Back on the subject of whether to go twin or single turbo.
I say if you can setup a twin turbo sequential setup go for it.
But if it only going to be twin turbo non sequential I see this will have no more benifits than a sigle turbo setup.
It only has down sides of;
more involved,
costs as you need 2 turbos (might be more or could be less?),
takes up more room in the engine bay,
the question come as to whether the oil pump can flow enough
more stress in designing.

Can anyone explain valve duration and how it varies between a 4 cyl and a 6 cyl engine, so I can better understand L18's views

phunkdoktaspok, duration of valve timing doesn't vary because of being 4-cylinder or a 6-cylinder engine. Of course it varies by camshaft selection.

What L18 is saying (if I understand him) is this, highly simplified:

4-cyl:
Exhaust flow from 0 degrees through 720
degrees
_-^-__-^-__-^-__-^-_


2-cyl:
Exhaust flow from 0 degrees through 720
degrees
_-^-_______-^-______

The flow is actually smoother than this diagram, as the exhaust valves are generally open for more than 180 degrees.

What I don't understand if how much difference it makes to the turbos. After all, a three cylinder feed will also have slow, maybe even dead, spots in the flow. If the exhaust duration is 240 degrees, "theoretically" a 3 cylinder engine might cover the entire 720 degrees. It's all theory, I doubt if there are any real tests done on this. After reading L18's posts, my concerns about 2-cyl feed would be: 1) don't expect it to put out more HP than a single turbo on 4-cyls and 2) Don't expect the turbos to last as long

On the other hand, we do have Go_the_datto's testimony that the A12TT worked well enough. AND IT SURE LOOKS COOL!!!

1200RC here's some inspiration:




It's the GP Sports S15

ddgonzal I understand how the 4 cylinder valve duration works but what I want to know is on a 6 cylinder the valves are still open for roughly 180 degrees, but because there are 6 cylinders while 1 exhaust valve is closing another exhaust valve is already opening ( meaning all 6 valves are open for 180 degrees each during this 720 degrees 4 stroke cycle)
Now what I am trying to understand is, if you take 3 of the 6 cyl's valves and connect them to 1 turbo you will still have ( dead spots as you say) during the 4 stroke cycle.
I understand on a 4 cylinder running 2 exhaust ports to 1 turbo you will have a longer dead spot but why is it bad for the turbos life on 2 cyl's and not 3 cyl's?

This is why I go back and say on a turbine wheel there is no fixed firing position, it comes down to gas flow, so if the turbo is sized correctly this dead spot is negligible.
And as the engines RPM increases this dead spot will have an even less negative effect on the turbine.

This is my view of a 4 cyl's exhaust valve pulsing. Please correct me if I am wrong;
An engine at 1000 rpm =
500 complete 4 stroke cycles.
This means on a 4 cylinder all 4 exhaust valves have opened 500 times each within 1 minute.
500 times in 1 minute equals 8.33333 times a second.
So all 4 exhaust valves have each opened 8.33333 times in 1 second.
Am I correct in saying this?

If I am correct do you think a turbo is going to be affected by this stop start pulsing of just 2 cylinders especially if the dead spot comes down to 100th's of a second?
This is why my thinking says it comes down to turbo sizing for gas flow as the pulsing is negligible even at 1000 RPM

NOTE my thoughts are only correct if my calculation are correct and if they are wrong please state where I went wrong with my calculations.

Cheers Steve.

thanks josh

what do you other guys reckon of 2332s idea of a balnce bar between the seperate exhaust manifolds on my setup, would it work well or not?, nobody commented on that?, lets think of ways to solve the problem if we can

The way that I am looking at it is it doesnt come down to the pulsing so a balance bar isnt going to make it better or worse.
I keep looking at it as to do with gas flow volume.
I would love someone to give me a reason why I am wrong, as just saying vehicle manufacturers have never done it doesnt sit with me as a reason why it will not work.

Let me start explaining my point again from the start

Steve, I hear what you are saying, but there is pulsing (even with a v8), and that pulsing will have more extremes with fewer cylinders. Tuned-length headers, crossover pipes, etc are used to get the pulses in sync for maxium flow. Flow is important to overall HP, but a concern here is pulsing and what that does to the turbine and compressor.

L18 is probably right in that it's not optimal with two cylinders, but that doesn't mean it won't work ...

The balance tube idea is interesting, but none of us really know how it would work. This concepts helps a naturally-aspirated engine in the exhaust system. In the 90s they used to put "H-pipes" in a V8 dual exhaust system, now it is shown the "X-pipes" work somewhat better. But this is after the headers (extractors) ... I've never seen or heard about extractors with balance pipes ...

Quote:Huh? I said it was a pulse. My diagram attempted to show it rises and falls, definitely not a "long constant force". So we agree on that.