Thread: Which turbo can I get away with

Originally Posted by dobbo

How much boost can a 4BD1 safely handle and how big can you go with a turbo?
I can't think of any reason why it could not handle a large LP turbine but is 10 - 30psi to much for a n/a engine?

With stock head bolts and gasket, 40 psi boost should be ok. The head gasket is known to fail if the boost pressure is over 60 psi, but the stock gasket should handle 60 psi if the bolts are replaced with studs and tightened correctly.

Not sure what you getting at with reference to a large LP turbine. It makes sense if you are talking about compound turbos, which consist of a HP and LP turbine and compressor. Diesels don't use large turbines (compared with petrol engines).

You need to do some research for a turbo suitable for 30 psi (many compressors would be outside their efficiency range at that pressure ratio).

Off the top of my head, something like a Garrett T3 with super 60 trim compressor, Holset HY35 and some BW's. (Edit: Holset HY35 are available cheap in USA because the dodge owners pull them from their Cummins to fit something larger).

Garrett TA3411 Turbine with a TO4B S trim compressor are known to produce 50 psi boost with the 4BD1.

And your injection pump will needs to be able to deliver more fuel to get the heat to drive a suitable turbo.

It's a bit like how long do you want your engine to last?, how many kilometers do you consider 'safely' to mean?, especially for a NA conversion.

from my 'research' about turboing a NA 4bd1 the most significant issue was the NA motor had higher compression than the turbo motor. The message to me was be cautious about how much air is pumped into a NA motor.

oh it'll go 90psi for a little while..

what do you want the turbo for? more bottom end torque or power up the top. Thats going to be the big dictator to the configuration you run...

t28- t42 is doable.


dobbo, FFS, for just a bolt on conversion with the standard "but thats how everyone does it" fuel tweak.

KEEP IT UNDER 20PSI....

do it properly and you can hit and hold 35-40 all day long.

(I know you wont do it properly you're purse strings wont be permitted to stretch that far unless you've adjusted the handbrake)

Originally Posted by rar110

from my 'research' about turboing a NA 4bd1 the most significant issue was the NA motor had higher compression than the turbo motor. The message to me was be cautious about how much air is pumped into a NA motor.

I've found various figures quoted for the compression ratio of turbo and non-turbo 4BD1's, they all seemed to be around 17.5-18. So no dramas there.

There are a couple of test mules in the US who're doing silly things to these engines and telling us how they get on.

But for a nice mild and drivable setup, T25-T28 turbos cover the range from lots of low end to more top end. If you get a T28, make it a ball bearing one or you'll probably be wishing for more down low.

Originally Posted by rar110

from my 'research' about turboing a NA 4bd1 the most significant issue was the NA motor had higher compression than the turbo motor. The message to me was be cautious about how much air is pumped into a NA motor.

I have not seen any difference in compression ratio stated for the na 4BD1 or turbo 4BD1-T. My workshop manuals state the same compression ratio for both.

You need to be more cautious about how little air is pumped into it.

Originally Posted by Bush65

I have not seen any difference in compression ratio stated for the na 4BD1 or turbo 4BD1-T. My workshop manuals state the same compression ratio for both.

You need to be more cautious about how little air is pumped into it.

Correct and correct again

"How much boost" is a BS Q when it comes to diesels, they can sustain massive boost, unlike petrol counterparts, the problem is the gas temp's required to generate that much boost, finding a turbo to work in that boost range is the next challenge

Originally Posted by Dougal

But for a nice mild and drivable setup, T25-T28 turbos cover the range from lots of low end to more top end. If you get a T28, make it a ball bearing one or you'll probably be wishing for more down low.

I bought a ball bearing turbo, Garrett GT28R. Very happy with the improvement in torque. Big improvement when it comes to plowing through sand.