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Discussion Starter · #1 ·
The MY89 T16S is getting some serious TLC at the mo. Head off, everything being cleaned/checked, tightened etc. After I've done the mechanicals it will be on the interior; I have some bargain leather to swap over and a headlining to do


Now I have sitting on the shelf a low mileage (30k vs 160k) NA head and I think I'm going to pop that on it's place. The exhaust cams are the same, but the intake cam on the NA closes earlier. I understand this will give better low/mid characteristics, albeit at the expense of some top end. I'm happy to live with this.

Does anyone have experience of this swap to confirm the change in characteristic?
 

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There's probably someone here who's actually used those cams, so only he/she will know for sure.

However, it's pretty clear that they should do exactly what you just described; the Intake Valve Close angle is sooner on the N/A which means there is less time for the reversion wave to make it past the valve and back into the intake system.

Also, the valve overlap between the N/A cam and turbo cam is the same, so there shouldn't be any issues there.

But, obviously only testing can tell for certain.

-Adrian W
 

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Are valve sizes & lift the same?

Probably worth some time doing some mild porting before fitting, might more than offset the top end losses you predict - you handy with a Dremmel Mark??
 

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Originally posted by Fliptop:
[qb]Are valve sizes & lift the same?[/qb][/b]
Yep. Only the duration is different. The part-number for C900 valves is actually superceded by the part-number for T5 valves which are a direct swap. Saab is pretty good about making things cross-compatible. Also, the only difference in duration occurs near BDC, so piston/valve interferance shouldn't be a problem.

It's worth noting after my comment about T5 valves being compatible with C900 valves that T7 valves are NOT directly compatible with anything but T7 heads without a lot of modification. They have thinner stems and a different grind-angle for the seats, even though they are actually the same diameter as all previous Saab DOHC valves.

-Adrian W
 

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Discussion Starter · #5 ·
Originally posted by Fliptop:
[qb]you handy with a Dremmel Mark?? [/qb][/b]
Funnily enough I did have a quick go with one at the old head, just to see if I could smooth things out a little. Maybe I was using the wrong type of abrasive, but it didn't seem to be that effective. Perhaps I ought to read up on it...
 

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There is a book with the title along the lines "How to Power Tune Cylinder Heads" Also one "How to Chose Camshafts" by Des Hamill availible from most motoring book shops and definitely from DemonTweeks (I may not have spelt that correctly). These will tell you how camshaft duration and lift affect performance and how to gasflow cylinder heads. They are well worth a read.

Generally the less the duration the less the power but the better the low end torque. Saab have fitted very conservative camshafts in order to maximise midrange torque. I would not have thought reducing duration will improve performance, unless in conjunction with an LTP and engine management changes.

I have been thinking about Abbot camshafts that have a duration around 260 degrees, which is still fairly conservative. These will increase power, but make it availible higher up the rev range. There is a good article in RetroCars from around February on Saab engine tuning. There is a list of backnumbers in each issue.

Hope this helps.
 

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Standard SAAB camshafts are 240 duration. On the scale of things this is mild. Abbot camshafts are inlet 250, exhaust 260, which are also pretty mild.

Fast road camshafts for normally aspirated OHC engines are normally around 280 degrees duration.

Up to 270 duration would give improved higher end performance within normal rev range without sacrificing too much low down torque in a Saab engine.

This assumes standard lift, which the Abbott camshafts have. Add extra lift and that should provide improvements throughout the range. I am just having a high lift 285 camshaft put in my TR7 engine. I'll report on that shortly.
 

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Discussion Starter · #8 ·
Well, I'll give the NAs a go and if I don't like 'em, I can always swap back. It's just that the torque arrives in an almighty peak at the mo and it would be nice to smooth it out a little


I'll report back- I hope to get the head back on this weekend, weather permitting.
 

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hi there,
you have to be a little carefull with overlap on engines which use lamda sensors for fueling, as on idle the extra overlap allows more unburnt air though the engine which makes the lambda sensor think its running weak when its not, causeing fueling problems.
Also because most standard sized turbos are very restrictive long duration on the exhaust cam can allow combution gasses to contaminate the next charge when on full boost as exhaust manifold pressure will be higher than intake pressure.
bye.
 

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the 1st thing done is to reduce the exhaust duration and kick the inlet lift up whilst keeping overlap to a minimum
i have the OE specs for the 16v turbo engine and a range of sport and race profiles and (keeping hydraulic profiles, mechanical is N/A engines really) the exhaust duration doesnt go above 242 degrees at 0.1mm, its the inlet you can go a bit further with
 
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