Automatic transmissions can present a problem for dyno operators as the relationship between wheel speed and engine rpm isn’t fixed like it is in a manual transmission. In this webinar we’ll talk about the inherent challenges an automatic transmission offers and discuss how to deal with these when we’re on the dyno in order to get the best possible results.

00:00 - It's Andre from the High Performance Academy and welcome to our 100th webinar.
00:06 In this webinar we're going to be looking at automatic transmission tuning tricks and tips when we're running automatic transmission cars on a chassis dyno.
00:16 Now this is something that I know a lot of tuners struggle with and some cars are easier than others, some cars are much more difficult than others and also some of the aspects of what we need to do, what we can get away with will depend to a certain extent on what type of dyno we're running the car on.
00:37 Now at the end of this webinar as usual, we will have questions and answers so if you've got any questions relating to running automatic transmission cars on a chassis dyno, please ask those in the chat and I'll deal with them at the end of the webinar.
00:53 Now the first thing is we will talk about what is the problem with running an automatic transmission car on a dyno? Surely it's no different to a manual, put the car in drive, put your foot on the throttle, job done.
01:05 Well there are a few considerations that we need to make and again some of this will depend on the particular transmission and how modified the car is.
01:17 One of the first problems we need to understand is that the relationship with a manual transmission and a clutch, the relationship between wheel speed and engine RPM is relatively fixed, provided of course the clutch isn't slipping.
01:34 So this makes it really easy to relate wheel speed on our dyno to our engine speed directly.
01:42 Now if we can just have a quick look at my laptop screen here, there's a quick graph, it's not a very good one but it's a graph that I've just managed to find prior to going live with this webinar on the internet and it just demonstrates the problem that we have with an automatic transmissin.
01:56 So this is actually from a Dyno Dynamics rolling road dyno.
02:00 Now on the bottom axis, our X axis we have our road speed.
02:04 So this is our roller speed and on the vertical axis we have our engine RPM.
02:11 So this is an engine RPM that's coming from a spark plug pickup on the engine.
02:17 So if we're running a manual transmission car as I mentioned, we're going to get a direct linear relationship as we can see here, I've just highlighted that with this red line.
02:26 However with the torque converter which we have between our automatic transmission and our engine, this relationship is no longer consistent and we've got a line here that sort of represents what we're likely to see from an automatic transmission.
02:45 So we can see particularly at lower RPM our relationship between our engine RPM and our road speed is really non linear.
02:54 As we move higher in the rev range, particularly right up high, we see that the relationship becomes a lot closer and we almost end up getting to a position where our relationship between wheel speed and engine RPM is fixed but there's still always going to be a small amount of slip in our torque converter.
03:16 So this is one of the things we need to understand when we are tuning with an automatic transmission, it's going to be a bit of a problem because we don't have that fixed relationship.
03:29 Now I'll just head back to my notes for a second and we'll continue talking about how this all relates.
03:36 Now one of the problems we have is because the dyno's looking at that relationship and assuming a linear relationship between our roller speed, or hub speed and our engine RPM, we're going to see an offset or an inconsistency in the way the torque and power is displayed, particularly at low RPM where we have that high amount of slip in our torque converter.
04:03 And really this goes hand in hand with one of the torque converters tasks in life is to multiply engine torque.
04:11 So when we're running a car on the dyno with an automatic transmission, what we're likely to see is a large and unrealistic increase in torque and hence power at very low RPM.
04:24 As we move through the rev range though and our torque converter gets to the point where it's slipping less, they'll never stop slipping completely, then we get a graph that is going to look much more like what we'd expect to see in a manual transmission car.
04:41 OK so let's talk about the problems we're likely to encounter when we're running our automatic transmission vehicle on the dyno.
04:52 Probably, while we've talked about these inconsistencies between engine RPM and road speed, easily the biggest problem we're likely to see with most OE transmissions is where the automatic transmission attempts to kick down as we go to full throttle at the start of the run.
