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questions about 944 engine

hi everyone i have a 1987 porsche 944 sohc 2.5 L. the tensioner broke thus leading the timing belt to jump off and i mess up some valves. i am planning on just changing the whole engine out. i found a guy selling an engine from a 1983 944. i was wondering if it would be a direct swap? i looked at the specs it seems that the older engine has about 10 less HP and is a little bit heavier compared to the 1987. it looks exactly the same why is it heavier and have less hp? i got the information from here Pelican Parts: Porsche 944 Model Specifications just wondering if someone can point something out before a buy and install this engine thanks,
Old 12-19-2010, 10:12 PM
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The older engine will not have the automatic tensioner. There are some subtle differences for sure, the electronics are slightly different and iirc they are not plug and play. I would try to find an '87 or newer motor.


Why not fix yours though? Pop the head off and make sure it doesn't need pistons, some new valves, a little head work, and you are good. Much easier than swapping a motor.
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Old 12-19-2010, 10:28 PM
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1) There was a change in compression ratio as well as DME tuning. The later engines have a different computer running the EFI system and they have higher compression as well. That's why they have more power. If you used the engine from a 1983 car, you would also have to swap out the DME in your current car as well as the engine wiring harness.

2) While internal mechanical changes between the two engines undoubtedly mean there's some small weight difference, the weights listed in the chart you link are for the entire car, not just the engine. There were subtle changes to the body and interior for the 1987 cars and that's probably what accounts for the difference in total vehicle weight.

3) For the love of God, just take the car to a mechanic and have someone who's qualified do the work. If you didn't understand that the different compression ratios in that chart explained the 8 hp difference and if you honestly believed that the engine alone could weigh 2,637 pounds, you do NOT have the necessary mechanical knowledge to swap the engine on your own. This is not a simple "starter project" that you can just jump into and hope for the best.
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Old 12-19-2010, 10:28 PM
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Usually swapping a good used head with straight valves is all you need to do to fix your problem, but the 83 motor should drop in without any problems. People are parting cars out in the pelican classifieds all the time. Unless your current motor is known to be wasted, it's better to just fix it rather than buy someone else's potential problems, as well as all the little minor details getting an early block hooked up to a late car.

Not sure about the power differences. I have seen some sources say the higher compression motors were introduced in 87, but most everything else says they were in 88 only. All of the motors before 88 had the same 9.5:1 compression ratio piston design in the US and had generally the same specs, but I have seen minor differences in reported power for various models and years. The 10 hp was from the 10.2:1 pistons used in 88 (again, I saw one list saying they were made in 87, too). The only other significant difference is the change to a slightly more aggressive camshaft profile in 85 (IIRC). The cams are all interchangeable between 8v motors and a late cam can be installed on an early motor for a slight boost. The steel tube exhaust headers in 87-88 were supposed to flow better than the standard cast headers, but the early versions (of the steel) were very prone to cracking. The updated design added an expansion section in the 1-4 header section. The Y-pipe connecting the headers changed slightly between early and late, with the secondary tubes being about 2 inches longer on the late part (maybe better tuning for the late cam profile). I have also seen pictures of a different intake port design with little "tabs" sticking out into the fuel injector path, but they must have been only a limited run, as most 8v heads have smooth ports. I don't know what kind of power gain there was from going to the smooth ports. Just for information does anyone know of the tabbed intake port heads I saw and what year(s) they were from? All of these little differences may account for the various specs of 145, 147, 153, 155 hp at either 5500 or 5800 rpm that I have seen. The 88 motor is 163-165hp at 5800 rpm. The nice plus to the 83 motor is they used sinter forged rods.
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Old 12-19-2010, 10:48 PM
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hey thanks guys for the input! aaron yea thanks for pointing stuff out to me on the chart i was starring at the 1985+ section on the compression, 1987 didnt see it till now. i know the engine doesnt weigh that much didnt click in my head and just looked at the numbers and didnt think twice haha. so i guess plans right now is the pull the head off and check it out. after replacing the timing belt and tensioner, starting it up you can hear the air flying through the valves. so i believe everything else should be ok besides the head. when the timing belt ripped i was in the parking lot and was just about ready to leave.

are all the 8v heads interchangeable?
Old 12-19-2010, 11:24 PM
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The '89 2.7l will not interchange with the 2.5l head. My understanding is that all other 8v are interchangeable.
Old 12-19-2010, 11:29 PM
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Quote:
Originally Posted by porsche4life View Post
I would try to find an '87 or newer motor.
for the record, mechanically, all 2.5L 8v 944 NA motors are identical. yes there are minor changes here and there but nothing you will ever notice.

electronically, the dme and afm are different but they are plug and play so long as they are plugged in as a pair (late DME/AFM need to be together, cannot use late DME/early AFM or vice versa). there is a different idle valve between early and late models but they operate basically the same and the dme doesnt care.
Old 12-24-2010, 10:16 PM
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Spencer is right. As long as the DME and AFM match there are quite simply no issues to contend with in the swap. IIRC early car owners swap out their AFMs and DMEs to get rid of the idle stumble inherent to all early 944 models.
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Old 12-25-2010, 07:29 AM
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Quote:
Originally Posted by v2rocket_aka944 View Post
for the record, mechanically, all 2.5L 8v 944 NA motors are identical.
As long as you don't consider the pistons to be a part of the engine, you're essentially correct. Personally I'd consider the later, higher-compression pistons to be noticeably different. The 10 HP peak difference isn't much, but the overall torque curve feels a little more solid on the later engines.

