Gear ratios, bigger turbo's and mapping

[Tom]

I'm not that technical and I have few quries from my title, and Im going to use Locky's dyno here to help with this,

 

Ok from looking at the dyno sheet it's clear that the most power is produced between 6500-8000rpm, now from factory I believe that each gear changed at redline will then put the next in at the cars powerband for maximum performance and what I want to know is now a car such has this one is modified is this then lost?

 

As say this graph was produced in 4th gear and then a gear is changed at 8000rpm from 4th to 5th would that gear change then put the car back in the power band from 6500rpm or will the car be out of its power band? and from below be near to 150bhp down from the powerband if the change puts the engine back to 6000rpm and is this something mappers tune to, so that full boost is achieved at each shift in the powerband? or is this down mapping and the turbo?

 

And have I made any sense here??? and am I being dumb

 

 

Tom.

[ADL Mark]

I see what you're saying Tom, but I think you're over simplifying things there.

 

There's other reasons other than dropping the engine back in to it's powerband that go towards deciding what gear ratios a manufacturer will use. Most road cars gear ratios will also be decided upon for things such as a good cruising (motorway use) rpm, good fuel consumption etc.

 

Cars like a Civic Type-R then yes the gears are designed to drop the engine back in to the start of it's power band otherwise they're next to useless, but every car is set up for different reasons.

[ADL Mark]

I know in cars like the Supra and the Celica/MR2, the gearboxes are set up with the top gear as an overdrive. So the next gear down (5th in the Supra, 4th in a Celica/MR2) is set up with 1:1 ratio and then top gear is set up as an overdrive for cruising.

 

1st gear needs to be set up with a reasonable ration to get the car moving on any incline and then the other gears are spread in between with differing ratio.

[Tom]

I mean purely for a performance view, not under normal driving, the type r being a good example that each gear change at redline puts the car back the the vtec zone for maximum perfomance, and say the type r was then turboed and it produced maximum boost say from 7k, ie 1500rpm after vtec is this something tuners consider and then raise the rev limit so it the next gear will be from 7k for better performance?

[ADL Mark]

Yes, but manufacturers don't generally build cars just with the performance view in mind, it's nearly always a compromise unless you've just been and bought a McLaren F1.

 

In the case of the car above I would imagine that the gearing would put it well outside of the powerband on the shift up to 5th, but that doesn't mean you're shifting up in to unusable power. MR2's don't have a particularly close ratio gearbox, but then they don't need it as they have plenty of torque to get them up and going again. It's a much different engine characteristic to a revvy Civic engine which flails when it's outside of it's powerband (VTEC range).

 

is this something tuners consider and then raise the rev limit so it the next gear will be from 7k for better performance?

 

This line though, totally confuses me?! lol..

[Tom]

Yes, but manufacturers don't generally build cars just with the performance view in mind, it's nearly always a compromise unless you've just been and bought a McLaren F1.

 

 

Thats not what i'm getting at it's once people start upgrading with bigger turbo's etc it's taking it away from how the manufacturer made it so are tuners adapting this?

 

In the case of the car above I would imagine that the gearing would put it well outside of the powerband on the shift up to 5th

 

This quote is what i'm getting at, if the car in theory is out of the powerband is this not something that is considered by the tuner so that an even higher rev limit is set so hitting redline in (x) gear will then put the next gear in the powerband? and therefore better performance?

 

 

Maybe I should just get the thread closed

[ADL Mark]

Ah, I see what you mean now. And no, that's not why a redline is raised and I very much doubt something that a tuner thinks of when mapping the car. They are more interested in getting the most out of the engine. The driver then has the job of making the most of the gearbox unless you're flush enough to be able to put custom ratios in.

 

To be honest, in something turbocharged and for normal use it's not really going to be an issue. If you were racing competitively then yes, you might want to change the gear ratios.

[Tom]

Ah, I see what you mean now.

 

Phew! lol,

 

And cool

[ADL Mark]