Speedo Calibration / Shift Points

[steveo]

welcome, always good to have another LT1 guy around!

For being sure that excel file works correctly first i put 2.93 , 235/70/15 values into excel file but results doesn’t match with my STOCK values.

that's normal kinda. it's a base and a divisor for setting the slope so with a different base and slope a similar conversion can be close enough. i'd try the spreadsheet values anyways then fine tune with GPS or radar gun, or something. the actual height difference of those tires isn't massive, depending on how much you give a crap about a perfect speedo, you might just consider tuning it in the middle of all three sets of tires and hoping for the best. i don't know how picky the cops (or how harsh the punishment) in istanbul is, but personally having the speedo +/- 5% never bugged me

Probably i have to change but is it safe for transmission to drive the car without change transmission related tables for a while because i want to take a log?

it'll be fine. the worst thing you can do is put a bigass throttle body on there without tuning it, because that'll short you a bunch of line pressure for a particular amount of engine torque. changing your tire size wont hurt much, you might not even notice.

[SerdarD]

Thank you for your precious amswers Steveo

Well then, i m going with the values in excel file. Then take a lot of log for a while . Meanwhile 10% over of speed limit is fine in here :) and i don't care about speedo, i was just worrying about transmission failure due to wrong speed readings.

thank you again.

[SerdarD]

Probably i have to change but is it safe for transmission to drive the car without change transmission related tables for a while because i want to take a log?
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it'll be fine. the worst thing you can do is put a bigass throttle body on there without tuning it, because that'll short you a bunch of line pressure for a particular amount of engine torque. changing your tire size wont hurt much, you might not even notice.

@steveo , i haven't chance to log due bad weather conditions in last 2 weeks meanwhile i read a lot over net and ppl talk about changes on tables of transmission shift points and TCC Engage / TCC Release , Kickdown etc.

My first message was long and complicated, did you notice that change is not just the tire size also rear end ratio change to 3.73 from 2.93 .

sorry to bother you but i have to think twice ( maybe triple) before i act cause it's really hard and high cost to find a specific 95 transmisson over here.

[steveo]

i wouldn't worry too much, lots of people drive for a few days without tuning for a gear change. go take a few logs if you want.

[JimCT_9C1]

Confirming the above - I drove for more than a few days and more than a few miles on my 3.73s on the original pcm.

The engine/transmission/pcm are all still coordinated with a gear/tire change. Shifts will still occur at the same indicated speeds, just a lower road speed.

Hope this helps,

Jim

[SerdarD]

Thank you both for answers.

@JimCT_9C1 is it possible to share your bin with 3.73 gear ? I would like to compare and try to understand the logic of related changes.

[JimCT_9C1]

My bin is not a good reference. You should be looking at a clean gear-change only bin.

Take a look here at the various stock bins with different gears, and look at the differences between them. See posts 6, 7, and 14.
http://www.gearhead-efi.com/Fuel-Inj...rmation-EE-EEB
If you have questions based on that comparison, post up over in the GM EFI subforum.

In the meantime you should be fine driving and logging, only your speedometer will be off.

Jim