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  • 530/531 head porting and polishing

I'm going to wade into this for a build that will ultimately be a 530 or 532 head with 38mm/46mm valves.

I'd been considering a 530 for its higher CR but research suggests the flow benefits of the 531 head will outstrip all other considerations.

Should I port with the valve guides removed, or leave them in? I'm replacing them either way.
I recently did a bit of work on my 531 head. I left the ports alone as I'm keeping standard sized valves, but deshrouded the plug and exhaust valve a few mm, smoothed the t-stat housing out and drilled the Group - A coolant holes in it. It's not answering your question but I had a look at Grottis' heads, and I found this useful:

That is interesting, thanks. I have a couple of 398 and 150 heads I'm planning to practise on. The Group A coolant passages are a neat idea and seem pretty achievable. I could even go all Clickspring on it and file them to the correct profile for the HG
I'll be doing some flowbench stuff in the not too distant future with a 38mm exhaust 531 head.

I'm not convinced on the need to drill holes into the head for coolant flow as its like opening up a thermostat, but i won't know until i compare directly between Sam's motor and my one with a infra-red temp guage. Based on my 122 with two temp sensors, one at each end, the difference in that is 5* at any time.


http://www.pbase.com/towerymt/531

A decent looking ported head by towerymt, there's a few threads on tbricks covering it too. Of course without testing, you may just cause stalling.

For the size of the intake port on an na motor, i hope you change from the stock intake, but there isn't that much to do to gain a lot of flow as such on a 531 with the casting shaped for fluid flow.


Vee_Que;c-147217 wroteFor the size of the intake port on an na motor, i hope you change from the stock intake, but there isn't that much to do to gain a lot of flow as such on a 531 with the casting shaped for fluid flow.
Something like a plenum? I'll probably buy or make a better plenum eventually but one thing at a time.
jamesinc;c-147208 wroteThat is interesting, thanks. I have a couple of 398 and 150 heads I'm planning to practise on. The Group A coolant passages are a neat idea and seem pretty achievable. I could even go all Clickspring on it and file them to the correct profile for the HG
The Group A mod also involves blocking one of the water pump / head water outlets, so that the coolant flow through the head is reversed. The mod results in an increase in cooling around #4. If you have a copy of Richard Prince's "Group A Owners' Manual", IIRC he has details of it there. Or have a chat to Scott, The Rev Doctor, up in Hornsby, who did a lot of Richard's engine work (and peddled it pretty well, too, especially at Bathurst).
bgpzfm142;147235 wroteThe Group A mod also involves blocking one of the water pump / head water outlets, so that the coolant flow through the head is reversed. The mod results in an increase in cooling around #4.
I'm not sure I follow here - the coolant in the head already flows from rear to front, drilling the different sized holes in the head just very slightly biases the cooler coolant towards the rear. Is the blocking of the water pump/head outlets that you are referring to the heater bypass that was done?
Awesome! Thanks for clearing that up.
I'll be doing some flowbench stuff in the not too distant future with a 38mm exhaust 531 head.

Keep in mind they don't run a heater either.
James have you got the picture from turbobricks where some guy sectioned a 530 and 531 down an intake port? Might be of value to you.
So from the looks of it, on a 531 head, here are the inlet side areas to remove:



Note: I think the material removal around the valve guide should be less than pictured - from another angle you can see that in a 531 head that area has some contouring added to promote swirl, so it's probably better to leave that shape intact and just clean up the casting.

Exhaust side:


The exact amounts will have to depend on gasket matching and the new valve seats, but it seems like for the most part the key processes are:
  1. Remove the sharp radius in the exhaust port
  2. Remove the lumps from the intake port and clean up the radius a bit
And more generally:
  • Polish the exhaust side
  • Remove casting marks and any sharp edges
  • Apparently, once the head is surfaced, it's a good idea to knock down the sharp lip around the edge of the combustion port as it can create hot spots for detonation.
Apparently not a good idea to open up the head side exhaust port to the gasket size
Samman88;c-147258 wroteApparently not a good idea to open up the head side exhaust port to the gasket size
If memory serves, it's a pretty close match to the gaskets already. Do you know why it's not a good idea? Just not much metal before you hit coolant passage or something?
Also wondering what the correct order of operations should be. I would think, because there's risk of damaging the valve seats, the best thing would be to port the head first, then have it machined for the larger valves.
It might be a myth but supposedly helps with exhaust gas reversion.
Going to remove the hot spots off your spark plugs? ;)

Don't do what I did and skate the die grinder across a freshly machined head!

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