Thread: Getting some 781's

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I have currently bought some bare 781 heads. Would it be worth it to replace the peanut port heads with the 781's. How much difference would there be. The motor is in a mud drag pickup. Nothing has been done to the motor except a new cam and some bearings. I don't think I would gain any compression. when I compared the chamber size I think both are 118cc. Also would it worth it to put bigger valves is these heads and maybe some port work if so how much would that cost. The motor right now runs really strong it would be hard to tare it apart for a few extra horsepower. Any advice is appreciated.

The advantage of the 781's is in the breathing...the ports are quite a bit bigger than your peanut port heads. At lower to mid rpms, you probably wouldnt gain much...but at the upper end, they would flow much better. Bigger valves would be a good idea, maybe 2.19 intakes and 1.88 exhaust. That's what I did with mine. A little unshrouding and short side radius work and the 781's would be awesome. They are considered one of the best "as cast" big block heads out there as far as flow goes. (Im talking oval port heads) Hang onto them.

I just finished up a pair of "049's" (nearly identical to the781's) for a street strip 454. I was able to do all of the port and chamber work as well as a four angle valve job myself, and still have $650.00 in these heads (including purchase price). I used the local machine shop to clean, magnaflux, suface and cut the valve guides down for seals. Sounds like these heads would be great for your application as long as you match all your components (cam, compression, intake manifold, carb, exhaust, rear end gears etc.) to the RPM range you want to make power.
Good luck.

Would I lose in low end torque with these heads, espically if I put in the bigger valves. Your saying in the higher RPMS it would help cause now it seems it doesn't like to keep pulling above 5000 RPM. So thats about where I shift. With the 781's it should keep pulling into higher RPM right.

I also might just use these heads in a later build of a 468. How much money would I have to stick into these heads to get them to perform for around 500 horse power. Maybe with 10:1 compression. Not a very big cam though I have to have good vacuum for the rules. 15 inches of vacuum at 800 rpm to be exact. Is it possible to reach the 500 mark. Thanks

Very easy to hit 500 hp with 781's....they are probably not a 7500 rpm head, as in all out drag racing, that's where you get into a rectangular port head. But for anything up to 6K or even more, I would think they would do fine. And no, I cant see where you would lose any torque on the low end, they are very good when it comes to low end tq.