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  • October 22, 2020, 02:02:53 AM

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Author Topic: EA831 in AMC Eagle SX4  (Read 672 times)

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Offline jebidia24

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EA831 in AMC Eagle SX4
« on: February 10, 2020, 11:10:40 AM »
So I'm looking at installing my spare EA831 from a 79 Spirit into my 81 SX4.  First a history lesson........For those that do not know, the EA831 or AMC 121 is a engine designed by NSU prior to their merger with Audi.  Upon VW's acquisition of Audi, the engine entered VW's engine stable.  VW didn't have any need for another 8v SOHC 4 cylinder engine as they had recently developed the EA827 engine.  Since VW already had the engine designs and machining complete they decided to sell the engine to other brands looking for SOHC 4 cylinder water cooled engines.  The first buyer was Porsche (who was co-developing a car with VW until they, VW, got cold feet) for their new 924.  This version had different pistons raising the compression ratio and fuel injection bringing its Europe output to 125hp and 122 ft/lbs for torque.  Not terrible for a 1977 engine only weighing 262 lbs.  The US version of the 924 EA831 had lower performance numbers due a lower compression ratio and smog emission controls.  In the US, AMC was looking for a fuel efficient engine which they could use in their car after the wankel pacer debacle.  AMC came across VW selling the EA831 and struck a deal with them.  AMC would buy the cast and machined components from VW and assemble them in their Indiana engine assembly plant they had recently purchased.  AMC didn't have much experience with (at the time) advance overhead cam engines but gave it their best? shot.  They lowered the compression ratio to 8.3:1 to give it better fuel economy but were not familiar with fuel injection as it was still quite cutting edge in the late 1970s.  It was VW's plan to have AMC build the engines for them and cease their European production so they didn't have to build them anymore and they could sell them to anyone who wanted them.  So AMC slapped on a single barrel carburetor and put steel plugs into the fuel injection ports cast into the head.  This new engine did get good fuel economy, especially for AMC (and any US auto maker) in the 1970s but sacrificed performance.  The AMC design only yielded 80 hp and 105 ft/lbs of torque.  This new engine also came mated to either a "new" Borg Warner HR1 (a rehashed Type 9 european gearbox) or a Chrysler Torqueflite 903 built for fuel economy.   Now, since VW didn't exactly give the design away (even though they had no interest in using it themselves) and the costly requirement of making it fit and work with AMC's antiquated design, the car was quite expensive.  In 1979 for example, if you went to an AMC dealership, the two highest price Spirits available were the 304 powered AMX and the 121 Spirit Limited.  It's safe to say that not many were sold.  The plan worked so poorly that AMC only had the 121 available in 1977, 78, and 79.  A large portion of the failure was due to Americans not being familiar with OHC designs and characteristics.  Another being it's painfully low performance.  These engines required high revving, high compression, and efficient fuel/air intake to be effective.  None of which AMC assembled them to do or advertised them as being optimal.  Porsche, on the other had, later built a turbo version with a revised compression ratio of 8.2:1 and an increased power of 174 hp and 180 ft/lbs of torque.  They later further increased it for their 924 Carrera GT to 216 hp and 220 ft/lbs of torque which is the factory pinacle for the EA831 in a production engine.  Porsche built both an IMSA/Touring and Group B rally versions of this engine which made power up to 277hp.  AMC discontinued the 121 due to low sales and high costs.  They replaced this engine with the infamous Iron Duke in which the design and characteristics were more aligned with American understanding and perception.  I have/do own both an Iron Duke and an EA831 and the 831 is a far superior engine.  The SD4 Iron Duke is a different story (I have one of those also but its for a different project).  Whew! That was long winded.   

