[steve25]

Here is something that some might find interesting in regards to a 1968 small valve number 15 casting .
This head is one of many that make use of the 1.96" and 1.66" valves , but being a 80 CC head does not have the deep low comp chamber in it.
This makes the valve bowl deeper which is what you want for a modification like this.

Here are the stock Number 15 Intake flow numbers@ 28" with the stock 30 degree seat.

.050". .100". .200". .300". .400". .450". .500". .550". .600".
35.9. 73.4. 133. 169. 177.6. 180. 182.3. 183.2. -----

Here's the flow numbers when converted over to a 2.11" valve with a 30 degree seat.
.050". .100". .200". .300". .400". .450". .500". .550". .600".

38.4. 83.2. 144.3. 173.6. 181. 184.9. ----- ------ ------
Flow gain.
+2.5. 10. 11. 4.6. 3.4. 4.9. 2.6. 1.7

Picking up over 30 cfm even just up to .400" lift will net the motor 7 hp per cylinder!

Here are the Intake flow numbers for a stock 1971 big valve casting number 96.

.050". 100". .200". .300". .400". .450"
39.5. 75.8. 135.3. 177.5. 198.8. 203.7

The converted small valve head has a 7.4 cfm advantage at .100" , and a 9 cfm advantage at .200" lift.

If you ran a Cam of .500" lift or less a converted small valve head would run pretty much just as good as a head that started life as a big valve head.

Here are some pictures, note how deep the 60 degree bottom cut goes into the valve bowl!

The main restriction point as you can see from the pictures is still the same being at a Throat size of 1.498 as compared to a stock big valve size of 1.600", which is why the high lift flow numbers do not yet match or best that of the 96 castings, but they will soon so stay tuned!

The nice thing about this conversion is your machinist does all the porting for you!

[Cliff R]

They also made the early heads with small valves and 45 degree intake seats. A few years ago we were getting a car ready for Norwalk and had the 455 nearly finished. We were waiting on a set of CNC ported KRE heads and custom roller cam, but they weren't going to make it in time, so we grabbed a used cam from the back room (Crower) and a set of 1969 #46 castings from a 428 engine. Working quickly I set them up for screw in studs, ground the stock valves/seats, installed better springs and put them on the big 455.

Right off the trailer the car ran 11.92 and ran high 11's in the heat of August for the next three days. We were not expecting it to go nearly that quick, 1981 Firebird with a TH350, Continental converter and 4.10 rear gears with 30" tall tires.

I'd be interested to know how well those smaller valves test with the 45 degree intake seats compared to the 30?........Cliff

[steve25]

I don't have a head to test that on right now Cliff, but as I have seen in doing the reverse from playing around with 1.94" valves SB Chevy heads doing such you would be looking at at least a 25 cfm total loss from across the range of .100" to .300" lift with a 45 degree seat.
This could make for a loss of 6 hp per cylinder.

Also that casting number 46 my have the big valve Throat size of 1.60" which would have it flowing more air above .450" lift then the number 15 casting used in my post.

[Cliff R]

Something else to consider here is that when you look at flow lost at very low valve lifts think about how many "modern" camshaft profiles pick the valves up much quicker with shorter total seat timing. This would tend to favor 45 degree seats vs 30 if you look at the whole deal from a dynamic standpoint not static.

There are a LOT of different factory SBC castings out there, and scores more available in the aftermarket. We've never had any trouble making tremendous power with the better factory offerings with the smaller 1.94/1.50 valves in them, provided we were using the better castings right to start with. The very early heads had much "tighter" combustion chambers which actually shroud the larger valves some. Same deal with the later 305 castings. When I used to build a lot of those engines I had a custom stone for my seat cutting equipment that I'd run down and catch the edge of the chambers to open them up some to help out that situation.

This wasn't really needed for the large 76cc chamber heads that started showing up in 1970 with the 441 castings as the chambers were more "open". Those heads were sort of a trade off compared to the early higher compression 186/041 castings. They reduce the compression ratio which looses power at every rpm, but the more open chamber design helps un-shroud the valves some. They have pretty much the exact same 165/65cc port volume so flow potential is the same.

