ALL Y87 cars must check in. VERY IMPORTANT!!!

[98_Roadster]

Alright, I lost intrest in this about 5 replys ago. Here's what I've got in the way of RPM's.
80MPH 2800RPM
70MPH 2500RPM
60MPH 2200RPM
I originally had 3:08's and swapped them to 3:73's along with the Auburn Posi. Before I bought the Recalibrator from SLP, the speedo was wack. The computer still had the MPH and RPM's the same as the 3:08's. What that meant is that my speedo was saying I was traveling at 72MPH. I was actually only driving 60MPH. I had my wife track me at 60,70, and then 80.

[V6Bob]

"And V6Bob, your thinking is flawed"

Yep. I was stupidly assuming the same top transmission gear for manuals and autos.

"because according to your calculations that would put your top speed into 180 mph"

Nope. It just means I can't pull anything close to redline in top gear.

[Backfire]

Using .7 for the trans ratio(fourth gear in A4) and 26.2" as the tire diameter, the following is about what your tach should read at 75 mph.

Rear|Engine Speed
3.08| 2076
3.23| 2177
3.42| 2306
3.73| 2515

One note, this assumes there is no slippage within the transmission. If you are on the gas and lockup is not present, these numbers will be off. The rpm's for an M5 are slightly higher since 5th gear is .74 instead of .7.
If you change the gears from 3.08 to 3.73 but do not adjust the computer, the tach will read accurate, but the speedometer will be off. Since it reads tranny output speed it still thinks the rear is rotating at 3.08:1, which means at 2515rpm the speedo will show 90.84mph instead of 75mph.

[ January 27, 2002: Message edited by: Backfire ]</p>

[Damien214]

It does seem to me that the people with Y87 are noticing much lower rpms while driving. The people who are being confrontational here are the people who have switched gears out from 3.08. I BELIEVE you guys I am at 3000 rpm.

I wasn't talking about my speedo, because at 75 mph on my speedo I'm reading 2300 rpm, but at 92 which is the equivalant of 75 mph I'm almost at 3000 rpm. Anyone with a y87 isn't going to have to worry about speedo calculations because they were calibrated to be correct. No one here yet has posted a y87 with rpms over 2500.

I definitely think we are on to something here, now the question that needs to be asked, is what did GM do to compensate for gears while still retaining cruising rpms and top speed. I'm gonna ask GM even though it may not help any.

[Damien214]

SOME people are WAY misunderstanding what I'm saying here.

First of all my speedo has not been recalibrated and is not even factored into this question, Keith I know what you were saying, that much I already knew, what I'm asking is if your rpms match ACTUAL Y87 package numbers. My speedo reads 2300 rpm at 75 because as far as my speedo knows, that is accurate. But in being clocked by another car, I know that I'm aCTUALLY traveling 75 mph when my speedo reads 92 mph

When my speedo reads 92 mph and I'm actually traveling 75 mph, my tach reads almost 3000. Hope this clears things up with everyone who is saying i'm wrong here.

I'm NOT interested in what rpms cars that started out as 3.08 are running, and the reason is because I ALREADY KNOW WHAT THEY ARE RUNNING BECAUSE I DID IT.

What I care about are the numbers from the people who have ACTUAL Y87 FACTORY EQUIPPED cars.

Who here is going to tell me that there is NO MAGIC GM TRICKERY here when Y87 car's rpms are CONSISTENLY lower than vehicles that have changed gearing later. To me this would stand as undenialable proof that GM has in some way made the driveline different in a Y87 car than in a non Y87 car.

Is it really all that hard to believe, or is it merely that everyone who doesn't have a Y87 car, would like to live in denial in telling themselves they do merely because they have changed out rear ends.

And about the aren't you the guy asking questions about changing tranny ratios comment. I have done lots and lots to my car and I have done it all myself. Things that VERY few members on this board can admit to, so when I ask a question about something, it's a VALID one. i have been on this board since the beginning and all anyone really wants is to increase the performance of the f-body, so why do I get all this head wind from some of the board members. WHAT IF *GASP* I'M RIGHT? Anyone who would NOT be interested in this info please raise your hand. Huh ANYONE? I do this all for not just myself but for everyone on this board, so why not leave the outside unrelated I'm smart and you're dumb comments to yourselves.

