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#41
Re: why go twin instead of a single turbo u ask
muke
Posted on: 2004/2/24 14:20
that sounds so awesome...my sedan scares tha crap outa me....bein in somethink like your ol' 1600 woulda been pure...i dunno...somethink cool....
 Quote:The best way to launch my 13B (with very large laggy turbo) was to drop the clutch just below boost and then let it come on boost. Using this system I was wasting heavily worked WRX's and fully tubbed V8's off the line using only 205 street tyres and well set-up suspension...true story.  
#42
Re: why go twin instead of a single turbo u ask
ddgonzal
Posted on: 2004/2/24 16:41
1200rc, don't let anyone discourage you. Go_the_datto made a A12TT and reported good results. Theory is good but shouldn't get in the way of getting anything done.
![Open in new window](javascript:CaricaFoto("http://datsun1200.com/modules/myalbum/photos/thumbs/255.jpg");) Go_the_datto's A12TT - He took more than 3-1/2 seconds off the quarter-mile time of his A12. Fairly impressive ... I can see how four cylinders per turbo would have an advantage. There are 720 degrees of rotation in a four-cycle engine, and an exhaust valve is open very roughly for 180 degrees. With four cylinders, there is 'some' exhaust flow all the time (though it varies from a lot to a little, i.e. the 'pulses' previously mentioned). With two cylinders, there is, roughly, exhaust flow only half the time. The question is how much does it really matter? With any four cylinder it will be highly pulsed during one cycle. Yes, the exhaust flow varies under operating conditions, but in our A-type engines, the open/close timing of the exhaust valves are fixed.
#43
Re: why go twin instead of a single turbo u ask
datsik
Posted on: 2004/2/24 16:57
Okay heres some maths. and some assumptions.
case one: one turbo asume (t25) turbine 53mm weight? : 500grams maths : moment of inertia (simplified) = (mass x radius x radius)/2 = 0.5 x 0.053 x 0.053 = 0.0014045 kg/m Case two: two turbos asume (t15) turbine 42mm weight? 380grams??? = .38 x 0.042 x 0.042 = 0.00067032 kg/m the two turbos WILL spool up quicker (in this case) but not by much. the turbotech.com.au website has the moment of inertia for different turbos listed. I have not used their values as I don't understand their figures, however, looking at their figures, two t15s (it looks like) have a total mass moment LESS than one T25 therefore it would seem (again) that two turbos would spool up quicker.
#44
Re: why go twin instead of a single turbo u ask
2332owner
Posted on: 2004/2/24 21:50
Okay what if a balance pipe were incorporated into the exhaust manifold. I know we don't have an answer on whether or not running each turbine with only two cylinders would be a disadvantage but if the 'pulses' were evened out with a balance pipe wouldn't 1200RC see the benefits of twins without the disadvantages that have been theorized throughout this thread? Just a thought.
#45
Re: why go twin instead of a single turbo u ask
phunkdoktaspok
Posted on: 2004/2/24 23:14
ddgonzal 1200rc actually owns go_the_dattos A12TT
#46
Re: why go twin instead of a single turbo u ask
L18_B110
Posted on: 2004/2/24 23:46
Quote:
understand what you are sayin with the V twin bike engine but this cant compare to a turbo but you can compare it to driving a turbo from 2 cylinders of a 4cyl engine which is what we are talking about here
#47
Re: why go twin instead of a single turbo u ask
phunkdoktaspok
Posted on: 2004/2/25 0:59
L18 I totally agree about autospeed not differentiating beetween the setups. Note that is why I made sure I did.
I also agree that people belive what they see, as if it was the gospel. I relate it to The Fast and the Furious. people see it and think man thats the best I gotta have that. I also understand and belive what you are saying of 3 exhaust pulses of a specific value over a specific time frame is more ideal than that of 2 exhaust pulses of the same specific value over the same specific time frame But to give tha argument this:Quote: The argument does not apply to 4cyl cars. A turbo works by the turbine being driven by exhaust gasses - obviously enough. But when you halve the number of cylinders feeding each turbo, you not only halve the total flow over the turbine, you have also made it operate on the turbine for half the time. Not big problem if you started with a 6cyl, but not so good if it was a 4cyl. Ever heard a V twin bike running? Nice way to drive a gas turbine huh? Between each pulse that is working on the turbine, there are the forces of friction and load on the impellor working against it's motion with only the spinning assembly's inertia to try to keep it going. Being so small, it has bugger all inertia working for it, so the turbine slows, then another exhaust pulse hits it and has to stop the decelleration before accellerating it again. That is not only bad for performance, it also mean reduced turbo life. Thems horse's apples. Thats like me saying running a turbo off 3 cylinders is worse and its going to limit the turbos life as compared to running it off of 4 cyl's for exactly the same reasons as you stated. Yeah there is more time frame inbetween the pulses of 2 cyl's when compared to 3 cyl's but the same goes for 3 when compared to 4. With the correct sizing this can be overcome. This will indeed make the turbos spool up as quick or quicker depending on sizing, and yes it will limit top end with this sizing vice-versa. Either way 2 or 3 cylinders isnt going to give the benifits of sequential twin setup.( bottom and top end) Yeah its not an ideal setup but to say no factory has done it and thats why 3 is better than 2, Is a joke. But you did agree your thoughts are that of if the factory hasnt done it, it must not be possible. Maybe this topic has gotten of subject abit. Back to the real subject Ultimately if its single or twin setup you will either have bottom end or top end power depending on sizing. Unless it is a true sequential twin turbo setup.
#48
Re: why go twin instead of a single turbo u ask
L18_B110
Posted on: 2004/2/25 3:03
Quote:
But you did agree your thoughts are that of if the factory hasnt done it, it must not be possible. No, I couldn
#49
Re: why go twin instead of a single turbo u ask
1200rallycar
Posted on: 2004/2/25 3:55
Quote:
Your logic that half the cylinders feeding 2 turbos is exactly the same thing as all the cylinders feeding one turbo is far too simplistic. Scratch the surface and think about how it all works. thats not what I am saying at all, im saying it's better to have the two but anyway, i cant be bothered rebutting all thats just been said [though it waas interesting to read] as i would be just repeating myself, so agree to disagree until i get back to you with more sound evidence that you may or may not believe, what do you guys reckon of 2332 owners idea of having a "balance bar" between the two seperate exhaust manifolds to each turbo, a bit like the GX twin SU inlet manifold has i guess, would this work well in evening things out a litle more? or just cause pressure loss in the exhaust that is operating at that time i'm going to send an email to autospeed to get them to clarify there statements and see if they have any suggestion on my setup
#50
Re: why go twin instead of a single turbo u ask
phunkdoktaspok
Posted on: 2004/2/25 6:03
Quote: But you did agree your thoughts are that of if the factory hasnt done it, it must not be possible. No, I couldn
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