Auto Tranny plus a turbo. Good or bad?
Sitruc_bc
11-13-2005, 02:17 AM
I heard from someone that turbocharging an automatic is'nt a good idea. True or false?
KManiac
11-13-2005, 10:32 AM
I have never heard of common statements against turbocharging an automatic. I find that a turbo works best with an automatic transmission because you don't lose boost at gear changes. But should you turbocharge a car with an automatic, be sure the automatic transmission used is strong enough internally to take the power pushed through it by the turbocharged engine.
Case in point:
I own a 1991 Dodge Shadow with factory 2.5 liter, turbocharger and automatic transmission. I have owned this car for close to 13 years.
About five years ago, the car developed a habit of momentarily cutting out under one half to fully open throttle situations. I was concerned, but it didn't seem to do this any other time. This continued for about a year. Then I began to "ping" in these situations. That is when I finally noticed the pressure readings on my turbo gauge. Normally when I would apply more than one half open throttle, the gauge would show boost of up to 15 psi immediately, then drop back to between 0 to 5 psi within a few seconds. Now, the gauge would peg out beyond 15 psi and stay there until I back off on the throttle. It felt to me as if the wastegate had ceased to function and there was some sort of over-pressure interlock that would cut the ignition when the boost got too high.
After driving the car like this for a year and a half, I finally took it to the dealer for a 90,000 mile service and asked them to look at the turbo. They discovered the vacuum control line to the wastegate was leaking and replaced the line. I got the car back and the turbo performed like new again.
Fifty miles and four days later, the transmission began to stick in high gear. I took the car to a good transmission shop. They suspected metal fragments had shed from the internals causing the govener to stick. When they disassemble the transmission, they found that a clutch plate in the front clutch pack had shed teeth where the plate contacts the input shaft. The transmission was cleaned and rebuilt.
One year and 8,000 miles later, the transmission again starts to stick in high gear. Under warranty, the transmission shop disassembles the unit again and cannot find anything wrong. The next day, I take the car on a 200 mile round trip. While returning home, I notice some type of rhythmic surging while cruising at 65 mph with cruise control. About 10 miles from home, I suddenly feel something go WHAM, which shakes the entire car and feel a sudden loss of car speed. It felt like I had run over something, but I did not. The car continued to cruise at freeway speed, but I had lost indication on the speedometer (the needle dropped to 0) and the cruise control dropped out, as well. I thought this was strange, but the car continued to drive and I saw no smoke and didn't hear any funny noises, at least not yet. About five miles down the road, I began to hear a screeching sound, reflecting off the sound wall next to me. The screeching would occur when I would apply throttle and stop when I backed off. Two miles later I took my normal off ramp off the freeway and stopped at the signal. When the light turned green, I began to accelerate, but found the transmission stuck in high gear. I instinctively pulled the selector into Low and the transmission went into a permanent state of "neutral". I had the car towed to the transmission shop.
When they disassembled the transmission again, they found that the splines meshing the rear planetary hub to the output shaft had sheared away. It appeared like something had jammed in the gear set, causing the these pieces to suddenly break. The technician was surprised to learn that I had driven the car eight miles on the freeway this way before it stopped working.
It became apparent to me that the transmission in my Shadow was not designed to take the full power output possible from the engine when the wastegate had failed. Driving the car for a year and a half with a disfunctional wastegate caused the engine to overstress the internal components of the transmission, leading to the two internal failures I experienced. Now, after almost three years, 22,000 miles and two transmission rebuilds, both the transmission and the turbo are working just fine.
My suggestion to you, if you are planning to add an aftermarket turbo to an existing automatic equipped car, is to consult transmission experts on the durability of that transmission with the anticipated power output of your engine.
Case in point:
I own a 1991 Dodge Shadow with factory 2.5 liter, turbocharger and automatic transmission. I have owned this car for close to 13 years.
