Manually shifting an automatic trans at the strip

Dave-R · Post by **Dave-R** » Mon Apr 21, 08 9:25 am

To get the best out of a standard 727 1st gear you need to rev the engine higher than on the 2-3 shift.
The chart below shows the ideal shift points on one particular engine.

But you may not want to rev that high for the sake of the motor so getting into second gear early might be the way to go. It all depends on the power curve of the engine concerned.

If it is a street car I would want it to shift up at lower rpms than I might use on the strip. So I would leave it in drive on the street and shift manually on the strip for those extra rpms.

Dave-R · Post by **Dave-R** » Mon Apr 21, 08 9:37 am

If you want to know the rpm drop when you shift you need to know the ratio between each gear.

A stock 727 automatic has the following gear ratios;

2.45:1 (first)
1.45:1 (second)
1:1 (third or drive)

The ratio between 1st and 2nd is 2.45 divided by 1.45.

2.45/1.45 = 1.69

So if you decide you want to shift to second at 6500rpm just divide 6500 by 1.69 and you get the rpm the engine drops to.

6500/1.69 = 3846rpm

Going from 2nd to 3rd the ratio is 1.45/1 = 1.45

Your best strip time is gained by having the most average HP between shifts. Where rpm limits allow.

MilesnMiles · Post by **MilesnMiles** » Mon Apr 21, 08 10:44 am

I'm very much a layman on this. But my trans shifts auto 1-2 at 5, 200 approx, but lower from 2-3 so I shift manually at that point. Its quite a lot faster on my et slips that way. I'de be happier if it shifted auto at the 'right' rpm all the time e.g 2-3 as well as 1-2.

Adam · Post by **Adam** » Mon Apr 21, 08 1:51 pm

Is it just about shift points? I swear my car accelerates much harder in 1st gear with the shift lever in 1 than D. From a standing start, it will blaze the tyres in 1, but only chirps them in D. I've no idea why this would be - it feels like less bits are spinning around in the box (sorry if that's too technical

)

Anonymous · Post by **Anonymous** » Mon Apr 21, 08 1:54 pm

Thats a bloody good point Adam. I have always thought that. I was always told if you want to get the most of the car, drive 1-2-D and not just 'D' and floor it.

Anonymous · Post by **Anonymous** » Mon Apr 21, 08 5:38 pm

Ivor · Post by **Ivor** » Mon Apr 21, 08 5:41 pm

Sandy knows...and so do I!

Adam · Post by **Adam** » Mon Apr 21, 08 8:05 pm

Something to do with the bands? Do tell. Where's Dunc when you need him?

My old Satellite was the same. Only a 318 with a 904 and 2.76 gears but it could lay a Bullitt style single stripe all the way down the road with the column change in 1.

Anonymous · Post by **Anonymous** » Mon Apr 21, 08 11:04 pm

There is no difference, Adam. It is all in the mind ...

Cannonball · Post by **Cannonball** » Mon Apr 21, 08 11:12 pm

Adam wrote:Something to do with the bands? Do tell. Where's Dunc when you need him?

My old Satellite was the same. Only a 318 with a 904 and 2.76 gears but it could lay a Bullitt style single stripe all the way down the road with the column change in 1.

right adam, whats goin on here is, in automatic you flatten the go pedal and the car burns the tyres but because during this short burnout the gearbox govorner thinks you have reached the required road speed and your trans shifts in to 2nd the burnout either stops or carries on if yer mtr has enough guts and again the govornor thinks it has reached the correct speed and shifts it in to top burnout deff stops hence a much shorter burnout,
in manual 1 the box cannot up shift hence you can blow the tyres away for as long as you want till basically you shift to 2nd, hope this helps

Anonymous · Post by **Anonymous** » Tue Apr 22, 08 4:44 pm

Clivey wrote:Thats a bloody good point Adam. I have always thought that. I was always told if you want to get the most of the car, drive 1-2-D and not just 'D' and floor it.

Problem there is if the valve body isnt set up for shifting manually it can cause the box to get sort of confused and get stuck between gears and may cause other problems, i know a 727 box is alot more robust than other auto boxs, i had a problem with a 904 box, when trying to shift manually with a stock set up it jammed between 2-3 and shredded the band causing damage to the gear drum (dont know what its called)
The upgrade kit comes with modified valves to go into the valve body so it changes how the fluid transfers in the body for manual changes, just thought id stick this in just incase anyone starts thrashing their box and this happens them too! im not an expert on this at all but i ended up having to replace the box even after a full rebuild,( oh and after another good thrashing)

best to find out first whether your box will take the abuse of manual shifting before trying it, or just get it modified to do so.

Adam · Post by **Adam** » Tue Apr 22, 08 7:08 pm

I must have been lucky, cos I made a couple hundred passes in that ol' Satellite, always shifting manually. I did put a shift kit in it, which significantly reduced the upshift delay, so maybe that helped.

And my Cornet definitely doesn't shift to 2nd when I chirp the tyres in D.

Anonymous · Post by **Anonymous** » Tue Apr 22, 08 7:34 pm

Mine was probably on the way out anyhow, i just added to the destruction!