05:11 We'll just do a really quick dyno example of this on our Holden Captiva and I'll apologise again for the fact that this Holden Captiva is not the most exciting car we've even dynoed but it will serve the purpose quite nicely.
05:29 So what I'm going to do here, we'll just go to my remote camera and, here's a gear lever, nothing particularly exciting about that.
05:37 So for this demonstration what I'm going to do is I'm just going to pull the car into drive, we can see that we have the option of Tiptronic or manual control of the automatic which we'll look at a little bit later on but for now we're just going to simply put the car into drive.
05:53 Right if we can just jump now back to my laptop screen and I'm actually going to scan while we're doing this quick demonstration with the HP Tuners software and probably the only redeeming feature of the Captiva is I can actually scan what the ECU's doing.
06:12 So what we want to do here is look at our engine RPM in our top graph.
06:16 So I'm just starting to run the car now and we also have in green just below we've got our road speed in km/h so what I'm going to do is just bring the car up to the settle speed and I'm just slowly applying more throttle, we can see the throttle position here in green on our third graph and we're just going to come up to our settle speed now.
06:40 So the engine has moved, the transmission's moved into 4th gear.
06:44 You can see we're sitting at about 1200 RPM, 35 km/h and 31% throttle.
06:51 So this would be the settle speed for the beginning of our run.
06:56 Now the problem is if I go to full throttle, watch really carefully what happens in particular to the two areas that I've got highlighted in the scanner, so the RPM and my throttle position.
07:10 So I'm just going to increase the throttle, we're coming up to 50% now and we'll go all the way through to 100%.
07:17 OK so you can see what's happened there is that the automatic transmission has kicked down.
07:23 It's actually kicked down in two gears.
07:25 So we've gone all the way down to second gear and it's flared the engine RPM up to 3000.
07:31 So that's one of the main problems you're going to see with automatic transmissions is the transmission attempting to kick down at the beginning of your run.
07:42 Now that's going to result in, particularly in a powerful car, the increase in torque when the transmission kicks down, you're likely to have problems with wheel spin on the dyno.
07:52 Certainly not a problem for our very underpowered Captiva here but a great demonstration nonetheless.
07:57 You're also going to end up, if the car kicks down part way through the run, with a really odd and completely useless looking dyno sheet.
08:07 So we need to make sure that the transmission is fixed in a gear.
08:12 And how can we go about doing that? We're going to talk about that shortly, I'll just jump back to my notes now we've had a quick look at that demonstration.
08:22 OK so the first problem we've talked about there is our transmission kicking down while we're attempting to perform a ramp run on the dyno.
08:33 Well I say ramp run but exactly the same can happen when we're trying to tune in steady state and we go past that throttle position where the transmission tuning attempts to kick down a gear.
08:47 We also have the problem of torque converter slip to consider.
08:50 Now we've talked about this already, now the two things we're going to notice here, one dramatically we're going to see an increase in the torque and hence power that's going to be displayed on our dyno at low RPM.
09:02 Once we understand how the automatic transmission works and we understand that this is an idiosyncrasy of what we're going to see on the dyno, this is really not a big consideration but another consideration that we do need to keep in mind is because we have torque converter slip that is inconsistent through the rev range, what it means is if we're looking at our dyno sheet and we're trying to relate an RPM point on our dyno sheet to an event that happened during the run, let's say a lean or a rich area in our tune or perhaps a knock event, then the RPM, the engine RPM picked up by the dyno, if it's relating RPM to wheel speed, may not be quite accurate, particularly as I've said, at low RPM where we can expect quite a large amount of slip in our torque converter.
09:55 So that's one thing to keep in mind, the RPM points between our dyno reading and what actually happened to our engine may not quite align perfectly so you can expect that to be another consideration.
10:09 Now the other thing that we need to consider as well is what's called a high stall torque converter.
