Port/Polish Questions

cr_bobcat

cr_bobcat

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Getting ready to start a port/polish effort on a C9 head from a 250. My goal is a mild street/strip job. I will be focusing on cleaning up casting flash, smoothing the short-side turn, working the valve guide bosses, cleaning the exhaust ports, and potentially port matching the exhaust. This is going onto the 200 that is currently in my mustang. I intend to cc each chamber after cleaning them up and try to match them as close as possible before having the head surface milled. I am shooting for a static compression ratio in the neighborhood of 9.5:1. Not at work so I don't have my homebrew program in front of me to let me know if that is achievable without flat tops and/or a zero-deck. This is just where I would like to head. I already only use 93 so this shouldn't affect me at the pump. Thinking chamber volume of 50-52 cc will suffice for what i want but I will double check when i reach that point.

The bottom end is stock as far as I know. My questions are
1. Is it wise to port match the exhaust to the gasket? I've read that this is good but have also read that it is best to leave the cylinder head port slightly smaller to prevent too much reversion.
2. I've seen plenty of examples of how to shape the intake valve guide boss that I'm confident i understand the proper form, however, I'm not as confident on the exhaust side. Should i maintain the teardrop form here as on thin intake or is this not as crucial on the exhaust side (ie. I can just smooth this guy with the top of the port?
3. Is it worthwhile to pop the freeze plugs and work the runner? I plan on direct mounting a 2V so i think I can access 1,3,4, and 6 but not overly confident i can do much for 2 and 5.

I haven't built a flow bench nor do i really have the time and space to do so. This means my goal isn't airflow optimization, but rather just to free the breathing up a bit for the old girl. I've been through the Falcon performance HB section on porting a few time and also been through Vizard's book. I more reading is no substitute for doing, but I'm sure I can achieve my modest goals.

Am I missing anything big here at all?
 
Howdy Back CR: All sounds good. Your concerns are hair splitters. In general, think of the intake as being drawn in by vacuum. Every thing will be hugging the inside curves. So that's where you will want a smooth, gently rounding path. Think of a string being drawn through. That's where the work need to be done.

On the exhaust the flow is being blasted out by combustion- hot and pulsing- so this is where you want to consider the outside path where the pulses a being bombarded against every wall and bounced off in a new direction. So raising the roof and smoothing and pointing the ricochet will help.

9.5:1 is a good street goal, even with a stock cam. Design your ignition curve to accommodate it. With a stock cam, cylinder pressures will be high, but the small bore and dished pistons are in your favor in controlling knock.

On getting into the log, you can get a pretty good look with good light and mirrors. About the best you will be able to do in 2 and 5 is to make sure there are no ugly casting flashings in the way. Knocking them down takes creative persistents.

Keep us posted and take pictures.

Adios, David
 
Hmmm. Didn't link in like I thought it would. Anyway, here is the before shot of #1.

http://i1361.photobucket.com/albums/r67 ... yjhs1u.jpg

It's not obvious here, but there are some decently sized pits on the back side of the intake valve. I'm having a lot of fun trying to get that smoothed out while minimizing the material removed. Also moving slow as I'm currently using a cordless dremel...

Edit: I moved the pics around so I updated the link. Should be able to see the "before" pics now for each combustion chamber. Should have the #1 done tonight. Realized I just don't have the right abrasives with the Dremel to get into those nooks. Need the tapered roll to get down in there. Just afraid I'll take out too much material with a stone. I'm pleased so far with the results.
 
Ok. I finally got the coarse grind done on the #1 combustion chamber. The lights are playing tricks on you here. The pic looks like there are major transitions in the chamber but it is just because i changed direction of sanding. The finger doesn't notice the change at all. I was afraid to go much furthar with the casting pock marks behind the intake valve. I took away the sharp edges. I don't know how thick the wall is there and i did not want to find out the hard way.

Am I on the right track so far? I figured I'd go with 1 more sanding to smooth it all together. I have not cc'cc'd this guy yet to know where I'm at. I didn't take "before" measurements because i was going to worry about matching once they were all done.

http://i1361.photobucket.com/albums/r67 ... 3sc0ux.jpg
 
Howdy Back: The picture looks great. Keep it up and keep us posted on your progress.

Adios, David
 
A couple of pointers of a general nature:

Keep some flatness in the short side intake radius; that is to say, make the intake port a little "D-shaped" on the floor, rather than totally tubular. That will help get the flow around the short side radius with a minimum of turbulence.

It also looks like the valve seats could be narrowed up considerably when you do a triple-angle valve job. And move the seats up near the outer edge of the valve so that there is only about .005 - .010" margin from the outer edge of the seat to the outer edge of the valve. This will make the engine think there is a larger valve in there due to the increased curtain area. The .005 - .010" extra overhang is there to keep the edge of the valve from hitting down on the seat and causing valve seat recession over the long haul. I also like to take a fine jewelers file and break the edge of the 60* cut into the throat and also the 30* cut onto the combustion chamber roof.
That, plus a 30* x .060" wide back cut on the intake valve will really wake that puppy up and make it ready for more carburetion.

I am tempted to also suggest a radiused head on the top side of the exhaust valve face, but that would remove some of the aluminized coating from the stock valves and that coating is there to dissipate heat so that mod is best left to race-only engines or engines with stainless or titanium valves.

Good luck with your project.
 
