Modified 8v project head

Discussion in '8-valve' started by mr hillclimber, Nov 5, 2007.

  1. mr hillclimber Club GTI Supporter and Sponsor

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    Bl$$dy hell!... the got the 33mm all the way in the port!?

    On the head in the guide I think a long shank burr... but these days I use a course big flute burr... it chops through aluminium like you wouldnt believe!... use them with caution!

    You can infact thin down the boss to not much thicker than the guide for very little flow difference.. it's just easier to chop it out.
     
  2. milesmk2 Forum Member

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    Yeah got it most of the way through the port just not quite into the throat yet cos my burrs arnt long enough (easy now).

    Right ok i'll just try and smooth the guide bosses down so they look nice then instead of getting rid of them completely as they are a pain to get to.
     
  3. mr hillclimber Club GTI Supporter and Sponsor

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    Work around, or remove, the guide boss from the throat end with a normal length burr. .Mind the chuck against the seat tho! Widen the throat area either side of the guide boss a little. .So it bulges at that point..not massive but subtly.
     
  4. milesmk2 Forum Member

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    Right ok. Saves me 30quid on another burr eh.
     
  5. G60KG

    G60KG Forum Member

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    This is a very interesting guide and Im still getting my 'head' round all the throats, seats bosses etc. I was wondering where and how much it would cost to have a self ported head flow tested to actually see if it has been done right.
     
  6. milesmk2 Forum Member

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    Not cheap. I've done about 10 hours work into it so far and I'm not finished yet.
     
  7. R.b!n_16v Forum Member

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    Mr H how did you back cut the seat?? just with a die grinder by hand or a special machine?
     
  8. mr hillclimber Club GTI Supporter and Sponsor

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    On proper heads they're done by my machinist. .on flowbench development heads they're done with a file in a drill and finished with emery paper.

    Back-cut or radius seats on valves are a must..even some aftermarket performance valves can benefit. I radiused off a seat on a big valve Ford Pinto head last night and picked up 2cfm across the board except right at peak. Like a power curve..don't just chase the top end..mid lift flow is important as its seen as the valve opens 'and' shuts.
     
  9. milesmk2 Forum Member

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    Ive been using this guide to port my own head, and have accidently gone through one of the inlet walls into a head bolt hole, is that the end of the line for this head now?

    [​IMG]
    [​IMG]
     
  10. Mike_H Forum Addict

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    No, lots of 'full race' heads are ported through into the head bolt holes, including the old Spiess/F3 type. Shouldn't really need to do that on a road head though.
     
  11. milesmk2 Forum Member

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    Good! I was about to throw the head away.
     
  12. mr hillclimber Club GTI Supporter and Sponsor

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    As Mike said above, no need to go that big on road engines at all. A 30-31mm port is fine to feed a std 40mm valve and still give almost 90cfm, which will feed a decent perfomance road/trackday & even some competition use. I can get just over 32mm ports without breaking through by offsetting a little, that will feed over 190hp with 100+ cfm, so you can see you need to go mad for normal use.

    I have sleeved them before to make it look a bit tidier but it's not needed as the gasket seals at the bottom and the head bolt seals the top.

    Your key improvements will come from the seat & throat area.... I'll try and update the dimensions asap but work is keeping me away from the keyboard at the moment.

    In fact if I dont do it now.... sleep is over rated anyway!

    Use a port size of 31mm with the std 40mm GTi valve.... you'll get more than enough flow through it and keep the air speed/port velocity up.

    The venturi below the bottom angle of the seat cut... roughly the area where the seat insert joins the head... needs to be between 34-35mm. The smaller size is fine...trust me, you will get good flow with it. Cut to just below 34mm to get the size, then by the time you blend it into the seat you'll be just over 34-34.5mm.

    The throat bowl area needs to be no bigger than 36mm, and blend into the main port. I recently tried a bigger throat area after some positive results during some crossflow development...it worked on the crossflow head so I thought it may move the older type head in a further positive direction. After opening out to around 37.5mm it gained nothing...ziltch...zippo... the flow curve followed an identical path... so dont waste time and effort going bigger than 36mm.

    The short side turn needs to follow the drop from the port floor... have a feel with yr finger (easy...!)... the floor starts to turn/drop into the throat then goes rough/lumpy.... blend the rough part back to follow the natural floor line.

    I cut the short turn back with more angle on the bigger valve heads with a positive result, but again, I've tried it on the std 40mm valve and it shows no improvement... dont waste yr efforts.

    The guides need to be removed and replaced by a pro machine shop really, or you can knock them out after warming the head in a hot parts wash tank or on a barbecue... they're not just for burgers you know!.... wear protective gloves though or the head will have cooled down again while you run around blowing on yr burning hands. A few good clouts with a very heavy hammer and a large punch will get them out... make sure the punch is smaller than the guide hole in the head but not small enough to jam in the centre... a punch will an 8mm guide nose and a bigger shoulder is the best option.

    I'll cover the exhaust sizing later... the above should keep you busy for a bit.
     
  13. milesmk2 Forum Member

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    Right ok. Ive pretty much finished the inlets now, just need a bit more blending then some polishing. As for the guides i got the old ones out with a hydraulic bearing press and a 1/4" extesnsion bar, seemed to work well.
     
  14. mr hillclimber Club GTI Supporter and Sponsor

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    Good man... I'll get the exhaust details up asap... time is short currently. Dont worry too much about finish, certainly dont waste effort making it ultra smooth or shiney, a sort of matt but smooth finish is fine... even the cutter finish is ok as long as the shape is right and there arnt any lumps.
     