Offline jebidia24

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Re: EA831 in AMC Eagle SX4
« Reply #1 on: February 10, 2020, 11:36:44 AM »
Ok, now on to the why and purpose.  I have a 81 SX4 which originally came with a 2.5 liter iron duke.  This duke (I highly suspect) was not original to this car as many of the bolts used during installation did not match.  This Duke had some oiling issues caused by excessive wear in the head which initially cased oil to burn in the piston chambers creating carbon deposits which made the engine "diesel" when turned off.  I had to pop the clutch to make it stop running with the ignition off.  At the time I also had a 258 inline six wagon parts car.  I initially swapped the 258 including crossmember and accessories into my sx4 and changed the transmission to a Jeep T5.  I recently decided to go a different route with this project and am building it as a "what could have been car".  As many are aware, in the 1980s AMC rally raced Eagle SX4s in SCCA ProRally in the Production Class where they did quite well.  At the time SCCA rules and the FIA's new Group B rules were not that far apart.  The US has typically always had a "run which ya brung" attitude (at least back then) and the FIA's Group B rules were basically open for the manufacturer to build whatever they liked as long as they fit them into the proper weight classes and homologated 200 special models.  I am trying to build a concept of what it would likely been like if AMC decided to build a Group B homologation special out of an Eagle SX4.  Neither the Iron Duke or the 258 are known for being powerful engines and a turbocharged 258 would be too big for competition (due to already large displacement and forced induction multipliers).  In all reality, if AMC were building an Eagle homologation special, they would likely did the American thing and put in either a 304 or 360 V8.  This was later done in the US for SCCA rally and a surviving version was recently restored by forum member RallyEagle (which can be seen elsewhere on this forum, you should check it out if you have't already).  AMC also used and homologated the Spirit AMX 304 into FIA Group 1 in 1979 to compete in the 24 hours of Nurburgring (which they won their class).  I had caught word through the AMC community that if Team Highball (the Amos Johnson team sponsored by AMC), had the opportunity to go back in 1980, they were considering using a 121 they had been testing a race version of which was as fast as their 304 V8.   

Offline jebidia24

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Re: EA831 in AMC Eagle SX4
« Reply #2 on: February 10, 2020, 01:19:53 PM »
And finally, the plan.  The SX4 is not a light car (it is by today's standards) for the power outputs available in 1981.  The original Iron Duke engine which came in my eagle made 84 hp and 125 ft/lbs of torque and weighed 375 lbs.  The car with this engine was painfully slow but it would do 70-75 on the freeway without issues (besides the ones listed above).  The 258 was a large increase in power and torque and was the best Eagle engine available from the factory imo.  In 1981 the 258 made 112 hp and 210 ft/lbs of torque with a hefty weight of 531 lbs.  The 258 is a heavy engine.  It is only 10 lbs lighter than the 304.  The weight of the car with the Iron Duke was 3049 lbs and 3205 lbs with the 258.  The 258 makes good torque and has a large aftermarket but it is primarily focused with increasing torque for off roading.  I'm not saying this can't or wouldn't have been done with the 258 but the engines high weight negatively effects the handling characteristics.  The EA831 only weighs 262 lbs and once installed in the car should weigh in the ball park of 2936 lbs.  The plan is to add a individual throttle body fuel injection kit for a Porsche 924 modified (if necessary) to fit the AMC EA831.  I also plan to add an aftermarket performance turbo cam and 924 turbo exhaust manifold.  The pistons already make a boost friendly 8.3:1 compression ratio assuming no piston ring blow by.  I plan on using a relatively small turbo as I want boost to come on at as low of RPM as possible and I do not want to overboost my engine.  Depending on how well this works I may go for a larger turbo in the future.  I am going to stick with my 258 crossmember and I will have to build motor mounts to integrate them into the existing mounting location.  The motor mount location on the EA831 are pretty far back on the engine and I would like the bell housing location to be the same as it is on the 258 (it will also move the engine back giving the car a better weight distribution,  if all goes as planned it will almost be front/mid engined).  This should give the oil pan enough room to clear the front driveshaft. The motor mount will have to come out at a 30-45 degree angle to properly mate with the engine crossmember.  This may require moving the oil filter.  I am also going to have to build a mount for the front differential since the EA831 doesn't have a provision for the diff mount.  I am thinking that if there is enough space I can just weld a steel plate at 90 degrees to the crossmember to replace the mount on the engine.  The next area of concern in the bellhousing.  As stated before, I already have a Jeep T5 mounted to my NP119 transfer case and I want to keep those.  So I will likely have to contact lakewood/holley to make a bellhousing that will go from the EA831 (supposedly an Audi 5 cylinder bell pattern) to a Ford T5.  I am not sure if a stock EA831 AMC flywheel or Porsche 924 flywheel clutch combos will work with the T5 input shaft or if I will have to get a custom set built for that also.  Hopefully I can just use a Porsche 924 flywheel (as they are available lightened for sport applications) and fit my spare 8 inch centerforce clutch (which fits my T5).  I may have to get a custom flywheel also.  Either way, the first step is to get the car down on the ground (its currently up in the air while I finish the rear LSD installation and rear disk conversion) and pull the 258 out to begin test fitting the EA831.  I'll post pictures as I get things figured out.

