RX8 Project – Part 11, Turbo’s #2 – Wastegates

So now the project is going in the turbo direction I need to be a bit wary with how I do it. The GT1549 turbo’s I chose had positives and negatives. They looked to be exactly the right size for the engine I had, they were fairly common in one form or another and importantly the price was spot on! I still don’t understand quite how but I managed to find someone on eBay with a matching pair of these turbos fully cleaned and rebuilt for £65 each delivered! So that’s the positives, now the negatives, firstly rather than the normal bracket bolted to rear of the compressor housing to hold the wastegate actuator. On these turbos it is actually cast into the housing and so it would make rotating the housing to fit the application considerably more difficult. The second problem is they have a factory fitted actuator which isn’t adjustable more than a small amount and I really didn’t want to start tweaking a completely untested engine with no idea what was going to happen with no way of keeping the boost below the 18 psi wastegate pressure!

So getting over these problems. Having looked at the rotation problem I came to the conclusion I should be able to make them both fit with no rotation changes needed. The backup plan here was to grind off the cast in mount and custom make a bracket using a bit of steel plate if it turned out I needed to later on. This takes us to the wastegate problem. I looked at a number of ways of providing a reduction in the actuator pressure including adding springs to the rod side of the actuator and even bolting the internal wastegate solid and fitting external wastegates to the manifolds I came to the conclusion the only real way of giving a wide but reliable range of adjustment while keeping the package as small as possible would be to replace the stock actuator with an aftermarket adjustable one.

Now this is where the plan goes a bit wrong about – after looking about for ages to find a sensible option at a half sensible price the best I could come up with was this : Kinugawa Actuator 

Kinugawa Actuator

I’m under no illusions here, this is a a cheapo unit! But I strongly object to spending the cost of the car on each wastegate. The problem is even though I got these for £68 each which really is very cheap they actually cost more then the pair of turbos! Considering all this it’s still a pretty good option because it is a ‘universal’ version. It comes with a range of springs for different pressures so I can start at just a few psi and swap the springs out as needed and also comes supplied with four different actuator rods.

So here we are – actuators!

Kinugawa Package

So at first glance they look ideal, but don’t let that fool you! There’s a couple engineering problems to overcome.

Actuator Flap clash

The first problem is this; the hole in the supplied rod end isn’t large enough for the flap actuator on the turbo. The solution is simply to drill this out to fit. I didn’t note the sizes, but it was a standard drill size.

Next up was that this ‘universal’ actuator was never really intended for a turbo this small and as such the shortest actuator rod is too long to allow the wastegate flapper to close so I had to modify that as well. The rods are nominally 6mm diameter but the end the rod end has a fine pitch thread meaning modifying that would need me to buy a fine pitch die to extend the thread. Luckily the end that goes into the actuator is a standard M6x1mm metric thread so that was the easier option.

Modified Actuator Rod

I measured how much I needed to shorten the rod to allow the flapper to just close at one end of the rod ends adjustment. The opening pressure of the actuator is set by preload so the more it is tightened greater the boost pressure. I then simply cut the thread down to the required point and then trimmed off the excess. The good news is if I made the rod too short I three more tries for each one!

Modified Actuator Rod

And here is the difference – it’s actually about 25mm less than it started out! Reassemble the whole thing and magically it now fits where it needs to!

GT15 Kinugawa actuator

The other thing you will need to do potentially at this point is change the spring. Once the actuator rod is in the actuator this is actually not too bad but be a bit fiddly. First of position the actuator so the rod is sticking downward between the jaws of a vice. Tighened the vice to hold the rod in place then undo all the housing screws. Lift off the top housing and carefully remove the diaphragm underneath. Next you need to carefully release the rod to take the load off the spring. then you just unscrew the rod and take the aluminium piston and the spring underneath out the housing. Reassembly is just the reverse but the key is to put tension on the rod again and clamp it in place again before refitting the diaphragm and cap otherwise it’s very difficult to get the diaphragm correctly positioned without any wrinkles that could cause damage or leakage.