10:17 Now these are common, particularly in highly modified drag cars and we're going to actually deal with those in a separate topic shortly so we'll deal with that within this webinar but I'll deal with it separately in a few minutes.
10:31 OK so now we know the problems we're likely to face so the kick down, torque multiplication at low RPM, the inconsistency between engine RPM and road speed, how can we go about dealing with this? How can we get the best results possible when we're dynoing an automatic transmission car on the dyno? I'm going to break this down into two separate parts because really it depends on the type of transmission fitted to the car.
11:00 Now with our more modern transmissions such as the one fitted to the Captiva here that we're running, we're going to have the ability to run the car, run the automatic transmission in manual mode or tiptronic as it's also referred to.
11:17 Now what that does is it gives us greater control because we can select a gear and within reason in most instances when we're in that manual mode, the automatic transmission will stay fixed in that gear.
11:31 Now this fixes the biggest problem that we've just discussed which is the kick down so let's have a quick look at that now, again I'll just start our Captiva and I'll just get our scanner running.
11:46 And we can have a look at what we're going to do here.
11:49 So with this car, OK it's a 6 speed transmission which is relatively common with a late model electronic automatic transmission, what I'm going to do is I'm going to run the car in 4th gear and for those of you who followed our earlier dyno setup webinar, it's in the archive if you haven't seen that already, you'll already know that the gear that we choose to run the car in, there's no one single gear that we must use and it becomes a tradeoff between the torque multiplication using lower gears which can result in erratic operation and wheel spin.
12:26 And at the other end of the scale there's a problem with exceeding the maximum speed limit of our dyno.
12:34 So what I'm going to do here, let's just go to our camera, our external camera again.
12:38 Just going to pull the car into drive now and what I'm going to do is just move into 4th gear and you do need to be a little bit careful when you're doing this, every car is a little bit different but we'll find that generally the automatic transmission won't shift into a higher gear below a certain RPM and with our Captiva, that seems to be about 2000 RPM.
13:03 So I'll just move our external camera back up to the dash now and hopefully we can see that, alright we've got a little number sitting on the dash saying that we are in 4th gear and we're at about 1250 RPM.
13:15 Alright let's just jump to our scanner software now so we can have a look at what's going on in the scanner.
13:21 So again we're looking at exactly the same parameters, we've got our engine RPM versus our road speed and again we've got our throttle position so right now we're sitting in exactly the same point as we were when we had the car in drive and I'm going to do exactly the same thing, I'm just going to very smoothly increase my throttle opening, we see we're going up to 52% now and just, this is actually a torque control in the ECU, I'm actually now at wide open throttle on the driver's pedal.
13:53 You can see we're still sitting at 1200, 1280 RPM and 35 km/h so that's fixed our gear, the car is no longer trying to kick down.
14:09 So while we're doing that, while we're there, let's just swap across to our dyno control and what we'll do, seeing as we're at this point is I'll perform a full throttle power run using the car now so let's get that run started, I'll just press the space bar and begin it now.
14:46 Alright so that's our run complete there.
14:51 And we'll just wait for the dyno to come back to a stop and we measured a fairly uninspiring 79 kW or 106 horsepower at the wheels.
15:02 My wife's going to be really happy with that.
15:04 Now what we can see is the dyno graph for the most part looks pretty well like we'd expect.
15:09 What we can see is we've got these big dips, now that's actually nothing to do with the automatic transmission, let's just jump into our laptop software and we'll see what's going on there.
15:22 And here I've got the scan of that run so again up the top we've got our engine RPM and we can see that for the most part, we do have a straight line there.
15:34 So that's good, that means that we've stayed in the one gear as we've discussed.
15:39 Probably the reason that my dyno graph is so ugly there, if we move down, if you're familiar with the HP Tuners software, you'll notice that we are seeing a huge amount of knock activity through this run and that's affecting the way the power the engine is producing.
