Loose Deep Valve Seats

[Nashfan]

Three valid points made ---

The seats have to be installed correctly.

ANY seat can come loose if the head is overheated.

The head aluminum alloy was O.K. for the era, but if you look up the specs it isn't as "robust" as today's alloys. Heat cycles (and anything over about 450F is going to be more detrimental) deteriorate the alloy strength. In theory the heads could be heat treated, but it requires knowledge of the Corvair head I have never seen presented.

I've never understood using 140HP heads for turbo applications. Yes they flow more, but doesn't a turbo overcome pumping losses of the small valve heads? The 140HP head has less material around the BIGGER valve seats and that isn't good for dissipating valve and seat heat. The other thing is a turbo boost needs HEAT to be retained in the exhaust flow and the bigger 140HP exhaust manifolds work contrary to this (larger surface area dissipates more heat). Look up boost pressured vs. exhaust heat. The more heat you loose out of the exhaust gases the lower the boost pressure.

Just my --- Feel free to disagree POLITELY.

The reason for using 140 heads for a turbo application is exactly because they flow more. To be a little more precise, they flow 50% more in stock form. The result of the extra flow is: more power at the same boost level or less boost is needed to make the same power. An extreme comparison- Crown MFG got 290hp out of small valve turbo heads at 30psi at the flywheel. This same hp was achieved at the rear wheels with ported 140 heads EFI + a roller cam and a very NON STOCK exhaust system. That engine only needed 18psi to get to the same hp. Theres a video out there of this car running on an autocross track... the boost response is lightning quick. The owner reports it feels every bit as quick as having 300hp NA V-8 in it. It also sports a 3.89:1 ring and pinion. Hope this puts an end to the silly myths out there about having to have a restrictive exhaust and tall gearing to make a turbo react quick!