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C900 Performance, Mods & Tuning Covers Tuning & Performance modifications for the Classic 900 (C900)

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  #1  
Old 10th March 2005
mr rx-7 tt mr rx-7 tt is offline
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Default Modification on the 900 t

When modifying the APC to boost into the red is it also wise to change the timing ?
So far I have a modified APC and a 3.0 FPR...
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  #2  
Old 10th March 2005
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evanXspg evanXspg is offline
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hey
I have a 3.0fpr in my glove box, I was going to install it before I upgraded my injectors but I wasn’t sure if that was a smart move.
I'm assuming you have stock injectors, what differences would you say there are, positive or negative to having a 3fpr with stock injectors?
I wish I could point you to a new upgrade but I'm right about where you are.
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  #3  
Old 11th March 2005
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Well, the more you retard timing, the less knock you should get at full boost, But, at a cirtain point, you will get lots of boost but not much power because the spark is lit too late and the combustion occurs too late as the piston is well on it's way down the bore.

So, I found that 15 BTDC at idle (near stock) and 7 or 8 BTDC at max boost is ideal for lots of power and higher than stock boosting. I get about 15psi without too much knock with slight apc adjustments. (about 1/4-1/3 into the red) The vacuum capsule on the distributor must be slightly modified to allow such a difference between the timing at idle and at full boost. Remove it, and make the arm able to travel downwards about 1mm farther. (just bend the metal peg stopper with a big screwdriver) That should allow the unit to change the timing 7-9 degrees on full pressure as opposed to the 4-5 degrees the unit provides without the modification.

Happy SAAbing!

-Rob
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  #4  
Old 11th March 2005
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I bent mine a hell of a lot more than 1mm and i am getting some knock as i cross into the red. Is it my rise rate or initial timing that's too advanced?
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Old 11th March 2005
mr rx-7 tt mr rx-7 tt is offline
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Quote:
Originally Posted by evanXspg
hey
I have a 3.0fpr in my glove box, I was going to install it before I upgraded my injectors but I wasn’t sure if that was a smart move.
I'm assuming you have stock injectors, what differences would you say there are, positive or negative to having a 3fpr with stock injectors?
I wish I could point you to a new upgrade but I'm right about where you are.
The car burns a bit rich, I can see soot in the exhaust where before there wasn't any. Other than that I have not noticed anything. I figure it's better to be safe than sorry. I was told I had enough injector (stock) to run into the red with just the 3.0 fpr.
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Old 15th March 2005
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Quote:
Originally Posted by mr rx-7 tt
The car burns a bit rich, I can see soot in the exhaust where before there wasn't any. Other than that I have not noticed anything. I figure it's better to be safe than sorry. I was told I had enough injector (stock) to run into the red with just the 3.0 fpr.
Yes, this should be fine. My stock FPR died last October and I had a spare 3.0 bar laying around so I just instaled it. It works great. No problems and smoother running. I think I've heard using a 2.8 bar is better for performance and efficiency.
-Dirk
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  #7  
Old 15th March 2005
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how do you tell if you're getting knock? just by how the APC retards boost? i'm running up to 16 psi, usually 15... don't hear any knock... all i did was mess with the wastegate rod ....
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Old 16th March 2005
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You'll feel it when it does. It kicks your boost back significantly.
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  #9  
Old 16th March 2005
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Well, if he has turned up the boost on the wastegate alone, the APC can't cut back on boost even if there is knock!!! You will feel the fuel cut-off though if you meet that...
Tweek your boost via the APC, not the actuator, that is the safest way...
Daniel.
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