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Thread: Down draft b.v. Pinto with variable velocity stacks shed build adventure

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    Down draft b.v. Pinto with variable velocity stacks shed build adventure

    THIS IS MY ENGINE BUILD...ITS MORE OF WHAT I DID RATHER THAN HOW TO DO IT...AND IT IS SERIOUS FUN

    IM AN ENGINEER NOT AN ENGINE BUILDER SO THE ONLY WAY TO LEARN IS TO BUILD YOUR OWN ENGINE AND READ A LOT OF CONTRADICTING STUFF..

    I SOON DISCOVERED THAT BUILDING AND ENGINEERING MY OWN ENGINE IS A COMPROMISE ...BEST DESIGN....BEST DESIGN THAT I CAN BUILD ON MY EQUIPMENT...BEST DESIGN THAT I CAN BUILD ON MY OWN EQUIPMENT AND AFFORD(CHEEP OR FREE)

    I HAVE USED AS MANY PARTS THAT I COULD SOURCE FROM ANY ENGINE THAT WERE TO MY DESIGN NEEDS SIZES ECT AND READILY AVAILABLE...

    SO TO BEGIN

    FIRST I NEEDED TO SEE WHAT WAS IN A PINTO HEAD SO I CUT ONE IN HALF AND SCANNED IT ON THE PRINTER





    THEN SIT AND LOOK
    AT IT FOR HOURS..

    DECIDED TO MAKE IT DOWN DRAFTED BUT COMPROMISE AND COME IN AT ABOUT 60 DEG...AND END BEFORE THE VALVE GUIDS TO MAKE SEALING EASIER..#


    MACHINES I HAVE ..16MM PILLAR DRILL...5" BENCH LATHE ..LOTS OF GRINDERS , WELDER AND A SURFACE GRINDER...

    ALL THE WORK WOULD HAVE TO BE MADE AND DONE ON THESE MACHINES..
    #
    THE PORT DESIGN IS EITHER GOING TO BE A PARALLEL PORT OR TAPERED PORT AT ABOUT 3.5 DEG..

    BUILT A JIG TO HOLD THE HEAD ON

    GOT HOLD OF SOME MAG DRILLS 40MM, 46MM AND 48MM..NEEDED TO GRIND THE SHANK DOWN FROM 19 TO 16MM



    FINISHED AND SITTING ON THE JIG



    PILLAR DRILL WAS TO FAST EVEN ON ITS SLOWEST SPEED SO AN EXTRA PULLY WAS ADDED (POWER STEERING PUMP AND PULLEY WITH A TRANSIT ALTERNATOR PULLEY WHEEL WELDED ON TOP)




    DRILLED THE HALF TEST HEAD READY TO BE FLOW TESTED BY TOM ..


    TURN SOME HEAVY DUTY GAS PIPE..... ONE STRAIGHT AND ONE TAPERED DOWN DRAFT TUBE...


    BEFORE


    AFTER ..TAPERED TUBE 37.5MM TO 46MM AND 100MM LONG



    NOW TO WAIT FOR THE FLOW TESTS.....

    NEXT CHAPTER FLOW TEST RESULTS AND FINAL DESIGN...

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    Great work, be very interesting to see your results but stop shouting! ;-)

    Cheers

    Matt

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    1970 Mk1 Escort Tarmac Rally Car

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    :thumbup:

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    Good idea the cutting the head and scanning it

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    Head on the flow bench...the port tube being tested is a tapered 48mm to 44mm on standard valves...
    you can see the straight tube on the right this is 44mm straight..




    they both worked ok ..good results but all the flow was really across the top of the valve..

    we started to make the internal diameter smaller and raise the floor and the flow increased..
    all the tests were carried out using stnd 2.0 valves and seats...

    the results






    a good starting point...and proves that big is not always better..

    as a reference guide we formed a profile of the port floor ...



    after more testing on my vacume box at home.... my max flow improvement was a fully tapered insert tube with the end internal size 37.5mm with a raised floor vain..
    entering into a 40 mm ported valve area with a 46mm valve...

    the angle of the inlet was also altered to 61.5 degrees....and the tulip style valve seems to flow best...

