gas flowing your own cylinder head


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Astra SRI
Not sure if this is the right place for this thread, if not maybe one of the moderators could advise?

I read a magazine article quite a while ago written by David Vizard about making a flow rig to compare flow rates through a cylinder head; before and after working the ports
I built such a rig and after a few teething problems got some encouraging results, Just wondered if anyone else saw the same article and bothered to build one? if so how did you get on?
The basic principle is to pull air through the head at various positions of valve lift then have a way of measuring the flow.
Do this with a stock head (bearing in mind what cam you intend to fit) then start working the head a little at a time and repeat the process.
You need a box which replicates the cylinder with a tapping one side attached to a manometer tube and the other side attached to a domestic vacuum cleaner, with the valves fully, closed turn on the vacuum and record the water level (this level sets the start for all subsequent tests) then progressivly open the valve in stages (50 thou at a time) upto or slightly over full lift and record water level at each stage.
Work the port and repeat the above, improvements in flow should result in lower figures at each stage.
Once the first port is as good as you can achieve you will have a pretty good idea what the optimum shape is and where best to remove material.
It's not quite that simple,

What vyou nhave to bear in mind is how to replicate actual airflow into a cylinder and out of it with an intake and exhaust manifold attached as they have a big affect on how it happens.........
The box I described does exactly that, vacuum on sucks air through the cylinder head as you open the valve, I agree it will be the wrong way round when you do the exhaust port but as Mr Vizard explained the exhaust side is less important than the inlet as you just need to get rid of the burt mix.
Intake and exhaust manifolds are already done for you if you buy decent after market items, perhaps with the exception that you may want to match them to the head first.
the only thing missing is you can not measure actual flow rates, but you don't really need them, all you need is to know whether you have improved flow or not and this does it quite well in my opinion.

HDi fun made a good point about going too far and hurting flow, the only way I can see of overcoming this is to use a head as a sacrificial head and just keep going untill it goes the wrong way then scrap that head and start with a fresh one with the knowlege you have gained then stop when you get the right readings.
None of this will be as good as professionally done head by someone with years of experience and the right machines, but I think you will get close for the cost of a second hand head and some playtime in the garage. as oposed to hundreds of pounds for a longman head or similar.

Tried it on an C16SE Vaux head and so far have improved flow by around 15% over standard acording to my figures. my intention is to have another go this winter and then try it on the Race motor and see what the rolling road says.
Just read both these articles sid, good stuff will try some of the rules and see how I get on.
wrote another reply last night but it went to the moderators before posting, bit long winded but may see that on here as well.
you post got moderated as it contained links (when you quoted sids post) after another 5 posts you wont have issues with link pics etc

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