Some folks don't think that bigger valves are needed. I really do think a bigger intake valve is needed even if you're running a stock cam. If you don't make the port any larger it costs next to nothing in low speed torque.

Streamlining the valve guide does not necessarily mean shortening it, but making it take up less space and being less of an impediment to flow.

SI Valves is supposed to sell through distributors, but I've have had them sell to me directly. Just call with part numbers.

Also, the spring retainers don't change with the smaller valve stem, just the keepers/locks.

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Joshua

and if one is not doing port / bowl work why spend the money on putting new seats in, and buying OS valves? Instead, spend that money on putting a really good seat profile on the existing seat diameter.

again, if the goal was more power at higher RPM's I would be on the larger valve bandwagon in a heartbeat.

Larger valves and a larger matching throat area will reduce velocity.
Larger valves will, because they are larger, increase valve shrouding.

here is an article with flow numbers that show, at low lifts, larger valves can have a net reduction in flow, but also look how close the flow numbers are.

https://www.castheads.com/info/gather-f ... rformance/

I have done similar tests on my flow bench with slant heads.
I flowed a 100% stock slant head, with stock valves, then flowed the same head with a lot of porting, oversized valves, good race seats.
The head with the large valves and all the port work flowed better across the board, but showed the biggest increase in flow at valve lifts above .350
To get the large valve head to flow really well at the lower lifts I had to do as much de shrouding as possible, as the bore is .084 over it was possible to do a lot to open the valve shroud a lot.
With an block only .030 over, you can't do as much.
So the bigger valves, in a smallish bore will increase valve shrouding, so why do that?

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Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

If you increase the valve size you absolutely should work the bowl area under the valve. I never said any different. Too many people go nuts in the port itself. I was advocating against doing that.

The port should not be smallest (and the velocity highest) at the valve seat. The air should slow and convert the dynamic pressure to static pressure as it turns, passes the valve and enters the chamber.

Have you tested a head with a larger intake valve and valve bowl work or did you move from stock to the more extensively modified head?

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Joshua

then flowed the same head with a lot of porting, oversized valves, good race seats.

which is a direct copy from previous post,,, so that information was there for the reading.
Josh, you are certainly a knowledgeable motor head, but I am not interested in continuing a
'chat box' debate. Maybe at some point in time we can do that over a pizza and a few beers, but lets not debate behind a key board.
The good news is Don asked a question and got some meaningful replies, perhaps we can agree there is not one single solution.

thanks
John

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Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

I do have these NOS valves coming that I won from Feebay. and I got a set of 318 valves, retainers and keepers coming from a guy on FABO.

IDK the condition of the valves and springs on the other 2 heads I have here, I'd bet that if I were to do those heads up, I'll find that those heads have at least a few valves that won't survive the rebuild.....and my kid has a /6 truck, so Id like to do up both "peanut" heads I have, and then I'll have the head off the kid's slant... so Ill still have 2 slant heads at that point....as long as none turn out to be cracked. so I don't think that these NOS valves will go to waste.... if I do buy the OS valves for the head going on this "new" engine.


Don't hate me for saying this.... but, as far as the head I'll do up for the engine in my other thread about planning a build, lots of good points raised here/ but you guys leave me more confused on "what to do" with the head for that engine, than I was when I started this thread.....
which I started asking, because I know that head prep is different between what I am trying to do here, and someone racing their engine.....

I understood that. I didn't know if there were maybe intermediate steps between stock and "a lot of porting..." Just wanting to be clear and ask if what I was proposing had been tested.
Sounds good John.

Cheers,

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Joshua

Sorry for the confusion! We have 2 camps here. John who doesn't feel big valves are warranted in a low speed 225 and me who does.

It's not that awful to swap the head. So maybe you use the NOS valves and build a nice stock-blueprint head and in paying close attention to other aspects of the build gives you find the horsepower you want. If not you can always build a big valve head and swap them.

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Joshua

Split the difference...………

Keep stock exhaust valves, and use enlarged intake valves...………
(don't need exhaust valve seats this way tooo)

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

One thing to remember is that the valves in the slant six were sized in 1959 for a 170 cubic inch motor. Chrysler did not increase the size of the valves or make any other changes to the cylinder head design when it stroked the 170 into a 225 cubic inch engine. So a 225 is starting with undersize valves before you begin modifying aything on the engine.

When you are improving a 225, anything you can do to increase flow through the cylinder head is an improvement, and improved cylinder head flow increases engine efficiency at all RPM levels. In a heavy vehicle where the engine turns low RPMs the effect will be less noticeable in the seat of your pants than if you are building a high revving engine for a light A body.

Well shucks,, those slants that did yomen low to mid RPM duty in: combines, air port tugs, fork lifts and tree shakers must have all been 170’s they could not have been 225’s because the 225’s had the wrong sized valves in them,,,

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Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

(1) build one head for the truck. Stock size valves, back cut with a three angle valve job. Clean up the bowl. Mill for desired compression.

(2) build another head for "high performance." Oversize valves, back cut, three angle valve grind, bwl hog, smooth the port.

(3) run some back-to-back tests. Drive with on ehead installed for a month, then drive with the other head installed for a month. Track fuel consumption, engine vacuum, etc..... Pick whichever one you like better.

Like I said, in low RPM use the smaller valves won't be as much of an issue. But if you are wanting to run high RPMs, the valve size is a definite issue. AFAIK, my 76 D100 has stock sized valves but it will run for hours on the highway at 3200-3500 RPM not problem. If I rebuild a head for it I will probably keep stock sized valves but clean up the bowl, smooth the intake port, back cut the valves, and do a three angle valve job. Even with 3.9 rear gears the truck will likely never spin the motor over 4000 rpm, so the stock sized valves should work just fine for me.

Quite honestly, on a low rpm grunt motor it really isn't going to care if there's a big intake valve or not. Would it be nice to have them? Sure it would, but when it's going to be a truck motor that gets used as a truck the world will not end.

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Official Cookie and Mater Tormentor.

will probably do up 2 of them anyways.... one for my truck, one for the kid's 80 stepside... that one has ~77k original, as of no NOT coming out for rebuild, but want a lil more power. and one for mine, '74 forged crank motor being built for my 85 longbed....getting one of 2 cams (both different from stock, I'm stuck on which one, discussuin for another time) on the kid's, Id like to just clean up the chambers, and have it to up the compression closer to what it should be (because that's what is "advertised" that they claim these engines came with-- though we all know better)
both will get a super 6 along the way. I have those. Exhaust for now will be stock manifold, possibly opened up somewhat/ that may change later. but not at the get go.

You need to realize the SB valves are a bit longer than stock slanty valves, like .200", there are rocker issues with that. Big block Mopar exhausts are a better tho' not perfect fit, but they work. You would need/be able to run BB springs w/the SB valves, but You need to pay close attn. to the installed ht. either way.