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    A quick sketch of the general design



    showing the vain at the shortside turn..

    I had already decided to fix the down draft tubes by mechanical means..this means i can change them if i need to and replace any parts when and if required..

    so lots of drilling to do..boring and counter boring and counterboring the counter bores..

    once the head is clamped on the jig each hole and mating part has to finished before the next hole can be bored.....so bore 48mm then counter bore 46mm then counter bore 40mm... then clamp the ally crush plates on the head and bore them 48mm all at an angle of 61.5 deg








    the hanging hammer is the automated feed..slide it up or down the arm to increaseor decrease the cutting pressure...each hole took about 3 hours to bore...

    all the holes bored and the ally clamp plates bored to match

    more sketch's to show the method of sealing the tubes in the head..cant think how to explain it ...(using o rings)





    now to start making the parts x4 off every thing

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    great stuff thanks for posting

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    Cracking read Mark There seems to be a few of us working on downdraught heads at the moment. Our methods may be different but we all want the same goal - to extend the life of the humble Pintosaurus and bring it kicking and screaming into the 21st Century, taking a few 16v scalps along the way!

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    Its sites like this that inspire... make us push our limits and the pintos...
    cheers mark

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    How do we call this? Taking minimum tooling to the absolute maximum? I'm sure many CNC operators can't get so far. Top engineering.

    About downdraught heads. I believe this is the only way to take the Pinto power to the level most people wanted to be. I mean over 100 Bhp/liter.

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    Thanks guys

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    All of the testing was done on an early 2.0 head...it soon became clear that to get the compression ratios i would need to use an early 1600 head...

    1600 head... all the holes bored and ready for cleaning



    and the ally clamp plates bored to match.. 48mm at 61.5 degrees..



    you will notice how close the bores are to the recesses in the head manifold face...they are at one point 0.75mm..they are closer because i needed to move the bores 1mm off center.. the reason is when boring 48mm it breaks through on all 4 sides (if you can imagine) at some point..by moving it 1 mm i can maintain an unbroken wall and keep the structure sound,,

    you will notice also that i have left the head as complete as possible and when clamped to the jig i used the head bolts and holes...this should help to keep everything in line

    making the inlet tubes...
    Heavy duty steel gas pipe..


    out side turned to shape ready for polishing


    "O" ring fit being checked..before final inner taper finish cut


    inner tapers finished ..pain in the a"$%..my taper slide only moves 70mm and i can only turn 100mm length..so every thing has to be turned re-chucked centered ..and reverse taper...good job im patient..




    before facing to length i needed to make the top hat

    top hat..


    and one down draft tube complete "o" ring and top had ready to be polished..


    The next problem was making the 45degree cut at 61.5 degrees in the ally top plate..

    A quick sketch to show what i mean

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    Before i can go any further..i need to finalize sizes...
    as mentioned earlier the best flow was with a 40mm bore on a 46.25 valve....the valve used was from an essex group 2 v6 so the length of 115.4mm would not work ..i need a valve 112 -113mm long(for a 1600 head)
    pic of the v 6 group 2 valve


    i skimmed the valve to 46mm and tested again results were the same and then 45.5mmstill no noticeable difference..tried 45mm but this meant altering the seat dimensions and angles..


    so i was looking for a valve 45.5-46.25 diameter...112-113 long single grooved and if stainless stelite tipped and with a tulip style end

    it was looking like i was going to have to find some alternative...lash caps or 3 ring collett ect..

    when i eventually found some nascar type derived valves almost perfect in the usa

