Changing second-turbo switchover point.

[carl0s]

Is it possible to lower the RPM at which the ECU decides to fire up the second turbo?

 

It seems that a BPU Supra should be able to provide enough exhaust energy at a lower RPM.

 

Can it be done?

[Soonto_HAS_soop]

if you knew the voltage that was sent to the VSV and you had a small box of tricks that checked the rpm and boost levels, and could output a voltage of the same magnitude, then I suppose it would be possible to change the rpm cut in of the 2nd turbo in sequential system by overiding the ECU with this addition control.

[carl0s]

I was hoping of just telling the ECU to do it at a lower point, so you still have all the pre-spool stuff going on etc.

 

There's talk on Supraforums of doing it with an AEM by changing L4 and L5 or something..

 

Is the switchover point definately fixed at a particular RPM on the stock ECU? It seems to be, but I've read talk about it being based on load as well

[Tricky-Ricky]

I think the idea is that its timed to come in when the ECU goes open loop or vicversa, so it can deal with the increased air flow, if you can get it to come in at an earlier RPM then i think you may have to force the ECU out of open loop, i am looking at trying to do this myself as in TTC mode both turbos are making a bar or more by 2800-3000 RPM and seeing 14.7 AFR is starting to worry me.

[carl0s]

Well if it was doable then it'd be well worth doing - as you say, both turbos could be online at 3,000rpm instead of the usual 4,000rpm as the gasflow is there to run them.

[Tricky-Ricky]

Just go TTC then, and save a fair bit of messing about;)

[carl0s]

Just go TTC then, and save a fair bit of messing about;)

 

Then you'd lose the low end response.

 

Best would be if you retained the stock seq. system but had it switch over ~1,000rpm lower than normal.

[Ian C]

Is it possible to lower the RPM at which the ECU decides to fire up the second turbo?

 

It seems that a BPU Supra should be able to provide enough exhaust energy at a lower RPM.

 

Can it be done?

 

A BPU Supra achieves it's BPU status by running a maximum boost of 1.2bar. It does this by derestricting the exhaust. 1.2bar is achieved with both turbos online. You can't put the cart before the horse and say the engine produces more exhaust gas *before* the turbos are spun up. BPU doesn't affect engine capacity or anything, so off-boost it's exactly the same, all the way to 0.8bar at which point a stocker stops increasing boost. So it's fallacious to expect a BPU to spin up turbos faster.

 

So that buggers up this discussions' basis from the word go However, onwards!

 

I was hoping of just telling the ECU to do it at a lower point, so you still have all the pre-spool stuff going on etc.

 

Is the switchover point definately fixed at a particular RPM on the stock ECU? It seems to be, but I've read talk about it being based on load as well

 

The stock ECU is a stock ECU, not an AEM. You can't tell it to do things differently. Ben explained how much effort it would be, you'd have to make your own sequential control system pretty much.

 

The switchover point on a sequential TT is fixed by RPMs. Once you are at 4000rpm, the VSVs are switched to enable both turbos to work. Load isn't accounted for, otherwise the sequential operation would take place at a predetermined boost pressure, so it's transition point would vary up and down the rev range. At 4000rpm+ the engine has enough exhaust gas flow to bring both turbos online immediately anyway. Leaving only one in the loop because the load is low simply adds complexity and an artificial lag effect when you boot the throttle as it goes through the sequential motions.

 

I think the idea is that its timed to come in when the ECU goes open loop or vicversa, so it can deal with the increased air flow, if you can get it to come in at an earlier RPM then i think you may have to force the ECU out of open loop, i am looking at trying to do this myself as in TTC mode both turbos are making a bar or more by 2800-3000 RPM and seeing 14.7 AFR is starting to worry me.

 

Nope, as above it's 3600rpm prespool, 4000rpm open the taps. Open/closed loop has nothing to do with it.

