Speedo Calibration / Shift Points

Hello Everyone,

I’m 47 years old, gearhead old school guy from Istanbul-Turkey and this is the first time that i m into PCM tuning world and would like to start with thanks to Gary Doug, Mark Mansur, Eaglemark, Steveo, kur4o, Brenden @Shoebox and all others i can not remember their names right now for their great effort and sharing about PCM tuning of LT1 cars.

I just swapped LT1 + 4L60E from 95 Roadmaster LTD Sedan to 79 Malibu Classic Coupe. Even i have swap all wiring, steering column, fuel tank etc. Shortly i might say i have 95 RM in a 79 Malibu shell. I took pictures of all steps and i can share if you need any info.

I have decided to cancel some futures such as Catalytic Converter, EGR, Air Pump and i have decided to keep CCP (EVAP)due to BLM cells issue. Canceled mechanic fan and now become to dual electric. All rest stays stock because it’s gonna be daily drive. I made my self ALDL cable and jump into PCM world as a noob.

I used EEhack to get the stock bin. 16209331 bin in 16188051 pcm and i’m gonna upload 16243171 which is newer and better. I have made all the necessary changes about canceled features, speed limiter, fan control etc.

I’m using Tuner Pro to change the parameters in stock 16243171 bin file. Here is my question :

My donor car RM had mechanical fan and external oil cooler which makes it V92 towing pack car as far as i know it should have 2.93 rear end with posi. And the tire size 235/70/15.

Now i have 3.73 in my malibu and tire size also gonna be different 205/75/14 for winter, 275/50/15 or 275/60/15 for summer i know i have to change the “Instrumentation Calibration” values in STOCK bin for exact speed reading on speedo and other calculations.

As suggested i have decide to use “LT1 OBD1 Speedo Calibration for $EE” excel file. 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.

	STOCK VALUES IN BIN	VALUES IN EXCEL FILE
Speedometer Scalar Base :	22	21
Speedometer Scalar – Divisor :	0.9960	0.992
Speedometer Scalar – Scan tool :	31.713	35.258
Speedometere Scalar – Driveshaft PPR :	40.021	40

I thought values in excel file might provide better readings for the calculations but i m not sure. Can anybody suggest me what should i do or calculate the values for me that i have to put in to bin file with 3.73 rearend and for 205/75/14 , 275/50/15 , 275/60/15 tire sizes ?

	205/75/14	275/50/15	275/60/15
Speedometer Scalar – Base :
Speedometer Scalar – Divisor :
Speedometer Scalar – Scan Tool :
Speedometere Scalar – Driveshaft PPR :

And one more question, after i put new values in to bin file for speedo calibration, should i have to change also Tables of Shift points, TCC, Kickdown mode, Line pressure control ?

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? Or it's deadly dangerous for transmission ?

Is there any article you suggest to me understand the logic for these tables?

Thank You !!!

welcome, always good to have another LT1 guy around!

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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.

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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

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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.

Thank you for your precious amswers Steveo :rockon:

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.

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Originally Posted by [COLOR=#F3F3F3

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?
[/COLOR]
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.

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@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.

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.

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

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.

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