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Thread: does my trans have too much slippage?

  1. #1

    does my trans have too much slippage?

    I have a BBC that dynoed at 612hp and 590 ft pounds. I am running a 28" tall drag radial. I have a 3500 rpm tci streetfighter converter. My motor makes its peak power at 5800 rpm. My car is street driven and weighs 3496 with me in the seat. the rear gears are 3.89. my trans is a TH 400 and the converter seems tight (2000 rpm max on the footbrake before the tires lite up.)

    I went to the track for the first time and ran a 11.25 at 117 mph I was on the rev limiter the last 200 ft before the end of the quarter. My rev limiter was set at 6200 rpm. my 60 ft was 1.67. My question is should I do a gear swap for 3.73, or should I have my transmission checked. It seems to me with my set up I should be able to go faster more like 125mph before I hit the limiter. any help would be greatly appreciated.

    stuck in the 11's
    steve

  2. #2
    Senior Member DYNO OPERATOR
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    You should be running faster than that. My Pontiac with 3.73 would turn about 6500 with 28" tires in the 1/4. Set your revlimiter higher and see what happens. Youre stall is probably to low, you should be in the 1.50's, at least, in the 60' with what you have.

  3. #3
    Quote Originally Posted by CamBirdRacing
    You should be running faster than that. My Pontiac with 3.73 would turn about 6500 with 28" tires in the 1/4. Set your revlimiter higher and see what happens. Youre stall is probably to low, you should be in the 1.50's, at least, in the 60' with what you have.
    I am going to raise my limiter to 6400, also I measued my rear tires and they are 27 1/2 tall not 28 as advertised. I will run some 28" tall MH (stickyer tires) next weekend with more air pressure. I will post the change when I get back.

  4. #4
    Senior Member MASTER BUILDER
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    Something to keep in mind, is that the rev limiter chips will usually come in about 200rpms sooner than the advertised, so that your 6200 would have been about 6000.

    When I do the math for the MPH, gear, and tire size it shows that 117 mph would need about 5600rpms without slippage. With the limit most likely hitting at 6000rpm's that shows that you have only about 400 rpm's of slippage on the top end, so it doesn't appear that you have a problem with either your transmission or your torque converter slipping. When you go up about 200 rpm's more, it shows that you would only reach about 122mph (the same as if you kept the rpm's the same and changed the gear to 3.73). If you changed your rear tires to a 29" tall, then you would be about 128mph with the rev limit up to the 6400.

    Right now your effective gear ratio is like a 4.56 with 32" tall rear slicks.

    Bill

  5. #5
    Senior Member SENIOR BUILDER chevynovaman's Avatar
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    I HAD A TCI SUPER STREET FIGHTER ALSO, SEEMED LIKE IT WAS WORKING OK UNTIL I DECIEDED TO GO TO AN EDGE CONVERTER, THEN I REALIZED THE TCI HAD NO TOP END, BELIEVE IT OR NOT, THE EDGE CONVERTER GAVE ME 500 LESS RPMS AND 1/2 SECOND FASTER THROUGH THE TRAPS AND WAS STILL BUILDING SPEED INSTEAD OF RPM.. 612 HP SHOULD RUN 10.50'S EASILY WITH YOUR SETUP.. I THINK YOU HAVE THE RIGHT SETUP AND GEARS EXCEPT CONVERTER.. OPINION,, GOOD LUCK IN 09
    1968 CAMARO 302 4 SPD IN THE ROUGH
    1957 CHEVY FUEL INJECTED LS1 4L60E BEAUTY
    1962 CHEVY II NOVA 496 LETS RACE

  6. #6
    Quote Originally Posted by sp2816
    Something to keep in mind, is that the rev limiter chips will usually come in about 200rpms sooner than the advertised, so that your 6200 would have been about 6000.

    When I do the math for the MPH, gear, and tire size it shows that 117 mph would need about 5600rpms without slippage. With the limit most likely hitting at 6000rpm's that shows that you have only about 400 rpm's of slippage on the top end, so it doesn't appear that you have a problem with either your transmission or your torque converter slipping. When you go up about 200 rpm's more, it shows that you would only reach about 122mph (the same as if you kept the rpm's the same and changed the gear to 3.73). If you changed your rear tires to a 29" tall, then you would be about 128mph with the rev limit up to the 6400.

    Right now your effective gear ratio is like a 4.56 with 32" tall rear slicks.

    Bill

    Well I raised the limiter to 6400 and ran M&H Drag raidals (325/50-15) I found out that they are also shorter than advertised just slightly taller than the BFG,s. 1 more inch in circumfrence. the chages at the track was it was about 10 degrees hotter and very humid (rained the whole night before). 60ft went to 1.60, mph went to 120, and et went to 11.20. still on the limiter long before the traps. The tires defintetly helped the 60ft but not the mph. I am thinking about a better converter but I think that will take away my street ability, and is more money than I am willing to spend at this time. The gear swap is much cheaper just gears, a pinion bearingand time. The rear end only had about 500 miles on it. I will just have to decide which ratio I am leaning toward 3.70 but would concider 3.50, because if it don't run faster than 11.0 I can introduce the car to the blue bottle and not the limiter. right now no racing until august no time and even less money.

    a little faster but still stuck in the 11's
    steve

  7. #7
    Senior Member RACING JUNKIE
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    Why so low on the rev limit? :?

  8. #8
    Senior Member RACING JUNKIE
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    Quote Originally Posted by Tod74
    Why so low on the rev limit? :?
    I agree with TOD, with you hitting the limiter, your killing your ET and MPH no telling what it might run if you upped the rpm chip.
    The main purpose of the rpm chip is to save your motor in case of a acidental over rev, I.E driveline breakage, etc.
    No need in having it that close.
    I run a 8K in mine car, just a thought>Cp
    ***IN GOD WE TRUST***

  9. #9
    Quote Originally Posted by Tod74
    Why so low on the rev limit? :?

    The power in the motor falls off quick after 5800 rpm. I shift at roughly 5900-6000. Bear with me I have been wrenching for years, but I am a newby at the whole racing game. Sould I set the limiter off the shift points and if so how much higher?

    thanks for your help,
    steve.

  10. #10
    Senior Member RACING JUNKIE
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    Quote Originally Posted by chevysteve2
    Quote Originally Posted by Tod74
    Why so low on the rev limit? :?

    The power in the motor falls off quick after 5800 rpm. I shift at roughly 5900-6000. Bear with me I have been wrenching for years, but I am a newby at the whole racing game. Sould I set the limiter off the shift points and if so how much higher?

    thanks for your help,
    steve.
    Your HP isn't going to fall off as much going over your peak HP as being on the rev limiter, I'll guarantee that. If you take gear out of it your not going to bump the rev limiter but I'll bet you slow down in ET. Raise the rev limiter, your engine can handle it. Let it rip.


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