All Small Six lets talk tubular....custom intake on the falcon log head.

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I can say thanks to ford six I have seen a handful of people who have successfully and been willing to share their cut off small and large log heads.

like anything I'm sure there have been many people who have talked about it and I was inspired and designed on paper several ways it can be done. I also went in depth designing and calculating variables to have a tuned intake for my engine.

I've also got a core to work with and machined off only the log so far and blasted it clean with walnut shell media.

so check out my recent log in the link and notice the beer cap for size reference. after cutting off the log I had to take a step back and have a beer. then the ideas started flowing like port on port carburetor, tunnel rake intake, aluminum intake options, and even thinking four barrel under a six to one collector with a nos fogger system.

lots of options and would like to hear ideas or people with experience doing it.

I've already got the build underway and am going with a tubular tunnel ram aluminum one piece bolt on intake so the design is on paper, supplies ordered, and in the hands of a qualified builder/ machinists.

so I would love to share all the info and time I've put into the design as well as pictures if I get some good feed back on this project so just look at this log and share your thoughts and I can go as in depth with my intake design as you can relate to it so get me in the sharing mood :) ... sort=3&o=1
study some of xctasy's posts on the small six for some really excellent ideas.
Sure hope you try something interesting with the shaved heads

Your pics also included a 2300 series carb?. I have been running an Offy Tri-Power setup with the 3 intake port adapter on a 250. Recently I modified the three input port adapter with a Hi-Rise Plenum with a 500cfm 2300 series which fits nice on a 2X4 steel plenum., considered cutting outer half of a log manifold for an added 2X4 / 2300 plenum component, there are pics somewhere with pipe-threaded stub ports welded to a plenum ... Your intake would be Hex-Power intake ? ...

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have fun
Thanks for the encouragement. That's right it's a 2300 series carb model 2305 progressive 500cfm Holley with mechanical secondaries so I engineered this intake around this carburetor even though with a custom intake I'm sure I could go up to 750cfm 4 barrel for all out race but it's designed for the street and this carb will give me best drivability and 500cfm is still a big jump from the 170ish from 1940 Holley.

Okay so ill catch you guys up to speed since I've already had this underway and has been years in the planning so it's a long read but I've gone over most options with welding the log and considered it but I'm going removable bolt on instead of welding the flanges and I looked into many fillers and rods but it's not easy to weld cast iron especially to steel or any other metal and even worse in automotive parts under heavy heat and pressure cycles. Even though people have done it and logs many miles welding steel to fast exhaust manifolds and what not so it is possible but I'm not getting into all the welding and metal working options that's a whole nother ball park.

Read up on the next posts and it's a lot to take in but let's talk if you can keep up because I believe I have the right audience here and people's experiences and feed back like power band who's done it will be helpful for all of us. I love your plenum design as well over the 3 offey setup which in itself is a hard mod to the log and you've gone and out a plenum on it....sweet!
I've had my 65 mustang 3.3l build going on the last 8 months now since my last rebuild that lasted years and just as i had everything ready for finally assembly I had the urge for a change. had a fully built 4.1l large log ford i6 head built with stainless steel valves, springs wih dampners, sspring cups, viton seals, oversized valves, and blended bowls. with a built up brazed intake for a direct mount 500cfm holley 2 barrel. the log is for sure a major upgrade that will over double hp over the originally small log with single barrel. naturally aspirated will make hp which is great for a 200. but I've got all that fuel capability and the head is still the limitation.

I have seen this head modified a small hand full of times with mixed results and dyno numbers. most seem to fall off the face of the earth(id heard about it once and never again from them.) so I decided to go back to a small log and cut off only the log, left exhaust intact. so all runners are open and my machinists is working on milling the runners flat then counter Boring to slide in 1.25 inch tubular stubs. that has all gone smoothly and I have a few ideas id like to get opinions on which would be what is the beat way to get stubs bonded to the antique cast iron head.

-my best guess is mild steel and braze with silicone bronze or a made for cast rod or even nickle may work with pre and post heat treatment required for some of these options
- second idea is orings around the stubs all on a flange then bolts or studs though the flange into the head(there is enough meat to drill and tap for this) similar idea to fuel injector rails.
-last idea may be jb weld the stubs.

hat is where the builder is stuck because cast iron is rarely welded to steel...let alone in automotive applications.

that's the main part if yout know what rod or filler to weld cast and mild steel with please let me know or I'm welcome to any ideas/input or comments.

from those stubs at a 45 degree angle I will weld up a tubular hi rise ram intake.

I spent a lot of time answering questions for this intake and calculation variables with my parameters.

my thought process started like this for my intake design.
- should I have 100% intake volume of the engine( 200ci engine with 200 inches cubes of intake volume.
-establish cross sectional area of runner. then I asked how long should runners be to be that volume. and is 100% engine volume ideal?
-best material for the build?(steel, mild steel, stainless steel and even looked into aluminum.
-how to find intake runner volume?
-size and length of runner will effect volumetric efficiency?
-what will my rpms range be along with power curves(peak torque and hp)
-how to get the tunnel ram effect and factor in valve closing pulse resonance going up and down the intake as valves slam such. this can be to your advantage with the correct length or will send terrible harmonics through your intake if not.

that's a start for anyone to ask themself when building a custom intake so you can have some data to start working with. also important to consider are under hood clearances issues.

