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What are the cons and pro's with twin turbo systems?

Every now and then, on this forum or other forums, someone willl bring up the discussion but I never get any pro's and con's. All I hear is, "the cons of a twin turbo setup out wieghs the pros".

I know there has to be more pro's and cons then, "twin turbo setups dont give enough bang for the buck as far as power goes"
Also, some of these topics are about V8s
Very few are actually about our 2.5L
I heard that engine displacement has a big thing to do with twin turbo setups?

I'm just wondering but wouldnt one of the pro's be that you can use one small turbo for faster spooling in the lower RPMs and a big turbo for the higher RPMs? Wouldnt this get rid of turbo lag and add more torque and horsepower through the whole pwerband then a single turbo setup?

deleted cuz its apparently a pos post

Not only does a twin turbo cost more to setup, it can also lead for more parts to fail.

And instead of running two smaller turbos you can run one huge turbo, and make more power with better spool up times.

twins will spool up faster than a HUGE single. Not taking sides...just stating facts. unless the each turob in the twin set up mwas really huge...

Honestly, I would look into getting the Stock Twins from a 3rd gen RX7. Do that with Water Injection, with short IC piping and you would be set!!!

BTW: RX7 13B's are suppose to put out as much Exhaust as a 2.6L V6 would so I would think that the 2.5L would be a PERFECT setup.

fieromx3 wrote:well for a smaller engine like our 2.5 u dont need twin turbo unless ur boostin like really high(30+psi). if ur boostin low there isnt a need for it single turbo with a v6 on low boost the turbo will spool up fast enough if u have chose the right size turbo. if u r boostin really high twin turbo can help alot by getting smaller turbos to spool up faster to get that high boost and also havin twin turbo with high boost will help get all of that air out of the engine quicker and more efficiently. if u have single large turbo with high boost it can easily get all of the air out but u will have alot of lag.

pretty much u onlt would want twin turbo if ur boostin high and want the turbo to spool quicker but you can still have it with low boost.

twin turbo just weighs more costs ALOT more but if set-up properly u can benefit from it. i hope i got this all right if not then flame me all u want.

This is somewhat garbage and confusing. You always seem to emphasize the word "boost". Low boost, lots of boost is a term that you use loosly to make your judgement based upon. I've been reading alot of your posts on F/I. My recommendation to you is to to buy a book. Namely "Maximum Boost" by Corky Bell. Sorry, but you've forced me say something here.

Well, if it is a 2.5 v-6, then space will be an issue. Back on track - several reasons exist for giving false consideration to using two turbos where one might otherwise do the job. Probably the most popular notion of the advantage of two turbos is reduced lag. This notion is generally hard to justify. Half the exhaust energy put through each of two turbines, with inertia proportional to the square and flow proportional to the cube, is not necessarily conducive to producing less lag. Multiple turbos imply more power. Power is, in part, a function of efficiencies. All other things equal, a big turbo is more efficient than a small one. Pizzazz is a reasonable consideration when turbocharging a Ferrari, but the same logic cannot be applied to a turbo installation on a pickup truck. Good reasons do exist for using two turbos. This is particularly true with respect to V-style or horizontally opposed cylinder layouts. Exhaust manifold design is one of the keys to high power output, and the two-turbo lay-out inherently offers superior manifold design. The heat loss of the cross tube in V-style engines can be considerable. Remember, it is in part this heat that powers the turbine.

A two part design will usually require two wastegates. Other than the minor problem of synchronizing the two gates, much greater control of turbine speed at low boost pressures can be achieved. The stability of boost pressure at high flow rates is also improved. If remote wastegates are used rather than integrals, the actual exhaust gas flow area can be enlarged by giving the gates their own tailpipes. Greater turbine discharge area is always an improvement to the system. Turbine discharge pipes from two turbos will virtually always give a large flow increase. For example, two 2 1/4 inch diameter tubes offer substantially more flow area than just one of 3 inches. A further reason two turbos offer superiority under certain conditions is that the heat is divided btwn two mechanisms, allowing each to operate with lower heat input. The heat absorbed into the materials of the turbo is proportional to the temperature of the gases and their mass rate of flow. The temperature will remain the same, but the mass rate of flow will be halved. Thus the operating temp. of the turbo will be reduced, and it's life expectancy somewhat improved. -

jaydog5678 wrote: Turbine discharge pipes from two turbos will virtually always give a large flow increase. For example, two 2 1/4 inch diameter tubes offer substantially more flow area than just one of 3 inches.

