Hos much hp can the model a fuel system support?

Before you need a fuel pump?
We're talking running a hopped up banger, don't know but absolutely max 100hp, will that be ok?

 

You must be talking about the stock tank location and gravity feed.
I don't think the stock carb will do it but I'm no expert on hopping them up.
I see 100 hp, up to 150 hp bikes on gravity feed to carbs all the time.

 

Get you a quart container and a stopwatch and measure the fuel flow

BHP- Pounds per Hour Gallons per Hour - Quarts Per Minute - Quarts in 30 sec

 

The reason you usually add a fuel pump isn't to do with flow rate

It is due to pressure, or the lack of it

In stock configuration an A has the fuel out let of the tank about 10" above the fuel inlet of the updraft carb, and easily gets enough pressure to feed the carb as a result of gravity

Change to a downdraft manifold, and you significantly reduce the height differential and therefore pressure

Go to an overhead conversion, and you usually have no height differential, and therefore no pressure

So any engine capable of doing 100hp will likely have a carb setup that won't support gravity feed very well

Fit an electric pump AND a pressure regulator if you have anything less than 6" of height differential between tank outlet and carb inlet

 

Needing a pump is more critical on the 28-29 A's as the tank sits lower in relation to the carb.

 

Thank's guys. No worries for now then !

 

Rokkern,

A fuel pump will be needed on any of the down draft type carbs, BUT the carb will generally dictate the pressure required. Stromberg 97 carbs will accept 2.5 to 3 lbs fuel pressure, and a Holley type carb will accept 4 to 5 lbs.

The stock carb ( updraft ) will not support a 100hp type engine even with a fuel pump as it does not have the CFM to flow a hopped up engine due to venture size primarily as well as jetting.

The Down draft requires constant fuel pressure and the height of the Model A tank just will not do it consistently for a lot of reasons, fuel capacity, weight and flow on demand etc.

We use the Holley Red fuel pump and adjustable regulator, which allows you to adjust from 1 lb to 7 lbs.

Thanks Max Sr, @ H & H Antique 1-818-248-2347

 

Just thought I would add CFM, based on a Brake Specific Air Consumption of 6 -7.5 which would be a pretty good range , for a flat head 4, probably closer to the latter.