An article in the September 2000 issue of GM High Tech Performance prompted me to put this together. They have quite a good analysis of a number of different heads, both aftermarket and GM, for the 350 CI small block motor. Twelve different heads were tested: Edelbrock Performer, AFR 190, AFR 210, World Products Sportsman II and SR Torquer, TFS 23 degree and Twisted Wedge G2, GM L98 Vortec and Fast Burn, Holley SysteMax, and a stock GM LS1 casting. All were tested on a flow bench for intake CFM, exhaust CFM and swirl RPM for a variety of valve lifts. Additionally a friend of mine (Grant Griffiths) took this data and graphed it against the other heads for an easy intake and exhaust comparison. Below is the information as it was presented in the magazine article. I take no credit or responsibility for the information or comments that are presented. All information below is presented as taken from article.
All the heads were flowed the same with the same extensions used for all the heads. This way the comparison numbers were indeed accurate to compare one head against the other. The only exception is the GM LS1 head, since it is a much newer head and designed for the newest type of fuel injection its ports are not the same as the rest. It was tested as close as could be to the other but it must be kept in mind that it was not exactly the same.
Brodix elected to not take part in this survey and did not supply GMHTP with a sample head. All heads were flowed on a SuperFlow 600 flow bench by the students at Northwestern College in Lima Ohio. One must remember that even though a flow bench is a good measurement device, it does not depict the actual airflow through the engine. Inducing turbulence in the combustion chamber causes the flame speed to be much greater and has been accepted to vary from 10 to 25 meters/second (compared to a normal rate of 0.5 m/s) This turbulence will be generated during both cylinder filling and compression. Swirl is similar to water going down a drain, in a cylinder it follows the perimeter of the bore. The other product of swirl is tumble, with the charge following the wall and then hitting the piston crown and rolling back up. To detect swirl and turbulence an Audie Technologies swirl meter was used, installed between the bore adapter and flow bench. It measures the mixture motion in RPM and has a very low friction coefficent wich allows very high reading with exuberant motion.
A wooden radiused inlet was made by the students and sized to the standard intake gasket dimension. This way shear was eliminated and more accurate flow numbers could be obtained. A slightly larger inlet had to be made for the AFR 190, AFR 210 and TFS Twisted Wedge G2 since they support an enlarged intake runner. The same type of setup was constructed for the exhaust port using an old set of 1-3/4 inch headers. To open the valves a Brezinski valve opening fixture with a Starret dial indicator was used.
Since the poppet valve spends more time traversing its lift that at the maximum lift, measurements were taken to see the results in this traverse period.
The clear winner of the group was the LS1 head by far, but it cannot be adapted to an older style block. It was included to show how far pushrod technology has come.
The next two charts are the inlet and exhaust flow in CFM per square inch of area versus the valve lift. Even though the lines are close together a small change make a large flow difference. Notice how far above the LS1 is in intake, with the AFR 190 and Vortec head coming in for a near tie in second. Hopefully if you are planning on upgrading your heads a look at this will help you make the choice that is right for you both engine wise and budget wise.
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