Hi all, I've finally gotten around to putting something together to show the progress of my1974 Mazda REPU Carburetor to GM TBI Swap. This is just a photo "show and tell" for now till I get finished and running. So lets get with it.


This is where I started, centered drilled the bolt holes into the adapter to fit the manifold.



Here is a couple of the adapter configurations that I tried before deciding on the one on the right.



Just used a couple of gaskets for locating where things needed to line-up.




An old carburetor gasket was cut to match and used to mark the manifold before I started grinding.



Mostly finished manifold after I make sure everything works and runs. I'll take thing apart and polish everything up.



TBI with last test adapter. You can also see the 94, 94 Ford Taurus SHO 3.0 V6 130 amp Alternator I put on.

 

Final adapter in progress.



The panel I made to put the Megasquirt, fuse box and relays on. this will all bolt onto the spot where the stock computer location, well if you can call the stock computer a computer.



Nice coil I found in the Megasquirt manual, it's from a 2005 VW Golf 2.0L it's 4 separate coils in one package.


This is what happens when the WIRE MONSTER goes out, gets drunk, then comes home and barfs in your truck.

 

Any updates on this project, how did it work out for you?

 

Well the old girl is setting in the driveway waiting for spring. Got it running last summer but that is about as fare as I got before life's little things took over. Hope to have more on this later this spring when it warms up. I'm getting eager to drive it. I'm using a MegaSquirt stand a lone ECU to control everything can't say this Electronic stuff hasn't thrown me a few loops, but this old carburetor guy is coming a long.

Allen

 

Interesting..
I've owned my fair share (lo5) 350 TBI's.
Is your throttle body modded at all, or just a stock one?

 

I put injectors for a 454 in it other than that stock.

 

I've modded a bunch of them myself.
You can unshroud the throttle bores, and thin the throttle shaft. It increases air velocity, and improves throttle response.
This is one I did last year.


As for using 454 injectors, deu to the restrictive airflow of the 350 throttle bodies, I bet you find it runs pig rich all the time.
Also the 454 injector bosses, and the pedestals are HD, and designed for higher fuel pressure.
As for the last part, you will need a higher fuel pressure. Did you do any kind if fuel regulator mods? You would want probably around 30psi with those injectors. The stock regulator is set at 13 or 14.
You can melt the solder on the adjustment screw at the bottom of the regulator. It has a small security torx head screw. A little turn makes a huge different to BTW. You could also change the spring to a 454 spring, but it would still require adjustment.
The 350 TB is not designed for those pressures. You have to rebuild it very carefully (injector seals, and gasket) or the pedestal will look like a fuel fountain when you pressure it up. I had one split on me at 20psi. So it's crap shoot...

I could go on, but all I can say is I wish you luck.

 

I forgot, I put the spacer under the Pedestal. For now, that’s all I’m going to do till I know it is going to work. Then I’ll Probably go ahead and change it over to the 2” bore TB. One of the problems that I’ve ran across is that none of the 2” bore TB’s have a Round Cable Linkage like below. Is there a way to mode that? I noticed that they are swaged on so maybe I could grind off the swag, drill and tape a hole to put a screw in to hold the cable linkage on.

I can pull out some of the richness with the ECU till I get the new TB put together with the mods you’re talking about, I’ll also have to do a little work to my adapter so it all lines up inside. The fuel pressures will stay stock till I make the change over to the 2” bore, I’ll have to use a different fuel pump; the one I’m using now only goes to 15psi and the TB is running at 13psi.

 

If your running the larger injectors at 13psi they won't fire properly. The spray pattern will be effected, and it will give you grief. (That's why you'll have an over rich problem).
You'd be farther ahead to use the 61pph injectors from a 350. The 74-80pph injectors (454) just don't work with the smaller throttle boddies at lower pressures. They "need" 26 to 34psi to spray the proper pattern.
The bummer thing being that you can't crank the pressure that high on the smaller base. The injector base will literally blow apart! 20psi is max on those, and even at that it's sketchy.
I'm not trying to be a dick or anything bud. I'm just trying to save you a major headache.
As for the linkage, you have to change the whole throttle shaft. Not real hard to do if you can get the screws out of the trottle blades, and the shaft isn't bent..

I wish you luck bud. It's a cool concept, and I'd love to see you get it running.

 

The reason that I've kept this conversation going is to learn; so that makes you a teacher, not a Dick, this is all relatively new to me I've read a lot but haven't had many conversations with people that actually know what there talking about. I'm very grateful that we have had this conversation. Thank you.

I'll be ordering new injectors before spring so I don't blow up. LOL. I'll take any help I can get.

PS: I'm writing a little booklet on how to do this, so do you mind if I use the information in that booklet?

 

Write that down man.. lol
I like keeping notes to.
Makes life easier for sure.
I was digging through a bunch of old parts this morning. I was trying to find the base I blew up. (But I think I threw it away).
I was gonna post a pic of it.
Anyway.
The top plate that houses the regulator split at 20psi, and I had a gas fountain under the hood!! The base could have been compromised from getting dropped or something? But I've read about it happening to other people. So it's best to err on the side of caution, and run a lower pressure.. lol
The 454 throttle bodies are 650cfm. The throttle, and injector bases are way thicker to take the extra pressure.

 

One thing you sould do for sure is toss that plasic air cleaner base. Avoid drop base air cleaners with these things. They like a straight shot of air. Thats why I always shave the air shrouds. That alows the air to travel staight into the throttle bores with no restriction.
Power bowl air cleaners, and velocity stacks work best.

That being said, I think your biggest hurdle will be the injector pulse rates. But if you get that dialed in it should work.
The rest is pretty straight forward. They're basically just an electric 2 barrel carb. Nothing fancy.

 

One more question if you don't mind. Sense the only throttle shaft with the cable linkage are small TBI, will it work with large butterfly's in the 2" TBI?

 

Unfortunately no.
The holes for the throttle blades are different. But if you can tig weld, you could weld it onto the other shaft. There's always a way.