Check out Nickerson's website under "What's New" in the Marine division in regards to a "blow through" system.
www.nickersonperformance.com/marine/marine.html

If you're running the carb in a box, and using solid floats you shouldn't have to boost ref. the PV.

The reason you Boost Ref. a PV is incase you have vacuum between the carb and blower, but boost under the blower. In a blow through system if there is boost on top of the carb there won't be any vacuum under it.

Doug

Does anyone know what nickerson does to enrichen there blower carbs "internally".
It seems just as many people with blower motors have there carb/s boost referenced as those who do not.
Does the amount of boost you run make the difference.
I would think that maybe you could get away without boost ref. on a lower boost setup(under 5lbs).
The jury's still out on what I'm gonna do.
I'm installing a B&M 250 on a 502 and I have a holley hp 1000 cfm carb I want to try and use.

Great point Profile, I am runnning 7 lbs of boost and like I have stated earlier, the Nickerson carbs work flawlessly

and from my own experience, the 250 B&M does not distribute fuel very well with a single carb. The outer clys will run lean, better fuel distribution with duel carbs.

Good luck with your project,

Kurt.

Maybe the answer to running the single 1050 on the 250 Blower is John B's setup of turning the carb 90 degrees from normal. He also stagger jetted his carb/carbs (he has a twin engine Cig) to run richer on the rear cylinders. I hope he doesn't mind me sharing this info.
I am letting Dean Nickerson take a stab at my carb. He has improved this configuration as per our phone call. I will share the outcome with all of you when the time comes.

Biggus can you expand on your experience with a single 1050 setup? Did Dean steer you to a 2 carb configuration? Do your engines warrant that setup?

ON BLOW THROUGH, it is important to use a smaller than you think carb. Jim at Arizona Speed and Marine is a good source, also. I just did a blow through ProCharger. If works great. No special machining, etc. was done, just practically out of the box-very small carbs, though!!!
BIGGUS and I have had the same experience with the 250 B&M.
Two small carbs distribute the fuel much better. Don't recommend using two 850's or anything nearly that big. You get the best performance with the CORRECT SIZE carb. I ALWAYS boost reference any carb in a draw through. I don't claim the experience of Nickerson, but I have never seen a non-boost referenced carb that did not have issues a boost referenced did not have.

US-1 Fountain is Externally Boost Referenced on the primary side only.
Let's see some real numbers.
Jet Size or Sizes?
Power Valve Size and how many?
PVCR diameter and is it the same in both metering blocks?
Are you using an Intermediate Circut?
Air Bleed Restrictions?
The point I am trying to make here is that there are many combinations available to achieve the final goal and that is to introduce just enough fuel at a certain point in your operating range.
When is the best time to have that Power Valve open?
Do you want it open when at cruise (3000-3500 rpm)?
Someone mentioned lean at lower RPMs and more fuel in the upper range. Makes sense to me.
There seems to be some satisfied people in both camps.

You can almost take a Holley out of the box and, if it is a performance carb. install about 4.5 power valves and go up two sizes on all the jets, index the power valve(s) and go try it out. Most of the time, if the carb is the right size, etc. to start with, you will be in the ball park. You DO NOT want the power valve to be open at cruise or you will get terrible economy. This is part of the tuning process. If you have questions, pm.
Have any of you checked out the newer Holley blower carbs?
Some have INDEXED POWER VALVES right out of the box. If you could do it without indexing or without power valves, don't you think they would?

Holley does offer a Marine Carb Part # 0-80597 for Supercharger application. It is a 1050 Dominator (4500 Series). It has Two Circuit Metering and No Power Valves.
http://www.holley.com/HiOctn/ProdLin...C/0-80597.html
I hope this thread does not turn into a pissing contest as all of this information is good.
Blown 1500, when you say "indexed power valves", are you refering to "externally referenced"?
I do agree that you would not want the power valves to be open at cruise for the simple reason of economy.
I would think that is where the Intermediate Circuit comes into play.
I have pondered this discussion since I started it 3 weeks ago. The feedback has been more than I expected and appreciated.

Mine is a 3 circuit metering with several airbleeds. Looks to be more than 1 way to acheive the same results, that's great. All good info.

Couple someone explain PV indexing? I haven't a clue as to what this is.
Thanks