So now we have two turbos with adjustable wastegate actuators with a potential working range covering something like 3-30psi!

 

RX8 Project – Part 10, Turbo!

So this is about the time this whole project started getting a bit out of hand, when I decided I was going to need more power…significantly more.

I looked into what options I had –

Option 1 – I could stay naturally aspirated and probably skim the head to increase compression a bit and get more out of it but tuning in this way can be very intricate and looked to be more involved than I wanted for the amount of power I could expect.

Option 2 – Supercharger, there are a few options here. Realistically the most common supercharger these days the Eaton M45 found on the modern Mini cooper S is just too small for this so sticking with the positive displacement type we can get an M62 from a mercedes CLK230 and with the right pulley ratio it would probably be ideal for moderate improvements. For real degrees of silliness an M90 might well be needed and these are a little harder to find.

Option 3 – Turbo, this gives a huge amount of options due to the prevalence of turbo engines at the moment and would give potential for significant power gains comparatively cheaply and without needing to align belts.

After debating for a very long time the best way to go for a road car I settled on option 3 primarily for the simplicity aspect – I know very little about the intricacies of high compression engines and I know superchargers require a level of alignment very difficult to achieve with DIY manifolds! The next obvious question is how much power? Well following finding out from Noble that the rods in the engine fold up at something a bit over 300bhp I decide that from a cost and complexity point of view I’d aim for about 280bhp as a limit so I could keep the amount of parts I needed to a minimum – famous last words!

Now there’s a huge online argument about whether two smaller turbos or a single larger one gives the best throttle response and performance. This isn’t an argument I want to get into but in my case I decided twin turbo was the way to go for two reasons. Firstly because I could close mount them under the engine to keep the overall engine package as small as possible and so simplify the pipework on the exhaust side. Secondly because due to the government publicising the benefits of diesel there are now loads of small cheap turbos about for very little money..

Getting into sizing most of the information is that Noble used two T25 turbos. Taking a look at http://www.boosttown.com/forced_induction/air_amount_calculator.php

We can see that for this engine at 6000 rpm and 0.7 bar of boost we need about 27 lbs/min of total airflow. Next we need the T25 Map for a common inducer size:

T25 Compressor map

Looking at the map for the normal T25 turbo we can see that with two turbos to share the load and so only needing about 13.5 lb/hr at 1.7 pressure ratio the turbo is right in its optimal zone. Not a bad choice all in all but these are old design turbos and as a twin turbo configuration the actual  amount of available exhaust will be limited so the turbo may not spool until a bit high up the rev range so I started looking at other options which would give a good improvement across a wider rev range. To achieve this a smaller exhaust housing was needed and this is where the diesel engines come in. Turbos used for diesel engines tend to have smaller exhaust housings for this very reason and they’re abundant. This led me to the GT1549, this is a manufacturer specific version of the GT1548 turbo, people have reported them to be good for 180-200bhp which is right in the area we want.

GT1548 Compressor Map

In many ways a similar map to the T25 but the spindle speeds are noticeably higher. The unit as a whole is much smaller but will have less weight in the rotating components and as a result of the smaller exhaust housing the turbo should generate boost at lower RPM. I used to have a map for the exducer which confirms this but have since misplaced it. Now before anyone tells me “you can’t use a diesel turbo on a petrol” consider this – this same turbo was used on both a huge range of diesel engines but also on the Saab 9-5 V6 petrol. That said there is also a VNT version of this turbo (GT15xxV), VNT turbos don’t last long on petrol engines by all accounts.

So here we are, the turbosGT1549 x2 :

So there you have it, a short post but a complete change in the direction of the project from where it started off and we’re only just getting started!

