Twin turbo manifolds??

[suprabad]

Twin turbo's (set-up properly) can make for a very tractable, very fun car to drive, due to minimal lag.

IMHO it's a lot more suited to daily driving than a big single turbo. Big turbo equals big lag.

If you're exclusively drag racing and just droping the hammer at 5k, or have an auto with a 4k stall and a trans brake...yeah no doubt, big single turbo is the way to go.

I remember the first twin turbo I ever drove ( a 90's 300 ZX) and I was shocked at the almost absence of turbo lag. By the way... that was a fun car to drive, right off the showroom floor. (Flame me if you want. but I have fond memories of that car.)

Twin turbo's are not retarded.

I just wanted to give the twins their props.:icon_bigg:icon_bigg

 

[OneJoeZee]

Twin turbo's (set-up properly) can make for a very tractable, very fun car to drive, due to minimal lag.

IMHO it's a lot more suited to daily driving than a big single turbo. Big turbo equals big lag.

If you're exclusively drag racing and just droping the hammer at 5k, or have an auto with a 4k stall and a trans brake...yeah no doubt, big single turbo is the way to go.

Care to explain the physics about these statements?

 

[Freshmaker]

Care to explain the physics about these statements?

It requires more of a thermodynamic type response imo

 

[OneJoeZee]

I already know the answer, I just want to know if he knows.

There's more to it than that. I would ask you to elaborate as well.

 

[Silent Deatz]

Ok, any other manifolds except the one from 935?

 

[Freshmaker]

I already know the answer, I just want to know if he knows.

There's more to it than that. I would ask you to elaborate as well.

Me? To over simplify the question: The power going into the turbo(s) is based on the temperature and pressure difference from one side of the turbo to the other. On paper, it doesn't matter if the difference in enthalpy is made by 1,2 or 10 turbos.

In practice, some situations can benefit by having multiple turbos to reduce pulse cancellations, runner restriction, runner length or who knows what else is sucking the power out of your exhaust. Holset had an interesting answer to the single/multiple problem by using a divided exhaust housing for years.

 

[OneJoeZee]

For those that are interested, refer to the following two posts instead of me paraphrasing.

All right guys, we need to separate lag/spool from power band.

Lag/spool is basically the time from going WOT to achieving target boost. This assumes you are already in the power band (IE stabbing the throttle at 2krpm and waiting 20minutes to get to 6krpm with a GT55 does not count). This would be like going full throttle at 5krpm with a GT40 and waiting a second to reach 20+psi.

Power band is an entirely different subject. This to me is the engine speed range which provides sufficient turbine power to achieve your target boost. So, a GT40 may have a power band from 4-7krpm and a GT47 may be from 6-9krpm (engine speed).

The reason I make this distinction is a single turbo rocks in one aspect and twins in the other. All things being equal (which obviously is never the case, but stay with me) a single turbo will always be more efficient than two. Now, that isn't to say that every large turbo is better than every small turbo, but if you had two that were designed and manufactured using the same practice the larger turbo would show superior efficiency.

That being said, the more efficient a turbocharger is and the larger the powerband. So, a single turbo capable of flowing 800hp will have a larger powerband than two turbos capable of flowing 400hp each. The more efficient single turbo will also require a lower expansion ratio which results in a better engine delta P and (finally) and greater engine VE (more power).

Now, when we talk about spool it's the opposite. The larger single turbo has significantly more inertia and will take more time to reach the target boost. How much more I can't say, but it's simple physics. I don't think this requires much explanation so long as everyone understands my definition of spool/lag.

If we take this a step further and look at just an inline 6 (like our beloved 2jz) it all becomes clear. Fundamentally, a turbine is most efficient under steady state (no engine pulses). The best we can do is to have as many pulses as possible to limit that time gap between them. Further, it is beneficial to have a twin scroll (divided turbine housing) as this eliminates the possibility of cylinder to cylinder scavenging and helps to get as much of the exhaust energy from the head to the turbo. An inline 6 is the perfect platform for just this. With a standard 4-stroke engine the most number of cylinders you can have feeding a single collector (with no chance of cylinder to cylinder scavenging) is 3. If you have 4 there can be times when two exhaust valves will be open at the same time. A divided 6 cylinder is perfect for this.

So, in short, if you want the most power go single. If you want the largest power band, go single. If you want the best response at corner exit on a road course, go twin.

Daniel

And

No worries socalguy, I was not talking about you. Doing a straight comparison between a single vs. twin is going to be VERY difficult because of the number of factors involved.

When comparing ultimate power it's really determined by two things (if we assume the same 2JZ engine at a given speed): 1) Boost & 2) VE.

