[steve25]

So I have two sets of 47 castings to port up.
One set had been fitted with 2.11” intakes and 1.77” exh valves .

The set I am posting up the flow results from the pair that still have there stock 1.96” intakes with a 45 degree seat and there stock 1.66” exh.

The exh numbers this head produced yesterday out of a end port where so surprising that I repeated the flow test again today to rule out fluke numbers that might have happened.

Note that the 47 casting has a date code of A 21 9, while the other head is this pair has a date of L 10 8.

Here are the stock flow numbers from this end port in the first column, and in the second column are the flow numbers from a stock 1971 96 casting with its 1.77” exh valve.

It’s too bad these 47 casting where not made with a 2.11” valve.

Flow @ 28”

.050”. 42.7
.100”. 62. 50.2
.150”. 86.5
.200”. 111.8. 95
.250”. 132.2.
.300”. 148.6. 128.2
.350”. 158.6
.400”. 167.4. 158.4
.450”. 174.3. 152.9
.500”. 180.3. 161
.550”. 184.2. 163.7
.600”. 188.2. 166.4

[ponjohn]

What are the goals for each pair of heads?

[steve25]

John the heads already fitted with the 2.11" / 1.77" set up are off a rebuilt and running 428 that's currently breathing thru hp Exh manifolds and a SD performance ported iron Intake.

The owner would like to have 500 hp to play with so with the Cam he is running these heads will need to flow 260 cfm by .550" lift.

The other set of heads are off 350 cid motor.
The owner will be swapping the 2 bbl Intake for a iron Q-jet Intake.
I am planing on keeping the stock 1.66" Exh valve and going up to a 2.05" Intake.

I figure a Intake flow gain up to 235 cfm will provide a nice power gain and without a major increase in port volume so it will still have great street manors.

[Cliff R]

A few years ago we built a pretty standard 455 with forged rods and Ross pistons. It was supposed to get a cam and CNC ported KRE heads from Dave at SD and be done in time for the Tri Power Nat's at Norwalk. When we found out that SD wasn't going to have the heads and cam to us in time I walked over to a shelf in the parts room and pulled down a set of 1969 #46 castings with the small valves in them.

They got a quick clean-up, ground the valves and seats (45 degree intake), drilled/tapped the end exhaust bolt holes, and replaced the pressed in studs with screw in studs. I had a slightly used Crower cam in the back room and quickly installed the cam (straight up) and the heads. The heads were not ported anyplace, not even a port match to the stock intake gasket.

We finished out the build with a 1978 Olds Q-jet and factory HEI distributor.

We were excpecting much from the car (1981 Firebird) at the track, just wanted to make the event with it. To our surprise it ran high 11's right off the trailer without any tuning anyplace. It continued to run 11.80-11.90's all weekend in the heat of August weather here in Ohio.

I've seen cars not run that quick with very well prepared and ported iron heads in similiar set-ups.......FWIW.......

[steve25]

Thanks for passing along that story Cliff and its interesting to see empirical first hand results .

The simple cut in stone fact is that in terms of the overall performance of any given engine combo that having too much air flow available that your NOT making use of detracts more from the average power curve of a motor then not having enough air flow to reach your hp goals!

The stock Intake flow of those #46 castings you ran that weekend was enough to make a honest 380 hp at the flywheel if you where running enough valve lift to access it.

[rohrt]

I would be curious to see what porting would look like while still keeping the 1.96 1.66 valves. Mostly due to porting a set of #15 that I want to use on a 400.

[steve25]

Rohrt. I sent you a pm.

[Cliff R]

A HUGE contributor to running well at the track is how the car is set-up. My example above shows that the engine simply becomes a small par t of the big plan when it comes to overal vehicle performance.

The vehicle the 455 with the stock #46 heads on it went into had 3.90 gears, TH350 (prepared here), and a custom built converter. It was finished off with wide DOT tires and hooked SOLID at the track. Some some food for thought to those building high HP engines and spending a TON of money on heads, roller cams, big intakes/carbs, bug zapping ignition systems, etc.

We were able to put that car solidly into the 11's with a "basic" 455 engine build using small valve heads that were untouched other than some good valve/seat work. Those heads also made high compression on the 455 build, another BIG contributor to running well at the track.

Even with all that said it clearly show us that you do NOT need to spend a butt-load of money on factory or aftermarket heads to have a strong running car. #46, 47, 15's and other small valve Pontiac "D" port heads have long been tossed aside by folks looking for the factory "high performance" big valve heads instead. Here I'd rather have a set of small valve heads as they can be bought dirt cheap and I'm working with "virgin" material when opening them up for 2.11/1.77 valves to keep them all at the same height and chamber volumes equal at the same time.......FWIW......

[neill]

Hi Steve, with the intake valve upgrade on the 47's will you be staying with the 45 degree seat?

[Gary H]

Originally Posted by steve25

So I have two sets of 47 castings to port up.
One set had been fitted with 2.11” intakes and 1.77” exh valves .

The set I am posting up the flow results from the pair that still have there stock 1.96” intakes with a 45 degree seat and there stock 1.66” exh.

The exh numbers this head produced yesterday out of a end port where so surprising that I repeated the flow test again today to rule out fluke numbers that might have happened.

Note that the 47 casting has a date code of A 21 9, while the other head is this pair has a date of L 10 8.

Here are the stock flow numbers from this end port in the first column, and in the second column are the flow numbers from a stock 1971 96 casting with its 1.77” exh valve.

It’s too bad these 47 casting where not made with a 2.11” valve.

Flow @ 28”

.050”. 42.7
.100”. 62. 50.2
.150”. 86.5
.200”. 111.8. 95
.250”. 132.2.
.300”. 148.6. 128.2
.350”. 158.6
.400”. 167.4. 158.4
.450”. 174.3. 152.9
.500”. 180.3. 161
.550”. 184.2. 163.7
.600”. 188.2. 166.4

That's difference is pretty incredible. Is the port shape or valve bowl area noticeably different between the two?

[DaleO]

This thread is really good for me as it has redirected me on a plan I had. I am running a 1969 400 with 46 heads which I was planning to replace with some rebuilt 670's and HO manifolds I have. Seeing what the 46's have done on a 455, and considering the smallish cam and engine I have, I can see it would be unfruitful for me to make the swap, at least from a performance standpoint. Thanks for saving me $!

[steve25]

Gary I can not do a physical comparison for you since the flow test I used from my files on the # 96 casting was from 1998 and I currently do not have a 96 casting to pull off my shelf.

I will take some dimensions and photos of the 47 casting on Monday and post them up for you, then you can relate them to what you have.

These flow results that I posted also show very clearly how especially if your racing in a class that calls for totally stock ports that having more then 2 sets of heads to flow test could turn up a much better power producing casting with the same part number.