so we have got an open scroll manifold or single scroll manifold and a twin scroll manifold
the open scroll manifold is um kind of what's most common in the aftermarket
so particularly on what we do a lot of which is astra vxrs the open scroll or single scroll
depending on how you say it where in the world you're from is the most common because
it suits the most common kind of turbo that we use which chen which is generally the garrett
turbos which is the gtx and then the g series more recently so the whole idea in open scroll manifold
is that all cylinders on the engine all fire into that one collector and then fire that gas
straight down the turbine wheel with no divisions in ports and then with a twin scroll manifold
you'll have four six um you know you can whatever multiple of cylinders you've got dividing into two
ports on the collector which fire either side of the turbine housing and then individually fire the
turbine wheel and actually try and help generate spin it the whole idea of open scroll is that
all cylinders of the engine fire into each primary as we call them and then collect in the collector
to fire that one side of the turbine housing that that one open turbo and it's much simpler
to fabricate um you know it's uh it's more common i think mainly just because the garrett
open scroll turbos are far more common v-band is a nice fitment people like v-band because there's
no gaskets involved and i think going back to the kind of early earlier days of vxrs or gsi's doing
uh garrett turbo conversion so a lot of time it was t25 so it'd be like a g28 a gt28
or sometimes a gtx 28 on a t25 manifold and a lot of the time sometimes it was because
of the manifold the specific brand manifold or you know several things
you never always struggle to get kind of a good gasket seal and so that was kind of how um i think
you know the industry kind of developed into using v-bands as a standard
um within the kind of vauxhall and opal community really um v bands became the way forward
it it offers a nice amount of adjustability they're much easier to use in t25 you're not going
to worry about stud snapping or you know surface flanges so you can get a really good gasket seal
you're not going to worry about any of those kinds of things it is much simpler
but there are some disadvantages and that is that the different power strokes of the
different cylinders can actually um not help each other in terms of
spooling up the turbo as fast as possible if you can split those power strokes and
actually split those cylinders the two cylinders that go up and the two cylinders that go down
and you've also got that kind of valve overlap if you can split that into a divided turbo manifold
like a twin-scroll manifold there is a lot of advantage to be gained that's not to say that a
v-band an open scroll manifold or turbo is in any way inferior to a twin scroll because there are
pros and cons so at kind of high rpm when that overlap doesn't really matter so much anymore
the the open scroll manifold totally comes into its own because there's no restriction
or restriction is probably not really the correct word but there's no lack of efficiency in firing
that turbine wheel because you've got all of the uh the turbine housing to kind of uh
to fill with all four cylinders when they're both when all four of them are getting through
that that kind of high volume of air that you'll see at high rpm so then as we look
at a twin scroll manifold the whole idea of a twin scroll is that we've got two sides of the
collector and they're actually divided so it's you know sometimes would be called a divided manifold
so sometimes twin scroll there's lots of different names for it depending on
um you know what kind of car scene you're from or whereabouts in the world you're from
what we've got here is we've got cylinder one and cylinder four coming together and powering
one side of the collector and then we've got cylinder two and cylinder three coming together
and powering the other side of the collector and it is split right down to the turbo and then
through the turbo it continues to be split right until it hits that turbine wheel we're trying to
divide those gasses as much as possible so when cylinder two and cylinder three are on their blow
stroke of the four-stroke um engine cycle they are pushing that exhaust gas out of the cylinder head
into the turbo manifold powering the turbo our cylinder 1 and cylinder 4 are actually
starting to draw air in so you can have with an open scroll manifold they'll they'll start to
not fight against each other but they certainly won't help each other so with the twin scroll
manifold you you kind of get rid of all that and that means a low rpm and this is for all
twin scroll turbos pretty much a low rpm they can just make so much more power and with with
the kit that we make this manifold for it makes so much torque at such a low rpm that it's
you know it's not it's not even comparable to what an open scroll manifold would be and even at the
top end we're not really losing that much power as a kind of a disadvantage over the open scroll
so with a z20 um for a street car a twin scroll manifold is almost certainly the way to go really