15:57 However we're not really worried about the actual tuning.
16:00 This by the way is a factory GM tune so if you're wondering, no I haven't tuned this car at all.
16:07 So what we're really more interested in though is what's happening to the transmission while we're tuning so you can see there by using the Tiptronic or manual function, I'm able to fix the car in a gear and that's allowed us to get a run that really looks very similar to what we'd expect with a manual transmission.
16:26 Now if we could do a back to back run between our automatic transmission and a manual transmission, what we would see is because of that lip in the torque converter and the torque multiplication at low RPM, we would have ended up with an artificially higher value for our power and torque than what we ended up with the manual transmission.
16:47 And also if we just, while we're in our data logger here.
16:51 While this is a late model electronically controlled automatic transmission, it does a pretty good job of approximating a straight line with our RPM.
17:01 So when I say a straight line, a straight line gives us our linear relationship between the engine RPM and the wheel speed.
17:11 What may be a little bit hard for you to see is just here at low RPM around 1900 RPM at the start of our run, we do actually have a slight blip in our RPM and this is a result of the torque converter there.
17:25 This is the result of the slip that we've been talking about.
17:29 OK so I'll just head back to my notes and we will continue, I'll just shut off our dyno fan as well.
17:37 So we've done the run there, we've used 4th gear as I've mentioned.
17:44 Now in a 4 speed automatic which is another pretty common option, particularly I've done a lot of tuning with GM product on the LS market and the 4L80 transmission is another common option there and in that sort of transmission I would tend to run the car in 3rd gear so just some ideas for you there in terms of what gear you could use but again there isn't one single gear that you must use for all cars and you're always free to do your own investigation and see what gives you the best results, what gives you the most consistency and gets you away from wheel spin and that upper limit on your dyno speed.
18:31 OK so again with our example here on the Captiva, the RPM is relatively locked right through, relatively consistent to road speed, what we will see on some engines or some transmissions is particularly again at low RPM we'll see a bigger flare in our engine speed so when that happens, we're going to end up with, let's just see if we can demonstrate this, let's jump back to my laptop software.
19:00 So what we'd see, I'm going to exaggerate this slightly, is we'd see our engine RPM do something like this before dropping back and then again from probably about 3000 RPM and above, the RPM should be relatively consistent in a straight line.
19:17 Now when we see a flare like this, obviously this is the torque converter slipping and it is going to give us a blip or a large jump in our torque and power on the dyno and we need to understand that this again is not very realistic, we're not going to be able to use that to help us with our tuning and we need to understand that it is related to the automatic transmission so we can all but ignore that.
19:44 If we do have a transmission, provided that it is slipping and doing exactly the same thing from one run to another, doesn't really matter what our dyno printout or dyno graph looks like, what we're looking at is, when we make a change that we go forwards or backwards, so did everything move up or did everything move down? That's the sort of things we're really focused on more than the actual numbers and the shape of that dyno curve and again, from the point where our torque converter stops slipping or is close to locking up, we're going to find that the dyno graph will look exactly the same as what we'd expect to see with a manual transmission.
20:26 Right, hopefully that's explained that a little bit better, I'll just jump again back to my notes now.
20:32 OK so we've looked at now the automatic transmission where we have the ability to run in a Tiptronic or a manual mode, that certainly makes our life a lot easier.
20:43 The more difficult or complex situation though is where we've got an automatic transmission that doesn't give us manual control, perhaps we've got a drive selection where the transmission will change gear by itself, we might have the ability to pull the transmission down into a lower gear, perhaps 3rd or 2nd or a low setting but we don't have the ability to have absolute control over the gear.
21:11 Now in this situation we don't want to run the automatic transmission in drive.
21:16 What we want to do is pull the car down into a lower gear and again I'll relate here my own experience with the GM 4L80 transmission which is a 4 speed transmission that I would typically run in 3rd, I think from memory the note on the gear selector is D3 so we pull it down from drive and that brings it into 3rd gear.