 

 

RX8 Project – Part 7, Introduction to flywheels

Having decided what engine I was going to use and deciding to keep the existing gearbox so I could retain the factory carbon prop shaft the next logical step was to work out how exactly to achieve that…

First off the engine I had bought was from an automatic and so had a flex plate rather than a flywheel. This is a comparatively thin piece of steel which gives the starter ring gear, which would be on the outside of the flywheel on a  manual, a fixing point and also mates the torque converter to the crank. In automatics the torque converter provides the rotating mass to smooth the engine pulses. So the first step was to get a flywheel that would work. My first idea was to take the factory RX8 flywheel which has quite a deep offset (i.e. it is quite dished) which would help correct for gearbox adapters which would space the gearbox off the engine. So I looked into simply machining off the back of the RX8 flywheel flat and drilling the bolt pattern from the V6 crank into it. While technically this would work there are a few problems.

RX8 V6 Flywheel Mod

(Taken from here : http://www.locostbuilders.co.uk/viewthread.php?tid=185939&page=2)

The image above shows exactly what I’m talking about, this is a factory RX8 flywheel modded onto a V6 crank. I believe the engine used in this case is the Mazda KLDE. While this all looks good there are a couple of issues. First is that the RX8 flywheel isn’t balanced as it stands, it forms a balanced arrangement with the rest of the engine and so needs modifying. I don’t have a picture of this but the weighted lip on the rear ranges from thin on one side to very thick the other. Aftermarket flywheels get round this by using balanced flywheel and a separate counterweight. Problem two is that the factory flywheel is cast iron, this has an irregular structure and can have flaws and other weaknesses from new but parts are generally made with a factor of safety to account for this but modification in this way will remove some of this additional strength and change areas of stress. I actually 3D modelled this change to see if it would work:

Original:

RX8 Flywheel Bottom OldRX8 Flywheel Top Old

Modified:

RX8 Flywheel Bottom NewRX8 Flywheel Top New

Having modelled this I performed a stress analysis of this based on the force created by the flywheel spinning at 8000 RPM. This is more than redline as it stands but it seemed prudent to plan ahead! It turns out the stock flywheel is only about 20% stronger than required based on the nominal ‘standard’ properties of cast iron. The new version would be below strength at this speed, dropping to 7500 RPM gave something around 102% strength. Not a number I felt confident in at all! Just to make a point here as people argue the safety of modded flywheels a lot (mostly from “I’ve done it and it’s fine”). I’m not saying it will fail modded like this, in fact the numbers suggest it is (just) strong enough here but there is no margin for error even on the ‘ideal’ material and cast iron does vary significantly. A given flywheel might be fine like this for years, but get a weaker one or one with a flaw or even give it a hard jolt when it’s at full revs and it may just shatter. If it does, be somewhere else!

So after deciding the mod wasn’t really the best idea I realised that all I needed was a flywheel that would bolt up and work. A fairly easy task at face value since it turned out the the standard Ford clutch splines (1″ dia, 23 spline) match the gearbox the solution suddenly seemed simple and I just needed a stock Ford flywheel and clutch for that engine. It turns out there were a few variations of the Ford flywheel depending if you went for an ST200, ST220 or just a vanilla V6 Mondeo but the difference between them seems to be some are ‘lighter’ versions to make the more special cars rev a little more freely. This is achieved by leaving out sections of the outer lip on the flywheel. In my case I had no idea if this project would ever work so I bought the cheapest! This is when another problem emerged:

 

Mondeo Vs S-Type Starter

Note the starter ring gear on each. The top is the S-Type flex plate, the bottom is the Mondeo one. It seems the Ford and Jag use a different starter motor as well. Add to this that the Mondeo flywheel puts the clutch far too far forward to mate to the gearbox and because the starter is on the engine side on the Jag but on the top of the gearbox on the Mondeo (because it’s transverse) – something we can’t do on the RX8 as the gearbox is wrong and there isn’t the room in the tunnel the whole idea falls apart! Modifying the cast one seems to be the only sensible option.

Around this time I happened to have a chat with a colleague at work who is a professional mechanical engineer and 3D designer I know through the job I had at the time and explained the problem and he directed me towards a machinist who did a lot of work for him and was well into cars. By chance a few days later this machinist came into the office and as soon as I explained the problem he just said “ah, we’ll just make you a custom one if you do a design”…. So I found myself with the challenge of designing a custom flywheel which as per the machinists recommendation would be made out of EN24 steel. As a comparison changing the models above to EN24 changes the safety factor to something around 300% from memory meaning we can lighten it significantly later if required and not risk weakening it dangerously.

