924Board.org

[safe]

Ah, distributor...

You must have some shed-business in the UK who can fix/modify distributors to a desired curve? I Sweden I think everyone that messed with those things have expired....
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/Magnus, Stockholm Sweden
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Porsche 924 -79 NA, EFI and Turbo.
Porsche 931 -79
Porsche 911 -77, 3.2 Targa
Porsche 911 -69, 3.6, Coupe

[924RACR]

I have a little more complexity to my maps down low; using ignition timing alone for idle control, like original, works great except for AC switching on... and driveability is excellent... Note that I am running an IC as well as 93 (US) octane - I think this is about like 99 octane in the UK, maybe a touch higher...


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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Raize]

I think my fuel quality played a part, apparently it loses octane with storage as well, so mixing 6-month old 99 with an equal proportion of 97 probably results in 97. I certainly don’t remember it knocking audibly except if really abused before putting it away for the winter.

I remember seeing 13.X on the AFR before I backed off. It’s running leaner than it did before winter when I was getting 11.X on boost. Possibly to do with getting rid of the in-tank pump or perhaps just the needle valve that controls the overall AFR is getting gummed up over time.

The control with distributor and k-jet is tricky, but at least I have tools like the knock sensor and the AFR gauge to help. So 31 BTDC without knock is possible at 0.2 bar but with 99+ octane and an EFI-perfect fuel map.

[Raize]

I think my fuel quality played a part, apparently it loses octane with storage as well, so mixing 6-month old 99 with an equal proportion of 97 probably results in 97. I certainly don’t remember it knocking audibly except if really abused before putting it away for the winter.

I remember seeing 13.X on the AFR before I backed off. It’s running leaner than it did before winter when I was getting 11.X on boost. Possibly to do with getting rid of the in-tank pump or perhaps just the needle valve that controls the overall AFR is getting gummed up over time.

The control with distributor and k-jet is tricky, but at least I have tools like the knock sensor and the AFR gauge to help. So 31 BTDC without knock is possible at 0.2 bar but with 99+ octane and an EFI-perfect fuel map.

[Cedric]

13s are lean for a boosted car for sure, thats need to be sorted.

My kjet have sat every winter for 6-7months and does pretty much the same AFR year in and year out
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1980 924 Turbo
www.instagram.com/garagecedric/

[Raize]

[morghen]

In my extreme tests for my SC kit while still on kjet, i ran 0.3bar, 6deg BTDC base advance, in 36 deg C ambient temp, AFR as lean as 13.5 on high revs, on 99+ OCT and i didnt detect any knock or see any effects once the engine was opened.

If you got knock at less boost and richer AFR, you either have too much advance or you're heating up the air way more, which can be poor flow, bad charger and so on.

Do you have pictures of your setup?
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Supercharger and EFI kits
https://www.the924.com

[Raize]

Seems that it was a fuel problem in the end. I adjusted the lower chamber pressure again and now I am getting 11-12 on boost and 14 on cruise. No more red flashing knocklink.

The lock nut on the adjuster was a bit loose so it may have backed off from vibrations.

Once again, wideband O2 sensor is the best thing I have ever bought for this car.

[Cedric]

[Raize]

Would it be terrible to run fixed timing (for a given RPM, will still have centrifugal advance obviously) for all levels of boost from 0 PSI up to 13 PSI? This would mean running the retarded timing necessary for it to not detonate at 13 PSI probably turning the distributor back another 10 degrees.

I would also file out the stop on the vacuum canister to allow it to advance 20-25 degrees rather than the 11-12 it currently does. This would give me all my original cruise timing back for economy by -6 PSI vacuum (it advances about 4 degrees per PSI of vacuum as I measured it)...

Thoughts on how much this leaves on the table vs doing it properly with advance being proportionate to boost?

[Raize]

Still knocking, clearly didn’t thrash it hard enough. Biiiig difference between doing some random single gear pulls and properly trying to race someone.

Pulled another 3 degrees. Also my car is still slow as shit, BMW 340i dropped me like I am not even moving. #### pay-to-win modern cars.

[Cedric]

[safe]

[Cedric]

[Raize]

In retrospect I should have gone turbo. There’s nothing wrong now except that it’s still slow. I have headroom to put a 50% bigger crank pulley on but after that I’m basically done.

On paper I thought it would be fast enough but in reality I don’t think so.