Rookie Daves Lie-too-us Seven

[Roman]

If you fit something like a 4.7 ratio but your gearbox isnt able to shift any faster than it did before you have this problem:

It's normally (for example) 3 seconds accellerating through 1st, 1 second gear change, 4 seconds through 2nd, 1 second gear change, 5 seconds through 3rd, 1 second gear change, 6 seconds through 4th.

total time 3+1+4+1+5+1+6 = power to the ground 85% of the time.

Then with a modified final drive you end up with:

2 seconds accellerating through 1st, 1 second gear change, 3 seconds through 2nd, 1 second gear change, 4 seconds through 3rd, 1 second gear change, 5 seconds through 4th.

total time: 2+1+3+1+4+1+5 = power to the ground 82% of the time.

Since you're spending less time putting power to the ground, if my shoddy maths is correct then in the above example it's the equivilent to losing 4.5hp across your powerband on a 150hp engine.

You get the illusion of more power since it gets through each gear quicker, and feels racier, but you end up slower overall. It gets even worse if you were previously topping out your speed in the 1:1 gear (fourth) but now shifting into an overdrive gear instead which has a higher transmission loss.

Race cars which have close ratio gearboxes and high final drives generally do so in conjunction with a gearbox that can smash through the gears almost instantly, and an engine redline that's much higher than a standard one. Also the top gear is generally a 1:1. As otherwise it's not worth the extra time spent chopping through the gears.

It's a bit more complicated when it comes to a track with corners, but personally I dont think changing final drive ratio acheives as much as people tend to think.

[Rookie]

You have completely missed the point of higher final drive and close ratio gearbox Roman. They are only there to keep a motor in the powerband for as long as possible. Also now I only use 2 gears on track 2 as opposed to the 3 I was using previously.

[Testament]

romans fancy maths clearly shows the answer is powerglide

[vivaspeed]

It's a bit more complicated when it comes to a track with corners, but personally I dont think changing final drive ratio acheives as much as people tend to think.

 

When you have no torques, it does make a difference.

[Vintage Grumble]

I found the change from a 4.3 to a 4.66 made a huge difference, got the car up in the revs where it makes power much bettererer.

[Roman]

When you have no torques, it does make a difference.

Only in first gear, as that's the only time you're out of the powerband. But there's generally an abundance of torque in first regardless. After that you're at the mercy of your gearbox ratios and how many rpms it drops between gear changes.

If the problem is that at 5500rpm you've got no power, and it dips to that rpm, it's the gearbox ratios that will fix the problem not the final drive.

 

I found the change from a 4.3 to a 4.66 made a huge difference, got the car up in the revs where it makes power much bettererer.

If you shift at redline each time, it's still going to drop by the same amount of revs per gear change regardless of final drive ratio.

A 4.66 helps you get out of the slump in first gear, but that's it. It moves the peaks, but it moves the troughs too.

I'll put together a technical illustration later with MSpaint to explain further

[Rookie]

I look forward to your MS paint Roman, but please know that diff ratio helps between gears just as much as the gearbox ratio does. Also shorter gears help a lot for acceleration.

[Vintage Grumble]

I was of the understanding it effectively caused your ratios to be closer? Though I have never really thought about it. When you need to get the motor over 5G as fast as possible, it really helps quite a bit.

[Testament]

It only changes the driveshafts relationship to road speed

[Rookie]

Which effectively makes the gears closer.

[Testament]

the road speeds get closer but not the engine rpms

if it dropped into a torque hole before it will still drop into it but it will be able to pull a little easier because you are going slower - this isnt neccesarily faster is what roman is saying.

so when you change gear the rpms drop the same amount, just the gearchange is at a different road speed.

you change the final drive to suit the track and the closeness of the gears to suit the engine.

i.e. put a diesel in the lotus

[Beaver]

Get a haircut you scruffy lout

[DodgySam]

He likes to have it tied back in a top knot...cos hes so hipster!

[HighLUX]

After injection comes turbo/SC?

[Rookie]

Not on this car/kent.

[Ned]

looks dope

[Vintage Grumble]

WHAT THE FUCK IS THAT WITCHCRAFT?

[xsspeed]

ooh wee ooh didnt realise you were making the trumpet manifold slide, just assumed it'd be a sliding plate, good jerb

 

Now you can setup the outboard injectors

[Vintage Grumble]

ooh wee ooh didnt realise you were making the trumpet manifold slide, just assumed it'd be a sliding plate, good jerb

 

Now you can setup the outboard injectors

 

They would have to slide back and forth with the trumpets?

[Rookie]

Yes, but the microsquirt wont deal with sequential injection so out boards are off the cards ATM.