I know it sounds stupid but here is the story. I have a 98 jdm b18c tranny 4.7 final. This tranny is said to have the b16a 1,2,3 gearing but the longer 4,5 gearing from the GSR right? The tires i have have on the car are the jdm 16 itr wheel 205/40/16. My younger brother has a 00 civic si. Well i did a rpm vs mph test. In the si at 4000 rpm i get about 70 mph in 5th gear, And with the jdm b18c tranny i get the same mph. How is it that the b16a2 tranny and the B18c with 4.7FD tranny get the same mph at the exact same rpm in 5 gear? I though the my GSR 5th gear would give me more mph per RPM in 5 gear compared to 16a tranny. Now here is where it changes. I changed my vss in the jdm b18c tranny with one i got from a member on h-t. The vss work fine, but now in 5 gear with my jdm 18c tranny i get more mph now than before. At 4000 rpm i can get close to 75mph. I don't know which one to believe now? I'm i getting the correct mph or not? how can i test this? The old vss made the mph same has the b16a. The new vss makes the mph have more mph in the same gear.

 

Do the speed sensors have the same number of teeth on the gear?

Also, don't forget to factor in the tyre size when calculating rpm/mph.

 

i have to count the teeth. The only thing i change was the vss and it made the difference. The only reason i'm concern is because i know it works with vtec, hopefully it doesn't hurt performance in any way meaning having a close gear ratio. I think i get more mph with this vss in each gear now.

 

I can't really understand what you are posting, nor your question.

The 98 spec jdm itr has the gearing you described: 1-3 same as b16a2, then longer 4th and 5th like gsr. It also has a 4.785 final drive.

The b16 gearing is the same as the jdm 96 spec itr. 4.4 final drive and no lsd.

The vss shouldn't have any affect on power output. Although perhaps there is something wrong with one of them? Are you saying you are using a different vss with your new tranny?

The mph should be roughly the same in 5th gear for you and your brother with the si. Why? Well the 4.7 final would make you turn more rpm's in 5th, but then you have a longer 5th, which will bring them back down and cancel things out.

Please also take into consideration rolling diameter of your tires. Even the same size in two different makes and models of tires have different diameter/ circumference, and this will affect overall mph as well.

Finally, it shouldn't be a big deal if it's only a couple of mph. The stock speedo and tach aren't incredibly accurate anyway.....

 

sorry i know it's confusing what i wrote. Basically i had to replace the vss in my 98 jdm itr tranny. Before i replaced the vss from the jdm 98 itr tranny my mph in 5 gear at 4000rpm was the same has my bothers 00 si 16a2 tranny in 5 gear at 4000 rpm. Now i have replace my 98 jdm itr vss ( noting on the car was change same wheel and tire combo) with a different vss I got from a h-t member. Now i get more mph at 4000rpm in 5 gear because i change the vss. Do you kinda understand.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by realis9 &raquo;</TD></TR><TR><TD CLASS="quote">with a different vss I got from a h-t member. Now i get more mph at 4000rpm in 5 gear because i change the vss. Do you kinda understand.</TD></TR></TABLE>

I understand. Maybe the calibration on the new VSS sensor is slightly different than the old one you had. It is a simple voltage signal that could be off ever so slightly from your old sensor. If it is only a couple of MPH difference, I dont think that is a big deal at all. There is inherently variability in every sensor and everything in the world.

 

the thing is what i'm trying to find out is which one is the correct one? the old vss or the new? how could i test for that?

 

Take it to a speedometer calibration shop if you want to know which one is the most accurate.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 98 Spec R &raquo;</TD></TR><TR><TD CLASS="quote">Take it to a speedometer calibration shop if you want to know which one is the most accurate.</TD></TR></TABLE>

or just calc the tires/wheels/gearing he has for 4000rpm. it'll be close enough.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Dave-ROR &raquo;</TD></TR><TR><TD CLASS="quote">

or just calc the tires/wheels/gearing he has for 4000rpm. it'll be close enough.</TD></TR></TABLE>

Bah.. math hurts my head.

 

Honda VSS's aren't exactly known to be 100% accurate. Odds are one's off.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Black R &raquo;</TD></TR><TR><TD CLASS="quote">Please also take into consideration rolling diameter of your tires. Even the same size in two different makes and models of tires have different diameter/ circumference, and this will affect overall mph as well.</TD></TR></TABLE>

Keep in mind that the rolling diameter of the tires affects the actual mph, but not the mph indicated on the speedometer. The relationship between the RPM and the indicated mph doesn't change when you change the tire size.

205/40-16 is 4.2 percent smaller than the stock 195/55-15 size, so that will introduce an error of roughly the same percentage between the indicated mph and the actual mph. (More precisely, the speedometer will read 4.4 percent higher than actual.)

205/45-16 or 215/45-16 are both much closer to stock and more suitable sizes for the ITR.

 

hmmmm i always thought it changed the indicated speed as well with different tire sizes. learn something new everyday. He should just take it too a shop and see which one is accurate.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by totsie7944 &raquo;</TD></TR><TR><TD CLASS="quote">hmmmm i always thought it changed the indicated speed as well with different tire sizes. learn something new everyday. He should just take it too a shop and see which one is accurate.</TD></TR></TABLE>

What Ken was saying is that the VSS signal won't change for a given RPM.

