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4H isuzu turbo fit

16994 Views 35 Replies 7 Participants Last post by  Kiwicamper
Hi guys
I have this manifold which fits a 4HF/G/E1 engines and I was wondering what turbo to fit to it I can get a GT25 for the 4HE1 but it doesn't have the T3 mount.
The 4HF1 is 4.2 ltr so I need to know what your suggestions may be.
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I can't read the numbers in the photo, can you post them up?
The "official from Garrett" T3 stud measurements are 86x44.5mm, each stud being M10 with an 11.2mm clearance hole.

So yeah, that's a T3.
Thanks, Any sugestions as to what turbo that I should use or what would suit bearing mind that it is a 4HF1- 4.2 ltr. I have had the pump set up to start fueling at 1850 RPM.
How much boost do you want?
Up to around 20psi a garrett GT2860R would be a good match with the 0.64 A/R turbine housing. Of course that's a T25/T28 flange so you could use an adapter. Aftermarket T28 housings appear to be available with T3 flanges.
If you're looking for a used one, then a nissan skyline or silvia etc would make a possible donor.
The silvia turbo is bigger (0.86 A/R exh housing) but is also ball-bearing. Isuzurover runs one on his 4BD1.
What is the equivelant in the Holset turbos? and I Think most of them come with the
T3 Mount
To be honest I have no idea about the holsets and their naming system confuses me. Carcrafter is probably your best source of info there.

The GT25 is a tiny fraction smaller exhaust wheel than the GT28. The old T28 is now called the GT2560.
Some aftermarket turbine housings exist for GT28 turbos, but I also have designed a T3-T25 adapter system which Isuzurover uses.
There's a guy on outerlimits4x4 called Matt McInnes who has recently come up with a very clever T3-T25 adapter design which can be used either way around (also fits T25-T3). But I don't know if he's selling them yet.
You might also consider a Garrett GT3071 (can be had with T3 flange) or one of the Mitsubishi TD05 turbos (don't know flange details).

I was talking recently to a Land Rover owner having a problem with the late wastegated Garrett turbo on his 4BD1T. His experience makes me think you need to be careful your turbine and housing are not too small.

He had a compressor failure and the shop he took it to damaged the turbine impeller while repairing it. They could not source a replacement turbine impeller (Garrett make the turbo for Isuzu and don't sell to others). So the shop fitted an impeller from a turbo used in a Nissan engine. The impeller size was close to the original - the housing had to be machined out a little, but it had an extra blade.

Now the engine has more boost at low revs, but chokes at higher revs where boost and performance have suffered. He is not happy with the outcome.
I'd be hesitant about running a turbo as large as the GT3071. One aussie who has put a GT2876R (0.64 A/R turbine housing) on his 4.2 toyota diesel isn't getting 10psi boost until 2300rpm.

Small turbines certainly do limit topend, I also spent some time talking to the person John mentioned above. I run an even smaller turbo on my 4BD1T and have the same behaviour but 1-200rpm sooner than he does. The turbo I currently run (T25 with a 0.49 A/R exhaust housing) is several sizes smaller than I usually recommend to others.

Sizing a single turbo is all about compromise, low end torque vs high end power.
Thanks fellas now I have some thinking to do. I just received the GT25 that is used on the 4HE1 engine but the compressor seems to appear slightly too small for what I would like to achieve.
Idealy it would be great to have max boost at around the 1850 to 2000 RPM range and then I can gear the drive train to maximise the torque produced.I am waiting on another turbo which has these specs

Trim-T 73
A/R -T 0.63,
Trim-C 70,
A/R- C 0.6
Flange-T Inlet T3
oil cooling

How would you think this would work

I can get a HE341 or the GT2860 but will these give me the boost at the disired RPM
Or what changes to the compressor and turbine should I do
That T3/T4 is much bigger both physically and airflow wise than a GT2860, I don't know exactly how it will compare to the holset.

Garrett's GT turbos are using smaller compressor and turbine wheels than the likes of Holset for the same airflow. This lets them accelerate to working speed a little quicker but makes them a whole lot more compact.
A Holset HX25 has the same airflow as an old T25 garrett, but the HX25 has a 56mm compressor wheel and the T25 has a 51mm.
From there the HX30 holsets step straight up to an 83mm compressor wheel.

Randy originally used an HY35 which I found these maps for (attached below), It looks like our engines will never stretch the limits of those turbos.
The HE351 is supposed to have the same compressor. Maybe it's just me, but I consider these massive overkill unless you're looking for 300hp on a single turbo. The green map (the smallest one) is capable of 45 lb/min (600cfm) at 45psi boost, that's going to give a 3.9 Isuzu about 300hp.


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Thanks '
So if I want the max boost to occur at around 1850 RPM then the smaller compressor will do it or is it the smaller turbine
You need a combination of a turbine that can spin the compressor fast enough at that rpm and a compressor that can deliver boost without surging.
Do you know the specs on the original turbo? That's a good place to start.

How fast does your 4H turn? I remember some of them hit the governor at 2800rpm.
Here's a pic of the 2 piece T3-T25 adapter I've designed up. This picture is Isuzurovers 4BD1 manifold.
He uses a GT2860R on it. It's 24mm thick.


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This GT2871R has a similar compressor map (where it matters) but smaller turbine:

There are about 5 different GT2871R's, some have wider compressor maps, others steeper.
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So your gonna see about 40lb/min out of the 3071 if you have enough fuel to spool it. I guess its hard to say without knowing how much fuel there is to spool the turbo. I have never messed with one of the 4h series and they are a very different animal from what I understand.
100% VE would see about 38 lb/min on a 4.2 at 3400rpm (assuming 20psi boost, 60% compressor efficiency, 60% intercooling, sealevel 20C etc).
That GT3071 has a map which I read as giving you heaps of air and flow at very low engine RPM am I thinking correctly? If so then this may be what I could use and achive my goal .
Early boost at low RPM and the power to maximise the engine torque at close to this RPM .
Although I would imagine that the EGT's would skyrocket if you fueled too much at this point.
Actually the GT3071 map shows it can't deliver much without surging below 1800rpm on your engine. At 1800rpm it should be able to do 20psi, but not much lower.

The compressor map however is only half the story, the turbine is the rest. It's the turbine which has to spin the compressor fast enough to deliver the low end boost. I don't think a 3071 will do that.
The first two numbers of garretts model code is the turbine size. So a GT2871 and a GT3071 both have a 71mm OD compressor wheel, but the 28 turbine is smaller than the 30 turbine, so it can produce boost sooner.

That GT35 turbo is a T3/T4 hybrid built for ricers. I think they're too big to run as a single turbo in a 4wd truck. 4wd's need low end boost, the heavier they are they more they need.
Carcrafter is running his engine in a light 2wd ute, which has quite different demands on the engine. He can run a bigger turbo without suffering.
Thats what I need Dougal the vehicle is an NPR300 4x4 which will be used in the top end and gulf country of Queensland, So heavy trecking is possible especially when it will be at the upper GVM weights.
which means that I should stick with the GT25 as used on the 4HE1 4.9ltr engine.
Can you get the specs from the 4HE1 turbo? Garrett can be pretty flexible with their model names so any chance to pull the covers off and check wheel measurements should be taken. Also housing A/R numbers.
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