8 replies to this topic

[Clubman_Jake]

Hi All.

 

I have a Maniflow Twin HS4 inlet manifold which I am attempting to fit to my engine.

It is a modified 1293 A+ engine, originally from a Metro. most of the engine work was carried out many years ago when my dad had the car - and he has no documentation or memory to prove what the exact spec is. So apologies for this lack of info.

 

 

The Maniflow inlet uses the same diameter tube all the way through - which in this case, is 1 1/2" or around 38mm.

There does seem to be quite a difference between the diameter of the inlet ports in my head, and those in the manifold.

The manifold is 38mm, and the locator ring seats are around 33mm. 

I am assuming the diameter of the actual inlet ports will be a few mm smaller than the locator ring seats too? - but I can't quite get access to measure this until I take the head off.

Does this 5mm (or more) difference just require a bit of port matching, or do I need a different head, or am I doing something else wrong?

 

Please bear in mind that I have never port matched anything before - so please respond like I have no idea what I'm talking about!

 

Thanks in advance for any help,

- Jake

 

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[imack]

Maniflow make that twin hs4 manifold with two different port sizes at the head face.
You have the larger bore version of the manifold that's designed to work with extensively modified heads that have fully opened up intake ports.
There's another version of the twin hs4 manifold that is the outer diameter of the factory manifold locating rings designed to work with more mildly worked heads where ports have been opened up to the standard gasket bore.

[Clubman_Jake]

Maniflow make that twin hs4 manifold with two different port sizes at the head face.
You have the larger bore version of the manifold that's designed to work with extensively modified heads that have fully opened up intake ports.
There's another version of the twin hs4 manifold that is the outer diameter of the factory manifold locating rings designed to work with more mildly worked heads where ports have been opened up to the standard gasket bore.

Ahhh... Now I feel stupid! But that's very helpful thank you.

 

I bought the manifold through Facebook Marketplace - so had no idea that there were two different bore sizes to choose from at the time.

 

Do you happen to know the effects of 'fully opening up' the intake ports on a mildly worked head? - I'm guessing that my best option is to get the smaller bore manifold, but I'm just interested.

 

I'm planning on taking my head off soon anyway - so will hopefully get a better idea of its spec/condition and decide what to do next.

 

Thanks again

[Alex_B]

From what I have read you need to be careful not opening up the intake ports too large, especially on a milder engine. The issue you can find with larger diameters is the port velocity drops which can cause issues with the fuel dropping out of suspension from the airflow as well as directly effecting the overall volumetric efficiency of the engine, although that last point relates to a number of variables so is tricky to quantify. Generally though smaller diameter ports suit lower rpm running which creates more of a restriction at higher rpm, where as larger diameter ports work better at high rpm whilst sacrificing lower rpm smoothness and power. 

There are much more knowledgeable people on here who I am sure will chime in with real world experience of the two maniflow manifolds and whether or not its worth port matching the head, but thats my tuppence in any case.

[imack]

There's a lot of material to grind out of a standard head to match the large bore maniflow intake and gasket, you'll break through into the pushrod tubes which will require sleeving.
The picture below shows the large bore competition gasket on a standard head race head ports vs standard and a large bore maniflow twin hs4 manifold on a race head.

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Edited by imack, 07 January 2023 - 09:41 PM.

[Earwax]

I will throw my 2 cents in also.... as an observer and definitely not a head porter/machinist.

 

For a road car I have used a small diam maniflow for twin HS4 SU on a mildly cammed 1310 and it was terrific... but that car was not wild at all

 

My humble advice would be either change to the smaller maniflow twin or even a Hif44 single AND then at some later time when you can see what is in the engine and what build type you are after you can then buy and build complementary parts that are known to work well together, so head development, cam choice, rocker type, diff ratio and type all considered at the same time.

[Clubman_Jake]

From what I have read you need to be careful not opening up the intake ports too large, especially on a milder engine. The issue you can find with larger diameters is the port velocity drops which can cause issues with the fuel dropping out of suspension from the airflow as well as directly effecting the overall volumetric efficiency of the engine, although that last point relates to a number of variables so is tricky to quantify. Generally though smaller diameter ports suit lower rpm running which creates more of a restriction at higher rpm, where as larger diameter ports work better at high rpm whilst sacrificing lower rpm smoothness and power. 

There are much more knowledgeable people on here who I am sure will chime in with real world experience of the two maniflow manifolds and whether or not its worth port matching the head, but thats my tuppence in any case.

That does make a lot of sense now that you've explained it - and it does seem to be pointing in the direction of the smaller bore manifold.

This manifold is going in a road car, hence lower rpm running, smoothness and power will need to be favoured.

 

Appreciate the help - thanks!

[Clubman_Jake]

There's a lot of material to grind out of a standard head to match the large bore maniflow intake and gasket, you'll break through into the pushrod tubes which will require sleeving.
The picture below shows the large bore competition gasket on a standard head race head ports vs standard and a large bore maniflow twin hs4 manifold on a race head.

Very helpful pictures - thanks for those!

 

picture 1 and 2 do illustrate the size difference quite well, quite a drastic change too.

This is definitely pointing me in the direction of the smaller bore manifold, as I doubt I will be opting for a full race head for my engine. Especially if extra work such as sleeving the pushrod tubes will be required.

[Clubman_Jake]

I will throw my 2 cents in also.... as an observer and definitely not a head porter/machinist.

 

For a road car I have used a small diam maniflow for twin HS4 SU on a mildly cammed 1310 and it was terrific... but that car was not wild at all

 

My humble advice would be either change to the smaller maniflow twin or even a Hif44 single AND then at some later time when you can see what is in the engine and what build type you are after you can then buy and build complementary parts that are known to work well together, so head development, cam choice, rocker type, diff ratio and type all considered at the same time.

Thanks for the advice, it's much appreciated.

 

And yes, that definitely looks like the right way to go - I do actually already have a Hif44 setup, so I think I'll fit that again whilst I decide whether or not to bother with the smaller bore Maniflow option.

And as you say - I'm probably best doing this once I've removed my engine and figured out it's exact spec.