How does the sequential system work?

[D1andonlyantman]

Hi everyone. Bought my supra a few months ago. So far so good. Still getting my head around the mechanical side of some bits, for example the sequential turbo system. Now I'm used to the classic manifold to turbo, then the gasses either go through the hotside turbine to make boost, or out of the wastegate, all controlled by the ebc. Job done. But on the supra the 1st turbo comes in, then the 2nd later on with the use of 2 actuators and what appear to be wastegates, although I'm told they're not as there is one main wastegate for the whole system? At a guess id say that at 4500 the valves open which allows boost pressure to go to the actuators which then somehow makes the 2nd turbo spool, but I've got no idea on the specifics tbh. Basically can anyone give me a brief overview on how it all works, because I like to understand all these things.

 

Thanks

[Sheefa]

http://mkiv.com/93-98-twin-turbo-faqs-2/#turbosystem1

 

Here we go mate

 

 

[Mike2JZ]

From low RPM you have 6 cylinders feeding exhaust gases to the first turbo up until the EGBV and IACV flaps open.

 

Once those valves open you have a situation where the first 3 cylinders are working the first turbo, and the second 3 cylinders work the second turbo.

 

The only other major component is the WG actuator on the first turbo which dictates the amount of boost allowed to either/both of the turbo's.

Edited June 8, 2018 by Mike2JZ (see edit history)

[D1andonlyantman]

Top info there. Cheers.

 

I've been looking at the TTC mod. I'm used to a single turbo, and am not really a fan of the way the 1st turbo starts to let off before the 2nd comes in. I know it's more laggy down low, but how often is that an issue really. Anyway, one of the methods ive seen says to just bypass a vsv so that the actuator has a direct feed to the manifold pressure and opens as the pressure builds, but another method says to wire open the EGCVs. My question is that wouldn't having the valves permanently open just make the lag even worse, and if you let the boost pressure open the valves as the pressure builds, turbo 1 would be running on its own for a bit longer, making the lag a little better?

[JasonR24]

I hate TTC. Honestly the low down power being non existent makes TTC useful only for diagnoses in my opinion. Many will disagree with me but when I was running it like that I hated it. If you’re getting a large gap of no power between first and second turbo the. You have a problem. If you use the sequential turbo system thread on here you will be able to diagnose it

[D1andonlyantman]

It's not a huge gap, probably 4000-4500 is pretty dead. Then it comes back with the 2nd turbo. It also sounds 10x better, it was so quiet before, now it has the rumble a 3L should. And all in all it just feels more familiar to me. By 3k things are getting going, 4k it's coming strong, 5k you're really flying. We're not talking a 5k spool up lol. It's not perfect but for me I think it's a more enjoyable drive. I'm BPU too which will obviously help, and manual is better for it too apparently

[Scooter]

http://www.mkivsupra.net/vbb/showthread.php?343594-sequential-issue-and-going-ttc-ideas-please&highlight=sequential

 

Loads of trouble shooting the transition here................link pipes collapse so doing these should improve even the TTC setup you have switched to.

[D1andonlyantman]

I'll be honest, the sound is a big selling point. It was way too quiet before. I drove past a mate a few nights ago and he said it sounded mental when I put my foot down. This car has everything to shout about! I'll have a read through the thread above when I get home from work. Cheers. Does anyone have an opinion on wiring open the T2 gas control valves? I'm thinking bypassing the vsv so the manifold pressure opens the valves is one thing, having it permanently open is going to share the exhaust gasses before T1 has even spooled which will only make everything laggier?

[Sheefa]

I hate TTC. Honestly the low down power being non existent makes TTC useful only for diagnoses in my opinion. Many will disagree with me but when I was running it like that I hated it. If you’re getting a large gap of no power between first and second turbo the. You have a problem. If you use the sequential turbo system thread on here you will be able to diagnose it

I could not agree more TTC is horrible.

 

 

[JasonR24]

I'll be honest, the sound is a big selling point. It was way too quiet before. I drove past a mate a few nights ago and he said it sounded mental when I put my foot down. This car has everything to shout about! I'll have a read through the thread above when I get home from work. Cheers. Does anyone have an opinion on wiring open the T2 gas control valves? I'm thinking bypassing the vsv so the manifold pressure opens the valves is one thing, having it permanently open is going to share the exhaust gasses before T1 has even spooled which will only make everything laggier?

 

By the time you’ve spooled up a BPU in sequential would have left you for dead. Proved that at santapod. Doing it just for the sound makes no sense and unless you’re running a full standalone ECU and supporting mods then it’s not worth it

Edited June 8, 2018 by JasonR24 (see edit history)

[Scooter]

I think 1 can be true in that the first turbo can wear earlier (whereas the 2nd tends to explode via overboosting) but then in a stock or modestly boosted modified car, with good oil servicing the turbo's last for a long long time, so it's not really noticeable?

 

2 I can see being true as you tend to trundle through traffic more off boost, but you are effectively just reducing the power/torque available (it's like saying a v8 that shuts down 4 cylinders is better.....well it is for fuel conservation/co2) it's going to be a small saving if anything.

 

3 TTC I think builds the turbos together more smoothly? errors in the sequential operation can hit the turbo's hard ie no prespool 'late hitting' 2nd turbo and vsv failure and overspeeding the 1st turbo etc. It can be quite savage but nothing compared to a single and they don't break stuff at modest power levels. The only issue I know of is the ECU is expecting a boost dip at the transition rev range and so some saying the fueling/timing isn't ideal there, with possible knock on effects

 

I don't think TTC has any mechanical/longevity downsides, but just drivability ones? Manuals you can largely shift around this if you drive it like an NA and keep the revs up in the 2nd turbo range, with auto's you can do that so easily. Novelty factor, noise and the sequential system not working correctly seem to be the reasons to use it.

Edited June 8, 2018 by Scooter (see edit history)

[Swampy442]

I know it's more laggy down low, but how often is that an issue really.

 

Well, every day, when you drive the car lol. Driven with TTC before and the car just fell stodgy, round town driving wasn't nice. The 1st turbo shouldn't run out of puff before the transition, you should feel constant power, then a nice healthy kick around 4k. In late cars, you get the low down punch of the VVTI and the torque of the 1st turbo, makes for a quick car

 

Its horses for courses but Im with everyone else, a sequential system operating well is a nice thing to have, why you'd want to lose that I don't know

[Samurai 20V]

Since we discussing the sequential system, does anyone know of an aftermarket ECU that comes with a base map for the logic of the VSV's already mapped?

[JasonR24]

Since we discussing the sequential system, does anyone know of an aftermarket ECU that comes with a base map for the logic of the VSV's already mapped?

 

I don’t think that exists. Spoken to a few people and they’ve all said it will run it in TTC. Although there must be if that Stu Hagen runs it sequential at 700hp

[Mike2JZ]

I have mapped a few TT's to run sequential using Link ECU. I can supply a file with the sequential logic if needed. You will need to do some wiring to get VSV's working on a P&P unit though

[Samurai 20V]

I have mapped a few TT's to run sequential using Link ECU. I can supply a file with the sequential logic if needed. You will need to do some wiring to get VSV's working on a P&P unit though

 

That would be great mate. I was considering the Kurofune to keep the stock ECU, but using the PNP will allow flexiblity to change to single without the stock ECU.

 

I'll PM you an email address.