Both the fat Koyo and SD will require some trimming of the fan shroud to clear the swaybar. The Koyo can use stock hoses, trimmed. The SD will need some aftermarket hoses, at least the upper. The Koyo uses the stock radiator 'ears'. The SD does not, but requires a bit of finagling to get in place as it uses 'all' of the real estate available. The SD is probably 10-15% better than the Koyo in terms of cooling. Given the price premium of the SD, and the fact that you are in the PNW, are you sure you need it? That 10-15% is critical down here in Socal as ambient temps can reach 110 or more in the summer and early fall races.
Car #: 94
Year : 91 Posts: 971
Mark, unless you plan to bump draft for laps on end in the heat of the summer, I'd get the thick Koyo and save some money. It worked great for me for years. When it came time for a new rad I decided to try the SD. The SD will still get hot under those conditions but it takes a little longer and seems recover a little quicker than the Koyo.
Region: NWR/Oregon; ICSCC
Car #: 70
Year : 1991 Posts: 1111
I have vague memories of putting Bruce's fat Koyo in my car at the July races at PIR when I was overheating, and not finding it to be a problem. I'll let you know how this one goes in when it and the hotter weather arrive.