    112mm long 214n stainless tipped and single cotter..7.96 diameter stems with swirl finished tulip design...the only down side is they are dished



    i was also looking for an exhaust valve as above but 36.5 to 36mm diameter...
    The only availabe size was 37.5mm so made an offset 37mm valve to see how much i would have to move it


    at max equal lift 1.1mm would be required to move the exhaust valve

    so purchased the 37.5mm exhaust valve

    46mm and 37.5mm valves


    Valves sorted
    now to calculate the total inlet/velocity stack length..keeping with my tapered port design
    i made a chart specific for my inlet diameter and cam profile for the best length at all revs



    with the chart like this you can see that 2 overall lengths are apparent 299 or 322mm

    i picked 299 as my starting point

    now i could decide on my throttle body injector position and butterfly position...

    then i plotted a line at the chosen distance from valve for my butterfly and measured the diameter of the tapered tube at this point



    the "average diameter of my tapered inlet system 37.5 to 54.5 over 275mm(25mm bell mouth =300mm) is 46mm

    the size of my butterfly is also 46mm
    and my valve is 46mm

    so the magic number is 46mm

    Now i needed to find a injection throttle body 46mm

    a trip down the farm and got a complete gsxr750 1999 set up perfect (all for some machine repairs)

    so working backwards ..from the i t bs buterfly position in the bodys... meant that my inlet tubes needed to be 90.3mm

    although the injector position from the valve and the buterfly position from the valve was correct the taper on the throttle body was wrong and the injector angle was way off

    test fitting with tape


    view down the inlet port on standard valve size

    injector end will need to be opened up 2.8mm and offset tapered 1.2mm by 1.5 degrees


    the top end just open 1mm by1.5 degree straight taper


    the injector angle bothered me as well,,,it would work ok where it was... but i reckon it would workbetter for sure by altering the angle

    quick sketch to see what i mean ..a before and after thing

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    Great progress, respect to you

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    Flippn awesome work matey, love this kinda in ya shed engineering all in the name of power,

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    Quote Originally Posted by rwd2ltrfiesta View Post
    Flippn awesome work matey, love this kinda in ya shed engineering all in the name of power,
    Says it all :thumbup:

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    Nice project there, I like the o rings sealing against the port near the valve guide and sealing against the alloy plate

    About the port shape, the tapered shape you have chosen looks like it will flow huge air, that would flow enough for 300bhp+, the limitation is the flow around the valve

    I would recommend using 90% inlet valve diameter for the inlet throat just below the valve seat, 41.40mm ID with a 46mm valve

    Can I ask what airflow you got with a 46mm valve and a ??mm inlet port?

    That is impressive flow with a 42mm valve!

    About the port shape, something you could try is a port shape that is smallest at the manifold face down to 37mm at this point for a brief 3 or 4mm distance, then slowly getting larger down towards the inlet valve, with the inlet system gradually tapering up to a 45mm ID parallel trumpet, this would turn the entire inlet system into a large long venturi in the true meaning of the word venturi rather a carb "choke" shape (very short and restrictive), I have done some flow testing with venturi's and holy hell they can flow air! what they do is to greatly speed up the airflow and raise the max flow vs a parallel port of Much larger diameter, having an inlet system like this would add a crap load of torque to the entire rev range by adding a lot of energy to the inlet system especially towards the start of the compression stroke (piston moving up bore but inlet valve still open)

    Venturi's work best with a small trailing angle away from the minimum ID, the entry angle is of much less consequence (in terms of air flow) it can be a large or small angle, if the trailing angle is too steep the air will flow though the minimum ID, then quickly turn around to try and "fill" the larger diameter just after the minimum ID and dramatically slow down and reduce the airflow, it is pretty amazing how a small change of trailing angle can have such a large influence on airflow, it is "what we can't see" that is changing the airflow, turbulence, which you can often hear on the flowbench

    Great work and will be very interesting to see how this goes, your O ring sealing idea looks spot on
    "Horsepower sells cars, torque wins races" - Enzo Ferrari

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    Hi jason.. tom flowed the origanal head for me...that gave me a starting point ..my flow box only tells me better or worse ....you are spot on...i added a filler on the short side effectively doing what you mention..the only difference is that i then opened it up so it could flow over the inlet filler and under(like a vane in a jet engine system) my finished port throat measured 40.8mm...i found that a sharp 3 angle 65 /45/35 seemed to work best...i have spoken to tuners with a flow bench who will flow it for me when its complete and i can get some exact data...

    cheers mark

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    This warms my heart, built in a shed with basically a few tools and ingenuity, it makes me proud to be British. I would imagine most developments were done this way years ago...love the automated feed with the hammer. What grade of O ring will you be using?

