# MC carb/16V manifold build thread



## ftwelder (Feb 27, 2008)

The first step on the project was to make the needed mods to the head. I had thought about some type of insert to fill the injector recess but disregarded those options and went ahead and welded them up. 








Because it is very difficult to make a perfect match of a surface, rather than filling the whole recess I build a bridge for the gasket surface that require far less filing.

I also did a gasket match on the ports (gasket is not fitted correctly in this photo) and removed casting flash and imperfections. I did all this welding while the head was bolted to the block and old cams still in place to prevent warpage.








Once that was done, I was on to the head flange. I draw with autocad (note, full 4130 computer cage) 








so I measured the head, manifold and gasket for specifications. I quickly noticed the stock manifold didn't fit the head very well. For added insurance, I made the first flange from wood paneling. I use a prototrac for small CNC projects. 








Some of the holes I drilled through, some I tapped for special pins for making sure the ports can be matched properly. I also left a bridge across the huge cutout for the water outlet in the head. This will also reduce shrinkage. 
I decided to machine a brace with the spigots in one-piece. I counterbored the back side for the runners to fit into. 








The next thing on the list was the runner tubes. Basically, I split a piece of tube and add or remove a wedge of material till I get the desired amount of material. This is important because the shape will not be established till later. One of the things on my checklist was to maintain port velocity where the runners widened to cover two valves. The required what would appear to be a bubble or convex curve on the outside or "long" side. This causes a low pressure area pulling mixture toward the outside wall. From the side the runner profiles are slightly concave in the same area. To do this I start with longer pieces and anneal them dead soft. The extra material on the end gets bent as I hold from there to press, hammer and form the seams closed, weld full penetration. I then remove the excess weld and refine the shape








I then press the ends of the runners into the flange. Because everything is designed on the computer, when it's in position, it's usually pretty close. It's all in the prep kids. 
















next is the weld-up. I use 4043 filler in 3/32" diameter. I am using a gas lens and 2% thoriated tungsten. I know this is going to shrink, can't be helped. One of the reasons for the spigot flange is to balance the shrinkage and keep the surfaces parallel. Since this is a manifold for a naturally aspirated motor, I am looking for smooth transitions and nothing to get things stirred up. I leave a gap inside of about 3mm and weld the spigot flange to the runners from the inside. I also weld up the inside of the head flange








then it's time to weld it up! 








Here is how it fits the carbs








hope this helps your future projects!


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## secondgen (Jan 9, 2004)

*Re: MC carb/16V manifold build thread (frankthewelder)*

Woooowwwww.








http://****************.com/smile/emthup.gif http://****************.com/smile/emthup.gif


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## WackyWabbitRacer (Apr 24, 2001)

*Re: MC carb/16V manifold build thread (secondgen)*

Very nice work http://****************.com/smile/emthup.gif 
Where were you when I still had the WackyWabbit racer.....








Cheers, WWR.


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## antichristonwheels (Jun 14, 2001)

*Re: MC carb/16V manifold build thread (frankthewelder)*

Frank That is uber cool. you oughta build'em for sale.


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## ftwelder (Feb 27, 2008)

Thanks for the kind words fellers. perhaps some tuning shops or racing business will take notice also.


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## diceman469 (Sep 3, 2003)

*Re: (frankthewelder)*

Wow. Let me know when you start making SRI's !!


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## horvath (May 29, 2006)

*Re: MC carb/16V manifold build thread (frankthewelder)*

first off ill start by saying that is some beautiful work.
is it necessary to fill the injector recesses? im building a manifold from a cut down stock lower intake and was just going to plug up the injector holes on the manifold, or do i need to weld up the head too?


_Modified by horvath at 6:22 PM 5-20-2008_


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## OVERPAR (Jan 6, 2005)

*Re: MC carb/16V manifold build thread (frankthewelder)*

Frank, looks SIIIICK. I'll try and get the TB up to you ASAP.
Guys, in the spirit of full disclosure, FTW was just inducted into the MTB Hall of Fame in '07. http://www.completesite.com/mb...d=162






















The man is Legend....and one helluva guy.

RJ


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## ftwelder (Feb 27, 2008)

*Re: MC carb/16V manifold build thread (OVERPAR)*

uh oh.. my cover is blown. huh, like my corrado! 
as far as filling the injector recesses. in my "old school" brain I would say, they should be filled. Big changes in port volume (specially bigger) cause a drop in port velocity. This allows fuel vapor to form larger droplets causing it to burn too slowly to be fully combusted. HOWEVER it could very well be that it for some reason causes an improvement. Weird things happen and someone with more port and flow experience may tell us otherwise.


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## ftwelder (Feb 27, 2008)

*Re: MC carb/16V manifold build thread (horvath)*

something I was thinking about was attaching the "port fillers" to the intake manifold. If you are using the stock flange with the injector holes, have someone spin up some plugs that go beyond the flange into the port.. I think you are on to something.. ! http://****************.com/smile/emthup.gif


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## horvath (May 29, 2006)

*Re: MC carb/16V manifold build thread (frankthewelder)*

thanks for the input guys. 
those "port fillers" dont sound like abad idea, it seems that they should work. i could always have the head welded though..


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## StormDriver (Dec 20, 2001)

*Re: MC carb/16V manifold build thread (frankthewelder)*

Dude, that is beatiful work. What carbs are you using.
How much to make me an identical manifold? Seriously


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## ftwelder (Feb 27, 2008)

I am using a flat slide mikuni with 39mm bores. There are issues that will also need to be addressed. The water port will need a new piece and may be the alternator won't fit. I am pretty much making the whole car and I have no way of knowing what stock parts will work with this. 
Let's see what else is involved in getting this to work and we can discuss biz later..


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## spam16v (Mar 1, 2003)

frank, you're over here too?? lol, how's my bike frame? hehehe, j/k


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## billyVR6 (May 8, 2000)

*Re: (frankthewelder)*

That is some great fab work, for sure...
If your looking for a side project, I am looking for a top notch CNC guy to make an intake flange for me.


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## Aladinsane07 (Jan 10, 2007)

*Re: (billyVR6)*

Those are some gorgeous, gorgeous welds http://****************.com/smile/emthup.gif


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## ftwelder (Feb 27, 2008)

*Re: (billyVR6)*

well, thanks for the compliments and the offer. I am more of a general fab guy than a machinist. I draw in CAD and have a CNC mill but I also do tube bending, forming, drawing, press, forge, weld sort of stuff. 
I haven't discussed marketing my services here with the owners of Vortex. I should make some inquiries before going further with this discussion.


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## junkyardjockey (Nov 11, 2001)

I'd like to see you make a custom flange that would bolt to the lower half of the 16v manifold & have the runners be about the same length & shape as the upper manifold runners but end right where the runners would go into the plenum chamber...that's where a custom built box will be to mount a downdraft 350cfm holley onto it.....:thumbup:


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