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Saab NG900 & OG9-3 Performance, Mods & Tuning Covers Tuning & Performance modifications for the Saab NG900 (1994 to 1998) & OG9-3 (1999-2002) & '03 Convertible

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  #1  
Old 17-01-06
rsvp9146 rsvp9146 is offline
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Default porting and polishing intake and exhaust manifolds

I have a set of spares, and I was wondering if it would be worthwhile to port out both manifolds on an otherwise stock 95 Turbo. I have already removed the intercooler silencer, as well as insulate the intake tube, ported out the throttle body casting (on top of the throttle) down to about a 1mm taper at both ends and removed 1-3mm overall. Magnaflow exhaust and also the airbox has been modified to remove the silencer, and I opened up the intake cone to 4" with a section of ABS to fit in the circular groove in the chassis, and then glassed it to the airbox. These mods have helped a bit, she spools up quicker..

Was wondering if I could expect any gains from opening up the circular port on the bottom of the exhaust manifold (seems a lot of material can be removed here without affecting strength or thermal problems) and clean up all the rough casting on the inside of the intake. I have access to all sorts of interesting tools to do this. Was wondering if it's worth my time....

Was also thinking of lightening the flywheel, however, I'ts already pretty damn light! If i were to do so, where would be the safest areas to remove metal?

Was also thinking of perhaps a thicker head gasket to lower the CR and then run more boost? Or is this just a waste of time? It seems that there should be enough play in the timing chain tensioner to allow this.

Last edited by rsvp9146; 17-01-06 at 12:56 AM.
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  #2  
Old 17-01-06
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in have a spare inlet manifold, exhaust manifold, TD04 turbo and cyl head waiting to be fitted, as for porting the exhaust manifold at the turbo end there is no point as the hole is the same size as the hole in the turbo, altho i have ported mine cus i'm fitting a TD04 from a 9000 which has a larger hole, you would be better off removing the head and porting that as there is a lot of differance in the size of the head ports compered to the manifold ports, as for dropping the com ratio with a thicker gasket i'm not sure how you would go about finding a thicker gasket and how thick would you need to go to drop it enough to give you the c/r you need
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Old 17-01-06
brewtide brewtide is offline
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Quote:
Originally Posted by boxman
in have a spare inlet manifold, exhaust manifold, TD04 turbo and cyl head waiting to be fitted, as for porting the exhaust manifold at the turbo end there is no point as the hole is the same size as the hole in the turbo, altho i have ported mine cus i'm fitting a TD04 from a 9000 which has a larger hole, you would be better off removing the head and porting that as there is a lot of differance in the size of the head ports compered to the manifold ports, as for dropping the com ratio with a thicker gasket i'm not sure how you would go about finding a thicker gasket and how thick would you need to go to drop it enough to give you the c/r you need
Just as a note, people have been known to double-stack or even 'triple stack' their headgaskets in order to do this.

To me, seems like it'd affect the C/R minorly and sounds really sketchy. Too many possible leak points, IMO.

But I just thought I'd throw it out there...

peace,
bny
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Old 17-01-06
saabski saabski is offline
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In my days of youth I spent many, many 'happy' hours opening out, cleaning up, polishing, porting etc etc. sometimes I recon I got oh.. 5bhp more. Now with bigger valves, higher CR and all the rest maybe 8-10bhp. Put in a high lift cam and then we were talking 25+ bhp. Still when you only had about 50 to start with, it was worth it.

When you have 100 200+ to start with... I wonder.
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  #5  
Old 17-01-06
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The gains from porting and polishing the head itself will be significant. The benefits are two-fold:

Reduction of pumping losses will net 10 to 12 hp alone; and

You can make more hp with less boost.

The gains from a decent p&p of a turbocharged head should net out to 15 to 20 hp all told. Unlike N/A cars, where p&p is both science and art, you can open up the ports more. Since the N/A car only has atmospheric pressure and the vacuum of the intake stroke to impel the air, you are limited in the amount of material you can remove. The bigger the opening, the more volume you can move through it, but at reduced velocity. With forced induction, opening the ports to bigger is better. Pressure is reduced but you have the charge to help keep velocity of the air mass high. Running 15 lbs of boost on the stock head and the same on the p&p head, you will see at least 15 additional hp if not more. Now if you were able to hog out the ports where your stock turbo could not supply 15 lbs of pressure (not likely) then you would be facing the problem that N/A cars have, albeit to much lesser degree (as even 10 or 12 pounds of boost gives you air mass significantly more velocity than atmospheric and vacuum alone). But if it were possible, then that would be the time to go more aggressive with a turbo upgrade. Remember, forced induction is just one way to increase volumetric efficiency. If you make the head as volumetrically efficient as possible, less boost will be needed to achieve the same amount of hp. So, p&p plus turbo equals more options for you to achieve the ultimate goal. And increased volumetric efficiency in the head can allow you to set up the car with MORE CR and/or ignition advance (with less overall boost) for more down low power if that is what you want (drag race), or you can increase boost for ultimate top end power.

