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Discussion Starter #1
Have a built 4r70 I plan on swapping in behind my TT racecar. Is there any specific reason to use a lockup converter or not? Not seeing a big price difference either way, and don't do much "overdrive" driving. It's got mvb already and I'm wondering if it's necessary/worth the hassle wiring it in?
 

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I don't know if any of this will help but since nobody has replied I'll give my .01 worth.

I wanted a lockup b/c I wanted to make sure the power would not be wasted if the converter was slipping. A "good" converter shouldn't have much slip but getting one that is 100% spot on is pretty rare w/o taking several attempts. I've seen people posting low dyno #'s and they assumed or discovered that the converter was slipping too much.

I was also planning on 900hp which I figured is enough power to pull it when it was locked up in 2nd and 3rd gear.

I also wanted a lockup for the highway.

ks
 

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^^^ This is basically the same reasoning for me to go with a lock-up converter as well. After talking with my transmission builder, he recommended a lockup tc to get the most from my setup. He built my vb and tc to match my car's blower and engine combo. His other points were I didn't need and slip to keep the engine building power and since I will be driving my car to/from the track, the transmission temps will be lower on the highway with the locking tc.
 

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Discussion Starter #4
Thanks guys, not seeing much of a price difference on either. Is there only certain gears to lockup? I'm starting to lean more towards he lockup, you make a good case on the slippage. I'm running a mvb and have to wire it in on switch and have heard so horror stories, basically due to negligence on the behalf of the operator.
 

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People have differing thoughts on when it should be locked up and I think people have had different results too so it probably depends on combo. Personally I would want it locked up in first gear but I don't think mine can do it but I'm not sure if that's b/c of the Quick4 controller or Dan Gilsdorf (Silver Fox Racing) has it built this way..not sure. Anyway, I do plan on locking it as soon as it gets into second gear.

Important: you do not want the converter locked DURING the shifts. My Quick4 controller unlocks the converter during the shifts then locks it back up automatically.

IMO, you will want a multi-disc converter. I personally wouldn't trust a single disc b/c it's too easy to crank up the HP on a turbo car.

ks
 

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At one point I had Dan at Silverfox build me a 4R70W trans for the drag car because it had the ability to lock up the converter in high gear (3rd) while racing, thus eliminating the slip in the converter and that was supposed to make better use of the power out the back end. Alas, the trans he built was not going to be able to take the HP I was going to make, so it got sent back. Ended up with a race built Glide that can take over 1,500 HP. Turns out that the Glide datalogs show only 6% slip in the converter in high gear, so I am good with that.
 
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Discussion Starter #7
Sorry for the noob question, but how exactly does it lock up? Electronically or fluid? Without running a trans controller, I guess it would be silly for me to try to lock up while racing, having to disengage before shifting and reengaging.
 

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Many seem to forget what a torque converter does. It multiplies torque. The lock up feature removes that multiplication. It's nice on the highway for sure but it can also be a pain in the backside on the drag strip.

Lock up has zero multiplication. Max multiplication occurs at the launch, and it diminishes as you reach the top of each gear, then right after you shift, you get some of it back again after the shift occurs. Also the slip you get between shifts actually helps keep the engine in it's power curve. But excessive slippage at the far end of the track can slow it down. But I think people place too much emphasis on slippage. A junk converter off the shelf will do that from time to time. Most GOOD converter builders will know what to do, and they're not cheap. You get what you pay for. Lockup is, again, nice to have on the highway. IMO if you're not driving on the streets much, I don't see a need for it. But I have not used lockup to split gears either. I could see that as a potential benefit depending on the converter. I wonder how much RPM drop there is between non-lock and lock at the top of high gear?

Sometimes going back to the KISS principle makes for a more enjoyable racing experience. And in my case, more successful.
 

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Fred at fb performace told me one benifit to locking it up on my4r70 that will help extend 3erd a bit if youre running the1/4mile and at the end of your run at your rpm limit under nonlock up engage it to lower rpm to extend 3erd.
 

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If your engine combination does not require a lot of stall speed, like above 4000, I would go non lockup. I have a 4r70w with overdrive and lockup on the same switch for when I hit the highway, but my engine is n/a and needs 4000+ stall. So, the converter slips more at highway speeds without the lockup.

Adding a lockup converter also adds several pounds of rotating mass to the crank due to the extra weight inside the converter from the lockup disc and friction plate. About 10 pounds on an 8" converter! This is quite a parasitic loss.
 

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Discussion Starter #11
If your engine combination does not require a lot of stall speed, like above 4000, I would go non lockup. I have a 4r70w with overdrive and lockup on the same switch for when I hit the highway, but my engine is n/a and needs 4000+ stall. So, the converter slips more at highway speeds without the lockup.

Adding a lockup converter also adds several pounds of rotating mass to the crank due to the extra weight inside the converter from the lockup disc and friction plate. About 10 pounds on an 8" converter! This is quite a parasitic loss.
Interesting thought.
 

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Question. If for instance a race car has a 5000 stall lockup, and you're running down track at full tilt in high gear, and you lock the converter, how much RPM drop is there?
 

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Question. If for instance a race car has a 5000 stall lockup, and you're running down track at full tilt in high gear, and you lock the converter, how much RPM drop is there?
Depends on how much it was slipping to begin with.

ks
 

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That is impossible to answer due to everything else that factors into the equasion. The converter efficiency, car weight, gear, tire height, horsepower, fluid viscosity, heat, all effect slippage at a given rpm. Normal driving, the converter lockup drops my rpm 3-400 rpm on a 4000 stall converter. Less stall, most likely less difference it would make.
 

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I would go non-lockup. Having had both, locking up the converter downtrack causes too much rpm drop. I used to have to run two different shift points to help compensate. Now I have a non-lockup converter that flashes to 4,200 on the leave (glide with 3.08 gears), and it cruises nicely on the highway:

 
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