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Performance Modifications for the NG900 / Old 9-3 This forum contains PERFORMANCE related Q&A's for the NG900 and 9-3. This may also include suspension.

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Old 06-21-2009, 06:04 PM   #1
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Port/polish the head

I got my P/P head back from the machine shop today. Here are a few pictures of the job. They had a machine that cuts below the valve seat and opens up the bowls, the canals and short radi were done by hand. They did not make the exhaust side as smooth as I did, but I think I will just try it this time and not spend any more time on it. The head will go to the machine shop so a valve job can match the porting job,

John
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Old 06-21-2009, 06:33 PM   #2
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it almost looks like the port divider could be knife edged alot more, and opened up a decent amount more, but i wonder how close they are to the fluid passages.

ever think have getting a saab head flowbenched?



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Old 06-21-2009, 07:39 PM   #3
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What are the gains by doing this? Will any engine benefit from porting and polishing or is this reserved for engines over a certain HP? Sorry for the newbie questions!!!
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Old 06-21-2009, 08:56 PM   #4
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it almost looks like the port divider could be knife edged alot more, and opened up a decent amount more, but i wonder how close they are to the fluid passages.

ever think have getting a saab head flowbenched?

We talked about the knife edge, but he felt that it can hurt performance and advised against doing that. The bowels are opened up a lot and the exhaust side is really opened up from stock and the short radi is flowed very well.

Bigger is not always better and you want to consider velocity and going really big can actually hurt the performance more than helping it.

I wish I knew a place that did flow testing at a good price. I just wanted the VE moved to the right to match my cams and turbo.

John
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Old 06-21-2009, 09:01 PM   #5
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What are the gains by doing this? Will any engine benefit from porting and polishing or is this reserved for engines over a certain HP? Sorry for the newbie questions!!!
If you inspect a stock saab head, you will find a lot of casting imperfections and sharp edges in the head. If you port match, clean up the imperfections and smooth the sharp edges that disturb airflow, increases of 20% have been shown in many heads.

This will help for smoother power transistion and aid in the flow characteristics of the head. It is usually felt mostly above 4k in many peoples opinions, so if you don't have a turbo that works well past 4k, the benifits are not very large, but by doing the simple things I listed, gains can be had. Many report gains of 20% flow and increases of hp in the 15-20bhp range.

I wanted to move the VE to the right about 1000 rpm and since the stock head works well from 2500-5500, moving it to 3500 to 6500 will really help my set-up since my turbo and cams don't really start flowing until 4k anway.

John
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Old 06-21-2009, 09:35 PM   #6
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We talked about the knife edge, but he felt that it can hurt performance and advised against doing that. The bowels are opened up a lot and the exhaust side is really opened up from stock and the short radi is flowed very well.

Bigger is not always better and you want to consider velocity and going really big can actually hurt the performance more than helping it.

I wish I knew a place that did flow testing at a good price. I just wanted the VE moved to the right to match my cams and turbo.

John
thats an interesting thought about the knife edge, i dont think that it needed to opened more necessarily but most port jobs ive seen have the initial edge thinned out more, although i most of the stuff i see is non turbo.

the short turn is touchy tho, since you need to get the angle right or you kill the flow, or not enough and you get no gain.

do you happen to have the pics vigge's posted previously of the cut open head?



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Old 06-22-2009, 12:09 AM   #7
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Making the ports too large seems it would hinder naturally aspirated applications more than forced induction. I think we all know you have no problems in the "boost" department.
Looks good. Enjoy the benefits and post the results!
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Old 06-22-2009, 03:45 AM   #8
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When I did mine I did knife edge the dividers a bit more than John's, especially on the intake side. I left a little more meat on the exhaust side due to the extra heat being there, I didn't want any cracks to develop.
I also ground the edges of the valve guides off (the edges that protrude into the air stream), and also that casting piece just before the air hits that guide, I smoothed that out.
I ground out the bowls (pocket around the valve guide), and the short radii i hit a little bit.
I basically tried to just eliminate any protrusions into the air stream and open up the cross sectional area a bit.
My head also got a full valve job, ground the seats with a 3 angle job, Enem stg. 2 cams and the higher tension springs Nick sells.
The engine is very smooth, and you can almost feel a V-techesque power shift above 4k rpm. You really can feel it open up at this point.
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Old 06-22-2009, 07:58 AM   #9
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I also ground the edges of the valve guides off (the edges that protrude into the air stream), and also that casting piece just before the air hits that guide, I smoothed that out.
did you spot face the guides? ie make them flat to the roof of the chamber?
if you did that can be a little dangerous imho, and is typically used in "race only" short term applications, as it severely reduces the life of the guides. although again, im not familiar with the saab valve guides, but i think this is kind of a universal idea.



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Old 06-22-2009, 08:06 AM   #10
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When I did mine I did knife edge the dividers a bit more than John's, especially on the intake side.
Am I blind, but I do see two pics of exhaust side.
My current head looks like this.
http://www.stcf.net/viggen/Head/
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Old 06-22-2009, 08:42 AM   #11
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thats some pretty work.

do you still have those pictures of the cut up head vigge? and do you have any flow data on a factory or ported head? i figure youll be the person that does.



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Old 06-22-2009, 09:13 AM   #12
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Am I blind, but I do see two pics of exhaust side.
My current head looks like this.
http://www.stcf.net/viggen/Head/
Yes, two of the pictures are exhaust.

You definetely went more on your head. I could have gotten the 1000.00 C&C port and polish, this was the much cheaper 450.00 P/P job.

I did not want to go too extreme. The only way to really know how the knife edge works or does not work is to use a flow bench.

I have studied the leading edges on my racing airplanes many times and we have tried sharp leading edges and it does actually cause more turbulane and does not help laminar flow characteristics and in short can hurt performance. The leading edge on the runner dividers can actually perform better in many cases with a rounded leading edge and you will get more uniform flow with less seperation.

I don't think that matters too much on the exhaust side since the air is following the divider out, not spliting it like the intake side.

I am having the 3 angle valve job done to match the ports and will see how she does.

John
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Old 06-22-2009, 01:52 PM   #13
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I see what you mean in terms of rounded edges flowing better than sharp. The first thing that comes to mind is a velocity stack.
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Old 06-22-2009, 03:16 PM   #14
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Am I blind, but I do see two pics of exhaust side.
My current head looks like this.
http://www.stcf.net/viggen/Head/
Yes you are correct thos e are both exhaust side pics, my mistake.
I did not port my intake side as much as yours Vigge, yours almost look machined, they are opened way up, hope it's not too thin.
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Old 06-22-2009, 03:20 PM   #15
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did you spot face the guides? ie make them flat to the roof of the chamber?
if you did that can be a little dangerous imho, and is typically used in "race only" short term applications, as it severely reduces the life of the guides. although again, im not familiar with the saab valve guides, but i think this is kind of a universal idea.
No I did not take them down that far, i only took down the edges of them right to the edges of where the i.d. is, where the valve stem hole is in the guide, just to that edge, and then rounded them off. I did not want to reduce the length of the guide as this could cause misalignment of the valve on the seat over time as they wear.
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