Project: Bespoke 1147 Inlet Manifold

[Jordon T]

Hi Guys,

My Herald 1200 is currently sporting a newly rebuilt Spitfire Mk1 spec 1147 engine with the correct twin HS2 1.25" carbs on a Mk1 Spec inlet manifold. It runs very well, but I've always prefered having a single carb as opposed to twins. David Vizard (tuning guru) and several other reputable enthusiasts share this opinion.

With this in mind and me being a Development Engineer within a cast-iron foundry; I've decided that I'm going to design my own bespoke inlet manifold, which will allow me to bolt a single HS4/HS6 onto the original 6-port 1147 head (a bespoke 8 port 1147 head is on the drawing board as a project for the future).

I think this is a nice project for me to literate for others and also seeks advice and constructive criticism along the way. So any opinions or advice, please post away!!

I've focused my research on the designs Triumph's own development engineers would have considered from the design of the "banana" shaped manifold of the 1300FWD and the Herald 13/60 and it's successor the "log" shaped manifold of the Toledo, 1500FWD and Dolomite. From what I have read, I believe the later log arrangement was more efficient and had better flown, the log design allowing the fuel/air mixture to atomise more efficiently. Is this correct? Does anyone disagree with this?

I've also looked into later British Leyland designed inlet manifolds such as the ones used the Metro's and Maestro's of the 80's. Long dropping branches with the carburettor setting in reverse. This was my first choice of design for my unit, but realised that the Herald's low bonnet line compromises this arrangement.

So I've come up with the design below. It's a log arrangement similar to that of the Toledo's, but with more internal curvature and a central splitter.

 

 

What do you guys think? 

 

Looking forward to your responses,

 

Jordan

[RobPearce]

I'm pretty sure what you've read is misleading you.

The 13/60 Herald, with its "banana" manifold, produced 61BHP. The 1300 Toledo only got 58. Now you might blame that on the SU carb but nobody thinks Strombergs were that much better.

The log manifold on an 8-port head supposedly gives better mixture distribution, which helps with emissions and economy. It's not good for flow and thus not good for power.

Of course, if you object to twin carbs, which are much better for power but not for economy or emissions, then maybe that's what you're after.

[Casper]

John Thomason wrote a series of articles in another club's magazine describing the use of a Toledo manifold and HS6 on a 1500 Spitfire.  I believe he also experimented with the 13/60 bananas.  John Kipping also recommended the Toledo mani as part of his 'ideal fast road' 1300 setup.

C.   

[Clive]

I remember the JT articles. It was on his std spitfire that he did mega road miles on during the week, and then raced it at the weekend (winning the series IIRC) He thought the single carb setup would be better for economy, and the twins fitted for racing better power.

JT did things properly. The differences were marginal both in power and economy when tested on the rolling road and his careful recorded economy figures. He also was very specific about the log manifold being supeioir despite appearances. I wonder if the differences between herald and toledo power were more down to the method of measuring the power (Toledo probably done under DIN conditions fitted with water/oil pump, alternator etc etc, the herald the power measured without any of that nonsense. Same as teh TR6 150bhp v later 125, the actual difference was much less than 25bhp)

I would think a single 1 1/2" carb would be adequate? But if going this route, why not EFI. Go on........

[Casper]

Toledo probably done under DIN conditions fitted with water/oil pump, alternator etc etc,

Correct.  58 DIN and 65 ISO.  c.f. 13/60 at 61 ISO.

Spitfire article Courier 216 Jun 1998.  See also Couriers 111 and 112 for manifold theory.

Also Courier 221 Nov 1998 for HS6/Dolomite manifold on a 1300 Spitfire

C.

[Jordon T]

Hi Guys,

 

Thanks for the feedback guys. 

 

I'm finding the DIN and ISO comparison quite interesting. So if we go by what Casper has said above. The Toledo was actually more powerful than the 13/60. This being entirely too the manifold design. I can't imagine the carburettor would have made that much difference with them both being 1 1/2". 

 

I'll dig out those issues of Courier and report back. 

 

Thanks,

 

Jordan

[Jordon T]

ust been doing some air flow calculations comparing the total area of the two inlet ports and the various combinations of carb size.

 

Here are my findings (mm);

 

Port diameter size is Ø30 x 2 = Ø60. 

Total port area is 1414mm2

 

Single HS2 1.25 = 896mm2

Twin HS2 1.25 = 1791mm2

Single HS4 1.5 = 1140mm2

Single HS6 1.75 = 1551mm2

 

So looking at these figures (and not taking valve seat/ opening area into account). The carbs in red would technical suffocate the engine and the carbs in green would delivery sufficient air flow. 

 

Question; if the total area of the carb is greater than that of the port size. does this mean that full throttle would technically be achieved without the throttle butterfly being fully open?

[Clive]

Look at toledo valve size too I think they were a big valve head, herald probably smaller?

And you have only compared the size of carbs, not what the engine can flow. So you may need to exercise those grey cells again! Remember in the normal twin carb setup, the gas flow is in pulses, not all 4 at once. Not 100% of course, but the thought experimet suggests a single hs4 would work fairly much the same on one or 4 inlets if they are taking turns....

I like threads like this, I can follow the gist of it....and learn from others.

[Casper]

 I think they were a big valve head

Toledo and 13/60 had the same size inlet valves.  The Dolomite 1300 had larger, but I have no power data for the Dolly.  

Note that the 1200 Spitfire engines had larger valves than the 1200 Herald engines.

Jordan.  The Toledo/Dolomite mani has a 'dead air' space at either end of the 'log', past the right angles to the inlet port(s).  I think John Thomason thought this important.

C.

