Flathead Valve Question?

[delaware george]

i have been seeing ads for oversized valves for flatheads and got to wondering...they say there is no need to change the stock seats..so would there be any benefit to this?..if the hole or seat is the same size,how would a larger valve flow more air/fuel?...getting ready to buy vavles for my 8ba,30 over,isky cam..and there doesn't seem to be any real price difference between the oversized or stock...any suggestions? thanks

[Bruce Lancaster]

I think what that means is that there's enough metal in the stock hard seat to bring it out to a 1.6.

[delaware george]

i saw them in hot rod and custom supply's catalog....they said no machining required

[Digger_Dave]

My engine is using 1.6 Chev valves in both intake and exhaust. The Chev valves "drop in" as long as you have adjustable lifters. The valves don't need any machining you just use the Chev valve retainer pieces.
I went a bit "overkill" by putting bronze sleeves in the valve guides. I used the type that are "knured" inside the guide after reaming them oversized.

Another trick I used is to put a valve, guide, spring and retainer in place; then marking where the floor of the "runners" (intake and exhaust) meet the valve guide; then take the guides and radius the top of the guide in a lathe. Stock Ford guides stick up in the runner passages.

As far as the seats go, I replaced both intake and exhaust with GM stellites. The block needs to be machined for the seats to be inserted in the block. The machine shop (automotive) that did my seats, machine the seat "pocket" slightly undersize, then put the new seats on "dry ice" (makes them shrink) and then drop them in place.

The intake seats don't NEED to be hardned, but the old ones were badly corroded, so replacing them all was the easiest way to clean them up.

Following Av8's porting instructions, allowed for a better flow coupled with the larger valves.

[Kevin Lee]

Did it actually use the words larger valve or did it say something like "high flow" or something similar. My point is maybe they just took material from the stem and claim better flow, more cfm, etc. with no machine work to the block. Just a thought. Removing material from the top of the stem is a common modification isn't it?

[delaware george]

that's probably it grimlok....i wonder how much of a difference they make

[Bruce Lancaster]

There is a lot that can be done on a valve grinding machine in the way of back-cutting, shaping the lip of the valve, narrowing stem, etc. as well as the work that can be done on the seats themselves on a seat grinder. There is lots of (350 chevy based) info on this in Vizards book on chev cylinder heads. The trick is to hold the book upside down so the pictures make sense on a flathead...
There are so many bottlenecks on a flathead that I think only a concerted attack on everything at once would be effective--enlarging the valves would likely do very little without working everything else in both tracts, and some of the modifications are of controversial effectiveness.
Philosophical issues out there as yet unresolved:
Relieving on relatively small engines, flow around back of valves, effects of 30 degree seats...
I suspect, based on lots of reading but absolutely no actual flowbench or dyno testing, that flow around a flathead valve is completely different than Yunick's description of flow around a good OHV valve both because the pocket is too small and shallow to allow the air to turn properly and because so much exit area is seriously shrouded.

[porknbeaner]

Maybe they don't consider a valve grind to be machine work. You can't even go back in with stock valves without a valve grind/machine work.
Probably what they mean is that you don't have to do any major mods to install the valves. If I went with oversized valves, I wouls at least blend the bowels (flatheads have bowels under the valve right?). But that isn't considered machinework.
Or else I'm totaly mistaken in which case disregard everything I just said.

[Smokin Joe]

BTW, the 1.6 Chevy valves are better and CHEAPER than the stock 1.5 Fords. I had to have new seats for mine due to corrosion anyway. With a flatty, I think anything you can do to improve flow will help. That air/fuel has to go thru a lot getting into and out of a flatty.

[286merc]

I cant see any reason to go 1.6" in a relatively mild engine, just makes the machinist richer.
1.5" Chevy performance valves are what most use for unblown street driven and they are a heck of a lot cheaper than Fords. Minimal work to stock Ford seats to use also.

The money you saved now will buy a nice air die grinder so you can get those exhaust ports opened up. Thats where you will get a big flow improvement, especially the end ones.

[delaware george]

i'm thinking the stock valves...was just wondering..the machine work is done and the exhaust ports have been opened and the block was releived before i got it....thanks for all of the input,i don't think i'd ever be as far on this project without all of your help...wonder how long it took people to learn all of this years ago? http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif

[Digger_Dave]

[ QUOTE ]
I cant see any reason to go 1.6" in a relatively mild engine, just makes the machinist richer.
1.5" Chevy performance valves are what most use for unblown street driven and they are a heck of a lot cheaper than Fords. Minimal work to stock Ford seats to use also.

[/ QUOTE ]

I should have added that my engine has a SCoT blower on top. I was looking for all the improvement I could find. So the 1.6 Chev valves were the easy way to gain that last little "poofteenth" as carps would say.

Then add the crank that Av8 is "carving" for me, should allow for some extra "R's."