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Old 03-06-2006, 11:09 PM   #1
josh...just josh
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Default pipe dreams of a parallel twin turbo subie

i was reading some thoughts awhile back on why the ole' boxer engine is an inferior design than than the inline 4 and one of the things that kept popping up was the issue of long pre-turbo piping and the intake manifold having to fead down long runners.

this got me thinking, twin turbos! not the staged, overcomplicated, vaccum tube riddled mess that was so popular in the early 90's with their ineffeciant turbos, but two, small, quick spooling turbos placed very close to each head. the turbos could each run half of the desired boost and spool like mad.

after running through some intercooling the twins could feed into a stock style intake with an oversized plenum or i have another idea. a split intake manifold, i have seen pictures of this before and although it would be a better design it would be compicated. keeping each bank in step with eachother would be hard as one side would require its own throttle body and airflow meter so it would be hard to keep one side from producing more boost and tearing the engine apart. engine management would have to be top notch but i think that it would be worth it.

i realize that this never would be in a production car as it is complicated and turbos are expensive, but wouldnt it be a cool as a custom build? i'm sure that there are great big flaws with this idea but to me it seems sound...
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Old 03-07-2006, 02:50 AM   #2
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I have heard that if you pipe dual turbos into the same intake, that the turbos will in effect "fight" each other with the boost. From everything that I have heard/seen though, twin turbos with their own intakes works increcibly well. I have had the same pipe dream as you and I would long have tried to impliment it if my tiny budget could afford it!!!!

Banks has been producing twin turboed diesel engines for a little while now and I'm sure that they would either have information available about engine management, or that information could be requested from them.

If you do ever start this project though, you definately have to post everything about it on here!!!
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Old 03-07-2006, 03:47 AM   #3
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and why do you (or whoever) think the boxer is inferior? thread?

i mean, roomates 3SGTE has longer intake runners.

ive been itchin and pondering of a custom build with dual plenums and ITBs..... mmmmmm, yum.
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Old 03-07-2006, 03:49 AM   #4
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Quote:
Originally Posted by Mighty Subie
I have heard that if you pipe dual turbos into the same intake, that the turbos will in effect "fight" each other with the boost. From everything that I have heard/seen though, twin turbos with their own intakes works increcibly well. I have had the same pipe dream as you and I would long have tried to impliment it if my tiny budget could afford it!!!!

Banks has been producing twin turboed diesel engines for a little while now and I'm sure that they would either have information available about engine management, or that information could be requested from them.

If you do ever start this project though, you definately have to post everything about it on here!!!
you are recalling FAT's twin turbo kit, and are incorrectly taking his flawed header and TT design and applying it to general TT systems. If properly designed the turbos should not fight each other.

I have a pretty sick idea for a TT kit, and once I finish my current GT40R H6 setup I am going to mock up the TT setup If i can pull it off it will be pretty revolutionary and awesome in my opinion

more details as it develops, I will start a thread when I actually start it, likely more so when its close to completion so the setup can stay secret. It is actually somewhat along the lines of josh's thoughts.

also, if you run "half the boost" you will always have half the boost, 7psi on each turbo will yield 7psi in the manifold, not 14.

Ben
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Old 03-07-2006, 04:04 PM   #5
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Quote:
Originally Posted by PHATsuby
and once I finish my current GT40R H6 setup

I thought you said you couldn't fit it there
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Old 03-07-2006, 08:37 PM   #6
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Quote:
also, if you run "half the boost" you will always have half the boost, 7psi on each turbo will yield 7psi in the manifold, not 14.

thats what i thought at first but i got to thinking... boost is relative to the amount atmospheric, but it's actually making pressure against the intake manifold. so i started thinking that shoving twice the volume at the same pressure into a shared plenum would make the setup act as an adder and add the boost of each turbo. otherwise there wouldnt be a real advantage to a single manifold with parallel twin turbos. but i guess that i'm prob wrong and the turbos and manifold pressure would just reach an equillibum (damn i'm a fine speller) at the psi of each turbo
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Old 03-07-2006, 09:03 PM   #7
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think about that a little more. if you have two balloons, each inflated to 7psi, and then somehow manage to junction them together without losing any air, are they going to increase in size because now there's "14psi" in there?
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Old 03-07-2006, 09:13 PM   #8
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right i realize that now, so there would really be any benifit to twin turbos on a single manifold would there?
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Old 03-08-2006, 12:46 AM   #9
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the same benefit as having seperate manifolds. either way, both turbos would have to be pushing the same boost. i think the benefit is the amount of air that is being forced into the engine. two turbos flow more than 1.

