On my draw thru turbo engines, they like high caranking speeds to get the air fuel charge to the cylinder. My current setup is two 12 volt batteries in parellel per engine. Its like this because the engines are hard to start sometimes and need extra cranking time. I have contemplated wiriing two 12 volt batteries in series for 24 volts just for cranking. Id probabl;y install a remote solenoid that is activated only during cranking. The starters are the old direct drive Prestolite started. This is on a carburated twin turbo draw thru system on a 454. I currently have one group 24 and a group 27 per engine, and the batteries are brand new. The engine has a decent cranking speed considering the old Prestolite starter, but Im wondering if doubling the voltage and thus increasing the cranking speed would help the starts. When I worked at Detroit Diesel in the cold test chamber, we would run a 8 battery bank in parellel for doing -40 cold start testing. If the engine would not start after several tries, we would rewire the leads and pump 24 volts into the starter just to get the engine to start and clear out the cylinders in preperation for the next cold start 24 hours later.

How about removing ignition power from key switch, and using seperate button switch ?
Will crank faster (won’t fight early combustion from advanced timing) then turn on ignition power when you want.
A good amt of people do this in cars/boats/etc

​​​​​​​Ayuh,.... Switch to one of the new PMM starters,..... Smaller, lighter, more power, for quicker starts,....

I'd just find better starters. Are these top mount for TRS?

yes, they are top mount

Volkswagon dune buggys we were rockin' often had 6V starters, with 12V systems. The starters turned pretty quick as you would imagine, but it wasn't likely very good for them, or reliable.

Doing the same for a high compression BBC using 24v on a12v starter would be harder on it. It would 'work', but for how long?

Far better to get one of the reduction style starters. Top mount is easy access to change it out.

Double Post....

The compresion on the engine is 7.5:1 and cranking timing is 8degrees

Cranking a BBC is never really an easy task.

I can crank over and start my Mack 672ci inline 6 engine, with 1 group 31 battery. Doesn't mean I would do it
If the high crank speed us what you need to fire them, I would find a good local starter/alternator shop and get their opinion on your plan and their suggestions. Then make a frequent removal and inspection.

I had an old 400M in my 79 Bronco that was a hard start due to high compression. I had a momentary contact button that interrupted coil power, I would press while cranking and then release, which made it much easier to start not fighting spark while cranking. You could do the same with a momentary button or pull lanyard while cranking then release. This Would also serve as a reminder to wear your lanyard. Everyones helm is different so this may not be convenient.

The extra effort and circuits required for a 24V start and rewiring to protect the electronics from seeing 24V would likely drive cost close to new gear reduction starters. It might be better to simply convert to the gear reduction starter. The gear reduction starters do seem to spin faster. By design, they spin slower but due to the efficiencies, they spin faster as there is less voltage drop. Are you certain your carbs bowls are still full when cranking?

Given the PITA factor of a failed starter and short life cycle of 24V starter an 18v start circuit may get you there with less "stress" on the starter. I believe you can get an 18V Battery but now charging becomes and issue. Pobably best to simply replace the starter and not do something off-label with solenoids and such. That, along with the momentary kill, to get things spinning without spark should get you there.

In the past, I had very good luck with starters from DB Electrical. You might call them and see what they can build for your application.
https://www.dbelectrical.com/starters/