Thread: Garrett GT28R on 300Tdi

your boosting is now coming on normally because its not bleeding signal pressure to the boost compensator on the IP out the Wastegate actuator.

You're also spinning the turbo up harder earlier and essentially exceeding its optimal performance specs. Essentially (and roughly) if the turbo is made to run at say 14 PSI and you close off the wastegate then fuel the buggery out of it you might make 17-18 psi BUT at the cost of an increase in temp of the air coming out of the turbo something along the lines of 15% increase per PSI and its exponential.

Manufacturers take advantage of this and slightly undersize the turbo so it runs optimally at the expected normal power output levels.

right off the top of my head the 28 should spool up a little later But more sharply than the stock tdi turbo

Yes fitting a new wastegate acutator like the one fitted will cure your woes But I reccomened getting the ones with a turnbuckle arrangement to allow easy tuning.

Thanks Dave! I haven't been pushing it to anywhere near the stock peak of 14-15 psi for fear of overboosting. My theory is that disconnecting the wastegate actuator then will not affect anything. Isn't the wastegate there purely to stop you going past the pre determined maximum boost?

I think you're right about the GT28R coming on a bit later but sharper (the impression I'm starting to get).

.... and the adjustable actuator rod - yeah, noticed that after you mentioned it . The one I currently have has an adjustable rod - nothing a hacksaw and a MIG can't fix if I'm stuck with buying a new one without adjustment.

Thanks again,
James.

you might need to look for a waste gate actuator with a higher pressure rating as that one is for a petrol engine at 6-7 psi

Originally Posted by rainman

Thanks Dave! I haven't been pushing it to anywhere near the stock peak of 14-15 psi for fear of overboosting. My theory is that disconnecting the wastegate actuator then will not affect anything. Isn't the wastegate there purely to stop you going past the pre determined maximum boost?

mostly but it also helps to shape the top end delivery depending on how the spring is set and a few other things. no it wont stop total over boosting you feed it enough fuel and you will overcome the gas flow ability of the wastegate and then the extra gas has got to go somewhere....

There are a whole family of GT28 turbos, ranging in size from a little too big to a lot too big for the 300tdi. What is it off and what size exhaust housing (A/R) does it have?

I think all your low end boost and torque will be lost.

Originally Posted by Blknight.aus

no it wont stop total over boosting you feed it enough fuel and you will overcome the gas flow ability of the wastegate and then the extra gas has got to go somewhere....

Good point/sounds logical. This explains how I managed to squeeze 16-17psi out of the standard actuator setting on a 300Tdi once (because my passenger wanted to keep up with two "nice" young ladies in a Mini on the SE Freeway ).

Originally Posted by Dougal

There are a whole family of GT28 turbos, ranging in size from a little too big to a lot too big for the 300tdi. What is it off and what size exhaust housing (A/R) does it have?

I think all your low end boost and torque will be lost.

It's a GT28"R", which I believe has an exhaust A/R of 0.64 (standard T250-04 is 0.47 I believe). It came on the vehicle so I don't know what it's supposed to be on. I had a bit more of a play tweaking the boost compensator on the week end, trying to fuel it a bit more down low and less up on boost, but I think you're right Dougal. It certainly boosts nice and hard but man is it a struggle getting it up there. I can see why this turbo seems to be used as a mod on the 3.9 litre Isuzu motors and not on the 2.5 litre Tdi.

Thanks so much for all of your help guys. I'll fiddle a bit more and report back, but I might just have an excuse to go VNT .


James.

what size exhaust have you got? how many mufflers?

Originally Posted by rainman

Good point/sounds logical. This explains how I managed to squeeze 16-17psi out of the standard actuator setting on a 300Tdi once (because my passenger wanted to keep up with two "nice" young ladies in a Mini on the SE Freeway ).



It's a GT28"R", which I believe has an exhaust A/R of 0.64 (standard T250-04 is 0.47 I believe). It came on the vehicle so I don't know what it's supposed to be on. I had a bit more of a play tweaking the boost compensator on the week end, trying to fuel it a bit more down low and less up on boost, but I think you're right Dougal. It certainly boosts nice and hard but man is it a struggle getting it up there. I can see why this turbo seems to be used as a mod on the 3.9 litre Isuzu motors and not on the 2.5 litre Tdi.

Thanks so much for all of your help guys. I'll fiddle a bit more and report back, but I might just have an excuse to go VNT .


James.

If you mean the "Disco Potato" turbo (GT2860RS), then it is miles too large - even for a 3.9 ISUZU.

I have a 2560 on my 3.9 and even that is on the largish side (great on the highway).