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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

04.29

00:00 - Before we jump in and actually start making modifications to our ROM file or even for that matter, start running the vehicle on the dyno, it's always a good idea to give some consideration to the modifications that have been made to the vehicle and the engine and how these might impact on our tuning.
00:15 If we think about this now, it's going to drive our decision making when we're going through the process of setting up changes in our ROM file and it can also help us make sure that we don't overlook any critical steps while we're going through the tuning process.
00:29 Now in our case, there really isn't a lot to consider here, the engine specification really is almost identical to stock.
00:36 We've got those couple of modifications I mentioned in the introduction, we've got the slightly larger Kinugawa turbo.
00:42 Now we know that for a start, this is going to end up making our boost a little bit lazier to come on, the turbo is a little bit laggier than stock.
00:51 This has also got an adjustable pre load on the wastegate and depending on how that wastegate has been preloaded, this can also have a big impact on how accurate our boost target tables are going to be and we may find, if we're not careful here that we're going to have a situation where the engine will overboost.
01:09 In this case, the turbo has been fitted to the vehicle for some time, even with a stock ROM in there.
01:16 We already have some runs on this and we know that the boost is relatively under control but as we move through the tuning process, we may find that we need to optimise those boost targets to suit the lazier nature of this turbo.
01:27 The other aspect here is that this turbo can well and truely outflow the potential for the fuel system on the car.
01:36 At the moment we're running stock injectors and a stock fuel pump.
01:39 So this is really going to be the limitation on how much power we can make.
01:43 And for this reason we are expecting that we're going to need to taper the boost down relatively low at higher RPM.
01:50 On the other hand, if we have upgraded injectors and a fuel pump that could cope, we'd be able to hold a lot more boost in the higher RPM ranges and see the true potential of this turbo.
02:01 Now the other aspect we've changed to the intake system is fitting an aftermarket air filter.
02:07 Nothing particularly unusual here, this is a stock air box, we've just got an aftermarket freer flowing filter element inside of that stock air box.
02:15 The considerations we want to make here are around what this is likely to do to our mass airflow sensor scaling.
02:23 Given that we have only changed the air filter element, the air box is still completely stock, everything up to the turbocharger is completely stock.
02:31 We could rightly expect that the factory MAF scaling should be pretty well on point.
02:37 Definitely close enough to get us up and running.
02:40 Now alternatively if you have made changes and fitted a larger MAF tube, before we could even start the vehicle, what we would need to do is make some assumptions around what that will do to our MAF scaling.
02:51 Good calculation there as we covered inside of the body of the course is to look at the cross sectional area of your factory mass airflow sensor the cross sectional area of your larger MAF tube, represent the difference there as a percentage and then you can apply that difference to the entire MAF scaling.
03:08 Obviously in our case, that's not going to be required so we can move on.
03:12 The only other real modification that we've made here is that three inch turbo back exhaust.
03:18 Particularly the fact it is from the front pipe or right off the back of the turbocharger, what we find is that with a lot of turbocharged vehicles, Subaru being no different, this can again affect our boost control.
03:29 Particularly if you do this with no other changes on a stock turbocharger you're likely to find that your boost will increase quite dramatically and this can also cause overboosting above our target so again this comes back to some potential changes necessary in our boost targets.
03:45 Again, because we've already run this car, we know that we've got control over our boost so not an issue for us there.
03:51 The last aspect I'll mention here is that we are running this on our local 98 octane pump fuel.
03:58 It's a good quality fuel but given the nature of the Subaru engines we do know that we're still expecting knock to be a problem so this is something we're going to be needing to monitor very carefully as we progress with the tuning process and we know that knock can be a very big killer of any performance engine, not least of all, Subarus.