OVAL PORT VS RECTANGULAR PORT HEADS -- Racepics.net's Heads Up Racing Association

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Date Posted: 21:59:24 05/11/03 Sun
Author: Undercubed
Subject: OVAL PORT VS RECTANGULAR PORT HEADS

We performed the flow tests of both heads on the exact same SuperFlow flow bench. He also performed the port work on the heads. So variables are kept to a minimum. I don't think you'll find a more appropriate "apples-to-apples" comparison. Here is his description of the work done on the heads:

The rect ports were, in my opinion, "mildly ported". The intake runners were gasket matched, the valve pockets were smoothed out to the runners, and both short sides were cleaned and smoothed... and of course any casting lines were smoothed. There was probably room for some improvements on them but not without removing a bunch of material. I was already concerned with them being 320cc on the intakes that the motor was going to be lazy so I didn't want to make them any bigger. Besides, the only gain was going to be at .600" lift and above. The low lift flow #'s were low and I knew it would only get worse with volume.

The oval port intakes were gasket matched to a Fel-pro intake gasket and was blended back about 2" into the stock cast port. Under the intake valve was blended in the same fashion (out to the stock port) to the full size of the valve right up to the seat. The short side was touched to nock off the high spots. Just the basic bowl blend / gasket match to me. The exhaust was bowl blended to the seat size and down into the stock port as well. I spent some extra time on the short side here. The short side was smoothed and radiused very nicely right up to the seat... and I'm talking less than 1/32nd from the seat and polished as well. I took some material off the top of the exhaust guide and blended out to the roof of the port also but the guide still had an obvious flat spot to it. Both intake and exhaust valves were relieved in the combustion chamber area the same amounts.
intake flow
Rec----Oval
.100" 66 73.1 +7.1
.200" 127 140.2 +13.2
.300" 184 211 +27
.400" 234 273.2 +39.2
.500" 284 302.8 +18.8
.600" 319 315.3 -3.7
.650 331 313.8 -17.2
.700" 301.1 - n/a

exhaust flow
rec--oval
.100" 55 60.8 +5.8
.200" 105 107.7 +2.7
.300" 134 139 +5
.400" 161 165.2 +4.2
.500" 183 186.4 +3.4
.600" 199 202.3 +3.3
.650" 205 208.4 +3.4
.700" 216.5 - ?

As you can see, the numbers speak for themselves. The oval port heads kick butt up until .650" lift, then the rectangular ports take off. The majority of all street/strip or weekend warrior applications are not running over .650" lift cams. Also, you have to take into consideration that the valve is at max lift at only approximately 8% of the time. So, low and mid lift flow numbers are VERY important. That's where the oval port heads really stand out. Technically, there is no winner or loser. It all depends on the application. This is excellent information to prove that oval port heads are the best choice for "milder" applications that are under 500 CI and have a max RPM in the 6500 range. No doubt, the rectangular port heads have their place. They are the choice for ALL-OUT performance. But for less radical combinations, the oval ports are the choice.

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Replies:

Heads -- Bryan, 18:26:47 05/12/03 Mon
- Its hard to understand the chart i attemped to make. If you look at the attempted chart you will see that it shows the ammout of lift then the flow # for the rect ports then the # for the oval ports. Rectangular ports came alive from around 650 lift and higher,Under 650 lift oval ports out flowed but not by much. -- Undercubed, 21:51:35 05/12/03 Mon
  - MALI'S BEGINNING.... (NT) -- JEN, 14:53:00 05/13/03 Tue
    - Mali's beginning.... -- Jen, 14:57:09 05/13/03 Tue