 

Toyota, for some reason, pretty much runs the first turbo at stoich levels of fuelling. Probably made for great economy figures, and as stock it works fine - but as soon as you put more efficient turbos in (hybrids, fast spooling single) they move denser air charges around and you need more fuel to deal with this. This however causes mondo problems for us piggyback tuners. It's a bastard to tune around but the E-Manage can do it due to having it's own pressure reference and some control over the injector signals. The upside to this is that once you put in more fuel you can wind on timing as well and still remain safely det-free.

 

Just go TTC then, and save a fair bit of messing about;)

 

If you want to do TTC mode properly, you'll need plenty of messing about As I've said before, initiating parallel mode just by swapping a couple of hoses or wiring open the actuators is the start of it. Stick like that and you'll get grotty response, a fat boost spike at 3800ish rpm, and you won't be fuelling enough until 4krpm+.

 

Then you'd lose the low end response.

 

Best would be if you retained the stock seq. system but had it switch over ~1,000rpm lower than normal.

 

But, as I said at the start, you aren't generating any more exhaust gas when BPU than at stock levels, until you get over 0.8bar. So an earlier switchover would be detrimental.

 

 

-Ian

[carl0s]

A BPU Supra achieves it's BPU status by running a maximum boost of 1.2bar. It does this by derestricting the exhaust. 1.2bar is achieved with both turbos online. You can't put the cart before the horse and say the engine produces more exhaust gas *before* the turbos are spun up. BPU doesn't affect engine capacity or anything, so off-boost it's exactly the same, all the way to 0.8bar at which point a stocker stops increasing boost. So it's fallacious to expect a BPU to spin up turbos faster.

 

But a BPU car pushes just the first turbo to 11psi (0.8bar). Surely by this point (3,200-ish rpm), it's fair to say there's enough going on there for both turbos to be running?

 

I know we're not increasing exhaust gas volume by going BPU, but we're increasing the pressure differential quite significantly aren't we?

 

Still don't quite get what you're saying. You seem (to me) to be saying that all BPU means, is that the car can go above 0.8bar, and that it doesn't affect the boost curve anywhere below where the 0.8 bar would have come in in the first place. That can't be right can it? As I just said, BPU sees the first turbo getting quite carried away with itself fairly early on.

[Ian C]

But a BPU car pushes just the first turbo to 11psi (0.8bar). Surely by this point (3,200-ish rpm), it's fair to say there's enough going on there for both turbos to be running?

 

The first turbo runs about 0.7 to 0.8bar as stock anyway. You can increase the boost on it but it's debatable if you get any power increase from it - I've experienced a marked power loss from upping the boost on #1.

 

The idea of Basic Performance Upgrade doesn't encapsulate upping the boost on the first turbo anyway.

 

Still don't quite get what you're saying. You seem (to me) to be saying that all BPU means, is that the car can go above 0.8bar, and that it doesn't affect the boost curve anywhere below where the 0.8 bar would have come in in the first place. That can't be right can it?

 

That's exactly what I'm saying.

 

As I just said, BPU sees the first turbo getting quite carried away with itself fairly early on.

 

I'm not sure where you got that idea from, but it's not BPU to increase the boost on the first turbo. First turbo mods are comparatively rare and don't bring back much in results.

 

-Ian

[Tricky-Ricky]

Quote:

Originally Posted by carl0s

Is it possible to lower the RPM at which the ECU decides to fire up the second turbo?

 

It seems that a BPU Supra should be able to provide enough exhaust energy at a lower RPM.

 

Can it be done?

 

A BPU Supra achieves it's BPU status by running a maximum boost of 1.2bar. It does this by derestricting the exhaust. 1.2bar is achieved with both turbos online. You can't put the cart before the horse and say the engine produces more exhaust gas *before* the turbos are spun up. BPU doesn't affect engine capacity or anything, so off-boost it's exactly the same, all the way to 0.8bar at which point a stocker stops increasing boost. So it's fallacious to expect a BPU to spin up turbos faster.

