200=400=350?

[turbo buicks]

ok wouldnt having a TH 350/400 w/a lockup converter be just like driving with the 200 w/a lockup converter until 100+ MPH where the 200 would shift into 4th and make use of the OD?

 

[MeanBuicks]

Well, at the track during WOT, yes.

However, more folks consider that at 45 mph during cruise a 2004R will go into overdrive and lock the converter for improved economy.

 

[2quiktocare]

I agree with Greg here. If you want to drive your car on the street you will be using the od a lot. If you live with your foot to the floor all the time (racing) the 400 with a lock up would be more efficient than a 400 without it. As far as a 400 being the same as a 200 4R up until 100mph, I don't think that is equal. The 200 4R has much better gear spacing and will keep you right in the power band of your car. Mark. Just MHO

 

[turbo buicks]

hmmmm, let me get one thing straight. whats being referred to as OD is really lockup, correct? like at 45 mph that jolt that hits, is that the converter locking up? and when i pull it into D and RPMs raise, thats the converter unlocking? anybody know the gear ratios for a 400 and/or 200? at cruise the 200 lock the converter AND go into OD gear?

 

[MeanBuicks]

Overdrive and lock-up are two completely different items.

Overdrive is just that, an internal transmission ratio less than 1:1. In the case of the 2004R it's .67:1. The engine turns 33% slower than the driveshaft in OD.

Lock-up is a function of the torque converter. It is a mechanical clutch housed within the converter that, when applied, eliminates any residual hydraulic inefficiency (slip) remaining at coupling. In other words, it's making converter output a true 1:1 ratio to engine rpm. Efficient non lock-up converters will still have 3-5% slip going down the road.

For more about transmission ratios, look here.

 

[2quiktocare]

What Greg said plus a lock up naturally occurs in stock application on a 200 4R after the trans shifts into third gear. A manual operation can be installed that allows you to enter lock up at any point. Mark



P.s. If you are talking about a plain th200 non O/D trans, it does not have lock up period

 

[turbo buicks]

so what is that clunk at 45 mph? converter locking up or OD gear engaging or both?

 

[2quiktocare]

You are probably going into overdrive at that point, but it shoudn't be a big cluck, just a positive change if everything in normal.

 

[MeanBuicks]

If the converter locks in third and remains locked during the 3-4 shift, it can make the shift rather firm.