Real World Flow Differences 2.08"/ 1.74" Valves vs 2.14"/ 1.81" Valves " Pictures Added"

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PROSTOCKTOM

PROSTOCKTOM

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I have a set of 452 heads that I took off a 470" engine we raced. They have 3/8" stem 2.08" /1.74" valves in them. The heads have had a serious amount of porting done and we moved the short side radius way over (offset rockers and epoxy), roof raised .350". This engine ran 5.60's in a 2100# foot brake door car in the 1/8 mile, turning the engine 7,000 rpms. No idea what they flow as it never mattered to us. When we built a 526" engine we used the same cam we had in the 470" engine, but used Edelbrock heads built the same way as we had done the iron heads. (offset rockers, epoxy). The new combination runs 5.40's, but we only have to turn it 6400 rpms. So the addition of 56 cubic inches, larger valves, and improved combustion chambers obviously helped the power production a bunch at 600 rpms less.

Fast forward 10-years and I decided to use the iron heads on a 499" engine I am building. The guides need some attention, so I am going to change to 11/32" and install new pro-flow valves. Since I couldn't find any 11/32" stem 2.08"/ 1.74" valves I had to buy 2.14"/ 1.81" valves and planning on cutting them down. Then I got to thinking about if there was really anything to gain from running them as is. This set of heads are a proven power producer and no doubt have tremendous air speed through the ports. I really don't want to mess up a good thing, but was really curious if I should maybe use the larger valves or leave a good thing alone. I probably wouldn't use the exhaust valve at 1.81" because I don't believe that matters as much as the intake size might possibly make.

So I am looking for hardcore data on what I might possibly gain.

Thanks,
Tom
 
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Don't write off a good exhaust valve. Look at factory Max Wedge heads with the biggest exhaust valve ever! I think there is a formula that shows exhaust needs to flow 75 or 80 percent of what the intake does. That said, Dwayne Porter may have the answers you are looking for. Good luck.
 
:popcorn: Got any pictures of the heads and the porting work? I certainly can't see a set of 2.14/1.81 valves hurting anything with the addition of matching bowl and chamber cuts.
 
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I guess I can't help much but I smile thinking about all the 2.25/1.81 valves I installed in 452 and 906 iron heads and then someone worrying about 2.14/1.81 valves. I didn't really know what I was doing, I just did what I wanted to do and whatever happened....happened.
 
All the data you need is in the intake valve's curtain area.

A larger diameter valve with dimensionally larger valve job potentially flows more mixture at any given lift point until port stall - all things being equal; i.e. no concern about shrouding, interference with exhaust valve.

This isn't a cylinder head specific bit of data, but a universal geometric one. I brought a visual aid that should help. All you need to do is increase the diameter of the valve to see that the curtain area increases as mixture only flows around the OD of a poppet valve. If need be I can demonstrate the actual math involved. Hope this helps.

On Edit: Forget about the choke smokescreen as we are only evaluating the valve curtain area here. I should have grabbed a different graphic, but all the others I have are covered with equations.

ValveSeatDwg.jpg
 
We never changed intake valve but did do the 1.88 max exhaust, picked up 3 tenths in the 1/8th. Now if it was because the seat was opened up or what but it did work. This was when everyone was pushing the 2.14-1.74 valves. (906 head)
 
I am almost never satisfied with not knowing why an experiment succeeded, failed, or showed no change. Teasing out the reason(s) for the outcome(s) can be incredibly valuable on their own, but that type of consideration, applied to all things, will help a person avoid charlatans wherever they may be.
 
Installing the larger exhaust valve in the factory iron head allows you to make some significant radius changes on the exhaust floor right off the seat. The Trick Flow head has an excellent exhaust port and runs a smaller 1.76 exhaust valve effectively.
 
Good exhaust ports...well...
Smaller throat and radiused.
Bigger valve, as mentioned will allow that.
You can 'with a big block dodge' apply that to the intake side in regards to the bowl shape. Sometimes it's not higher flow # as it is quality of airflow.. other times not.
What's it doing past the valve and how is the ssr/bowl effecting that. Certainties hold a tight set of ingredients/guidelines to be just that...but mostly...its still learning and unique to the mods done and that particular combo. I know ...blah blah blah... right.
 
MOPAROFFICIAL said:
I'd like to hear from more people how fast they are going with a 2.08/1.74 valve in a 906 head.
Click to expand...
1979, 11.60s 118 1/4 3000 pound Duster, with me 3160. 383 auto St. Hemi vert 4.88 gears. Stock valves in the 67 head, back cut intake with a file on the drill press, no port work. According to one calculator it was 400 HP
 
My .02, and keeping this strictly in terms of factory BBM iron heads........