Offline vangremlin

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Re: EA831 in AMC Eagle SX4
« Reply #3 on: February 10, 2020, 06:19:31 PM »
Good luck and thanks for the history and sharing your plan.

We had a 78 Gremlin with the AMC 121 engine and performance was NOT it's middle name lol.  We had some issues finding some of the parts like a hose that went from the intake manifold to the head at the rear, the flex plate, and maybe some others.  Maybe you'll have better luck finding some of those parts searching in the Porsche world.  We bought the car in 2008 after it had sat for 6 years and had been overrun with mice while it sat in a field.  We got it running again pretty easily but had to have the transmission rebuilt.  We sold the car about a year later and the new owner installed a 401 and painted it Panther Pink.  He donated the 121 to the Rambler Ranch.  I found a couple pictures of the engine at the Ranch and attached them.  Also attached a couple pictures with the valve cover off, we replaced the gasket to try and address the oil leak.  Amazing how clean the inside was. 
Here are a couple short videos of when we first got it running.

https://youtu.be/8KHFV-_4xSg

https://youtu.be/Y-lO6Hrfku4

Again, good luck, sounds like a cool project.

« Last Edit: February 10, 2020, 06:50:21 PM by vangremlin »
1981 Kammback 258 - "Pepe"
1980 Coupe 258 - "Ginger
1972 Gremlin X 304
1978 Gremlin 4 cyl 121 - sold
1964 TBird 390 - sold

Offline Taylor

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Re: EA831 in AMC Eagle SX4
« Reply #4 on: February 11, 2020, 06:44:05 PM »
Wow, very informative. Lots of info I never knew before.
Thanks for the post.
2010 Toyota Rav4 Daily Driver (better mileage)
1985 AMC Eagle Limited wagon 🖖🏼🦅
2005 Ford Excursion 4X4 wife's around town daily driver.

Offline RallyEagle

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Re: EA831 in AMC Eagle SX4
« Reply #5 on: February 11, 2020, 08:04:45 PM »
Great read Jebidia24.  Success with this endeavour.

Offline jebidia24

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Re: EA831 in AMC Eagle SX4
« Reply #6 on: February 20, 2020, 04:07:00 PM »
So I bought an Ebay flywheel for a Porsche 924 with bolts and it bolted right up to my engine.  Almost like it was made to......because it was.  I also found a Porsche 924 EA831 technical document that contains all the engine specifications and compared them against my AMC 121 manual. Beside the one manual being in metric and the other in standard (so conversions were required), all the parts specifications for the NA Porsche EA831 and AMC 121 are the same.  This leads me to believe what I already thought, which is that both engines use the same parts, for the most part.  When they say "the engines are assembled to different specifications" what they are referring to is the AMC 121 being carbureted and having different pistons (8.3:1 compression ratio for AMC 121 vs 8.5:1 for the 1979 US spec Porsche 924, its 9.3:1 for the Euro spec).  Now I understand that the Porsche 924 Turbo head is different, it's just different in the same way its different from the NA Porsche 924 head.  Thankfully this should really open up the tuning capabilities for anyone who has one of these engines still running. 

 

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