Gearing questions 7.5 rear

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Stupidquestionspro

Master Mechanic
May 23, 2019
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Tampa Bay Area
Yep. Guess this question will keep on waiting since I can’t find a tach cheap enough for my budget that doesn’t have terrible reviews and I haven’t gotten everything I need yet to crack open the rear end.


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rogue_ryder

Master Mechanic
Oct 27, 2017
267
549
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Colorado

Or



I’m betting that you tach is off. My cars tach also reads 1000rpm at idle. I’ve just chalked it up to the tach is mostly for looks in this car.


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Stupidquestionspro

Master Mechanic
May 23, 2019
369
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Tampa Bay Area
Thanks unfortunately more than I want to spend and maybe it could be the tach thought it’s weird because the motor sounds to my untrained ear like it’s hitting the right rpm so who knows


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hoffa65

Master Mechanic
Mar 11, 2019
319
416
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Atlanta GA
I see no dead spot, it just hits the TC's stall (2700) then moves up normally, auto shift points are abit low if that was a WOT run, should be 4k plus
 

Turbolq4

Royal Smart Person
Sep 25, 2017
1,732
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Nampa Idaho
Cheap method for gear ratio check. Jack up and support rear end of car. Place trans in neutral, see how many full rotations of the driveshaft you get before the tire turns a full rotation. My guess would be really close to two and a half turns of the driveshaft per tire rotation.
 
Oct 14, 2008
8,806
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Melville,Saskatchewan
Are you aggressively spinning the tires at that 2700 rpm launch? My 88 did good burn outs with 2300 and 2400 rpm flash stall, just mashing the gas. If it isn't spinning the tires a lot, you are not launching at 2700 rpm.
 

Stupidquestionspro

Master Mechanic
May 23, 2019
369
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Tampa Bay Area
This is just on the street flooring it from a dead stop I’m not launching or flashing or otherwise to my knowledge and my converter stall is 1700 from what I read from TCI


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pontiacgp

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Mar 31, 2006
29,270
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there seems to be guessing what your car has, I suggest you find out what you car actually has so you can narrow down what the problem is. Have you tested the in and out temperatures of the catalytic cemverter to see if it is partially plugged?
 
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hoffa65

Master Mechanic
Mar 11, 2019
319
416
63
Atlanta GA
This is just on the street flooring it from a dead stop I’m not launching or flashing or otherwise to my knowledge and my converter stall is 1700 from what I read from TCI


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The video shows the TC flash at 2700ish, you say your speedo is right on, if so the Speed/RPM reflected in the video is correct for 2:41 gearing and tire size per the RPM calculator i posted earlier.
This run sounds better after the throttle cable replaced compared to the first one. Still make sure the blades open fully when pedal is to the floor
 
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Stupidquestionspro

Master Mechanic
May 23, 2019
369
107
43
Tampa Bay Area
there seems to be guessing what your car has, I suggest you find out what you car actually has so you can narrow down what the problem is. Have you tested the in and out temperatures of the catalytic cemverter to see if it is partially plugged?

There is a lot of guessing unfortunately because I’m trying hard to figure it out

I have no cats at all it’s true duals straight back to mufflers


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