Carb info for the turbo design.

Well I finally got the time to take the carb apart today. With the help of my bud Greg we did some tear down and research for you guys. The first pics of the two carbs are for reference. One is the 81 and the other is for a 74. Other than the electronics on the 81 there's not a lot of difference between how they really operate. 4M and an E4ME for reference.

The mistery of the boost referenced power valve is forever solved as well. There's very little difference between the NA cab and the boost reference one and you CAN make one if you have the right parts. I'll explain this as I go through the pics. Both Greg and I are suprised no one figured it out but since we have and now know how to do it you guys are gonna have a fit. And it's so simple even a newby could do it if you have a a drill press and basic metal working skills. I think this means you can do it as well Aj. LOL (you knew it was coming):biggrin:

The first pic is of the base plate. This is the most important part and without it you can't have a boost reference to the power valve. As you can see I used straws so you can see where the port is. This port is what Makes the carb so special. It doesn't alow vac to influence the power valve. It isolates it so you can use the boost for a reference to keep fuel flowing when you let off the throttle.

The next three are of the body of the carb and bases. This passage is for the power valve to get it's signal. Between the two of them is why the carb is so special. Well now for the best info. The base is the clue, not the body! With the proper base you can turn any of the 4M carbs into a boost referenced carb and all you need is the right sized tube and a couple of drill bits. No jokes, it's that simple!

I have a bunch of base plates so I started looking at them to see what is needed to do this. The 4 base plates I'm showing are all 4M but for different apps so you won't see much of a difference in them. I highlighted the areas you need to look at. This is normally where the power valve gets a vac signal from in an NA carb, but in the turbo carb this is blocked off. That's what the tube sticking out of the front is for. You have to look at the passeges really carefully to see what I'm talking about. I have two boost carb bases and I only have 1 carb so it will go on another body to make it work. If you want to build one you MUST have an NA 4M carb to do it. You will also need the base off of an E4ME because they don't have the passage for the vac signal to the power valve . Nothing's drilled there which is exactly what you want. The other benifit for this is the fact that the hole to the power valve is started but it's just dimpled so you don't have to worry about figuring out where it goes. You will need to measure where the tube goes on the front of the base and I'll give the measurements for that later as well as the size pipe you need and what drill bit to use. I'll also add the depth of the hole on top so you drill it out without going through the base plate.

Now if someone will let me borrow a PEVR valve I'll see if I can make one so we don't have to scrounge them any more. I have a good idea of how they work but I need one so I can make sure I'm right and make a substitute instead of having to scrounge them and hope they work.

I saw that but wanted a simpler version just using some one way check valves. A mechanical versoin would be easiest after all. Since you're the first to see the info rate the thread when I'm done with it.

LOL I guess I do think a little to much Dan. Just want to make sure the info is out there for the rest of the guys.:biggrin:

That was one thing we lookd at yesterday Freddie. Any of the 4M designs have the same base design and the only difference we noticed was the way the power valve vac hole is made. The E4ME doesn't use this feature since it's electronic. It has the same base but also has the extra ports you need just like the turbo specific carb. I guess I should take some more detailed pics so everyone can get a better idea of what I'm talking about.

Maybe this will help you some.
http://www.turbobuick.com/forums/before-black-non-sfi-tech/143192-turbo-carb.html

No problem. Rich is a great source of info for all of us and I thank him for having the before black website to refer to. It saves lots of time if ou just remember to look at it once in a while.

A basic understanding of it is that it removes vac when the turbo spools up. You'll need 2 people to check it. Suck on the line that's hooked up to the carb from the pevr and see if you get any resistance. If not you then need a small (8lbs) amount of pressure on the turbo side of the valve and see if it cuts off flow.

One of the lines is the check valve that closes off the vac signal. If none of the ports seem blocked up then you probibly have a bad one. Think of it like a faucet. The pressure from the intake after the turbo closes the valve.

Here's a link just in case you have any more questions. Freddie was nice enough to start his own thread to help with understanding how these carbs work. Thanks Freddie.

http://www.turbobuick.com/forums/be...adapting-non-ccc-q-jet-turbo.html#post2446399