Interesting. I see the "mushroom" or "umbrella" shape on the primaries, and see how that would increase the signal and decrease the CFM.

And, I see the differences on the secondaries. I wonder what that would do to a 400?

 

That will depend more on the manifold design. If you are concerned, do you still have the corroded 780? If so send the main body, I know how to switch boosters.

 

Good idea. Yes, I have it and will send it soon - once things settle down a bit.

As for the manifold design, I can only hope that Weiand did a good job and designed in good distribution. After all, they weren't constrained by size nor much by cost. Having said that, I'll check with Tim to see if he knows of any distribution problems.

 

FYI, One of those "recommended by a friend" things.
I had to look up the numbers off that carb.

Holley 730 CFM 1969 Cobrajet GT Carburetor Holley List 4609 Date Code 294 | eBay



Damn Gary, you could buy a QFX 1150 for less than that!

 

You might show him the picture of the bottom view. If he feels it isn't an issue then I will leave it alone. If you have any extra choke housing attaching screws throw them in too.

 

Many times such a recommendation is from someone that doesn't really know, but in this case the friend is quite knowledgeable. And I think the idea was more of a "would you like to try" than a "you should buy". Plus, I believe the recommendation was predicated on the fact that this carb has the unusual boosters that increase the signal, and it was a Ford carb so fits with the build theme.

Dad's funeral was yesterday so I haven't had time to even think about talking to Tim, but I may get to send him a message today. And I'll send him one of the pics of the boosters - good idea.

As for the screws, you are talking about the ones that hold the housing to the body - right?

 

Damn Gary, sorry to hear that about your dad. I know you will miss him, I still miss mine and he died in 2009.

On the carb, yes, the ones that hold the housing to the body. BTW, since that post Jim has possibly found a nice carb from Quick Fuel Technology, interestingly enough, located in Bowling Green KY, same as Holley. It is advertised as a 735 cfm model.

 

Thanks, Bill. The last two weeks have been a bit of a blur. Dad fell and broke his hip. That sent him to the hospital and things went downhill from there until he passed away after a week. Meanwhile our son and family moved from DE to St Louis and I was hoping to help, but couldn't. And both Janey and I were supposed to be in Nashville to help our daughter and family move - first to Oklahoma now and then to Nicaragua. So the day after Dad died Janey was on a plane and I made the funeral plans. Then I drove to Nashville and we helped them box and load and come back to OK in time for the funeral. So now we are blessed to have our son, his wife, their 5 month old daughter, our daughter, and her 3 year old twins under our roof. Later today our son and family head back to STL, but the other three will be here off and on until January so not much will get done on the truck while I play with the twins. But, I'll get out to the shop from time to time and will get the screws for you.

Also, since you know how to swap boosters, what is the possibility of swapping the annular ones from a 4180 to a 4150 or 4160? I have a 4180, but since they only come in 600 CFM form, which Tim says is too small for this 400, I wondered if we could effectively make a 750 version by swapping boosters?

I don't know if boosters for a 600 are smaller than those for a 750, but probably so, which would mean this idea is probably a no-go. But I thought I'd ask nonetheless. And, if I do get some shop time I'll see if I can measure the various boosters.

 

The 600 cfm boosters are a vertical design with a straight tube from the edge. We used to install them in the larger body castings to improve response off idle. Might be an idea, the 4180 wasn't around when we sold Preston in 1978.

 

What does it take to swap boosters? Is that something I can do?

 

You actually have all it takes, look closely at the boosters on the metering block/plate end. You will see that they are "rolled" in place. Carefully drill into the rolled are with a 3/8" (I think that was it) drill maybe 3/32" then use a punch to push the booster out. To install, use a good epoxy, with both pieces oil free and push it in, make sure it is centered and vertical. once it cures, clean up (de-burr) the inlet area.

One caveat, we actually had to drill out and tap the air bleeds so we could change their sizes. I don't remember where we got them, but we had some little brass air bleeds we used to increase the size as the easier pickup on the smaller boosters would cause a rich top end. We did have to open up the mixture feed passage on the 600 cfm boosters in the 780 cfm body, or it would go lean at top end.

Now you are learning all of Preston's old tricks. We were way ahead of everyone else including some of the now big names.

You would not believe how much I can get by blueprinting a carb 30 min work on a Holley 650 2 barrel = 15HP more on the dyno. I set up a big (Oldsmobile 425) Rochester 2 barrel for an oval track class that required "factory" carbs, ie Rochester on GM, Carter or Stromberg on Chrysler, Ford on Ford. He dynoed that one, it ran as strong as a 500 cfm Holley 2 barrel.

 

Bill - Lots of questions. So, let me set them out and then post the pics:

1. Screws: Are the choke housing/body screws 8-32 or 10-32. The 4150 and 4160's I have are 8-32 x 1 3/16" while the 4180 takes 10-32 x 1 3/4", probably due to the pull-off that is incorporated in it. If 8-32 I may just send some stainless SHCS's I have instead of robbing one of my carbs as I don't have extra - if that's ok.
2. Boosters: I don't see the "roll" you are talking about that keep the boosters in. I've included some pics of the corroded 4150's boosters and the 4180's primary boosters and don't see the roll.
3. Booster size: The annular boosters on the 4180 are .925" OD vs the straight-leg boosters on the 750 CFM 4150 that are .630".
4. Tips: Ok, so one tip is replacing the boosters, but what else did you do? I've reworked Q-Jets to get better performance on my boat, but that was limited to ensuring the blades were coming open, cleaning up the flashing on the casting, and other similar things. It worked, but not likely as much as you got.

Here are some shots of the place where the boosters hit the body. Can you point out the roll?

This shows the annular booster on the 4180's primary:



This shows the straight-leg booster on the primary side of the corroded 750 CFM 4150's body:



Another view of the primary side of the 4150:




This shows the straight-leg booster on the secondary side of the corroded 750 CFM 4150's body:



This shows both sides of the 750 CFM 4150 with the .630" boosters:



And here's the .925" annular primary boosters on the 4180" and the .630" secondary boosters:

 

Gary, the choke housing screws are 8-32.
One of the tricks is simply deburring all the casting lines, boosters etc.
Other trick is either using the phillips head throttle plate screws, or if you have plenty of the straight slot screws find 8 that line the slot up in-line with the air flow.
Use loctite on them and remove the portion that protrudes. I then use a center punch to upset the end of the screw.
The roll is on the metering block face, not inside the bore, see attached pictures.

 

Ok, now I see what you mean by the "roll". And you use a drill to take enough of the rolled portion off to allow you to gently drive the booster out with a punch. Then insert another booster and use epoxy on the outside of the booster to sort of recreate the rolled portion. Got it.

Did some further reading tonight in various of my books and found that two of the call tho boosters which are in your carb the "truck" boosters. Here's a pic with the truck booster on the left and the economiser booster on the right:



And here's the standard booster vs the truck booster:


Here's one showing the vacuum curve of the annular discharge booster:

 

Gee, I remember when the 4500 was first introduced, about 1968 or 9 I was working with Preston Carburetion when Fred and James Pennington first opened up. The early 4500s had an intermediate nozzle in the main body just above the throttle plates.

We always put the epoxy on the outside of the tube, then pressed it into the main body.