I'm just posting this because some might find it interesting reading, and others might find it useful. Dart still doesn't offer these with the Platinum improvements in wet flow, which is a shame. They make you step up to the 200s, which isn't always good. They offer the aluminum 180s called the Pro 1 with the Platinum combustion chamber shape, and better flow, but it costs more than AFR's basic 180 without being any better. These Dart iron 180s are nearly obsolete, but here's what good porting can do for them: .100" from 55/46 to 61/53. .200" from 113/95 to 124/110. .300" from 175/129 to 181/144. .400" from 207/153 to 223/171. .500" from 228/166 to 243/186. .600" from 223/172 to 242/195. Without a length of header pipe, but with a radiused entry. To get these results you really hafta spend alot of time on the short turns of the exhaust ports, you almost can't go too far, and they are sensitive. But I got nowhere near hitting water. These heads are thick. The bronze giudes had to be replaced because they were barrel shaped inside, it only took a bad assumption on assembly and a few miles of street driving to discover this. So while they were off for guides, I flowed, ported and re-flowed them. The swirl was decent, and my grinding was a slight help.