Herald 12/50 Exhaust vs Factory Twin Carb Exhaust

[Jon J 1250]

Hi,

There isn't an exhaust forum area, so I decided to put this here.

As many will know the Herald 12/50 exhaust manifold has a longer branch to the exhaust front pipe than the standard 1200 manifold, presumably for better gas flow.

The factory twin carb Heralds all used SU H1 Carbs with a short inlet manifold and a cast exhaust manifold with a longer branch to the exhaust front pipe as well. (it was quite different to the 1200 Spitfire HS2 setup)

Does anyone know if the these exhaust manifolds are dimensionally similar enough that the Twin Carb exhaust manifold will mate up with the 12/50 front pipe without modification?

(I am intending to fit a Herald twin carb kit to my 12/50 this winter)

Regards

Jon

[Casper]

Yes, the exhaust manifolds are identical apart from the fact that a 12/50 manifold has the inlet manifold cast with it.  I assume there is sufficient space to bolt on a Spit 4 or Mk 2 inlet manifold, but some treatment with an angle grinder miogh be needed !

I have all the bits but cannot check the fit at the moment.  If you need me to do so I can.

C.

[Colin Lindsay]

I've done both angles ie removed the carb end of the 1200 manifold to fit a different inlet manifold, and the lower bit to fit a different exhaust manifold. Easily done with care, with a grinder. I can't clarify at present but is the 1250 manifold the same as the 1200 version? I seem to remember this in an earlier thread where they were different at the exhaust end - could be wrong though.

 

[Casper]

Quote

is the 1250 manifold the same as the 1200 version?

No, the 12/50 is longer than the 1200/948.  The 12/50 uses an exhaust the same as Spitfire 4 (Mk 1) and possibly of larger bore.

[Jon J 1250]

 

2 hours ago, Casper said:

No, the 12/50 is longer than the 1200/948.  The 12/50 uses an exhaust the same as Spitfire 4 (Mk 1) and possibly of larger bore.

HI,

Fortunately I have a NOS twin carb exhaust manifold so don't need to cut off the original inlet. The inlet manifold is right for the Herald H1 SU's, the Spitfire uses HS2's on a much longer manifold to clear a tubular 4 branch exhaust and  requires support from beneath. I might go to this setup one day as I do have an old pair of HS2's on a Spit Mk1 manifold, but I'll wait until the engine needs overhaul first as I may as well gas flow the head at the same time.

Net expecting much of a performance gain from the Herald TC H1's but they do look rather nicer than the Solex.

I will need to buy a new front exhaust pipe soon-ish as the original is looking a bit tired, so not sure if to get a TC one or a 12/50.

The TC manifold looks same as my 12/50 manifold below to me (ignoring the integral inlet). I do wonder if the internal bore is smaller though.

[Colin Lindsay]

Vey very nice! As long as it runs ok it certainly looks good!

[Badwolf]

You cannot put that in an engine bay. It is far to pretty. It needs a varnished wooden plinth and then displayed under spotlights.

 

 

[Jon J 1250]

Thanks both, appreciate your nice comments.

I keep the engine bay pretty tidy too but I see what you mean about the wooden plinth! lol
I decided not to refit the Triumph plenum and air filter box as the carbs too pretty to hide under that, so using these Unipart HS2 pancakes instead. Though it does mean i'll need to find a bracket for the choke cable.
I may even try out some Coopers filters as found on the Frogeye Sprite, but want to make sure they work first...thinking about it the Sprite must have a bracket for the choke cable so I'll start looking there.

They used to look like this so a big improvement!

[Pete Lewis]

had a good search through the triumph tune manaul and i dont see any clues about which needle you need if fitting 

a pancake filter to HS1   

you may be ok but the free flowing filter will reduce the intake vacuum and less fuel will be drawn from the jet with a std needle 

 a stonger damper spring may work well 

Pete

[Jon J 1250]

Thanks Pete for taking a look, I am a bit of a novice when it comes to trying different needles, I'm not sure what I need to look out for besides really obvious problems.
Any advice gratefully received

I have the standard Triumph SU H1 needles ( think) but of course they are probably for the 948cc engine, not the 12/50 1147cc, so I am going to start with with EB (rich) needles, which should also help counteract any reduced pull over the venturi.
I'll be using a Colortune plug to check the mixture over a range of engine speeds, we'll have to see how it goes...

Cheers

Jon

[Pete Lewis]

trouble with colour tune

all needles have the same diameter needle at idle

the colour you get running a light engine is as daft as a brush compared to whats needed on normal loads 

they are a good clue but not at all an excact result , ears amd drive are the best 

Pete

[Jon J 1250]

11 minutes ago, Pete Lewis said:

trouble with colour tune

all needles have the same diameter needle at idle

the colour you get running a light engine is as daft as a brush compared to whats needed on normal loads 

they are a good clue but not at all an excact result , ears amd drive are the best 

Pete

Thanks good point, I will have to use my senses.

Meant to say regarding damper springs, as I understand it, H series carbs don't usually have springs on the piston as they are weighted (HS's have them), but I have a couple of springs from a spare pair of carbs just in case.

[Pete Lewis]

that woud probably work   the spring holds down the piston so the increaded air velocity over the jet pulls out more fuel and richens it up

use engine oil in the dashpots 

Pete

[daverclasper]

2 hours ago, Pete Lewis said:

all needles have the same diameter needle at idle

the colour you get running a light engine is as daft as a brush compared to whats needed on normal loads 

they are a good clue but not at all an excact result , ears amd drive are the best 

That's what I've wondered about the lifting pin technique at idle being accurate, across rev range? 

[NonMember]

No, the lift pin doesn't give any indication "across the rev range". All it does is set the base idle mixture. However, if your needles are correctly matched to the engine, as established by many thousands of miles of development effort, and maintained by production process conformity, then the base mixture is the thing that's likely to be off. It's only when you've meddled with things that you need to worry about the rest.

[daverclasper]

Ahh. Thanks