Flathead Valve vs Chevy Valves

[GOSFAST]

Let me start a separate post here about the Ford vs Chevy valve controversy, it will make it a bit easier for me to follow the topic without jumping around. I know the valve combos have been done by many here but we've learned over the past 40+ years most times and on most builds the (longer) Chevy valves are NOT necessary, no matter what anyone believes! Even today if we needed a larger 1.550", 1.600", 1.625", etc, (not longer) we would simply order a set from our friends down at Ferrea Valves. We would order ANY head diameter we need but leave the length OEM, 4.820" (nominal). I have already used some 1.750" (intake) diameters, in my opinion a total waste of time and money!

There's one other dimension that I haven't seen mentioned, actually anywhere in any post (my own included), even past ones, but it would pertain to the valve "margins", the thickness of the face of the valves.

If you think about it for a minute this real dimension MAY play a very large role in the overall spring-height scenario for sure, follow:
most Chev valves are mfd to the original OEM specs (dimensions), with some racing valve exceptions this is true for the most part. The OEM's will normally have about an .085"/.090" (nominal) margin (especially when using Chevy exhaust valves), the Flathead's I have on the shelf here, all new, come in around .050"/.055" (nominal). This fairly large difference comes into play with the topside spring heights/pressures during the final ass'y. Technically speaking, even though the Chevy valves are listed as being approx .100" longer that the OEM Flatheads if you factor in those "margins" it makes the Chevy valves slightly shorter than the .100". You wind up "seeing" only .040"/.050" difference on topside! The final spring heights and pressures will reflect this difference.

Like I've mentioned up here numerous times we do not use the Chevy valves in any builds anymore and it's for this reason I had totally forgotten about the "margin" thicknesses. Like I stated above here, if we needed any type "special/custom" valves mfd, we simply contact the guys down at Ferrea, they will make almost any configuration we desire! We've only used these type valves on Flatheads on very rare occasions due to the cost factor, most builds here do not need these custom valves.

Now, here's the issue, when you choose the Chevy valves (with these thicker margins?) over the OEM Flatheads you WILL most likely end up addressing this difference on the topside (valve-to-head)?? Think about it for a minute, I'll use a nominal measurment between the difference on the Ford and Chevy valve margins, let's say .040" for arguments sake. If the Chevy valves have that added height sticking above the deck surfaces it MAY have an effect on the "piston-to-head" clearances after the fact. If this proves true it's just one more reason to avoid these valves. Once more, if we need some slight add'l valve length (.060"/.080" simply add some lash caps. The lash caps add to the valve length but have no effect whatsoever on the spring heights/pressures.

This possible add'l issue I mention above here is one that Casey (in the other post) may also end up experiencing, we call it "the domino effect", solve a perceived problem (believing longer valves are needed) while simply creating another, and it's no fun when your in the middle of the build with a number of (possibly) useless new parts on the bench.

I would also add this, and it will make life easy for many here, if you are considering purchasing ANY components for a decent build and I'm not talking a "repair" here, but basically a complete new build, I strongly recommend getting ALL the related parts as a single purchase, this would be with respect to a "top-end" package (like all the valve-train parts), AT THE SAME TIME. In other words, when buying individual pieces and trying to get EVERY last piece to "match" in the end is likely going to cause some grief, not sure how much, but it's what we've learned over the years. Most builders of the Flathead's should have this down to a science, all the correct parts on the first shot, it's very easy at this point at least for us.

Let me touch on regrinding previously run cam blanks, I doubt very much anyone involved in that business is going to remove anywhere near .080" from the "base-circle" (the heel of the lobes), it sounds unreasonable to me. I don't grind cams here but that amount sounds like a "stretch"? The total removed for chasing add'l valve-lift would definitely be offset using the lash caps, and again, with absolutely NO effect on the spring heights/pressures. The OEM (Flathead) installed heights would remain a constant? On the non-rotator platform this should be about 2.125" (nominal).

(Add) Casey, the valve head margins is the "lurker" I meant earlier.

Thanks, Gary in N.Y.

P.S. I will add this again, begin your build with the components that aren't going to create headaches, try to get the correct ones from "day-one", life will be much easier at that point! Another very important issue, don't be afraid to ask any shops you're contemplating using for your build ANY questions at all, if they "squawk" or seem "non-compliant", move on. I realize this is difficult in many areas due to the limited shops/builders around but I would not settle for "second-best" on any work at all. For many years we've tried to take advantage of today's technology and reverse-apply it to the Flathead platform. This is the reason we started (very long ago) with the bronze guides, it is a "positive" in the end. Same with respect to torque-plate/finish-honing the blocks, with the extremely light ring-packs used today we felt (also a while back) it was time to use these methods on EVERY build, race or not! Using this scenario the rings are literally "broken-in" on the dyno. Even without the dyno between the finish on the bore and the "new" ring material, the rings seat reasonably fast/easy.