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Ok, I got a question about a turboed auto tranny set up. WHY does everyone think it's a bad idea. Except for the obvoious about the power lose with the torque coverter... which over all from cam to wheels should never be more then 10-15% even with stock... and the mild possiblity that ya blow the gearing, where is the big hub bub, bub? I mean; first, for the most part, nissan engines have a pertty uniformed powerband so getting the turbo up to those super high revs really isn't gonna get ya that extra push like it would in a honda, and second, with a pertty good aftermarket can releive alot of stress on the tranny, and even out the power loss. So what am I not seeing? Hell, you know that those "funny" cars that run at like 300+ 1/4 run auto!
 

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Turbos don't start making power until about 3200-3500rpm. The auto trans has a torque converter stall speed of 1850-2150rpm (SR20) or 2450-2750rpm (GA16). So, from a stand-still, you get about the same launch as NA. It essentially feels like you dumped the clutch in 2-nd gear in a manual trans when you take off.

The auto trans cannot handle the power of a turbo engine. The clutches burn out. This is due to the 'soft' shift of the stock trans. The clutches slip by design to make the shifts smooth. This builds up a lot of heat when your engine is making 70+ more horsepower than stock. In my car it took 18 months of mostly street driving to wear them out at 5.5# of boost (~180WHP).

That's not to say an auto trans is no good for turbo applications in Nissans. You can have them rebuilt to hold the power, and get a high stall torque converter. I drove to Level 10 in New Jersey and had them redo my trans ($3200 at that time). According to them it is now good to 300+WHP. I have had it for more than 3-1/2 years, and it has been trouble free. I get 2.0sec 60' (I'm working on it, and think I may be able to get 1.8-1.9 eventually) at the drag strip and 8.7sec @ 78mph in the 1/8 mile at 9# of boost.

Lew
 

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Discussion Starter #4
lshadoff said:
Turbos don't start making power until about 3200-3500rpm. The auto trans has a torque converter stall speed of 1850-2150rpm (SR20) or 2450-2750rpm (GA16). So, from a stand-still, you get about the same launch as NA. It essentially feels like you dumped the clutch in 2-nd gear in a manual trans when you take off.

The auto trans cannot handle the power of a turbo engine. The clutches burn out. This is due to the 'soft' shift of the stock trans. The clutches slip by design to make the shifts smooth. This builds up a lot of heat when your engine is making 70+ more horsepower than stock. In my car it took 18 months of mostly street driving to wear them out at 5.5# of boost (~180WHP).

That's not to say an auto trans is no good for turbo applications in Nissans. You can have them rebuilt to hold the power, and get a high stall torque converter. I drove to Level 10 in New Jersey and had them redo my trans ($3200 at that time). According to them it is now good to 300+WHP. I have had it for more than 3-1/2 years, and it has been trouble free. I get 2.0sec 60' (I'm working on it, and think I may be able to get 1.8-1.9 eventually) at the drag strip and 8.7sec @ 78mph in the 1/8 mile at 9# of boost.

Lew
wow... that was quick! LOL... so then I was, for the most part, correct. Change to a torque coverter with a high stall and stronger liquid clutch so it doesn't burn out... then beef up the gearing on the tranny (THAT is the expensive part!!! 3 g's??) and I'll solve most of the problems.
 

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James said:
you don't think that's expensive?

that's 3g's for the tranny alone, another 500 to ship it there and back... and the cost of the turbo components...

like I said, expensive... :)
if ya gone so far to buy a 2 grand turbo, even if you have a manual, you're gonna have to beef some of the gear... so that sorta a givin. Just about anything is gonna be expencive. If it's not, it's either not worth it or not a quality car.
 

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evil_001 said:
wow... that was quick! LOL... so then I was, for the most part, correct. Change to a torque coverter with a high stall and stronger liquid clutch so it doesn't burn out... then beef up the gearing on the tranny (THAT is the expensive part!!! 3 g's??) and I'll solve most of the problems.
Go to http://www.levelten.com to see the prices.

They didn't do anything to the gears in the transmission.
- They installed new clutch packs with high performance friction material. The plates are thinner so they could get more plates in each pack which increases the contact area.
- They replaced the pump with a high pressure pump to create more clamping force on the clutch packs.
- They modified the valve body to make the shifts crisper.
- They installed a 3200rpm stall converter (with the new pump, the stock converter doesn't fit). They sent me to a dyno so they could get the right converter based on my engine's power.

Even with all that, they said to pull the dropping resistor when I go to the drag strip. This puts full pressure on the clutch packs immediately on shifting. The shifts are jarring, and no good for the street. Even with the reworked valve body, shifts under full power generate a lot of heat which shortens the friction material lifetime.

Lew
 

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on an auto trans, less time between shifts means less boost pressure loss, this is why high performance million dollar drag teams use autos. driveability is also a big advantage, which is a huge part of the reason for manufacturers like volvo, porsche, audi, saab, etc almost always offer an auto trans on their factory turbo'd cars. I know a guy who has a 99 Volvo V70R that puts about 450hp to 4 wheels equally from a single trubo 5-cylinder on stock internals, while pegging a 25 psi boost guage on the high setting. The only transmission you could get in a 99 R was an automatic, and his is has never been touched. If I didnt love shifting my own gears as much as i do (in know, it sounds funny) no doubt would i throw in an auto
 

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Well, I have seen

I live in Jamaica, where we have JDM Bluebirds as our "domestics" , with your Stanza, Altima's and Maxima's being the odd ones out. This guy who lives couple miles from me has a factory 1991 SR20DET Automatic. The designation is: SSS-II Attessa, I have no idea what the SSS or Attessa designations mean, some info would be appreciated. I also saw a taxi driving a 1990 SR18DET automatic, my mechanic says those were common back in the day.
 

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92redwhiteandblue said:
If I didnt love shifting my own gears as much as i do (in know, it sounds funny) no doubt would i throw in an auto
it doesnt sound funny i sold my sentra auto for a 200sx that had more miles on it only cause it was a 5speed was always a dream as a kid/ im still pretty mutch one but to have a standard and now YAY
 
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