To this day folks that really know their way around SBC's search in vane for the early 441/336/487 castings for circle track SBC builds that require factory heads with the larger 76cc chambers in them for that reason........Cliff

[steve25]

Well with any head from any brand motor when you start comparing seat duration numbers numbers to max lift duration numbers the fact can't be denied that there is always more seat timing going on so the valves always spend more time open at lower lift points then at peak lift, in fact twice as much time on average then at peak lift points.

I guess my point is the a flow gain at mid lift of let's say 5 cfm per cylinder can make for twice the power increase then 5 cfm at gained at peak lift.
The only issue that really comes into play more here is that peak port velocity will take place for a longer period of Crank duration so having the needed amount of minimum port area is even more critical!

[rustyrelic]

Steve25,

Are you talking about 68 full size here?

[steve25]

I do not follow your question, what do you mean by " full size"?

[Skip Fix]

I have a set of #15s off a 70 455 I thought would always make a nice CR for a 400 with some bigger valves in them.

[rustyrelic]

Steve25,

I should have been more clear. I have a pair of #15 from a 400 from a 68 Bonneville. When I rebuilt the engine with Summit 2801 I elected to go with some 4X small chamber heads which I had shaved in an effort to recover some of the lost compression. The big heavy car even with 3:42 rear is pretty much a dog. Would hate to think I missed out by not going with the older heads.

[pmd400]

I thought all small valve heads were 45* intake seats? Iv got a '72 7j2 head in the shop now to have flow tested. I'll report back with results. They are the only head with 1.96/1.77 valves. Intake valves have 45* seats. I'm hoping to mill the heads to 85cc and clean up the bowl area for 200cfm to use on a 400 build

[steve25]

Rustyrelic, the 80 cc chamber of the number 15 casting converted over to a big valve Intake ( 2.11" ) like in your 4X heads would certainly help your lack of power.

PMD400, there where a few post 67 castings like the 15 with the 1.96" Intake valve that got the 30 degree seat, there where also a few 1972 castings that where on 350 motors that had the big Exh valve like you have.

I would do your flow test in stock form and then convert those heads over to 30 degree seat 2.11" valves.

If you follow what I did and then open up the Throat of the bowl a bit you should top 200 cfm rather easy!
I can post up seat and bottom cut dimensions of the rework I did tomorrow to use as a guide.

Skip, yes those 70 castings would be a great starting point for a 400 build!

[steve25]

Here's step 3 in reworking this casting.

I started of with opening the top of the Throat to 1.66" as you can see in the photo, I then spen 4 minutes of grinding time ruff blening that back into the bowl.
The key here is to not blend down too much at the rear of the bowl.

After this work the remainder of the Throat that was a stock size of 1.498" is now at 1.630" as it tapers down from the upper 1.66" size.

Here are the new flow numbers.
2.11" valve 30 degree seat.

.050". .100". .200". .300". .400". - .450". --- .500". --- .550". .600"
40.9----83.7-----146.2----176.9---191.3----193------196-------197
Flow gain over test #2
-1.8-----.5--------1.9------3.3------10.3------8.1-------11.1------12.1

Flow gain over stock w/ 1.96" valve.
--5------10.3-----13.2-----7.9------13.7-----15.7------18.7-----19.7

The last shot shows how deep the 1.66" template goes before the taper to 1.630" starts.

[steve25]

I had some time over the weekend for more minor tweeks so here's the test results.

This time around as seen in the first flow test I opened up the Throat more to about a 1.630" so that I could loop in ( still will not drop straight in passed the Throat pinch point ) the 1.66" template as seen in these photos down onto the top of the valve guide.

The second flow test is showing the result of doing a gasket match and cutting back the push rod pinch point.

The gasket match and blend in work on the common wall took the average pinch point width from ,901" up to .975".
The blend in work as seen in the photos needs to go in passed the push rod buldge on the common wall .
The port match picked up 8.5% more area.