The VSS reads on the output from the diff, so an input rpm of 4000 with the gear ratios in the tranny will result int he same signal no matter what the actual speed is.

However, the indicated MPH on the guage will be different for a given actual speed with different sized tires.

Ok I'll just answer the original question.

205-40-16's with a .787 5th gear and a 4.785 FD is approx 70.96mph ACTUAL.
195-55-15's with a .787 5th gear and a 4.785 FD is approx 74.09mph ACTUAL.

Both of the above are at 4000rpm.

I was hoping that suggesting the math would prompt the OP to just do the research themselves.

So which VSS is more accurate. Well in this case the "original" (the first one) one more closely matches the actual (at 4000rpm) so I'd use that one.

edit: put the wrong vss in that last sentence. doh. now it's what I meant to say.


Modified by Dave-ROR at 6:56 PM 11/29/2005

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Dave-ROR &raquo;</TD></TR><TR><TD CLASS="quote">The VSS reads on the output from the diff, so an input rpm of 4000 with the gear ratios in the tranny will result int he same signal no matter what the actual speed is.

However, the indicated MPH on the guage will be different for a given actual speed with different sized tires.</TD></TR></TABLE>

What Dave says is true, but may be somewhat misleading. Usually, someone doesn't know what his actual speed is, only what the speedometer says, and I assume that's the case with realis9 when he states what speeds he is going at 4000 RPM.

realis9, if you are referring to speeds INDICATED ON YOUR SPEEDOMETER, then the size of your tires doesn't matter. The car "thinks" it's going a certain speed because a sensor measures how fast the rear axle is turning, and doesn't "know" if the translation into actual mph is affected by tires other than stock size.

Hope that makes sense.

 

i'll take a pic of my speedometer at 4000 rpm tonight with the new vss and post it. given an hour i'll be back

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by realis9 &raquo;</TD></TR><TR><TD CLASS="quote">i'll take a pic of my speedometer at 4000 rpm tonight with the new vss and post it. given an hour i'll be back</TD></TR></TABLE>

No need.

I already told you what your actual speed was (approx anyways) at 4000rpm in 5th gear with your tires and tranny.

The original VSS gave you that speed. Therefore, use the original VSS.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxtasy &raquo;</TD></TR><TR><TD CLASS="quote">

What Dave says is true, but may be somewhat misleading. Usually, someone doesn't know what his actual speed is, only what the speedometer says, and I assume that's the case with realis9 when he states what speeds he is going at 4000 RPM.</TD></TR></TABLE>

Wasn't trying to be misleading

 

i took pics of the rpm last night in 1,2,3,4,5 gear at 4000 rpm i will try to post some pics of them. At 4000 rpm in 5th it was almost a 80mph. i will get the pics up tonight around 9pm when i get home. So please check back.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by realis9 &raquo;</TD></TR><TR><TD CLASS="quote">i took pics of the rpm last night in 1,2,3,4,5 gear at 4000 rpm i will try to post some pics of them. At 4000 rpm in 5th it was almost a 80mph. i will get the pics up tonight around 9pm when i get home. So please check back.</TD></TR></TABLE>

Again, that's really not needed. I told you what your approx ACTUAL speed was at 4000rpm in 5th gear with your tires/gearing. Just pick the VSS that reads closest to that (in INDICATED) and be done with it. All the pics will show is what your VSS is sending, which doesn't really matter if you are trying to figure out which is most accurate for your actual speed.

Since the "original" one from the tranny read lower, use that one. 80mph = GSR fifth gear with a 4.4FD, you should be reading a lower speed with the GSR fifth and 4.,785 LSD, so switch back to the original VSS.

Not sure how to make this more clear?

 

well the original vss i had in my jdm tranny went bad, so i bought a used one from an h-t member and i started this post because i was concerned about not having the more accurate mph. if the speed limit in I75 is 70mph if my speedo says 80 I'm really going 70mph. So that mean i would have to purchase a vss form a 98-2000 jdm itr tranny to get back my correct reading? I still have my old vss that does not work can i just try to take parts off the new one i got to repair the old one. I think it might of been the plug on top of my old vss that went bad that is held by 2 screws. Can i switch the plugs on top?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by realis9 &raquo;</TD></TR><TR><TD CLASS="quote">well the original vss i had in my jdm tranny went bad, so i bought a used one from an h-t member and i started this post because i was concerned about not having the more accurate mph. if the speed limit in I75 is 70mph if my speedo says 80 I'm really going 70mph. So that mean i would have to purchase a vss form a 98-2000 jdm itr tranny to get back my correct reading? I still have my old vss that does not work can i just try to take parts off the new one i got to repair the old one. I think it might of been the plug on top of my old vss that went bad that is held by 2 screws. Can i switch the plugs on top? </TD></TR></TABLE>

Ah, I didn't know the original one broke.

You could get your good one recalibrated, wherever that is calibrated (last time I had that done it was on the speedo itself but it was a mechanical linkage not electronic).

Or you could get one from the JDM tranny I guess. Not real sure on that one, I just thought that you switched it because you thought it was sending the wrong mph.