View Full Version : How far off will speedo be?


chevelless502
09-14-2009, 05:57 PM
I just put a new rear end in the car and the old one had 2.73 gears and the new one has 3.42 gears. Can anyone tell me how far my speedo will be off till i can get it tuned?

Thanks
Andy

NSSANE02
09-14-2009, 06:00 PM
It's not a set number, more like a percentage. It's going to vary depending on your speed.

kbras12
09-14-2009, 06:01 PM
its a percentage for sure! get a tune and fix your speedo

NAAllTheWay
09-14-2009, 08:04 PM
im pretty sure for that gear change every 5mph it says you are going its really around 4. so when it says 75 your going 60...pretty sure thats close to exact.

NAAllTheWay
09-14-2009, 08:07 PM
if your wondering how i got that, devide 342 into 273...you get 125....that means when it would say 125 your real speed is 100. its all relative to what speed you are going. so your speedometer is always going to read 125% of your actual speed.

chevelless502
09-14-2009, 09:15 PM
if your wondering how i got that, devide 342 into 273...you get 125....that means when it would say 125 your real speed is 100. its all relative to what speed you are going. so your speedometer is always going to read 125% of your actual speed.


Makes very good sense. Thanks


Well i would get a tune but im planning some more stuff for it soon and dont want to pay for several tunes as i go along. Plus there is no place close to me. Im thinking maybe buy a hp tuners or efi live and do it myself?

Andy

NAAllTheWay
09-14-2009, 09:48 PM
yea most the handheld tuners will re-calibrate for you, around 300 bucks maybe, me personally, i would just leave the speedometer they way it is and keep up with the flow of traffic, saves money, if you get a tuner tho with most of them u will always be able to read codes, so i guess it just depends on weather or not thats worth it, hope that answeres your question.

90TSiAWD
09-15-2009, 02:26 AM
Have you got to test out the new 3.42s? Thinking of doing the same swap myself.

chevelless502
09-15-2009, 05:54 AM
Have you got to test out the new 3.42s? Thinking of doing the same swap myself.


Yes had it out last night and its a major improvement over the 2.73. Had i not of run onto such a deal on the complete rear end i bought with the 3.42 in it i probably would of went with 3.73 but i am very happy with what i did. The "fun factor" went up alot for sure.

Andy

90TSiAWD
09-15-2009, 09:16 AM
Cool, its the same deal with me ran into a complete rear minus backing plates for 200

406malibu
09-15-2009, 10:17 AM
if your wondering how i got that, devide 342 into 273...you get 125....that means when it would say 125 your real speed is 100. its all relative to what speed you are going. so your speedometer is always going to read 125% of your actual speed.

100% correct. :nod:

therobman
09-15-2009, 10:41 AM
way off get it tuned

marors1
09-15-2009, 01:13 PM
you will want to get it tuned. Your shift points will be off as well, so it will basically short shift all the time and you will be in high gear at a lower actual speed.

jts98z28
09-15-2009, 01:32 PM
you will want to get it tuned. Your shift points will be off as well, so it will basically short shift all the time and you will be in high gear at a lower actual speed.

x2...i went from 2.73s to 3.73s and at WOT it doesnt shift into 3rd unless i let off the gas

NAAllTheWay
09-16-2009, 12:55 AM
if im not mistaken it wouldnt short shift it will not want to shift...if u gun it ull prolly hit the rev limiter, not possitive on that one maybe someone can correct me or agree

chevelless502
09-16-2009, 06:50 AM
you will want to get it tuned. Your shift points will be off as well, so it will basically short shift all the time and you will be in high gear at a lower actual speed.

Yes i have noticed this being true that the shift points are off now. I dont live closer to a tuner at all. Can a local GM dealer do this maybe?

marors1
09-17-2009, 03:09 PM
If you don't want to buy an HPtuners box (which is somewhat expensive for just tuning shift points) maybe you could do a mail order tune. I don't recall who does that here because I have never needed one, but I think there are some guys around here who could do it for you and probably only have you out of your car for a week or two. You would just need to tell them what gears you went from and to and it is an easy change in the software. I did it in hptuners and it is really easy, there is basically a built in algorithm that takes care of changing an necessary parameters.

Personally, i would say you should grab the HPtuners package if you plan on doing other stuff to your car, and I don't think that a GM dealer can change anything to a non-stock ratio (3.42 is stock for a manual trans but I don't know how GM's programming boxes work).

Good Luck.

BobDoLe
09-17-2009, 05:42 PM
another thing you could do is jump on the regional section and see if anyone with hptuners in your area can do a quick adjustment. it will cost them 2 credits ($100) to tune your car + whatever their time is worth to do it for you.

marors1
09-17-2009, 11:07 PM
where are you in Illinois? if you are in the northern suburbs, we could maybe work something out since I get down to Kenosha relatively often. Also, what year and model is your car?

