THE NEW 81 FROM STROMBERG
Pic Tim Sutton
We all know about the Stromberg 81 carburetor, right? The 97’s smaller brother. Standard fit on the infamous ‘thrifty’ Ford V8-60 motor from around 1937 to 1940. Designed with a tiny 0.81 inch diameter venturi and 1.0625 inch throttle bores. Rated at various different cfm (cubic feet per minute of air) depending on who you talk to and whose equipment you test it on. Hard to find. And pricey too, nowadays. Yet more importantly, holder of almost legendary status among the 4-banger (and V8-60) cognoscenti.
Why? Because two of these babies on pretty much any 4-banger Ford motor (or V8-60 Midget for example) is, and has always been, the sweet set-up if you want both high performance AND road-going flexibility. In short, the smaller 81 venturi are better suited to the smaller engine size. Two 97s might work great on a flathead Ford V8, but stick them on a smaller engine and they will see far lower vacuum at the carburetor (same straw – smaller lungs). Use carbs with smaller venturi and they will see higher vacuum, which helps maintain quicker air speed/throttle response when you open up from lower rpm.
Early R&D was carried out for us by Norm Schenck at Competition Fuel Systems, in Michigan, who stuck an original 81 on his flow bench and got 109.6 cfm max airflow at 1.5in HG vacuum. 3D modelling then helped us develop a short venturi insert with a tiny step at the bottom so it is clamped into the 97 bowl casting by the new 81 base casting. In final manufacture, the real parts actually flowed 116cfm due to the super-smooth finish on the inserts and accurate turbulance-cheating fit. But most important, the booster signal curve is the same shape as the old 81, but a tiny bit stronger for even better response.
The 81 carburetor has a half-inch accelerator pump bore. We make 81 pumps so decided to make a press-in sleeve for the pump well, adding a small 0-ring at the bottom to stop the gasoline returning back up the gap between sleeve and pump wall.
After extensive testing, we decided on 0.036in main jets (original stock jetting was 0.035in) with a stock Number 71 power valve. We were also able to retain the stock 97-size air bleed sizes – 0.040″ high speed and 0.103″ low speed (idle)…and the stock 97 emulsion tubes.
While we did prototype tests with aluminum inserts in a 97 base casting, sleeving the 97 base casting down to 81 size was not a full production option. So we tooled up for a whole new cast iron base casting to original 81 spec.
This means 1.0625 inch throttle bores with new OE 81-size throttle plates, which are now also available to 81 carb rebuilders of course. The 81 always used the 97-style throttle shaft so we had that covered. Note how the transition ports exit just above the throttle plate.
Pic: Charlie Yapp
So how do they go? Well, the first two off the line went to Charlie Yapp, in Ohio, to test on his own 1929 Cabin Speedster. Charlie is known for publishing Secrets, Vintage Speed & Sport magazine, covering all things Ford four-banger for near on 30 years now. And for developing and manufacturing a long list of cool Model A/B-based performance heads and other parts through Scalded Dog Speed Parts. The Speedster’s 125hp Model B engine is packed with his own products, of course, including the cool Roof 101 Cyclone Four-Port OHV conversion. This is what he had to say:
“To say these Stromberg 81’s are nice is an understatement of a highest magnitude. With a pair of nice old rebuilt 97’s pushing my Roof 101 OHV speedster around, I have been under the impression that the camshaft I’m running was the primary problem with my lumpy idle and twitchy tachometer . . . Wrong! It was the old carbs and their crocky idle circuits.
When I swapped out the old for the new 81s, the entire experience of getting her to run and driving was refreshed and smooth as a baby’s butt. She idles gently down to under 600 rpm (instead of an uneven 1200 rpm) and doesn’t stall when I step on it. I do not need to pump the pedal to fuel her up . . just turn the key and there she goes with stock jetting.
I have one of the “Rattler” flywheels and now the lack of vibration is even more impressive. The top end was exciting as I hit 65 mph so quickly shooting out the freeway ramp I thought I must have misread the speedo. Wow! The speed, pickup and smooth acceleration has made it imperative that I own a pair of these. . . . Donna was equally impressed by its ease of starting and smooth acceleration and going up hills without slowing down. Highway gas mileage was coming in at 18.5 mpg. Very impressive Sir!“
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