Discussion and questions related to the course Understanding AFR
Hi there, I’m new to fuel injection as always have run carbs, I will be fitting fuel injecting and a turbo to my 21.76 using a emu ecu classic, can you tell me if tuning a aircooled volkswagen engine should be any different from a newer water cooled engine and would it still be possible to tune to lambda 1.0 and what would be a good AFR to start with?
Many thanks Graham.
Since you won't have a coolant temperature with an air cooled car, the best substitute is cylinder head temp. Oil temp can be used, but it often lags and isn't always representative of the necessary temperature compensations needed for good starting, and warmup.
I would start tuning with an AFR target of 0.95 for idle/cruise. Recommended targets for boosted operation are probably 0.82 to 0.85 to start with, although you might run a bit richer especially if you see the cylinder head temps climb quickly in boost.
I assume you've done your homework and have a long block that will accept the increase on torque and power?
As David said, higher engine thermal load will mean you're going to need to monitor the head temp. I'd also see what is available for the engine's cooling to improve the airflow - for example, some manufacturers had 'tropical' fans with higher blade count for inproved airflow - ah, some aftermarket upgrades - https://www.chircoestore.com/vw-custom-parts/vw-hot-rod-performance-cooling-fans/. Light to cruise AFR I'd suggest 1.0-1.1, though, as it will give better fuel economy, reduce oil contamination, and as the engine is producing less heat at the same rpm as under power, still run cool - also better for the enviroment.
If you're using the OEM system, check the thermostat that opens and closes airflow is free to work correctly or, unless you're going to use it in extremes of cold, fix it in the maximum cooling position, and on that - you can potentially gain a useful boost in cooling with a larger, external oil cooler (with thermostatically controlled adaptor?), rather than relying on the small OEM one - some of those engines didn't have oil filters, so also an excellent time to fit one of those, too.
You may find this of interest - https://lnengineering.com/type-4-store/dtm-cooling-systems.html?limit=8
You can get tin-work from various places, such as here - http://vwparts.aircooled.net/VW-Cooling-Tin-Alternator-Generator-s/84.htm?searching=Y&sort=5&cat=84&show=50&page=1 - if yours is damaged, or missing, it could make a big difference in cooling. NOTE, the seals are critical - replace if there's any doubt!
Thanks for replies David and Gord, much appreciated