...the carburators for my blower set-up. In a past thread, you mentioned that Holley's don't work well in blower applications w/o some work. I have a pair of 4150's that I intend to use. I am in the process of removing the choke towers and blending (by the way, thanks for the tip on the tube thingys), and would like to do as much as I can to prep them for use on my motor.

Can you give me any tips?

As always, Thank you!!!

 

I also removed my choke towers and blended them with a die grinder. One of my carbs had a bad internal leak and I couldn't find it for a few weeks and until I borrowed a metering block from the mustang , it solved the problem. I had a bad metering block.
The other carb looked like someone bunched in the floats, I assume automation crunched them, both front and back. Of the 3 new carbs I bought the one with the internal leak was the best.
Anyway for the blower you want the carb power valves indexed off the intake manifold, not the one on top of the blower but the intake.
To do this you can either buy special ones from holley that like mine use a special tube from the intake directly to the power valve of using devcon alumim remove the existing blow check valve, fill in part of this area and redrill for a reference tube.
When I started doing each carb I dismantled them , using a flat glass plate made sure all surfaces were flat, the gaskets needed to be scrapped off and all new gaskets bought.
Anyway I immediately drill the butterflies, all 8 throttles for bypass, installed .015 wires in the idle circuit, drilled and taped the transfer slots for screw in jets, left jetting alone, removed the springs from the power valves completely, vacuum holds them closed, boost blows them open,
Lean out the carb using the idle circuit, not jetting.
Hook up reference tubes to the intake.
I run 15-1 cruising down the highway, plugs are white but the minute the boost crosses from vacuum the power valves open giving you 13-1 under any boost.
I run 43 degrees advance, use electronics to bring it in, use a timing computer to pull timing out under boost.
I get 15 mpg driveing 1/2 and 1/2, car never ever fouls plugs, runs cool enough that most of the time I run no fan, easy starting and shuts down clean.
Holley really makes it easy with their new blower carbs.
While I find alot of problems with holley, particularly too rich at idle once reworked they give me no problem
You need the power valve, don't try to get along without them ever, no way except all out drag, never on the street,
You need them reference to the blower boost, not the vacuum under the carb, you will have fantastic vacuum under the carb, 18-20 inches.
I run lots of boost, 12 pounds, 15% overdrive for real bottom end grunt.
It makes for really nice around town pull, sure if you run alot of wide open runs you would be pushing it but with 15% around town pulling away from lights I often see 10 pounds without pushing it.
Alot of my mods I don't really know until I tear the carb down then I start fixing what I feel needs changing. I will redrill, tap and thead in jetting, I do like the .015 wires in the idle circuit and I still like the holes in the throttle plates.

Pulleys? I made a special pulley for the blower. It has the accessory belts in front, not behind the blower belt. This allows the alternator and power steering pump to be mount infront of the heads, one on each side, down low.
Using the stock setup with the accessories behind the blower belt forces you to mount the accessories high or off to the sides to clear the motor.
I like my setup alot better.
I think I have a spare blower pulley with the accessory pulley in front down in the shop?????

 

Thanks for the quick response Norval. I've obviously got a lot to learn, but look forward to digging into it. As you might guess, I've got a couple questions: 1) you say to index the power valves off the intake, and then say they should be referenced to the blower boost. Is this two different things? 2) I'm a little confused with the comment about the tube directly to the power valve "of devcon alumim" remove the existing....???? 3) I understand, that with pump gas, total compression ratio should not exceed 12.4:1. Blower boost will be based on this number, minus "static" compression. You mention 15% O/D, 12# of boost. What total compression are you looking at with that much boost?

 

With a blower you have two sources of vacuum. One directly under the carbs but above the blower itself and one in the intake manifold under the blower. When running with say even 5 pounds of boost the intake under the blower is seeing 5 pounds while the intake under the carbs but on top of the blower is seeing a high vacuum. If the power valves are getting their signal from the intake under the carbs they stay closed because hey we have a good vacuum, no need to open and vacuum is keeping us closed.
But what is really happeining, the motor is seeing 5 pounds of boost and needs the extra fuel.
I block off the existing power valve reference points which is under the carb with devcon alumimun and drill a new hole with hoses that connect to the intake under the motor. Now the carb sees what is happening at the motor, not under the carbs so when add fuel is needed the power valves open regardless of what the intake on top of the blower is telling it.
Remember as you build boost in the intake on the motor the vacuum under the carbs is really good and the power valves are totally confused if they are seeing the vacuum under the carbs.
Hope this helps.
I actually run 14.5 compression with a boost/retart and 94 octane fuel.

 

Norval, why didn't you go DPFI by now??

GENE

 

Gene I know carbs, I know how to make them work smoothly, how to get descent gas mileage and every year I have expensive modifications that I seem to be doing.
With fuel injection I have to start learning all over again.
Something about not being able to teach an old dog new tricks???
I can work through any carb problem. I actually have a carb carefully cut up for referenceing every passage and if I have a problem I just take out the carb and work through why the problem exists and do something about it.
I feel my carbs are well dialed in, give me about 15 mpg and don't load up ever.
Maybe someday Gene but not now.

 

Thank you Norval!

 

Your welcome and I hope I explained it better the second time. You can buy these carbs already set up this way directly from Holley.