924Board.org

[xanderdeg]

So I bought an na engine out of a '77. Once i get it up on the stand I'll start pulling it apart.

I plan to FULLY tear down the engine and replace every single piece that needs replacing or looks like it will need replacing in the near future.

Now for the build:

I want more power, now before you tell me it can't be done please understand that I'm NOT looking to smoke my friend's mustangs and burn rubber. Just looking for a modest 10 - 30 hp increase.

I UNDERSTAND that it is hard to give these engines more power...
I UNDERSTAND that I may end up homeless after putting all my money into this build for a tiny 10hp increase.

Now, all that being said; I'm looking for suggestions for what can be done (no matter how outrageous) to this engine to give it more power, don't hold back because "it's just a theory" or "it won't work". I'm young and I'm looking for an adventure..

Who knows? Maybe in the end it will become a collaboration of all the board's ideas and be a pretty funky engine (whether or not it has more power or not) it would be cool to have an engine that's built off of the board's crazy ideas!

Don't waste time telling me I'm dreaming or naive; I already know that I am both of those

[Rasta Monsta]

The key to your happiness lies in larger displacement and higher compression.

Stroke it, you little canucker.
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Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3

[MikeJinCO]

I think the '77 is just too hard to work with. I got the Mad Electrician's later larger valve head. Have done preliminary flow tests on my homemade flow bench and it is going to the head shop today for a 3-4 angle valve job. The inlet ports at the throat are much better than the older small valve head(I did some porting on my '77 head also, also. I am going the route of a S2 931 block in hopefully good enough condition to give a high compression motor to go with Webers and a set of MSDS headers. I expect re-tuning Webers for altitude to be an absolute b***h.

On my homemade flow bench I tested the later head 3 ways, bare e manifold with no inlet horn, with a stock intake manifold and with the manifold and a stock throttle body. I only did the intake port. I'll make the exhaust match the Header and go from there.(Also most of the exhaust valvers were in bad shape, tow completely burned.

The flow went up considerably with the intake manifold over the bare head due to the better runner configuration and no intake turbulence. When I put the stock throttle body on it choked it way back. One thing I would look for is an AUDI throttle body if staying with stock injection. One of my other thoughts was to saw the intake manifold apart, smooth the castings to improve air flow as much as possible(we are not trying to mix gas up there) and weld it back together. These aluminum castings can be reworked with an electric drill and a simple $30 porting kit. I added a 4" lg steel rod with a slot in it for emery paper.
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Mike


'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)

[morghen]

Did you just misspell your "screen name"?

As others said and will say...stroke it if you can afford it...if not get it to higher CR, run an improved cam and exhaust. Fine tune the CIS and if you dont have the late type ignition, get it...or get a programable ignition.

My advice would be NOT to go with carbs.
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Supercharger and EFI kits
https://www.the924.com

[ideola]

The cheapest way to get more power on an NA is to use the complete long block that you have, but replace the NA slugs with S2 931 slugs. This will yield ~10.6:1 CR. The budget rebuild would be those components with a crankcase gasket set, head gasket set, fresh main and rod bearings, and a set of TotalSeal rings. You need to make sure you get the wrist pins with the 931 slugs because they are shorter than the NA wrist pins.

If at all possible, you should replace the early head with a late NA head. Head work is expensive. At minimum, you should lap in the valves and replace the valve stem seals (which come in the head gasket kit). The problem you may run into is worn valve stems / guides. You can get OEM equivalent replacements for fairly cheap (both valves and guides), but the machining work is usually not cheap. Part of the problem is finding a shop that has the correct bits to remove the 924 guides if they are worn.
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erstwhile owner of just about every 924 variant ever made

[WEASEL149]

If I was building an NA for power I wouldn't stroke it, I'd bore the hell out of the block to ~90mm and have some custom pistons made up along with a custom bi-metal head gasket.
This would give a nice rev-happy over-square engine with less frictional loss and probably ~2150cc.

I'd probably use a ported 931 head with the chambers modified to take advantage of the larger cylinders and de-shroud the valves as much as possible. Big valves would possibly work better in this configuration. Between the head and the pistons I'd aim for around 10.5-11.1CR.

Everything else would be lightened and balanced as much as possible for higher revs and a high lift, long duration cam fitted with solid lifters etc.

Full engine management along with possibly 2 stage injection at higher pressures and everything else should give a healthy power increase and a lofty rev limit.

Wouldn't be a cheap option but it's about time more NA's had some TLC and money spent on them.
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1979 UK 932

[Joes924Racer]

I ran a diy port job, reground cam, msds headered, msd ignited, rebuilt motor for a couple of yrs awhile back .... Stroke it with a efi kit and lighter flywheel ,head work or build a turbo motor .
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1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

[fiat22turbo]

20-30hp? Yeah, stroke it and up the compression along with some head work.

OR

artificially increase the compression ratio with a turbocharger/supercharger.

The stock CIS system can adjust to handle a decent amount of mods, provided it is in good shape. Invest in a decent programmable ignition system and some dyno time as that is where some power can be found.

The stock intake manifold isn't too bad, the plenum is a little small and the throttle body is a pretty big restriction, but the throttle body can be replaced with a larger one from an Audi or a VW with CIS.

The CIS fuel distributor can be a bit of a restriction itself, but the only way around this is to move to programmable EFI, which can be a challenging undertaking when you do it in combination with a bunch of changes to the engine. I would either add EFI to the existing stock motor and debug it while you work on the other engine, or wait until you get the new engine in and working well before you decide to change over.

Either way, budget some dyno time to get whatever solution you go with fine tuned and to work out any bugs.

If you go the turbo/supercharger route you may want to keep the static compression ratio at the lower end to avoid detonation and/or expensive/hard to find high-octane gas.
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Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)

[xanderdeg]

So far it seems like stroking it and boring it are popular options along with some intake work..

Would a port/polish be worth it?

[Fifty50Plus]

[xanderdeg]

Anybody think weber 40's would be worth it?

[ideola]

Webers are cool, but not cheap, and about the last thing you should consider doing.

Have you figured out a budget yet????
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erstwhile owner of just about every 924 variant ever made

[xanderdeg]

Budget is: I'll pay what I need to pay but I'd prefer to save some money...

Still haven't gotten it up on the stand yet so the rebuild hasn't started yet but I'll get there...

[xanderdeg]

Alright so that never happened...

Planning to start the build through the winter, I put off anything porsche all summer as some of you may have noticed.

I've educated myself a little more and I'm thinking I'll put in some high compression pistons, new cam, a newer head as ideola said (would a '78 head be better by any amount? If not just how much newer should I go?) or possibly a 931 head if I can get my hands on one. Headers,

[vatoisimo]