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I've just modded another. Here are some pics. The stop is the round post. The actuator arm is painted red for clarity. File so as to increase the gap between the round post and the actuator arm, at the location shown as bottom. The red actuator arm is L shaped near the round post, file the L where it contacts the post on moving out (up in the pic) from pressure on the diaphram.
 

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Does anyone hanve any dimensions as far as how much to file, grind, or bend? It would be great if someone was able to figure out what the equivelant measurement is per degree of retard or simething like that.

Jay
 

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I modded my diaphragm, but ran into a problem. I think i screwed up the refitting of the diaphragm. What I am encoutnering is intial timing being too retarded. The rpms creep up but the boost shoots ups very fast. It jump to 15 psi at 3000 rpms, but to get to 3000 is does take some time. Does the little hole in the arm on the diaphram supposed to catch something inside the distributor?
 

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This I think, is where you have gone wrong, the arm should be hooked over a little peg on the advance/retard inside the distributor. It can be a little fiddly to get back on & maybe easier to remove the distributor.
 

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And demands a bit of patience aswell... Took me ten minutes to fit the vac-advance unit back on after switching distributor...
Daniel.
 

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iv'e just finished this mod and its very worthwhile :cheesy: just went for a blast and you can notice the difference alright :cheesy: cheers to kaas and saabdaniel for pointing me in the right direction with this one 8)
 

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No problemo mate, and yes, it is indeed a worthwhile mod! noticeable better throttle-respons because of higher set ignition, and more boost allowed because of more retard when boosting... sweet :D
Daniel.
 

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Hmm, reading the Saab manual for my car ('78 99T), the vac capsule is supposed to retard under boost. But looking at the capsule, there is no round stop like that. And when at atmospheric pressure (i.e. zero), the arm is hard against what stops it in the case. When a vacuum was applied, the arm moves, when pressure is applied, nothing. A brand new Bosch capsule is identical.

Question 1) does the c900 T8 with the H engine have this pressure retard capsule?
Question 2) does the capsule fit the B engine dizzy?

I'm wondering if I'm getting knock up the top becuase my engine isn't being retarded (I'm running with an APC and ~1bar on a good day, down to about 0.7 otherwise.

Cheers :)
 

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T8 and T16 have the same capsule, but all the other og900 models have a different capsule with no boost retard. All I can say is that the turbo capsule is larger, and the non-turbo is a lot smaller.

Perhaps someone can give you the Saab part number for the capsules so you can check out if you have the wrong part?

-John
 

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Thanks :)

I have no idea what the Saab part number of the vac capsule I have is, I bought the capsule through the local Bosch distributor, who rang Bosch UK technical for the part number. The one delivered and the one on the car both have the number 2027 stamped on it, the part number of the new one is 1 237 122 027. Visibly, the c900 ones differ from mine by having a "belt" round them, the wide section that presumedly gives extra travel inside.

I guess I could speak to Bosch myself and see what they say :) Problem is I doubt I could get a refund on teh bit they've sent as it came from Germany :(
 

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Ok, bosch have shed some light. My dizzy SOEN'T have pressure retard. But the 79- dizzy's do. Ok, nice and easy I thought, just get a 79- capsule. Er, nope. Same part :-?? So it would seem that the difference is somewhere inside. So a parts list for both is winging it's way from Bosch UK to my good self. Now, at the last but one Kodak, I came away with a dizzy rebuild kit (thanks David :)). I wonder if it is for the later dizzy's, and if it happens to contain teh bits I need. It does have the base plate which has the stops etc. for advance/retard...
 

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alan forsyth said:
iv'e just finished this mod and its very worthwhile :cheesy: just went for a blast and you can notice the difference alright :cheesy: cheers to kaas and saabdaniel for pointing me in the right direction with this one 8)
Hej Alan :D
What is your ignition timing now? At idle and with pressure?
 

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hej lars , the timing is now 19 deg btdc at idle and its running sweet :cheesy: no knock since adjusting the apc, whatsoever :cheesy: :cheesy:
 

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Goddag Allan "It meens good day" Do you know what degress it is retarded to with 1 bar pressure on the vac capsule an at at idle?
And what is your specs. on your APC?

Try say "Din turbo 8 kører langsomt" to Daniel :D


Lars
 

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:roll: @ Bosch UK "technical". The sheets turned up today, and what's the ONE part that's different between the two dizzy's? Yup, the capsule :roll: That'll teach em to listen to some bloke drivel on about how it could be done inside the dizzy itself with me wondereing how on earth it could manage that when there's no movement available on the one thing that has pressure on it.

Oh well, at least it's a simple swap! Next question, I don't suppose anyone has a capsule off a c900T so they can tell me what the number stamped on it is :) I'm hoping it's 2721. That would make it the same as the 99T one...
 

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Willy Wonka said:
I'm at 9º btdc. Connect the vac back to the intake and read the timing. My vac has been modified to allow 23º btdc at idle. I like the high advance because it allows the engine to breath while not under boost. At 10º btdc the apc cuts out about .25 bar earlier with my set up. I hold 1.5 bar. I paid $3 for a junk yard vac cap, and modified it.
Hi Willy, why don't you have knock? I have to set mine at 4 degress btdc with pressure on the vac. capsule?

Thanks

Lars from Denmark
 

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Got it :) Looks exactly like the one in the picture at the top of the page - except the pipe nipple is at a different place on the bulb. I shall be fitting it in a minute, and trying it out tommorrow morning :)

I'm hoping not to have to actually mod it as yet, as in theory this should change my on-boost timing quite a lot anyway.
 

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nutcase said:
trying it out tommorrow morning :)
WHAT? Go for a drive NOW, it will make a hole lot of difference, I'm sure of that, we want to know the results, so get on with it! :lol:
Daniel
 
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