Swirl Head Porting for the first time and head casting defect
Hey guys. The current head on my van has a valve seat that drops every once in a while, so I am preparing to put a new head on. I have a spare swirl turbo head that is a non-oem unit with the non-magnetic exhaust valves. In photo one there is a casting error in the bowl. It doesn't touch the fire ring area, what do you guys think? Anything this may cause? Second photo is where i smoothed out the flaw. Third photo is me taking a shot at mildly de-shrouding the valves with a carbide bur (It's mild as I don't want to reduce the compression much). I made some sheet metal pieces that covered the valves and also used a scribe to be sure the deshrouding is all the same distance outwards. I still need to smooth it out with sanding rolls. Feel free to tell me if I did anything wrong. I will do the same to the other 3 chambers, and then turn my attention to the runners. For that I will take the valves/ seals out.
http://i1240.photobucket.com/albums/...pso3diaa7z.jpg
http://i1240.photobucket.com/albums/...psdglofzin.jpg
http://i1240.photobucket.com/albums/...ps9xexyozk.jpg
Re: Swirl Head Porting for the first time and head casting defect
That's not a "flaw" so to speak as it's more than likely something having to do with part location during machining. I have seen this on EVERY head I've ever messed with.
I will let the more experience "magic" people speak up to the rest of what you asked, but that's what I know....
Re: Swirl Head Porting for the first time and head casting defect
I too have seen this on every head I have ever seen on the turbo cars.
Re: Swirl Head Porting for the first time and head casting defect
I've seen it too, not to say that rounding off those sharp corners isn't a good idea...
I would try to give it a bit more of an "undercut" to help turn the air towards the piston, rather than allowing it to "crash" into the cylinder wall though. A smallish ball rotary file should do the job, probably 1/4 to 3/8", hard to tell by the picture, and even harder to tell by memory! :-)
Mike
Re: Swirl Head Porting for the first time and head casting defect
Just to give a little more feedback, I have done chamber work to 3 heads...all of them had this "feature". I blended them all into the chamber as well as knocked all of the sharp edges down to prevent hot spots. I also have eliminated the "point" in the center of the 2 valves on a swirl head, but I'm not too sure that was the best idea anymore. However, laying back the quench pad from the valves is a GOOD thing....allowing more low/mid lift flow....which is HUGE!
Re: Swirl Head Porting for the first time and head casting defect
Well I only deshrouded the valves(finished with 180 grit) and port matched the runners to the gasket, trying to mimic other ported heads I have seen. I didn't touch the bowl area or very far in the runners. Let me know what you think. I'll be installing it soon.
http://i1240.photobucket.com/albums/...psqjaobhcg.jpg
http://i1240.photobucket.com/albums/...pshaxqxkve.jpg
Re: Swirl Head Porting for the first time and head casting defect
I'm no expert, but wouldn't not working on the bowls and runners leave most of the benefits of chamber work unrealized?
Re: Swirl Head Porting for the first time and head casting defect
Quote:
Originally Posted by
cordes
I'm no expert, but wouldn't not working on the bowls and runners leave most of the benefits of chamber work unrealized?
I'm certainly no expert either, but I would agree with you. I've not attempted to port a swirl head(yet), but when I did the G head on my Scamp, I spent 75% of my time on the ports. The casting bosses for the head bolts are a major restrictor on several, if not most, of the ports. I spent a lot of time removing metal, and reshaping the sides & roof of the ports. It was my first time, and I really don't know if they are "right" or not. I went off of pictures and information I had found in various sources over the years.
I can tell you this much, it runs like a raped ape, and winds to 7K without any struggle, so I must have done something right....:thumb:
That being said, I know porting for a turbo motor can be a whole different animal than N/A. Hopefully some more experienced porters will chime in...
Re: Swirl Head Porting for the first time and head casting defect
I ported the head on my GLH including the intake and exhaust bowls under the valve. I used a ported Direct Connection head as my guide and spent a lot of time removing material.
When you remove the valves you can see an offset between the runner and the bowl. This offset is what induces the swirl effect. If you make a radical change to this shape, you will lose the swirl effect and may cause poor flow characteristics in the port.
I also deshrouded the valves more and smoothed the combustion chamber. Deshrouding allows for better flow when the intake valve opens. Smoothing may help reduce detonation points.
