iron heads for a 408?

GTXperience said
Hey BJR,

Is this a general rule of thumb for a 408? Are you talking about an "all out 408" or a street/strip version? I am very interested in your thoughts re: this. I am coming up on now choosing the heads for my 408 and am still trying to figure out the best route to go for my application.

TIA.

GTX,
Sorry for not getting back to you before now as I've been very busy. This would be a street strip version as for all out racing you could go up to 20% more in port volume and flow. The port size and flow is all in relation to piston speed which is determined by rod length, shorter rods faster speeds and longer rods slower speeds. Short rod engines need larger ports and more flow and long rod engines need smaller ports and less flow. As the differences in the BBC and the BBD, the BBC has a 4" stroke and 6.135 rod and a 290cc port in a 990 square port head and the 440 BBD has a 6.768 rod and a 182 cc port in a 452 head. Yet the power is similar and the Tq. also.

The optimum crank angle is 10-12* past TDC for best Tq and Hp. This is where the rod ratios come in play and this is why Mopar likes a 1.80-1.85 rod ratio. And I know someone is going to say well the 360 is 1.72 rod ratio, this is true and this is why you have seen alot of these engines in trucks and vans and large passenger cars as the rpm's would have been kept lower. The only way to help this out in a larger stroke engine is to move the piston pin location, but this can get expensive.(custom pistons)

My 404 ci engine needs a 196 cc port runner and 315 cfm's of air flow, the heads that I have on it are 184 cc's and flow 316 cfm's with a 2.08 valve but this is a BBD. If you can get the flow without haveing the port volume then the engine will respond better and ET quicker as port velocity will be better. And this you'll see in the 60 ft. times.

The heads that I would use on a 408 would be the 190 or 177 commandos, if you can afford the 190's this would easily get the job done and get the flow that the engine would need. I did a set of these and they flowed 324 cfm's and were 196 cc's with a 2.02 valve. A smaller head would give more Tq and low rpm Hp which is more desireable for street, something like a head in the 160-170 cc range and flows like 270-290 cfms @ .600 lift. This would mean that the low lift flow #'s would have to be very strong, something like 170/220 @ .3/.4 lift. Hope this helps you decide on what you want for heads.