Drivetrain and gearing for Turbo

[powerband]

what would you say is generalized performance gearing differences between a typical performance NA vs moderate turbo 250/200 built only for drag racing and occasional cruise not daily driving.

other turbo threads got me thinking - what happens to useful powerband (sic 8) ) with moderate turbo built 250/200 ?

no use winding the log six out past useful

have fun

 

[First Fox]

Another one of those win/win situations with a turbocharger. TYPICALLY with an N/A tune, you want to run higher numerical gears as low end torque is GENERALLY lessened and you need to get the engine into the sweet spot sooner via gearing. The downside of this of course, is you will be buzzing down the freeway at some stupid high RPM. This is not really the case with a properly sized turbocharger because they "like" load and start boosting sooner with lower numerical gearing because of said load. AND you get to chug down the interstate at a more economical rpm. 8)

Theoretically if you geared the turbo engine really, really short, (think super-mega granny gears) the turbo wouldn't boost at all due to there being such a light load and how quickly the gears come and go. You would go through the gears and would be bouncing of the rev limiter without an ounce of boost.

It is better to lean on the taller side of gear choices with the turbo, within reason. If you are plugging numbers into a gearing calculator and say 3.73 or 3.55 are looking good for you rpm wise, you would get quicker spooling and likely better performance with the 3.55 or even higher like a 3.27. Gotta remember our redline with these sixes. We don't have a lot to play with in that regard and the turbo needs to boost early and does not need to move a lot of air at a high RPM.

There are some good calculators out there that will give you wheel speeds in all gears. Here is one, but it requires you to input transmission ratios. They can be found with a quick google search if you are not a nerd like me and don't have them memorized.

http://www.apexgarage.com/tech/gear_ratios.shtml