Ensuring consistent engine startup and performance

[wkrtsm]

Wanted to share some experience gained over the last 40 years of owning a 912 which relates to always getting a fast and reliable engine start, and performance. This applies to an owner who wants to introduce more constants into the complexity equation, with less headaches and money spent for restoring to OEM conditions.

Below are listed the changes made that had the greatest impact on reliable startups for the least amount of money.

1. Use OEM Bosch plugs for your engine which are gapped to correct settings. This had the largest impact, because as I experimented with a lot of different plugs, I began noticing that after I went back to OEM Bosch plugs gapped to the right settings, there never was a problem with startups. (this was like an amazing Eureka moment, truthfully, or replacing a variable with a constant in an equation -- never changes).

2. Breakerless Pertronix ignition (no mechanical points in distributor). Distributor points burned out constantly, and when they do the engine usually doesn't run well (i.e., problems starting). I have used Pertronix breakerless points for 20 years and never had a problem. This was also like replacing a variable with a constant in an equation -- never changes.

3. Use Weber 44 IDF carbs. In spite of restoration gurus treating the OEM Solex carbs like gospel, to me they were too variable and were not as robust as Webers (better performance over a wider range of environments -- i.e. fuel type, temp, mixture settings, engine ignition timing). As soon as I went to Webers, startups became more reliable and consistent - like a constant in an equation -- never changes.

The above is what has always guaranteed fast startups - hands down. Items 1 & 2 are probably less than $175 (plugs and Pertronix). Whereas a Weber carb kit can be >$750.

Below are some performance mods I have used:

1. Use velocity stacks on carbs ($20-$50), which reduces backflow (popping) for non-plenum carbs like Solex or Webers -- due to the resonance which builds up. These can be installed underneath the air cleaner. I read somewhere, for the 1600 cc engine, the optimal distance between the top end of the air intake throat to the intake valve should be 16" -- and that's what velocity stacks do -- i.e. extend this distance. Change this distance, and you change low RPM vs high RPM torque.

2. Headers (tuned exhaust). I installed Sebring headers, and today the closest product is Bursch tuned exhaust.

3. High performance camshaft. Since I have a big bore piston kit and Weber carbs, I needed a higher performance cam. Installed the Tricom 105, which is a little erratic.

4. MSD Ignition (multiple spark discharge). This provides up to 9 sparks per ordinary spark below ~3000 RPM and greater discharge capacitance, which increases fuel burn efficiency. Under the OEM ignition, you're throwing away a small fraction of unburnt fuel-air mixture out the exhaust valve. This translates to additional HP. Some entries on RENNLIST suggest there's no benefit since it doesn't do anything above 3000 RPM that's different from the OEM Bosch. However, the MSD Blaster coil, which can be used, offers fasting charge buildup in ms, which means faster and hotter sparks. Use the MSD Blaster coil and MSD ignition, and not the MSD ignition and Bosch coil.

4. Big bore kit. Adds more combustion displacement to engine.

5. Always use premium fuel.

With all of the above mods, without ever having dynoed the engine, I am probably pushing 110 HP instead of the OEM 90 HP.

Historically, I would say that use of Bosch plugs, the Pertronix breakerless points, and Weber carbs have resulted in guaranteed fast startups, as I haven't had startup issues for 15 years (when I invoked these mods).