Sequential System - a discussion

Will be selling (in about 3 weeks time) my std UK turbo's. The have covered a genuine 38,000 miles. For the first 27,000 miles they ran standard boost, after that the No.2 turbo ran 1.1 bar, so nothing excessive there.

What are they worth?, any offers?

std UK turbo's. The have covered a genuine 38,000 miles. For the first 27,000 miles they ran standard boost, after that the No.2 turbo ran 1.1 bar, so nothing excessive there.

Is that 38000 miles from new or have they been rebuilt? That's an incredibly low mileage for a 9+ year old car!

They must be worth a good few quid. Seems like 30 odd thousand mile J-spec turbos are going for around £250 nowdays but I would think these are probably worth 50% more than that.

[pedantic]

"No.2 turbo ran 1.1 bar"

I was under the impression that both turbos run equal boost once #2 comes online, no?

[/pedantic]

Anyway, good luck with the sale.

when will they be avalible mate?

HI Jake

Its 38,000 from new. I bought the car 2 years ago with 27,000 on it, had been owned by a local senior aged guy from new, I waited years to get this car, thought he would never sell, I got a tip off that his new SC430 was in, so a few days before he got it i went and bidded him for 2 hours! until he accepted my offer. I doubt the second turbo ever spun before i owned the car as it still had a shiny shaft when i checked it a few days after i got the car. A few people have mentioned £500ish. The 1.1 bar on the second turbo was via a blitz sbc ID, how i wish I could of had both turbo's at that.

Hope to take them off in 3 weeks time, soon as my upgrades arrive. Car is currently off the road, resting in my garage. Best offer by them will do.

Guys don't forget these are UK spec - they don't fit a J-spec without the associated manifold and down pipes. But Chief's car won the UK vs. Ireland Dyno battle recently so they are strong turbos.

Chief - the sequential system runs both turbo's at the same pressure once the 2nd one is upto speed....honest guv If they didn't you'd get an imbalance in the system and No.1 would be stalled by intake air being forced back into it if No.2 ran more boost.

The boost pressure is registered at the manifold...so it's the pressure created by both turbo's not just one.

Bad news alex, my car ran std boost on No.1 the whole time. You e mailed me a picture of a mod to raise the first turbo pressure which I never got around to doing. Even my dyno plots show the large increase in boost when No.2 come on.

I wish you were right on this one as it would have made life easier.

Alex is right Chief. You've misunderstood how the sequential system works.

It's no big deal and doesn't make your turbos any less desirable.

I understand the system, No.2 is the overall control of boost. However i would like to know how plumbing a boost device in the compressor housing/actuator of the No.2 turbo manages to increase the boost of the No.1?. I had a seperate boost gauge fitted and the Blitz sbc ID which also monitors and neither ever showed more than std boost on the No.1. I contacted Blitz (racelogic) they had no idea how to raise the boost on the No.1 either. Alex forgets he knew of this problem and e mailed me the answer, which was a bleed valve on a 'H' connection, which I admit I didnt ever get around to doing.

I have fitted two electronic boost controls and one manual system to the Supra and i have yet to have the first turbo increase boost. 10,000 miles of driving and it stayed the same, to my dissapointment. However you must have the answer to my prayers so I'd appreciate it if you would post the "plumbing" needed to get increased boost on both turbo's thats tried and tested as it has been a source of irritation to me, and no doubt a few other Supra owners. Please help us out. :-)

Hi Chief,

I'm no expert but as I understand it you can't much raise the boost that Turbo1 makes *when it's working on its own* because the engine revs just aren't high enough yet. (Less revs = less exhaust flow = less boost)

Once the revs have increased enough and the second turbo is fully online both turbos will be making the same boost because if one was trying to make more boost than the other the difference in pressure would leak across to the other one and equalise the pressure.

No?

HI Jake,

In theory you are totally right, in practise when i wind up boost only No.2 does it. I believe what my gauges told me. This may puzzle you, as it did me, but thats how i have found it. Have you managed to get your car to boost evenly on both turbo's by using the boost control device plumbed into No.2?, if you have I'd love to see the rolling road graph. Maybe you just know the way to plumb in the boost control to do this. Do share I'll need this info again very soon!. Please post it, you'll be helping a load of people. (Not least me!) :-)

Alex is right Chief. You've misunderstood how the sequential system works.