If we assume, as we should, that you are operating at a fixed boost level, then VE is all we care about. Since we are talking about a given engine, we don't need to worry about head design, cams, intercooler, etc. It comes down to engine delta P. A single GT4088R can flow ~70lb/min. A single GT28RS can flow ~35lb/min. So, using two of them should provide the same potential. Meaning, the compressor(s) can provide the same maximum amount of flow.

So, everything else being equal, both setups would make the same power. This brings us back to the VE stuff I was talking about. The twins will require more energy because they are less efficient. This will raise the backpressure on the engine and hurt VE. So, you wont make as much power and you will make it later.

Below is a ROUGH match I did. You can see that the twins spool later because of the lower efficiency. I assumed the same VE for both cases (and BSFC) so that is why the power number are line for line in the upper rpm. The max boost line on the twins is lower because the compressor map I was using didn't go to the higher pressure ratios so I kept the boost down. As I said, this is rough. I don't think you'll find a GT4088R that spools that quickly in reality which probably means some of my VE assumptions were a little....optimistic.

Daniel

But to stay more on topic, I think Drewgo may make some twin manifolds. Or maybe you can convince BIC to make you a set of his manifolds. Other than that, there's a few premade kits but they are rare and fairly hard to come by. Blitz, Greddy, and HKS all made twin turbo kits for the 1J.

 

[Freshmaker]

I guess im feeling like the devil's advocate...

SupraWood made a good comparison of two specific turbo cases. It would be far fetched to make that generalization for every single/twin discussion though. He picked small turbos that were out of their own efficiency range (said so himself) vs a bigger turbo in its efficiency range.

 

[OneJoeZee]

Lower efficiency, which is just the nature of the beast with two vs one. Never mentioned anything about being out of their efficiency range.

 

[Freshmaker]

Your second quote, half way in he says the twins are less efficient.

Either he is saying the turbos themselves are less efficient, or they are less efficient because there is 2.

 

[OneJoeZee]

Your second quote, half way in he says the twins are less efficient.

Either he is saying the turbos themselves are less efficient, or they are less efficient because there is 2.

Less efficient because there are two.

Twins just tend to spool later. I've experienced this with my own setup. The power is more linear than a single but full boost comes later.

 

[Rich]

+1 on the quotes from Daniel, it's all about efficiency and you can't change physics- and thermodynamic laws. There is also the bearing resistance which in a twin set-up is double, athough this will play a minor role.

People tend to think about stock twins and their quick response when talking about twin set-ups and big laggy single turbos when talking about single set-ups and then compare and say twins are better. However, both are in a completely different ball park. Compare both options at the same power level and a single for our straight six engines will always be more efficient.

Rule of thumb; one turbo per cylinder row will be most efficient, so for a v8 you will want a twin set-up to have the turbo's as close to the heads as possible.

 

[Freshmaker]

Ignoring manifold design for argument sake, two turbos aren't inherently more or less efficient than one turbo.

+1 on the quotes from Daniel, it's all about efficiency and you can't change physics- and thermodynamic laws. There is also the bearing resistance which in a twin set-up is double, athough this will play a minor role.

Physics and thermodynamic laws, now your talking my language. Can you point me to the particular ones your referencing?

 

[foreverpsycotic]

I want that new fangled sequential t57 setup from the boys at Sound Performance. Too bad it goes for right around $10,000. They can also strap two t67s on the same manifolds.

 

[Rich]

Ignoring manifold design for argument sake, two turbos aren't inherently more or less efficient than one turbo.




Physics and thermodynamic laws, now your talking my language. Can you point me to the particular ones your referencing?

Try to pick up a copy of this book: 'Sport Compact Turbo's & Blowers' by Joe Pettitt ISBN 1-884089-88-7

here's a link:
http://www.allbookstores.com/book/9781884089886/Joe_Pettitt/Sport_Compact_Turbos_and_Blowers.html

He can explain it a lot better than me
There's a LOT of theory in there and also a lot of practical examples, including a 2jz.

 

[Rich]

Ignoring manifold design for argument sake, two turbos aren't inherently more or less efficient than one turbo.

When you're aiming for the same powergoal, yes, a single IS more efficient. Read the book and you'll agree with me and others on this board who understand this concept.
Not trying to put you down or something, it's just a matter of understanding it

 

[RacerXJ220]

Aftermarket twin kits for any of the JZ engines is bling. It's so much easier to just go single. If you want to pay double or more for a kit, go for it. It isn't really going to matter whether or not you're going single or twin unless you really care about whatever efficiency theory you're reading up on.

Personal preference be what it is, if you can find a good twin kit, and if it's what you want, then get it. If it's an older kit, then improve on it.

