Posted 01 May 2020 - 03:37 PM
Can someone point me in the right direction to discuss a Mini 1300cc, 8 port head? I want to understand what the implications/changes that might need to be done ( if any) to the engine I have already built. Many thanks!
Please contact me via DM.
(Modified by Admin, please do not put your email out on the open forum. Thankyou)
Stage One Kit Fitted
Posted 02 May 2020 - 07:01 AM
Mike,
Posting your email address on a public forum is a recipe for getting spammed. Whether mods allow it or not I would advise against it.
The forum has provision for private messaging between members which negates the need for posting email addresses out in the open but why not for a start discuss your interest in 8 ports in the technical section as this is what a forum is for? The topic will interest many I’m sure.
Whilst the complexity of fitting an 8 port on a 1275 isn’t exactly rocket science it isn’t exactly straight forward either as it requires a special 8 port cam. Much attention should be paid in achieving enough clearance between the conrods and this cam, as of all factory rod only the (small journal) cooper s rods leave enough space. Many use aftermarket rods nowadays which also allow big journal cranks to be used. Saenz rods are about the nicest and lightest set of rods available (SH engineering) , but MED, Swiftune, and Minispares also do some nice alternatives.
With rod clearance solved you need to turn the eye to desired compression ratio. The later Minispares incarnation of the Arden 8 port head has increased deck height to allow running sensible CR on big bore 1275 CC and larger engines. The original castings as intended for smaller bores don’t leave much room to do so. Anyway, in addition to rods now is the time to carefully select pistons with the right dish, machine the block to the right deck height to carefully arrive at the right compression ratio (the arden head being alloy it favors higher CR than an iron head).
Now you also need special push rods at 8 port lengths and I am sure the rocker assembly needs some careful setting up as well. Oh and of course you need a 4 branch exhaust manifold.....as you can see the costs are rising and we haven’t even talked induction yet!
The classic way is going Amal, which are motorcycle carbs. A pair of webers is also seen but imo aren’t much suited as they stick out way too much AND need wonky inlet manifold geometry to make it all fit the tight spaced inlet ports. Injection is the sensible modern alternative especially since an 8 port is much more suited for injection than a 5 port since there’s no charge robbing between cilinders as with siamese ports. This then needs trigger wheels, sensors and an ecu of course....
Up Into Fourth
Posted 02 May 2020 - 08:11 AM
The morning after the Christmas Motor Club Dinner, I have an "8 Port head"
One Carb Or Two?
Posted 02 May 2020 - 10:05 AM
Mike,
The topic will interest many I’m sure.
Whilst the complexity of fitting an 8 port on a 1275 isn’t exactly rocket science it isn’t exactly straight forward either as it requires a special 8 port cam. Much attention should be paid in achieving enough clearance between the conrods and this cam, as of all factory rod only the (small journal) cooper s rods leave enough space. Many use aftermarket rods nowadays which also allow big journal cranks to be used. Saenz rods are about the nicest and lightest set of rods available (SH engineering) , but MED, Swiftune, and Minispares also do some nice alternatives.
With rod clearance solved you need to turn the eye to desired compression ratio. The later Minispares incarnation of the Arden 8 port head has increased deck height to allow running sensible CR on big bore 1275 CC and larger engines. The original castings as intended for smaller bores don’t leave much room to do so. Anyway, in addition to rods now is the time to carefully select pistons with the right dish, machine the block to the right deck height to carefully arrive at the right compression ratio (the arden head being alloy it favors higher CR than an iron head).
Now you also need special push rods at 8 port lengths and I am sure the rocker assembly needs some careful setting up as well. Oh and of course you need a 4 branch exhaust manifold.....as you can see the costs are rising and we haven’t even talked induction yet!
The classic way is going Amal, which are motorcycle carbs. A pair of webers is also seen but imo aren’t much suited as they stick out way too much AND need wonky inlet manifold geometry to make it all fit the tight spaced inlet ports. Injection is the sensible modern alternative especially since an 8 port is much more suited for injection than a 5 port since there’s no charge robbing between cilinders as with siamese ports. This then needs trigger wheels, sensors and an ecu of course....
That's making the BMW K1100 head sound like a really good, straightforward idea.
Stage One Kit Fitted
Posted 03 May 2020 - 03:14 PM
The most straight forward is 7 port which is basically a bolt on mod. You can use any 5-port cam giving access to a wide range option ranging from mild to wild, your normal 3 branch lcb is a straight fit as well. On the induction side most 7 ports feature dcoe type flanges allowing a straight fit of a wide range of throttle bodies or trusty old carbs.
A 16V BMW K conversion isn’t a straight bolt on as it requires a different lay out of head studs for a start. Again no rocket science, but like the Arden build, this requires some advanced level engine building techniques and machine work. The head also requires extensive welding and machining to make it ready to mate with the modified A-series block. Add some pulleys / idler bearings for the cam drive in addition to external oil routing and revised cooling flow path as well as a dedicated 4 branch exhaust manifold and again you have quite a project on your hands. SC can of course offer ready to be assembled kits which makes the task so much easier, but in theory also more costly.
For fast road in honesty there isn’t much between 7-port or 16v as far as outright performance goes. The latter is truly in a class of its own when extensively ported and running race cams allowing 170HP+.....this requires revs to be made though so be sure to invest in all steel bottom end in order for everything to hopefully stay in one piece.
Edited by evoderby, 03 May 2020 - 03:15 PM.
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