Thread: 4BD1T Turbo Sizing and Performance Prediction.

powerband said his 6x6 is an 1989, with the IHI turbo. So it sounds as if Land Rover must have used the pre 1989 Isuzu 4BD1T engine in at least some 1989 6x6's.

The post 1988 4BD1T has a free float Garrett turbo, and no boost compensator on the fuel injection pump, compared to IHI turbo and a boost compensator on the IP.

From what I have read, in information from Isuzu, together with reading between the lines, the IHI turbine housing is on the tight side and creates high exhaust manifold pressure, which combined with valve timing more suited to the NA engine, hurts performance.

powerband may have a problem with the boost compensator, e.g. perished or split diaphragm, as Dougal noted.

However IMHO, if the fuel injection pump hasn't been touched, he should try screwing out the full load stop screw a little (not too far if you don't have a pyro to measure EGT) before thinking about another turbo.

I'm not against another turbo, there are far better turbo's than the old IHI on early 4BD1T's (or the Garrett used on the post 88 4BD1T), but don't expect much improvement without going beyond a turbo swap.

The exhaust manifold used with the IHI turbo doesn't have the mounting flange in a very good position for other turbos.

Because the 6x6 is a heavy beast, it wont be as drivable with a large turbo as compared with what a 110 4x4 could get by with.

Originally Posted by Bush65

powerband said his 6x6 is an 1989, with the IHI turbo. So it sounds as if Land Rover must have used the pre 1989 Isuzu 4BD1T engine in at least some 1989 6x6's.

The post 1988 4BD1T has a free float Garrett turbo, and no boost compensator on the fuel injection pump, compared to IHI turbo and a boost compensator on the IP.

From what I have read, in information from Isuzu, together with reading between the lines, the IHI turbine housing is on the tight side and creates high exhaust manifold pressure, which combined with valve timing more suited to the NA engine, hurts performance.

powerband may have a problem with the boost compensator, e.g. perished or split diaphragm, as Dougal noted.

However IMHO, if the fuel injection pump hasn't been touched, he should try screwing out the full load stop screw a little (not too far if you don't have a pyro to measure EGT) before thinking about another turbo.

While the IHI does have a tight A/R housing (0.42 A/R equivalent) I think it's biggest problem is being designed for higher PR at the expense of efficiency.
In good condition and with a tuned boost compensator on the pump it will be a very good turbo for getting the 6x6 moving at low speed.
But it will give away both higher rpm power and fuel economy compared to the better turbos.

The boost compensator is a great device, but it needs a good diaphagm another adjustment point internally to allow max fuel with no smoke off-boost. I did that here:
http://www.aulro.com/afvb/isuzu-land...ml#post1626607

A worn/torn diaphragm in the boost compensator will restrict fuelling across the range. My current pump was calibrated to stock years back by an injection shop that didn't notice the diaphragm was worn to holes. The driving experience was on/off as it took a lot of boost before the diaphragm would move and then more fuel and boost would leap-frog each other quickly.
Like driving a vehicle with an oversized turbo it just killed the low end.

I fitted a new diaphragm and EGT instantly jumped to about 900C sustained. The boost onset also became a lot more gradual and predictable. Low end boost and drivability improved immensely.

Later when I got the boost and fuel tuned in I went back into the boost compensator to add the extra adjustment point above. This is to allow max usable off-boost fuel without causing smoke.
It was an excellent upgrade that likely saved my bacon when I popped a boost hose while passing a truck. The compensator mod left me with enough power to keep going. Before then I'd have been left with not enough power to maintain 100km/h in 5th, let alone finish passing it.

To tune in the boost compensator you need to pop the wastegate arm off to run with no boost. Then go for a drive and load up the engine in high gears while watching the EGT. You'll only be able to run about 650C with no boost and no smoke. Keep spacing out the needle with washers until you get this. Needle out is more fuel, needle in is less fuel.

Ok thank you for your help & spot on diagnosis. Yes I did have a torn diaphragm in the boost compensator. So have replaced it, went for a drive and can notice that the motor picks up better as I take off in 1st. Also I may not have my foot down as far at 100kph but could be mind over matter. I will have to test on some hills. Taking into account the weight of the 6x6 is the GT2259 still the best option? Paul.