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    Thanks......All the o rings are viton ..high temp and 25% compresion reflection...fuel resistant as well...

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    Racer Decade Plus User RWD fords rule's Avatar

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    Top work with a drill press and lathe btw, I like the auto feed

    What you can do with a flow box (as I still use as they are very handy for A - B - A - B testing as you said) is to make some simple orifice plates to get a good idea of what CFM the item is flowing, I used some 2.5mm thick mild steel plate, I cut approximately 5 to 6" OD round discs and then placed them in a lathe, 3 jaw chuck hols them well if you place the disc into the grooves in the jaws, then drill a large hole and use a carbide tipped boring bar to bore the hole out to the exact size you need, then set he boring bar to 60* and reduce the hole to a sharp point at front of the plate, (machining the back edge away leaving the front edge the same ID as before) give it a rub of a flat honing stone on the top of the plate to knock off any burr and you now have a true sharp edge orifice

    I tried a 45* cut but increasing to 60* made the edge a lot sharper

    The formula is 91.14 CFM (@28") per square inch of sharp edge orifice area (based on a 0.62 flow coefficient for sharp edge orifice)

    Orifice radius squared x 3.14159 x 91.14 = CFM @28"

    Flow the plate with the sharp edge facing upwards, you need a good few plates to select from but very cheap making them yourself on a lathe

    Just adds the capability of getting a decent flow figure, not exact but pretty darn close to calibrated orifice flowbench figures, ten you know if a head flows say 200CFM @28" and 14mm lift, and another head flows 230CFM @ 28" you know the second head flows 15% more at that valve lift point, even if the 200CFM is off by a few CFM the 15% change will still be the same

    "Horsepower sells cars, torque wins races" - Enzo Ferrari

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    Time to make the ali clamp plates...they look easy to make but the angles are compound 45 deg at 61.5 deg x 4...
    this is what i am talking about


    earlier i bored the holes out at 61.5 degrees


    so made another jig ..and a holder for my die grinder..


    and started to grind the ally plates with stones



    i soon found that the grey stones ware-out quicker than the ally cuts...but the pink stones work a treat..plenty of wd 40...and when they get clogged just spin them on the bench grinder and good as new..


    all 4 holes counter sunk and the finish is a good polished finished ..good for sealing the o rings..

    next i need to make a angle plate for the top clamp studs...there is no where in the head to drill the required holes..
    and the angle plate will also act as a load spreader..
    quick sketch of the angle plate


    after cutting and welding the finished article the studs were drilled and tapped into the angle then plug welded underneath.

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    This is crazy. I'm just in a process of buying a new milling machine (11.000€+VAT). Seems like I can better invest the money in a MIG welder, sheet steel and some tubes to do the same job.

    Just keep going!!!!!!

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    Quote Originally Posted by onyd View Post
    This is crazy. I'm just in a process of buying a new milling machine (11.000€+VAT). Seems like I can better invest the money in a MIG welder, sheet steel and some tubes to do the same job.

    Just keep going!!!!!!
    agreed!

    tbh lots of stuff is like that though, my diy home made flow bench cost literally a few pound, am i better of spending thousands buying a professional purpose built one? or perhaps 15K on a serdi seat cutter when my new way stuff does the job just not as nicely and much slower, but is the difference really worth 15K, probably not!

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    Right, and don't start jumping for a Serdi. The old way of cutting or grinding is not worse. Every time I got a leaked seat on the dyno, it comes from a Serdi. Not as accurate as people are trying to let you believe. One machine shop very close to me is still using the "Steal bar in guide and cutting tool". Never ever had any leaking seat. If I hear Serdi, I'm worried. Only if you know where to keep attention it's OK. But only if.

