Spicy Spitfire

It's easy to say a car "feels" better after upgrades, but a dynamometer is the real test.
Swapping to a European intake manifold and carbs netted serious power gains.
The stock European air cleaner looked trick, but it's probably choking our performance a bit. We'll try something less restrictive soon and measure the results.

We’ve made some progress with tuning our Triumph Spitfire project. The car had been running a sticky and horribly restrictive single Stromberg carburetor, but we switched to a dual SU carb setup from a European Spitfire. After installing them, we knew immediately that the new carbs were better: Both power and drivability improved remarkably. When combined with the European factory exhaust manifold, the little Spitfire was absolutely transformed.

We took our refreshed project to the SuperChips dyno facility in Longwood, Florida, and made even more improvements. After adjusting the valves and setting the initial timing at about 10 degrees, the dynamometer indicated that our Spitfire was producing just over 60 horsepower. That was a nice step up from the previous best run of 47 horsepower with the single carb setup. Further timing and carburetor adjustments brought us to nearly 70 horsepower at the wheels.

Feeling pretty good about our progress, we pulled off the European factory air cleaner to see how restrictive it was. All hell broke loose on the next dyno run. Air/fuel ratios that were in the low-13:1 range went completely lean, so we aborted that test and went back to the drawing board. Apparently, our European air cleaner was much more restrictive than we thought.

We’ll source a less restrictive air cleaner and make some other adjustments before testing again. We feel we can expect horsepower figures in the mid-70s with the right setup. Look for a full story and more details early next year in an upcoming issue of Classic Motorsports.

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View comments on the CMS forums
spitfiresteve None
11/21/10 9:05 a.m.

I have a '79 Spitfire that I put 4 Mikuni flatslide carbs from Performance Research Industries on to replace the single SU. The engine has been bored .30 over, fast road cam installed and now the throttle response is instantanious! I love to see articles about this often forgotten Triumph.

mikecyc78spitfire New Reader
11/24/10 1:49 p.m.

I'm running the same carb setup with two freer flowing filters, but need to really dial them in. I get much over 75 mph and the engine just loses all grunt.

pro4art New Reader
1/1/11 9:20 p.m.

1500 Spits won't go anywhere unless you get the compression up. It's a smog engine, and stock a 40HP beatle is faster. LOL.

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