Ok, I'll give it a try till the pros chime in... there is almost no difference- they are D-Port heads like any other. For example, my 68HO has #16 heads just like the base 400. In '69 they gave the 400HO/RAIII a special casting #, but not much difference otherwise. There are slight differences to the valvetrain, such as HD springs and lifters, and oil drippers inside the valve covers, but these are not special cast round port heads as with RAII or RAIV. From a collector's standpoint, they are most valuable if paired with a matching engine and/or car, otherwise, there is no reason to buy them individually. From a performance standpoint, any 400 can easily be made to HO or RAIII specs by buying the cam, Long Branches, and carb.
Oil drippers are on my '68 and '69 400 birds as well, so it's not an HO/RA only thing.
Agreed, RA III heads are for restoration, not performance. A set of '68 #16 will do just as well as will any number of other castings when properly rebuilt.
Vikki 1969 Goldenrod Yellow / black 400 convertible numbers matching
There is little difference +/- a few percent across the HO RA and standard D ports from 67-72. Differentation noticed from casting flash/core shift.
Benefit? There is none unless you have expendable income.
my first reaction was very little difference for lots of money...but didnt want to stick my head out too far, and say so...LOL ..I could be wrong...have been before, but Tom proved me right this time...so now I know!
That's exactly why I threw out the flow chart. Can't argue with actual numbers..... You could say that certain heads are better and you would be right. But how much better? Not much, check the chart.
Checked the chart on the D-port heads after '67, 17% difference on the intake and 24% on the exhaust - worth doing a bit of selecting. Looks like the '70's heads (5C, 6X) are not as good on the exhaust as the earlier ones. But as they say, the tests show general trends and individual heads will test differently.
Of course a good porter should be able to even those numbers out and add another 15-20% without too much cost.
Those heads as tested were of mixed quality. Some were worn out heads with known issues, others were rebuilt. I do not believe the numbers should be taken for direct comparsion.
Vikki 1969 Goldenrod Yellow / black 400 convertible numbers matching
Sorry, I typed the wrong number, should have been 4C, not 5C. Even with the small amount of seat leakage (which doesn't matter once the valve is open) and the guide leakage (which might but is very minor), the results are pretty consistent. The authors suggest that the numbers be used for comparisons between different heads but dyno tests would be even more informative.
The 1.77 exhaust valve heads on average flow about 18% better than the 1.66 valve heads - on the exhaust of course.
Those heads as tested were of mixed quality. Some were worn out heads with known issues, others were rebuilt. I do not believe the numbers should be taken for direct comparsion.
I disagree, the numbers are good for comparison. As TOHCan points out, the heads that were tested have very minor defects. I believe it lends more to the authenticity of the chart when these minor defects are pointed out. It shows that each of the heads was put through a qualifying process before testing. The chart shows insight that we can't get from any other source but a dyno. And until someone reputable, like Wallace in this case, does a dyno chart then this is the best thing that has been published. Better than opinion, conjecture, ect. It's an awesome chart that actual testing was documented.
As it was a flow bench test, comparisons are relative only to heads tested on the same bench/same conditions.
Yes, it's a good reference. But you can't use it to compare to Edelbrock or Kauffman or other heads, nor will a particular set of the same heads test the same on another bench.
These comments are not meant to disparage Pontiac heads, I run stock heads on my cars, but instead to highlight that "your results may vary" depending on condition, modifications, bench used, setup and other factors not accounted for in the bench tests. Maybe better, maybe worse. But not likely exactly the same.
Vikki 1969 Goldenrod Yellow / black 400 convertible numbers matching
Never had a stock D-port head flowed, but seen many 67-70 heads.
Gon'a stir the pot a bite
Things i've noticed; The M/T RA heads usually had smaller chambers then A/T RA heads. Same with FB-GTO's vs big cars. About 72 vs 75 cc's, or anything in between. Had a set of 48's at 71. Even had a set of 12's at 69. 70 RA D-ports used different valves and springs then 68-69's. As of course the 67's. Each year the casting became alittle cleaner then the privous.