So I haven't made a lot of progress lately. It's been a struggle finding time to get out into the garage. This morning I tried putting the gasket up against the head to see what I was getting myself into wrt port-matching the exhaust. I found that the gasket I got is going to leak like a sieve. Look at the pictures below to see what I mean for cylinder #1. Is this a casting flaw? Cheap gasket (got it from RockAuto)? Or what am I looking at here?

http://i1361.photobucket.com/albums/r67 ... pdtr5j.jpg

http://i1361.photobucket.com/albums/r67 ... 8srrzg.jpg

http://i1361.photobucket.com/albums/r67 ... a1w4lu.jpg

http://i1361.photobucket.com/albums/r67 ... 28jnte.jpg

What I'm not sure of is if I'm going to have to add material to the exhaust ports and then try to open the ports up. Obviously, this is the worst case scenario. The other thing I can do is ping Does10s to see if he has a CI gasket that I can use as a comparison.
 
things are looking good so far. a couple of things;

1: polish the combustion chambers, but do not polish the ports. on the intake side you want a bit of roughness to create a bit of turbulence to keep the fuel in suspension and on the exhaust side it will carbon up anyway thus wasting any polishing effort there. the chambers however will benefit from polishing.

2: regarding whether or not to fully match the exhaust ports, or leave the ports a bit proud to prevent reversion, that will depend on how efficient you make the exhaust system. if you are going to use headers, then leave the ports a bit proud, if stock exhaust manifolds, then match them.
 
I'm making the cumbustion chambers nice and smooth. I was only going to use a coarse wheel in the intake port. I had intended to use coarse and fine on the exhaust port. Wanted to avoid ridges for carbon to deposit on.

For now, I'll be mating up to a stock exhaust manifold but intend to upgrade later. I still have stock valves and will stay that way till CI gets sorted out. Which means the head will get pulled later down the road anyway, so I can leave the ports proud for now, opening them up just enough to help with the breathing.

Does that all sound reasonable?
 
Lots of work, but rewarding when you have the photos and can see how far you've progressed :beer: Somewhere I have a photo of myself entirely covered in soot from porting my head.
I found that having a light shining from the opposite side of the exhaust passage worked well in addition to overhead light. Not so easy to do on the intake side though...
 
This was a response I posted on another thread regarding what I plan on doing for the clean-up of the combustion chambers. Just thought I would repost here to keep my thread on the port/polish up to date.
---------------------------------------------------------------
As far as cc'ing the chambers goes, head to your local farm supply store. I haven't measured the volume of mine yet (currently doing a port/polish effort myself) but this is what I bought.

1 small sheet plexiglass
40 cc syringe
Marvel Mystery oil
white lithium grease

1) Cut the plexiglass down to a square big enough to cover the combustion chamber (4" by 4" maybe? just double check).
2) Drill a hole on one end of the square that is large enough for the head of the syringe. I chamfered the hole just a bit for ease of use. Make sure the hole is near the edge of the chamber so that you reduce the chance of an airbubble getting trapped.
3) Grease up the back side of an intake and exhaust valve and drop them in. Swirl them around a bit to make sure you get a seal.
4) Install a spark plug. Use the exact same sized one you plan on installing.
5) Tilt the head ever so slightly that one edge of the chamber is above the other (tryin to reduce air bubbles).
6) Put a bead of grease around the outside edge of the combustion chamber and place the feed hole on the top as close to the center edge of the chamber.
7) Start pumpin in the oil, keeping track of how much you've put in.

I haven't done this yet, but I worked it out in my head and am just going to assume it'll all come out as planned. :beer:

This won't be exact, but I'm not building an engine for NASCAR either.... I'm going to try to match to 1/4 cc if possible. It'll just depend on the gradient of the measurement marks on my syringe. I plan on measuring all 6 first, finding the largest one, then make a determination as to whether or not the difference of the different chambers is worth the hassle of grind->check->grind->check->etc.

Quick math I just did showed the following. I would think (seat of my pants SWAG) that a threshold of 0.1 C/R difference per cylinder would be acceptable. Hopefully someone will correct me if I'm way out of bed here though. Too be honest though, 0.5 cc seems like a lot of material to remove, so I should be pretty close already. Even 0.25 material will probably feel like I'm sanding forever.

Volume_Diff C/R Hit
0.25 cc 0.02 <- Negligible
0.5 cc 0.05 <- Negligible
0.75 cc 0.08 < - Borderline too much
1 cc 0.11 < - Too much
 
So I've finished the first go at the combustion chambers. So far I've cc'd 4, 5, and 6. They came out to 61 mL, 61 mL, and 61.5-62 mL. Fairly pleased so far. This is a C9 head and what I've read is that these castings can vary from 58-62 cc (1 mL = 1 cc for reference). My guess is that these started off at the 60-60.5 cc range. On #6 I wasn't paying enough attention and gouged into the lip away from the spark plug and I'm guessing this is the majority of my source of difference thus far. We'll see how it all works out. #1 had a pretty bad casting flaw in it that was a pit as opposed to a protuberance. But I don't think I'm going to have to do anymore coarse grinding and whatever I do from here will be polishing. Once I get a chance, I'll snap some picks and upload to the gallery.

Soon it'll be time to start working the pockets and making a decision on how much to mill the head. I don't foresee really getting the block zero-decked, so I may go tighter on the chamber volume. By my initial math, assuming stock piston dish and deck height, I think I want to be in the 45-46 cc range which means taking off 0.070-0.080". This should leave me in the 9.3 - 9.5 CR range depending on what gasket I use.

:beer:
 
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