And yes, whether you p&p the head or not, smoothing out the flow from the manifolds to the head are worthwhile things to do. You will get smoother idle and will get some increased volumetric efficiency out of it.
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Old 18-01-06
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I thought our heads, manifold matching and valves were pretty good as standard? He says his car is otherwise mainly stock. It's a lot of work when mega improvements can be made with intercoolers, chips and downpipe

Manifolds, well, maybe a bit if you are already at 250BHP and aiming for more
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Old 18-01-06
adeptid adeptid is offline
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Has anyone mentioned a pre-annealed copper head gasket to raise the head a bit more to lower the compression? I know that John at: www.saabsavior.com, can hook you up with what you need and perhaps even have one machined to a particular thickness for your individual needs to make up for the need of a higher sitting head to lower the compression ratio.
Also, I understand that an intake manifold off of a '91-'93 9000 is already "ported" out and readily fits in place, fwiw, and anything that will open an engine up more to allow it to breathe better is a good thing!!

p.s. Tell him (John) that Frank sent you and drop me your digits already, rsvp, so that I can get some tips.

Last edited by adeptid; 21-01-06 at 09:43 AM.
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  #8  
Old 19-01-06
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Later cars (definately the T7, maybe some later T5's too) came with a thin copper head gasket.


I remember when I was considering using a 9k block with T7 head, Boxman told me to make sure that I use the 9k head gasket, because the pistons on the 9k are less dished than the T7. If I had used a 9k block with the copper hg, it would've raised the Compression Ratio.

In other words, there is a stock saab part that would do it, assuming it could still seal on the older block/head.

That said, you dont need to lower your cr to run more boost. Just beware and be aware of any detonation while you tune your car up the ladder.
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  #9  
Old 19-01-06
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Boxman may also have been concerned about valve/piston clearance on the exhaust stroke. Sometimes, especially on heads that have been milled a few times, clearance can be reduced to just a handful of mils using even stock thickness headgaskets. This potential problem can be greatly exacerbated by going to an even thinner gasket, to the point of cantact between the piston and the fully opened valve. And if the piston profile is different, domed vs. flat vs. shallow depression, there is a new variable in play affecting that already tight clearance.
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Old 19-01-06
Adrian W Adrian W is offline
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It's not quite fair to say that "bigger is always better" on porting a turbo head. Excessively large ports can cause a serious drop in off-boost or low-RPM performance. However, since most turbo owners with ported heads also have big turbochargers, this lack of low-end grunt is generally blamed entirely on the turbo, even if it was not entirely the turbo's fault.

The purpose of a ported head, or ported anything, on a turbo car is to reduce the required boost pressure to generate a specific massflow (power). In the case of the cyllinder head, if your ports are too big, or too small, for your application, you will defeat the purpose of the port-job in the first place as you'll be forced to raise boost to compensate for the poor match.

Porting the manifold probably won't have any significant negative effects and it should have a fair positive effect. I'd be skeptical of 15 hp from pumping losses alone. Generally, the increase in VE cannot even create that much additional power from a ported manifold alone. Pumping losses from the manifold ONLY will more likely be in the 5 hp range, if not lower.
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  #11  
Old 20-01-06
adeptid adeptid is offline
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Granted, Adrian, at least everyone is of common consent that "porting" is a "good" thing. One can only hope that those who have decided to pursue this avenue of increased horsepower have done so with some research or have, at the least, sought the advice and insight of someone of actual application experience.
As for me, I've always found the best practice is that of the one most commonly used, i.e., "match porting", with a variant of some "reverse engineering" thrown in for good measure. For example, start with a turbo and "match port" the runners, intake and exhaust all to the same diameter as that of the turbo..., it seems to work well enough.
I will have to say that I find it hard to understand why so many people seem so readily eager to offer a dissenting opinion to discourage people from having any porting/polishing work done to their engines when there has and is sooo many posts on this site regarding and encouraging the use of "high flow intake/filter systems, not to mention the numerous products on the market from air intakes/FIPK systems to larger diameter/redesigned exhaust systems that are all designed to remove inherent engineering restrictions to increase air flow so that the engine will be able to "breathe" better..., just like what porting and polishing do. Quite contradictory if you ask me.

Last edited by adeptid; 22-01-06 at 02:03 AM.
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