In tunercat how do I change th gear ratio?I have an 87 bin.Or will I have to manualy go through the bin to change it?

 

There's nothing that can be done for mechanical speedos. You'll have to change the gears in the tranny.

Tim

------------------
TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

 

Actually, you have to also make a change to the Speedo Gears for SD cars also. There is a "correction factor" called "Pulses/Mile" but it only affects the ECM internally for the VSS calculation, not the speedo itself. I use it to "syncronize" my ECM to my speedo, but nothing more.

As for "other things", a Lower Gears (higher numerically) tend to like the spark to come on a bit quicker, while taller gears (low numerically) tend to have a lazier spark table that take their time getting to the max spark advance. This tends to be the biggest difference I have noticed between BINS with different gear ratios.

Ultimately, you should play with your spark (and fuel) to find out what your engine combo likes the best anyway. There is a very narrow range of only a few degrees of spark advance where the engine runs it best and where it runs "okay, but not the best".

On my car, I found this "band" to be less than 2* of spark advance, but the difference is almost .4 seconds from a "standard 20 to 70 MPH test" that I do to quantify the effects of my changes.

 

I have a 87 formula so I do have an electronic speedometer.The problem is with this bin is that its for 3:27,mine is 3:42.So My actual speedometer is correct but the vss read about 5mph lower.I guess I'll adjust the pulses/mile.

 

I cant find a pulses/mile on my 87 or 89 bin.

 

"Actually, you have to also make a change to the Speedo Gears for SD cars also. There is a "correction factor" called "Pulses/Mile" but it only affects the ECM internally"


Notice this ONLY applies to SD cars. You have a MAF car.

------------------
1991 Z28 5.7 TPI

ZZ4 heads, ZZ4 cam, Harland Sharp roller rockers, Accel base, SLP siamesed runners, 52MM SLP Throttle Body, Hooker Headers, Flowmaster catback, MSD6A ignition, Home made ramair system, aluminum driveshaft, WC 5-speed etc

 

I haven't had the chance to change my vss gear and my speedo is reading a lot more than it should. I went from 2.73 to 3.73s what exactly does the ecm use the vehicle speed to calculate? I know it controls the tcc unlock/lock and I corrected that (turned it up to 60mph as a temp fix).
You guys have me worried, btw, I have TBI 8746, not MAF or TPI SD.

 

I have always had my speedo off 7 mph.When I switched to tpi it stayed the same.When I converted to the 165 ecm I change the the speedo gear.I found the right gear and my mph is up 7mph,now speedometer is right.But through my scan tool the vss mph is 5-7 mph off.I have ordered memcals from gm before.They need a rear gear ratio before its ordered.I know thats the reason for my vss being off.I guess tunercat just does'nt have a table for gear ratios "yet".Gear ratio code would be related to the vss,I guess.Anyone with some ideas.

 

Actually - You CAN change the speedo via PROM changes for the electric speedo 730 cars. Dave Zug did this on his '91 after installing a 6 speed. He has it documented on his site. I have lost the address but I'll drop him a line to the get the URL.

Tim

------------------
TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

 

That would be most excellent Tim. Heck of a lot easier to change the eprom than speedo gears. Also, useful for minor corrections due to tires.

 

http://www.delanet.com/~tgp/92Z28/02-730-vss4T56.html

Have it bookmarked.

 

There is a correction table but nobody has found it yet.Once someone does then tc will add it.Or find the address in the bin.Until I find the table in the bin(not tc) I will just manually redo my spark and maf tables.But really if you want your car to run right that needs to be done anyways.It just seems that nobody knows or understands how to use the maf tables very well.

 

I clicked the link and it did not work.
Getting ready to change the rear gears in the Z.

 

For openers, you'll always see an error in your speedo calibration, vs speedometer, vs actual MPH.

It's a federal law that they read a min of 5% slow. Not the word min., so you can easily see 5-8% errors with everything being correct.

 

sounds like uncle sam want us sheep to drive around under the speed limit.

 

I read his page, and i think one of us even emailed him when i changed my rear. Turns out the correction factor he found just fixed large changes in frequency, such as for the higher (or was it lower) ppm of the 4th gen T56. It was a multiplication factor, not a percentage change type deal.
Although i reckon you could do it in the code, if you can build in * 16, you can do fractions too...

 

Ed is right..... the scaling for the CLUSTER in the 92 car is on a large scale... but to get the INTERNAL VEHICLE SPEED right it is done at another prom location, not the hardware multiplier I talk about on that page... and small corrections are possible there... the document, by the way is now at:

http://www.eecis.udel.edu/~dzug/92z2...0-vss4T56.html

enjoy..

~Dave

 

This is also one of my old post.This a another example of a lack maf knowledge.I have a eletronic speedo and ordered that prom from the dealer.The dealer said in his books there is different part numbers in 87 for different gear ratios.So there must be something to address gear ratio in the maf code.Rbob is by far the most talented code reader here.If there is something in the code I'de bet he could find it.But someone needs to address this issue.Maf is my heart,I want to see it progress.

 

Tony, first part of the board is DIY. It appears you criticizing the board because no one (including yourself) dug into the MAF code to see if there is a Pulse Divisor Switch like SD? Well, go dig into the code yourself instead of expecting others to do your owne work.

As for WHY there are unique Memcals/BCC/Bins for different gear ratios is usually the spark table. I have found on many bins (regardless of system - SD, MAF TBI) where the only difference is the gear ratio tends to be the spark tables. I have also found a great difference from MAF scalar table from BIN to BIN for the same car. In fact, the MAF scalar table is often the ONLY difference. Do some "Binary Compares" of various bins and look at the difference.

 

I don't even have maf anymore(on my formula).I was just trying to help,sorry.