This is a complex one assuming we have one carb throat for each cylinder of the engine Should the whole tract be one size for optimum power.Should the port in the head be 32 mm for 32mm choke size Same for manifold Ideas please. Its not my forte.

Ian B , not my forte either , but i will at least give you some thoughts. I believe it is the relation between DCOE size ( presuming weber/dellorto since choke mentioned) and the head type/chamber size shape. so no i don't think 32 carb throat must match a 32 port entry... from my reading and limited experience with 1275s, there is a gradient to the port to increase speed flow.. so say 45 at butterfly, 38 at choke and maybe 35 at port mouth.... in my estimate the true porting 'skill' is getting cross sectional areas just right for the valve sizes and reducing short side radii... ... sounds good... but far too clever for me to do, so i leave it to those far more experienced

Pure coincidence that my engine has 36mm venturis in the 45DCOE, 36mm ports and 36mm inlet valves. I think the manifold is also 36mm. However the port shape around the valve guide and the short radius is probably more important. And it was all done by to match the capacity, chambers and camshaft, compression was made to match the whole setup for 98RON fuel. 127hp and 113ftlb from 1411cc.

So two answers give differing observations. You are right that it is complex, and unless you have been personally developing porting, fueling, cam solutions, i don't think you can weigh in with confidence. There are a few regulars on here who do just that, and have been for a long time, so i would also defer to their combined wisdom.

cheers
michael

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the world is a book, and those who do not travel read only a page
66 Mini Minor sponsored by http://www.lifeonthehedge.com.au/ The Dog Harness Specialists
It was a pleasure ausmini. I'll miss all you misfits and reprobates

Thankyou gents .I await hopefully from what those that have flowbenches etc that I don't have to add.
Yes I can appreciate that going from smaller to larger cross sectional area would would reduce speed and filling of the cylinder.
My cooper s has a head with too large ports and it has lost a lot down low Yes I read the Vizard book and the ports were done to visually impress me lol.Rev it hard and it goes like stink 1310 1.5 rockers 286 kent cam and twin 1.5 su with slightly modified BF needles to get it right off idle and red springs.
Next project is 7 port elder with GR cam and stroker in a nice metallic red clubby.

My 1360's head setup is much the same- 45DHLA Dellorto, 36 chokes, manifold and inlet ports 36mm, and 36mm valves.
Michael and I are also running the same cam (RE282 sprint). I'm also running 1.5 rockers.
One head difference is the chamber shape- my head was bathtubbed (for turbo?) by someone in the past. I then decked it to reduce the chamber volume for 11.0:1 C/R.
[edit] I'm also running 31mm exhaust valves in this 940 head (was cheaper than fitting seat inserts, 15 years ago).

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Again not my forte , and always wanting to learn. What were the standard head(s) port sizes, eg was a12g940 with Cooper S valves different from others?

and also i have noted quite a bit of variability in the inlet manifold diameters in aftermarket manifolds (eg a cannon i have is large cf redline.. both shorties approx3.5 inch)

Mick i'll have to go and measure my race set up.... you have got me curious. weber 45, 40 chokes ,, but not sure of ports.. running 36 inlet and 31exhaust valves

I had 38 chokes in mine when it made 86.6HP ATW (on MRC's dyno) back in 2007, it is more driveable with 36s now and I don't feel the top end has suffered.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Thanks Doc The reason im looking at this is that Ken suggested that his heads were to suit small and large bore. Mines a 7 port that got stolen of GR by a scumbag but GR delivered another Graham is so busy and I think had to shelve this for now
I intend running two 40DCOEs and I notice two little black texta marks on one intake port that may have suggested an intention for a couple of mm increase in port size.
With the volume of work, the phone calls all day I don't think he ever got to continue with it but he is doing a cam for me and im never in a hurry running my own business and lifes problems.
Motor will be 1412 with Elder crossflow Grahams cam something like a 282
Appreciate all help Thanks for the replies Ian

Are you going to use an elder 8 or 7 port ? In an 8 port it is slightly easier (than a 5 porter or even a 7 porter as the exhausts have a very odd interaction. ) to give a ballpark number of what you need minimum CSA wise. It is still very tricky though.

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no time to finish me bleedin car ..
1982 Blue-White Roof.

http://aseriesmodifications.wordpress.com/

I am looking at inlet ports and its a 7 port.
I can see a reduction in CSA between the 32mm DCOE chokes and the inlet manifold and inlet ports
It makes me wonder if it will be a bottleneck

I'll go out on a limb and say unlikely. Only when it would be quite a severe pinch (causing flow separation) and/or it would actually be the point with the min CSA on most heads this is the choke at the valve.
. easier to take of metal than to put it back
A flowbench and a port mold would be the place to start imho but as GR knows these heads it would just be like reinventing the wheel

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no time to finish me bleedin car ..
1982 Blue-White Roof.

http://aseriesmodifications.wordpress.com/

Just to give an idea of the complexity of this discussion for all of us keyboard engineers, have a read of this article about the valve seat angles alone. They concentrate on US engines, mostly drag racing, but is still relevant to an A-series head.

http://www.enginelabs.com/engine-tech/cam-valvetrain/valve-seats-will-50-or-55-degree-angles-work-for-your-engine/

Thanks to M1100 for the link.

cheers
michael

_________________
the world is a book, and those who do not travel read only a page
66 Mini Minor sponsored by http://www.lifeonthehedge.com.au/ The Dog Harness Specialists
It was a pleasure ausmini. I'll miss all you misfits and reprobates

Think about the forces that hold your flywheel on or a ball joint in place and then think about trying to open valves with a high degree valve seat. Every time the valve opens you are trying to break a tapered fit. It is madness!
Unless of course the HP figures are there.

Back in the old days, Holden 6 grey motors ran 30deg inlet seats. Ostensibly for better flow, but I dunno.. they weren't renowned for HP output. An FJ Holden barely made more than a 1942 Willys Jeep side valve 4, of similar displacement.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Thanks guys and I take on board the vizard stuff the port isn't the restriction in a 5 port.Its the bowl the radius and the valve shape and seat .OK maybe I just taper it smoothly to the intake ports on the head and leave well enough alone that Im not sure on.But it sticks in my head lol why have a 32mm weber choke when the ports are smaller .
AAaaarggh lol