There are different breeds of both. The 2V open chambers were on the H-code engine and are very streetable and can run on low octane gas well. They have a lower torque curve, so you will be seeing your power band alot more in daily use. 4V heads, open or closed, make gobs of power, just higher in the band, usually above 3500 RPM. Its commonly accepted they aren't as streetable as the 2Vs for that reason. The best by far is the Aussie 2V: a 2V head, closed chambers for high compression, with 4V valves. I'd love to get me some of those babies, but they're a little hard to come by.
-Jason
'72 Mach 1 || '90 Talon TSi AWD
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"Thats not a leak, my car's marking its territory!"
"If you've done it, it ain't braggin'." -Roy Rogers