speedo vs. digital TT speedo, which is accurate?

[Yoshi]

Okay, I'm not sure if anyone can help me with this one, but here's the deal. I have a HKS Type-1 turbo timer on my SR 240. I calibrated it per the instructions to use it's digital speedometer function, I want to use that over the stock speedo because it can go far past the 120mph...

The problem is this:
30mph and under, the stock speedo and TT speedo jive.
30-50mph they seem to get out of sync
50mph and up, the TT speedo gets exponentially off from the stock speedo.
example. at 30mph both speedo's read the same 30mph
at 65 (according to the stock speedo), the TT say I'm going 62
at 80 (according to the stock speedo), the TT says 74.

The obvious thing to try would be to have another car pace me, or make friends with a state trooper ;) I don't like either idea... pacing is not the most accurate way to do things by far and I don't feel like asking a trooper to do anything, hehehee

So which one is accurate? or is neither accurate?

[Dousan_PG]

depends how the turbo timer is wired up!

my suggestion:

GET A RSM! or Blitz unit

wires directly to ECU and you program all that info in, and it will be very accurate.

[Yoshi]

Originally posted by dousan36
depends how the turbo timer is wired up!

my suggestion:

GET A RSM! or Blitz unit

wires directly to ECU and you program all that info in, and it will be very accurate.

I dunno how much that helps me.
I mean, I already have the HKS installed and running, and it kicks ***. I like it a lot, it has a billion features... and seeing as wiring and placement for TT's isn't the quickest/easiest thing in the world, I'd much rather stick with what I've got... also AFAIK, the HKS Type-1 is the only TT that works in standard over metric formats, which is worth it's weight in gold as far as I'm concerned ;) Thanks for the suggestion tho.

[Dousan_PG]

what's it wired up to? like does it wiring into your speed sensor or something? how's it wired in?

the rev/speed and blitz units wires straight into your ECU=very accurate.

i dont know how the turbo timer is wired in at all.

[uiuc240]

stock speedos are notoriously inaccurate. they overestimate for your safety. that way, you think you're going 80, but the cop's radar sees 74. i like that.

i would say the TT readout is very accurate if setup properly, because it probably looks at your rpm and just uses a simple gear ratio calculation. as long as you know tire size and what gear you're in, that's all you need.

Eric

[DuffMan]

Use the tach to determine which is correct. Of course your tach could be incorrect too, but probably not by a lot.

[andrave]

everytime I drive by a "your speed" sign its always like 3-5 mph lower than my speedo reads, and the differential gets greater at high speeds. for instance, when mine hits speed cut at (what is it, 110 or something?) mine will often have the needle "off the charts" down into 120 territory.

[Tuck&Poke]

I have a solution! this is the sure fire way.
Step 1: measure a 100ft str8 line on a street
Step 2 (pt1): Drive the car at a set speed (make sure it stays at the same speed) over the 100ft area. Make sure you at the speed already before you hit the 100ft marker otherwise your numbers will be hella off.
Step 2 (pt2) Have a buddy time you when you hit the 0ft mark all the way to the full 100ft and record the time.
Step 3: Using a simple calculation Rate = Distance/Time you can figure out how fast you were really going and see which one was closer

[knightrider]

thats a little too involved, but i believe your TT would be more accurate because its prolly more accurate than the notoriously inacurate nissan speedo, also a while back i found a site where you entered all your gear ratios, and your final gear, and it gave you a chart with a bunch of rpms, i used it to recalibrate my speedo when i took the needle off and forgot to mark it. ill look for that site again

alright, a little searching through my favorites and i found it, its http://www.smokemup.com/ its got lots of little automath stuff, its pretty good stuff,

[Steeles]

Originally posted by dousan36
depends how the turbo timer is wired up!

my suggestion:

GET A RSM! or Blitz unit

wires directly to ECU and you program all that info in, and it will be very accurate.

hey Dousan does the RSM have compensation for Final gear changes? that and the speed cut are two things I want one for..

[Dousan_PG]

ill find out tonight, steeles

[Steeles]

kewl

[Steeles]

so uh... what did ya find out?

[Dousan_PG]

i found out im lazy and prefer watching "Super Autobacs Race Queens 2002" video tape rather then do research for you :p

remind me tonight...


:D

[Steeles]

send me a copy of that tape and we'll call it even lol. cant blame ya for that one bro :) hmm gotta go catch the Matrix so dont forget. cause I cant remind you

[Dousan_PG]

when i sent you the stickers, i'll send the tape too. i'll throw on some option stuff at end too. its 45 mins of race queens.

[Agent_S13]

Yoshi-

I have the same problem w/ my speedo off and I got my techtom and it takes readings from the ECU like Dousan said. I have also been w/ another car on the freeway and we compared speedo readings -- Our cars are off.

From 0-40 they are fairly accurate but then it just gets worse exponentially... 60 mph on speedo is 55 mph all the way up to 80 mph... any higher and it gets really bad. Like 110 on my speedo is only 101 on the techtom.

You probably did wire it correctly, your TT will have a better idea of how fast you're going.

-Aaron
'91 240sx coupe

[Yoshi]

Originally posted by dousan36
when i sent you the stickers, i'll send the tape too. i'll throw on some option stuff at end too. its 45 mins of race queens.

hey dousan, if I paypal ya a few bucks for a tape and shipping can I get a copy too? :P

[Steeles]

Originally posted by dousan36
when i sent you the stickers, i'll send the tape too. i'll throw on some option stuff at end too. its 45 mins of race queens.

sweet! D1 actuion is always good :) so you checked that feature yet?

[Dousan_PG]

um..sorry forgot haha
i will do it today...must work on car (alignment) and get some tires mounted tomorrow and er.....bunch of other stuff
got a s15 passenger seat right now :p so cheap. had to use the s14 headrest. its not 'mine', it belongs to dorifto but since i paid for it its mine for now. :) and his car is in HI so...i might get a brix soon so it will look so hot w/ the brix. the s15 seat is MUCH nicer so jealous

anyways.

i will today! :)

sorry yoshi, no can do.

[RedlineRacer]

Just get on a highway that has mile markers and go 60 miles an hour for one minute when you pass one mile market. If you pass the next mile marker and exactly one minute, then you are accurate.

[Steeles]

Originally posted by RedlineRacer
Just get on a highway that has mile markers and go 60 miles an hour for one minute when you pass one mile market. If you pass the next mile marker and exactly one minute, then you are accurate.

thats hard to do with no cruise control and ADD.. those two minutes are forever.. it's like following a conversation with michelle... no lacy.. crap what is that boys name? oh Dorifto180 :D yeah.. I hate that kid.

um..sorry forgot haha

haha your as bad as that lindsay kid! its cool no rush. well the stickers and tape are but the infos not :) I gotta run up the street and see if they got them scanned yet and some prices. ....