josh
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Old 03-08-2006, 11:50 AM   #10
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they might be ABLE to flow a larger volume, but if they are both running at the same boost it isnt going to matter, into a comon intake they will just flow enough for the manifold pressure to reach what they are putting out, there just isnt going to be the motivation for the air to flow more if the pressures are already the same, the only thing that i could think of is that maybe this might make the turbos more effeciant at the same psi as they are having to flow a smaller volume of pressurized air each
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Old 03-09-2006, 02:04 AM   #11
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most turbo cars use a single plenium beacuse it is cheaper and simpler to do, there is really no advantage to a dual plenium steup other than shorter runners (and longer runners have their own avantages, think "Tunnel Ram") and in the case of the dodge viper, at least in the previous generation, they ran dual pleniums to make the runners LONGER. logner runners make for better low end torque in N/A cars. I don't know how they affect boosted cars so it may or may not be a disadvantage. that said, dual pleniums would be way up there on the cool factor.
oh, and, like this
http://www.atspeedimages.com/doningt..._f1_engine.jpg
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Old 03-09-2006, 05:13 AM   #12
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side note, but wave tuning in FI doesnt really apply, at least not even close to the level of NA cars obviously.

that has been the debate. In general, it is easier to use a single turbo, and you can get similar spool up and overall power output.

i can see possibly using twin turbo, for uniqueness, packaging purposes, a bit better spoolup.

thats the thing, if one turbo flows 300cfm at 7psi, if you have two, you are flowing 600cfm at 7psi, you are doubling flow, not pressure. running dual TB's can give throttle response benefits as well, this is my plan

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Old 03-09-2006, 05:17 AM   #13
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Quote:
Originally Posted by Hyper
I thought you said you couldn't fit it there
hehe, you are thinking of the GT42R I used to have, that wasnt going to fit in the conventional places, I could have made it fit but it is HUGE, the 40R is a big turbo by wrx standards but substantially smaller than the 42.

my old GT42R was capable of flowing 100lb/min, with a twin turbo setup of two GT30R's which i could theoretically flow 104lb/min due to certain design ideas I may be able to have better spool and throttle response and area under the curve compared to the 42R, that is one example where a TT setup may be beneficial, but again I have no dyno numbers to back that up, just speculation.

Ben
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Old 03-09-2006, 08:36 AM   #14
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why build ur own when subaru allready make a twin turbo motor? cant sum1 just put a legacy twin turbo motor in their impreza?
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Old 03-09-2006, 12:13 PM   #15
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Quote:
Originally Posted by noturbo
why build ur own when subaru allready make a twin turbo motor? cant sum1 just put a legacy twin turbo motor in their impreza?
if you did a search you would realize the problems and reasons why its not that easy. IMO it really isnt hard, if you are doing the swap you should be able to easily fab your own downpipes, but those TT setups, as has been said can pretty much be matched with a single turbo engine.

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Old 03-10-2006, 08:57 AM   #16
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Twin turbo impreza's have been done, they work, but not any better than a good single turbo setup. If someone was to go nuts and do a dual FMIC with short pipes to the intake manifold and lots of other little goodies it might be pretty cool, but hard to beat the large single turbo for power and efficiency.
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Old 03-15-2006, 04:19 PM   #17
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I'm not sure exactly what Hurlyey 2.5 WRS was refering to, whether he means 2 plenums like TBird Man was describing or a dual unified plenum which is much different. To clarify, the picture you posted is just separate plenums (I think, unless there's something hidden inside haha) but what is also refered to as a dual plenum intake is where you have a cone shaped plenum with a slot down the side that allows air to flow into another larger plenum that houses the velocity stacks. The purpose of this is to evenly distribute air to each cylinder. After that, the length of the intake runners really depends on the intent/purpose of the motor due to the "echoing" pressure waves that form in the runners when the valves slam shut. If you want to see power gains down low you want to have longer runners so that that pressure wave hits the intake valve right as it opens. As the engine speeds up you'd want shorter and shorter runners, so its really a purpose based decision.

A good example of the DP intake is the Audi R8 motor. Notice the tapering first plenum that leads off to the much larger main plenum. I guess in this case it is a dual dual plenum intake
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