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Last edited by tickford_6 on Thu Jun 13, 2013 9:48 pm, edited 1 time in total.

Hey TICKFORD brah.

Do you, or I, (or both) want to start editing up a document out of all of those information sources? I need to find a place to live, and the (X)missus is starting to spew on me still being here, so I gotta get busy with other stuff... Still, if it's still like this when I do have plenty of time I'll start compiling some bits, if you do some other bits...?!

i can help put something together. will have no time for about 3 weeks though

Some good links there tickford_6, awesome idea for a thread too

Depending on how far i get on with this 91AA head im working on, i might do a bit of a write up like WagonDad has done with heaps of pics.

Heres an image Fiend edited a while ago which was from one of those porting threads.. Has had the 3 pictures in that thread blended into one picture to make for easier viewing

Hey guy’s this is something I wrote up on the Perth Falcons site.

I have done a lot of research and this is my interpretation from many different sources, strangely enough they have worked at least on the flow bench.

I don’t know about port sizing for a specific cam but the work I have done has netted good flow while maintaining the correct port velocity for a hot street engine, I am running the Wade 1636. Port size is largely dictated by valve size and the rev range your motor will spend most of its time at, for a street driven car this is around 2000/3000 rpm this is good because our 4.0L engines produce most of their torque in this rev range.

Port size to valve ratio, I looked at the port as having five parts.

1 - The throat - This is the area directly below the valve also called the minor diameter. On the intake the minor diameter needs to be around 88 to92% of the valve, so for a 47mm valve this should be 41.3 to 42.3mm, mine ended up 88% 41.3mm. For the exhaust the ratio should be 85 to 87% so for a 41mm valve this should be 34.8 to 35.6mm, mine ended up 85% 34.8mm. It is very important to maintain the minor diameter on the exhaust as this creates a venturi helping to pull air out of the cylinder. I kept both these ratios at the lower end of the scale because our engines are not high revving with relatively low lift cams. The minor diameter should be the smallest part of the port, everything after this point should be as consistent in cross sectional area as possible, with some exceptions.

2 – The bowl – This is the area directly below the throat opposite the short turn radius. This area can be slightly larger to create low pressure area to draw air in on the intake and pull air out on the exhaust. On the intake I didn’t do much work here other than to clean up the casting and machining marks and blend the bowl into the throat. With the exhaust it was pretty much the same but again making sure the throat/minor diameter remained at 85% of the valve diameter.

3 – Short turn radius – This is the area directly below the throat opposite the bowl. On the intake this is the area where I gained the majority of my flow with the second flow test, the 4.0L head has quite a well shaped generous short turn, I started by laying the short radius back effectively moving it further back into the port, what this does is increase the diameter of the radius making it flatter allowing the air to stick to the port wall and not separate/delaminate and cause turbulence, it is important to have the last 5 to 8mm of the radius coming onto the throat as close to right angle to the valve as possible, this straightens the air out as it hits the back of the valve giving a more even spread of air around the whole valve diameter which in turn gives better fuel distribution in the cylinder. Next was to widen the short turn at the 10.00am and 2.00pm positions almost creating a flat floor or D shaped port, what this does as with laying back the short radius opens up the cross sectional area around the valve stem and guide, effectively giving back the cross sectional area taken up by the valve stem and guide. You can also widen the sides of the port either side of the valve guide to achieve the same thing.
With the exhaust the short turn is not as generous, you cannot lay it back or remove any material other than to smooth out casting and machining marks. The exhaust port is not straight like the intake, it heads of to the left and then straightens up, most of the work I did was on straightening this kink out, now the water jacket is somewhere behind this bend so caution is advised, I removed about 2mm of material and also as with the intake removed material from the 2.00pm area to flatten the floor a bit creating a bit of a D port.

4 – Mid port – I didn’t increase the mid port size at all other than to remove casting marks, this was mainly to maintain port velocity. Intake ended up 37.00mm and the exhaust was 35.00mm, with the exhaust this maintains the constant cross sectional area but with the intake it is smaller than the throat size, this isn’t in keeping with maintaining a constant cross sectional area equal to the throat size but what this does is accelerate the air approaching the bowl, the larger bowl slows the air helping it turn the corner then the expanding past the valve to fill the cylinder.

5 – Port entry exit - The intake entry I port matched removing only the material required to get a good match. I did tapper the port matched head back into the port approx 35mm just to smooth out a lump in the original casting. The exhaust exit I enlarged to 37.5mm, this is a diverging tapper from mid port just behind the valve guide to the port exit, what this does is complete the venturi from valve 41.0mm to throat 34.8mm and then to port exit of 37.5mm. You don’t want your exhaust port exit to match the extractor pipe, you still require an anti reversion step to discourage the exhaust charge coming back up into the cylinder. My primary pipe is 35.0mm I/D but the pipe has been flanged to a larger diameter creating the reversion step.

Heres a Link to some photo's that will help explain a few things. In the "HeadPorting" album.

http://s860.photobucket.com/albums/ab165/johnhavlin/

Awesome job. I like the work on the BBM too

Simplest way to port and polish ya engine is to put sand in the intake BAWAHAHAHAHAHAHA..


Good Read.. +1 for sticky, (is already sticky good stuff)

there is a link to this thread in the guide to 6cy.