My '90 Integra is blowing white (unburned) smoke under hard acceleration. You can't see it any other time, but get hard on the gas and there's a big whitish smoke screen out the back.

Someone thought it might be worn exhaust valve guides, except I don't think there's a lot of vacuum in the exhaust ports when hard on the gas to draw it out, is there?

Is there any kind of bypass or w.h.y. that could be causing the problem? Engine is all stock, about 120k miles on it. Any ideas?

Thanks!