21:43 Doesn't fix all of our problems though because in D3 as we'll find with most of these sorts of transmissions, at low RPM which is exactly what we're going to see when we're settling the car on the dyno at the beginning of the run, if we go all the way to full throttle we're going to find the transmission will still kick down into 2nd gear.
22:05 So this presents a bit of a problem, how do we actually run the car through on the dyno if full throttle is going to result in the gearbox kicking down.
22:15 Well the solution is that we need to be a little bit careful with how we begin our ramp run with this sort of transmission.
22:23 Again I'll just relate my experience with the 4L80.
22:26 So what I would do is select 3rd gear, I'd set up my ramp run between perhaps 1500 RPM and 6500 RPM and again if I had gone to full throttle during the settle time or right at the very beginning of the run, the transmission would kick down into second and essentially ruin any results I was likely to get.
22:46 So the solution to this is we need to be a little bit careful with how and when we actually transition to full throttle.
22:56 So what I would generally do is begin my run with somewhere around about 75-80% throttle.
23:02 And this needs to be felt out, you can do this by using your scanner and finding the throttle position where you're right on the brink of the transmission kicking down into that lower gear.
23:16 And you're not going to do any damage while you're finding this point, what we want to do is just be right on the limit of where the transmission will kick down into the lower gear.
23:25 So when we find that point and we stay below it, the transmission will stay fixed in 3rd.
23:31 So then we can actually begin our run.
23:34 Now obviously at this point we're not quite at full throttle and what we want to do is transition from whatever our starting throttle position, let's say 80%, through to 100%, as we move through the rev range and at a certain point, the transmission will no longer try and kick down and again we need to find that point as well.
23:55 So again relating to the 4L80, I would start my run from about 1500 or 1750 RPM and around about 2500 to 3000 RPM, somewhere around that point, I could smoothly transition through to 100% throttle.
24:11 So this needs to be done via trial and error and using our logger to see exactly what we're doing and the important point is once we've found what works for that transmission, we want to repeat those settings as closely as we can for any subsequent runs.
24:29 Because obviously if one run we start at 70% throttle and the next run we start at 80% throttle, that's going to affect the power and torque reading on the dyno.
24:40 So what we need to understand is definitely the lower part of the rev range is going to be something of a compromise in terms of the power and torque reading of the dyno.
24:51 We may see some inconsistencies depending on how and when we apply the throttle.
24:56 But I guess the important point to really understand here is generally in these situations, we're already reflashing an OE ECU so we're not really tuning from scratch so this part of the rev range is already tuned to some degree with the factory or OE tune and we're only making small adjustments and really in my own experience, again probably the areas we're more interested in, more focused on anyway will be higher up in the rev range.
25:27 Now the other thing which that leads me to is we also need to understand that how we tune the car on the dyno also needs to be related to how the engine is actually going to operate when we're out on the road or the racetrack.
25:44 Now the fact that our transmission is trying to kick down when we're running at very low RPM on the dyno, that's exactly what's going to happen when we're out on the road or a racetrack and we go to full throttle.
25:56 So what this means, what I'm getting at here is we don't necessarily need to beat ourselves up too much over trying to optimise the tune down at very low RPM as this is an area at wide open throttle where we're probably not actually going to be operating the engine in anyway so tune the car or the engine in the way it's actually going to be able to be used.
26:22 OK so this leads me to the next point which is high stall converters and this requires a little bit of attention as well.
26:32 Now high stall converters, just to give you a bit of an idea on what these are and why they're used, every torque converter has a stall point which is basically where the torque converter essentially locks up, never quite locks solid but essentially if we bring the RPM up, this is the point where the torque converter stalls and the input drive is transferred through to the ouput to our automatic transmission.
