Siamese intake ports 1

[EngJW]

Hello,

A week or two ago there was a thread where someone posted a good link to an article about siamese intake ports. Well, I have been searching here for the thread and also with Google, and can't find it. I wouldn't ask, but I have seen threads disappear before. Anyone know where it is? Sorry, my memory doesn't work too well anymore.

Thanks,
John Woodward

 

[kradicke]

John,

This was the link I originally posted:

http://www.planet.eon.net/~chichm/efi/siamese.htm

The page is specifically related to the difficulty of setting up EFI on an engine with siamesed intake ports.

Kai

 

[EngJW]

Thanks. Don't know why I couldn't find it.

According to this article, with a firing order of 1-3-4-2 (or written as 2-1-3-4), the inner cylinder starts its intake stroke first and gets to draw from the manifold, while the next cylinder, the outer one, has to draw from a port that is already flowing into the inner cylinder. Thus, the inner cylinders run rich and the outer cylinders run lean.

A few years ago I worked on a V4 with the same 1-3-4-2 firing order, except 1 and 3 were paired on the left bank, 2 and 4 on the right. It always appeared that the temperatures were higher in 3 and 2, which should be the lean cylinders according to the above. We also scuffed pistons in these cylinders.

It makes more sense to me now.

John Woodward

 

[derekwhite]

I never thanked you for that excellent link Kai. Thanks! If I put the EFI on the A engine I'll probably grind a custom cam so that I can use the exhaust ports for inlet to get around this problem with simple batch injection. How big can the 1275 "A" exhaust valves go? I could never understand why so many earlier engines had more exhaust ports than inlets?? My Austin Sevens also do and I'm thinking of doing a cam that reverses this for them too.

Cheers, Derek

 

[evelrod]

Derek, I am using 31mm (1.216&quot EX and 36.6mm (1.445&quot IN valves in the 1380cc A+ engine in my '63 Austin Cooper.
I am using APT rimflow valves and have had no problems in the 5 or 6 races on the engine. So far so good!
I am using one of the Kent 'scatter pattern' camshafts, LCB headers (2 inch out the back, no silencer), 13.4 CR and, 45 DCOE.
The reverse port thing has been tried with less than stellar results (it's still a 5 port head). No sense reinventing the wheel. Go for broke and buy one of the 8 port crossflow heads and you solve any "top end" problem (rules permitting) so you only need to deal with the 3 main bottom end!!!

Vizard hashes all this out in several books and a call to APT, Mini Mania or, Mini Spares will get you any practical stuff as well as a complete parts supply.
Give me you email if further info is needed.

Rod

 

[EngJW]

Rod,

With reversing the ports, is there ever a problem with putting twice the heat into one port? Also, the siamese port may not be cooled as well.

John Woodward

 

[evelrod]

Hi John. I haven't had anything to do with the reverse port head layout, just did a little reading/research when I was contemplating the insanity of building another "A" engine (last was a 'bugeye' back in the '60's). The best I could find was that they were attempting to increase the intake flow which probably worked (???) but that left two ports for the four exhaust valves. I have a hard time with that concept and apparantly so did they as it failed to approach the stock arrangement in hp output. The rules I race by restrict me to the stock cast iron head with the original 5 port layout. The little 1275 is making about 140hp in top form and the 1380 a bit more. Mine is making about 130hp at 6725rpm from 1380cc. I know that is not earth shattering but is pretty good for a siamesed port intake and a 3 port exhaust.
As to heat in a siamesed exhaust port system---don't know (no problems with it in the mini yet) but it was common in many engines not the least of which were all those Ford flathead V8's and the duplexed ports on the stock cast ex manifolds of SBC and early Olds, Cads etc.
I would definitely use one of the alloy 8 port designs if the rules allowed it. Cost is not a factor as the modified iron OEM heads are $1400 at APT (that is why I did my own)!

Rod

 

[EngJW]

Thanks Rod,

We have an air cooled V4 with siamesed ports, and every now and then someone proposes reversing the ports. I suspect that any problems with the induction flow would be just transfered to the exhaust. Also, our siamese ports do not have as many cooling fins as the exhaust, so I think we would have a tremendous heat problem, and our exhaust ports are hot enough as it is.

John Woodward