Alright, I've been playing around with this for over a year and I think I've finally got to a point of kicking this off. I have a local machinist who is well respected and tired of doing SBC's day in and out.

The assumption is that removing a blockage of 1/8" from the middle of the port is similar to opening to port walls on each side by an 1/8", due to the boundary layer. Bowl and roof work will still be done, but hopefully to a lesser extent than what a "serious" port job requires to achieve similar flow.

I've made a comparison of stock sizing against what I consider the "front runners".



Right now I'm leaning towards the Navigator intake and Ranger exhaust valves.

Spring options are limited, but I'm eventually going turbo, so I don't think limited lift will be an issue.

Guides will likely be the 1998 Windstars.

In theory, the head will go under the knife next week.

The machinist has a SuperFlow and plans to flow it "as cut" before we start doing any port work.

I'll keep you posted...

_________________
Brooks

'72 Dart Swinger
'71 Plymouth 'Cuda

Cheap, Fast, Reliable
Pick 2!

I'm doing a 7MM head myself. It makes a difference for sure. You'll need to flow one port before and after so you can have an accurate "apples to apples" comparison. Meaning, flow the port with the stock stem valve with no port work and then the same port with the 7MM valve installed with no port work. That way you'll get a true evaluation of what the valve swap alone will give you.

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There's no such thing as too much cam....only not enough engine!

What parts are you using? I'd like a few more options on valve springs, but haven't put as much effort into them as the other pieces.

_________________
Brooks



'72 Dart Swinger

'71 Plymouth 'Cuda



Cheap, Fast, Reliable

Pick 2!

I guess the Idea here is a bigger valve with a thinner stem?


Is that correct?


Is there any drawback to running a 7mm stem such as longevity? or parts stength? I see that there are obvious flow and Weight advantages.


Would the 7 mm Valves be better than a stock type Backcut type valve stem?



Thanks,


Greg

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http://www.youtube.com/hyperpack

Interesting. Thanks for doing some leg work on valve sources/sizes. I would have thought this was not a big advantage, but I am prepared to learn something here if someone gets data.

I would recommend using a valve with a bit longer stem than stock so you can run higher lift and not have to cut down the top of the valve guide boss too much. Many of us have used SBC valves, which are about 0.10" longer than stock, with bigger cams.

Thanks and all the best,

Lou

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Home of Slant6-powered fun machines

Thoughts......

Are you installing a hardened exhaust valve seat?

If so, this will limit your exhaust diameter because the larger valves seats have a tendency to hit water when the head is machined for the seat.

Thus the tendency to use the smallest valve seat possible with only a 1.44 exhaust or stock exhaust diameter.

1.5 may be too large (unless you cut down the head diameter)

The windstar is closer to the common 1.44, plus it has the longer stem....


Rocker arm geometry:

Will the tip of the rocker arm stay within the bounds of the smaller valve stem?

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Lots of great questions that are going to be met with lots of "I don't know's". I'm trusting my gut to some extent and keeping myself open to learning in the meantime. For sake of comparison, I'm planning to do one cylinder and then evaluate the gains.

Longevity
I don't think the 7mm valves will be at a disadvantage. The motors that these pieces are designed for are 100,000+ mile designs. If I was sourcing from something more exotic than a Ford minivan, I'd worry.

Exhaust Seats
Is hitting water a matter of depth or diameter? As I've read on over-sized valves, I see lots of references to the Ford 300 pieces. As I searched, I used these as guidance for size. In theory, if you can fit seats and 300 exhaust valves in a Slant head, you can fit the ones I'm looking at.

Rocker Geometry
I'm hoping that using "stock-ish" length valves will keep the rocker as centered as it would be in original form. I could see a situation with lots of cam lift where the rocker would sweep right off the edge of a smaller stem. I'll have to do a mock-up after machining to see where the rocker pad is at various lift points...great question!

Keep the questions coming...it's giving me lots to think about...

I'll keep you posted!

_________________
Brooks



'72 Dart Swinger

'71 Plymouth 'Cuda



Cheap, Fast, Reliable

Pick 2!

Would a Lash Cap on the top of the stem in any way help in this situation?


Greg

_________________
http://www.youtube.com/hyperpack

Yes

_________________
Brooks



'72 Dart Swinger

'71 Plymouth 'Cuda



Cheap, Fast, Reliable

Pick 2!

Hi Brooks, I see you are in Lincoln,


One of the Most Respected Slant 6 engine / Head builders is in Lexington.

His Name is Mike Jeffery.


Sorry I don't have contact info to send you now, but you might want to also collaborate with him on this project after harvest.

He's about 3 hours from you
https://www.google.com/maps/dir/Lincoln ... 2d40.68447

Greg

_________________
http://www.youtube.com/hyperpack

Does anyone have contact info for Mike? I've heard the name several times, but no one seems to have a number for him...

_________________
Brooks



'72 Dart Swinger

'71 Plymouth 'Cuda



Cheap, Fast, Reliable

Pick 2!

308-324-3576 is Mike's home number. Very friendly guy. Does not do internet...

Hope you can get together with him! He has done 3 heads for me so far, which have worked very well.

Lou

_________________
Home of Slant6-powered fun machines

I don't have my flow bench anymore but did a lot of head testing pre 1990. Not on slant six but predominantly BB mopar (before you could buy aftermarket heads and even larger valves) I was surprised to see an improvement in flow with the smaller valve stems but it was there. At least 5 %. I have two slant six heads with small stems. One is .343 stems using modified chevy valves from a 305 and the other has .312 stems using aftermarket stainless on intake valve and .343 necked to .312 in the port stainless based on the chevy valve.. Both have a lot of time on them with zero trouble.
Personally regarding exhaust seat inserts I wish that idea would go away. It is completely unnecessary now. However I realize I am wasting my breath despite many years of experience doing it without. It is entirely possible to get a slant six head to flow enough to supply 100%volumetric efficiency and a wee bit more. Camshaft selection and Intake manifold and header lengths seems to be the bottle neck. Once I cured that I scared myself.
don

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8 cylinders are for folks who cant make HP

So, after doing some more looking, valve springs may be the part with the most availability. Comp Cams sells a spring that is designated as P/N 26918 for the Ford 3.8L V6.

Using the cross-reference information on their site, the 26918 is actually their spring for the LS motor and will support up to 0.650" lift.

I'm starting to get excited to see this thing come together...

_________________
Brooks



'72 Dart Swinger

'71 Plymouth 'Cuda



Cheap, Fast, Reliable

Pick 2!

There's no reason to use a Ford spring just because you have a Ford valve. There are a lot of retainer and lock combinations that will allow for different springs. Beehive aka conical springs are a nice way to get the retainer and spring weight down.

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Joshua