NA to Turbo Diesel Conversion 6BG1

[SPF40plus]

Hey everyone,
I'm in the process of putting together a turbo kit for my FTS700. First up, this has been way more annoying than expected and no local businesses seem to be interested in supplying parts and helping with dyno testing. I've tried speaking with a number of local businesses over the last month and I'm not getting very far - so any info you can share would be greatly appreciated.

So the basis of the kit is a Holset HX35W (internal wastegate) with twin scroll 12cm housing, which has a divided T3 flange; and a 450mm x 450mm x 100mm intercooler with 3" tube all round except for the feed pipe from the air cleaner, which is 4" tube.

Questions:
1. When the turbo is connected, and the air intake is pressurized, I'm assuming that having the tappet cover breather attached to the manifold is a bad idea. I'm going to use the port (which is in the middle of the manifold) to attach the boost gauge. The question I have is whether the breather should just have a filter attached to the end and bolted down somewhere, or whether I should plumb this back into the feed pipe between the air cleaner and the turbo?

2. I have to buy or make an adapter plate for the T4 size exhaust manifold to attach the T3 turbo flange. there are commercial options available or I can make one. I am considering cutting a 25-30mm thick adaptor out of mild steel as this will be deep enough that the bolts or studs do not go all the way through, and the area for the gaskets is maintained on both sides. It also means that I can drill a hole in one side and mount the EGT thermocouple in the adaptor, rather than drilling holes in the exhaust manifold. Does anyone have any reasons to not do this? The extra height of this adaptor is okay, but don't have room to make an adaptor that is more than 35mm thick.

thanks in advance for any info .

 

[Johnboyy]

yes and yes basically.

run your breather either to a catch can, or to the inlet side of the turbo.

Flange adaptor with built in EGT also sounds fine, might also be useful in terms of turbo alignment. don't just think in 1 dimension, you can rotate the turbo relative to the mainifold flange by just drilling your holes out of line with each other, or you can also machine the block in a taper to change the angle. Either options might help with alignemt/clearance

 

[SPF40plus]

Flange adaptor with built in EGT also sounds fine, might also be useful in terms of turbo alignment. don't just think in 1 dimension, you can rotate the turbo relative to the mainifold flange by just drilling your holes out of line with each other, or you can also machine the block in a taper to change the angle. Either options might help with alignemt/clearance

Thanks for the tip. I'm going to make a block out of softwood, sit the turbo on it and see if it needs to be tilted either way. I hadn't considered twisting it but I can see where that could be useful.

Does the thermocouple need to stick into the middle of the exhaust flow or can I make a rebate/cove so it is not a significant restriction on one side? I've read instructions from multiple manufacturers, and they all say something different.

 

[Johnboyy]

Follow the instructions of the unit you buy to decide how far it needs to stick in

 

[SPF40plus]

So, next question...
I've been reading up on experience with (and theory about) intercoolers and piping.

What I have found suggests that intercooler piping that is too big, causes the turbo to spool faster, but it then takes longer to build pressure because the turbo needs to fill the large pipes - it creates lag. Conversely, if it is too small then the turbo compressor wheel is subjected to higher backpressure and that limits performance too.

Has anyone had experience on the same motor with two sizes of intercooler piping (or having put a larger or smaller intercooler on). I'd be interested to know what your experience has been with this.

Depending on boost, the 6BG1 looks like it will only need to flow between 10,000 lpm (~350cfm) at atmospheric pressure and 21,450 lpm (~760 cfm) at 18psi boost. This equates to ~47 lb/min of air and fuel for the purposes of a turbo map.

Initially I was going to use 3" tube, but now that I look at it, I don't think any more than 2.5" is necessary. From my rough calculations 2.5" tube (with 7 x 90 degree bends) will only create 0.06 bar (0.9psi) of back pressure at 42 m/s, while 3" will create 0.03 bar (0.4 psi) of backpressure at 31 m/s.

Info on any experience with this would be appreciated.

 

[Dansale]

What I have found suggests that intercooler piping that is too big, causes the turbo to spool faster, but it then takes longer to build pressure because the turbo needs to fill the large pipes - it creates lag. Conversely, if it is too small then the turbo compressor wheel is subjected to higher backpressure and that limits performance too.

Depending on boost, the 6BG1 looks like it will only need to flow between 10,000 lpm (~350cfm) at atmospheric pressure and 21,450 lpm (~760 cfm) at 18psi boost. This equates to ~47 lb/min of air and fuel for the purposes of a turbo map.

Initially I was going to use 3" tube, but now that I look at it, I don't think any more than 2.5" is necessary.

Hi SPF

In principle, you're right about the intercooler pipe size thing... bigger ones would logically take longer to fill with air, but in my experience, I couldn't ever tell the difference.

A convenient way to check which size will work is to look at engines with similar power output...
For example: I'm in Australia, so I just look at the 6 cylinder Isuzu and Hino turbo trucks at the local rental yard, the 250 - 300hp trucks seem to have around 2.5" piping.

