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Disadvantages of a turbo 400

This is a discussion on Disadvantages of a turbo 400 within the Drivetrain forums, part of the LSx Technical Help Section category; Originally Posted by 408WS6 I have a TH400 in mine. I really like it. The only thing I don't like ...

  1. #21
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    Quote Originally Posted by 408WS6 View Post
    I have a TH400 in mine. I really like it. The only thing I don't like is no overdrive for highway driving. But my car doesn't see much highway driving, and very little street duty so I'm not worried about it. If you want a bullet proof transmission and overdrive (have your cake and eat it too) you should go with a 4L80E. Its basically as strong as a TH400 but with over drive (and alittle heavier). There are drawbacks to the 4L80E though. Main one being cost. Look at spending about 4k for 4L80E and converter. You might be able to pick one up on ebay for alot less from a reputable seller, but buyer beware (and you get what you pay for). Also, if you have a '98, the PCM will not support the 4L80E and you will either have to shift it manually or buy a stand-alone PCM (I think TCI makes one), but these are very pricey, $900 I think. Can you tell I've given this some thought?

    But there are other advantages to having a 4L80E: being able to lock up the converter on the dyno, and being able to electronically control your shift points. I can't tell you how many times I wanted to lock up my converter for various reasons. But at the end of the day, the TH400 is an excellent value and performs very well at the track (but expect painfully low dyno numbers).
    does it just show low numbers or does it actually kill some power?

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    Member 408WS6's Avatar
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    Quote Originally Posted by stoney2677 View Post
    does it just show low numbers or does it actually kill some power?
    The TH400 is very misleading on the dyno. My converter slips like 15% which probably accounts for most of the hp loss on the dyno, but at the track it keeps up with and even beats cars that dyno 500+ rwhp. I really don't know the answer to your question as to why TH400's dyno so low, but they put down the numbers at the track is all I can say.

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    Moderator Firebirdjones's Avatar
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    Turbo 400's do take a bit more HP to turn,,,as compared to say,,,a 350 turbo or 4L60E. The 400 is just much larger inside,,,more mass to turn. Although if you spend some money you can build them with lighter aluminum parts and free up HP, with less recipricating weight.

    I run turbo 400's in 4 different cars, love that transmission. Hard to kill it. I have a stock rebuilt 400 turbo behind my 638 HP chevelle that cuts 1.5 60 foot times in a 4,108 lbs. car,,,,it's held up great over the years without even a hickup.

    As far as the overdrive part,,,,it's not that big of a deal,,,guess most kids are so used to overdrives they forgot how it was done back in the day for many years. Shucks I drive the chevelle everywhere with 4.10 gears and a 28 inch tall tire,,,,60 mph is right at 3,000 rpms with a somewhat loose 10 coan converter. It's not that bad really.

    I have driven my 1970 firebird accross country many times with it's 400 turbo and factory 3.31 gears,,,with 28 inch tires it cruises effortlessly at 70 mph,,,only about 2,800 rpms or so,,,and gets 16 mpg to boot.

    Most racers will ditch the 4l60E not so much because of strength reasons,,,,but because the gear spread they have flat out sucks for racing. You can build the 4L60E to be pretty stout and take abuse,,,,but that 1-2 shift just kills ET as the engine struggles to gain back rpm.

    The overdrive is nice but I can't stand that damn 3.06 first gear ratio in the 4L60E.

    Alot of racers also go for the 2004R, factory in the Grand Nationals and Monte SS's,,,,since it has a much more friendly 2.76 first gear, again though, it too has to be built to take alot of abuse. But the 1-2 shift rpm drop is much more tollerable.

    The 4L80E to explain in the simplest of terms is just a 400 turbo with overdrive. It is based of the 400 turbo design for the most part and has the exact same gear spread as the 400 turbo.
    2.48 1st
    1.48 2nd
    1.00 3rd

    If you want the best of both worlds,,,,the 4L80E is where it's at. It's strong and has the overdrive gear for the whimps that are afraid to spin a few rpms No real disadvantages to a 400 turbo in my book.

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    Member 408WS6's Avatar
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    Quote Originally Posted by Firebirdjones View Post
    As far as the overdrive part,,,,it's not that big of a deal,,,guess most kids are so used to overdrives they forgot how it was done back in the day for many years.
    WORD to that brotha!!

    I didn't even know what overdrive was until my 3rd car (a brand new '91 Z28) and even then the overdrive got on my nerves! LOL

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    Moderator Firebirdjones's Avatar
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    Quote Originally Posted by 408WS6 View Post
    WORD to that brotha!!

    I didn't even know what overdrive was until my 3rd car (a brand new '91 Z28) and even then the overdrive got on my nerves! LOL
    My kinda guy

    Shucks I've only been around overdrives for a few years,,,but my daily driver still sports a 1.00 final drive ratio

    My chevy 1 ton (454/400 turbo and 3.73 gears) is my tow vehicle pulling 10,000 lbs. of enclosed trailer around,,,,65 mph is about 2,800 rpms but I wouldn't have it any other way.
    I can't stand the overdrives for towing,,,can't use the overdrive function anyway,,,and you still have that damn converter locking in and out in 3rd gear when you hit a grade,,,,drives me bonkers.
    They may have fixed this issue in the newer trucks though, as my fathers 01 3/4 ton has a tow/haul mode and has the 4L80E,,,,,but I wouldn't know,,,,I'm happy with the old school stuff

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