 

So that buggers up this discussions' basis from the word go However, onwards!

 

 

Quote:

Originally Posted by carl0s

I was hoping of just telling the ECU to do it at a lower point, so you still have all the pre-spool stuff going on etc.

 

Is the switchover point definately fixed at a particular RPM on the stock ECU? It seems to be, but I've read talk about it being based on load as well

 

The stock ECU is a stock ECU, not an AEM. You can't tell it to do things differently. Ben explained how much effort it would be, you'd have to make your own sequential control system pretty much.

 

The switchover point on a sequential TT is fixed by RPMs. Once you are at 4000rpm, the VSVs are switched to enable both turbos to work. Load isn't accounted for, otherwise the sequential operation would take place at a predetermined boost pressure, so it's transition point would vary up and down the rev range. At 4000rpm+ the engine has enough exhaust gas flow to bring both turbos online immediately anyway. Leaving only one in the loop because the load is low simply adds complexity and an artificial lag effect when you boot the throttle as it goes through the sequential motions.

 

 

Quote:

Originally Posted by Tricky-Ricky

I think the idea is that its timed to come in when the ECU goes open loop or vicversa, so it can deal with the increased air flow, if you can get it to come in at an earlier RPM then i think you may have to force the ECU out of open loop, i am looking at trying to do this myself as in TTC mode both turbos are making a bar or more by 2800-3000 RPM and seeing 14.7 AFR is starting to worry me.

 

Nope, as above it's 3600rpm prespool, 4000rpm open the taps. Open/closed loop has nothing to do with it.

 

So what was the point of Toyota mapping the ECU to go open loop at the point where both turbos are making more airflow than just the one turbo? if not to supply the correct fueling

 

Toyota, for some reason, pretty much runs the first turbo at stoich levels of fuelling. Probably made for great economy figures, and as stock it works fine - but as soon as you put more efficient turbos in (hybrids, fast spooling single) they move denser air charges around and you need more fuel to deal with this. This however causes mondo problems for us piggyback tuners. It's a bastard to tune around but the E-Manage can do it due to having it's own pressure reference and some control over the injector signals. The upside to this is that once you put in more fuel you can wind on timing as well and still remain safely det-free.

 

 

Quote:

Originally Posted by Tricky-Ricky

Just go TTC then, and save a fair bit of messing about

 

If you want to do TTC mode properly, you'll need plenty of messing about As I've said before, initiating parallel mode just by swapping a couple of hoses or wiring open the actuators is the start of it. Stick like that and you'll get grotty response, a fat boost spike at 3800ish rpm, and you won't be fuelling enough until 4krpm+.

I was of course referring to doing the TTC mod the proper way IE wiring or removing the EGCV and the IACV and sorting the fueling rather that trying to get the VSVs to switch at a lower RPM.

 

Quote:

Originally Posted by carl0s

Then you'd lose the low end response.

 

Best would be if you retained the stock seq. system but had it switch over ~1,000rpm lower than normal.

 

But, as I said at the start, you aren't generating any more exhaust gas when BPU than at stock levels, until you get over 0.8bar. So an earlier switchover would be detrimental.

 

 

 

-Ian

__________________

 

I love my job. It pays for my Supra.

 

--------------------------------------------------------------------------------

Last edited by Ian C : Today at 17:27.

[Ian C]

Nope, as above it's 3600rpm prespool, 4000rpm open the taps. Open/closed loop has nothing to do with it.

 

So what was the point of Toyota mapping the ECU to go open loop at the point where both turbos are making more airflow than just the one turbo? if not to supply the correct fueling

 

I'm not sure what you mean. I'm saying that the second turbo comes in at a preset RPM and load has nothing to do with it. The VSVs open no matter what boost pressure you are at, if you are at or above 4000rpm.

