81 auto trans shift characteristics and boost

[madkaw]

I know there isn't much interest or talk about the auto trans , hence little info to search. My daughters auto seems to work fine, but I don't know what is normal shift rpms under hard acceleration. I figure I would post and hopefully get some feed back to learn some of the idiosyncrasies of this car. Her car under hard acceleration the trans shifts at about 4750rpm-does that seem right?

I'm not sure about these boost guages, but hers never goes over 3lbs of boost. So neither the rpm or boost gets anywhere near the red on the guages-is this also normal?

I was reading about changing the rod length to alter shift patterns, but it sounds like a non plausible solution for me.

I appreciate any feedback.

[woldson]

Can she drive a stick?

 

You should be at full boost by that rpm, I believe.

[madkaw]

So full boost would be what? I am not familiar with these l28et and I don't think the manual tells you anywhere what your boost guage should be reading under full throttle and max rpm. That's why I am looking for input from other l28et drivers as far as what their stock 280zxt operates. This info would also help me determine whether the engine is performing correctly. The car seems to accelerate well, but the boost guage never exceeds 3. I have nothing to compare to but from what I read on this site and I don't know anyone that owns a 280zxt to ask.

[Challenger]

My 81 turbo would usually shift at just past 5000 during full throttle runs. As for the boost guage, could be broken or have bad connections or you might not be building that much boost.

 

Can you get past 3psi at part throttle going say 35-40 mph? Boost isnt always proportionate to RPM.

[roger.svoboda]

read the gage first that isn't 3 psi the gage is calibrated in mm of Hg. the gage says x100 on the face. So you are getting 300 mm of Hg boost which is about 5.5 psi not too bad for stock set up. check out the conversion factors on line.

there are two things that work the shift point on the auto. There is a kickdown solenoid that triggers under full throttle. there is a vacuum modulator that has a hose running off the back of the engine down under to the tranny. There must be some sort of adjustment on that as the rod seems adjustable that goes into the tranny. I didn't want to play with it so I stuck in a 5 speed. Supposedly Nissan got the best numbers with the auto as the engine could stay at full boost right on up to the end of the power band. but me old fashioned like to diddle the stick. very easy to install boost controller on those guys. Cheap way is to put a tee in the line to the waste gate actuator and bleed off some pressure. I just put a brass slug in the hose I stubbed out of the tee and started drilling a hole larger and larger. When I got to a #35 drill I believe it was then I was getting around 10 psi boost with the hammer down. A kit with manual boost controller using a pressure relief valve to pop the waste gate is on line. Pull out the safety valve or whatever they call the thing that relieves excess boost pressure and replace it with a 1" pipe plug. Most folks say stay with 10 psi max boost unless you do some more things.

[RUZN]

I have a Auto Turbo 1981.5 Currently. On stock I was running 6hg to 7hg Sooo... But I also replaced all the rubber hosing within the 1st week I bought it.

 

Then I switched ECU's to the 1987 300zxt ECU and changed to 1994 240sx throttle body 1990 Maxima TPS and upgraded to the collant cooled and oil cooled turbo from the 300zxt. But the turbos where the same exactly other than extra cooling. Now I bleed off into the intake using a Tconnector that runs to a Air valve that I slightly open and run that to the intake. So I can acheive 12psi but I run at about 9.5 to 10psi with no intercooler and barely get over 80oC.

 

And I run her good.

that auto took upwards of 13psi without any issues and yes my shifting to was at 4750 until I switched to the 300zxt ECU which for some reason shifted more in the 5200rpm range on WOT. I would think cause its an auto transmission it uses trans pressure to determine shift points.

[madkaw]

This is the info I was needing guys , thanks for your inputs. Like I said I don't know much about the zxt's , so I need to be schooled. Ruzn, what hoses were you refering too specifically?

Roger-thanks for the correction on the guage, now that you mention it I now remember that it was not lbs. I also read about the rod adjustment, but it sounds more like a rod replacement.

I now how bigger problems now though, since the car died on my daughter yesterday on the highway. She said it was cruising nicely, but in traffic it died. She also said it made a whistling niose at around 70 and it growled when idling-so it sounds like it might be giving me it's first problems.

[roger.svoboda]

when my son did that he said it sounded like a weed whacker. Turbo sheared the bucket wheel shaft. luck on that one.