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jabe1807
Norway
192 Posts |
 Posted - 07 Dec 2011 : 21:52:05
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I just had to put on the webers
and the exhaust to take a picture
I have measured the combustion chambers
and the volums are between 45,0 ccm and 45,5 ccm.
I think Holbay has 43 ccm.
So maybe my head is modified?
The head is nr 7437,
is that nr telling something?
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Edited by - jabe1807 on 07 Dec 2011 21:55:03 |
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1922
United Kingdom
549 Posts |
Posted - 19 Nov 2011 : 19:24:21
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You could have a modified Holbay head. Holbay used to offer a 122bhp "Rally" engine that had enlarged inlet ports, and a 1840cc 130bhp "Marathon" engine with enlarged ports, larger combustion chambers and larger bores. I've seen several modified heads that looked like yours, some started as Holbay heads and some as standard heads.
Don't be concerned about the smaller manifold - this should increase the gas speed and improve mid-range power. Ford 351 Cleveland v8 engines are often fitted with an inlet manifold that is smaller than the inlet ports for this exact reason.
For a 1725 engine with a standard Holbay cam I would use the standard Holbay manifold. If you plan to use a higher lift cam (like the Holbay E128) then it would be worth enlarging the inlet manifold ports to match the head.
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Edited by - 1922 on 19 Nov 2011 19:29:20 |
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Paul
United Kingdom
60 Posts |
Posted - 19 Nov 2011 : 02:08:55
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Absolutely right. The Holbay manifold won't mate directly with a standard head because the Holbay port sizes are smaller but there is a Deronico manifold which fits a standard upright head (Audax cars) and takes the twin 40DCOE carbs.
My Alpine won't float!  I need one which does!! |
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1922
United Kingdom
549 Posts |
Posted - 18 Nov 2011 : 21:05:57
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I think I remember someone posting on here that the Holbay ports are smaller than the standard - hopefully JSPH120 has his ruler handy
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Edited by - 1922 on 18 Nov 2011 21:06:57 |
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jabe1807
Norway
192 Posts |
Posted - 18 Nov 2011 : 20:46:42
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The inlet on my head is 33 mm diametre, the same as on a standard 1725 head. Manifoild is 27 mm.
My head is bought as a Holbay head, number 7437. Is it possible that my head is from an early production and therefore it is that big diametre?
I will measure the volum of the combustion chambers to see if there are any different from Holbay. I think the volum should be 29 cc (I will check that, I have correct volum somewhere).
I have bought a (nos) Holbay camshaft from UK. Hope I have got a correct one. |
Edited by - jabe1807 on 18 Nov 2011 20:48:04 |
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1922
United Kingdom
549 Posts |
Posted - 17 Nov 2011 : 20:28:47
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I don't know the diameter of the standard Holbay inlets ports - but I remember that they were much smaller than holes in the gasket. I think they matched the inlet manifold.
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janmarine3
South Africa
286 Posts |
Posted - 17 Nov 2011 : 18:14:43
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The cam should also tell a story... are you going to install a standard Holbay cam or do you know what cam comes with that head ? |
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JPSH120
United Kingdom
1180 Posts |
Posted - 16 Nov 2011 : 21:18:54
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This is a normal Holbay head;
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jabe1807
Norway
192 Posts |
Posted - 16 Nov 2011 : 20:55:15
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I will use the orginal Holbay exhaust (4-2-1). Have no oil cooler. I dont think H120 had one.
Are the combustion chambers different from holbay? I dont know if the inlet are bigger than orginal. What is the orginal diametre?
My inlet manifoid have smaller diametre than the head. Hope it will be correct combination.
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1922
United Kingdom
549 Posts |
Posted - 16 Nov 2011 : 20:14:19
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Interesting combustion chambers, and are those inlet ports larger than normal?
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janmarine3
South Africa
286 Posts |
Posted - 16 Nov 2011 : 04:39:19
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wow ! cool....what exhaust system are you going to use and will you use an oil cooler ?
Jannie. |
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jabe1807
Norway
192 Posts |
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Topic |
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H120/ Holbay Replica
1807/P10102112.jpg, 
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