Thread: 25 PSI boost on 300Tdi

Originally Posted by B92 8NW

Bearing in mind the information in this post RE information from Allard on setting up their VNT kit, what is the maximum amount of boost that a Tdi will handle (using the standard turbocharger) ?

I'm assuming the weakpoint is head gasket / head.

What's the bottom end like?

The VNT turbo they are using has a larger compressor wheel that is reasonably efficient at higher boost pressure. The compressor of the stock 300Tdi turbo is getting too far out of it's efficient range above 18 psi - it can easily provide 22 psi, but is not moving more air, is putting too much heat into the air and increasing the drive pressure (increases pumping loss and reduces VE).

A 300Tdi will handle the boost - I over tensioned the head bolts when I had a VNT turbo on my 300Tdi. You can get MLS head gaskets now, which should be much better - I would be tempted to try 30Psi with an MLS gasket and head studs, or even with over tensioned bolts, and with a suitable turbo.

Having said that, no head gasket will last well in a 300Tdi that has badly overheated and softened the head.

Rick130 pointed out some lube issues recently, so probably an area that needs to be addressed if intending to push the performance of a 300Tdi.

Interesting. Thanks John.

I haven't seen any stud kits available for the 300Tdi but I'm sure an engine shop would be able to work a solution out from seeing a set of the head bolts.

I might try 18 PSI and up the fuelling as appropriate. Already have an upgraded intercooler.

Joel, 18 psi should be safe, IIRC JC has been running customer cars there for a while.

I've been running 17psi for quite a number of years now with upped fuel delivery, but as John said, I've had bottom end problems (big ends) which look like the OE bearings at the least can't cope with the increased loads, at least in a heavily loaded and flogged 130. It may not be near as big an issue in a lightly used Disco, but far too many 300's show advanced big end wear before 300,000km even running stock boost and fuel.

I was hoping to avoid these issues by running the premium syn oils but instead of plain abrasion wear I had stress fractures, delamination of the overlay and signs of overload on the shells, just to be different I suppose.

I am chasing more power too, as most people would be with a tdi haha.

I have had the pump tweaked and dynoed as soon as I bought the car, 62kw at the wheels, but on 33's and looking for 35's I want a few more kw's.

Max boost at the moment is only 16psi, but with the stock intercooler my egts easily reach 720deg on hills with a little too much throttle. (Only takes a tiny bit less fuel to drop egts 50deg or so) That said, I am hardly ever at full boost. Normal acceleration around town 13-14psi, 100kmh crusing around 9-10psi @ 440degrees.

I think uprated intercoolers can drop egt's around 40degrees? That would help me out, then I could safely boost 18psi with a bit more fuel and keep max egts where they are now.

Can I ask where you got your intercooler from and how much? I was looking at changing my grille and putting a front mount in, but it looks like a big PITA. With auto and a/c there are coolers and condensers and stuff everywhere! The allisport direct replacements and the like easiest option but they are around $600.

Originally Posted by zuno555

Max boost at the moment is only 16psi, but with the stock intercooler my egts easily reach 720deg on hills with a little too much throttle.

Im fairly sure 720deg is wayyyy to hot for a diesel!!?? i thought the safe limit when tuning diesels was ~550deg??

Glad to be proven wrong..

Steve

Originally Posted by Jim621

Im fairly sure 720deg is wayyyy to hot for a diesel!!?? i thought the safe limit when tuning diesels was ~550deg??

Glad to be proven wrong..

Steve

550* post turbo or 720* pre turbo are reasonable limits.

A bog stock 300Tdi will exceed 620* pre turbo.

Originally Posted by rick130

550* post turbo or 720* pre turbo are reasonable limits.

A bog stock 300Tdi will exceed 620* pre turbo.

Definitely - mines as bog stock as they get, and I've had 640* pre-turbo on a long climb towing the camper.

Steve

Originally Posted by steveG

Definitely - mines as bog stock as they get, and I've had 640* pre-turbo on a long climb towing the camper.

Steve

You win

The highest I ever saw was around 625*, but i ran a 6mm probe too, so there was probably some lag there.