Quote from Honeywell Garrett turbos Inc. website. "The notion that two smaller turbos will build boost faster than one large turbo is not always accurate because even though the turbos are smaller, each one is only getting half of the exhaust flow." http://www.turbobygarrett.com/turbob...r/faqs.html#t2


See I keep hearing people in many car forums that are like twin turbo is better, becasue the spool is quicker I always argued if you have the space for one turbo do a sing turbo, I understand twins on a V style or something else like the subaru H style. But not an Inline. Were not talking sequential I mean Parallel turbos. But I see posts about people wanting to put like to t25s or something smaller on a 4banger . then when they net one togather people are like "wow that must spool Quick as hell." some people are total retards.

 

hold on, surely the inertia of two smaller turbines is less than one large one and so it would make sense to have two smaller ones?

efficiency is a steady-state thing so eventhough a single turbo setup might be more efficient, transient response is perhaps not quite as good as the twin?

I thought it's mostly to do with the amount of boost you want to run and the rpm range you want to operate (plus the engine size). Besides, if you had an in-line 6, it might get a bit difficult if to get the exhaust mani and the other plumbing right.

Not saying I'm right and they're wrong or anything, just saying that there are many, many factors and like everything else, there's more than one 'correct' answer. I mean, the 335 has two turbos and Bugattis have two per bank. I doubt their engineers are so retarded as to use a 'wrong' setup...

 

he wasn't talkin about cars that came twin turbo he is talkin about people who want to make there setup twin turbo. i am workin on engineering and completely agree with u about how if the engineers made sumthing the way they did there is a good reason for it.

 

true, but then why put a twin turbo in a supra when single big turbo supras go hella faster?

 

cause the original engineering of the supra probably met its goals with the setup they ended up using. don;t forget $$ is a big factor

 

Sorry for not making myself clear - the two examples were used mainly because there should be little doubt that they didn't get it right. The point I was trying to make is that perhaps there are times when the single is not the 'best' solution. Like if you want to add a turbo to a straight 6 engine or something.

On the whole, I'd imagine that making a single turbo car a (parallel) twin probably doesn't gain much advantage over a properly sized single, all things (such as plumbing) being equal. The inertias of the compressor wheels are pretty much comparable to the flow (i.e. two smaller turbos flowing half the lbs/min will have roughly 1/2 the inertia) so there's little to gain there on that alone.

Where things might get intersting is the heat rejection, perhaps. While the gas exchange in the 1/2 size turbo means it will have the same primary means of heating/cooling rate as a bigger one, it has more surface area through which to lose heat which might be a bit of a bonus. But then again, that's probably a 2nd or even 3rd order effect...

 

There is the cool factor in doing something that not everyone has done. I would agree that it is not always a performance advantage of twins over a larger single and that has been shown in several articles over the years in Turbo Mag and others. I think the results were that it is a wash if sized properly. I think a twinturbo setup on an EVO would be cool and perhaps even perform well. Examples of a few setups I have fabricated.

The first TwinTurbo setup on my 240Z using 2x 16G(7cm)



Got bored so I made something different



TwinTurbo setup I made for a buddy



Finally, single turbo RB25 setup that went 10.5@131 on 93 octane(no meth)

 

nice work on those twin setups!

 

240z tt Hey man nice set up on the z. I have an 83 280zxt with the le28, which I'm keeping. A friend has a 78 280z that we are going to put in a rb25 in when he gets back from the dessert. How difficult was the swap? I've been searching the z boards it looks fairly straight forward swap, any advice you can give before we start like any major problems, unexpected cost you had?

 

I believe some cars come from factory with a twin turbo setup , like the Supra or BMW 335, for the sole reason of space. One turbo sticks further out than two smaller turbos. Also the visual and psychological impact of twin turbos may well play a large factor in the selling ability of the car. The general mentality is more is better over bigger is better. As for the inertia Idea, You have to rember on a 6 cylinder engine with a Twin turbo setup only 3 cylinders are powering a single turbo. So it would be like running a small turbo on a 1.5L 3 cylinder engine. But there is more friction on the turbine shafts because there are two sets of bearing in play here. On a single turbo setup you on;y have to support one turbine shaft with only one set of bearings. So the inertia would be about the same from a single turbo or twin turbos, But a single turbo Setup will have less friction acting on the turbine shaft than Two Separate Turbos. Also the Supra wasn't a TRUE twin turbo setup. The turbos wer conjoined and shared the same turbine shaft, to eliminate the possibility that one turbo may spin faster than the other. So it was more like One turbo with Two compressor wheels and Two Turbine housings and Two Compressor housings and Two Turbuines, but one turbine shaft.

 

Both set ups have different charecteristics in power delivery. Saying one or the other is "better" without defining the particular application is purley your subjective opinion. Plus, who cares.

 

Apexi had an Integra Drag car a long time ago and it was twin turbo 1.8 B18C engine. It was pretty fast.

 

IDK Ok Better or not. Maybe I should rephrase. I mean Twin turbo shouldn't give you an advatage over single turbo.

 

Parallel twin turbos do have an advantage over a single. Just because they have half the flow, doesn't mean they have half the inertia. The combined inertia of twins is less than that of an equivalent single. However, the difference in lag between the two setups isn't all that great. Also, bigger turbos tend to be more efficient as they operate with slower speeds and usually the trade off between slightly less lag and little bit more efficiency tends to favor toward the single.

The only time it really becomes worth it for parallel twins is in a flat or a V engine, where all the extra plumbing to route to a single turbo starts to really impact the response of the engine. Twins tend to shine in this engine configuration.

 

this is directed at the op but i want to quote x for emphaiss. there's a balance to be achieved. the idea is that with two turbos you can potentially reach a faster spooling setup than an EQUIVALENT flowing single turbo.

other factors come in like system weight, complexity of installation and just how much the real benefit is and IF there's antoher way around it all.

two turbos blowing 40 lbs per minute is prolly two tiny turbos which is going to spool faster than a gt47 moving 80 lbs per minute (this is a **** example but you know where i'm going with this). that said... it's true an inline 4 prolly sucks *** at moving any number of turboes... even 1. that's why you only see tt systems on inline 6 motors.