As for being "plug and play" if the DME and AFM match, again I disagree.

Yes, the car will run as long as the DME and AFM match, but it will not run properly unless you're using the right DME for the engine. Pre-85.5 cars use ML 1.1 or ML 1.2, while post 1985.5 cars use ML 3.1. While the AFM is indeed the primary difference between the two, the pinout does differ for the harness connection, specifically with respect to the altitude compensation signal.

There's a bloody big difference between just getting it to run and getting it to run right. If you want to do things the right way, you will mate an 85.5+ engine to an 85.5+ ML 3.1 DME and you will mate a pre-85.5 engine to a pre 85.5 ML 1.1 or 1.2 DME. Taking shortcuts by frankensteining things and using two different systems is fine if you need to limp to a mechanic's in an emergency, but it's just not the way to do things long-term.
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Old 12-25-2010, 10:03 PM
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I would say it is best to use the DME version and engine controls that the car came with, unless you want to (or have to) swap the entire wiring harness around. The 87 and earlier 8v shortblocks/top ends are all the same and can fully fit up to early or late external components such as vacuum lines, intake/exhaust manifolds, belts/hoses, sensors, etc. The '88 blocks are all the same as all of the earier motors except for the pistons. You'd just have to swap a few external things around from the motor that was in your car or one from the same series to fit a motor from a different series. The DME versions are a little different in their internal construction and operation, but they both do the same thing basicly the same way. THe only difference that makes matching DME to engine important is the '88 motor with the higher compression pistons which used a different tuning. A late DME can be converted with a chip from an '88, but an early DME probably won't work well with the '88 pistons and cannot be updated with a chip.

So short blocks can swap around pretty much any way early or late. The DME, vacuum lines, engine controls/sensors, and wiring harness, while being mostly the same parts, differ between the early and the late enough that it's much easier to leave them in place and just swap the short block. My current motor was out of an 86 944 but the block and internal parts were cast in 84 by the date stamps, and it fit up to my 87 924S with no issues.
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Old 12-26-2010, 12:24 PM
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Quote:
Originally Posted by AaronM View Post
As long as you don't consider the pistons to be a part of the engine, you're essentially correct. Personally I'd consider the later, higher-compression pistons to be noticeably different. The 10 HP peak difference isn't much, but the overall torque curve feels a little more solid on the later engines.
North America-spec 944's from 83-87 all had the exact same power output. In 1988 the compression was raised but I don't think it was even 10 hp. In 1989 with the 2.7L the HP was about 160 but torque was substantially improved, if that is the motor you're talking about.

Quote:
=AaronM]
Yes, the car will run as long as the DME and AFM match, but it will not run properly unless you're using the right DME for the engine. Pre-85.5 cars use ML 1.1 or ML 1.2, while post 1985.5 cars use ML 3.1. While the AFM is indeed the primary difference between the two, the pinout does differ for the harness connection, specifically with respect to the altitude compensation signal.
Didn't know about the altitude signal difference. Good to know.
Old 12-26-2010, 09:50 PM
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easier to repair what you have and cheaper and less headaches. just remove cyl. head and replace exhaust valves(usually the only ones that get bent) check intakes to be sure and reassemble. i have a good used 85.5 cyl. head. regards tom
Old 12-27-2010, 09:56 AM
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I have an 83 motor in my 87. Direct bolt in EXCEPT.

1. There are changes to the power steering pump mounting brackets spacers.

2. The temp sensor for the gauge is different DME temp sensor is the same.

3. I think there was a difference with the speed and ref sensor mounts as well but either will work with either motor. (I am not 100% on this one)

The good? The 83 motor has forged rods.

When I was racing years back we actually prefer the 83 short block. We then used an 89 head and cam. Skim the head and you have your compression back very close to the post 85.5 motors. Some minor work to the intake and exhaust ports was the final piece of the build.

The whole DME AFM thing is only if you are swapping the electrics around. You can not mix and match early and late with each other. IF you are doing a strait motor swap dont worry about it just use what came with the car with want ever 8V 2.5l motor you plug in.

BUT as others have said fixing your motor is a much better option unless there is fatal damage to pistons or the cylinder walls. does not usually happen unless you broke or dropped a valve.
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Old 12-27-2010, 03:45 PM
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Fix the motor you have. PU a decent head and do the belts and be done with it.
Replacing it with a motor that is unknown and thus susceptable to the same issue is not a great idea.
That said if you did decide to swap it I have a few comments. The later the motor the better, period. There are lots of little changes and improvements in the motors every year. The very early motors have different crank oil passages, a less aggressive cam, and less oil pan baffling. Yes they have forged rods which is nice, but at 100k miles they need rehabed too. The automatic tensioner comes into play in late '87 and is a plus. The early motors have different wiring harnesses as well as a different AFM and DME. You can swap these all out if with the motor. The only issue to watch is the '88 not only has higher compression pistons, but it has some different tuning in the DME.

Good luck. Unfortunatly you are about to put as much into the car as it is worth.
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Old 12-27-2010, 06:26 PM
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