Interesting Overdrive Ratio Info.

[chris718]

Although i am not a fan of the gear venders od unit or the the chrysler 518 overdrive transmissions,they are much more efficient when operating in overdrive than traditional gm units(2004r 4l80e) with an overdrive ratio planetary located in front of the compound planetary gearset.the gv and 518 have a rear mounted od planet located behind the compound planetary gearset.to produce overdrive output must be faster than input.if the planet is located in the front it takes more energy to overdrive the larger mass than if is located in the rear.viewing the input and output speeds of a 4l80e or late 518 (new model designation)on a scan tool will shine light on this "speed biasing".now the 700 is in a class all by itself.the front planet alone produces first gear,the rear [planet overdrives this ratio in second to produce second gear,third is direct drive and fourth is the rear planet overdriving direct drive.the aod,now that a whole different story,very efficient in first and second but lacking in third and fourth but still better than the traditional gm units

 

[chasmat2316]

Chris are you a fan of the 700? do you think one would live behind a mild BBC in a 90'454ss P/U ? or would I be better with the TH375 & a Gear Vendors unit? By the way I just picked up your manual on the 2004r, lot's of great info! Thanx Charlie

 

[norbs]

Interesting, but i have a question, what is more effcieint a 4l80e or a GV with a 400.

 

[jgme]

Interesting information but I would have to ask about magnitudes for the efficiencies. Are we talking about 50-100% difference in overdrive efficiency or maybe fractions of a percent? Overdrive is usually used under low power transfer conditions. Is it worth worrying about? Under high loading conditions typically turbo Buick owners use the first three gears. When trying to get every last 1/100th of a second in the quarter mile then power transfer efficiency does become an issue. Although, the efficiency also has to be balanced with weight and reliability.

 

[chris718]

i love the 700r4 and its a great choice for your application as well as turbo buicks although everyone is afraid to use them.awesome spool up in first gear from a dead stop with the 700 verses the 2004r and it is much more efficient,no direct drum .2 planets produce 5 ratios.as for percentages of lossi havent calculated but they are at an educated guest in the 8 to 15 percent range.the need to worry is up to the individual.the point of the post is to point out differences in the principles of operation of the powertrains in question.

 

[chasmat2316]

Hi chris thanx for the info, sorry if I kinda hijacked your post - thought it was a good place to ask. So you think a 700r4 would be a better choice than a 400 with a GV unit for my truck? Thanx again! Charlie

 

[chris718]

700r4 and if you change ecms the lock will work to as the ss 454s were also wired for the 700.just look at the pigtail in your wiring harness.they work great.if you are interested in a unit give us a call.

 

[chasmat2316]

Chris will a 700 live in my truck non lock up with the right mods, or should I stick with L/U? Sometimes I tow a lite open car trailer. Thanx again Charlie

 

[chris718]

lock up

 

[CTX-SLPR]

How does the 4L60E compare to the TH700R4 in durability? I have the option of using a computer control system that will run it. Also anyone make a bold on bellhousing for the TH700R4 or 4L60E onto a BOP pattern?

Thanks,

 

[MeanBuicks]

The 700R4/4L60E input drum setup creates a boatload of inertia. Practically half the transmission guts spin around inside that thing! Even in Neutral. Also, the 3.06 to 1.63 first to second ratio change is pretty harsh. Regardless, they can be made into a pretty good performing unit for a street car.

I'd say that reliability wise, most late model (1988-1993) 700R4s can be made to run just as reliable as a 4L60E. Each has it's advantages when it comes to control. The 700R4 is simple to adapt needing only a proper TV cable set up and a TCC control provision. The 4L60E offers awesome custom tuning potential via the computer operated controls but that comes with added expense that some may find cost prohibitive.

If you've got a line on a computer control system, you'll be very pleased with the 4L60E. You'll enjoy dialing in shift feel and shift points just like you want them.

A bellhousing would be a decent idea for the later two-piece style 4L60E transmissions as they are expressly designed for such a thing. I've never thought much of the aftermarket replacement bellhousings as the pump mounting bolts weren't designed to support the transmission and it introduces centerline concentricity errors in the driveline. The simple solution is to just use an inexpensive Chevy-BOP adapter plate. Problem solved.