valve is a two-way fish-tank valve purchased at Super Pet, and the tee is also from Super Pet. You'll also need several feet of 1/8" diameter hose.

Pull the stock hose off the nipple at the manifold. Connect a short piece of the new hose to the nipple, then the tee after that. Connect the side branch of the tee to the boost gauge. Put another short piece of new hose to the remaining connection on the tee. The bleed valve gets installed with one of the metered ports to this hose, the other metered port open to atmosphere, and the un-metered port gets connected to the stock vacuum hose that goes to the ECU.

You could install the bleeder valve with the bleed port closed and the main port open and play with the settings, but I had a hard time with that. I did some calculations, and determined that the "resistance" of each branch should be pretty close to equal to obtain the desired result (with slightly more resistance on the "bleed" branch, no more than 50% more resistance than the main branch). The second set-up, I pre-set the valve before installing it, estimating "resistance" by blowing through each port. That arrangement worked out perfectly for what I wanted - didn't even have to change the setting after installation.

I would NOT recommend running 24 psi of boost in this engine if you want it to last. VW's own documentation indicates that peak design cylinder pressure for this engine is 130 bar (~ 2000 psi) and with that much boost (i.e. 39 psi absolute manifold pressure) you'll be right around 130 bar without even allowing for any combustion ...

18.5:1 compression ratio results in the pressure at the end of compression stroke 59 times higher than at the beginning of compression stroke because of the temperature increase from compression, not counting some loss due to heat transfer and leakage. 59 times 39 equals too much!

Brian
'96 Passat TDI

 

[Peter Cheuk]

Sorry for not posting earlier but it's been a busy weekend (hey, gotta pay for those mods somehow!). I redid my bleed so that the line going into the final 'T' blows straight at the bleed, with the perpendicular output going to the ECU. The 'Ts' that I'm using are so restrictive that the bleed consists of nothing more than the 'T' and a 18" section of 1/8" hose to act as a muffler (Or else you get this very loud whistling noise). Now I get peak boost of about 20PSI and sustained 19PSI under WOT. The line to the boost gauge is tapped about 10" from the intercooler connection and the bleed is about 8" from the ECU on the same line.

TDI Power, the camera car was a GLX with VR6, noticed that on the final turn I was pulling away from him?

 

[Keith]

A question for GoFaster:

So, (130x14.7)/59 - 14.7 comes out to around 17.7psi of boost. From what you're saying, we shouldn't run mor than that amount of boost after the intercooler.

What about VW's racing 1.9TDI that had around 170-190hp? They must have been running more boost than 17.7psi. What do you think they did to enable it to run safely?

Keith.

 

[SkyPup]

I'm not sure but I think that they lowered the compression ratio of the pistons to get higher BMEP through the engine using higher boost levels.

 

[GoFaster]

Probably stronger crankshaft, stronger rods, better head gasket, lower compression pistons (I think the 115hp European engine has lower compression, too), and they don't care about the engine lasting 500,000 km!

I agree, 18 psi of boost is about the most I'd be comfortable with.

Brian
'96 Passat TDI

 

[Peter Cheuk]

Brian, so, from what you're saying, my car with its 20PSI peak and sustained 19PSI of boost will probably blow a headgasket? Cool.

 

[GoFaster]

Maybe, maybe not.

No doubt there is a certain factor of safety in VW's indicated design limits. And even if your system is set up that way, not even you drive so that the boost gauge is pegged all the time!

What we don't know, is what the limiting factor in the peak cylinder pressure is. I suspect it's the clamping force of the head bolts, which is what prevents the head gasket from blowing, but it could be the fatigue limit of the connecting rods or crankshaft, too. Regardless, if VW says the limiting cylinder pressure is 130 bar, I think I'll keep it below that to be sure ...

If it's a metal fatigue-related issue, the engine will continue to operate for quite a while if there's an overload, but the life of the fatigue-related component will be shortened. Every time you use that overload capacity, a little bit of that component's life gets used up, until boom!

If it's a head-clamping-force related issue, it's not like that at all. There's a certain safety margin, then if you exceed that cylinder pressure just once, bye-bye head gasket.

I've had this happen. Before my Yamaha FZR400, I had a Kawasaki EX500, which has an engine known for marginal head gaskets. A coil wire broke internally, causing the coil connection to randomly and intermittently go on and off. Obviously the engine quit running, but the tachometer varied between zero and pinned past the redline while coasting down because of the random ignition events (the tach ran off the coil that was acting up).

At some point, the plug fired at say 120 degrees BTDC with the engine still spinning at 8 grand. The piston came up anyway, and the pressure blew the gasket. But since the engine quit, I didn't find out until after fixing the ignition problem. The engine started up again and ran, but promptly overflowed the coolant and overheated.