Provided the port work in the runner is adequately sized to keep up with the addition of a bigger valve(and the SSR is shaped to help curtail flow separation with the bigger valve) ...... and that the throat percentage between the two valve sizes will be retained....... at something in the .700” lift range for a flat port head(346/902/452)....... I’ll call it a 5-10cfm gain going from a 2.08 to a 2.14.
With a 906, the gain will be similar but will often occur at a lower lift, then just flat line from there........ or might even lose a few cfm at the higher lifts.

This would be for what I would consider a “normal” porting job.
On a “max effort” head, the results could be way different.

On something like in the pic(this is a 346 head), a 2.08 would be low/mid-270’s....... a 2.14 would be low/mid-280’s.

For the lesser ported heads, and under .600” lift combos, the bigger valve doesn’t change the “big number” that much, but really improves the area under the curve.
(This assumes some amount of blending/porting will be done with either size valve.
The outlier to that are 915 BB heads. The chamber walls are closer to the valves than the open chamber heads, so without chamber mods to accompany the larger valves, you may not see any appreciable gains until the valve is up past .300” lift or so.)

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PRH said:
My .02, and keeping this strictly in terms of factory BBM iron heads........

Provided the port work in the runner is adequately sized to keep up with the addition of a bigger valve(and the SSR is shaped to help curtail flow separation with the bigger valve) ...... and that the throat percentage between the two valve sizes will be retained....... at something in the .700” lift range for a flat port head(346/902/452)....... I’ll call it a 5-10cfm gain going from a 2.08 to a 2.14.
With a 906, the gain will be similar but will often occur at a lower lift, then just flat line from there........ or might even lose a few cfm at the higher lifts.

This would be for what I would consider a “normal” porting job.
On a “max effort” head, the results could be way different.

On something like in the pic(this is a 346 head), a 2.08 would be low/mid-270’s....... a 2.14 would be low/mid-280’s.

For the lesser ported heads, and under .600” lift combos, the bigger valve doesn’t change the “big number” that much, but really improves the area under the curve.

View attachment 1715972488

View attachment 1715972490
Click to expand...

My heads have had a serious amount of porting done and removed the short side radius (pushrod protrusion). The side wall is now straight all the way in (offset rockers and epoxy) and the roofs are raised .350".

Tom
 
My heads have had a serious amount of porting done and removed the short side radius (pushrod protrusion). The side wall is now straight all the way in (offset rockers and epoxy) and the roofs are raised .350".
Click to expand...

Obviously your heads are far beyond what is typically done with factory castings.
Therefore, I wouldn’t consider whatever results were gleaned from valve testing on heads that weren’t configured like what you’re working with to be valid.

In my mind there’s only one way to know for sure what a larger valve would do in those heads........ and that’s test it and see.

I see the questions as........ how much more flow would you need to see to make the bigger valve worth the effort?
And....... does that seem like a realistic expectation?

From the configuration you’re describing, I’d expect a bigger valve could be worth fairly significant gains.
I’d probably go bigger than 2.14” myself.
 
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Trying to get quality photos shining a flashlight at them is an issue. I shot one of a stock intake port vs the ported intake (reflection and shadows is killing the ported image) and the camera angle isn't helping either. They are actually much better looking in person than the photos shows. Also the intake face has been flat milled on the ported head, so it's a little confusing to look at and realize just how much has been changed.

As you can see in the photo of the stock port the pushrod area kills the port width. I took some quick measurements for reference between the two.

The stock port opening measures 2.17" x 1.14", but quickly necks down to around 2.05" x .900" because of the protrusion. Removing that area and using offset rockers really opens it up.

Ported head at the opening measures 2.575" x 1.17" (The roof is raised .405", not .350" like I thought it was) and does not neck down any longer in the pushrod area, so there is a huge improvement in port volume and flow. The floor is stock as cast and you can still signs of that.


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Tom
 
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I don't know about flow numbers however I went from stock 906's, to Hauser what he called stg 5 BV 906's on my 440-6 bottom end with a Dom Team G, 850DP, and a .650/.650-290@.050 CC sft cam, 2" f/wells. Stock heads went a best of 11.2@118+ to 10.71@125 with the BV 906's, no other changes apart from HS r/rockers.
 
I’ve never tried opening up the port opening on a stock BBM head like what the OP has done, so I have no idea how that would impact the flow numbers on otherwise unported, mildly ported, or heavily ported versions.
(I guess that’s where the flow bench comes in handy)

But I do know the std port opening itself is big enough to support nearly 360cfm........ which I have gotten out of std port Victors without making the port openings any bigger than how they came ootb.
 
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