Hmm, that isn't nessicarily true. I do HVAC for a living and know for a fact that most of the time two smaller pipes do not even equal the flow of the larger pipe. Like 1 8" can supply 2 6" and yet the 8 " still has backpressure because the two 6" don't flow as well. I don't have my fancy flow chart with me but honestly, I wouldn't say that without doing the flow calculations.

BuGS wrote:Honestly, I would look into getting the Stock Twins from a 3rd gen RX7. Do that with Water Injection, with short IC piping and you would be set!!!

BTW: RX7 13B's are suppose to put out as much Exhaust as a 2.6L V6 would so I would think that the 2.5L would be a PERFECT setup.

3rd gen RX-7 twins aren't usable on any car other than rotary, they're goofy OEM application specific housings. Google it, you'll see what I mean. Forget the idea of using twins from an RX-7 or Supra. Trust me.

The long story short is that it's enough of a PITA to do a single install on this platform, trying to do a twin install in a small engine bay is just a recipe for frustration. Even a "big" turbo on a 2.5L motor is going to be small enough that spooling shouldn't a big problem, thus nullifying the arguement that twins would be "better".

Sometimes there is a good reason why there is a path not travelled...

Few benefits + massive PITA + costs doubling = the reason why there are no twin turbo MX-3s out there.

BuGS wrote: Hmm, that isn't nessicarily true. I do HVAC for a living and know for a fact that most of the time two smaller pipes do not even equal the flow of the larger pipe. Like 1 8" can supply 2 6" and yet the 8 " still has backpressure because the two 6" don't flow as well. I don't have my fancy flow chart with me but honestly, I wouldn't say that without doing the flow calculations.

That is true in a twin setup. We're not talking HVAC. Exhaust flows in pulses, not in a steady stream like an HVAC unit will put out.

eh im not gonna buy that book i dont care if im wrong or not i know it just not completely but i probly didnt word it right for at least u guys to read i guess and i dont have many posts where i said crap in f/i but i do realize i sometimes do make the most retarded posts on here but im not smart really either so yea.....o well i said u could flame all u wanted so i should have expected that

jaydog5678 wrote:

BuGS wrote: Hmm, that isn't nessicarily true. I do HVAC for a living and know for a fact that most of the time two smaller pipes do not even equal the flow of the larger pipe. Like 1 8" can supply 2 6" and yet the 8 " still has backpressure because the two 6" don't flow as well. I don't have my fancy flow chart with me but honestly, I wouldn't say that without doing the flow calculations.

That is true in a twin setup. We're not talking HVAC. Exhaust flows in pulses, not in a steady stream like an HVAC unit will put out.

But Air is Air, The Flow dynamic priciple should work the same. And I thought you were talking about the Intake side. The Spin up and boosting on the cold side is somewhat constant, it does not pulse as much.


And For the Guy who said you can't use Twin turbo's off of a 3rd gen, I wish you lived here. There is a guy running a 2.6L V6 Bronco 2 with RX7 Twins. Just because they are OEM specific housing doesn't mean you can't use them. He works at an exhaust shop and made a custom manifold. And like I said before, the 13b's put out as much exhaust as a 2.6L V6 would. So although is it specific for the rotary, it doesn't mean it can't be used elsewhere...

fieromx3 wrote:eh im not gonna buy that book i dont care if im wrong or not i know it just not completely but i probly didnt word it right for at least u guys to read i

Stop spreading confusion...It's damaging to someone that wants to learn. This is after all, a sight that we can all learn from eachother. I'm not flaming anyone but if you don't fully understand what is really happening with a twin turbo setup, please for our sake, don't bother to post.

Bugs wrote:But Air is Air, The Flow dynamic priciple should work the same. And I thought you were talking about the Intake side. The Spin up and boosting on the cold side is somewhat constant, it does not pulse as much.

Turbine = hot side
Compressor = cold side
The Compressor side dosn't pulse and if it did we'd be in big trouble.

jaydog5678 wrote:

fieromx3 wrote:eh im not gonna buy that book i dont care if im wrong or not i know it just not completely but i probly didnt word it right for at least u guys to read i

Stop spreading confusion...It's damaging to someone that wants to learn. This is after all, a sight that we can all learn from eachother. I'm not flaming anyone but if you don't fully understand what is really happening with a twin turbo setup, please for our sake, don't bother to post.

