Dazed and Confused
Join Date: May 2012
Location: Upstate New York
Re: 351w HO build
No personal experience with that combo, but I was always told a 1.6 ratio is safe. Are you changing compression ratio? Given how low it was in 84, 1.7's should work, but not sure if it's going to buy you that much given the low compression. I would definitely check piston\valve clearance prior to sealing the deal. The GT40 heads probably exhibited the best flow characteristics from a stock set of heads, the best being the last generation, the GT40X (aluminum) used on the 5.8's prior prior to the replacement with the Modular series.
The determination of the push rod length is based on the lifters and the at rest position of the rockers, if the rest of the valve train is pretty much Ford standard, then the push rods should be factory length.
If you're going this far, I'd also do something to open up the intake and go with 2 1/2 inch dual exhaust. Most of the disappointments I've heard over the GT40's is based on that. The intake and exhaust remained stock with these wonderful heads in between. It's the equivalent to having a one inch pipe with half inch fittings on either end and expecting a higher flow rate.
Ever notice that there's so many high performance parts available for GM products?
Did you ever think that maybe they NEED them?