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wkbrdngsnw
05-01-2012, 01:11
This is just interesting enough to need posting. I'm probably one of the few idiots that would actually put FI on a flathead 6 instead of doing a motor swap. It just wouldn't be as cool to put a 350 and an auto in it.

As always it has to start with the back story -

Now don't go having a heart attack. This was never a restoration candidate. When I got it there was just a frame and a pile of parts. Ranks right up there with the best $500 ever spent. It is a civilian cab on a winch frame with 2 different front fenders so I feel less bad about not keeping it original. I went for what the truck might have been after the war as surplus. Took 3 years to get it put mostly together. Took it wheeling with some friends and broke a wood body mount and had to limp it back. I realized it wasn't going to be my primary 4x4, thus my purchase of a CUCV but that is a different story.

It then sat for about 4 years being used mostly like a tractor. I built a snowplow and a lifting A-frame with roll bar to support it.

It never ran right since it had a carb off some sort of jeep that was missing parts and proved difficult to find a carb kit for. The first attempt was to make a 4 barrel to 1 barrel adapter but never was able to get it anywhere near right. Probably due to the lack of vacuum signal at the venturi. A 2 barrel was also tried and still wasn't that good so the truck just sat there.

Them the crazy idea of using TBI came from my conversion on the international scout. I could have used the stock GM ecu for the 4.3 but I don't like the "hacks" that you have to do to make it think it is still in the original truck. You also have to remove the EPROM to do any tuning. My choice is the Megasquirt DIY ECU. Its basically a simplified version that comes as a blank circuit board and has to be assembled. To tune it you just plug in the laptop.

To make this work I needed a new intake manifold that would accept a GM TBI. I had to machine the flanges that bolt to the block in the same way the original manifold. To get the shape they where traced, scanned, and then programmed into the CNC to cut them out.

The top flange also had to be machined to accept the throttle body. Add some mandrel bent exhaust tubing and sheet metal, weld together and there's a manifold. A block-off for the intake heat had to be made as well but that's just a plate bolted over the hole.

After all that I was lazy and just threw the tank from my S-10 project in the bed and hooked it up to get it running. Hopefully a more eloquent solution will follow.

The next problem was the throttle linkage. There was much debate about cable vs mechanical. I kind of like a good mechanical linkage so that's the way I went. The factory rod pushes up slightly and since the TBI is on there backwards the throttle plates rotate the other way. They also are on the opposite side. The solution is a shaft with a disc on either end that rotates. The trick is one is on the top and the other on the bottom so it changes the direction. Probably not the greatest solution but it seems to work.

Add a coolant and air temperature sensors plus an O2 sensor and its basically ready to go. It already was converted to 12V neg ground with an alternator.

As of right now it starts, runs, and idles. In fact the idle is actually better that the truck the TBI came off of. Now I need to dive it around and do some tuning.

OD_Coyote
05-01-2012, 15:55
Cool idea and the beauty is you could always unbolt the mod and go back to the carb if you wanted to. I would be interested in hearing how she goes down the road once you get her dialied in.

bigzirb
05-01-2012, 21:16
I love the idea. Keep us posted about how it is when you get it all dialed in. If you have to tear back into it the only thing I would put out there is this. Your manifold is a pretty good adaptation of how the original was, but the original is for a 1 barrel carb. If you have to re work it I would suggest the center tube stay in place. Then leave one of the other tubes in place and move the other outer tube to the outside of the TBI flange. I suck at pics but here goes.
____ XXXXXXXX New _____ <engine (The X's are just for spacing,lol)
i-H-i XXXXXXXXXXXXX i_H-i <manifold

Think looking down at a box with one inlet on the top left(to front of engine), one on the right side (to center of engine), and one on the lower right (to rear of engine). That might allow a more even airflow to the cylinders from each of the throttle venturies.

I am NOT bashing your work. On the contrary, I think you have done something that I have never seen before. I just had to throw out what popped into my head as I was reading your post.

wkbrdngsnw
05-02-2012, 00:26
After the first few times around the block it went from being really rich off idle to somewhat close. Having an O2 sensor helps tuning alot. The software makes it really easy since you just data log it and it runs through the data to adjust the fuel table for you. After that I went out on a major street and got up to a whole 40 mph. Its slightly better than it ever was with the 1 barrel. Its one of those things that the more you drive it, the more data it can collect and the better it will run. 1st and 2nd are good, 3rd is a little sluggish right off the shift but picks up. 4th still lugs but that part of the fuel table isn't seen as much so I'll have to drive it some more to have it tune that area.

As far as the manifold, it was definitively inspired by the original. I was going to do research on making it the proper plenum volume, intake runner length, and equal length runners. Then I realized that it was a flathead with a whole 100 hp.

The plenum is actually a triangle shape to make it wide enough to fit the width of the throttle body. This shape was selected to to and make it easier for the mixture to get from the outer bore into the runners which are at a slight angle. It was also hoped the air from the outer bore would run along the bottom and be the preferred path to the middle 2 cylinders and the inner bore would split over that flow and go into the outer cylinders. I'm not sure that's what is happening but it was a good thought. It would have been better to be a rectangle and have the outer cylinders come in the middle of each side but that would have made the outer runners even longer than the middle one.

I checked the plugs and the front 2 are richer while the other 4 are good. The throttle body is centered on the plate but that makes the actual bores forward about .5". The throttle blades also lean that direction so I think they are acting like an airfoil and directing the mixture forward. That is most likely why the mixture is richer in the front 2.

onegmjack
05-02-2012, 00:44
Sounds like a great project.Keep use informed on the results.Probably a lot of trial and error.
You may be on to something,like you said parts or kits for the older carbs are getting to be none to be found.

papabear
05-02-2012, 08:09
I'm interested.
Any chance of seeing a few pics of the whole truck??:)

wkbrdngsnw
05-02-2012, 17:41
Some video of me driving it around. Yes, I am a little rusty on the clutch thing.

onegmjack
05-02-2012, 17:46
Moving right along,sounds good.

WolfWalking
05-02-2012, 22:46
OK, this is something I might like on my WC-63 when I get it running. I can use all the performance upgrades I can find. Keep us informed, especially when you get the manifold dialed in.
:):):):arrow::)

WolfWalking
05-02-2012, 22:46
OK, this is something I might like on my WC-63 when I get it running. I can use all the performance upgrades I can find. Keep us informed, especially when you get the manifold dialed in.
:):):):arrow::)

onegmjack
05-02-2012, 23:08
I mostly like to stick to OEM,but when it is not to be found or found worn out.This could be a way to solve runabilty problems.

nattieleather
05-04-2012, 13:57
Looks good and sounded good. You might give some thought to chainging the distributor to an electronic one also. A good hot spark will help the EFI work a little better.

wkbrdngsnw
05-05-2012, 01:03
I contemplated doing electronic spark control through the computer but once again it seemed overkill. I did that on my scout and a year and a half later I am still trying to fine tune the spark table. If I wanted to add it later its about $30 in components to add to the computer. The wiring harness I bought even has the extra wires. Its recommended to at least upgrade to the PerTronix module but it can be triggered by the original points which is most likely what I'd do. I do have a 12V coil in there without a ballast resistor so it might be an idea in the future to do the conversion to keep the points alive. As of right now, I'm going to up the gap from .02 to .035 to go with the 12V coil when I put new plugs in. When I do that it should give me a better read on the plugs since the front ones might have been fouled a bit from the carb days.

wkbrdngsnw
05-16-2012, 12:20
Its nice to have it back to work. There is no way the engine hoist would pick the engine and the whole drive train.