Brian
'96 Passat TDI

 

[SkyPup]

Brian, I have that TDI History Paper which includes some of the information from the VW-AUDI Engineering Design teams SAE series of papers on the 130 bar combustion pressure limits in the new TDI engine design as compared to the previous VW non-turbo diesel engines.

Here is a short excerpt from the portion about the redesign of the engine for incorporating the turbocharger into the setup (the original turbo back then was a KKK16 wastegated unit o[erating at 0.8bar max) also the original compression ratio was 23:1. This was the original TDI granddaddy engine first sold in the AUDI 100 5-cylinder 2.5 liter TDI.

An increase in stiffness between the cylinder head and the engine
block as well as a change in the tightening procedure as essential modifications for the turbocharged Diesel engine. Cylinder head bolts are increased from 11mm to 12mm along with deck thickness. Extensive testing was done to optimize the cylinder head gasket in conjunction with the cylinder block modifications. The cylinder head gasket has to give reliable sealing for combustion pressures up to 130 bar with a sealing land of only 6mm. The cylinder block and head were also designed to withstand combustion pressures of up to 130 bar. The limiting value for turbocharger boost pressure on a diesel engine is peak compression pressure, which has been limited to 130 bar on this engine.
During the development of this highly-stressed high-speed direct injection engine, it was evident from the outset that the long term durability of the pistons would be a key factor in the reliability of the complete engine. In a direct injection diesel engine, the combustion chamber is largely defined by the cavity within the piston. Especially important is to keep the volume above the piston at top dead center to an absolute minimum. The most critical points are the rim of the combustion cavity where the hot gases have high velocities resulting in high thermal heat transfer. The risk of thermal heat fatiguing of the materials is particularly great in this area. Another part of the piston subject to cracking proved to be the intermediate portion above the gudgeon pin up to the base of the combustion cavity. To solve this problem where very high pressure exits, the spacing between the gudgeon pin bosses was reduced.

Hope this helps, so far I have almost 10,000 miles on two different TDI's running max peak boost of 23 PSI with 18 PSI on tap anytime. So far no problems and no indications of any problems, although as you have stated, the engines are more stressed than the OEM's and therefore should not be expected to last as long. However, extra special loving care and attention paid to each of these fine engines may make a considerable difference in their longitivity as compared to some fruitcake with an OEM motor and the inability to read the instructions!

 

[TDI Power]

Thank you everyone for your input.

This boosting bussiness sounds kind of risky, but being power hungry I am willing to try it! As long as I stay within 18-20 psi MAX, I think I should be OK.
First I will install the gauge and will get used to the stock readings, then I will make my baby bleed. Hopefully that will increase some power and decrease the smoke that my P-Box creates.
All this will be done on the line going from the black intercooler pipe....as I hope this is the right one because I cant find any other lines from the intake manifold. I have not checked this yet, but that line should go to the ECU....very bussy lately.

Also about the bleed valve, if one end of the valve is open to free air, can't any dirt get into the air line? I know the air blows out, but what if there is a vaccum or when the engine is off the pressure is balanced.

Pete....I am not surprised the VR6 is loosing you. You probably have 20 ft/lb more torque than him/her!

------------------
98 Jetta TDI

 

[diesel des]

I know the 130 bar limit was for the older vw IDI turbo diesel engines such as I have eg 1.6 td. There compression ratio was 23:1. The 1.9 TDI is probably different. The up in diameter of head studs from 11mm to 12 mm was in 1980-1981 for the 1.6 idi diesel. It does not count for the TDI. I am sure the tdi can handle much more than 130 bar max pressure.

The race TDI 1.9 put out a official 190 bhp but by the end of the 1998 rally session was putting out 220 bhp. It was running 35 psi boost. The only mods are:

Lowered compression to 18:1-18.5:1 from 19:5:1
Different injectors
Ported head with modified valves (bigger I think)
Bigger VNT turbo.
Different fuel pump
Remus exhaust
Bigger oil, water and intercoolers

It possibly had better head studs also but I am not sure.

It used a standard crank, block, pistons, rods etc.

 

[Keith]

If the TDIs start blowing headgaskets, Raceware makes a 12mm headstud kit for the VW turbodiesel engine.

I have an unopened Raceware set waiting to be deployed on the TDI, that was originally intended to be used on a Quantum TD.

Keith.

