Cummins 4BT & Diesel Conversions Forums banner
1 - 20 of 79 Posts

· Super Moderator
9,683 Posts
Discussion Starter · #1 · (Edited)
The 4BD1T's came with a selection of different turbos depending on their year and original market.

Early (1985-1986) motors came with an oil cooled IHI-RHB6 turbo for which parts are becoming very rare.
The major diameters of both it's compressor and turbine wheels are 60mm. It is basically a japanese T3 size turbo. A workable turbo but not very efficient. It produces more backpressure for the same boost than later, more efficient, turbos.
It is wastegated, the exhaust housing scroll on my 1986 build engine has A/R of 11cm which is equivalent to 0.42 inches A/R. The wastegate should be factory set to approx 12psi.
The mounting flange on this turbo is split port with 8mm studs on a 73x35mm pattern. It has it's own high mount horizontal manifold. The mount pattern is not compatible with any other common turbo, but T2/T25 turbos can fit if the holes can be slotted.

A wastegated high mount T25 turbo was used on industrial 4BD1T and 4BG1T engines. The manifold is very similar to the top-mount IHI manifold but features a single port and T25 stud pattern (M8 studs on 73x40mm rectangle). The turbo used on the 4BG1T industrial was a MHI TD04HL-15T-12. This is a low boost turbo that will work in an automotive application but won't realise the performance potential.
Most T2/T25 turbos will bolt directly to this industrial T2/T25 manifold.

The later 4BD1T's (post 1988 update) and the early 4BD2T's had a non-wastegated (free floating) TB25. Several model codes exist including 466898 in Bush65's pictures below. It uses a T25 bearing core (water jacketed) and compressor, but has a T3 mounting flange which bolts to the factory manifold at an angle of approx 60 deg.
This non-wastegated (freefloating) turbo has a large turbine housing (0.87 inch A/R) and sized to run all day long in an NPR at ~3000rpm. It will not provide enough boost at 2000rpm for most swaps into smaller vehicles.

Some of the later 4BD2 engines (possibly 94+) have a wastegated version of the T25 turbo with a 54mm compressor wheel and 0.67 inch A/R turbine housing. Several model codes exist for these turbos including 465675 and 466409. The CHRA number 430425 on both. This is the best factory turbo and sufficient for mild performance increases over stock. The 4HE1 turbo (model code 700716) with a 60mm compressor wheel uses the same turbine (P/N 435257-0002) and may be a slot in upgrade. Keep the wastegated T3 turbine housing and slot in the 4HE1 turbo.

To gain more peformance from the 4BD1/4BD2 engines a turbo which provides boost earlier and provides more boost through the rpm range is desirable.
Many turbos exist from other engines and can be swapped in for a reasonable cost, but all require adaption to the intake manifold.

· Registered
2,145 Posts
My 4BD1-T workshop manual only has the IHI turbo. It has a few specs:
- type RH-B6A
- max permissible speed (continuous) 130,000
- pressure ratio (maximum) 2.8
- exhaust gas temperature 750 C maximum allowable at turbo intake
- turbo uses imperial sizes for nuts and bolts

· Super Moderator
9,683 Posts
Discussion Starter · #3 · (Edited)
Turbo Part numbers.

Factory IHI RHB6
Turbospec. VI35 8603
Serial No. RHB6 06088C (this is IHI's part number)
Parts No. 894422 4980 (this is the Isuzu part number)
Exhaust housing 11R (this is the A/R ratio)

An IHI RHB6 I got for parts
Turbospac. CI60 8809
Serial No. RHB6 17 0060
Parts No. 894418 3210 (appears to be an Isuzu number).

Mounting flange on these IHI turbos is 8mm bolts on a 34x73mm rectangle. It is similar to a T25 but not quite, you can slot a T25 turbo bolt holes to make them fit an IHI manifold.

High Mount T25.
Tell me if you have the part numbers for this one or the manifold it fits.
Mounting flange is 8mm bolts on a 40x73mm rectangle. This is the standard T2/T25/T28 mounting pattern.

Side Mount TB25 freefloating (no wastegate).
This turbo is found on later 4BD1 engines, it isn't a sought after turbo, the large exhaust A/R hinders low end response.
The mounting flange on this one is the garrett T3 pattern, 10mm bolts with 11mm holes on 86x44mm rectangle.
51.3mm/40mm cold, 60 trim 0.48 A/R cold
50.6mm/46.1mm hot, 83 trim, 0.89 A/R hot
Code XD 0219J
Isuzu 8-9438-290-00
Garrett 466898-6

Side Mount TB25 wastegated.
This turbo is found on early 4BD2 engines, it is a good choice for people wanting to keep their engines stock.
The mounting flange on this one is the garrett T3 pattern, 10mm bolts with 11mm holes on 86x44mm rectangle.
51.3mm/40mm cold, 60 trim 0.48 A/R cold
55mm/42mm hot, 58 trim, 0.67 A/R hot
Code XE 0201J
Isuzu 8971056180
Garrett 466409-1

Side mounted TB25 wastegated with a larger compressor wheel.
This turbo is found on some 4BD2 engines, it is similar to the above turbo but has a larger compressor wheel. It is a good choice for people wanting a modest performance increase over stock.
The mounting flange is also garrett T3.
Isuzu 466409-002 (info from turbomaster)
Garrett TB2568
Stock turbo on later 4BD2T's
54.3/42mm compressor wheel - 445347-0003
Turbine 435255-0002 closest in turbomaster is 435237 which is 53/39mm 11 blade
Turbine A/R 0.67

The T3 flange, has 10mm bolts on a 86x44mm rectangle. This is a very common mounting flange used by Holset, KKK, Schwitzer and many others.

· Super Moderator
9,683 Posts
Discussion Starter · #13 ·
Holset H1C

Anybody running one of these? A friend gave me one that seems to be recently rebuilt. Non waste gated, but larger than th Garrett
Not the H1C, but the later holsets which are essentially an updated version of the same thing get good press. Nexxussion and Carcrafter have both used them.

· Registered
1,113 Posts
Bob's response is helpful nonetheless, as my other option is a Garrett off of a '95 NPR. Space is tight in my van, with the non-waste gated Garrett almost hitting the doghouse. I am putting a 3" exhaust on to let it breathe better, but the turbo just seems to make noise without boost. The local turbo shop has not been able to I.d the application of the Holset, so it may be best to try the Garrett, first.
1 - 20 of 79 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.