Bugs wrote:But Air is Air, The Flow dynamic priciple should work the same. And I thought you were talking about the Intake side. The Spin up and boosting on the cold side is somewhat constant, it does not pulse as much.

Turbine = hot side
Compressor = cold side
The Compressor side dosn't pulse and if it did we'd be in big trouble.

Ya then why were you talking about exhaust gases??? Oh well, But to get back on Topic, Twin turbo setups are twice expensive (2 turbos, usually turbos are the major cost) and Honestly I like to do most the work myself and if you can't weld up custom manifolds and stuff I would just stick to Getting the V6 groupbuy stuff and going with a nice Single turbo setups. But I am wondering how the V6 would do with one of those new Twin-scroll turbo's on the new Legacy's in Austraila, Titanium shaft, and an awesome twin exhaust chamber thing for awesome spool up...

jaydog5678 wrote:

fieromx3 wrote:well for a smaller engine like our 2.5 u dont need twin turbo unless ur boostin like really high(30+psi). if ur boostin low there isnt a need for it single turbo with a v6 on low boost the turbo will spool up fast enough if u have chose the right size turbo. if u r boostin really high twin turbo can help alot by getting smaller turbos to spool up faster to get that high boost and also havin twin turbo with high boost will help get all of that air out of the engine quicker and more efficiently. if u have single large turbo with high boost it can easily get all of the air out but u will have alot of lag.

pretty much u onlt would want twin turbo if ur boostin high and want the turbo to spool quicker but you can still have it with low boost.

twin turbo just weighs more costs ALOT more but if set-up properly u can benefit from it. i hope i got this all right if not then flame me all u want.

This is somewhat garbage and confusing. You always seem to emphasize the word "boost". Low boost, lots of boost is a term that you use loosly to make your judgement based upon. I've been reading alot of your posts on F/I. My recommendation to you is to to buy a book. Namely "Maximum Boost" by Corky Bell. Sorry, but you've forced me say something here.

Well, if it is a 2.5 v-6, then space will be an issue. Back on track - several reasons exist for giving false consideration to using two turbos where one might otherwise do the job. Probably the most popular notion of the advantage of two turbos is reduced lag. This notion is generally hard to justify. Half the exhaust energy put through each of two turbines, with inertia proportional to the square and flow proportional to the cube, is not necessarily conducive to producing less lag. Multiple turbos imply more power. Power is, in part, a function of efficiencies. All other things equal, a big turbo is more efficient than a small one. Pizzazz is a reasonable consideration when turbocharging a Ferrari, but the same logic cannot be applied to a turbo installation on a pickup truck. Good reasons do exist for using two turbos. This is particularly true with respect to V-style or horizontally opposed cylinder layouts. Exhaust manifold design is one of the keys to high power output, and the two-turbo lay-out inherently offers superior manifold design. The heat loss of the cross tube in V-style engines can be considerable. Remember, it is in part this heat that powers the turbine.

A two part design will usually require two wastegates. Other than the minor problem of synchronizing the two gates, much greater control of turbine speed at low boost pressures can be achieved. The stability of boost pressure at high flow rates is also improved. If remote wastegates are used rather than integrals, the actual exhaust gas flow area can be enlarged by giving the gates their own tailpipes. Greater turbine discharge area is always an improvement to the system. Turbine discharge pipes from two turbos will virtually always give a large flow increase. For example, two 2 1/4 inch diameter tubes offer substantially more flow area than just one of 3 inches. A further reason two turbos offer superiority under certain conditions is that the heat is divided btwn two mechanisms, allowing each to operate with lower heat input. The heat absorbed into the materials of the turbo is proportional to the temperature of the gases and their mass rate of flow. The temperature will remain the same, but the mass rate of flow will be halved. Thus the operating temp. of the turbo will be reduced, and it's life expectancy somewhat improved. -

UH OH... Im calling corky and telling him youre plagiarizing his materal.

Franko wrote:
UH OH... Im calling corky and telling him youre plagiarizing his materal.

Who else besides Corky that can explain it any better. At least someone else has been reading his book.