Note that in all of these test so far all the porting work is still just ruff and not blended or polished in, also the valve job is still undersized , coming in at 2.034" OD for the 2.11" valve, in other words there is more air flow below .500" lift sitting here right now to be had.

Test 4 , Throat rework to - 1.630".

.050". .100". -- .200". --.300". --.400". -450". -- .500". --.550". .600". .650"
44------86.8-----148-----176.4---191.3. 193.8. -- 195. 198.4---200.7---202.4
Flow gain over stock.
8.1------13.4-----15-------7.4-----13.7-----13.8----12.7----15-----17.5-----19.2
Test 5 , gasket match.
44.5----86.8-----148.5----180-----194.6---197-----198.4---200.9--203.8----205

Flow gain over test 4 from gasket match.
.5-------=------.5---------4.3-------3.3------3.2------3-------2.5------3---------2.6
Flow gain over stock.
8.1------13.4---15--------11.7------17-------17------15.7----17.7-----20.5----21.8

As expected, no Earth shattering numbers seen by the port match at least at this level or air flow!

At this level of flow gain the port has 9.5% more port velocity over stock up to just .500" lift, this will lower a motors rpm of peak torque and HP by that same 9.5% since the main point of flow restriction is still the same in the head.

If you have a motor that is over Camed Or want more peak power but want to have better throttle response yet run 3.23 or under gears , then this is a good way to fly.

A motor that was making peak power at 5500 rpm would now make more peak power but at only 4980 rpm.
Of course if you have a race only motor you could stuff in a 9.5% larger Cam duration wise and not have to resort to steeper rear gears.

[steve25]

Here's how deep the port match needs to how on the common wall.

[Will]

Steve - you have your own flow bench?

I sure would like to see what a ported set of small valve heads would do with the original valve sizes.

[steve25]

Yes I do Will, a Superflow model.

I guess your taking power wise in your question on "see what they will do"?

If that's your question I can help you out and say that with there stock peak intake airflow level of 183 Intake cfm @28" you could make iabout 400 hp in a very well built and tuned full out race motor, I mean in terms of level of VE above 100%.

With a street motor if you ran .550" lift at the valve you could make 47 HP per cylinder on a motor of 400 cid or more.

[steve25]

For those of you wondering what the flow difference is between the small valve heads with a 30 degree intake seat and those with a 45 degree seat, here's your answer.

1968 #15 casting 30 degree seat.
1974 #4X casting 45 degree seat.

First row of numbers 30 degree, second are 45 degree.
.100"---.200"---.300"---.400"---.450"---.500"---.550"---.600"
--73.4---133----169-----177.6---180----182.3---183.2
--57.2---114.7--156.5---183.2---193.5--198-----199----201.5

The result is running the head with the 30 degree seat and a Cam of .500" lift would have you making 3 hp more per cylinder for almost a 25 hp gain overall over the 4X 45 seat heads.

[steve25]

Will, I am sorry I answered your question wrong yesterday .

A fully ported small valve post 1967 head high comp head ( tall short turn head) like the number 15 should be able to achieve peak flow numbers of 260 cfm thru it's 1.96" valve if you ask me.

I have never fully ported up a post 1967 small valve head, but I have done so on a 1965 389 cid 77 casting fitted with a 1.94" valve and yanked 252 cfm out of them and would still feel good about there remaining port wall thickness holding up on the street

[Will]

Thanks Steve, that's what I was after - what kind of flow numbers could you get with the stock valve sizes.

Based on your tests of 30 vs 45 degree seats it sure looks like the 30 degree seats would be the way to go if the heads are ported. Get the substantial low lift benefits of the 30 degree seats and increase the mid and upper lift numbers by opening up the throats and bowls. Hmm....

[steve25]

Will, like I posted the Intakes ported while making use of the stock 1.96" valve should go 260 cfm@28",on the Exh side I have no doubt that with its stock 1.66" valve size it can be ported to any flow ratio needed within reason to keep up with the 260 cfm thru the Intake side.