Custom Manifold out of Steam Pipe
Turbo Mini Forums

Hi all,

I have had a good search and can see a number of different exhaust manifolds thaty have been made.

I am about to pull my motor out to fit my quaife 8-)
and while i am there i am thinking of making a new exhaust manifold to replace the std unit.
on the last day i went on i made 179hp at the crank on 12psi and got 139 on 14psi at the wheels, so i have good power now but i just feel and always have felt that the std metro manifold is restricting the power.
I was going to use some steam pipe of around 35mm ID and about 2.5mm wall thickness or so (see what they make and then decide)

I am going to make a pretty much replica of the std unit just bigger ID really, does anyoen have any good suggestions for my to take into account and use etc?

thanks guys

Grant

179hp on 12psi 1293cc of pure A series
14.0et @101 mph

just one thing is whether it is worth it? im pretty sure that MW is still on standard manifold, and that is capable of flowing 300+BHP. (not sure the the nitrous would make a difference in this factor? its still flowing enough air for that power surely?)

anyway for my manifold i was thinking of using a decent grade stainless but i am not that far yet so i havent really put that much thought into it.

how about getting the standard manifold ported and see what this does to you power?

just food for thought mate.

mmmm food....

As I see it the exhaust manifold is unlikely to be the week link. The Metty manifold is nicely shaped and unbreakabe. remember it's essentially feeding a big blockage in the form of a turbine.

Do you run a T3? or something else on the Metro manifold. When I fitted my T2 I did a poor job and it was restrictive. A few hours with a dremmel showed a massive gain in power (I worked on the elbow on the turbine exit at the same time)

A more efficient turbine will give much better results though, unless, like me, you have created a restriction.

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Looking at it, I'd say the biggest restriction apart from the turbine was the exhaust valve/elbow/port. Either add a mm to your exhaust valve, a bit more lift or a bit more duration..

That's what I think.

I'm totally convinced that in an A series, there is not enough exhaust area for flow, hence why longer duration exhaust profiles work. Eg MG, Ph2, Kent Megadyne and lesser gains are got from equal length cams eg: piper.

I would totally match the port to the manifold and probably work both bits. The gains wouldn't be so much over a N/A motor, but they would be there.

Bugger off, I'm getting there.

No point in slowing the gas flow in the manifold for it then to be speeded up in the turbine nozzle.

You would just be creating a geater pressure loss due to the change of energy state.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

all good points guys, thanks for the thoughts.
I already have a 12G940 head with MK1 S valves and the RE13 cam and the manifold has had some tickling done on the entry and exit areas, trouble is you cant get into the bends to open that area up more.
with still using the carb how does one make anywhere near 300hp reliably? ( i know there is no such thing as a reliable A series lol)

just thought the manifold might be a restriction on flow, I am using a T25 of a nissan and it can easily boost up to 20psi but i think it not that more efficient from 15psi to 20psi plus right now its hard to tell with so much wheel spin, hopeing the quaife will help there.

thanks guys

Grant

179hp on 12psi 1293cc of pure A series
14.0et @101 mph

Hi,
It seems engine reliability is ok @300 bananas, but the g/box is a whole different story!
Cheers,
Gavin :)

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with regards to exhaust manifold diameter, i used 1 1/4" as this was all i could get hold of, I heated and squeezed the pipe to the square shape of the exhaust ports and it matched them for size pretymuch perfectly, the exhaust ports in my head are pretty big though, big enough i had to trim a large bore competition gasket a little to match them.

witout measuring i would guess that ports opened up to the turbo gasket would need a pipe size of 1"

her are some pics from when i made my manifold, i'm sure i posted them before but can't fnd the thread.

Grant - speaking to my turbo guy and Graham - we decided the exhaust manifold wasnt the restriction.
In my case it was the turbo itself and the dump pipe elbow (mine was sharp and not flowing)

I would seriously invest in the new turbo - like I said to you, John at Precision will go you a hybrid for a great price... whatever specs you want basically.

