690 exhaust flow numbers?

[jim_ss409]

Does anybody know how much 690/583 heads will flow on the exhaust side? I've read that the intake will flow about 260 cfm stock and maybe 280 ported but I don't think I've ever seen any numbers for the exhaust.

 

[models916]

some numbers

Back in the late 60s I had gotten some flow number from SpeedCraft in Franklin Park Illinois. I know they flow tested their own stuff back then. The numbers I have for stock exhaust port on 690 head is: 170 open flange, 181 with a pipe. Not sure how accurate this stuff is at this point, but at least it seems reasonable. I am not sure if they had Serdi 3 angle valve job or just as ground stock.

 

[jim_ss409]

If you use the 181 cfm figure for the exhaust and 260 for the intake you come up with an intake to exhaust ratio of a little less than 70%. That's not bad but they say that 75% is a better number for maximum performance. So, if you ported the intake side and got about 275cfm you'd want to aim for about 206 on the exhaust side. It might be hard to get that much flow, especially on the two centre ports that are lower.

 

[Skip FIx]

I flowed the intake side of my 690s on my bench a few years ago.I think they were closer to 250 on my bench. I had also heard they are like the Vortec SBC head ,often porting looses flow.