Port sections

ChrisJC · Post by **ChrisJC** » Wed Sep 17, 2008 7:08 pm

I cut a cylinder head up with a hacksaw last night:

Chris.

Pocket rocket · Post by **Pocket rocket** » Wed Sep 17, 2008 9:22 pm

ChrisJC wrote:I cut a cylinder head up with a hacksaw last night:
Chris.

Bl**dy vandal

bodger · Post by **bodger** » Wed Sep 17, 2008 11:55 pm

thats not a bad port shape as STD really , i have seen a lot worse

Ian Anderson · Post by **Ian Anderson** » Thu Sep 18, 2008 7:11 am

Bet it's a bugger to get that to seal again!

sidecar · Post by **sidecar** » Thu Sep 18, 2008 8:04 am

Cheers for the pics, very interesting!

You can see on the exhaust port how it actually gets bigger in cross section then smaller again, I bet the most of the people that gas flow them remove material from the roof near where the exhaust flange joins the head so that the top and bottom of the port is diverging not converging.

I'm planning to make a set of headers for my lump at the moment and have noticed on my scrap engine how the exhaust ports are not at 90 degrees to the gasket face of the flange, is makes things a bit more of APITA. (My headers need to go up not down to get over the steering column

)

Pete

kiwicar · Post by **kiwicar** » Thu Sep 18, 2008 9:01 am

You can see why the heads respond so well to opening out behind the valve seat and to waisted valve stems. And also why only on very thoroughly worked heads do you open the inlet runners!

.
Mike

RoverP6B · Post by **RoverP6B** » Thu Sep 18, 2008 10:04 am

Hello Mike,

I must be a bit dim, but why do you only open out the inlet runners on heads that have been extensively worked?

Why would you not open the inlet runners only and leave the rest of the head as original?

Thanks in adavance

Ron.

ian.stewart · Post by **ian.stewart** » Thu Sep 18, 2008 10:41 am

Exhaust gasses, as an expanding gas will need more area to get from the engine, inlet gasses, port them too much and the gas speed drops and atomisation of fuel starts to drop from the Air/Fuel mixture wetting the bores rather than staying in the flow, its another reason why a good head should not have the inlets polished untill you are right at the top end of performance, even this is doubtful, as the rough surface makes an turbulant surface and keeps the mix together,
My question is, what are the heads, SDI P5/6 or later 10bolts

ChrisJC · Post by **ChrisJC** » Thu Sep 18, 2008 11:00 am

I believe the heads are either Range Rover or SD1 EFi heads. They are definitely 14bolt.

You're gonna tell me that I've chopped up some rare head now!!

Chris.

ian.stewart · Post by **ian.stewart** » Thu Sep 18, 2008 11:03 am

No, I was just curious, I would love to compare them with the later 10 bolts, just to get an Idea of how much can be taken out

RoverP6B · Post by **RoverP6B** » Thu Sep 18, 2008 11:10 am

Hello Ian,

Thanks very much indeed.

Ron.

ChrisJC · Post by **ChrisJC** » Thu Sep 18, 2008 12:55 pm

Well if somebody has some 10-bolt heads, I'd be happy to cut them in half!

I doubt if there's any difference though.

Chris.

kiwicar · Post by **kiwicar** » Thu Sep 18, 2008 1:51 pm

As Ian said, also keeping the port velocity up delays flow seperation on the region where the flow starts to turn to go into the cylinder, the flow on the inside of this turn can become highly turbulent effectivly producing an area of very poor flow rate, net result you make the runner bigger and it flows less.
Mike

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Port sections

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