Better gearing
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Better gearing
Had my 90 s vett L98 for about 14 years and this is what I have TH 400 trams with a gear vendor and man/valve body hocked up to a B&M shifter , G44 diff 3.07 . Getting fed up with the high rpm at cruise looking for some input for better ratios . Love the pullaway but I think I can afford to loose a bit .Thanks
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At the time of doing the mods the most who I asked said don't run the700 as it just won't last behind 600 HP so I had Frank lupo from dynamic transmission, s build me a beefed up th400 and we stuck the gear vendor on the back . Not looking to undo all of that just some advise on rear end gear selection , I live in the England so parts are not there on the shelf for me . And I am by no means a expert on gearing . Thanks
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From: Glenbeulah Wi
That does not make sense, a gear vendor and 3.07 ratio should be good. At 60 MPH with a 3.07 ratio and no overdrive of the gear vendor unit should only be 2400 RPM with the .78 overdrive it should only be 1871 RPM.
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Be back tomorrow with numbers, I'll take the flak because I should have wrote it all down . But was doing some boat run RPMs Vs speed for correct props on Sunday so now I have all sorts of numbers jumbled up .
Apart from last Friday I haven't used the car for a while but I allways thought I would have a top speed of 150 mph if I ran flat out at 6000 rpm so I am going to guess its 50 mph at 2000 rpm , and the overdrive was def working as I watched the rpm drop every time I pushes the floor button .
Apart from last Friday I haven't used the car for a while but I allways thought I would have a top speed of 150 mph if I ran flat out at 6000 rpm so I am going to guess its 50 mph at 2000 rpm , and the overdrive was def working as I watched the rpm drop every time I pushes the floor button .
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From: Park City Utah
It's a good thing that you're going to verify some fact, b/c something is way off. You're not running go-kart tires are you? 
Using any one of a number of calulators, and inputting the gear ratios for a THM400 trans, the rear that you claim you have, and the od gear ratio that you said you have, you should be going 65-70 at 2000 RPM.
Disregard the "5th gear" column, but PLAY WITH THE NUMBERS HERE and see for yourself. Either your OD isn't working, your rear gear isn't what you think it is, your speedo is way off, or you have teeny-weeny wheels and tires.
Using any one of a number of calulators, and inputting the gear ratios for a THM400 trans, the rear that you claim you have, and the od gear ratio that you said you have, you should be going 65-70 at 2000 RPM.
Disregard the "5th gear" column, but PLAY WITH THE NUMBERS HERE and see for yourself. Either your OD isn't working, your rear gear isn't what you think it is, your speedo is way off, or you have teeny-weeny wheels and tires.
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It's a good thing that you're going to verify some fact, b/c something is way off. You're not running go-kart tires are you?
Using any one of a number of calulators, and inputting the gear ratios for a THM400 trans, the rear that you claim you have, and the od gear ratio that you said you have, you should be going 65-70 at 2000 RPM.
Disregard the "5th gear" column, but PLAY WITH THE NUMBERS HERE and see for yourself. Either your OD isn't working, your rear gear isn't what you think it is, your speedo is way off, or you have teeny-weeny wheels and tires.
Using any one of a number of calulators, and inputting the gear ratios for a THM400 trans, the rear that you claim you have, and the od gear ratio that you said you have, you should be going 65-70 at 2000 RPM.
Disregard the "5th gear" column, but PLAY WITH THE NUMBERS HERE and see for yourself. Either your OD isn't working, your rear gear isn't what you think it is, your speedo is way off, or you have teeny-weeny wheels and tires.
Although I have had the car for a long time I haven't driven it that much ,as soon as I got the power out of it that I wanted I got back in to powerboats and the car took a back seat . I all check rear end ratio .but I am sure it is 3.07 . Std wheel size . Just been informed by gear vender I should be at 93 mph at 3000 rpm in OD . That's never happend I would be very happy with them numbers . The car has allways driven how it drove last Friday I just assumed that how it was because I changed to a Th400 , thanks for your help I appreciate it .
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Iam back ! First I checked rear end it is a 3.07 .speedo was spot on against GPS .
2000rpm=34mph
3000rpm=49mph
4000rpm=62mph. All done in 3 RD no O/D
3000rpm= 60mph
4000rpm=75mph. O/V. On
I watched the revs and it's defiantly going in all 3 gears but not a big drop from 2nd to 3 rd .
I will have to find a auto/ trans. Expert over here to see what's going on .
2000rpm=34mph
3000rpm=49mph
4000rpm=62mph. All done in 3 RD no O/D
3000rpm= 60mph
4000rpm=75mph. O/V. On
I watched the revs and it's defiantly going in all 3 gears but not a big drop from 2nd to 3 rd .
I will have to find a auto/ trans. Expert over here to see what's going on .
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From: Park City Utah
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Put a scanner on the ALDL and that should confirm your tach error. I had the issue with mine when I bought it, I was planning on building a 3.90 or a 4.10 rear and I was interested in what RPMs I'd be faced with so I did a GPS with my '90 ZR-1 and using the factory tach it said I was already at 4.0+. Put a scanner on the ALDL and the error became obvious.
I use a different calculator than Tom and I use measured tire dimensions based on "load" but my numbers are very close to the calculator that he used and gave you the link to. The one I use is used to figure the RPM drop between shifts based on tire, axle ratio, transmission.
The tach error isn't linear or a fixed % like a speedometer. It's erratic as hell.
If your car has C68 A/C you could use the display there to confirm the error also I'd think. The scanner on the ALDL will confirm! I had a GV in an '85 dually with a 4.56 rear. Drove 100+ miles a day to and from work. Fuel was certainly an issue.
Last edited by WVZR-1; Aug 27, 2014 at 03:28 PM.
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Put a scanner on the ALDL and that should confirm your tach error. I had the issue with mine when I bought it, I was planning on building a 3.90 or a 4.10 rear and I was interested in what RPMs I'd be faced with so I did a GPS with my '90 ZR-1 and using the factory tach it said I was already at 4.0+. Put a scanner on the ALDL and the error became obvious.
I use a different calculator than Tom and I use measured tire dimensions based on "load" but my numbers are very close to the calculator that he used and gave you the link to. The one I use is used to figure the RPM drop between shifts based on tire, axle ratio, transmission.
If your car has C68 A/C you could use the display there to confirm the error also I'd think. The scanner on the ALDL will confirm! I had a GV in an '85 dually with a 4.56 rear. Drove 100+ miles a day to and from work. Fuel was certainly an issue.
I use a different calculator than Tom and I use measured tire dimensions based on "load" but my numbers are very close to the calculator that he used and gave you the link to. The one I use is used to figure the RPM drop between shifts based on tire, axle ratio, transmission.
If your car has C68 A/C you could use the display there to confirm the error also I'd think. The scanner on the ALDL will confirm! I had a GV in an '85 dually with a 4.56 rear. Drove 100+ miles a day to and from work. Fuel was certainly an issue.
Iam ok with spanners by stay away from anything with electrickery .
Thanks again paul