why do I need 3/8" valve stems?

[shelbydoug]

While it's on my mind, IF I'm rebuilding my original heads, and doing new bronze valve guides, why do I need to stay with 3/8" valve stems? Why not just go down to 7mm stainless like on the small blocks?

That would certainly add some pocket volume?

Is there some inherent flaw in the design geometry that requires a stem that big? I don't see it?

Anyone know why?

[The Going Thing]

Many are going to the small block chevy valves on SB Fords.  11/32. Even on FE engines.  Have you ever held a 427 2.25 stainless valve? They are damn heavy.

[shelbydoug]

Many are going to the small block chevy valves on SB Fords.  11/32. Even on FE engines.  Have you ever held a 427 2.25 stainless valve? They are damn heavy.

That's my point. My AFR sb heads are using all Chevy lightweight cut back valves. SB Chevy springs, etc.

Why not just rebuild the FE heads that way also?


My engine builder inititally recommended just putting the iron heads aside and installing a set of Edelbrocks like you used but why not extropolate on that further?

I don't need to hear the dynosaur roar through the valve train. Why therefore, even retain the 3/8" pushrods? The more I think about it, the more ridiculous it is.

This is why, when I was a kid, when we would listen to the SOCH's come up to the starting line, reving away, we would all put on Flack jackets and helments!


Yes. I know what these components weigh, I rebuild my own head assemblies.

2.25" stuff weighs in pounds per piece. Kind of like WWII SS88's going through the Sherman's armour and spinning around in the turret "a little".

[Royce Peterson]

When we rebuilt the heads on my 427 we used Del West titanium valves with 6MM stems. They are the same price as 3/8" stem valves. The 6mm stem is plenty strong and allow more airflow. Bonus: the lighter valves require less valve spring which reduces rotating torque.   

While it's on my mind, IF I'm rebuilding my original heads, and doing new bronze valve guides, why do I need to stay with 3/8" valve stems? Why not just go down to 7mm stainless like on the small blocks?

That would certainly add some pocket volume?

Is there some inherent flaw in the design geometry that requires a stem that big? I don't see it?

Anyone know why?

[shelbydoug]

Thank you for your feedback Royce. That solution makes sense.

[2112]

Be careful using skinny pushrods. The flex and will bend. The flex leads to valve float.

If you are using garbage Comp Cams roller lifters, expect them to implode in short order.

[pbf777]

     Converting from the 3/8" to an 11/32" valve stem on the FE is not new news, as we have practiced this for decades, and K-Line has been producing a thicker than the standard bronze valve guide liner for as long as I can remember for this purpose, a particularly effective product when working with the iron cylinder heads.         

     Adoption of the larger stem diameter by the O.E.s was a natural progression as the valve head diameters increased, as examples from both Ford with the FE, GM with the BBC, and others, this if only for the retention of the larger valve heads as most valves were of two piece construction in the period with the head and stem welded together.  And I,m also sure the greater diameter and hence increased circumference providing greater surface area to support this larger, heaver unit, aids in extended guide bore/valve stem life, was also deemed preferable.  Remember, at the then intended engine R.P.M.s for standard production applications the increased weight was not really a problem.

     And, only if your intentions include pushing the performance envelope to the upper extremes would I get to concerned in any great values anticipated, as there are always trade-offs in most any change of engineering.         

     Scott.

[The Going Thing]

I agree. The 6MM stuff is new to the game. If they have indeed come down to the 190.00 a set for intake and exhaust they will go in my heads at some juncture.  The spring pressures are dictated by lobe profile, cam-type and functional RPM range.

As for pushrods, I went with ISKY 3/8" pushrods. I was lucky enough that the pushrod length they stock was fine with my adjustable rollers.
Lunatti was the only other that stock FE cupped rods. They were shorter than the Isky and only 11/32.

[pbf777]

     6MM, equals .236", or in general terms something just short of 1/4"; well, I don't know if it's such a good idea for something that's not a max-effort where there is deemed a value in such, this coupled with a limited operating time between servicing application.  Remember, the FE is not an over-head-cam engine, and adopting what works in that arena, over here, even it it seems priced right, just might bite you!       

     Scott.

[gt350hr]

   6MM stems are common in Nascar engines. They are used for one race ( or 1,000 miles) and replaced religeously. They are all over epay for cheap.  At 7,000 rpm ( instead of 9,800) they should easily last 5,000 or more unless they are used with seat pressures over 180 and or use with a roller cam. Titanium does not have the tensile strength of  steel and they WILL break. Sometimes it's at the lock groove , other times it's at the transition from stem to valve head. NO QUESTION that they improve air flow around the stem.
   Those same Nascar engines use a 1/2" diameter pushrod!!!! Pushrod deflection (less)  is FAR more important than pushrod weight. FE pushrods flex like crazy ( when observed on a Spintron tester) because of their length and "sweep" at the adjuster. I had a set of "dual taper" pushrods back in the '70s that improved my rpm capability by 1,000 rpm with no other changes due to the loss of flex and attending harmonics.
   Randy

[shelbydoug]

   6MM stems are common in Nascar engines. They are used for one race ( or 1,000 miles) and replaced religeously. They are all over epay for cheap.  At 7,000 rpm ( instead of 9,800) they should easily last 5,000 or more unless they are used with seat pressures over 180 and or use with a roller cam. Titanium does not have the tensile strength of  steel and they WILL break. Sometimes it's at the lock groove , other times it's at the transition from stem to valve head. NO QUESTION that they improve air flow around the stem.
   Those same Nascar engines use a 1/2" diameter pushrod!!!! Pushrod deflection (less)  is FAR more important than pushrod weight. FE pushrods flex like crazy ( when observed on a Spintron tester) because of their length and "sweep" at the adjuster. I had a set of "dual taper" pushrods back in the '70s that improved my rpm capability by 1,000 rpm with no other changes due to the loss of flex and attending harmonics.
   Randy

NASCAR has a different reality then SHELBYDOUG.

We are getting to the point of my discussion with Lee Holman. When you look at individual components on the 427s, they are all 8500 rpm capability.

The valve springs were the  limiting factor. They were not 7000 capable.

I don't need 3/8 push rods, valve stems, etc, to go 6500 rpm, when I can use sb components instead and go easy 7500rpm.

Did the FE and sb engine people need to be separated in the lunch room?

[Wedgeman]

Which side of the room for FE's.....LEFT.....or.....RIGHT ?....

[2112]

NASCAR has a different reality then SHELBYDOUG.

We are getting to the point of my discussion with Lee Holman. When you look at individual components on the 427s, they are all 8500 rpm capability.

The valve springs were the  limiting factor. They were not 7000 capable.

I don't need 3/8 push rods, valve stems, etc, to go 6500 rpm, when I can use sb components instead and go easy 7500rpm.

Did the FE and sb engine people need to be separated in the lunch room?

I had trouble with 3/8" pushrods at 6500. Went to double tapered 7/16" pushrods from Trend.

[The Going Thing]

The Isky Chromoly 3/8 pushrods are strong.  The issue is intake manifold clearance that decreases even more at higher lifts with large pushrods. Thus far the 3/8 pushrods clear with the C7ZX intake.

[gt350hr]

   If 3/8ths is a limiting factor on diameter the wall thickness can be increased from .080 to .120 and dramatically increase pushrod strength. Small blocks use a shorter pushrod and rarely need a 3/8ths diameter pushrod for performance use. Most do not run engines at RPMs above 6,000 long enough to know if they have a valve train harmonics issue. There are several tell tale signs.   
   Randy