Because you're converting an NA engine to turbo, I imagine you'll retain the existing injector pump? I think thats a great idea, because even with fuel delivery volume turned RIGHT up, the existing pump probably wont ever deliver enough fuel for you to melt / hurt the engine. A conservative setup that should last a long time. The turbo kit you described sounds ideal, the big intercooler is a great choice. Dont be scared of running plenty of boost, (because your fuel volume will be constant at a given rpm), the more air you jam into the cylinders, the cooler EGTs it'll run. Keep it under, say 1100*F sustained.

Is the T4 manifold divided?

EGT thermocouple needs to be in the middle of the exhaust flow for accuracy and response times.

A couple of hints from when i last time I made a turbo flange adaptor plate...
- Buy the manifold and turbo gaskets, and sit them one on top of other, line up the gas holes. Check if any of the bolt / stud holes want to be in the same spot..... if they do, you'll have to shift one gasket across a bit until all the holes clear.
- Try to drill and tap all the adaptor bolt holes all the way through, then you can run studs instead of bolts, really helps when trying to install these things in a tight space.
- Once you've drilled the gas holes, use a die grinder ( i like a rounded christmas tree shaped carbide burr) to port match the adaptor to suit the gaskets, both sides.
- EGT probe in the adaptor plate is a great idea.

Sounds like a great project vehicle too!! Good luck!

Daniel

 

[SPF40plus]

Hi SPF

In principle, you're right about the intercooler pipe size thing... bigger ones would logically take longer to fill with air, but in my experience, I couldn't ever tell the difference.

A convenient way to check which size will work is to look at engines with similar power output...
For example: I'm in Australia, so I just look at the 6 cylinder Isuzu and Hino turbo trucks at the local rental yard, the 250 - 300hp trucks seem to have around 2.5" piping.

Because you're converting an NA engine to turbo, I imagine you'll retain the existing injector pump? I think thats a great idea, because even with fuel delivery volume turned RIGHT up, the existing pump probably wont ever deliver enough fuel for you to melt / hurt the engine. A conservative setup that should last a long time. The turbo kit you described sounds ideal, the big intercooler is a great choice. Dont be scared of running plenty of boost, (because your fuel volume will be constant at a given rpm), the more air you jam into the cylinders, the cooler EGTs it'll run. Keep it under, say 1100*F sustained.

Is the T4 manifold divided?

EGT thermocouple needs to be in the middle of the exhaust flow for accuracy and response times.

A couple of hints from when i last time I made a turbo flange adaptor plate...
- Buy the manifold and turbo gaskets, and sit them one on top of other, line up the gas holes. Check if any of the bolt / stud holes want to be in the same spot..... if they do, you'll have to shift one gasket across a bit until all the holes clear.
- Try to drill and tap all the adaptor bolt holes all the way through, then you can run studs instead of bolts, really helps when trying to install these things in a tight space.
- Once you've drilled the gas holes, use a die grinder ( i like a rounded christmas tree shaped carbide burr) to port match the adaptor to suit the gaskets, both sides.
- EGT probe in the adaptor plate is a great idea.

Sounds like a great project vehicle too!! Good luck!

Daniel

Thanks for the detailed answer.

I have wondered how much difference the pipe diameter makes on these lumbering engines. I know it makes massive difference on performance petrol/gasoline engines, but that is a different game.

I'm not planning to change the fuel pump, and I'm only looking for 30 - 40% more power. 220hp should be fine.

Thanks for the tips on the adaptor plate. Yes, you have to love clashing bolt holes.

Yes the t4 and T3 flanges are divided, and the turbo is twin scroll. I'm looking forward to seeing how much difference the twin scroll turbine housing makes. It is supposed to spool up 1000 rpm earlier than the single volute version. I should have 8 psi at 1000rpm. Fingers crossed.

 

[Dansale]

Thanks for the detailed answer.

I have wondered how much difference the pipe diameter makes on these lumbering engines. I know it makes massive difference on performance petrol/gasoline engines, but that is a different game.

I'm not planning to change the fuel pump, and I'm only looking for 30 - 40% more power. 220hp should be fine.

Thanks for the tips on the adaptor plate. Yes, you have to love clashing bolt holes.

Yes the t4 and T3 flanges are divided, and the turbo is twin scroll. I'm looking forward to seeing how much difference the twin scroll turbine housing makes. It is supposed to spool up 1000 rpm earlier than the single volute version. I should have 8 psi at 1000rpm. Fingers crossed.

You're welcome.

The reason the intercooler pipe size makes a difference with turbo petrols is that the air FLOW rate dramatically changes constantly, as the engine goes from vaccum to boost to vaccum to boost etc. The turbo has to constantly refill the whole cooler system each time you open the throttle. Whereas with a diesel, the turbo is always on boost, always providing PLENTY of airflow through the induction system to the engine. Very little lag. Packaging and actually fitting the cooler and pipework in the enginebay is the primary challenge with a deisel / truck.

Divided manifolds and turbine housings are usually preferred with the diesel engines, for responsiveness and spool times. Two small volutes keep what (precious little) exhaust gas energy and heat we have, moving, as to hit the turbine wheel as fast as possible, for good spool and drivability.