[Paudman]

But if going this route, why not EFI. Go on........

Because it's more fun and more of a challenge to make what's already there, better... 

I like the sound of this; can it be made so that it will take a variety of carbs ie Stromberg AND SU alternatively, to test the benefits of each?(Moveable stud positions?) I've messed about with carb adaptors to do the same job but a more professional item would be very welcome.

[Casper]

So looking at these figures (and not taking valve seat/ opening area into account). The carbs in red would technical suffocate the engine and the carbs in green would delivery sufficient air flow. 

Not an expert in carb theory but for a 1200 the Solex formula (d = 0.82 x Sqrt(cylinder volume[cc] x Peak revs[4.5 x 1000]) gives 30mm for the diameter.  The Herald was fitted with a 30.  The 948 was slightly overcarbed at 28mm c.f. a calculated 26.  But I believe that the venturi of these carbs is way less than the notional diameter.

C.

[Bitumen Boy]

I always felt the Solex carb on an 1147 was restrictive, and seemed unable to flow enough fuel at higher revs. I also found it the single most unreliable component on the whole car, and eventually came to loathe it so much that I went to the trouble and expense of tracking down the parts for a twin carb conversion - the engine was already a mk 1 Spitfire unit, just what turned up locally when I was looking for one to rebuild, so I got more benefit from the twin carbs than may otherwise have been the case.

However, given the scarcity of suitable manifolds for the twin carb conversion I would have been most interested in something suitable to fit a single SU in place of the Solex with as little fuss as possible. I still might be interested as simplicity is something I value highly in a car and the twin carbs take up rather more space than I'd ideally like. 

I'd be tempted by the idea of a second Herald if the right car came along at the right price, but the right Herald for me definitely wouldn't be one running a Solex carb... 

[Jordon T]

Hi Guys,

 

Thanks for the comments above. I've read the articles in the Courier as suggested by Casper, and done some further research. I've come to the conclusion that a single HS4 would be best suited to engine setup I have. However, I've redesigned the front flange so that a single HS2 could also be bolted. This is beneficial for if i choose to cast several manifolds for 1200's which aren't Spitfire tuned (low comp and 12-52-52-12 cam). I myself will be conducting road tests with both carb sizes fitted just to satisfy my own interest.

 

You will also notice I've included a line bored channel for manifold warming, and removed the central splitter to aid turbulence and further improve the fuel air mix. 

 

I'm going to design and 3D print the pattern tooling hopefully next week and will have a few castings made for the week after. Fun stuff!

 

Regards,

 

Jord

[Nick Jones]

Interesting project.

I experimented a bit in the manner of John Kipping though without his thoroughness and documentation with 1 x HS4 (Dolomite log manifold), 2 x HS2 and 2 x HS4 on a fairly well tuned 1300.  The single only really lost out to the twins over 5000 rpm (and gave nice manners below that, especially during warm-up) and the HS4s only gave advantage at 6000+ (engine revved to 7000).

Conversely I remember 2 x HS2 (originally mk 1 Spit I think) making a very noticeable difference when fitted to my '65 1200, with the high compression SAH head making a further step change.

I note you state cast iron foundry....... If you can do aluminium as well I have a bunch of ideas regarding FI manifolds!

Nick

[Bitumen Boy]

Have you considered incorporating the exhaust manifold in your design? Suitable cast exhaust manifolds are thin on the ground and probably aren't in fabulous condition if you find one, while the tubular type are probably going to be remanufactured now and we all know how great the quality of such parts often isn't. I also feel - though I appreciate you're doing this more for interest than profit - that someone interested in fitting a single SU instead of twins to an 1147 would likely prefer a cast exhaust manifold over a tubular type. Also, a one piece design wouldn't need any extra plumbing to warm the inlet, a "hot spot" as per the originals would do nicely and means fewer parts to go wrong. I'll have a look at mine later if you want, but I think using the warming tube requires an extra connection to the waterpump housing that the standard Herald part doesn't usually have, OK new alloy ones are available but it means more trouble and expense to do the conversion. If you do decide to go down this route, I would suggest that the exhaust manifold should be akin to the longer, larger bore later type as per the 12/50 Heralds, the earlier type seems rather restrictive.

[rustbuckit2011]

Interested Jordan- if for nothing more than to play with! I have always been interested to see what can be squeezed ot of the 1147. I think for torque this would be quite interesting- and for a boosted application it would be a godsend- thinking about sc12 toyota superchargers again....

[Eric JS]

To Jordon T

I have just found this string on the internet, I know it six years down the line but you could be the man I need to talk to?

Did you make any of your inlet manifolds as I am looking for one for the Herald engine fitted in my Standard 8.

Hope you can and do reply

EJS

[65redspit]

Mine makes 114.8 bhp on twin 40 webers and is still smooth enough to idle properly and drive normally on the road … no superchargers needed

[Matt306]

On 13/07/2018 at 12:10, Jordon T said:

ust been doing some air flow calculations comparing the total area of the two inlet ports and the various combinations of carb size.

 

Here are my findings (mm);

 

Port diameter size is Ø30 x 2 = Ø60. 

Total port area is 1414mm2

 

Single HS2 1.25 = 896mm2

Twin HS2 1.25 = 1791mm2

Single HS4 1.5 = 1140mm2

Single HS6 1.75 = 1551mm2

 

So looking at these figures (and not taking valve seat/ opening area into account). The carbs in red would technical suffocate the engine and the carbs in green would delivery sufficient air flow. 

 

Question; if the total area of the carb is greater than that of the port size. does this mean that full throttle would technically be achieved without the throttle butterfly being fully open?

That would work if all four ports were sucking at the same time but only one is sucking. Although no expert on this either.