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Thread: Intake manifold porting question

  1. #1

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    Intake manifold porting question

    I just put my Webber on not to long ago and when I put it on I was really wanting to pulling the intake and port out where the carb bolts on and make a good flow threw there and get rid of the two holes for the stock carb. I want to know if it is ok to take that center cross out with out hitting water I plan to take it off and grind some aluminum off with my carbide bits and make a good flow threw there soon and just want to know where to be extra careful. Any help will be greatly appreciated.

  2. #2



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    the water is in the bottom of the manifold, so that will not be an issue. My friend wanted to do the same thing for the intake for my weber, but we haven't got around to it - only been 22 years or so.
    Last edited by pennyman1; 12-03-2013 at 05:34 PM.
    Pennyman1
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    I would say as long as you don't go beyond the actual bottom of the manifold you will fine with just removing the webbing, are you going to do the runners as well with a gasket port.

  4. #4

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    As for the runners I'll probably just clean up casting a little bit and call it good, I'd live to take the head off and do a valve grind and a timing chain and gaskets and all that good stuff but my daily driver at the moment. Thank you guys for the help also

  5. #5



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    If you have jet valves, then port and polish all you want. If no Jet valves...I would kind of keep it roughed up in the intake side since it makes the fuel become atomized better before it gets into the cylinders. Unless you have fuel injection which would be a spray right from a nozzle injector. Keep your edges of the intake ports nice and square and sharp. Don't want to round them off so much as you want to match them up.

    The exhaust port matching and cleaning might actually do a bit more help since the exhaust has to travel much farther as it pulses to exit the containment of piping. The intake is short in compare.

  6. #6

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    This is how my dad and i cut mine out. On the primary hole there is a steel ring with holes for the path to the egr. What we did is ground out that whole section and then used professional jb weld that can be machined after it dries and filled the entire hole with extra out side the hole to fill the void of what we had cut out. let it sit for 2 days on a wood stove to bake the jb weld and then smoothed it all out nicely to help the flow of fuel. we pluged the hole because i live in montana without any emissions bs, and didnt want any fuel going down the hole and just sitting at the block of plate. hope this helps

    Click image for larger version. 

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  7. #7



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    Very nice job, that's exactly how it should be done.
    Josh
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  8. #8

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    Thank You! My dad use to build ford race motors. so he has been teaching me a thing or two.

  9. #9

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    I'm in the midst of installing a weber myself and I was trying to decide if I would port match my intake. As you said I want to take my head off also and port it mildly seeing as I don't have a any mods really on this engine.

  10. #10

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    looking forward to your results

  11. #11

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    Port matching the head to the inlet manifold is a good entry level mod to perform. It will improve throttle response and the engine will idle smoother. Preparing the walls of the inlet manifold is pretty easy too - all you will need is a power drill, a flexible drive and a flap sanding drum that will just fit into the inlet runners. You don't want to go wild with the flap sanding drum. The idea is to get a uniform finish on the walls by removing high spots, undulations in the casting and casting wall mismatch/slag. A few tips when prepping your manifold - #1: wrap the chuck on the flex drive with tape so if it accidentally hits a wall, it doesn't bite chunks out of it (it will do it a lot faster than the sanding drum will...) #2: don't use full rpm's (take your time and move the sanding drum gradually in and out to get a consistent finish) #3: use a really light lubricant while smoothing the runners out (a little water or silicon spray worked for me) *using a lubricant will decrease the chance of the sanding drum from skipping if it hits a high spot - if the drum grabs while inside a runner it will bounce all over the place and ruin the finish... #4: make sure the inlet manifold is secure while you work on it (I clamped mine down to a bench) if the manifold can't move you will have more control over the process. Oh, and an obvious one - make sure your new inlet manifold gasket is trimmed of any overhang into the ports.

  12. #12

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    This is kewl...........I'm gonna give it a try, once I look deep into myself and find the patience to do this........I tried already with a pencil grinder......guess what?

    It didn't turn out too well.

    But I like the idea.
    ~~~~~~My toys~~~~
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  13. #13


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    Now remember you don't want a glass smooth intake if you are running a carb or TBI as you need some turbulance for the air and fuel to mix.With Carb/TBI all you really want to do is gasket match the ports and get rid of any large casting ridges.Polish the crap out of it if its MPFI Big mistake most people make is polishing the intake till it's mirror smooth then wonder why they lost performance. Same goes for heads. Intake should have a rough surface where as the exhaust should be as smooth as possible. I've been porting and polishing heads and intakes for over 20 years and I learned from an old drag racer/engine builder what to do and not to do.

