I have a hi-po '70 440 and it does not have 10:1 compression. I believe it's 9.25 or 9.5:1. Mike Sutton and others would be more likely to know the various compression ratios. I've never even had the valve covers off, so it hasn't made much difference to me. As far as hopping up the 400 I don't think he can use the same intake manifold. The carb sure. The cam and heads are interchangeable. That's how they made Road Runner 383, but the intake won't fit. _________________________________________________________________ Take advantage of our limited-time introductory offer for dial-up Internet access. http://join.msn.com/?page=dept/dialup