purely because there aren't enough disadvantages to outweigh the con to what to outweigh the
advantages you get of all of that low end rpm you know you at all at the kind of lower lower
end of the rev range so maybe two and a half to four and a half thousand or five thousand rpm
the advantages gained from the twin scroll manifold far outweigh the disadvantages
of the open scroll manifold at a high rpm so a kind of for a street car where you never well
some people will be driving at a high rpm quite a lot but on a street car where most of your work is
done at low rpm and um building boost pressure you want to you want to get that done quickly
and a twin scroll manifold and twin scroll turbo setup really aids that really gets that done a lot
faster so why why doesn't everybody just have a twin scroll manifold um on everything all the time
a lot of the reason is the twin scroll turbos are often a bit more expensive and that makes the kits
often a bit more expensive it certainly did when we first started using the efrs they were quite a
lot more expensive than a kind of gtx 2867 or a 2871 as was what we were using quite a lot then
but a lot of times also packaging as well so because you're forced to get cylinder two
and cylinder three and cylinder one and cylinder four together it actually makes the two manifolds
even though the turbos are sitting in very similar positions quite a lot different um
and especially when you're looking at a kind of external wastegate manifold a twin scroll
external wastegate manifold you then also have two wastegates as well so it just makes packaging
a whole lot more difficult this manifold is actually um our internal gate manifold for the
z20 engine where we offer the six two five eight the six seven five eight and the seven one six
three seven one six three's pretty good but probably a bit too good um probably not quite
the right phrase but it's it's a bit too much for this this kind of setup on the z20 engine really
we've always found it never really works quite as well as the six seven five eight six seven
five eight is in my opinion the ultimate kind of street car too but if you're not really
interested in going on track days or anything like that you just want the fastest street car
the 6758 with this uh internal wastegate manifold is the one to have
but just going back to the packaging you can you can see the manifold is a lot more challenging
to fabricate in terms of we we can't just put the primaries wherever wherever we want them
in order to make the most compact manifold you know we've got kind of
primary hanging out the edge here this one comes over the top of the other two
to try and get the one and the four on the same side so there's a lot of things to consider
when it comes to the the turbo side of things with a twin scroll manifold just like with the
collector the the turbo is divided so we've done a internal wastegate versus external wastegate
turbo video before so we'll put a link to that in the description so i'm not gonna go into it in too
much depth but i just wanted to demonstrate how the collector's divided and so is the
turbo manifold right down into the kind of what you know what you would traditionally call like
the the kind of snail shell part of that turbine has in the kind of curly bit that sits around the
outside of the turbine wheel that's divided right round inside there and you can see it's divided
right round right until it kind of meets back up with the collector again as it kind of hits that
turbine wheel so those gases are divided for as long as possible and that gives the best effect
of that twin scroll turbo and then with an open scroll turbine housing so i've just got
the turbine housing on its own here you can see a bit better all of those gases are firing into that
one main area and then they'll all come around to the turbine wheel just together on their own so
you can see the gases are coming round there and then they'll exit here right where that little
piece is onto that turbine wheel and drive it so really when it comes to deciding um you know what
what kind of setup you want to go for there's so many things to consider there really is no one
size fits all the oems all tend to be using twin scroll turbos nowadays and that's just because
it's a lot easier to make that low down power and that's generally where people want it on
a road car people want low down horsepower because it makes the car feel faster quicker
if it's a race car they don't really care what power the car makes at 3000 rpm because it's
never going to be there it's always going to be up in the rev range where the engine is you know
churning through the most amount of air and it's most efficient so there isn't a best there isn't
like a one size fits all do your research really and ask the tuner a lot of time people say to
me what turbo should i get which is the right setup for me i can offer advice but given that
we're not going to be the ones actually tuning the car definitely not our area of expertise
ask the tuna see what recommendations they can give see what experience they've got
and that goes for any car really not just the voxel stuff that we do
all cars you know speak to the people that are actually going to be doing the software on the car