Thinking this over, I'd like to bet you two are way wrong on this, I spent a lot of time trying to raise the boost on No.1 and it didnt happen. After a careful study of the workshop manual, it was clear that one would have to interfere between the compressor housing and actuator of each turbo. Altering the boost on No.2 will not affect No.1 at all. Can be done if you have an AEM system. Something tells me you guys have not had the practical experience of wrestling with this for months on end.

Still waiting for the plumbing diagram.

these mourne men are hard to shake off!

maybe these will help?

I know how the system works, only too well, you cannot raise the boost on no1 by simply plumbing a bleed device on no.2. Thanks for the pictures, however I also have the Toyota manual for the engine. The diagram I am after is the one where these guys plumb in one boost controller on no.2 , of whatever make, and manage to control the boost level of both with it.

Question is still out to Alex and Jake, spit it out, how does the raising of the boost on No.2 have anything to do with raising thew boost on No.1. ??? Ask CW, he will agree with me. You two made the comment saying that your bleed system plumbed on to no.2 governs the entire system, well i say "horse shit!". I have a load of R.Road graphs of my car with no.2 only plumbed in and i can prove that the no.1 boost stay's the same because the power stays the same. Reading Toyota manual's and thinking you have it sussed is like reading about sex and never getting it. The practical experience of fitting various boost controllers, electronic and manual then rolling road testing is the evidence. Next week I shall stip my sequential system when fitting my new hybrids, build them up and still never find what these guys are talking about cause it just cant be done, unless of course you do it my way, two manual valves, not running no.1 anymore than 1bar of couse in case it stalls no.2 :-)

LOL, when the second turbo comes online at around 4000rpm, the sequential system then begins to run in parallel.

So, once both turbo's are 'on song' they work together from that point to produce maximum boost.

and to clarify further, you cant run the no.1 turbo at higher boost than the no.2, or else when they try to work together around 4000rpm the first one stalls the second, lol.

still waiting for the experts to let us know how their bleed device on No.2 alters the boost on no.1 ? lol, or maybe their confusion is that the no.2 governs the boost level, hence why you can run more on no.1.?, this may be true but your bleed device still wont raise boost on no.1 when its plumbed to no.2 lmao.

I'm not quite sure what you're getting at now. The other guys on here are simply trying to point out that one turbo doesn't produce less boost than the other when the second turbo kicks in.

The second turbo is what determines boost level as that is the only one with a built in wastegate. There is a modification that can be done to turbo no.1 to produce more boost, but from what I understand from others that have done it, there is no point exceeding 0.9-1.0 bar as it begins to mess up the sequential operation.

Matt, I stated that I had run the no.2 turbo @ 1.1 bar and had not interfered with the boost of no.1 at all. However, all i have got in response is that if i run one @ 1.1 bar I run both at 1.1bar. Not true. The no.2 might govern the overall boost, however there is no way the system can raise the boost on no.1 beyond 4000rpm. The extra boost to achieve the 1.1 bar was provided by the bleed device on the no.2 turbo. I totally agree that 1.0bar is a max on no.1 or things go wrong. As the turbos are seperate I fail to see a way that the no.1 can raise its boost without being interfered with regardless of what rpm its at. If it normally bleeds off boost above 0.8 bar up to 4,000rpm then what on earth could make it boost harder above that rpm? Its my understanding that the no.2 provides the extra boost with its boost controller fitted, but the question remains "how does the bleed device on the no.2 physically alter the boost of no.1 above 4,000rpm?" . I have studied the toyota ,manual on this and it seems clear that no.2 can produce whatever boost it likes without interfering with no.1. I am willing to be corrected by any factual evidence, but i see no grounds for it.

both turbos are online together after 4000rpm, the boost after 4000rpm is for both turbos, 1st turbo cant be running .8bar when the second one is online at 1.1bar as the airflow through both turbos is equal after 4000rpm. Thats why the sequential system is so good, small single turbo at low rpm and then two small turbos working together after 4000rpm.