More to come…

RX8 Project – Part 4, The New Engine

Following part 3 where the original rotary engine proved to be a lost cause I decided to research possible engines  that could be swapped in but there were a few criteria and limitations I had:

Size – The RX8 has a reasonable size engine bay overall but due to the size and position of the standard engine there are some limiting factors to consider. I’m aware others have swapped V8’s (among others) into RX8 shells but this generally involves extensive modification of the engine bay, steering rack and even front cross member due to the length of the engine.

Weight – The RX8 is famous for being very balanced largely due to the compact size and resulting low mounting position of the standard engine. No standard piston engine will quite match up but I wanted to get as close as reasonably possible.

Power – The standard RX8 was available with either 192 or 231 bhp and so I wanted to get to ideally the upper figure (even though mine actually started as the lower 192 model) or even exceed it if possible.

Cost & availibility – I wanted  and engine that was cheap to buy and for which spares were cheap and readily available. This was always intended to be a budget project to swap the engine more cheaply than replacing it.

After considering a huge number of options from things people have done before (VW 1.8t engine) to completely off the wall ideas that would probably upset all the RX8 purists (1.9 turbo diesel?) I eventually came across a couple really  promising candidates – the Mazda KLDE and Ford AJ series engines. These are both very compact aluminium construction V6’s which should be short enough that no modification to the front cross member should be needed. It became apparent pretty quickly that the KLDE was hard to find and attracted a comparatively high price so I ruled this out.

The AJ V6 is related to the older KLDE and is available in a few flavours. It was produced as the AJ25 and AJ30 (2.5 and 3.0 litre respectively) and were used in a a range of cars in slightly different configurations including the Ford Mondeo ST220 (along with US Contour and Taurus), Jaguar S-type and X-Type along with several others. Some (including the S-type version) have VVT.

S-type V6
S-type V6

So after an eBay search and a hard earned £165 (including delivery) later I had this prime example of an AJ25 from an S type Jag sat on my driveway. At this stage I went for the 2.5L because the 3.0L version attracts a more premium price and since I had no real idea if it I would ever get it all together I bought the cheap version. Since the block is identical for both the logic was if I made one fit and decided I just didn’t have enough power I could swap all the custom parts over to a 3.0. Clearly there’s a lot of extraneous parts on here I won’t be using and once much of this is stripped the true compact size of the engine is a bit clearer.

Stripped AJ25
Stripped AJ25

There are a few reasons I picked this version of this engine. One was that the Mondeo version, which is more common, has the water pump driven from and extended camshaft on the rear of the engine because in the Mondeo the engine is in a transverse orientation. To fit the engine to the RX8 the engine will need to be installed longitudinally and the rear will have to be very close to the firewall so this is a non-starter. The Jag version has the water pump front mounted so avoids this problem. The Jag version also includes direct acting mechanical bucket cam followers and VVT. Sadly the 2.5L generally only offers 200bhp in this configuration so it’s a little down on where I really wanted to be but the torque is 240 Nm compared to the 211 Nm peak of the 231 bhp RX8 and a considerably wider torque band so it should still go well.

Around this time I found out that the Noble M12 uses this same 2.5L engine running as a twin turbo at 325 bhp. The later M400 uses the 3.0L version of the engine but they again two turbos to it and get something in the order of 425 bhp out of it with minimal additional modifications. Reports from Noble suggest it is capable of even more but was limited because they were planning on upping the power later selling this as  another model but due due to the change of direction and ford taking the engine out of production this never happened. More info can be found here : Noble M12 History

I also made the decision to keep the RX8 gearbox so I could retain the standard carbon prop shaft in the RX8 so next up is the challenge of making an engine made by Ford, which was salvaged from a Jag, fit the gearbox from a Mazda!

More in part 5…