  15. milesmk2 Forum Member

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    Ok I'll try and smooth it out with the burrs when I can. I had heard that polishing does sweet fa for it.
     
  16. Louie2shoes Forum Member

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    Dear Mr Hillclimber,

    This thread is awesome and really inspiring! The whole thing is pretty new and scary to me but I am not easily deterred! I have picked myself up a few bits and bobs to get started but have a quick question for you. I have a MK3 8V Gti with an AGG engine and have purchased a spare head off Danster to work on. Basically I would like to know what things I should do differently to the steps you have described as my head appears to be quite different to the one you have used. Any advice on getting started would be great.

    Thanks

    Louie
     
  17. mr hillclimber Club GTI Supporter and Sponsor

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    Hi Louie

    More or less as in this thread really. Tell me what valve size your planning on using and I'll give you some porting & throat sizes to work to.

    From memory it has the odd shape inlet ports with the raised cut out for the injectors?

    If so, ignore the cut out & treat the rest of the head as per this tread.

    Good luck with the project...if in doubt dont be affraid to ask before you do anything.
     
  18. danster Forum Addict

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    Yeah, the AGG head has the raised section in the inlet port to house the injector that fits in the inlet manifold.
    It has 7mm valve stems with the 39.5mm inlet and 33mm exhaust valves.
    It was a low mileage head so I imagine the valve guides will have little to no wear, so may want to avoid disturbing them with the added cost that entails.
     
  19. Louie2shoes Forum Member

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    Thanks guys. There's your answers!:thumbup: It was the injectors that confused me as I couldn't see where they fitted on the AGG head. I did a quick engine inspection on the car and figured that they were seperate, hence the elongated inlet. Good to have that confirmed though. Thanks for responding.
     
  20. mr hillclimber Club GTI Supporter and Sponsor

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    If yr going to stick with the std valves size's Louie then work to these specs...

    Inlet...

    Main port from manifold face to short side turn... 31-31.5mm...use couple of old valves turned down to help keep the port round and consistant...a valve at just under 30mm and one at just over 31mm will help with the roughing out stage and the finish stage. Try and keep the port away from the head bolt holes in that area..it's generally not a prob on that size, but if you wander you may break through, though thats not a problem either.

    The venturi, just where the seat insert joins the head casting is a good place to create it, needs to be 33.5-34mm.

    The main throat bowl/valve pocket should be 35.5-36mm. You will need to be ultra carefull in this area if your leaving the guides in place...it can be done though. You'll need a 8-10mm parralel wall/thimble shape burr to gradually ease between the guide/guide boss and throat wall. I would use a fine or double cut burr to start with to minimise snagging and regular spray's of WD40, and keep the grinder speed up...and yr hand steady. Try and work the wall away first to give some extra room, then ease the guide boss down to a touch over guide width. The bowl doesnt need to be 36mm all the way, it should start from just under the venturi to around halfway, then taper into the roof/guide area.

    You'll see a natural turn from the port floor into the throat area...try and follow that line through to blend the short turn. This is'nt an easy area to work with the guide still in place, so carefully remove with a fine burr and finish with emery tape in a split rod and a medium speed...DONT OPPERATE A DIE GRINDER AT FULL SPEED WITH A SPLIT ROD & EMERY TAPE!!!!...IT WILL LIKELY SNAG, BEND THE ROD, AND TRY TO RIP THE GRINDER FROM YOUR HANDS!

    Once the seat is cut to 3-angle style, you'll need to blend the lower angle into the venruti/throat...you'll find pics of that in this thread, but work to the above size's not what the pic looks like...since I've had the flow bench I've learnt as much of what is'nt needed than is.

    Exhaust...

    The venturi needs to be 28-28.25mm, then the throat opened to 31-31.5mm. Gentley radius the short turn...there isnt much material there and the natural turn is sharp. The main port isnt a bad size, you can open the top part a bit wider and taper it halfway down the wall...dont open the whole port to the gasket line or anything like that.

    Again as above...once the 3-angle seat is cut, blend the lower angle into the venturi/throat.

    Dont grind any material from either inlet or exhaust port floors...it's ok obviously when doing the final clean up/blend, but dont deliberatly cut anything away.

    All valves need back cutting...inlets more critical than exhausts...there must be a step free transition from valve back to valve seat contact point on the inlet...the exhaust is less fussy here. the exhaust valve face does like a small radius around into the seat...be ultra carefull not to damage freshly cut seats.

    The same goes for when grinding....keep the collet/chuck of the grinder away from clattering into the seat...a deep gouge may not cut out when the seats are cut...just be carefull when moving the grinder around.

    60 grit emery paper or flap wheels are a good enough finish, you dont need to make anything ultra smooth or shiney.

    Bare in mind to reach the sizes above you need to allow for finishing...cut the sizes to under then finish to size with the emery. Dont go in hard with the cutters or you'll have gouges you wont get out...it wont really effect flow but just does'nt look great.

    You can gently taper around the edge of the valve guide to break the sharp edge of the shoulder on both inlet & exhaust guides.

    If you want a touch more flow, it's worth measuring up the inlet seat to see if it'll take the O.E hydro MK2 GTi 40mm inlet valve...the std seat may take it like the crossflow heads do. The stem is 8mm instead of 7 so the guides will need changing, but the gains from the bigger valve diameter far outweigh any potential loss from the thicker stems...in fact I've never seen a measurable loss. You'll also need to change collets/caps & poss springs...you'll need to eye that up...and check the spring seat base...I've not seen a std AGG head in that area. And check the overall valve length/cotter groove positions.

    Hope thats a help to get you going Louie...shout if you get stuck.
     
    Last edited: Nov 30, 2011

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