Timing two engines in series.

[allrightmike]

   I believe Ivo's car had the flywheel ring gears meshed together.
Mike.

[funsummer]

i had a little bit to do with this  subject,
Except all my experience is with diesels.
Some time a go some of the large cranes i used to maintain ran 3 diesels into a common gear case. The engines i have done this with were V12 Cummins KTA38 all mechanical injection pumped, there was no electrical balancing or load sharing.
These engine all ran ZF 6 speed transmissions fitted with omega drives which are a style of lock up converter that has a shuttle valve mounted to the driven plate, as Rpm increases centrifugal force over comes a light spring and the valve spool activates a converter lock.
We ran greatly differing states of tunes in the 3 engines due to worn parts and availability of correct parts, the diesel injection timing is set on these engines with a offset key way on the each camshaft which effects each bank Intake/Exhaust and injection. There is 2 cams per engine as the pushrods run on the outside of the cylinders. Some times we had engine ready for rebuilds running beside freshly rebuilt units.
I never experienced any issues whilst the engines were under load, we would some times have instances of rattling gears and couplings when the engines were used just above idle with low load. There was allways a lot of pushing and pulling going on between the engines.
I think the most notacble thing was the complete lack of response and lag between throttle commands and rpm. every engine by itself would be quick energetic, but once all coupled up you noticed it became a large elephant instead of the tigers. It was easy to see which engine was leading by the black smoke when been pushed.
I think the spark timing of 2 petrol engines whilst important will not greatly effect the running unless everything else on the engines is also perfectly matched.
This is the reasons why electronic load sharing in diesel power house electricity generation is now so important. Before electronics could automate the load sharing it was common to spend 10 minutes of every hour gently balancing the load between engines and tweaking woodward mechanical governors to control engine surging. All it would take is a slightly worn helm joint on a fuel actuator arm and the whole power house becomes a surging over speeding noise on its way to a guaranteed black out.
I do miss the those times.
Joel
 

[338Raptor]

I agree. It’s not as critical as synchronizing engines on two generators. Since the engines are mechanically linked together any small differences in timing, fuel ratios, etc are not going to be noticeable.  Just tune them identically and that should do it.

[TomP]

The two engines connected together isn't much challenge. Mickey Thompson's streamliner had two Cammers where one ran the front wheels and the other ran the back wheels. I read the account of that driving experience online somewhere. Two gas pedals and he worked them both independently!

[Sand hauler]

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.460ford.com/forum/42-general-tech/128709-question-tractor-pullers-drivetrain-multi-engines.html&ved=2ahUKEwj2n5bApbznAhVOMawKHSWvAHsQFjAEegQIARAB&usg=AOvVaw2XtNKGm7D-D-DItkVYd47D&cshid=1580975519034