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Practical Reflash Tuning: Step 2: What Modifications Have Been Performed?

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Step 2: What Modifications Have Been Performed?


00:00 - The next step of our process is to get an understanding of the modifications that have been performed to the engine and the reason we want to do this is understanding these modifications is going to help guide us in the sort of changes that are going to be necessary to our calibration and this will help make sure that we don't overlook anything as we go through the tuning process.
00:22 This can be really easy to overlook at it can also be a little bit tricky particularly if you're tuning for customers and you've got a customer that's brought in a car that's maybe been modified into you for a tune and maybe they've bought the car as is and they're not actually completely aware of all the modifications but it really is important to dig into this and make sure you've got a thorough understanding of what has been done.
00:44 We've already covered this briefly, we'll go into a little bit more detail here.
00:48 So to start with, moving from our existing calibration or existing state of tune, the vehicle was fitted with a VCM Suite over the radiator cold air intake and this relocated the mass airflow sensor right on the front of the throttle body.
01:02 It's a very common modification we see in the Australian domestic market vehicles, very effective at improving the airflow into the engine freeing up quite a lot of power compared to the restrictive factory inlet track, factory airbox and air filter.
01:16 Also it does a great job of getting us cold air into the engine particularly when we are at cruising speed.
01:23 To optimise the airflow on the other side of the engine it was fitted with a X Force 1 7/8" stainless header and a high flow catalytic converter coupled to a 3 inch mild steel cat back exhaust system.
01:35 So we've found that this combination works pretty well to optimise what is the base factory engine.
01:43 So that was how the engine was at our stage 1 level of tune.
01:45 For our worked example though we've gone a little bit further and we've fitted a Kelford HS108D camshaft.
01:53 So this is getting on to being about as big as I would stick into a stock LS2 or L98 engine and there are some considerations around the cam size that I'll just talk about for a moment here.
02:05 One of the aspects is that the cam will affect the drivability of the engine and that probably goes without saying but particularly when coupled with the 6 speed automatic transmission, there are some considerations around the stall speed of the factory converter.
02:20 Understandably as a factory converter, factory automatic transmission, that stall speed is quite low, this is important for good fuel economy and drivability but we're getting to a point when we go to a larger camshaft we will need to increase the idle speed and what this does is it creates a situation where the vehicle will tend to push a little bit when it is in gear.
02:42 So when you're in drive for example at a set of traffic lights, if you don't have your foot fairly firmly on the brake pedal, the car will tend to push forward so this is right on the verge of where it really would benefit from an increase in stall speed with the converter but we've proven this combination is workable with the factory automatic transmission.
03:03 The other consideration here is around the tuning and I've already talked about this a little bit.
03:09 The HS108D is not really compatible with the mass airflow sensor, won't work too well with the mass airflow sensor, particualrly where it's been relocated right in front of the throttle body.
03:19 And this is again due to the reversion that we tend to see with a lot of overlap.
03:23 With this instance we're going to go to the speed density operating system.
03:28 And this also requires another hardware piece from VCM which is simply a unit that replaces the mass airflow sensor in the inlet trap, they offer that, they also offer a auxiliary intake air temp sensor which we will need to do this.
03:42 This is really plug and play.
03:45 The reason we need that auxiliary air temp sensor is because the air temp sensor in stock form is located in the mass airflow sensor.
03:51 Understandably getting rid of that mass airflow sensor also removes the air temp sensor.
03:55 So the speed density conversion kit from VCM Suite includes an AC Delco air temp sensor which fits in the underside of the replacement unit for the mass airflow sensor.
04:06 It comes with a lead which has the factory mass airflow sensor connector or mating connector on the other end making it literally plug and play so that covers the hardware aspects there.
04:18 When we are going to a large cam like this, we also do need to give some consideration to how that's going to affect our tuning, what are we expecting from this? Well for a start we already know we're going to be going to a speed density operating system so we're going to be having a volumetric efficiency system or table for our tuning.
