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Discussion Starter · #1 ·
3.42s, TransGo Shift Kit and 2800 Edge Stall.

My wagon turns ~2500 RPM when crusing at 70MPH. Seems awfully high after looking at Engine RPM calculators. I have tuned for correct tire size (within 3%) so what could be causing this?

Does stall speed effect crusing RPM? The converter is locked so I wouldn't expect this.
 

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3.42s, TransGo Shift Kit and 2800 Edge Stall.........Does stall speed effect crusing RPM? The converter is locked so I wouldn't expect this.
1. Cruise RPM is not effected by stall speed.

2. What size tires you running? With stock diameter tires (27" on the SS), you should be running at just under 2100 RPMs @ 70 MPH........at 2500 RPMs you should be at about 83 MPH.

3. It is possible that your car has 4.10 gears.....just possible, since 2500 RPMs with 4.10 gears = 70 MPH.

KW
 

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Discussion Starter · #3 ·
I've got a wagon with 27.7" tires (245/40/20s) which is close to the 28.3" stock tire size. This means that my RPMs should be even LOWER! I don't think that my car has 4.10s. I bought them off of ebay and they were supposedly out of a cop car (3.42s), but I didn't count the teeth or anything.

It must not be locking up, then. I can hit the brake and have it kick out of lock up, right? If it isn't locking up, that means that it is "slipping", right? I will double check this on the way to work tomorrow.

I've got a post on the Engine Problems section about problems with vibration during converter lockup. I'm thinking more and more that my Edge Converter is junk!
 

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Discussion Starter · #5 ·
Z28 dash
 

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Discussion Starter · #6 ·
I guess it is possible that my PCM is tuned wrong.

Maybe I am really going 83 MPH and don't know it cwm2.
 

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It's easy to figure your actual rear end ratio. Raise car, mark a tire and driveshft and turn exactly one tire revolution - count the driveshaft revs. If you're not sure about your speedo, use or borrow a GPS - it will have a speed function.
 

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Yeah, checking the speed with the GPS would be the first thing to do, to make sure you are actually going 70. It's not difficult to misjudge speed between 70 and 80. Could it be your PCM is tuned for something completely different.

I have 3.73 and I don't think I am turning 2500 at 70, but somewhat under it, maybe 2300 at most. And I have smaller than stock tires, 26.6".
 

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First off, be suspicious of any factory analog gauges. My roadmaster speedo is anywhere from 2-4mph off depending on speed (and sometimes it's dead on). The Z28 cluster's tachometer in my caprice is 200rpm high across the range. It says I'm doing 2700rpm at 75, which I'm not (i'm actually doing 2500). A scan tool will tell you the actual engine rpm.
 

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Discussion Starter · #10 · (Edited)
Thanks for the suggestions

I will defintely recheck my gear ratio but I'm 95% sure that they are 3.42s. I thought I was going to have to pull the cover and count teeth but the tire rotation thing is a WAY better idea. I guess if I thought about it long enough I would have figured that out.

Could a slipping converter be causing these higher RPMs even in lockup? I'm thinking that this is all related to my "Vibration When Converter Locks". This would explain vibrating (grabbing and releasing under light throttle) and higher RPMs during cruising.
 
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