So I'm looking at getting a valve job done, and am wondering just how much difference porting the head will make. It would probably be a template job done by hand.

My /6 is super-ized and in a 71 D100 with a 727 AT. 3:23 rear end.

Anyone with experience out there?


Thanks,

Joe

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Joe Hoppe

71 D100 225 Super Six 727 AT on 2008 Crown Vic CopCar frame

64 Valiant Wagon 225 904 AT 3:23 8.75"

Daddiojoe, I have experience on exactly one slant six head. I just tried to apply all the conventional wisdom from other heads into the /6 one. One thing I discovered is, it's tight quarters in there! I really went hog-wild on the exh side, but I never hit any water. I concentrated on the "pockets" behind the valves (but in my case, I kept the stock dia. valves), didn't leave much of a guide boss as I remember (bronze pressed-in guides). On the exhaust side, I concentrated on the roof and sides and just tried to blend in the floor so the air would stay moving as quickly as possible at the floor. Blended in the radius from the floor to the "pocket" while removing as little metal there as possible. Had exhaust seat inserts installed, and carefully blended them in, too, when the machine work was done. The intakes, I mostly opened up the pockets and cleaned up the casting in the runners, leaving a little roughness. The exhausts I polished like a mirror. I had all of the intake installed heights indexed to each other (as far into the chamber as possible) and same for the exhausts. Then I equallized all the cc's to the largest chamber and polished the chambers, not mirror-like, but pretty smooth. Just a hint of casting "dimples" left. With a .090" milled head, stock block and cast .060" replacement pistons, I ended up with just a scosche over 9:1 compression, which was exactly what I was shooting for. Oh, yeah, I used 340 springs with dampers on my mild cam.

Was this the "right" way? I really don't know, but I don't think I made any major screw ups. The car runs 15.7@90 with a Carter four-barrel on a 3.23 gear. I'm told I need to loosen up the converter, among other things, to improve my E.T. (but I'll be keeping that 3.23, thank you!). The motor has GOBS of mid-range pull, so I feel like I must've done something right.

One thing the machine shop screwed up was they cut my spring seats way down without asking me first. It was kind of silly, because they ended up shimming everything right back up. I pointed out that unlike the small-block chevies they screw with all day long, there is water right under the spring seats on a /6 head. I even sectioned a junk head to show them how precious little material they had left me with. And I had to press on some machine bushings to help locate the springs and get the tension back up on the dampers. No problems other than that in about eight years, though. Just beware.

"DW"

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If it ain't broke, fix it!

.......tapetty tap tap tap... *waits patiently for next response*

I KNOW someone else here must have some head porting advice to offer. I was kind of anxious to see some other folks' experience myself. I know, I know, don't wanna give away all the secrets here. It's not black magic, but if you're like me, working out of your garage (no flow bench), it is trial and error, and you've got basically one shot at it per head. So good, bad or indifferent, this will be the head you will run.

I alwez hear a lot of hype about going to bigger valves in all heads. Now I'm not going to say that I see no benefit to that whatsoever, but I talked to a few /6 race guys who had done some head mods back then (about 8 years ago, before everyone was "on-line", maybe some of you are here now), and I got mixed reaction on bigger valves. One guy told me it slowed him down.

I approached the situation on a very tight budget at that time, and between that and the fact that the /6 ports are so small even AFTER porting, I felt big valves on my /6 head would be sorta like putting a huge door at the end of a very narrow hall. So I just simply had some new stock-sized valves backcut. My theory is, at least in my application, I'm better served to OPEN the stock dia valve farther than I am increasing the diameter.

One thing I do wish I had done differently would have been to find some other valves with a similar diameter/length (or had them cut) and narrower stems. I could have had the guides bushed to whatever size I wanted, and could have picked up a little flow by reducing the size of the obstruction in the port.

Let's hear some more porting input.

"DW"

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If it ain't broke, fix it!

I'm not a porter, only a little porting on V8 heads. Only know what I've been told or read. No flow bench experience.
Everything I've seen is most home brew port jobs will be an improvement if the short turn is not touched. If the short turn is modified without use of a flow bench, it may kill the port flow.
I feel a home grown job is great for stock and moderate oversize valves. Too big of a valve can be worse than stock. The throat above the seat should be 85-88% of the valve size. If the throat isn't opened big enough, the oversize valve is hurting low lift velocity. If it's opened too big, then it kills the turn into the chamber.
I plan to do a slant six head. Will use either a SBC 1.72 int and 1.50 exh, with the exh cut down to 1.44-1.46, or a SBF 1.78int and 1.46 exh, with the int cut down to 1.70-1.72. I know some one with a flow bench and may get some tips from him.
That's all I know and it's not much.

Cecil

I dunno, Cecil, you sound pretty dang knowledgeable to me.

One thing my feeble, alzheimer's riddled brain seems to remember from the head I did is that the runners/pockets and "throats" don't exactly line up, that is to say that the valve head/stem centerline is offset in each port. I remember that kind of left a "cavern" of sorts on one side behind each valve, and some very abrupt changes in direction at the seat. That is where I got real experimental and creative, but whether I achieved positive results is really impossible to tell. I'm sure the net gain of my home grown port job over stock is positive, but I have no idea how the air is really flowing in this thing. I can see where bigger valves might have helped in this area, but not done away with the funky contours completely. In other words, you might get 88% throat area above the seat, but it may actually go out beyond the seat on one side and you'd have a big "ramp" on the other. Any thoughts on this? We need a better head casting, that's what I say!

"DW"

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If it ain't broke, fix it!

Dennis,

Just a thought - your description of the asymmetry of the port relative to the valve/pocket may not be a bad thing. I've seen reports that things like that can serve to produce "swirl" - more tumbling/mixing motion of the charge as it enters the chamber that helps fuel mixing and better burn. I recently read an example that SBC heads were supposed to be better on this than SB Fords because of this asymmetry.

I have done a very small amount of blending on my two heads, and plan to do some more this fall - we'll see what happens...

Lou

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Home of Slant6-powered fun machines since 1988

I'm no expert eather but I'm in the process of doing my third /6 head there is allot of old posts to search that helped me immensely. However I beleave can pass on a real time saving tip where it comes to gasget matching and starting the roof. I'm a long time woodworker by trade, there is a carbide router bit with a 1/4" shank a 1/2x1/4 cutter with a pilot bearing mounted on top,sometimes called a bottoming bit. Using a good quality gasket, make a match using 1/4" alluminum,linen board or simaler material. I like to arch the top and bottom of the exhast ports, install template with flat head machine screws in the stud holes.set the router to cut just under a1/4" of material go slow and use a smooth runing router. remove the template and continue on the sides and bottom two more passes for the roof a larger bearing must be installed to ride on the previous cut this will create a stair step effect that will reduce grinding time a give consistant bench marks to grind too. I was suprized how well the high nickle cast iron cut though the bit broke right at the end of the job, avoid chattering and make sure the collet stays tight hope you like it Bruce J.

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78b4ramSnortbed/6

Good point, Lou. And as I remember, it was mainly a factor on the intake ports. I guess I should be glad our /6 heads are "squirrel ports"

"DW"

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If it ain't broke, fix it!

I will do a "bump" on this thread just to keep it towards the top.
I have some info. but no time, hopefully tonight.
One thought, a SL6 head is designed around 170 cubic inches, valve size and port volume is based on the 170.
What this means is that any work you can do to open-up the head port and improve airflow for a bigger Slant, will help it alot.
I spend at least one hour of deburring / porting time on *any* SL6 head I have apart, just grinding-out the big overhang under the valve seat is a big help.
DD
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