D

chevelless502
09-17-2009, 11:24 PM
where are you in Illinois? if you are in the northern suburbs, we could maybe work something out since I get down to Kenosha relatively often. Also, what year and model is your car?

D

I have been looking at hp tuners and thinking hard about buying one cause i will be doing more tuning in the future. Just not sure which one to get? I need to do some searches for those answeres on here i guess.

The car is a 98 z28.

I live near Macomb IL, about 250 miles south and west of chicago.

boughtitdone
09-17-2009, 11:34 PM
speed inc. might work with u i took my ta up and some how the tune for gear didnt take long story short i mailed it to them on a wed. and had my ecm back by 11 am friday

bamalt1
09-17-2009, 11:37 PM
Trifecta Performance can do a mail order tune where they send you a tuner you just hook to your obdII port instead of sending in your pcm. Most tuners will either give a huge discount or even free retunes if you do more mods.

marors1
09-17-2009, 11:40 PM
That would be quite a haul to meet up with you, I am sure that there is someone more local to you, as BobDoLe said maybe ask around in the regional forums.
As far as what HPtuner to get, I have the standard version of the unit ($499), and there is the one that is made for easily hooking to wideband O2 sensors and stuff, the Pro version. I didn't see the need for spending an extra $150 on the pro version, but there are obviously reasons for getting it if you are planning on doing some modding that could use those features.

I would suggest checking out the PCM forum here on LS1TECH, and also go over to the HPtuners forum. Both areas have a huge amount of info. I can definitely say that there are neat things you can do with HPtuners, but it takes a lot of fiddling around to figure out how to tune things exactly like you want them. I like it, it is pretty much fun as long as I have the time.

I hope you can get your car adjusted with a minimum of trouble.

D

jimbo98z
09-18-2009, 04:58 PM
http://www.grimmjeeper.com/gears.html

http://www.5speedtransmissions.com/gear_calculator.html

Either of those will tell you everything you need to know. I've got an excel spreadsheet that lets you enter in what gear ratio you have, what you used to have, speed, rpm whatever and it will calculate everything else. I just can't find a link to it anymore... :bang:

johnlv6
09-18-2009, 05:03 PM
yea most the handheld tuners will re-calibrate for you, around 300 bucks maybe, me personally, i would just leave the speedometer they way it is and keep up with the flow of traffic, saves money, if you get a tuner tho with most of them u will always be able to read codes, so i guess it just depends on weather or not thats worth it, hope that answeres your question.

That also racks up miles and decreases your resale value. I saw a few Camaro owners that did that when I was car shopping. ex. "Car shows 80,000 miles, but I did a gear swap to 4.10's two years ago...so it actually only has like 50,000 miles." That's just stupid, IMO.

chevelless502
09-19-2009, 06:55 AM
That would be quite a haul to meet up with you, I am sure that there is someone more local to you, as BobDoLe said maybe ask around in the regional forums.
As far as what HPtuner to get, I have the standard version of the unit ($499), and there is the one that is made for easily hooking to wideband O2 sensors and stuff, the Pro version. I didn't see the need for spending an extra $150 on the pro version, but there are obviously reasons for getting it if you are planning on doing some modding that could use those features.

I would suggest checking out the PCM forum here on LS1TECH, and also go over to the HPtuners forum. Both areas have a huge amount of info. I can definitely say that there are neat things you can do with HPtuners, but it takes a lot of fiddling around to figure out how to tune things exactly like you want them. I like it, it is pretty much fun as long as I have the time.

I hope you can get your car adjusted with a minimum of trouble.

D


Yes i agree, that would be a long haul. Thanks for the offer on it though. I think with my mods i have planned and the way i will have to go about it, (alittle at a time), getting an HPtuners might be my best bet. I already have the laptop so that part is out of the way at least....lol.

NAAllTheWay
09-20-2009, 09:46 AM
yea i dk where you live at, but if u live in illinois you can always go to speed.inc in shaumberg, they can do it for you, they you dont have to pull your computer and mail it, or me personally, i might consider a hypertech or diablo tuner, around 300, so you will spend an extra 200 prolly, but you can program your car to shift harder, read trouble codes, mess with rev limiter, top speed governer, and of course, after you do the gear and down the road decide you want a different gear, you can change it again yourself for no additional charge, thats just what i would do, that or if you have a tuner within50 miles just drive there, prolly shouldnt be more than 100

chevelless502
09-20-2009, 10:19 AM
I am about 250 miles from speed inc so thats a problem too. I keep thinking i may hook up with a used hp tuners but they all want about new price for them when i do find one.