K-26's can be replaced by twin GT2871R's

 

[Freshmaker]

When you're aiming for the same powergoal, yes, a single IS more efficient. Read the book and you'll agree with me and others on this board who understand this concept.
Not trying to put you down or something, it's just a matter of understanding it

It wasn't a put down at all. A technical dispute is hardly a place to get upset. But, it's to bad no one feels confident enough in the material to present it themselves. I will see if I can get a hold of that book so i can know where you and the others on this board are coming from.

Edit: otherS

 

[Rich]

Glad to hear you're one of the people here that can discuss normally and don't go yelling if someone doesn't agree with them. I must admit I added the last sentence afterwards because I so hate the mindless yelling and calling names, so to avoid that I added that last sentence.

But to get back to your comment, understanding a concept is one thing, getting it across to somebody is something else. I'm not a teacher, but I do try to explain stuff I know. This however is a bit too complex, it would take me too much time to write it all down and even then I risk missing out on things and we'll end up in a whole different discussion.

I do advise people to pick up some good technical books to gain a good solid knowledge when you start tuning engines, the web is full of good info, but in my opinion it doesn't beat a good written technical book you read back to back.

 

[suprabad]

Twin turbo's (set-up properly) can make for a very tractable, very fun car to drive, due to minimal lag

IMHO it's a lot more suited to daily driving than a big single turbo. Big turbo equals big lag. .

If you're exclusively drag racing and just dropping the hammer at 5k, or have an auto with a 4k stall and a trans brake...yeah no doubt, big single turbo is the way to go.

Care to explain the physics about these statements?

I see that some of the basic physics have already been covered, so I’ll resist the urge to demonstrate how smart I am at the price of redundancy.

But I will say this:

My post refers to my observations based on practical experience, and is the product of owning and/or driving a plethora of vehicles over the course of many years. It is an opinion (accurate I believe) but inherently subjective, as are all opinions by way of definition.

I felt obliged to share this opinion because the notion that “twin turbos are retarded” or employing two turbos is “throwing money away” is factually inaccurate, and shouldn’t be viewed by the uninformed or the impressionable as fact.

In fact, you yourself stated:

Twins aren't really worth it unless you have some good reason to do so.

Your opinion as stated above clearly implies that there exists “good reasons” under some circumstances to use a twin turbo set-up. If twins were “retarded” or “a waste of money” how could there be “some good reason to do so”?.

And in fact there is a good reason to do so, and I’ll get to that reason in a second, but first:

I already know the answer, I just want to know if he knows..

While I am not, nor do I claim to be Dr. Science, and I admittedly do not hold a P.H.D in thermodynamics or mechanical engineering, I am of reasonable intelligence and considerable experience. And yes, I do understand the basic mechanics, physics and thermodynamic laws as they apply to the internal combustion engine and the turbocharger…including enthalpy.

Twins just tend to spool later. I've experienced this with my own setup. The power is more linear than a single but full boost comes later.

This statement is just flat wrong . The reason is:

Because although one turbocharger is more efficient than two turbochargers, a smaller turbo takes less energy to spool than a larger one of same design.. (Stay with me here for a second and I’ll get to the point.). And yes, one turbo per cylinder bank is optimum (with regard to the tendency for two turbos to cause scavenging of exhaust gasses between the two exhaust valves that would be simultaneously open, thereby causing them to have both uneven enthalpy and virtually unpredictable pulse pressures at the turbochrger’s inlet.

This uneven pressure in constant variation (pulses) would affect both of the turbochargers speed and make it near impossible to get even levels of boost out of them (again, we’re talking about one bank of cylinders).

But this is only applicable when two turbochargers are run in parallel.

The car I used as an example (300ZX) is a sequential twin turbo, as are most twin turbos used on an inline engine. You neglected to address the physics of one turbo vs. two turbos in any context other than parallel. The smaller turbos used on sequential forced intake systems are smaller and therefore more efficient when viewed individually.

This is significant because:

Since they are spooled up individually with the second turbo effectively off-line until the first is spooled up and boosting, and then using that pressure to spool up the second turbo, you have more than made up for any efficiency deficit that would cause the two turbos to “lag” more than a big single turbo.

If fact the whole reason for two turbos on a single bank of cylinders when used sequentially, is to attain greater boost levels at significantly lower rpm. And this it does quite effectively, resulting in an engine that has boost (i.e. power) at much lower rpm’s (the assertion that a single turbo would have a wider useable power band is absurd), with the trade-off being a small loss of top-end boost (this is where the efficiency of a single is an advantage).

All supramania dogma notwithstanding, only those who put high rpm (top end) power above all else would benefit by running one big turbo over two smaller sequential turbo’s.


:icon_bigg