  14. #14



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    Yep, Ford is right and as you know they installed them MCA jet valves because of this issue with breaking up the molecules of the fuel. One other thing I would think of was that the slop in the manifold to the head mating is never perfect so to undercut the intake a bit so it catches no edges on the way into the head. Keep them edges sharp. If you plan on doing exhaust side I think I would think twice on that one. WHat I hear is to not port match exhaust unless it is really bad or the exhaust manifold is smaller then the head ports. They really push the sharp edge thing too, no bull nose edges.

    Going to start sending geezer101 all my parts for rework fitting so watch for a semi truck with FedEx written on the side.

  15. #15

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    Cool

    To BradMph - hey, it's your postage but don't expect it to find it's way home for a while! lololololol Anyway if you take a close look at the finish you will notice that the walls have uniformed ribs as a result of the drum sanding - this will be more than adequate to ensure there is enough turbulence in passing through the manifold without the air fuel charge laminating. As for the port polishing process I am in 2 minds of how it affects performance. I would put money on losing torque straight up (on an engine such as the G63B - 1 to 2 ftlbs max) but the benefit will offset the minimal loss. To get the engine to idle and rev smoother and be more responsive is fair trade to me so I went for it. A stock inlet manifold is about as poor as you can get for performance - different length runners, awful casting plugs, high spots and deflections all over the place, sudden sharp changes in flow direction, that !@#$ing EGR garbage!!?! (...a long list of crimes) And, after I show you how bad the head I worked on was, you'll understand why I put in the hours...And, as for the exhaust port matching thing - DO NOT DO IT. Exhaust gas pulse (the harmonic pressure wave that travels up and down the exhaust system) will scavenge the unburnt air/fuel charge out of the combustion chambers and fubar engine performance. Only go down this path if you have the resources to manufacture a set of pulse tuned headers and have a specific engine tune to optimise engine performance (this is a specialised engine tuning technique and requires a big effort in R & D) I'm sure I've got you guys talking now

  16. #16



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    I hear ya on the casting issues and I can see there are many areas that need to be worked since the factory did such a wonderful job in the casting department (cough cough). I have even grabbed the dremmel and worked the intake flash and garbage that came stock. Even the outside of the part had leaking mold marks all over it. As for all of us talking, I think we are actually doing more watching for sure. I definitely enjoy seeing an entirely different way of performance updates then the usual and always check your thread.
    So much time polishing that tird is by all means good knowledge and just not on our engines, but all engines. I want to see what happens when you turn that key over and if it idles so smoothly you will not be able to hear it running. You making a Rolex out of a Timex my friend and the patience you have to do this work is by far remarkable. Don't let us stop you by all means. Glad your in our forum, I have already used some of your info and I'm sure there will be more.

  17. #17

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    i wouldn't do any port matching on these motors, they come pretty well port matched from the factory, the only part the needs to be addressed is the hard machine shelf as seen in the last picture right here. that is what is called the "short turn radius" this is a horrible video, but it explains it pretty well https://www.youtube.com/watch?v=n6RyuVdWuRc

    the basic idea is that for production the just cast the head the cut the valve bowls on a huge cutter straight into the combustion chamber. all you want to do is smooth out the knife like shelf so the air can bowl around the top of the valve like it's suppose too

  18. #18

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    Quote Originally Posted by thehive View Post
    i wouldn't do any port matching on these motors, they come pretty well port matched from the factory
    That is the only saving grace on these heads. After dressing the inlet manifold walls and fixing the gawdawful effort in the head ports, I butted it all up and there was barely 1mm diameter difference between the head and inlet manifold. I chose not to resize the inlet port on the head by opening it up the full depth of the port but instead used a bigger flap sander and buzzed a small ramp into the port (similar to the factory technique). I figured that it should be enough to maintain the air charge velocity into the head. I made a few small adjustments while the valves were still out as I was able to get a finger in through the inlet valve seats and feel for any shelves or lips that would mess with the overall alignment -
    I put a lot of thought into how to the ports should be prepared - how the gases flow into and out of the combustion chamber, what surfaces affect air/fuel charge onto the backs of the inlet valves, attempting to mirror match the galleries so they behave the same way when gases flow into and out of them (as best as I could with the way the head was manufactured anyway...). It was mostly observation and plausible theory, plus a google here and there. If I have to do this again (no BradMph, no freaking way lol) I would get the valve guides removed and take out the ramps on the bases of the guides as this would make a big improvement to flow.