27:02 So when we modify the engine, particularly modifications that make a huge drop to our low RPM engine power and torque, something like perhaps fitting a large camshaft, it's common to install a high stall converter to allow the RPM, the engine RPM to increase, this improves the torque multiplication of the automatic transmission or the torque converter I should say and particularly in a drag application, allows us to get a better 60 foot time, get off the line a lot better.
27:37 So the problems we're likely to face on the dyno are really going to depend on exactly how aggressive the converter is or how high the stall point of the converter is so for a really mild converter, which may be fitted behind a late model GM LS2 LS3 with the 6L80 transmission, we might be looking at a mild high stall converter where the stall point is raised perhaps 500 to 1000 RPM from factory and that's probably not going to make a significant difference to our tuning but if we look at the extremes where we may be using a 5000 RPM stall converter, it's going to make a huge difference to our tuning.
28:25 Now what's going to happen with this type of converter is essentially when we put the car in gear, and we put our foot on the throttle, the torque converter is going to allow it to slip, or the engine RPM to come up to that stall point or somewhere around about that stall point.
28:44 So what I mean by this is if we put the transmission into first gear, we hold our foot on the brake and we apply the throttle, the engine RPM is going to come up to somewhere around about that stall point, 5000 RPM and then the torque converter is going to lock up and it's going to hold the RPM consistent there and if we then step off the brake and actually launch the car down the road or track then obviously the RPM is going to increase as our road speed increases.
29:14 The relevance of all of this is with a high stall converter, it essentially becomes impossible to tune the low RPM high throttle position area of our fuel and ignition maps and the reason for this is we simply can't access them on a rolling road dyno.
29:34 We really can't do much up to the point where that torque converter locks up and our road speed actually starts increasing inline with our engine RPM.
29:47 OK so this makes it, as I've said, impossible to tune that lower RPM range fully.
29:56 However again I'll just relate back to what I've been saying, what we also need to understand is that this is also the same way the car or the engine is going to respond when we're actually driving on the road or the racetrack so we're simply not going to be able to load the engine up at let's say 2000 RPM and wide open throttle.
30:18 Any time we apply throttle, we're going to come straight up to that stall point before anything really happens.
30:26 So while it can be frustrating, particularly for tuners that are familiar with mapping engines with manual transmissions, there is this large chunk of our RPM range in both our fuel and ignition maps that we're simply not going to be able to access properly and fully map.
30:48 So how do we deal with this? Well first of all as I've said, it doesn't strictly matter as much as what we would have in a clutch transmission car because the engine isn't going to be able to operate in those areas anyway.
31:03 Doesn't mean that we can completely ignore those areas of our mapping because even when we just give the throttle a large blip when the transmission is in neutral, the engine's naturally going to transition through these areas of our fuel and ignition maps anyway.
31:23 But since we have no way of accurately mapping these areas, the only option we really have is to extrapolate the shape of our fuel and our ignition tables that we've already come up with above the stall RPM, extrapolate those down into the lower regions.
31:42 Now that's going to hopefully at least have our fuel and ignition close and again I'll just reiterate we don't need to beat ourselves up too much on these areas because the engine can't be held, it can't operate under load in those areas anyway so they're only even going to be a transient area that the engine is going to pass through quickly.
32:08 Now the other aspect when we're tuning a high stall converter that needs to be considered is managing the torque converter or transmission fluid temperature.
32:20 Now what I mean by this is it'd be common for us to begin doing a ramp run at perhaps 1500 or 2000 RPM and obviously we'd extend our RPM all the way through to whatever the maximum rev range that we want to run the engine to would be.
32:38 So let's say that's 1500 through to 6500 RPM.
32:43 Now with a typical automatic transmission with a tight converter as we'd see in an OE application, like the Captiva we've just run up, we see that we almost get that approximation of our run and I've mentioned we do tend to see a slight flare in the engine speed at very low road speeds.