    Unfortunately, I do need a new milling machine. The old one is worn out and takes to much time to make accurate things.

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    i dream about having a mill.. making by hand takes 6 days planning and 1 day making...but im old school marconi man there were no cnc when i did my apprentice only paper peg boards and files...drawings were even in metric and imperial....
    im that old

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    That's not old... my only engineering qualification is O level Metalwork from 1975

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    Quote Originally Posted by onyd View Post
    I'm just in a process of buying a new milling machine (11.000€+VAT).
    That is small money for a new milling machine sounds too cheap tbh, the best value you can get in a manual mill is spending around €4k on a very good series 1 Bridgeport with power feed on X axis and 3 axis Sony DRO, I have had one for about 2 years now and all I can say is that it is the best money you will ever spend, no more searching to find something that will do the job or spending hours adapting parts to make them work, that plus a decent lathe = a lot of creative freedom to say the least!


    @ Mark
    Some really good looking work going on in this thread, tbh in a way it looks like your skills are going to waste, some day you have to get yourself a good mill, it will repay you in a year or two max, and you will wonder how you got things done without one, once you get one you are never going back!

    Keep the posts coming
    "Horsepower sells cars, torque wins races" - Enzo Ferrari

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    Quote Originally Posted by onyd View Post
    Right, and don't start jumping for a Serdi. The old way of cutting or grinding is not worse. Every time I got a leaked seat on the dyno, it comes from a Serdi. Not as accurate as people are trying to let you believe. One machine shop very close to me is still using the "Steal bar in guide and cutting tool". Never ever had any leaking seat. If I hear Serdi, I'm worried. Only if you know where to keep attention it's OK. But only if.
    Completely agree, most serdi seat cutters, (all of the modern ones) use rotating guides, this is a really poor method of locating the seat cutter, if there is ANY wear on the guides the seats will leak, you have to fit new guides every time the seats need re cutting to ensure the seats are in line with guides

    A fixed non rotating hardened steel guide is 300% better for seat concentricity/parallelism to guide and seat sealing
    "Horsepower sells cars, torque wins races" - Enzo Ferrari

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    funny thing ..back in the late 80s i used to repair all these machines and could have had a workshop full for free ..but had no interest then...now of course i want them but im not in that game any more life he..

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    I only use my milling machine to correct small errors, no production. For 11K you can find nice machines here (China, Taiwan, I know but some of them are not bad at all). Not pro but more than enough to do the job. All my real milling and turning I send to a company with full CNC workshop. I have to make money for living, if I have to do milling myself I gain nothing.

    I did wanted to buy second hand again. For 10K you can find a German Deckel (new price probably 40 - 50K ) but I'm always worried if something go wrong (it seldom will with a Deckel) but the day you have to call them 10K will be spent fast for a repair.

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    Racer Decade Plus User RWD fords rule's Avatar

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    I wouldn't like to spend that kind of money on a China/Taiwan machine, make sure it has hardened machine surfaces, not sure what machines you have over there but in the UK you could find a good CNC X + Y for around €6k, CNC have ballscrews with zero backlash, can be used manual with head fixed of course but most have a much higher HP and stronger spindle, a lot of advantages, for 11k you could get a very nice CNC X+Y mill but maybe not the case in your country
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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    Quote Originally Posted by RWD fords rule View Post
    I wouldn't like to spend that kind of money on a China/Taiwan machine, make sure it has hardened machine surfaces, not sure what machines you have over there but in the UK you could find a good CNC X + Y for around €6k, CNC have ballscrews with zero backlash, can be used manual with head fixed of course but most have a much higher HP and stronger spindle, a lot of advantages, for 11k you could get a very nice CNC X+Y mill but maybe not the case in your country
    Are you talking about prices for new machines or second hand? The machines sold here for 11K are new and not so bad at all. Not for production but OK for what we have to do. X - Y - Z automatic and electronic readout of position. Indeed, engines are only 2Kw I believe. I don't need CNC because I can't work with the programming anyway. If I need complex milling I prefer to give the work out. Even if you have the machine you probably don't have the right mill etc... I don't have the time anyway. If you know I'm almost 100 carburetors behind, you got an idea how much time I got for complex machining.