 

[SkyPup]

Yeah Keith, those have been in my mind too! How much was a set/

Diesel Des, those facts I posted are for the TDI engine specifically. I did not post all the internal mods made to the engine over the IDI engine type, there were quite a few more to the crankshaft, rods, connecting bearings, etc. The purpose was specifically for the adaptation of the turbocharger to the design of the original base diesel engine 4,5,6 cylinders. VW sold off the 6 cylinder to Volvo and AUDI-VW used these modes on ALL THE TDI's ever built for production.

 

[tomo366]

Alright guys check out this as an alternative to the homemade bleed device. www.dawesdevices.com/boost.html

 

[SkyPup]

tomo366, those work great on the A3 TDi's with the GT15 wastegate. Ask Keith, Peter, or D'Nardo about it.

 

[tomo366]

skypup,
How about B-4'S?

 

[Peter Cheuk]

Tom, D'nardo has one (courtesy of Skypup) but he hasn't installed it yet. I have a feeling that it won't work properly on our cars because the wastegate is computer controlled. We will find out as soon as D'nardo finds the time to install his.

 

[GoFaster]

Wow, impressive specs. And with more-or-less stock components inside. I really wonder about that 130-bar design cylinder pressure limit, having seen this. I'm sure they are using better fasteners to hold the head down ... anyone really pushing things should check how much stronger those Raceware fasteners are than the stock ones.

Looks like much of the hot-rodding is done the old-fashioned way: cams, porting, valves, and the like!

One must remember that the race engine doesn't have to last half-a-million kilometers, in fact it probably gets rebuilt on a regular basis. They don't care about pistons getting eroded slowly by the hot high-pressure gases (it happens...) or exceeding the fatigue strength limits of the crank and rods (they'll replace them).

Brian
'96 Passat TDI

 

[Keith]

Skypup, I think the Raceware headstud kit cost me around $150. From what I heard, a headstud kit holds a cylinder head down much better than the stock stretch headbolts.

One way to help make the piston stronger, is to apply a ceramic coating to the combustion surface to keep the piston cooler.

Keith.

 

[diesel des]

Some stuff from the 1.6 idi td SAE paper that you might find interesting. It explains the diffrences in the turbo engine. This all hapened in the early 1980's

" The increase in stiffness between the cylinder head and the engine block, as well as a change in the tightening procedure for the cylinder head baits, are essential modifications required for the turbocharged Diesel engine. As already mentioned thread size was increased from 11 mm to 12 mm along with deck thickness. The tightening procedure was changed from torque controlled to angle controlled. This technique is applied to both the 4- and 5-cylinder turbocharged Diesel engines. Deflection measurements indicated that even under increased forces, deflections stayed well below the usual limits.

The oil circuit had to be adapted to the specific needs of the engine because of the higher thermal loading. In addition to the conventional pressurized lubrication system, oil lines with upwards directed jets are mounted in the crankcase at each cylinder to provide additional cooling of the piston bottoms. A lubrication circuit was also added for the turbocharger bearings. Both features are shown schematically in Figure 21. The oil from the turbocharger bearings flows back into the oil pan via a flexible tube. The oil pump capacity has been increased by approximately 15 % by an increase in the width of the pump gear from 26 to 30 mm. Before entering the oil fitter the oil flows through a heat exchanger, which is cooled by the engine coolant. Figure 22 shows the cooling of the piston bottom. This special oil cooling lowers critical piston temperatures by approximately 30 C.

The chemical and material properties of the cylinder head aluminum alloy have been optimized. The swirl chamber insert material also had to be adapted to the higher thermal load. For similar reasons the crankcase deck thickness has been increased and the region of the cylinder head-bolts was strengthened.

A number of changes were made to the crankshaft. The front end of the crankshaft was reinforced. The highly loaded crank-pin, at cylinder 4, has its radius induction hardened and the oil hole ground while radii at the other pins are roll-hardened. A torsional vibration damper is used.

The top groove contains a rectangular ring with its contact face inclined to the cylinder wall thus providing a sharp lower edge to reduce blowby and oil consumption. The ring is made of high tensile cast graphite iron with a chrome surface 0.16 to 0.25 mm thick. The second groove is fitted with a tapered ring made of cast iron with a conical contact surface of 2,5 degrees. The design is of the reversed torsion ring type and helps to control blow-by and oil consumption even after long operation. The third groove is fitted with a beveled, spring loaded ring with contact surfaces hard chrome plated and profile ground, and a centerless ground tube-like spring, which is narrow wound near the ends. Because of the small height of only 3 mm a high degree of flexibility is obtained at a relatively low tangential force, while good oil control is maintained. The piston ring set is shown in Figure 25.

Intake and exhaust valves were modified for the higher loads. While the naturally aspirated Diesel engine uses CrSi 9 valve steel, a material with higher thermal stress was selected for the turbocharged Diesel. Valve seat wear has been reduced to acceptable values by proper selection of the valve seat material.

