OKA 413 _ A New Hope

Well, the next exciting installment

As discussed earlier I replaced the factory H1C turbo with an upgraded HX35 (non waste-gated) turbo. This improved performance marginally and was a simple bolt in, same overall dimensions replacement. The only appreciable benefit here was an improved design, more robust and newer turbo but not a significant performance increase (without re-tuning) .

Since my last post I've obtained a suitable HX35W (wastegated) turbo which is marginally longer than the existing non waste-gated version so is not a direct 'drop in' replacement. Some exhaust modification is required, not hard but fiddly and should make a significant difference, when tuned correctly, particularly in lowering EGT's I'm hoping.



The waste gated HX35W is at the top of the picture with the (Cummins 6BT) factory H1C underneath. Inlet dimension (3") and mounting position/flange are the same but the added waste gate lengthens the turbo by approx. 35mm which means modifying the exhaust plumbing accordingly.

Choosing the 'right' HX35W can be a bit daunting as this is a generic designation covering many turbos for many applications. To make it more confusing identical turbos can have different part numbers. I confined my choice to genuine Holset HX35W's that were originally intended for Cummins 6 cylinder diesel engines and not cheap 'knock offs' which abound in the after market/eBay world. I spoke with other Cummins Oka owners to see what they were using and ended up with this one.



All genuine Holset turbos have a manafacturers plate like this attached. The number at the top, in my case 4042738 identifys this particular turbo. A site such as this can give additional information to help in selection.

Turbo Specifications

eg. This informs me that this turbo was originally intended for a 2005-2012 Cummins ISB 5.9 litre 6 cylinder diesel engine (a newer version of my Cummins 6BT engine). It also tells me that equivalent part numbers are 4039508, 4043248 and the OE or original equipment Cummins part number is 4955174. Other details include turbine and compressor impeller sizes, part numbers etc.

Deciding on a particular turbo spec. is the first part of the journey the next part is to buy OE or after market, I decided on OE as I'm a bit wary of the cheap after market turbos out there, some of them may be quite good but I don't have the expertise to pick the good from the bad so stick with OE for known good quality though to be fair there are after market turbos out there that have better than original components but these are definitely not the 'cheapies' on eBay.

This bloke has some pretty good first hand information when selecting a turbo

eBay vs genuine Holset HX35 turbo

The next step is to source your turbo of choice, this is where it's real handy to have the equivalent part numbers as this is what defines the actual turbo. and how it is advertised.

There's three different 'types' of genuine turbo out there, new, used and 'new - dismantled'. There's a specific 3 letter acronym for this used on US sites that I can't remember but essentially what it means is that (for example) a new crate engine has been dis-assembled and the parts sold off separately. This can return the vendor a better return when buying up NOS (new old stock) and on selling.

This is what I bought earlier this year.

Holset HX35 turbo

It cost me $424 at the time. All up cost was $642 including air freight from Hong Kong and GST/import costs which I thought was pretty good.

So far, so good .............................. now all I have to do is get it installed



Deano

In conjunction with (or separate to) the above turbo upgrade I'll be installing an inter-cooler. This has been a long and drawn out process deciding on which variant of inter-cooling to install.

For those not into it, basically there's two variants, air to air and water to air inter-cooling and it's all about decreasing the temperature (and increasing the density) of engine intake air. With air-air inter-cooling air flow is used to directly cool the engine intake air basically by passing intake air through a large radiator in a similar fashion to an engines coolant and is the most common method used.



Here's a shamelessly stolen photo of Nuggets Oka 224 showing its air to air intercooler, a comparatively easy fit in an XT compared to an LT which had its radiator much further forward.

With water-air inter-cooling (sometimes referred to as after-cooling) a separate 'heat exchanger' system is used to transfer heat from the engine intake air to a coolant and then remove this heat via a radiator. There are two variations that I know of to this method. One system that was originally used by Cummins had the inter-cooler mounted on top of the engine and used the existing engine coolant to absorb heat removed from the intake air. eg. The A in Cummins 6BT-A refers to 'after-cooled' and is a very simple and relatively cheap method of inter-cooling though not particularly efficient as the air coolant temperature is engine coolant temperature.This system was designed primarily to allow for cleaner less polluting combustion.



Cummins 6BT A showing its water to air intercooler directly mounted on top of the inlet manifold.