 

Toyota would have mapped it to supply what they considered the correct fueling regardless of when the sequential changeover took place. If it was at 3500 or 4500 you'd see it go mad on fuel at those rev points instead I guess I suppose they worked out when the best time was to bring the second one in from an air delivery, power delivery, lag amount, and driving conditions viewpoint. If you are at 4000rpm or above you are probably hooning it, so out of closed loop you go and bring both tubbies online...

 

-Ian

[Tricky-Ricky]

Thats more or less what i was saying, i didn't mention load, Carlos did, I'm just surprised that it seems to be relatively happy at .8 bar and 14.7 AFR

[carl0s]

 

I'm not sure where you got that idea from, but it's not BPU to increase the boost on the first turbo. First turbo mods are comparatively rare and don't bring back much in results.

 

-Ian

 

I haven't intentionally gone out of my way to increase boost on the first turbo. It's just what happens when you 'go BPU' (decat, exhaust, etc).

 

It happened on my UK spec car (see here) and my Jap car does it without any bleeder valves etc, just does it all by its self.

 

I know it's out of the first turbo's efficiency to do this, which is why I'm saying open up the other turbo, then we're coming back into efficient use of that same exhaust energy that's 'too much' for the first turbo alone, hence me starting this thread.

 

Maybe there's another reason for it, and I'm imagining what I've been seeing, or maybe my boost gauge is dodgy, but I basically see 11psi from no1, and it feels like the car is strangled, waiting for those revs to hit the magic point when all of a sudden the extra power will come from the second turbo.

 

I imagine if the second turbo was set to come on earlier, then you wouldn't get the 'bpu kick' of no2 coming online, and it'd be more progessive like stock changover.

[carl0s]

The first turbo runs about 0.7 to 0.8bar as stock anyway.

 

Ah, I missed this bit. Does it? Hrmph

[carl0s]

Last bit for tonight on this..

 

It is said doing the TTC mod gives additional power in the 3,000 - 4,000 rpm range. Doesn't that fit in with what I'm suggesting?

[Ian C]

Sort of. All exhaust energy goes into spinning up two turbos instead of one. So it takes longer and you lose the low down response of just the first turbo. But you do get both on boost faster.

 

However to get the first one to spin up and then get the second one online, exhaust gas needs to divert to the second one to do this. If you don't want a nasty drop in boost (and from that a nasty drop in power delivery) from the first turbo then you have to wait a bit longer for the engine to be spitting out enough exhaust gas energy to keep #1 spinning while it brings #2 online as well. That's probably around 3600 rpm

 

A properly set up TTC with remap and boost controller config can indeed give good results from 3000rpm upwards.

 

-Ian

[Tricky-Ricky]

 

A properly set up TTC with remap and boost controller config can indeed give good results from 3000rpm upwards.

 

-Ian

 

Glad to see your a believer at last Ian:)

[Steve]

A properly set up TTC with remap and boost controller config can indeed give good results from 3000rpm upwards.

 

-Ian

 

 

Is that speaking from recent experience

 

 

I am loving mine now.

[Kranz]

A properly set up TTC with remap and boost controller config can indeed give good results from 3000rpm upwards.

 

-Ian

 

And with a decent set of hybrids & a dollop (technical term) of Nitrous??? Can we see boost at between 2000 and 2500 rpm???

[Ian C]

Glad to see your a believer at last Ian:)

 

Believe me I'll still rally against the crappy "swap two hoses and let god sort it out" TTC conversion We spent about 4 hours out on the road sorting out Smarty's and if you saw how much fuel I had to add in under 4000rpm when on mid to high boost, the idea of running TTC with no remapping would make your toes curl

 

You can further improve matter with some ignition advance, it's amazing what you can add in and still be safe if you use V-Power or some other 98+ fuel

 

-Ian

[Tricky-Ricky]

I quite agree, it needs to be done the proper way or not bother, i know what you mean about the timing, it must have a fair bit of retard due to the early positive boost as std.