Mongo

The question is derived from John Pirtle's site and specs of the A28 auto.

https://members.rennlist.com/pirtle/s4atrans.htm

Researching this in the archives, I couldn't find any clear confirmation if swapping in a Euro converter into a US S4 auto is compatible. I did find one for S2 cars only.

Euro cars had the following stall speeds based on transmission codes and its torque converter installed
:
A 28.05/06/08/09/11 =

2200…2600 1/min

US cars appeared to have received the short end of the stick (1987 A28 code and what's in my car):

A 28.12 =

1750…2150 1/min


If I were to get my hands on euro converter, would the TC swap be direct and interchangeable with no additional modifications? Assuming all torque tubes for S4 cars US and ROW have the same spline counts and shaft diameters.

Imo000

Find out if the flex plate, the converter sea and the pump are the same.

danglerb

The Euro motor may get a LOT more benefit out of the higher stall speed than a USA motor.

928FIXER

The issue between the stall speeds is the final drive ratio of the vehicle and the RPM that the engines runs when cruising down the highway.You would not want a 2600 RPM stall converter if the engine speed is below that RPM when cruising down the road.If the stall is higher then cruise PRM,the converter does not "lock up",and no I'm not talking about a converter with a clutch in it.The term lock up is/was used to describe the speed at which the converter has minimal slippage.If the lock up is not met,the converter is always slipping and generating massive amounts of heat.
That said,I have a hi stall euro converter in my 79 that I converted to 4 speed from the 3 sp trans years ago.I also have a 2.92 ring and pinion in that final drive unit,so cruise RPM is above the 2400 or so actual RPM that the converter stall at.The 4 sp trans and 2.92 made a good combo as far as I was concerned.Rip snorting tire shredding torque on take off with the same cruise RPM that the engine was designed for.
My 86 with the 4sp auto has a 2.22 ring and pinion and the cruise RPM is in the 15 to 1700 RPM range,which I have always felt made the 32 valve car seem very sluggish as it is way off the cams.

Mongo

I am aware of the ups and downs of stall speeds with a Camaro SS in the family with a 2800 stall. Now that is slippage. We're it not for the 4.10 rear that is..

But a 600 RPM difference is not that significant for a 928.

GregBBRD

​​​​​​

No. Not a direct swap, but not difficult.

'87 and later torque converters are larger in diameter and thicker than the pre '87 units. The entire bell housing on the transmission is considerably larger to accomodate these converters.

The "early" torque converters have the same oil pump drive design, splines, diameters as the larger "late" converters, so there is no problem installing it into the later transmission. The smaller diameter isn't an issue....just more room inside the bell housing.

The problem is the thickness. The early convertor will not bolt onto the flexplate and still be adequately engaged into the oil pump.

You will need to build some spacers to sit between the converter and the flexplate, and obtain some longer grade 12.9 bolts to be able to accomplish this.

All that being said, as mentioned above, you will want to carefully consider engine rpms versus gear ratios to make sure you are not allowing the converter to slip at normal cruising speeds. You might find that this change will cook the fluid very quickly, raise the engine water temperature, etc.

The other variable, which is a bit unpredictable, is torque. The amount of slip in a "fan style" converter (which all 928 converters are) is determined by the amount of torque. The more torque you have, the more slip. And the low end torque of an S4 engine is completely different than a "aggressive camshaft low cylinder filling efficiency at lower rpms" Euro 2 valve engine.

For example, a big high torque stroker engine will raise the lock-up of a Euro converter well above 4,000 rpms....completely useless.

GermanMotorwerks

I just built a 1984 928S That I drag race. I can not get my 60 foot times below 2.0 seconds. Where can I find a 2.92 Final drive and stall converter? my number is 971-333-0969

mj1pate

Got excited… I thought Greg was back on the forum.
I have a ‘88 auto in my 86.5. The original trans 4’th “gear” was frustratingly lethargic on acceleration at any speeds below interstate speeds. The ‘88 trans even more so in that application . HOWEVER, 3 “gear” works quite well up to interstate speeds. I watch engine temp a great deal and the biggest factor for how hard I push acceleration is how long it takes to get to operating temp, which takes a while. Even then, operating temp is a shade below the first hash mark, unless it’s a hot day with AC on.