The more common method of water to air or W2A inter-cooling is to run a separate closed system (the same as an air conditioning system) that has its own separate inter-cooler, radiator, fan, water pump and coolant and is the method I have chosen primarily as any failure or damage to the W2A system does not impact on the existing engine or air intake integrity. Generally, it should be hell of a lot easier to install a W2A system such as this in a LT Oka than a comparable air to air system, at least I hope it is. There might be more components (and cost) but IMO running 19mm heater hose is lots easier and potentially more reliable than a connecting a dozen or more metal pipes, silicon bends, clamps and bracketry together. If building a vehicle up or for a partially dis-assembled vehicle it might be a different story. Fitting a 75mm (or more) thick air to air inter-cooler between the air con 'radiator' and the engine radiator in a LT can also be quite 'challenging'. Basically my reason for going W2A is simplicity and reliability.

Here's the main components.



On the left is a 600mm X 300mm X 25mm aluminium radiator with the W2A inter-cooler on the right. The inter-cooler is basically 300mm square and 100mm thick with 76mm inlet/outlets. Both were bought 'second hand', the radiator quite cheap because two side fixing lugs (which I don't need) have been broken off and the inter-cooler (imported from the US) and brand new for a project that didn't get off the ground. $200 the pair which I thought was pretty good
I've yet to source an electric fan(s), water pump, remote filler neck/expansion tank hoses, barbs etc.but at least I can get a wriggle on installing these two main components.

The inter-cooler will mount here



The existing air inlet 'cross over' pipe will be going and the rear mounted coolant catch tank may need to be moved to the left. A new inlet manifold flange plate with 76mm hole is on order and will bolt straight on top of the inlet manifold where the cross over pipe went and connect with a simple 90 degree bend to the inter-cooler (blue arrow). The inter-cooler (hot) air inlet path, red arrow, from the turbo outlet is as shown.

The inter-cooler radiator will mount here.



It's actually easier to mount it here under the cabin floor and just above the bash plate than in front of the existing radiator and it doesn't interfere with the existing airflow or require grille or other modification. A couple of simple mounting brackets and some air vents cut into the bash plate and there you go , well that's the theory anyway.

All I need is the time ...................................

Deano

Unfortunately the wrong link for eBay vs genuine turbo in my turbo post. Here's the correct link

eBay vs genuine Holset HX35 turbo

Please amend Martyn if you could as I can no longer edit my post.

Thanks Deano

Deano I will forgive you this time as I understand how the lock down and more importantly the Grand Final being played and hopefully won by Brisbane has adversely affected Victorians, but the blue beast is #050

Sorry mate , I did pick this up after I posted but the time out on editing is pretty sudden death since the site moved servers and I couldn't change it. Serves me right for 'pirating' your photo titled oka 224 and I didn't pick it up

Deano

ps. You bloody banana benders will NEVER be forgiven for stealing "The Greatest Show on Earth", but if the "boys from old Fitzroy" win it won't be all bad

The inter-cooler radiator is now installed. It was a fairly 'fiddly' fit but not particularly difficult. A couple of bits of 19mm RHS, a bit of flat, and a handful of rivnuts and all done

The radiator was fiddly to fit due mainly to the size (600x300x25) and the necessity to clear a/. the drag link, b/. the radiator return pipe, c./ the bash plate as well as being vertical and in an unobstructed air path. A 500x250 radiator would have been a LOT easier to fit.

It ended up looking like this.





The bash plate rear mount will be 'dropped' by about 40mm so that the bash plate clears the bottom of the radiator by 10mm or so. Originally the rear of the bash plate stops just above the tie rod leaving it unprotected so dropping it by 40mm will give the tie rod some protection

Next I'll cut some shallow U shape 'louvres' into the bash plate and bend them up to horizontal to direct air flow onto the radiator.

For additional cooling I'll add a 12" electric fan (with a suitable controller) to the radiator. I've got a pair of these but reckon one should do the job. I picked these up fairly cheaply ($25 the pair) from a 'bloke up the road' who had them on his 4 litre Jaguar. They're Davies Craig 12 volt/130 watt fans and are fairly generic and readily available.

Sorting out the electric fan has been an interesting exercise. What I thought would be a pretty straight forward job was a bit more complex than I expected.

Here's a pic of one of the fans (they're both the same). Note the attached air flow sticker. More on the concave annotation later.



When I got these fans the backs of the fan(s) looked like this.



Which, when reading the 'must face front of vehicle' instruction would tend you to think the fan mounted on the back of the radiator but contradicts the direction of air flow sticker as you're hardly likely to put the fan behind the radiator and blow air forward
against the natural air flow of the moving vehicle. The fan also rotated in the opposite direction to the arrow shown. The fan operated OK but airflow was less than I expected.
Whilst the direction of rotation can be changed quite easily by reversing battery polarity on the +ve and -ve leads to the fan motor it just didn't make sense to do so. The motor has a red and a black wire which pretty well tells the way it's supposed to be connected. Hmmm .................... there's something not quite right here. I removed the fan blade and found this.