Originally Posted by powerband

Ok thank you for your help & spot on diagnosis. Yes I did have a torn diaphragm in the boost compensator. So have replaced it, went for a drive and can notice that the motor picks up better as I take off in 1st. Also I may not have my foot down as far at 100kph but could be mind over matter. I will have to test on some hills. Taking into account the weight of the 6x6 is the GT2259 still the best option? Paul.

Great news. There is likely more to be gained with some fine-tuning of the boost compensator.

In order of size for turbos.

The GT2259 is the fastest spooling option and can still deliver ~250hp worth of air at 3200rpm. Max boost 30psi.
The MHI-TD04-19T is the next fastest spooling option, can do higher rpm than the GT2259 but still only 30psi.
The HE221 is slightly bigger than the TD04-19T but can deliver more boost. Up to 45psi.

could some one tell me the best size exhust pipe to use? the engine pipe is 2.5" dia, and about 3 feet long. will i continue with 2.5" or go to 3"?
This engine is a test engine out of the first 6x6 army ambulance! is it worth putting a intercooler on it?
cheers Phil

Originally Posted by izu

could some one tell me the best size exhust pipe to use? the engine pipe is 2.5" dia, and about 3 feet long. will i continue with 2.5" or go to 3"?
This engine is a test engine out of the first 6x6 army ambulance! is it worth putting a intercooler on it?
cheers Phil

3 inch everywhere you can fit it. Yes the intercooler is worth it.

Thanks Dougal, I will take your advice! after reading some of the interesting posts you fellers put up,I have a lot to learn about diesel performance, very interesting! Phil

I posted this on 4BTswaps.com, it belongs here too:

Originally Posted by Dougal

As promised, here are some graphs from prediction on the 4BD1T with a HE211 and HX35-12:



So this is for a 4BD1T running a HE221 and HX35. Fuelling is to 180cc/1000 shots which it can do from about 1500rpm to the rev-limit shown. Intercooling loads get pretty high, I've show A/F ratio at 18:1 flat for simplicity and I'd expect EGTs to peak at around 760C. So clearly you need to run a little leaner than 18:1 or have better intercooling than this example to be completely comfortable. Even though it will be smoke-free.

The green line is total boost, light blue line levelling off at 13psi is intermediate boost from the HX35. The HE221 lights early and builds significant boost before the HX35 comes in. This is where boost is higher than drive pressure. I've wastegated the HX35 at 13psi in this example. Mainly to keep intake temps down for the HE221 so it's aluminium compressor wheel won't overheat and lose strength.
As RPM builds so does drive pressure. A little past 2000rpm they are equal, from there the drive pressure keeps building to about 65psi at 4000rpm. I've got total boost continuing to climb to stay on top of the engines air consumption droppping. Leading to a max of ~48psi boost at 4000rpm. It is pure coincidence that air consumption meets boost pressure at this point.

Expected power? Well over 300hp. Should be over 350hp if everything is good.
Expected torque? About 800Nm (590 ft-lb).

Problems?
Well I think the HX35-12 exhaust housing is too small for ideal. Potential for surge, but mainly it wants to keep building more boost than we need. Wastegate flow gets up to 35% of total which is why I think a bigger turbine housing will keep it away from surge and reduce drive pressure.
The HE221 is also bigger than needed. A smaller and more efficient compressor would help.

So I took those ideas and ended up looking at the TD04HL-19T (16T was a good match, but harder to find) and GT3582. But drive pressures were only showing about 4psi less. Past the GT3582 there isn't a good selection of cheap turbos to try. They end up around $1-2k each.

The most effective way to drop drive pressure is to bypass the small turbo at higher flow. But this is tricky to acheive and needs done on compressor and turbine. Even heavily wastegating the small turbine (50% bypass) with the largest available GT3582 housing I was showing ~10psi reduction in drive pressure.

But this is splitting hairs. 30hp difference in pumping loss is less than 10% and would require some huge complications in plumbing and turbo wastegate setup for an rpm range virtually none of us are using.