Twin Plug Ignition: Installed view
Twin Plug Ignition: Details view

The Twin Plug Ignition

This component package is now in limited production and available for prompt delivery. Please call to discuss your project for best results.

In line with our non-invasive approach, the Twin-Plug requires modifications to only six of the stock engine parts: Heads, Side Horizontal Tins, and Air Channels. No other modifications required; all else is purely bolt-on.

Modifications to the car required to fit the Twin-Plug engine are simpler yet: None. All wiring, gauge hookups, heater and throttle linkages are untouched. Bolt it into your stock 356 and go.

  • Availability: Special Order
  1. Distributors/gear case:

    Individually machined, fitted and finished. Advance set for optimal twin-plug operation. Tune up parts (points, condenser, rotor and cap) not included.

  2. Drill heads:

    Your heads, drilled and fitted with inserts for the second set of plugs, no other head-work included. Other head-work on request.
    Price: $750.00

Twin Plug Power: 28% power increase

<< Go Back

The image is a 356C engine, #716232. It was built and modified by Precision Matters to test several products and measuring tools, all aimed at improving street-useable power and response on pump-gas.

The image is a 356C engine, #716232. It was built and modified by Precision Matters to test several products and measuring tools, all aimed at improving street-useable power and response on pump-gas.

In line with our non-invasive approach, it is strictly 'plug-in'; absolutely no modifications to the car, the wiring, the throttle linkage or anything else is required to fit it to a B or later 356. And it retains full function of both car and carb heaters.

Modifications to the engine itself are also minimal:

The 36mm Zeniths include CNC-modified manifolds as part of the Kit.

The Twin-Plug package is amazingly spare of engine modifications; heads are drilled for the additional plugs, side horizontal tins and air channels (flapper boxes) are modified for plug wire management. That's all, every thing else is bolted on.

Engine weight is increased by approximately 6#. Horsepower increase, depending on the comparison, ranges from 28% to 40%

Given the common difference between theory and result, we are very pleased at the result: On the dynamometer, we found a 23-horsepower increase (from 83 to 106 horsepower) from this baseline engine, all under 5,000RPM. The increase came from changing to Precision Matters 36mm Zenith carbs/CNC-modified manifolds, Precision Matters Twin-Plug components and increased compression ratio. That amounts to a 28% improvement at speeds where you drive. Compared to an earlier engine of the same spec as the baseline engine but a lower compression ratio (9.2:1 vs. 9.5:1), there is a 40% increase in the same speed range.

In-car performance has been absolutely exemplary, with a smooth idle, strong and clean acceleration from nearly any RPM, with no 'stumbling' anywhere. Unlike most hot-rod engines, you don't know it's there until you need it. Fuel economy is strictly a product of your right foot, but shows improvement where it can be measured. Engine temperature tests are not controlled yet, but no increase has been noted and a decrease looks likely.

'Yeah, but how fast does it go?' Dunno. Over the years, I've had the pleasure of several extended 100-MPH runs in a C coupe and it feels like it would do that well. Like most modern engines, it has power reserves you don't bother to use; full-throttle has been necessary only a couple of times, but fun at other times. It's squirted up the Northern California freeway hills and on-ramps, and around kids in 2-liter winged-things. It may make 165-size tires marginal in the wet. It also has enough power that it could drive an air-conditioning compressor and still deliver performance...

Details, specs and pricing are listed on the appropriate Product pages.

A booklet summarizing the engine prep and modifications plus the tests/dyno charts is available:

  • $25.00 plus S/H.
  • $15.00 plus S/H to past customers

<< Go Back