924Board.org

JohnRichard · Joined: 10 May 2009 Posts: 5 Location: London, KY

Greetings!

I just bought a 924s from a friend of mine. I have been reading all I can about it, and the differences from the other Porsche's I am a little more familiar with.

While I am waiting on a new fuel pump to get here, I decided to go ahead and see what kind of engine mods I can get out of the way, since its torn down any way.

I would like to stay n/a with this car, and wanted to know how much abuse the bottom end will take. I would like to up the redline, and upgrade the top end, but if the bottom isn't up to the task, then there is no point. I am going to get a mild street/weekend track cam.

Any thoughts? Sorry if this doens't make any sense... I'm really tired.
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'87 942S -

gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

There is very little you can do inexpensively to gain HP from the 2.5L engine.

However, you could switch to higher compression pistons from a 88 924S or 944 (.5 point) or a 944S (1 point higher). This will mean that you would probably need to modify or update the ECU to prevent detonation.

You could also have have the crank drilled to oil the rod bearings, as these engine have a tendency to starve the #2 rod bearing, and destroy them.

Another way to go would be to replace the 2.5L engine with a 2.7 from a 89 944, or a 3.0L engine.

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

Or an LS1. Renegade Hybrids has a very highly developed kit that costs under $3k, and the all-alumninum LS1 motors can be had used from around $1500.

Or, you could blow $15k to get similar power from a 2.5. Just make sure your Triple A is up to date!
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

JohnRichard · Joined: 10 May 2009 Posts: 5 Location: London, KY

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

Higher compression pistons tops are already cut.

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

John Brown · Joined: 07 Nov 2002 Posts: 903 Location: Leesburg VA

The fellows have covered all the directions. Choose according to your personal philosophy. Some thoughts.

You mentioned a cam. The stock cam timing is very conservative and so a new cam is a good place to improve over stock.

The 'high compression' pistons from late 2.5L if sourced at a reasonable price are a good idea assuming as you say the motor is torn down anyway. I wouldn't pull it apart just for these pistons. Lately though it seems I see these things at silly prices. Keep in mind that replacing pistons should probably - though not absolutely - require new rings and honing the bores. Once you spend all that it makes no sense (to me) to pay $500 for a set of used pistons (plus rings) when a complete 'custom' piston with rings is about $1100. At, say, $200 or less it seems attractive (to me).

Upping the rpm of course is a time-honored hot rod move. Keep in mind this is an inline 4 which even with balance shafts still vibrates. Which is why both the 2.7 and especially 3.0 motors had more problems than the 2.5. The 3.0 especially had internal failures notably with oil pickups even driven only and sedately on the street. What with the work involved I am not a fan of converting from a 2.5 to either 2.7 or 3.0. Heck, if you are going to go that route why not just do the LS1!!!

Drilling the number 2 rod journal can't hurt. I recommend only drilling the #2. That's the one that needs the oil the most. You can do it yourself but will need a VERY good drill. The elves did a VERY good job hardening the journals. The crank will require balancing. The Porsche cranks are nicely balanced as is but the drilling is enough to ruin that.

It is just barely possible to install slightly larger valves. But you run right out to the edge of the valve seat inserts and smack into shrouding from the cylinder walls. The cam is a better place to spend money. BTW, the oem valves and valve seats are high quality. With any luck no matter how much mileage you can spiffy up whatever is in it now.
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John
80 931 - #931 44Cup
99 Escalade - tows track cars
gone but not forgotten: original 924.org car - 82

ic932 · Joined: 11 Feb 2005 Posts: 1104 Location: UK

JohnRichard · Joined: 10 May 2009 Posts: 5 Location: London, KY

After much reading, I am seriously thinking about going the Turbo + Megasquirt route. I already am planning to do the MS system, and I can scrap the ITB setup for a nice large single throttle body and a good sized small turbo (say 10 - 12 psi boost?).

I'm still going to get the cam!
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'87 942S -