3.8L with 3.73s and A4....PLEASE RESPOND

[MaxBrightGreen97RS]

Okay, I have heard that going with 3.73s isnt that bad on top end. One guy told me that he easily went to 125 with it. Some other people said that it might top out at 90. Who here has this setup with their speedo RECALIBRATED?????
Please respond.

[cb4]

I just received my 3.73's and I already have a HPP3 so I can recalibrate my speedo with that. I don't know when I will have them in but I will post results when it's done

[cb4]

I also have an a4

[Only4U]

http://www.camarov6.com/cgi-bin/ulti...&f=23&t=001172

[CamaroBill]

Bad news, cb4, you can raise your top speed limiter with HPPIII but you can only recalibrate your speedo for 3.42s. I know this from experience (for the past 3,000 miles I've been driving around logging 10% extra miles and having the speedo off by 10%).

[xjarayax]

You need to buy a JETSCU2000, as well as get the programming for 3.42s, it's the only way to do that right now.

[Only4U]

even so, your shifts will still be off--you'll lose power too with improper shift points.

[sped214]

Call me ignorant, but I don't understand. Changing the gears will affect the speedo, that's a given. The RPM's of the motor will not change, just the RPM's at a certain speed will change due to the different gear ratio. The way I understand it, the shift points are determined by the Fluid Pressure, TPS, Speed sensors and RPM's. I'm unclear as to why the shift points would change due to the speedo being off... Maybe someone could enlighten me as to what I'm missing? Thanks...

[ September 12, 2002: Message edited by: sped214 ]</p>

[Only4U]

<blockquote>quote:</font><hr>The way I understand it, the shift points are determined by the Fluid Pressure, TPS, Speed sensors and RPM's. <hr></blockquote>

older cars worked like this and a lot of the older cars ran off of what the reluctor wheel did in the back. the newer models are more "sophisticated" and run off the computer. the computer tells the car when to shift all the time. never does any fluid, rpm, speed, or climate ever make the car shift on it's own--it's all what the computer wants. "sophisticated" doesn't always mean better either.

[PiLOTLiTE]

<blockquote>quote:</font><hr>Originally posted by Only4U:

it's all what the computer wants.<hr></blockquote>

Umm, so how exactly does the tranny know when to shift? Magic?

The computer takes information from sensors in the car which in turn it uses to decide when to shift. Those sensors would include at least throttle position and engine rpm, so sped214 is correct on that. What other sensors might be involved I don't know, but I'm sure theres more to it than that. As for shift points being off, my A4 shifts just fine with my 3.73s, and I upgraded from 3.08s. So far the only thing I can see that has changed is my odo and speedo being off by around 17%.

[Only4U]

<blockquote>quote:</font><hr>The computer takes information from sensors in the car which in turn it uses to decide when to shift. Those sensors would include at least throttle position and engine rpm, so sped214 is correct on that. What other sensors might be involved I don't know, but I'm sure theres more to it than that. As for shift points being off, my A4 shifts just fine with my 3.73s, and I upgraded from 3.08s. <hr></blockquote>

<blockquote>quote:</font><hr>The computer takes information from sensors <hr></blockquote>

to answer a quote with a quote:

<blockquote>quote:</font><hr>the computer tells the car when to shift all the time <hr></blockquote>

of course i'm not a moron, i know the computer doesn't do everything on it's own; but the way you said it, makes it seem like i was saying the tranny was a computer, and not a transmission.

as far as your shift points go, they'll get worse. if i'm correct, you just recently changed your gears, right? well, they don't shift just fine forever. and you are losing more power than you think too. when i got my pcm reprogrammed i went from losing to my friend by a car length, to winning by a car length. of course, the cat-back had a little to do with it, but my shifts are a lot later now. anyway, to each his own; if you think they won't get worse, it's not going to stop them. but in due time you'll see what happens.

[PiLOTLiTE]

I'm confused as to why it would take time for the shift points to get worse. If you change something (like the gears, but other stuff such as intake/exhaust too) shouldn't the computer be screwed up right when you did it, and then take time to learn to correct it? Not the other way around.

But assuming you are correct, and the shifting will get worse, what is the cause? Obviously the gear swap is the main thing, but what inside the computer gets screwed by it? I know the speed sensors are off because the speedo/odo are wrong, but shifting is determined by the TPS and engine RPM, it shouldn't matter how fast you are going if the computer knows those two things. Neither of them could have been affected by the gear swap. So what would be affecting the shifting, causing me to "lose more power than i think," and why would it get worse over time?

[Only4U]

<blockquote>quote:</font><hr>If you change something (like the gears, but other stuff such as intake/exhaust too) shouldn't the computer be screwed up right when you did it, and then take time to learn to correct it? Not the other way around. <hr></blockquote>

first off, like i said, the computer controls when the shifts happen, not the transmission or rpms. so therefore, it doesn't matter what happens, the computer will never "learn" the right settings.

<blockquote>quote:</font><hr> But assuming you are correct, and the shifting will get worse, what is the cause? <hr></blockquote>

well, i'm sorry, i really can't answer this, to tell you the absolute truth, i really can't prove this with any technical reason. i can tell you that it happened to me and a few other guys on the board i remember talking to about the situation. the only thing i would assume is that one particular thing, whether in the transmission or in the computer, is getting thrown off by the incorrect shifts every time the car shifts without correcting itself, and slowly this particular thing builds up it's "incorrectness" great enough to make a big impact in shifts, and continues to do so until the shifting gets fixed. of course, if you go long enough, you'll see clutch/flywheel problems and your whole transmission will need a rebuild. the mechanic i worked with this summer explained it in great detail why this happens and why it is bad for an auto transmission to shift early, but i don't think you would be able to understand the words that came out of his mouth even if i could remember it--was very complicated.

but, like i said, i can't prove this theory because for one, everyone's computer/car is different. some people's car hit the limiters when their computer isn't programmed right, some people actually shift way too early (most cases) so i can't say that it will in fact get worse for you--but it would make sense and if i were you, i would only expect it to eventually happen. if it does not, feel lucky and be glad you were one of the few.

[Formula]

From the sounds of things, it would seem that the computer looks at the speedo a lot to shift.

lets say with 3.08s you shift at 6000 rpms which is 50 mph (guessing). When you put the 3.73s in, your speedo is thrown off by 25% (guess), so if your going 40 for your shift with 3.73s, the speedo will say 50 (which is fine). That makes your 1-2 shift good. Now second gear tops out at 80 (guess) with the 3.08s, with the 3.73s lets say it tops out at 65, that means your speedo will read 81.25 when it shifts and will shift 1.25 mph early, therefore messing up the 2-3 shift slightly. And in third lets say it shifts at 105 (I think im off but you should see what i mean) that means with 3.73s your probably going around 85, and the speedo will read 107 and make it shift early again. It will shift 2 mph early. Then with the 3.73s you'll bounce the speed limiter at around 95 mph (118 on the speedo).

I'm just trying to figure it out for myself, I want to put 3.73s in too, but I would like to know whats going to happen. I think this happens at a much larger scale too, because peole say they are shifting thousands of rpms early, 1 to 2 mph would only be a couple hundred at those speeds.

[ September 13, 2002: Message edited by: Formula ]</p>

[MaxBrightGreen97RS]

Guys cmon...can we start a new topic about this? Please read my first post of what THIS topic is supposed to be about. I am well aware of the shift points changing and the speedo being off. I asked about the overall performace and especially top end change of 3.73s on an A4 with recalibrated speedo!!!!!!!!!