Difference between 87 and 88 924S/944 Engine?
07-15-2008, 04:11 PM
#3
Race Director
All 87 8 valve NA motors had 9.5:1 compression ratio with a "large dish" in the piston tops. (No 87 motor has 10.2:1 pistons. That is an error perpetuated in a FAQ file for the past 10-15 years).
In 88
All markets all around the world had 10.2:1 compression ratio with "small dish" in the piston top for 8valve NA cars.
The DME was also changed to take advantage of the increased compression. Actual hp gains can be tough to pin down. But my best info is the following
82-87 USA spec Rated 110 kW and 147hp (SAE rating rating varies form 143 to 147)
88 All markets Rated 118 kW and 158hp (Din rated at 160 hp) So gain was 8 kilowatts or 9 hp
Of note the Euro 944 had flat top pistons and 10.6:1 compression. They were rated at 120 kW and 160 to 163hp(SAE to DIN rating)
Rating Standard Note when comparing power levels in HP there are different ratings. Euro cars used the DIN rating standard which produces about 3 more hp than the SAE net rating standard. However it seem like the SAE rating changed at some pint since early US 944 are 143hp SAE net and later (before 88) cars are 147 hp SAE net. Even so they are all rated a 110 kW by Porsche. Looking the hp ratings for the entire 944 line it appears that kW are the native unit used to generate power ratings. Then these numbers were converted to DIN or SAE net depending on the market. As such I prerfer to compare power by using kW and then using a standard unit convesion to hp as it makes the numbers more compareable.
07-15-2008, 05:08 PM
#5
Race Director
Infact pistons along and 88 chip will work (you may need 88 program on the 87 chip for socket issues). A number of 944 spec guys stick 88 pistons in 87 and earlier blocks with good sucess. Some even run stock early computers, but they maybe giving up hp. Other guys run 9.5:1 pistons with shaved heads to get to about 10:1. Interestingly on the track there is no clear edge for a car with 88 pistons, shaved head or even stock 9.5:1 unshaved heads. All seem about the same and dyno numbers are more dependant on the particular car.
Since 88 pistons have been allowed in 944 spes from day one we have been closely watching for any real performance gain from the 88 pistons. After 6 years of this we have yet to see one even if on paper is the thing to have.
BTW... I currently run a 9.5:1 motor that uses an 84 block and 87 head. This what I was able to put together with spares after I had rod bearing blow up my bock back in 2002. This motor has run strong for 5+ years. At one point I got my hands on an 88 924S parts car and put that 10.2:1 motor in my race car. Net result was no change in on track performance (I even used both 87 chipped which was legal back then or 88 DME) and swapped the old one back in when I had issue with that 88 motor. I have been on that 84/87 motor for years now. I did build up the 88 motor as spare, but it has been sitting in my build stand 90% complete for 2 years or so. Why? I never felt the need to swap out my existing motor as I did not feel there was anything to gain.
Now however I may swap the motor just beacuse I am thinking after 5 years and some 60+ races it may be getting abit old and tired.
04-27-2010, 11:40 PM
#6
Rennlist Member
Sorry to drag up an old thread, but I may be swapping an '88 motor into my '87 924S, and I just wanted to double check on whether or not I could get away with running the 87 DME. I think eventually, it would be optimal to get a proper '88 chip in there, but for now, would the OEM '87 fuel and ignition map work (ie not grenade the engine)?
04-28-2010, 10:57 AM
#7
Race Director
You can run a 87 DME with no issues. I have swapped back and forth between my 88 DME and 87 DME and other than a higher idle with the 87 DME (150 rpm) the 88 motor I have or runs the same the best I can tell.
