3.73 rear gear 28 tire. 4400 rpm Cruz at 70 - Chevelle Tech
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post #1 of 44 (permalink) Old Sep 9th, 19, 11:43 AM Thread Starter
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3.73 rear gear 28 tire. 4400 rpm Cruz at 70

I’m baffled. Is my converter slipping that much? It’s a 2800 stall tci. With tci super street fighter th400.
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post #2 of 44 (permalink) Old Sep 9th, 19, 11:48 AM
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kevin
 
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Re: 3.73 rear gear 28 tire. 4400 rpm Cruz at 70

probably is a bit. too much gear for the street with a 1:1 output transmission... imho....
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post #3 of 44 (permalink) Old Sep 9th, 19, 11:48 AM
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Justin
 
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Should be around 3100-3200 rpm at that speed
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post #4 of 44 (permalink) Old Sep 9th, 19, 11:53 AM
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Steve
 
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Re: 3.73 rear gear 28 tire. 4400 rpm Cruz at 70

Something is slipping.

With a 3.73 gear and 28" tall tire, you should be turning 3133 rpms at 70mph.

Now, assume a few hundred rpm max for slippage if you don't have a locking converter, so say 3300 or so. 4400 is excessive at 70 mph with 3.73 gears and a 2800 rpm stall converter.

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post #5 of 44 (permalink) Old Sep 9th, 19, 12:00 PM
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Re: 3.73 rear gear 28 tire. 4400 rpm Cruz at 70

The MPH was from a GPS I assume?

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post #6 of 44 (permalink) Old Sep 9th, 19, 12:19 PM
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Re: 3.73 rear gear 28 tire. 4400 rpm Cruz at 70

Is the tach wrong? My 70 SS factory tach with an MSD box reads fine at 1000 rpm, but the difference increases as rpm goes up. My 3.31 car with 26" tall tires is 3500 at 60 mph which I know is no way right.
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post #7 of 44 (permalink) Old Sep 9th, 19, 12:26 PM
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Greg.
 
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Re: 3.73 rear gear 28 tire. 4400 rpm Cruz at 70

Something is not right or !?

TH400 Manual Reverse VB with a Dynamic 9.5" 3500 to 6,500 Stall Converter
S60 Strange Rearend with 3.70 Gears
27.8" Diameter Rear 15" Tire

65 MPH at 2,800 RPMs in 3rd Gear 1.00 Ratio

That 4400 RPM sounds like it is a 4.10 to ?.?? Rear Gear Ratio

67 Chevelle Malibu SS Cdn
Born 283 / PG / A51
468/TH400 2,500 stall/ S60 3.70 Gs
Prev Best on M/T ET S/S #3454 street Tires/Dress 2018/05/20
60' = 1.664
1/8 = 7.532 et / 91 mph
1/4 = 11.814 et / 115 mph
NEW Best with 3,500+ Stall TC 2019/06/23
60' = 1.561
1/8 = 7.411 et / 90.18 mph
1/4 = ??.??? et / ??? mph


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post #8 of 44 (permalink) Old Sep 9th, 19, 12:33 PM
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George
 
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Re: 3.73 rear gear 28 tire. 4400 rpm Cruz at 70

Try another tach. Mine was off by 800rpms...I was thinking trans/converter. It was just the tach luckily.
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post #9 of 44 (permalink) Old Sep 9th, 19, 1:54 PM Thread Starter
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Took speed reading with gps. New tach. Verified with timing light. Very close. 30 rpm difference. Could just be my eye. Also at wot from 80mph the rpm rpm goes to 5700 immediately and climbs with speed. Low speed wot if difficult to test. Below 55 tires just spin and 1st gear is basically for idling.
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post #10 of 44 (permalink) Old Sep 9th, 19, 2:54 PM
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Dave
 
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Re: 3.73 rear gear 28 tire. 4400 rpm Cruz at 70

My guess would be the torque converter. How old is it? If you end up replacing it, dont buy an off-the-shelf unit from Summit/Jegs. Call a shop that specializes in torque converters. I've had good experience with Edge Racing converters.

First one was in blue_69_malibu's car (th350) and it works GREAT. Based on that experience, I replaced the awful converter in my S10 Blazer's 700R4. Swapped out a total POS Summit brand converter for the Edge. I picked up a full second in ET. Drivability was better too. It was $625-650 delivered.

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post #11 of 44 (permalink) Old Sep 9th, 19, 4:47 PM Thread Starter
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Converter is new tci 2800 stall. This first picture just now when it was cold. Pull out of driveway and got to 70 Cruz immediately. 2nd photo is after 3 full throttle 0-120 runs then 70 Cruz. What the hell is happening. Rpm rose over 1400-1500 rpm at the same 70 Cruz. Only difference was 15 min of driving hard.
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post #12 of 44 (permalink) Old Sep 9th, 19, 5:26 PM
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Re: 3.73 rear gear 28 tire. 4400 rpm Cruz at 70

got another tach to try?

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post #13 of 44 (permalink) Old Sep 9th, 19, 5:27 PM
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Re: 3.73 rear gear 28 tire. 4400 rpm Cruz at 70

GOt another tach to try? If no, but a cheap one at O'Reillys or someplace.

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post #14 of 44 (permalink) Old Sep 9th, 19, 5:46 PM
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Re: 3.73 rear gear 28 tire. 4400 rpm Cruz at 70

Let off the throttle and see if the tach falls rapidly to the numbers it should read and then tip back into the throttle and see if the tachometer jumps back up to the 4500rpm if it does then you have converter issues or trans issues.
I have seen some B&M and TCI converters that had a ton of slip.
Back off the throttle and RPM would drop 1500 RPM.

When I finally stepped up to a Coan I was amazed.
Actually had less slip at the end of the 1/4 mile than my 1800 stall B&M.
And the Coan was a 4500 stall converter.

I have some new junk air core tachometer in one vehicle and that thing will jump around with my single point distributor. The manufacturer said install a resistor in line.
Not happening.
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post #15 of 44 (permalink) Old Sep 9th, 19, 7:08 PM Thread Starter
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Just went and swapped out my auto meter monster tach from the Camaro to the chevelle. I know this tach works. 100%. Installed it in the chevelle and nothing. Just out of frustration I put it on the positive coil wire and it works. Neg coil wire. Nothing. Hooked the original back up to neg post on coil and nothing. Put it on positive and it works. So both tachs now only work on the positive coil post. But slightly Erratically. Am I missing something? Also just installed a trans cooler 5 min ago. Figured maybe the old one was clogged.
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