Quote: The 273 heads will have less velocity because they have a slightly larger port volume. Not that they would be a bad choice for that reason, they would make less pumping losses. That is also a reason for me to consider the magnums, I have a set of them and the 273 heads but no 302s...
I called my buddy that owns the flow bench. He recalls the velocity was greater on the 273 head vs the swirl port. He's going to pull it up on the computer and I'll post the numbers. Also remember that with the magnums you'll need the corresponding valve train and intake in order for the heads to work. There will be a lot of port mismatch with a Magnum/273.
Here are the numbers off my head. i tried to scan the test data but it wouldn't show in color and was impossible to read. I'll try and explain what is depicted on the sheet.
Used a 302 Swirl port vs the stock 273. both had the same modifacations except we stayed with the stock intake size on the 302 and only modified with a stainless valve. The 273 used a cut 1.88 stainless valve down to 1.84. We found this size ideal for the 273 to prevent shrouding.
First test
273 with a 1.84 intake, 1.56 exhaust with alittle bowl work Same on the 302 except larger intake and exhaust valve. 113% max velocity on both heads
2nd test
273 head with same mod with the addition of more port work, 70 degree bowl cut and 3 angle valve job. 302 the same, both had Ferra valves
Gained 116% on the 273 and 115% on the 302
1st test
The flow numbers showed a big differance with the 273 showing max flow of 166.9 cfm at .400 of lift with the flow curve remaining steading and not falling off until .475 of lift.
The 302 however showed a max of 161.8 and started to fall off at around .500 lift
2nd test
273 showed 169 cfm at .450 lift where the 302 showed 163 cfm at .450 then dropping off.
273 and 302 had the same modifacations.
what bore was that tested on, a 273 bore, or a 318 bore, or a 4" (360) bore?
Got an answer for you. They were tested on a 4" bore plate