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    ok time to start the rough cut/sizing on the valve seats and port chamber..

    in testing i found 40mm bore on the valve inlet worked(ends up40.8mm when cleaned) so made a spindle that fitted my valve guides and fitted the 40 mm cutter


    fitted the head on my boring jig aligned the angles and bored out 40mm x 8mm deep

    then needed to unshroud where the new valve would be ..so made a 46mm valve out of a washer and old valve


    then ground the area required keeping it within a 92mm bore size..after skimming the head it will end up about 91mm ish (room for manouver later if required)

    i cut then cut the 3 angle seats by hand ...as mentioned earlier 65' 45' 30' worked best..i tried variations even 5 angle 60' 65' 70' 45' 30'

    i made the cutters for the 65' 60' 70' because i only have 45' and 30' cutters

    welded a bolt on an old socket chucked it up and turned the socket to 65' and the bold to my valve guide diameter...then welded some 4mm tool steel to the 65' angle ..relieved the edges on the rake and used a socket to turn cut the cast like butter


    not pretty but works..


    the rough cutting finished and the valve guide ground away and the inlet tube pushed into place, all looks to plan so far

    after the new guides are fitted ill finish seats and chamber



    you can see the end of the new inlet tube if yo look closely..( there black because i blued them to stop them going rusty)

    check fit of the 46mm valve looks massive...ground the area for the exhaust valves ready for when i offset the guides and start to cut them


    mark

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    That's a great idea using a washer welded to an old valve to protect the seats when unshrouding. I have a little unshrouding to do, so I'm definitely nicking that one! Great stuff

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    Racer Decade Plus User RWD fords rule's Avatar

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    Great work!, I like the diy 65* seat cutter and using the mag/annular cutter to bore the throat / bowl area

    88 to 90% of valve diameter is usually recommend for the throat diameter so you are right in that range, 41.4mm would be the upper limilt, a std 2.0 valve would almost fit in there lol!

    For the exhaust 88 to 89% max is the recommended to make a nice radius seat shape acting as a venturi

    About the seat angles I think a 4 angle seat is best with every seat being 1.6mm wide, 35* top cut, 45*, 60*, 75* blending into the 90* bored throat, that ends up with just a tad under 90% throat diameter, the 35* top cut would blend into the chamber a little easier than a 30* cut but a small difference, same angles for exhaust just all of them made 1.8mm wide to end up with an 88.5% throat diameter

    Top work Mark, big thumbs up from me
    "Horsepower sells cars, torque wins races" - Enzo Ferrari

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    Thanks jason
    Ii didnt try 35' top cut, didnt enen think about it..cool for the exhauste dimensions ...on the test head i used 34mm on the exhauste(mainly because i had that size mag drill) but now i have moved the valve over 1.15mm and i dont no for sure how thick the walls are ..it would be like boring 36.3mm....i found the 1600 head is not the same as the 2.0 in wall thickness in some areas...what do you think 33mm (would be 35mm) ...cheers mark

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    Re: Down draft b.v. Pinto with variable velocity stacks shed build adventure

    I think 33mm would be the upper limit, I previously bored a 2.0 head to 34.3mm for a 38.1mm valve, but only bored up minimally, might be best to chop up a spare head if you have one and see what the wall thickness is like

    The limit would likely be the bowl area and up towards the guide, be careful removing material from the sharp turn in the exhaust port it is temping to port too much from that area to straighten the port but best to take say 3mm max and leave it at that at the sharp turn, I think there is 5.5 to 6mm material thickness around most of the ports, and a lot more material around the valve seats and throats
    "Horsepower sells cars, torque wins races" - Enzo Ferrari

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