Picked up a low mile 1974 472 for my International Scout.
Now I'm thinking about putting 425 heads on it. Supposed to be worth 40 hp, but not sure about the torque. And better thottle response I've heard. Is this a good idea? I'm looking for all the grunt I can get between idle and 2500 rpm.
What mods would be necessary? Drill steam holes?
What should it cost for a valve job if I find some good used 425 heads?
Al from MTS was doing some experimenting with the 425 heads on the bigger motors. I'm not sure exactly what has to be done to make them work.......I have heard about the water ports though. It's my understanding that the only advantage to the 425 heads is the chamber size, 96cc's compared to 120cc's on the later 472/500 heads.........I don't think the 425 heads flow as well as the 472 heads either.
You might try getting ahold of Al to see what he has done to his. MTS (Maximum Torque Specialties)
Good luck and keep us posted.
As I understand it, the only reason to put 425 heads on a 472/500 motor is to raise the compression which in turn can give you more power.
Also, I believe the '74 472 came from the factory with flat top pistons. This may cause clearence problems.
The 425 heads don't flow as well, they have smaller ports. It would take quite a bit of work to get them up to spec with good 472 or 500 heads. It would be easier just to try and find a good set of 472 or 500 heads and work from there.
Originally posted by caddydaddy The 425 heads don't flow as well, they have smaller ports. It would take quite a bit of work to get them up to spec with good 472 or 500 heads. It would be easier just to try and find a good set of 472 or 500 heads and work from there.
I have good 472 heads that I could have ported (and milled down to increase the compression). But I'm not looking for top end power, and I don't want to spend a lot of money. It seems for my application (heavy 4x4) that stock 425 heads are better then stock 120cc heads. What do you think? Will ported 120cc heads have more torque/throttle response in the 1500-3000 rpm range then 425 heads?
The Big Inch Cadillac book didn't say much about the head swap.
I think I heard somewhere that a set of ported 425 heads with larger valves flowed about the same as a set of stock 472/500 heads. It seems, the only benefit of the 425 heads on a 472/500 is the higher compression.
The 425 heads should work for what you want but the high end will suffer from the lack of air flow.