Author Topic: Cylinder head - inlet port shape  (Read 1229 times)

Offline Jeffers

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Cylinder head - inlet port shape
« on: 10.11. 2009 11:09 »
Hi,

Having stumbled on the Forum a few months ago I've been inspired to restore my 1960 A10 which I've owned for 20 years but has not seen tarmac for the last 7. Knowing that the original cylinder head was going to require some serious work I bought a replacement from ebay which was reputed to have been overhauled by SRM.

The guides, mating surfaces etc all seem good and I checked that the casting number (if that's the correct way of identification) matched - 1066. Everything measured up well until I looked down the inlet port. On the original head the inlet splits to the two cylinders with a smoothish V shape but on the replacement head there is a flat face as you look down the inlet, more a paper cup profile if you know what I mean, which then splits to the two cylinders.

Can anyone tell me whether this is significant and which of the two is correct?

Thanks

Jeffers

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Re: Cylinder head - inlet port shape
« Reply #1 on: 10.11. 2009 18:46 »
G'day Jeffers, welcome.
                               It should be V shaped as your original. Does it look like it has been ported ? I would imagine the flat will slow down induction and create turbulance meaning less performance. Once installed you will need to check for induction bias ( one plug lean, other rich ).
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Offline Jeffers

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Re: Cylinder head - inlet port shape
« Reply #2 on: 10.11. 2009 21:29 »
Thanks for the quick response Muskrat - that's what I feared. The flat area is so regular and clean that I thought it must have been as designed. There's no sign of any other porting.
Hey ho - back to the drawing board then but it's better finding out now.

Offline A10Boy

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Re: Cylinder head - inlet port shape
« Reply #3 on: 11.11. 2009 00:08 »
Don't be too hasty there.

Maybe it would be wise to check this out first, it could be that the flat area has been introduced deliberately to create swirl to keep fuel in suspension. I read about this sort of thing in an old book yonks ago, it could be designed that way.
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Andy

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Online Triton Thrasher

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Re: Cylinder head - inlet port shape
« Reply #4 on: 11.11. 2009 08:05 »
there is a flat face as you look down the inlet, more a paper cup profile if you know what I mean, which then splits to the two cylinders.


Thanks

Jeffers

I don't understand that description at all.

A flat surface on the inside of a curve is supposed to improve flow.

Aren't you tempted to try it to see how it goes?





Offline Jeffers

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Re: Cylinder head - inlet port shape
« Reply #5 on: 11.11. 2009 16:30 »
Thanks for the comments A10 & Triton. Probably didn't describe it well but as you look down the inlet the V shape where it splits to the two cylinders has a flat area approx 1/2" square machined into the pointy end of the V. It looks like a professional job if not the original design.

I did some rough measurements this morning and the distance from the end of the manifold to the flat area is almost identical to the same measurement to the point of the V in the original. The manifolds are the same length so this suggests to my untrained eye that it hasn't just been machined down but must have been cast this way. Is that likely?

Because it was an ebay purchase I don't know whether the seller had some idea it was not standard. I'm a couple of weeks away from fitting it all together but as I've spent a fair bit of time cleaning the head up I'm going to follow your line and give it a go. Maybe it'll give a few more bhp!

Offline LJ.

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Re: Cylinder head - inlet port shape
« Reply #6 on: 11.11. 2009 17:13 »
Jeff... Any chance of a picture of what you describe? A picture is worth a thousand words as they say.
Ride Safely Lads! LJ.
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Re: Cylinder head - inlet port shape
« Reply #7 on: 12.11. 2009 07:48 »
So, has someone increased the inlet size on a milling machine and put the cutter so far in that it's made a flat circle where the manifold divides?  Sounds like bad practice, but that doesn't have to mean there's a problem that you'd notice.