The fog started to lift and things became clearer, the fan blade assembly had been installed backwards on both fans and by the look of it from new. This is actually a pusher fan(s) that goes on the front of the radiator. With the fan blades installed the right way round the direction of flow sticker is now correct, the face rear of vehicle instruction is correct as is the direction of rotation arrow. The airflow volume is significantly greater, so a tick in every box

What I couldn't figure out was how come the airflow had increased so dramatically as the fan pitch and direction is the same no matter which way the fan rotates or is mounted and its mounting is symmetrical so how come the face forward/face rear instruction ?

Here's a closer look at the other (leading) side of the fan, ie. the side that should be facing the incoming air.



What surprised me here is that the curve of the blade (as opposed to the pitch) has such a significant effect on airflow. For this fan to work effectively the convex side of the blades must face the incoming air with the concave side towards the outgoing airflow.

This is probably simple 'Aerodynamics 101' but it was news to me. You're never too old to learn

Deano

Aeroplane wing works much better than a plain old louver, i guess that's the difference...

Just wondering, (i'm sure you thought about this!) why were you concerned about having the IC rad vertical? It could be horizontal if you wanted it to... Best rad design incorporates a bit of forward 'lean' so the heating effect of the airflow going through the rad is helped 'up' and out of the rad core etc. Might have made the packaging a bit simpler? As i said, you may have thought of this...

cheers, al

Hi Alister,

I suspect you're right with the wing analogy but not really my field I would have thought the 'lean' of the fan blade or its pitch would have been the main contributing factor to the amount of air it could move and not so much the curve of its blade. It really came as a surprise that this was not the case.

As for leaning the radiator forward, yes it would have made installation easier and may well have given a bit of bias to outgoing airflow but my concern was that natural airflow through the radiator would be decreased as the cooling fins could act as a barrier to the airflow. I recall that Peter James mentioned some time ago that his Hummer had an angled radiator with the cooling fins/tubes angled so that airflow remained unimpeded.

If fan blown airflow was to be my primary cooling method I could have mounted the radiator at any angle and used both fans to achieve this. For natural airflow to be effective I figured the radiator cooling fins need to be in line with the airflow and not angled as this would impede the natural flow of air. I did consider angling the radiator forward and angling the louvres in the bash plate to be perpendicular to the radiator but decided not to as keeping the louvres horizontal should hopefully give better protection from stones etc. bouncing up from the road.

So basically it came down to this, a vertical radiator with natural airflow and one part time 'assist' fan or an angled radiator with two fans with one or both operating continually depending on load. I went with the KISS method for reliability/efficency. Another consideration was electrical load from the fan motors. Each fan motor is 130 watt, 260 watts for the pair or around 25 amps at 12 volts so significant considering my alternator is a nominal 85 amp generic Bosch.

There's the reasoning for the direction I've gone, all good in theory, now for the practice

Deano

Hi Deano, yep makes sense and i'll just write this for a bit of info. F1's don't have a thermofan, they rely purely on the air coming in from the front to cool the rad's (there's one on each side). They lean their rads forwards for a bunch of reasons but one being that as the air goes through the rad it heats up and wants to go up, leaning the rad forward actually helps this process even while they're sitting stationary (although they can't do this for very long).

Honestly it's hard to say which direction airflow is travelling on a vehicle without testing, but either way, with how little heat needs dissipating with an IC i don't think you'll have a problem, and what's more your setup looks good... and a lot more complete than mine for the moment!

Deano the standard alternator is quickly found wanting when running electric fans. When I first fitted the auto the single fan on the transmission cooler would run a lot in summer in slow going or constantly climbing and resulted in a flat starting battery as the combo of trans fan, trans electronics, the Oka's bus aircon with four internal fans plus the power required for stereo, gauges and everything else constantly exceeded the alternator's output.
I bought a brand new Cummins/AC Delco 160 amp alternator that fitted straight on the 6bt that put out 100 amps at idle which solved the problem.
There is a bloke on ebay that sells them regularly as they upgrade gensets to 250 or 350 amp ones and he sells the unused 160 amp ones for around $60 US.
Rob Alley has a 250 amp version on his Oka. The model number of mine is a 24Si and the larger one is a 28Si I think.

Dean and Kaye Howells wrote: ...
This is probably simple 'Aerodynamics 101' but it was news to me. You're never too old to learn

Deano

Yeah i think Icarus mentioned it on page 3 or 4.
I'll see if I can search the tablet.

Holmz wrote:

Dean and Kaye Howells wrote: ...
This is probably simple 'Aerodynamics 101' but it was news to me. You're never too old to learn

Deano

Yeah i think Icarus mentioned it ......................