I have all these answers in my notes for my build and engine specs.

so far tubing cross section is limited to 1.25 inch tubes so I calculated if each runner is 28 inches from valve to throttle body that would give me 207 cubic inches of intake volume which equals the engines displacement of 207ci.

from there narrowed down peak torque should be at 3195 rpms. from there the ram effect I'm after which is the valve timing pulses going up and down the runners and the valve closes. this is happening at the speed of sound so it would take over a ten foot runner to get the ram effect on the first order pulse length. so naturally you may have to divide runner length to be on the 4th or 5th pulse. nascar intakes work off the 3rd pulse so 4 and fifth is desirable for a street intake.

so I decided. to factor valve timing and duration for my application, vs peak torque rpm, along with intake runner variables. I came up with a runner length of 32.4 inches to hit the 3rd pulse and fourth pulse would be 24.144 inch length of each runner. so kinds of in the middle of the 28 inches I calculated roll see where 100% intake volume vs displacement would be. room. Is not an issue I will have these going straight up and down in the air out of the hood.

so I decided that with my limitation of a 1.25 inch diameter tube I would like to build the intake runner each 32.4 inches long.

this is a hi performance street/strip engine and just off calculations I've come up with that which should provide great low end to mid range torque torque and add some real horsepower. the consensus says long skinny runners for a torque motor and short and fat for rpms.

so first off and idea beat way to weld or braze tubular stubs to the cast iron head?
second enlighten me on the intake design to make sure I'm going in the right direction because I'm stuck with 1.25inch tubes so length is my main concern.
2 the originally plenum is only 1250cc=76 cubic inches so ill be at 207 cubic inches for this intake build. more then double stock. as well as originally this was an economy engine with a single barrel at 175cfm. check out the photbucket link I tracked down a holley produced on the early 70s designed for the australian crossflow 3.6-4.1l inline six so much different from a 2300 holley with revised passages, factory annular booster, and its mechanically progressive like a webber 32/36 or holley 5200. so I will be more then double stock flow numbers and should retain the best drivabilty, performance, and economy if I can stay off the pedal it will be cruising off only one of the venturis.

3 so to make this manifold happen I need a pole on these options
-welding one piece intake straight to the head. it would be mild steel tubes or stainless steel. welding with bronze silicone on a tig welded(heard it penetrates better then grazing) so it could be welded with that or I've heard really good things about certanium 889sp for mig and certanium 89t on the tig. its a nicole content made for cast repair or cast to steel with no pre or post heat juat weld and let it cool at room temp.

option two would have a flange with six tubular stubs across it. then the tubes would press into the runners with o rings and I would drill and tap the head to bolt the flange all the way across the runners. since it would be removable I will go aluminum in this case and I am leaning toward this because it may be the easiest to maintain and reproduce Incased the head ever cracked or something.

so those two are the best ways I can think. let me know what everyone thinks and if yiu have another idea I'm all for it. welding sounds nice because I know down the line an o ring is more prone to give. so the second flange idea I'm only considering because I could then go aluminum and not have to stress about any welding. but if I go with mild or stainless steel id prefer the one piece all welded.
I do believe I have found the satisfactory answers to most of my questions for this intake build but I need some real world builders that know what these engines like.

I made some final calculations and found peak torque for my engine and camshaft will be at 3300rpms. intake cross section for the tubes will be one inch and a quarter. on the second sound wave length from valve to plenum(6 tubular runners to a 6 into one collector with tapered ends under the carburetors base plate. two options on design from here in regard to the last variable undecided: length of runners? the second induction wave would need a length of 23.29" for each runner, 3rd pulse for ram effect would have a shorter length of 15.32" since fourth wave doesn't leave enough for design of my intake with 11.33" runners I left the decision between the first two...

the engines a low to mid torque engine designed with a valve timing arounder that, a low torque header home fabricated too so it should be making good low end torque so between the two options the longer 23 inch runners I would consider to be a low torque design with the carburetor and fuel so far away so I think the 15 inch will still produce mid range torque and hopefully help pull in the higher rpms with the fuel and intake capable of that. or should I go with the 23 inch length and keep everything designed around the low end torque.