Re: Swirl Head Porting for the first time and head casting defect
I was under the impression that de-shrouding the valves had a big effect of flow. But it makes sense the runners are where most of the gain is. I just needed to replace the old head and figured I do some quick (relatively) port matching and deshrouding.
Re: Swirl Head Porting for the first time and head casting defect
Quote:
Originally Posted by
jefo
I was under the impression that de-shrouding the valves had a big effect of flow.
On the swirl head making changes to the shape of the chamber can modify the pressure spike inherent in the design which can reduce detonation.
Re: Swirl Head Porting for the first time and head casting defect
Quote:
Originally Posted by
mopar-tech
On the swirl head making changes to the shape of the chamber can modify the pressure spike inherent in the design which can reduce detonation.
Do you have a picture of before and after? To help me better understand
Thanks!
Re: Swirl Head Porting for the first time and head casting defect
Quote:
Originally Posted by
jefo
I was under the impression that de-shrouding the valves had a big effect of flow. But it makes sense the runners are where most of the gain is. I just needed to replace the old head and figured I do some quick (relatively) port matching and deshrouding.
It can have a big effect on flow at low lift. It can dramatically improve the "area under the curve", but without supporting mods in the bowl and ports, it may not do that much for you. Port velocity, and flow require a systematic approach. It why you don't use a set of Edelbrock heads on a small block and still run the stock 2 bbl carb... Those better heads can't do their job without the rest of the system balanced.
It's the same reason our 2 piece intakes are so sought after. A fully ported head isn't going to show it's full potential with a 1 piece intake, it just can't flow enough(well, at least without serious modification).
Will the de-shrouding you did help a little? Sure. At low lift you're not maxing out the port potential, but it won't do everything it can, without balancing everything in front of it.
Re: Swirl Head Porting for the first time and head casting defect
I guess I will have to find out what the difference is with testing! The head and a hybrid turbo (46 trim, stage 1 .63) are on and it pulls 21 hg at idle. sweet!
Re: Swirl Head Porting for the first time and head casting defect
Quote:
Originally Posted by
mopar-tech
On the swirl head making changes to the shape of the chamber can modify the pressure spike inherent in the design which can reduce detonation.
Pretty sure what is being said here is that deshrouding (too much) can have a negative effect, too. The 782 is a "fast burn" design. What that means is that the combustion event happens quickly is terms of crank degrees. The faster the combustion event can complete typically means the chance of detonation is reduced. As the chamber grows in size, through excessive porting, deshrouding, etc ... the spark must advance to keep peak cylinder pressure @ around 14* ATDC where the piston will induce the most power/torque. By advancing the spark, we've extended the combustion process in crank degrees which allows more time for hot spots within the chamber (plug tips, hot carbon deposits, exhaust valves) to react with the air/fuel mixture. The result being a chamber that is more prone to detonation and/or pre-ignition.
Re: Swirl Head Porting for the first time and head casting defect
Quote:
Originally Posted by
puppet
Pretty sure what is being said here is that deshrouding (too much) can have a negative effect, too. The 782 is a "fast burn" design. What that means is that the combustion event happens quickly is terms of crank degrees. The faster the combustion event can complete typically means the chance of detonation is reduced. As the chamber grows in size, through excessive porting, deshrouding, etc ... the spark must advance to keep peak cylinder pressure @ around 14* ATDC where the piston will induce the most power/torque. By advancing the spark, we've extended the combustion process in crank degrees which allows more time for hot spots within the chamber (plug tips, hot carbon deposits, exhaust valves) to react with the air/fuel mixture. The result being a chamber that is more prone to detonation and/or pre-ignition.
This is exactly what I found when I went a little too much on valve deshrouding. I regret touching the chambers at all, and overall, this head has never been able to match the previous head for peak torque and horsepower numbers on the same dyno.
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Re: Swirl Head Porting for the first time and head casting defect
Re: Swirl Head Porting for the first time and head casting defect
Even though this thread is 5 years old I think it is important to note that in the pictures of his porting work yon need to look at the fire ring areas by the raised area for the spark plug. You will notice erosion near the fire ring. This is caused by detonation. If the head isnt milled to eliminate this, it will continue to detonate, ultimately killing the head, pistons and related parts. I know this because I am presently working on the same problem
