the Z24 dyno mule story

Stage 2 - Weber 32/36DGV carby

The stock Hitachi DCR384 carby is a decent size, however it was released in the early 80’s when carbys had to try and meet stricter emission standards and therefore you’ll find all sorts of valves and solenoids hanging off the carby.  Due to it’s complexity, they often malfunction and unless you are a Hitachi carby expert, they can be a real pain to troubleshoot.  Also, from a performance point of view, the vacuum secondary of the Hitachi is not a performance orientated design. 

That’s where the Weber 32/36DGV carby comes in.  The Weber DGV is a simple carby design that’s been around for years and has stood the test of time.  It’s one of the worlds most common carby that's used for conversions on 4 and 6 cylinder engines.

Besides it’s simple design, the DGV carby has a mechanical secondary, which gives improved throttle response compared to the vacuum secondary of the original Hitachi carb. 

The original carby was unbolted, the Weber adaptor plate was then fitted to the manifold, and one of our reproduction 32/36DGV carbys and air cleaner assemblies was bolted on.

The 32/36DGV setup felt more responsive and liked to rev out better.  After a few days of on-highway tuning to get the cruise mixtures lean, and the WOT mixtures rich, it was back to the dyno to see what power difference we could measure.

Dyno run #2

The Z24 made 61kW@wheels (82hp) on the dyno

The Hitachi does have larger butterflies and chokes than the Weber carby, so in theory, it should make more max power, but for whatever reason, in this case the Weber conversion gave a massive 17% power increase.  This power increase was bigger than we expected, but providing the carby has the butterflies opened fully, and is delivering the right air/fuel ratio, that’s all that is needed to generate max power, so this was checked on the Hitachi carby, it was stripped and cleaned before being fitted to the engine, and the vacuum secondary butterfly was confirmed to be opening properly.  No other engine changes were made when doing the carby swap, except for the air cleaner.  Same ignition timing, and very similar a/f ratios.   

The chrome air cleaner was also removed to check if power changed, but we consistently measured 82hp with and without the air cleaner, proving our air filters are very free flowing.

In summary, the 32/36DGV carby conversion is very worthwhile mod.  The stock Hitachi carb setup is renowned for being heavy on fuel, so you can tune the Weber primary circuit to be quite lean for cruising, and tune the secondary circuit to be richer for max power.  This is how we tune the Weber carbys (either reproduction or genuine Euro Webers) we use in our kits, and also the carby that was used for these dyno tests.

Check out Stage 3 - T3 turbo kit and blow through Weber 32/36DGV