  19. #19

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    ...oh, and thanks for the positive feedback guys. The L200 wasn't a runner when I bought it and I don't have a deadline to get it operational (if I did, I woulda been screwed from day one - I am yet to find anything on it that doesn't need repairing, rebuilding, removing, replacing or beating to death) I am really enjoying reading threads and posts of members here that have a combo of solid methods and new approaches. I am already getting my mad scientist on but cash is tight so I am making do with what resources I have and keeping an eye out for those "too good to pass on" items and the privilege of playing musical parts with Mitsubishi gear.

  20. #20



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    look in the manual section for the mopar performance writeup on these motors - it has a section on porting that talks about all the mods to do to increase flow for up to full race motors, including the mod you are talking about.
    Pennyman1
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  21. #21

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    do you have a link to this?

  22. #22

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    Honestly, geezer, are you available for hire? LOL

    I'm joking.

    Kinda.

    Maybe Brad and I can go splitsies on shipping a crate of Mitsu crap to get reworked and send it over the ocean to you.



    This is just...speechless.

  23. #23

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    After showing my fellow Mitsu fiend this beautiful example of quality Japanese metal casting we came to a number of conclusions on how it left the factory. #1 - this was the example in the QA office to show the inspectors what faults to look for (slag, misaligned/poorly formed plugs, poorly installed plugs during casting, casting slag embedded into the cam supports etc, etc...) and some idiot sent it out to be assembled. #2 - "C.O.A.F" (cast on a Friday) "The Asahi's are calling fellas!" #3 "C.O.M.L.D." (cast on my last day) "Why am I getting fired? I don't understand..."

    I have invested approximately 30-40 hours of labour into returning this head into a viable unit. I did go back over it once as there were a few areas that I felt needed more attention. The floor of the cam bath had been welded up and 'repaired - or something...' at some point and was done so badly the cam hit the welds in 3 places (it had actually bashed grooves into the edges of the lobes). And then I installed the cam back into the bed - and it was like 'throwing a hotdog down a hallway' (I love that expression you guys in the states use ) so I did something kinda dodgy to rectify it by undersizing the cam caps. I refaced the mating surfaces then linished out the high spots where the bearing faces had been butchered by wayward metal. I got it to a state where it had gone from 0.5mm play (I could actually jiggle the cam up and down with the caps bolted down) to being firm and smooth. My autopsy on the G63B ended up with this synopsis - an oil failure caused cam bearings to wear excessively, oil supply from the exhaust side was barely adequate but dropped significantly when transferring to the inlet rocker rail causing excessive inlet rocker shaft and rocker wear. This engine ate itself...

  24. #24



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    I have seen where they can line bore the cam bearings and put actual bearing in to fix that issue, but it ain't cheap, and with the price of new heads, not worth it. If you want to see some fine work on the 2.6 heads, go to www.b2600.com - they guys are mazda b2600 truck owners that took the mitzu motors that came with them and came up with all kinds of mods. They even critique the various aftermarket heads and tell you how to make them better - check them out.
    Pennyman1
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  25. #25

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    I opted for attempting to return my head to a serviceable state as I had already invested nearly $400 on it plus all the manual labour time. I know that the line bore and cam bearing shell install is a possibility but as pennyman1 pointed out - it ain't cheap. If I was forced to get another head I'd have to go through the same process, add the extra outlay for another head and possibly end up in a similar situation (and the difficulty in sourcing an non-hydraulic head). A new head is $350 - bare. And then I have to factor in freight (extortionist at best), all new valvetrain hardware to assemble it, plus port work to optimise it. Straight up I'm looking at $800-900. Ouch... I admit that going through the process of refacing the cam caps was time consuming but time is free. I had to check and recheck every cap until the cam felt like the amount of bearing drag on it was equal and it didn't feel like it had any areas that bound up it. I have some end float but in comparison to what it was like before, I am confident that it won't have any oil pressure issues and should be good for a hundred thousand laps at least.

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