Verifying the AeroVee Secondary Ignition Timing

[pfhoeycfi]

I did the in flight timing verification again this morning. I thought I'd give it a try in the colder air. With just the primary on, my average CHT is 7 degrees F cooler than with just the sec on. How large of a delta warrants making an adjustment to the secondary ignition? Interestingly, the average EGT was 34 deg higher with just the primary on vs with just the secondary on.

Peter

[Bryan Cotton]

Peter,
Of course they don't really give you a magnitude in the manual. I think my CHTs varied by a few degrees but I honestly don't remember how much. I'd be happy with 7 degrees, especially 1) if you are happy with your mag check and 2) the engine runs good and shows no sign of detonation or anything and 3) static or climb RPM is good on the secondary ignition.

Of course if Sonex gives other guidance I'd go with that. I set my secondary ignition with a timing light. Basically I put a mark on my flywheel when the motor was at TDC. Then I put a mark on the case which lined up when running on the primary ignition. That took me a few tries to get right. Then I swapped the inductive pickup to the secondary and checked again.


The post is here, go to the bottom of this page:
viewtopic.php?f=7&t=3232&p=48273

Edit: The NA Aerovee looks like a different animal than the turbo. Both my ignitions are set at 28 degrees.

[pfhoeycfi]

I think I will try that if I can find someone to sit in the airplane. I bought that HF timing light but haven't used it yet. One thing I do need to look at, with primary only at 35" mp (max continuous power), after about 1.5 minutes 2 of the EGTs busted the high limit. EGTs remain within limits with both or sec only. I'll pob fly this test again.
Thanks,
Peter

[Bryan Cotton]

Yeah you don't want to do that solo. One good thing is you don't need high RPM to check the timing, it is fixed.

The Aerovee Turbo secondary timing is retarded compared to the primary? That makes sense for high EGTs I think. The fuel has less time to burn in the cylinders, so more burns in the exhaust. I wonder why they are not both fixed at 28 BTDC like the vanilla Aerovee.

I realized after I've posted the same thing twice in this thread. Whoops!