Yes, Vikki, you're right, you can only compare heads that have been flowed on the same flow bench. I compensate for weather conditions and calibrate my flow bench to make sure that I get consistent numbers over the years but I don't use other people's numbers directly against my tests. That's why I usually make a note of the percentage difference from stock rather than quoting the numbers.
The numbers that I have for a set of stock 48s show around 230 cfm at .500" lift, the Edelbrocks 285 cfm at .500" lift. That's about 25% better and that translates to about 50 hp on the dyno depending on the combo.
If 12^3 cubic inches = 1728 cu. in. = 1 cu. ft., and 230 cfm = 1728*230 = 397,440 divided by one cylinder displacement on a 400 at 50 cubic inches = 7948.8 cylinder fills out of a stock head per minute.
Seems to me that the intake side of a #48 head is pretty healthy already! So why the improvement in dyno results unless you head up over 8000 rpm?
Vikki 1969 Goldenrod Yellow / black 400 convertible numbers matching
My #48's flowed 170-180 and were sent to Kauffman and opened up to 230-240. If 48's flow at 230, I may as well disregard the $5000 pair of RAV tunnel ports that flowed 235 @ .600 (according to that chart)
I have flowed most every pair of Pontiac cylinder heads I have come across including a set of #37 RAI heads. All 67-71 D ports I checked flowed the same (+/- a few percent). The 37's flowed close to two pairs of #16's and 62's I have.
These were all virgin heads with stock, untouched chambers. No credence paid to seat leakage or guide wear. When I compared 4 or 5 pairs of one head number you get a mean average.
All were tested on the same bench. Maybe that bench was conservative...
Si Vis Pacem Parabellum
1967 Starlight black PMD Engineering 400 Auto 1968 Alpine Blue 400 4 speed 1968 Verdoro Green 400 HO 4 speed 2013 1LE 2SS/RS Inferno Orange Camaro.
I see I did it again. The 48s had moderate porting but stock valve sizes. Sorry for not catching that earlier. A set of '67 326 2 bbl heads flowed 180 cfm (intake) on my flow bench, same as the OHC six heads. My fully ported OHC intake ports flow 230 cfm at .450" lift with a 1.94" valve. Maybe that will help the comparison by providing some baselines, Tom.
I flow at 28" of water corrected to STP, which is now the industry standard but wasn't always. The biggest difference is usually because of a lower test pressure on the flow bench. Some were tested as low as 10". Some newer flow benchs still test at low numbers but convert to the 28" standard. I question how accurate those numbers really are but I don't have access to one to check.
Again, numbers can be most reliably checked on the same flow bench even with corrected numbers. I know my flow bench tracks quite well with the SF-600 numbers on the intake but is conservative on the exhaust, up to 17% lower at certain points.
To correct old readings to 28" from say 20", divide 28 by 20 (or whatever the old test pressure was), take the square root and multiply the cfm reading by that number.
Vikki, in a perfect world where the valve opens to the full lift number instantly and the air fills the cylinder just as fast, we wouldn't need better ports. Unfortunately the valve reaches peak lift for only a small part of the lift cycle and the air has inertia. That reduces the amount of air that actually gets through the engine using good stock heads to about 80% of what is possible at the torque peak and declines from there as the rpm builds. More flow means more go because in this imperfect world that gives the engine a better shot of air and allows more airflow at higher rpm, which is where hp is made. The right engine combination and proper intake and exhaust tuning can take the volumetric efficiency (how full the cylinder actually was) over 100%, effectively supercharging the engine. And 8000 cylinder fills per minute equals 16,000 rpm! Would that it were true!
Mid-range flow is very important! That's another thing to examine when checking flow numbers, not just the big numbers at .600" or .700" lift. I have software that shows the average cfm over the lift range as well as the individual numbers so I can see what is happening. I'll take a port that flows great up to .400" lift and then flatlines over one that only excels at high lift.
