24 replies to this topic

[fatmini]

firstly whats a port ? and how does it effect the engine/head

secondly why is a 7 port a easyer option than a 8 port ?

whats the diffferance onther than 1 port ?


i did do a search but am still none the wiser

cheers

[The Matt]

A port is the section of the head where the fuel/gases flow in and out of the engine. They are effectively the big holes in the head.

A mini engine is 5 port, two inlet ports and 3 exhaust ports (all at the back of the head, where the manifolds attach). The A series engine is quite odd in this sense. The two centre cylinders share the centre exhaust port, the two outer cylinders have an exhaust port each, the first and second cylinders share one inlet port and the third and fourth cylinders share the other. It's a pretty funky design really. The majority of other 4 cylinder cars are 8 port.

An 8 port head (the likes of Arden) has 4 exhaust ports at the back of the head and 4 inlet ports at the front. So, you can run different fuel systems, exhausts etc. With an 8 port you have to run a specific camshaft. To fit an 8 port head is a costly affair, probably IRO £3K all in I'd say. You also have to have a special made exhaust manifold. EDIT: The camshaft has to be a special profile because the valve locations are different (on a normal mini head the valve layout is exhaust-inlet-inlet-exhaust-exhaust-inlet-inlet-exhaust, on an 8 port head, I don't think they are 'paired' because they do not share any ports).

7 port heads retain the exhaust manifold at the back of the head, so you can use LCB's, 3 into 1's etc, but they have (well most common examples) 4 inlet ports at the front of the head. You can then use the normal mini bolt on bits (LCB's, normal camshafts etc.) and slap a pair of Weber 40's on the front. This is why some people prefer to use a 7 port head. You can buy a 7 port head for IRO £1K, you can run camshafts and exhausts that are standard mini items. You just have better fuelling options.

[fatmini]

the penny drops !! lol thanks for that !! on this note will it fit under the bonnet with no mods to the bonnet ?

ive seen a grey mini on here some where with a 16v conversion .which has the best modded bonnet ive seen can any 1 tell me who makes it and post a pic please !

[who_loves_the_mini?]

whether it fits all depends on what fuleing system you go for. You can get webbers to fit under a round nose but i believe you will loose slight power as the manifolds are very short. With a clubman front you would get slightly more room for carbs. Injection may be able to fit under a standard front but this all depends on air filter choice

[Dev]

How big is your wallet?

If you go for the 7 port (usually a minisport design) remember that Bill richards can do you an 8 port for less that will be better.

[who_loves_the_mini?]

If you go for the 7 port (usually a minisport design) remember that Bill richards can do you an 8 port for less that will be better.

how much does Bill Richards charge for 8 ports? If you bought a bare casing and had the head sorted by someone other than minisport, ie MED, morspeed etc, you could get a 7 port for £1500 or so

Also has anyone done any research into how much better the 8 port is than the 7 port?

[fatmini]

twin 40's manifolds will be to short will they ? how can u get longer 1's then ? i know nothing !!!lol


ps : wallet is 210mm x100mm x 40mm

Edited by fatmini, 11 May 2007 - 01:17 PM.

[who_loves_the_mini?]

you can get a variety of webber manifolds depending on what you after. You can get, 3, 5, 6 and 7" manifolds and maybe a few more but not certain

Webbers work better with longer manifolds so you may end up either sacrificing power, if you went with a shorter one, or cutting a whole/having a bulge in the bonnet if you went for long manifolds.

[fatmini]

cheers ive been told in the past manifold length will effect ur torque more than anything ? probly rubbish ?

what sort of power upgrade will this mod create mini sport says 20% ?

[The Matt]

The thing with the manifold length:

On a normal A-series engine, the inlet ports are spaced further apart than the two chokes of the carb. The longer and straighter the inlet manifold is, the less this effects the fuel in the siamese ports. Effectively, you are letting the mixed fuel/air in on less of an angle with a longer manifold. Have a look at the manifolds on some 5 port minis fitted with Weber carbs and you'll see what I mean.

On an 8 port or 7 port head, the carbs are more in line with the ports. You have one choke per inlet port and the heads are designed to be fitted with twin choke carbs. I can't remember where I read this, but I think there is a 38DCOE that is supposed to be ideal for them because the spacing is perfect. (Don't quote me on that as that may have even been for the BMW K conversion kit).

It's all about how restrictive the inlet system is and when the carb choke is directly in line with the inlet port, you've got a much better start point than with the siamese inlet design of the A-series.

Vizards good book covers all of this I think, well, the bit about the inlet restrictions of shorter manifolds. In effect, I believe that with a shorter manifold, the two centre cylinders don't get as much flow as the two outer cylinders.

[Dev]

The casting costs about 1500 from mini sport. BRR will build you a "pukka" (to use Bill's words) 8 port for that.

Put it this way i would let Bill build me an 8 port, i wouldn't let Minisport build me a seven.

Also why go 7 when you can go 8?

PS not having a downer on minisport, as i get lots of stuff there i just wouldn't build my engine there.

[fatmini]

ok cheers for the advice ill pass it on

[who_loves_the_mini?]

£1500 gets you a full race 7 port, bare casing is £1k. Id buy the bare casing and get someone to machine it to my spec, would work out to be the same price but you'd have a better head at the end of it.

http://www.minisport...ve-product.html

Im not saying the 7 port is better as i havent had any experience with that or the 8 port but i doubt you'd be able to build a 8 port for the same price or cheaper than the 7. If someone knows how much power the extra inlet provides on the 8 port it would be great

[miniboo]

as for fitting it under a mini bonnet you will be very luicky as you have a minus so if you thinking of it for this then NO it wont fit.

lots of bulges will be required

[fatmini]

yeah thought that was the case ,have u seen any off the shelf bonnets that will accomidate it ?