Discussion in '8-valve' started by mr hillclimber, Nov 5, 2007.
do you bias the porting to reduce shrouding effects? or does it not make much of a difference?
There is a slight bias anyway which I follow, but our friend 'compromise' comes into it too. I've tried different bias in the throat which works well subject to the porting...change one thing and it effects other areas.
Ah compromise, him again
Yep. .he likes to pop up and throw a spanner in the works.
Wow! Cheers for all that info. That's amazing! Once I've read through this a few times and digested it I'll make a start. God I love being out of my depth! Ha ha. I ordered some burrs today but couldn't find any flap wheels the same size as you've mentioned. I did find some proper tiny ones on ebay (10 x 10mm) from china I think? They came in packs of 10 so I reckon I'll get some of those for now. I'm not sure about replacing the valves yet. As Danster said, the mileage was pretty low on the head so I may just stick with what I have for now. Unless of course I accidentally damage one of the guides whilst grinding! I'll post up some pics when I get started.
Thanks once again Mr H. Really appreciate your time and knowledge!
Ok, I think I've processed enough of the info you provided to make a start on things. Head is stripped, cleaned up and ready for destruction! But before I do that...Please could you look at the images below and make sure I've understood your instructions in terms of what should measure what, and where.
I figured I would start at the seat end and create the venturi first. So do I work to these measurements below the insert or do I take the insert back too?
From the inlet side I want to work to this measurement (using a machined valve as a guide), avoiding the port floor and the injector area (as indicated).
Finally, the bowl area wants to be this measurement, starting below the venturi (start line) and blended in to all other areas. This should open out the area around the guide/guide boss.
If this is correct I'll give myself a pat on the back and get started. The rest, including exhaust ports, should be fairly self explanatory. Thanks again for the advice and hope you all have a great Christmas!
Just looked at this again and realized that the measurement I wrote on the valve seat should be 33.5mm - 34mm. Also, further to your suggestion about fitting 40mm valves, the seats measure about 41mm so I'm guessing that's probably not enough.
Very interesting tread, i thought i would share some picks of my setup. The cylinder head i used is not from a k-jet motor, but a rather newer version with mp9 electronic fuel injection. You will see that the angle of the port in relation to the valve is much less compared to the k-jet setup's rather odd 90' angle, therefore the smaller angle provides for slightly less resistance to air flow and should theoretically make a few ponies more in terms of HP gained. The valve guide was left in place during porting and also chopped to provide even less resistance to airflow.
Below is a pick of the port matched intake manifold
Below is a spacer plate made up to allow the use of the traditional carb or k-jet manifold if you wish to do so, unlike the k-jet system which injectors sits on the cylinder head itself, the injectors sits on the intake manifold slightly further from the valve to allow for some better atomization of the fuel before entering the cylinders, also at a smaller angle from port in relation to valve.
I will have a look and see if i can find some picks of the bottom view of the valve seats etc...
Quick question about the long shank burrs.
Mine has a 6 inch shank and I find when in the grinder it does not stay stable so is near impossible to use, plus I can only find burrs with 2" and 6" shanks. How do you over come this problem?
I was considering chopping the shank in half so that its only 3" but I don't have anything that will actualy get through it.
angle grinder will cut it,
Please forgive my ignorance, just how do you replace the valve guides?
Can they be pressed out and back in again ?
I am paranoid that i will mess up my 3A head by porting, but i really want to try !
I have the tools including an air powered die grinder
The only thing stopping me is A: the dodgy focus on the pics stoppig me seeing exactly what i'm doing,
B: removing/replacing guides
PS where do you buy them ?
As tones said. .A grinder or cutting disc will go through it...clamped in a vice first of course.
They're generally fine at 6" tho as long as you don't try to run the grinder at full speed!
I use extensions with std length burrs a lot...I'll pop some pics up.
A motor factor should be able to supply...an engineers can supply and fit when the seats are cut.
They can be but most are worn so will need replacing. .plus they'll pinch up and will need honing. .or you run the risk of the valves seizing in the guide...leave them to the pros unless your used to doing them..have the right equipment and have the provision for getting plenty of heat into the head.
You wont mess it up if you follow this guide...or i can run through any specific areas yr not sure on...here or pm.
I think the trouble is my die gringer only has one speed which is 25,000 rpm, so it looks like the angle grinder is coming out.
Miles is your die grinder electric or air? If electric you need to get yourself an adjustable rheostat so you can back of the power going to the grinder and slow it down, if it's air just back of the air feed pressure
Its electric it is. Reckon screwfix do rheostat?
Rheostat is an old fashioned word and I think you will need a thyristor based speed controller. Shouldnt be expensive, I have made own from scratch years ago using components. Should be off the shelf maplin/RS type stuff.
Right ok, I'll have a gander on RS's website later on when I get home.
BBQing it up at Chew Valley lake right now and its awesome!
Am I showing my age there Jon?
Hello Jason, was nice to meet you on the sunday at Inters.
Out of wonder i know you said going into the head bolt holes if ok, but what if some one ground a hole just under where the lower valve spring cap sits? Would that be ok or would the head burn oil like there's no tomorrow and run like a bag of nails?
Old age, like death and taxes, comes to us all...
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