I read on the original ford six 200 with a single barrel in dyno tests just with out the carburetors spacer (carb closer to runners) there was a 10% power increase then before with the spacer. I ran this engine in stock configuration and different that test for myself and it was noticeable from the pedal. with the carb closer to the runners it had a much sportier feel and would rev and pull much faster! with the spacer it was a dog and would rev much slower and had a very powerful torque pull like a tractor. I liked it much better with out the spacer.

so my thought is to keep it close to the runners and go with the shorter length of 15 inch runners. I've got annual booster that help throttle response especially neccesary in a build like this to make sure all the fuel is atomized and distributed evenly.

so I've got all my build plans and feel confident with my designs so week end is when I will get into the fabrication and id imagine 25-45 hours will go into it over the next few weeks unless I can knock it all out in a weekend(possible)

1). input on the runner length described in this post what do you think of a 15 inch length?
2)what do you think of the six to on collector under the carb vs building a plenum ontop the tubes?
and last
3) what would you do have it all welded as a one piece intake on the cylinder head?
-or build it all on a flange and make it removable or(" bolt on")... if you can entertain that idea?

both are same amount of work and time for the two options and are with possible ....I'm leaning toward one piece and can remove the head if I need to clean or maintain it. but I do really think with press in tubes with orings on a flange would be the more modern look. this is an antique car too so one piece also retains the simple nostalgia.

So that's a little catching you guys up on design I'm pretty much going to do my thing and start building unless I get some serious feedback on it over the next few days that can persuade me.
I'm going to recommend a slightly more radical approach - Individual Runners. Motorcycle carbs are cheap and very tunable or you could go with the EFI throttle bodies as well. Microsquirt that thing for under $500.

Several years ago I tried an IR approach using Mikuni carbs on the Locost. While it ran well at speed I had difficulty getting it to settle into a good idle. Mostly I attribute that to my lousy approach to linking all six carbs together.

But my recent experience with my son's Zetec powered MGB has been really good. We used Keihins from a Kawasaki ZX9R. With no tuning at all it fired up and ran extremely well and was only just a little lean on top end. We richened up the main jet a little and it is a blast to drive. It pulls from idle to the 7500rpm redline with no hesitation or flat spots and holds idle smooth and solid. We had to use a regulator to keep the fuel pressure down to under 2psi.

Eventually we plan to switch the carbs for EFI Hayabusa throttle bodies. Cheap and easy to adapt - you just clamp them to an intake tube. The injector bungs are integral and the end carb holds the TPS sensor. The bodies separate by taking the threaded rods off. You can then add two more with the appropriate spacers and link them by just tacking on a straight flat tab to the linkage.

Carb or EFI, it is super easy to add these to the ex-log head by just brazing on some tubing for the intake. As far as length, don't overthink it. There are so many variables that go into tuning the total engine and intake tract length, volume, and cross section are only part of the equation. Point is, it won't really make a big difference if you made the runner 4 inches or 15 inches. Just do whatever is most easily packaged under the hood.


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I love port on port I've got a 750 kawasaki and have had to do a rebuild once on the 4 linked together carbs so id say that's within my realm since I have rebuilt a good amount of bike carbs. its a great option and has been done check out this video on a 200 ford with six cvk40s, and a comp cams 252h which is undercammed.

id like to stay with an intake rather then flange for six carbs just to keep it highly tunable with a holley and would be much better for power adders. I do have some interest for port on port carbs on a 200 but I'm much more motivated to do the tubular intake. ... ata_player

I'm also confident I've got a solid removable intake design that my machinists agrees with so i do see how bike carbs could mount right on the tubes of individual runners and if I can make it all removable I sure would love different intake setups
and this will be much easier to see once the removable flange is made. ... ata_player
good project will be watching with interest .

have you seen/used the pipemax programe ?

can calculate all the inlet runners sizes , lengths, exhaust size and lengths, cams lift etc etc to complement it all as a package

approx $70 - takes abit of understanding to interpret the results

maybe all academic -and you're on your way .
I have not used that software but i have been looking into some more engine software and that looks reasonable. Thanks
you really think runner length won't matter much? I plan to set it up close as possible to the runners.
Runner length is just one of several things in the equation. For example, suppose you carefully compute the diameter and length of the optimal intake for a particular rpm or load, yet the cam is operating elsewhere, or the exhaust is operating elsewhere, or your gearing is elsewhere, or the timing, or fuel curve.......

You could painstakingly design a total engine system that optimizes (or at least has fewer compromises) all these and end up with something like a 300 hp 3.3L M3, but in our case with a chopped-log case we already have so many intake, exhaust, camshaft, ignition, combustion chamber, etc. compromises that a couple of inches of intake runner, one way or the other, probably doesn't significantly affect the outcome.

Would it make a difference? Sure. You might move peak power or peak torque up or down by a few. I'm just saying that in the real world sometimes just getting everything to fit is a better solution than optimal runner lengths. Example : This design works great - but wont fit a Mustang.
jack is right, unless you are building a race engine, dont worry too much about having the perfect pipe length, diameter, or the pipes being equal length. remember the very first compromise is going to be making the package fit the area where it is going to sit.
rbohm":ul7mzdfo said:
jack is right, unless you are building a race engine, dont worry too much about having the perfect pipe length, diameter, or the pipes being equal length. remember the very first compromise is going to be making the package fit the area where it is going to sit. I would love to keep the momentum going but I won't have the supplies till next week so I estimate this will take shape between the next 2-3 ill update it when I'm making progress but I'm loving all the great info and interest on here.

I will really be anxious to see what this will do to rear wheel hp and torque because off my simulations I expect to see significant gains but real world I would be extatic if I could get into the flywheel 250-270 hp which I think is realistic.
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