924 Engine Building
02-14-2003, 10:34 AM
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924 Engine Building
Hey guys. I picked up an extra engine for my '78 924 and I would like to build it up a bit. I was wondering if anybody had any tips that they might have done or if there was any printed material about building up a 924 motor. Has anybody tried to turbo charge the early 924 motors?
Thanks in advance for any assistance.
Keith
'78 924
'74 914 2.0
'75 914 3.0T in progress
Other non-Porsche
Thanks in advance for any assistance.
Keith
'78 924
'74 914 2.0
'75 914 3.0T in progress
Other non-Porsche
02-14-2003, 12:14 PM
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I've souped up the 924 NA to a level where I think I attained about as much as anyone could attain on say $5000 worth of investment. But other guys have gone hog wild.
A few problems exist with forced air induction on the 924 NA:
1. Cost - by the time you do all the work, for the performance you get, you're really better off with a 924 Turbo. Supercharging a 944 costs in the $5000 USD range, so for the 924 NA you're probably looking at that amount or more. The 924 NA version was turbocharged using a nearly bolt on system called the BAE turbo, a dealer option. It's also been supercharged using everything from a motorcycle supercharger to Eaton units by various people. You can snap on a BAE turbo system, if you can find one (they're rare), but the problem is, in my experience, they simply blow up the car (or the user blows up the car through improper installation and tuning). Either way, the BAE IS a time bomb: I've seen the same BAE unit get sold by a guy, installed, then bought back by the same guy after the car blows up. Twice, to two different buyers. They're really not the way to go.
The basic 924 block is the same as the block for a 924 turbo, roughly speaking. The difference is the piston shape, which you probably know is dished in the turbo, and nearly flat in the NA version.
2. Inappropriate platform - To run a proper turbo installation, let's say you get all the parts from a 924 Turbo and want to swap them onto the car. You're still screwed, cause even if you swap over the turbo, wastegate, exhaust, you're stuck with flat pistons giving 9.3:1 compression whereas the turbo motors had 7.5:1, 8.0:1 or 8.5:1 compression - you're facing wicked problems with detonation (i.e., boom) unless you swap out the pistons. So now you're into major motor rebuilding. This says nothing about what you might want to do to the fuel system or the brain box.
Conclusion: You're better off buying a 931.
Printed Material
I think a guy named Butera did up a supercharger on a 924 NA. You can look for that article. I'll give you the article names from home next time I log on from there.
What to do with a 1978?
1. The head is the bottleneck on the 924. Try a number of things to allow the air to flow more volume, like,
(a) Port and polish the head - You can do this yourself if you're careful and you read about it. It's probably the best performance mod you can do to that car. You can feel it in your ***.
(b) Clean up the head, recondition it - I did this and it was worth every penny.
(c) Use high RPM valve springs to raise your redline - I did this and it was great. Forget about larger valves, it's a pipe dream.
2. Exhaust - From the cat back, install a wider more free flowing exhaust.
3. You can swap on an Audi 5000S throttle body for more flow - I've done that and it kind of makes for a car with higher top end. It doesn't really help your car with low end grunt.
4. Lighten up - Remove your heavy stock fans with lightweight aftermarket fans, drop the spare, drop the tools (these three items maybe 25 lbs), drop the pads from the rear deck (12 lbs?), get light weight wheels (20 lbs), drop the backseat (12 lbs), lexan rear glass, fibreglass doors exist ($), as do fibreglass hoods.
Bigger bucks
5. You can take out the motor and lighten up the piston and rod assemblies, statically balance the rods and pistons, then dynamically balance the engine assembly. (5 hp max, but you're in a smoother running engine now). Freshen it up while you're there with new bearings and maybe rings.
6. Lighten your flywheel
(For items 1 through 6, you're now up to about $4K-$5K without new fiberglass or lexan, even if you do some of it yourself. And remember, once you've got the engine out, you're now finding need for new clamps, pipes, hoses, nuts, bolts, and it all adds up).
If it were me, I'd work backwards from the exhaust and see where that takes me. Then I'd work on fully restoring the car, rather than souping it up. I'd save the souping up for a time when I've got the cash and the rest of the car is perfectly running. Look for future problems with cooling, and electrics. Get them fixed before souping up the car.
Good luck
A few problems exist with forced air induction on the 924 NA:
1. Cost - by the time you do all the work, for the performance you get, you're really better off with a 924 Turbo. Supercharging a 944 costs in the $5000 USD range, so for the 924 NA you're probably looking at that amount or more. The 924 NA version was turbocharged using a nearly bolt on system called the BAE turbo, a dealer option. It's also been supercharged using everything from a motorcycle supercharger to Eaton units by various people. You can snap on a BAE turbo system, if you can find one (they're rare), but the problem is, in my experience, they simply blow up the car (or the user blows up the car through improper installation and tuning). Either way, the BAE IS a time bomb: I've seen the same BAE unit get sold by a guy, installed, then bought back by the same guy after the car blows up. Twice, to two different buyers. They're really not the way to go.
The basic 924 block is the same as the block for a 924 turbo, roughly speaking. The difference is the piston shape, which you probably know is dished in the turbo, and nearly flat in the NA version.