33:04 If we tried to apply that same technique to a high stall converter, what we're going to find is that when we're trying to target 1500 RPM or the dyno's holding the road speed at whatever should equate to 1500 RPM, the torque converter's just going to slip massively and our RPM will flare right up to 5000 RPM.
33:26 Now that's where our RPM is going to sit while the dyno allows the road speed to slowly catch up and at the point where our road speed catches up and our torque converter locks up, at that point then we're going to find that our engine RPM will start to increase.
33:43 So this gives us our 5000 RPM to 6500 RPM rev range where we can actually perform our tuning.
33:52 Also gives us a really unusual looking power and torque curve on our dyno because essentially our power, our torque being measured has stayed relatively consistent all the way through the rev range up to the point where the torque converter has begun to lock up.
34:06 Problem with this as well though, or it might be a little less obvious is while that torque converter is slipping massively at low road speed, we're putting a huge amount of heat into the automatic transmission fluid and this can very quickly damage the automatic transmission and the torque converter so we need to be aware of this and we need to understand how to manage this.
34:32 So when we're dealing with a high stall converter, what we want to do is find out what the stall point for the converter is and we really want to focus the beginning or low speed, beginning RPM or road speed part of our ramp run, we want to focus that at very close to the point where the torque converter locks up initially.
34:52 So we'd only be doing our ramp runs from perhaps 4500 RPM and above and this is going to limit the amount of slip in the converter and hence it's going to control the amount of heat being put into the automatic transmission fluid.
35:10 Alright we're going to move into some questions and answers very shortly so if you do have any questions, please ask those in the chat and I'll deal with them shortly.
35:21 So really just to recap what we've gone over here.
35:25 Automatic transmissions I think a lot of tuners think that they're a scary type of transmission to tune and they're going to result in all number of problems when we're on the dyno and the reality is it's simply not that bad.
35:40 We've got 3 things that we've really discussed here.
35:43 First of all, if we're dealing with a late model electronically controlled automatic transmission, where we can lock the car in a gear, in that case really the results are actually going to be quite similar to what we could expect with most manual transmission cars.
36:00 The only difference is because we're likely to see the torque converter slip slightly at lower RPM or slightly more at lower RPM, this is going to affect the shape of our power and torque graph and remember we may not always have a linear relationship between the RPM that our dyno is showing and the RPM that our engine is actually pulling.
36:22 Moving on, we had the example where we've got an automatic transmission where we can't lock the transmission into a gear.
36:32 And in these cases, what we're going to use is probably 3rd gear in a 4 speed automatic or perhaps 2nd in a 3 speed automatic.
36:41 And in these instances we're probably going to have to feather the throttle slightly at the beginning of the run and ease into the throttle to prevent the transmission from kicking down at low road speeds.
36:55 And then we've also talked about the high stall torque converter where this is going to limit our ability to access in particular the very low RPM high load areas of our fuel and ignition maps and remember this isn't as big a consideration or big a concern as most tuners may think because if we can't access these areas of the fuel and ignition maps while we're on the dyno, we're also not going to be able to access them on the road or the racetrack so these areas of our fuel and ignition curves really only become an issue during transient throttle application so where we're actually free revving the engine and the way I deal with those is to extrapolate the shape of the fuel and ignition curves from the areas that we actually can tune.
37:42 And a last tip there with a high stall converter is to try and make your runs across the area of the rev range where the torque converter is actually locked and if we can do this it's going to limit or reduce the amount of heat being placed into the automatic transmission fluid.
38:03 Chris has asked, what about locking the converter as well as the gear? In some automatic transmissions, electronically controlled automatic transmissions, we may have the option of locking up the converter.
38:18 In general though there is still going to be some amount of slip and it really is going to depend on the control that we have.
38:28 In particularly actually, something I should have mentioned, in particular in some scanning software, we may have the option of selecting or fixing a gear inside the scanner control software so that's the case for the Captiva that we've got here as our example using the HP Tuners scanner, we can actually select and fix the gear that the transmission is running in.