04:38 However the stock VE table is unlikely to work well with that large cam.
04:43 If the cam is doing what we expect, what we can hope for or expect is an increase in the engine's VE at higher RPM, this is how the cam would deliver more power.
04:53 But there are no free lunches here so with a large cam, we would also expect the volumetric efficiency to be decreased at idle and low RPM so we know there's going to be a swing in our VE table there.
05:04 From my own experience going from a stock cam to this particular cam, we tend to find on a good quality fuel, the engine actually becomes a little bit less knock prone and again from my own experience we're going to be typically expecting to see somewhere in the region of perhaps 25 to 27° of ignition advance at high RPM.
05:22 Doesn't really matter if you don't have this experience because the dyno is there for us to find out what the engine actually wants.
05:29 There will also be some other requirements around our electronic throttle body control which will be essential for our idle speed control which we'll talk about as we go through our base file configuration.
05:41 That idle speed, again as I've already touched on, we know that we're going to need to lift that idle speed, that's really important and a mistake that a lot of people make.
05:49 It's going to be very difficult to get good results if we try and retain the stock idle speed target.
05:56 So depending on the cam size, probably anywhere from 700 to 800, 850 RPM would be a suitable target idle speed.
06:05 This idle speed increases as we increase the size of the cam.
06:08 Just to have a look at that cam, let's just jump into the laptop screen for a moment and we've got the specs for our HS108D.
06:16 So that's the part number from Kelford.
06:17 Little bit meaningless if you aren't dealing with Kelford's part numbers but basically any mainstream supplier of cams for the LS vehicles will be able to provide something with similar specs.
06:28 Here we've got our cam lift or actually we're more interested in our net valve lift here which is 630 thou on the intake and we can see 610 thou on the exhaust.
06:39 The advertised duration here, reasonably sizeable at 284° on the intake, 292 on the exhaust and of course we also have our 50 thou duration which is 236 on the intake, 242 on the exhaust so these are the sort of numbers that are important for comparing cams from different manufacturers, the lift at the valve as well as the duration at either 50 thou or the advertised duration, these are the important numbers when it comes to specifying the particular cam profile.
07:11 To go along with that cam we have also fitted a Crow Cams timing set so this is a vernier adjustable timing set.
07:19 The style of vernier adjustable timing set where we actually need to remove the crank pulley, crank sprocket and align it on a different mark in order to make timing adjustments.
07:31 This is double row which is essential with a cam of this size.
07:34 With small cams you can get away with a single row timing chain but again important to talk with your cam manufacturer and make sure that you are using a suitable timing set for the cam, using a single row timing chain with this cam is not going to end particularly well, particularly over the long term.
07:51 Another little trick with the cam timing sets is to make sure that the trigger pattern on the cam sprocket is matched to your existing one.
08:03 There are actually a few different variations on this and really until you've got the engine apart it can be difficult to know what you've got so just making sure that that timing pattern is the same, if not you're going to get the engine all the way back together and find out that it won't start and run.
08:18 Also with that double row timing chain there is a requirement in some instances to clearance the back of the timing cover so those are a few considerations there.
08:27 We've dialled or degreed that cam into Kelford's recommendations just to make sure that everything is absolutely on point.
08:34 Also to go along with the cam timing set, we have installed a set of Kelford's beehive valve springs.
08:41 Again pretty common upgrade and essential when we are going to a larger cam like this.
08:46 If we tried to run this cam with the stock valve springs, again it's not going to end well, we need a valve spring that provides the right spring pressure to suit the cam that we are running.
08:56 An again your cam manufacturer will be able to recommend something suited to whatever you are choosing.
09:02 Lastly in terms of expectations with this tune, because of the cam's ability to flow air at higher RPM, we will be raising the rev limit as well so you'll see how we go about that as we move through the tuning process.
09:16 Now that we've got a good understanding of what's been done to the engine and what we can expect with our calibration, let's move on with our next step.

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