Twin or single turbo

[John_M]

OK. So I know that the big power Supra's tend to be single turbo but at what stage is single better than twin?
i.e. Up to what power can you take a sequential twin turbo set up?

[Chris Wilson]

IMO you might squeeze an iffily reliable 400 BHP from the sequential set up. I am somewhat unusual in having the opinion that many "hybrids" based on the stock sequential turbos are a lot of hype, as I think the exhaust (turbine) housings are too small to support a much better flowing compressor side. As the turbine housings are totally bespoke and unique to the TT Supra, with virtually no meat to enlarge, the only possibility is cut back turbine blades to aid high exhaust gas flow, at the expnse of efficiency. You can't get bigger housings per se. Next stage is parallel twin turbos or a single. Again, I am fairly unusual in saying that such conversions as I have seen in the UK rarely work to their proper potential as so few people accept the mapping and hardware costs to get these things working properly. I believe mapping on the rolling road or road itself to be ridiculous, initial safe mapping MUST be done on an engine dyno. Many will diasgree, and it's their perogative

I also believe that if people were totally honest a lot of twin, none sequential, turbo owners would say they were disappointed with their engines real life, every day performance. For sure, big BHP figures can and are produced, but the loss of that low RPM torque and power is devastating in real life driving conditions. For a track day, manual car, you may like the power delivery of big twin none sequentials, but to ME, i would miss that lovely sub 3000 RPM torque the stock set up provides. If anyone is lucky enough to have a pal like mine with an SL55 AMG Mercedes they will let you loose in you can see what the next generation of low end torque monsters can provide. They make a stock Supra TT's low end grunt look like an F1 engines power delivery curve. And, whether you like, know or believe this, it's what 99% of road driving in a heavy car needs, a mass of low end torque.

All IMO. But of course, I am right

[alex h]

Whilst I can see where chris is coming from I'd say that at least on a manual you don't miss anything by going Single, because it's easy to drop a cog and drop into the rev range where the turbo is on-song. A T-57 can be at full boost way in advance of the stock TT system and while it's building boost it's building torque, and it will out power the sequential system at the topend...it's all about sizing the turbo to your application and needs. If you want low down response you have to sacrifice ultimate power, on a 3L turbo engine anyway...if you want ulitmate power the slider shifts the otherway.

I don't think it's really fair to compare a supercharged V8 5.5 with a 3L I6 TT now is it Chris!

[wez]

Go for a smallish single setup and its very streetable, i am just starting to get the real potential from mine now as I have now mapped upto 1bar boost and if i am cruising and boot it there appears to be almost no lag at all, plus its much more predictable than the sequential system.

I should have my 3.5bar map sensor sometime this week and I am hoping Chris W will install my new suspension and injectors very soon as well.

[chiefgroover]

Chris, I live in hope of a big sequential system. If the system is electronically governed on the first turbo to run a max of 1 bar (as some poeple claim), surely a mod to the ECU can overcome this?. A kit with new altered VSV's etc and a pair of bigger turbos must be possible? Just because Japan does not offer such a kit doesnt mean Europe cant be first!. Maybe we need an electronics designer to work with a turbo designer to get this?, well thats my thoughts anyway, meantime I'll just keep dreaming. and if you can do it, I'll be your first customer.

[chiefgroover]

Originally Posted by [b

Quote[/b] ]And, whether you like, know or believe this, it's what 99% of road driving in a heavy car needs, a mass of low end torque.

All IMO. But of course, I am right

Now go and make the system !

[wez]

You could always use an AEM and then there is no restrictions apart from physical flow, you also have complete control over when then different VSV`s open.

[chiefgroover]

Wez, can your aem be set for say 1.1 bar on BOTH turbos? and can it map to suit the changes. Do you have a dyno graph of your car.
I wonder if I had an AEM, plus a pair of big turbos could have the very powerful sequential system i crave?.

[alex h]

Making a larger sequential system would be nice but completely prohibitively costly! + once you start using bigger turbo's to get more power overall you're just going to knacker the lowdown response in the same way as fitting a single.

[chiefgroover]

Alex, ever been in a 2.6 audi turbo car? they pull from very low down with a fairly big turbo. STT system aimed at about 600bhp max would be my idea.
Using big twins for sequential I would expect to be laggy, but custom designed turbos with different A/R ratios maybe could be the answer. Why do two turbos have to be the same?.
The general mindset is "NO" to uprated STT systems, but i'm not convinced, it could be more of a defeatest attitude than unrealistic development?