38:52 I think from my recollection, we may have some torque converter control in that scanning software as well but unfortunately again my own experience is while we can select to lock the torque converter, it doesn't still work like a clutch where that is fixed right through the rev range.
39:11 Mike's asked, what about just disconnecting the kick down cable? We've been talking here about later model automatic transmissions where there's a transmission control module linked to the engine control module in charge of kick down.
39:28 Certainly if you have a kick down cable that you can disconnect and prevent the transmission from kicking down, that is an option.
39:36 The aspect though, again I'll just reiterate is the low RPM area that we're worried about, even with the transmission still able to kick down, we're able to get through that low RPM area of our rev range by manipulating our throttle position relatively easily and that gives us a quicker and easier solution to running the car up on the dyno.
40:03 So again really here it comes down to how much time you're prepared or able to put into preparing the car to run on the dyno and if you don't have the time available to disconnect a kickdown cable then nursing the engine through that lower RPM range is certainly a viable option for you.
40:24 TDE Champ has asked, if working with a highly modified car, would it make more sense to run the engine on an engine dyno before installing to get more control in tuning? Look certainly that is an option but the reality is that's quite an expensive and time consuming option and realistically in my own experience, it's just simply not necessary, mainly for the reasons I've already touched on.
40:50 The areas down at low RPM and high throttle position, if we've got a high stall converter, it's an area that we're not going to be able to actually apply load out on the road or track anyway so the engine's simply not going to operate in those areas.
41:05 Yes it's an area that we're not going to be able to gather any data on the dyno from but because the engine's not operating there, it really becomes sort of a bit of a moot point in my own experience or my own opinion I guess I should say.
41:21 So just looking back over my own experience, we spent probably the better part of 5 or 6 years tuning probably I guess 100s of what in the New Zealand market is the Holden Commodore HSV fitted with the LS1, LS2, LS3 V8s and over the course of that time we dealt with a number of cars that were fitted with high stall converters, large cams, superchargers or combinations of all of those things and I've never had a situation where I couldn't get a really good result and a really good repeatable result on a chassis dyno by applying the techniques that I've just discussed.
42:04 My most difficult car to tune on a chassis dyno was actually an old Holden Monaro that was fitted with a very modified 5 litre V8 backed by a high stall converter and it was fitted with a centrifugal supercharger and that particular engine made around about 550 wheel horsepower and it ran to about 6500, 6800 RPM and it had about a 4000 RPM stall converter, it really was built purely for the drag strip.
42:37 So that was a little challenging to run because as I've kind of touched on, we really couldn't do anything on the dyno below that stall point.
42:46 Now one thing I will just elaborate on here, that car was built for the drag strip but it was also a weekend cruiser.
42:54 So you do need to be aware that the lower RPM range where that torque converter is slipping, we're still able to drive the car and operate it there at lower throttle position.
43:06 So in this instance, probably the road is the best place to see exactly where the engine is operating under those conditions.
43:15 It's when we apply more throttle that the torque converter slip becomes more of an issue and will end up coming up to that stall point much quicker.
43:23 So we can operate at low load and low RPM but we can't operate at high load and low RPM at that point, we're just going to move through to the stall point.
43:36 Alright that looks like it's taken us to the end of our questions, so hopefully that's given you some insight and some confidence in being able to attempt running automatic transmission vehicles on a chassis dyno.
43:48 As I've mentioned, it does require for vehicles that you're not familiar with, it does often require a little bit of experimentation about which gear is going to give you the best results and about how much throttle position you can apply before the transmission kicks down as well as what RPM you can start transitioning through to full throttle during a ramp run, again to prevent the transmission from kicking down.
44:16 As usual if you've got any further questions, please ask those in the forum and I'll be happy to answer them there.
44:22 Thanks for joining us guys and we look forward to seeing you all next week.