By the way I discovered the 906 bulb replacement and absolutely no one had ever even considered it before, I will spend 2 hours just staring at my car and asking one question over and over and over again, HOW CAN I MAKE YOU BETTER? and i believe so far i have been successful, so please

Help me, Help you
HELP ME, HELP YOUU!!!

Thank You and peace, and by the way i need as many Y87 guys to reply to this as humanly possible. If I'm wrong then I want to know damnit so i can venture elsewhere, butttt if i'm right. I'm gonna keep track of numbers so we can make this pretty conclusive. I'm also going to need numbers from anyone who has changed gears from 3.08 to 3.42 or higher. These will be needed for comparison. Just because my car is WAY off the norm doesn't mean everyones are.

Let's get this rolling guys, lets fight for performance and knowledge and come out on top, for there is no knowledge that is not power.

[Backfire]

If your car is actually doing 75 with 3.73 and is running at 3000 rpms, then the trans ratio you think you have would be about .8351 instead of .70.

To me it sounds like the converter is not locked up and thus the engine rpms are higher. It could be that because the computer thinks its going faster than it is, some presets with engine speed/throttle position/rpm/vehicle speed/etc is causing the non lock up operation.

One other note for 10SecondDream, after looking through your other posts, you have 275 40's on the rear of your car which is slightly smaller than factory(about 2" in circumference) That will also make your rpm's higher for a given speed.

[ January 27, 2002: Message edited by: Backfire ]</p>

[strobhen]

Thanks backfire [img]smile.gif[/img]

Me & 10sec were discussing this earlier and I thought it might have had something to do w/ the torque converter as well, or how it is controlled.

Sounds to me like a pretty good reason in conjunction with the slightly smaller tires.

I say you need to get your speedo fixed 10sec & then re-check rpms. That might just fix it.

[eurokiller]

10secdream look hear for some info
http://www.f-body.org/gears/

[Damien214]

GREAT Eurokiller that seems to be 100% accurate on everything except what my car actually does. With 3.08 gears my car ran those numbers and it appears that people with 3.42 gears are also running those numbers. Unfortunately with my gears I'm supposed to be running a little over 2500 rpm and I'm 500 higher than that. Is there a possibility that the torque converters are different between Y87 and 3.08, or perhaps the way the computer controls them? It seems to me that if any one of the Y87 guys ran my gears they would be right about in the 2500 rpm zone.

How could the computer control converter lock up?
And I still need to know if anyone here saw any noticeable decrease in rpms from having the speedo recalibrated. Perhaps that is the problem. The problem is the SCU2000 has so much lag it probably would still screw up the computer. I'm gonna go find a Y87 PCM and see what happens. In the mean time anyone who has had the spedometer recalibrated, did you see any rpm drops?

[knowledgefreak]

just wondering if in 3rd gear at 70mph you are at 3700 rpms. I have y87 3.42's a4 and of course at 70 1:1 im at 3400rpms

So are you in 3rd or 4th gear when at 75?

[Damien214]

4th gear, is the one I'm talking about.

[John_D.]

I can check on my rpms, but I have a question for you first.

I get 3 rpms in a given gear, depending on whether I have let all the way off, am holding the pedal just enough to maintain or slightly increast speed on level ground, and more if I am on it but not enough for it to downshift...

Which one of these three would you be most interested in, if I am going to write it down for different mph's?

I can hold about 1/2 throttle, and watch the rpm's hold steady, but the mph go steadily up, about 10mph but still at the same rpms. I think it has to do with the factory torque converter and when lockup occurs. It was pretty weird the first few times I noticed it.

Holding steady at 55mph I was turning just under 2k.

[ January 27, 2002: Message edited by: John_D. ]</p>

[Damien214]

Using cruise control would be the best if you can.

[eurokiller]

Did you enter your tire size in the calculator? Maybe the person's speedometer that clocked you was off. Or maybe there really is something else. I have a manual though, so it really doesn't affect me

[mike malloy]

900 rpm's@ idle
1600 rpm's @35mph
2200 rpm's @55 mph
2450 rpm's @75 mph
this is off my 97 camaro with the y87 option