Technical Blown Flathead Carburation

I have a 4-71 blower on my Flathead, which was on there with the carbs when I bought it. The carbs are 2 Holley 2110 2 brl carbs with 1.5” throttle plates and no power valve, with 78 jets. Some folks I’ve spoke to feel it is over fueled. I don’t plan on running the car wide open all the time, just a nice cruiser. Any thoughts or recommendations would be greatly appreciated.

 

When I built my blown FH my blower was a Weiand 172 and my motor was a 276CI. with a mild Isky cam. The blower produced 4-5 lbs of boost and I used 2 Holley 94's. Motor was backed up with a T5 trans and 3.78 gears with 700-16 tires. Started and ran great.

 

I run three 97's on mine, it was over carbed initially when I tried to run the carbs together. I switched to progressive linkage and it works a lot better. I can't see on yours how they are connected.

 

Fire it up and see how it runs. If it is over carbed you'll know. Remember blowers have higher carb/air flow requirements than naturally aspirated motors.

 

Overjetted maybe, not overcarb'd

 

There's two sizes of 2110 carbs. Can you read the venturi size of the carbs do you have 1-1/16 or 1 -5/32 ?
With a 471 depending on the drive ratio you can easily get 8 pounds of boost. What you don't want is a set of carbs that are to small.

Here's a fact once a flathead begins to detonate because of a lack of hydro carbons also know as gas with a decent octane rating you end up with holes in the tops of the pistons. On the subject of pistons are they forged or plain old stock cast slugs?
Ronnieroadster

 

The carbs are 1-5/32.

 

That's good the 1 -5/32 are the size I run on the blower set ups with no power valves also the flow 365 CFM each.
The 78 jets may be a bit large but its best you drive a bit to see if the plugs foul any. A larger jets size is needed when there's no power valves. When new the Holley 2110 1-5/32 carbs came with no power valves the tuning was always by the jets size.

 

Thanks for the info, much appreciated.

 

Another question; with my set up, what would/should be the fuel pressure?

 

Fuel pressure will be the same as a single carb, fuel flow is what you should be concerned with. Gallons Per Minute or GPM is what you are concerned with. Use a by pass regulator and a return line to the tank. Your fuel pressure will be in the neighborhood of 4.5 PSI. With a moderate pump there will be plenty of fuel on hand for the carbs to draw from.

I know very little about your setup or what you plan for the motor but I would think that something in the 110 GPM range would feed it. If you are boosting more than 10 PSI that could change at an alarming rate. Most guys are not boosting anything but a race car that high.