|12/28-30/00: A Funky Hobbs type switch… Over New-Years weekend, we had sort-of a snowstorm, and this was optimal shop-time… I had been hunting around for a hobbs switch which could be adjusted to the various pressures we use, and couldn’t find anything suitably cheap and funky… So I cut an old Carter fuel pump in half, gutted it, and made a little bracket that would hold a set of points from an old Rambler, open using the spring tension from the points. To hold it open rather than closed, the “far” end of the spring needed to be mounted in a different spot, and a certain amount of bending and fooling around was necessary to get it just right. When the boost rises, the diaphragm in the fuel pump starts to move, it is opposed in this movement by the stock fuel pump spring, and perhaps a few washers to increase spring tension enough to keep things quiet until the working range of 4-10 psi is reached. Then, as the rod on the diaphragm starts to move, the threaded on extension making the rod long enough to reach the points assembly starts to push on the backside of the point breaker arm, pushing the normally open set-up to close. The points must be insulated from the body of the device on the spring side or it will short the circuit, so a little block of plastic was carved to hold the far end of the spring in place with a machine screw (which also is the terminal post for one of the connections of the switch. By adjusting the “point gap” in the traditional way, adjusting the little threaded extension on the diaphragm rod and adjusting the preload on the fuel pump spring (with the washers) I was able to cause the points to make contact at any desired psi level! To check this, I made up a little junction block where I could hook up a small compressor, a pressure gauge and an adapter to connect a hose to the switch. I also had a little bleed valve in the circuit to adjust air pressure. I hooked an ohmeter up (could use a light or buzzer) to test continuity of the switch, and gradually increased pressure, waiting for the rod to push the points shut and close the switch. I’m sure most fuel pumps and points could be adapted to make this switch. The only thing to remember is that there is really a lot of power in the diaphragm at the max of 10-20 psi most will be running their cars, and the setup should be adjusted so that it is just making a connection when you are out of rod movement, if not, and the bracket holding the points isn’t strong enough, the whole thing will twist itself into a pretzel! |
Next, I made a Blow-Off valve as mentioned in various TurboForce publications using a pipe tee, a Stude exhaust valve, a brass plug and a spring. Chucking the tee into a lathe squarely was accomplished by threading in a nipple and tightening the chuck on that. Then, the taper of the valve seat could be made. Later, using some valve grinding paste, I made the seal fairly air tight by lapping the valve in (used a drill to do it….). The hardest part was getting a good seal on the plug which acts as the “valve stem”. I suppose I could have used a real valve stem and seal, but good ones would have cost money! Instead, I picked a size hole a bit smaller than the valve stem, and drilled it in the plug. Since I didn’t have a reamer, I then sanded down the valve stem itself to fit the hole….. If there is too much leakage there in practice, I’ll just put a short length of radiator hose over that whole end of the tee with a bung on the end and a hose clamp to the tee (sort of like a little carb box idea….). Again, I used my little test set-up to add spring tension until I got the valve to release at 15 psi. You may remember that I already have the radiator cap device as a blow-off valve. It started to sound incapable of handling the amount of air necessary when boost approaches 10-15 psi, so I will probably set it up to open at 2 or 3 psi to fill an air tank. I will be using the compressed air early in spool-up to eliminate any lag by injecting it on the backside of the turbo compressor vanes…..Remember the canning funnel? Made an adapter out of a piece of aluminum plate which matched the top of the AFB and had a groove just the right size for the i.d. of the funnel. This was then epoxied to the funnel. I had to make some little grabbers to hold the plate . onto the carb. These need to be rather strong if they are to hold 10 or more psi.The regulator needed to be mounted somewhere, and since I wanted a fuel pressure gauge visible reading pressure right at the carb, I needed to do some creative plumbing. The regulator has two outlets, and I used one for the gauge, the other into the carb. The regulator screws right into the carb now using some brass fittings which I soldered together. Now, the gas inlet/filter, which was on the far side from the fuel pump, is more convieniently plumbed for hook-up.Also made up some long nuts to make bolting the intake manifold back on a bit easier. Next I’m adding a stub to plumb in the blow off valve and fitting on the intake plenum to gauge the “true” boost and as a location for a pressure switch which will ‘arm’ the air injector only when pressure is low. This can be an oil indicator light sensor according to a little test I did with my set-up mentioned above. This particular sensor turns on until about 3.7 psi. Just long enough to get the lag out, but not long enough to waste all the stored air.
1/8/2001: This weekend I made a mount to hold the blow-off valve, probably on the fender wall. I also machined a stub for the blow-off valve take-off and welded it onto the “filler neck” where the radiator cap valve is mounted. I tapped a stub on the intake manifold to mount a “T” just below the carb. The “T” will go off to the boost gauge on one side and an oil light indicator switch. This switch is set to turn OFF when the pressure gets up to about 3.7 psi. This will ‘dis-arm’ the compressed air “Lag Eliminator” (hence to be referred to as LE). Next I pirated the housing off the 2nd 2.2 turbo which was GIVEN to me to prepare it for a quick swap later in the cold garage. Inspecting the turbo, it is just fine. I’ll store it in a safe place until I can get a housing over that turbine. I then studied the housing and figured out a good place to put the injector for the LE. I very carefully drilled this sort of oblique hole and then made an aluminum ‘injector’ to screw into the hole from the outside which would accept a hose from the LE set-up. Made it out of aluminum to match the thermal expansion of the aluminum housing, which I suppose was a good idea. Also, in rereading the article on sealing the the AFB in Dick’s Turbo book, I decided to make up a seal for the accellerator pump shaft. I turned a little rubber seal and then an aluminum washer which I epoxied in place in the top of the carb.
Home page Next Chapter