Because of the valve temperatures being approximately 100 to 150 C higher a better valve head material is also used for the exhaust valve. In order to prevent hot-corrosion a chromium-nickel-aluminum-plating is applied by the plasma technique.

Valve seat rings for both intake and exhaust are made of a high alloy casting material.

The crankshaft main bearings and the connecting rod bearings are of a three material type. They are identical with those of the naturally aspirated Diesel engine."

 

[diesel des]

All The Info I could find on the VW TDI rally car. Sources : Car And cars
Conversions october 1998
Volkswagen audi car May 1998

Standard engine
bassed on 4 cylinder 110 bhp @ 4150 rpm
177lb ft @1900

Motorsport engine1997 spec
Max power is a quoted 187 bhp (unofficialy 200+ bhp) @ 4100 rpm
boost 2.53 bar (37.2 psi)
max torque 258 lb ft @ 3550 rpm with 220 ft lb availabe between 2000 and
3900 rpm
Fuel efficiency increased over 110bhp standard engine on a fuel consumed per
horse power basis.
43% thermal efficiency
The Block, Cranck and head are taken from the standard 110 bhp engine
production line.
compression ration reduced from 19.5 to 18.5:1
The head has been "ported"
The Garret turbo has been modified but retains vairable geometry design.
Fuel pump modified (not clear if it means a diffrent pump or just wound up
standard pump)
Enlarged holes in the 5 hole injectors.
Cam and valves "Blue printed" with diffrent opening, closing times. Valves
are larger
A lighter flywheel has been fitted and engine mounts strengned
The engine runs a "Chipped" version of the standard Bosch EDC 15 EMS
computer
Their is no more black smoke than the production engine.
The CAT is retained as it does not effect the power output
Fitted with Remus exhaust
Large intercooler
Large rad
Large oil rad
Driver says it is pulling well between 1500 and 4500 rpm
max rev 5000 -5250

1998 spec engine has more aggressive boost and fueling figures to give up to
an unoficial 220 bhp in the cooler uk climate


Gear box
6 speed Gemini Transmissions sequential gearbox
gearbox oil cooler

Brakes
325 x 28 mm discs at front standard discs at rear

Pro flex suspension

info from The Golf December 98
5 Cylinder in mrk4 golf touring car

2.5 l tdi
245 bhp
370 ft lb torque
4 plate carbon clutch
Xtrac transmission
19 inch wheels
378 mm vented discs with 6 pot calipers

 

[SkyPup]

Very nice indeed! Numerous design changes were integrated into the new A4 TDI design superceeding the A3 models too. Wish I had access to one of those Rally motors! Simply awesome that they can withstand so much boost. RaceWare here we come!

 

[diesel des]

I have raceware head studs in my 1.6 TD and still have managed to blow a few head gaskets with them. This was mainly due to high boost and way over advanced injection timing. The raceware studs are good, but they don't work miracles! As for reliability, I don't think a race TDI engine has ever failed to finish due to and engine problem. They have run at 187 bhp in 24 hour endurance races against BMW M3's in Germany and have newer popped. There are some standard engines I doubt would last 24 hours flat out.

 

[Peter Cheuk]

I had received an email from Randy at Raceware outlining his products for our cars. He mentioned installing them as a preventative measure. He said something like: You remove the head bolts one by one (presumably in the tightening order) and bolt up one of the head studs. Tighten to spec. Remove the next one and repeat until you've removed and replaced them all. Then he said to drive your car and let it cool to stress the headstuds. Then you retorque them to spec and that should do it.

While the Raceware headstuds won't eliminate the possibility of a blown headgasket, it should reduce the possibility. To me, it sounds like a worthwhile thing to do.

 

[SkyPup]

The pressure created by the compressed burning gases in the VW TDI engine applies a force to the top of the piston equal to the area of the bore times the chamber pressure. Our TDI's have a cylinder bore area of 7.7 square inches (79.5mm bore) with 1911 PSI (l3O bar design max.) operating pressure creating a maximum compressive power load of 14,715 pounds (7.35 tons) on the piston during each combustive event.

Compare this to a naturally aspirated Chevy Vortec 350ci (5.7 liters) V-8 gasoline engine with a bore area of 12.56 square inches (4.0 inch bore) and 800 PSI operating pressure creating a power load of 10,048 pounds (5.0 tons) on the piston. The VW TDI is putting over 50% more operating pressure on its pistons than the Chevy's! Of course, the TDI diesel is built to handle this load, but this is also a VERY good reason to use the best oil possible and change oil regularly.