I think his failure was due more to Thermodynamics than Aerodynamics , I'll be taking a more cautious approach

Deano

Dean and Kaye Howells wrote:

Holmz wrote:

Dean and Kaye Howells wrote: ...
This is probably simple 'Aerodynamics 101' but it was news to me. You're never too old to learn

Deano

Yeah i think Icarus mentioned it ......................

I think his failure was due more to Thermodynamics than Aerodynamics , I'll be taking a more cautious approach

Deano

Hence no Aero 102 made it to a tablet.
That was all wright

I think that the radiator for your intercooler is way to small and may result in an engine that’s hard to tune. From my experience of setting up two w2a Intercoolers the size of the radiator makes quite a difference. Mine runs a 600x500x55 radiator and I think works well. The one I just did has the same intercooler But the radiator is 600x400x40 and it’s not as efficient as mine. Both of these are mush bigger than yours. You will need to go really conservative on your tune so when your working it your egt’s don’t go to high. I think this will happen when your intake temps get high.
Just something to think about.
Rob

Thanks Rob for your input and the benefit of your experience. #413 was 'recently' tuned by AG Diesel here in Melbourne with the priority's being reliability and efficiency. The end result was also a 30% increase in power to 150 rear wheel HP and a much more drive-able vehicle. Not much power by some standards but ample for our requirements and this with a standard H1C non waste-gated turbo. The H1C has been replaced with a HX35 non waste-gated from a later 6BT and is working well. Compared with similar Cummins powered Okas #413's EGT's can be around 100 C higher when cruising ie. in the 400 C's when cruising on a warm day. The only difference being #413's non waste-gated turbo, hence a HX35W waiting to go in.

In the mean time I figured cooling the input air should make a significant difference to EGT's and it is my motivation for going down the inter-cooling path. I didn't go into any sort of scientific dimensioning for the inter-cooler radiator, basically this one came up for $50 and it fits so I decided to give it a crack I've really got no idea as to the quantity of heat to be removed but if this set up proves inefficient it will be relatively easy to increase the thickness of the radiator, either way it should be a lot better than having no inter-cooler at all. I can also go to dual fans but this should involve an alternator upgrade which I'd rather avoid, 'where do you start and where do you finish ?'

My Davies-Craig fan controller can handle two fans and comes with a temperature probe which I've installed into the bottom tank as I figured the return coolant temp is more important than the 'hot' side. I figured one of these would be a good idea to gauge what exactly is going on

Prosport dual temp gauge

I'll keep plugging away and thanks again Rob for your input it's much appreciated.

Deano

Dean and Kaye Howells wrote: ... #413 was 'recently' tuned by AG Diesel here in Melbourne with the priority's being reliability and efficiency. ...
...

How much did the efficiency improve?
What litres/100 is it doing now?

Holmz wrote:
How much did the efficiency improve?
What litres/100 is it doing now?

It depends on how you define efficiency really, the improvement in performance and ease of driving was marked. A much easier and more pleasant vehicle to drive now. The obvious technical change was the high speed AFR across the 'power range' say 1800 - 2100 rpm was improved from around 25:1 to around 22:1 which is the actual sweet spot for this type of engine. Cruising EGT's dropped a fraction say 40 C maybe. Fuel consumption is basically unaltered from around 16l/100 k's for my 'normal' driving. ie. highway cruising at 92-95 kph which was the same with the Perkins.

Easier and less tiring to drive, fewer gear changes makes the Oka experience more 'comfortable'. So I guess the efficiency improvement is more power and less gear changes whilst holding the same speed for longer with the same fuel consumption.

The real lesson out of this was to get the engine properly tuned by someone who knows what they're doing.

Deano

Dean and Kaye Howells wrote:

Holmz wrote:
How much did the efficiency improve?
What litres/100 is it doing now?

It depends on how you define efficiency really, the improvement in performance and ease of driving was marked. A much easier and more pleasant vehicle to drive now. The obvious technical change was the high speed AFR across the 'power range' say 1800 - 2100 rpm was improved from around 25:1 to around 22:1 which is the actual sweet spot for this type of engine. Cruising EGT's dropped a fraction say 40 C maybe. Fuel consumption is basically unaltered from around 16l/100 k's for my 'normal' driving. ie. highway cruising at 92-95 kph which was the same with the Perkins.

Easier and less tiring to drive, fewer gear changes makes the Oka experience more 'comfortable'. So I guess the efficiency improvement is more power and less gear changes whilst holding the same speed for longer with the same fuel consumption.

The real lesson out of this was to get the engine properly tuned by someone who knows what they're doing.

Deano

Thanks.
I say that the tuning goals were "efficiency and reliability"... but usually power wins in most cases.
And the ease of driving was not a goal.p... which is usually what is many people goals.