About five years ago, the car developed a habit of momentarily cutting out under one half to fully open throttle situations. I was concerned, but it didn't seem to do this any other time. This continued for about a year. Then I began to "ping" in these situations. That is when I finally noticed the pressure readings on my turbo gauge. Normally when I would apply more than one half open throttle, the gauge would show boost of up to 15 psi immediately, then drop back to between 0 to 5 psi within a few seconds. Now, the gauge would peg out beyond 15 psi and stay there until I back off on the throttle. It felt to me as if the wastegate had ceased to function and there was some sort of over-pressure interlock that would cut the ignition when the boost got too high.
After driving the car like this for a year and a half, I finally took it to the dealer for a 90,000 mile service and asked them to look at the turbo. They discovered the vacuum control line to the wastegate was leaking and replaced the line. I got the car back and the turbo performed like new again.
Fifty miles and four days later, the transmission began to stick in high gear. I took the car to a good transmission shop. They suspected metal fragments had shed from the internals causing the govener to stick. When they disassemble the transmission, they found that a clutch plate in the front clutch pack had shed teeth where the plate contacts the input shaft. The transmission was cleaned and rebuilt.
One year and 8,000 miles later, the transmission again starts to stick in high gear. Under warranty, the transmission shop disassembles the unit again and cannot find anything wrong. The next day, I take the car on a 200 mile round trip. While returning home, I notice some type of rhythmic surging while cruising at 65 mph with cruise control. About 10 miles from home, I suddenly feel something go WHAM, which shakes the entire car and feel a sudden loss of car speed. It felt like I had run over something, but I did not. The car continued to cruise at freeway speed, but I had lost indication on the speedometer (the needle dropped to 0) and the cruise control dropped out, as well. I thought this was strange, but the car continued to drive and I saw no smoke and didn't hear any funny noises, at least not yet. About five miles down the road, I began to hear a screeching sound, reflecting off the sound wall next to me. The screeching would occur when I would apply throttle and stop when I backed off. Two miles later I took my normal off ramp off the freeway and stopped at the signal. When the light turned green, I began to accelerate, but found the transmission stuck in high gear. I instinctively pulled the selector into Low and the transmission went into a permanent state of "neutral". I had the car towed to the transmission shop.
When they disassembled the transmission again, they found that the splines meshing the rear planetary hub to the output shaft had sheared away. It appeared like something had jammed in the gear set, causing the these pieces to suddenly break. The technician was surprised to learn that I had driven the car eight miles on the freeway this way before it stopped working.
It became apparent to me that the transmission in my Shadow was not designed to take the full power output possible from the engine when the wastegate had failed. Driving the car for a year and a half with a disfunctional wastegate caused the engine to overstress the internal components of the transmission, leading to the two internal failures I experienced. Now, after almost three years, 22,000 miles and two transmission rebuilds, both the transmission and the turbo are working just fine.
My suggestion to you, if you are planning to add an aftermarket turbo to an existing automatic equipped car, is to consult transmission experts on the durability of that transmission with the anticipated power output of your engine.
neon_rt
11-14-2005, 12:38 PM
The Automatic transmission in the Avenger is only rated to about 250ft of torque and about 250 hp. As long as you stay under that amount of power, it should be fine.
The more power you put through it, the shorter time it will last. If you put too much through, it will just break.
The more power you put through it, the shorter time it will last. If you put too much through, it will just break.
Sitruc_bc
11-14-2005, 05:31 PM
Crazy stuff dude! And thanks for all the info! My tranny is doing something stupid right now. I don't know what it is. Every once in a while, it will make a grinding noise, and sometimes white smoke will blow out the exhaust. But before I turbocharge my car, I'm going to have it all looked at, just so it's in good shape. I believe the former owner of my car, rodded it alot, since they look sleek and all that, so he probably hammered on the throttle alot, and here I am, getting all the after affects. Oh well, I'll build it better and stronger!!
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