Your turbos ran 1.1bar, you cant say your second turbo ran at 1.1bar as thats clearly not true. Both turbos together ran at 1.1bar with your first turbo running stock boost before transition. You could argue the toss that neither turbo on their own hit 1.1 bar as its the combined boost that counts but the simple answer is your turbos were run at 1.1bar.

JB

Yup, spot on Branners!

1st turbo cant be running .8bar when the second one is online at 1.1bar as the airflow through both turbos is equal after 4000rpm.

Here is the question - how does a turbo thats actuator opens to prevent more than o.8bar of boost know that the engine is now working above 4,000rpm and alter its operation to hold more boost and achieve 1.1 bar? Surely whatever its set at is what it will run boost wise. What mechanical or electronic device on the std car allows controlled dual boost levels on the no.1 turbo.? this question is the core of the debate.

You could argue the toss that neither turbo on their own hit 1.1 bar as its the combined boost that counts but the simple answer is your turbos were run at 1.1bar.

Now we are getting close on what i have been saying. In the continued absence of a reasonable explaination how boost became controlled dual stage, rather than single level, surely the operational mode of the second turbo which has the bleed device (fools the actuator) is doing all the work in raising the boost.

I think it is also important to consider that while both turbo's have the same housings, they have different part numbers. To quote Toyota's sales broucher

"The first accelerates response at low revs, the second joins it in the mid range and boosts power in an explosive surge to the 6,800rpm red line.

Perhaps we should consider the effects of different a/r ratios, if indeed thats what they have. Still looking for "evidence" of boost level management on the no.1 turbo.

Thank you for the reply's everyone, it surely is a great debate.

The way I understand it is that the 1st turbo spools up first and then opens an actuator to pre-spool the second turbo, (this is what I understand is how the no.1 is 'restricted' to 0.8 bar). This relieves the pressure that would otherwise be placed on the no.2 turbo by suddenly opening up 4000 rpm worth of exhaust gasses.

At 4000 rpm the VSV's electronically open, which then join the two turbo's in parallel operation. Both together are then controlled by no.2's wastegate to control total boost.

Yep, agree with Matt, that was my understanding too.

At 4000 rpm the VSV's electronically open, which then join the two turbo's in parallel operation.

This I agree with 100%. Looking at the turbo setup we have 4 actuators.

One on the exhaust, one on the air bypass valve, one on the second turbo, which Toyota refer to as the no.1, and one on the no1 turbo generally called the exhaust bypass valve. Despite the first turbo's actuator being called the exhaust bypass valve, if you look closely at the diagram earlier in the post, you will see its positioned on the exhaust side of the first turbo just where any normal actuator would be located. Given that the turbo's boost is controlled by more than just the vsv's, then we have to ask how can this turbo boost more than 0.8bar of thats what the actuator is set at?. Also to be considered is the fact that both turbo's blow in through a "y" becoming a single flow, and if one flow was weaker it wouldnt matter as everything is going the one way and the real overall boost level is actually the sum of both flows.

I would prefer if the system worked as so many believe, as thats a better system IMO, but as I cant measure the first turbo's boost under these conditions it makes it hard to prove. Another question must be asked. If the first turbo's boost was raised by a bleeder to 1.0bar, surely when the vsv's did their job @ 4000rpm the car would then produce more boost on the first turbo as the electronic system would be unaware of the cheating bleed valve. More than 1.0bar as we know causes problems, but yet some claim they have done this successfully, which kind of diminishes the "boost is altered by the vsv's on the first turbo" theory.

Its a complicated system we know, but maybe for too long we have believed they both blow the same pressure theory as I cant find any mechanical or electronic evidence to prove it, and disproving it is just as tricky.

This puts me in mind of the big bang theory, which scientists pushed on to us, until they sent up the Hubble, then they found out it was way off to their amazement. Even the most ardent evolutionist wouldnt now dare try and defend it. So if you dont agree with me on this one, keep your minds open, as i wouldnt still be writing here if i didnt think that we were close to having a better understanding of the sequential system. Why cant some wee Jap dude who designed it read this thread and tell us for sure what way it really is!.

This might help

Technical FAQ link