If you cant do that, I would just change the dump pipe to make sure it flows.
If you go too big on the manifold, you loose airspeed and potentially not spool up the turbine as quick or as much.

The quaife will help the wheel spin - REALLY helped in my case... thats for sure.

Im not sure how the std metro mani flows, but I dont think 'bigger' is really the answer - maybe 'better' style of manifold.

Cheers,
Pete

1132cc Turbo ~120 bananas ATW - Fun Fun Fun

This is my manifold build thread:

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=149485

I used the next size down sched 10 pipe at 28mm bore.

Now you may think that using a larger size pipe will be advantageous. However, you need to consider the science of the energy conversion process from the exhaust valve to the turbine nozzle.

Basically the gas comes out of the cylinder fast through the valve seat, slows a little in the port and manifold and then gets speeded up very fast to go through the turbine nozzle.

The pressure difference between the cylinder head face and the turbo flange depends on two factors.

1. Pressure loss due to friction
2. Pressure loss due to changes in velocity.

Making the branch ID bigger will reduce 1. but will increase 2.

Within the range of practical sizes 28 or 35mm, due to the very short length of pipe, it is very likley that the increase due to 2. will outweigh the advantage of 1.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

ok So most of you feel there is more than enough flow in a std metro manifold, Im still not convinced, just do to the fact the ports size in the manifold are so small much smaller than my head.
when i pull the enhine out in a few weeks i will take some pics of it and see what you think, i will also look to give it some more porting and see if i can get into the corners a bit more and maybe evencut back some more of the section which seperates the pipes at the flange.

Peter, I am not convinced my turbo is not good, yet it is not a ball bearing unit but it still flows very well and is a great match as i can pump out over 20psi and have seen it jump to around 25 on a few occasions and my intake temps still stay down at around 45 degrees at that boost so i feel its pretty efficient, but i might be wrong

179hp on 12psi 1293cc of pure A series
14.0et @101 mph

grant have you anyone nearby that offers the ''extrude hone '' service ? google it .

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Hi
I'm no turbo expert but if you're saying it's not effcient between 15-20 psi then that's your problem.
As you run towards the edge of the comp map you'll be generating a lot of heat into the charge.
As others have said bigger bore on the exhaust manifold will lose air velocity.
A GT series turbo should give better results than the T series too
Cheers
Gavin :)

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WB/EGT gauges. Click here for customers write-up

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My Mini build diary

On 11th Nov, 2008 Bat said:
Hi
I'm no turbo expert but if you're saying it's not effcient between 15-20 psi then that's your problem.
As you run towards the edge of the comp map you'll be generating a lot of heat into the charge.
As others have said bigger bore on the exhaust manifold will lose air velocity.
A GT series turbo should give better results than the T series too
Cheers
Gavin :)

179hp on 12psi 1293cc of pure A series
14.0et @101 mph

Hey Grant,

Not saying the turbo isnt good - saying that the boost curve and power produced is different with the GT that I got. Eg, at 7psi boost NOW I make more power than I did at 11psi with the old turbo.
Having said that, my old turbo and your current turbo are very different - lol Mine was shit yours isnt haha.

I still think that your manifold is ok - in fact was at GRs and discussed your manifold, etc with him.

He is saying that the manifold IS a problem because of the exhaust manifold haviing two tiny slots ... that its restrictive.

What size exhaust do you have?
Ill go have a look at the Metro Manifold this afternoon on my way home - as Ivan has one there... stock.

So - in a roundabout and long winded way - what I am saying is - yes build a new exhaust manifold out of steam pipe - BUT dont go too big or you loose airspeeed. Try that new manifold with your T series and a bigger dump/exhaust (if you can) and see what it does... you can always change the turbo later anyway...

Pete

1132cc Turbo ~120 bananas ATW - Fun Fun Fun