2. Inappropriate platform - To run a proper turbo installation, let's say you get all the parts from a 924 Turbo and want to swap them onto the car. You're still screwed, cause even if you swap over the turbo, wastegate, exhaust, you're stuck with flat pistons giving 9.3:1 compression whereas the turbo motors had 7.5:1, 8.0:1 or 8.5:1 compression - you're facing wicked problems with detonation (i.e., boom) unless you swap out the pistons. So now you're into major motor rebuilding. This says nothing about what you might want to do to the fuel system or the brain box.
Conclusion: You're better off buying a 931.
Printed Material
I think a guy named Butera did up a supercharger on a 924 NA. You can look for that article. I'll give you the article names from home next time I log on from there.
What to do with a 1978?
1. The head is the bottleneck on the 924. Try a number of things to allow the air to flow more volume, like,
(a) Port and polish the head - You can do this yourself if you're careful and you read about it. It's probably the best performance mod you can do to that car. You can feel it in your ***.
(b) Clean up the head, recondition it - I did this and it was worth every penny.
(c) Use high RPM valve springs to raise your redline - I did this and it was great. Forget about larger valves, it's a pipe dream.
2. Exhaust - From the cat back, install a wider more free flowing exhaust.
3. You can swap on an Audi 5000S throttle body for more flow - I've done that and it kind of makes for a car with higher top end. It doesn't really help your car with low end grunt.
4. Lighten up - Remove your heavy stock fans with lightweight aftermarket fans, drop the spare, drop the tools (these three items maybe 25 lbs), drop the pads from the rear deck (12 lbs?), get light weight wheels (20 lbs), drop the backseat (12 lbs), lexan rear glass, fibreglass doors exist ($), as do fibreglass hoods.
Bigger bucks
5. You can take out the motor and lighten up the piston and rod assemblies, statically balance the rods and pistons, then dynamically balance the engine assembly. (5 hp max, but you're in a smoother running engine now). Freshen it up while you're there with new bearings and maybe rings.
6. Lighten your flywheel
(For items 1 through 6, you're now up to about $4K-$5K without new fiberglass or lexan, even if you do some of it yourself. And remember, once you've got the engine out, you're now finding need for new clamps, pipes, hoses, nuts, bolts, and it all adds up).
If it were me, I'd work backwards from the exhaust and see where that takes me. Then I'd work on fully restoring the car, rather than souping it up. I'd save the souping up for a time when I've got the cash and the rest of the car is perfectly running. Look for future problems with cooling, and electrics. Get them fixed before souping up the car.
Good luck
02-14-2003, 04:33 PM
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Wow!!! Thanks for the info. Sounds like a bit of experience there. I appreciate your sharing it.
I am all for doing major engine rebuild. I have two motors now so I might as well make a monster out of one of them. Not adversed to making my own down pipes and adapter plates for turbo hook up either.
The reason I bought the second motor was due to a persistant problem I had with the original. I kept going through rear seals on it. I replaced it about 4 times and it would last for a while and then start leaking again. Have you heard of this at all?
I am all for doing major engine rebuild. I have two motors now so I might as well make a monster out of one of them. Not adversed to making my own down pipes and adapter plates for turbo hook up either.
The reason I bought the second motor was due to a persistant problem I had with the original. I kept going through rear seals on it. I replaced it about 4 times and it would last for a while and then start leaking again. Have you heard of this at all?
02-14-2003, 05:13 PM
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Yes. The rear seals on the 924 NA engines always are reported to leak. The best you can do to fix up the rear seals is follow the rebuild instructions given by Porsche 'precisely'.
If you really wanna monster, you can also consider bumping the compression on the NA or doing that and adding 45 Webers.
You said "Not adversed to making my own down pipes and adapter plates for turbo hook up either." If you decide to do a rebuild for the purposes of making a turbo, let me know. Though I don't advise it, I can sell you a set of unblemished MAHLE 7.5:1 compression pistons with 86.5 mm diameter from a previous rebuild I did on my 931. I also have a spare K26 turbo hanging around and some pipes.
You'll also probably need a 931 head...but wait, Do you hear that sound? That's the sound of money flying out of your wallet.
See also
<a href="http://www.geocities.com/eturbo924/Enhancements.html" target="_blank">http://www.geocities.com/eturbo924/Enhancements.html</a>
<a href="http://members.tripod.com/darrin_smith/porsche/924jobs.html" target="_blank">http://members.tripod.com/darrin_smith/porsche/924jobs.html</a>
If you really wanna monster, you can also consider bumping the compression on the NA or doing that and adding 45 Webers.
You said "Not adversed to making my own down pipes and adapter plates for turbo hook up either." If you decide to do a rebuild for the purposes of making a turbo, let me know. Though I don't advise it, I can sell you a set of unblemished MAHLE 7.5:1 compression pistons with 86.5 mm diameter from a previous rebuild I did on my 931. I also have a spare K26 turbo hanging around and some pipes.
You'll also probably need a 931 head...but wait, Do you hear that sound? That's the sound of money flying out of your wallet.
See also
<a href="http://www.geocities.com/eturbo924/Enhancements.html" target="_blank">http://www.geocities.com/eturbo924/Enhancements.html</a>
<a href="http://members.tripod.com/darrin_smith/porsche/924jobs.html" target="_blank">http://members.tripod.com/darrin_smith/porsche/924jobs.html</a>
