I've been doing a lot of reading on this forum and it seems that swapping my stock heads (1984 351W engine - no idea which head casting) for a set of GT40 heads would really wake the motor up. If I did this, would I need a new camshaft, and if so, what's a good choice. Also, will the stock length pushrods work?

Thanks,
Frank

 

Sorry.. GT40 heads alone won't really wake the motor up... it needs a cam for that and I'd suggest something like the comp 35-234-3 or 25-238-3. No need for different length pushrods with the head swap either as long as the heads haven't been shaved.

 

Thanks Paul.
What's the difference in the two cams you suggested?

Frank

 

Both cams are a healthy upgrade from stock but still well within what the factory valvetrain can handle. The 234 cam is rated as producing strong low to midrange power while the 238 is a better midrange cam. Use the 234 if you haul a lot and have stock axle gearing and the 238 if the truck has more gearing.

 

Thanks. Truck has an NP435 trans and 3.55 gearing.

 

You might look into some CNC ported factory heads (Powerheads is one source) or check around on craigslist for some aluminum heads. I see the GT40 heads for ~$300 a pair uncleaned and ~$450 a pair rebuilt here in Dallas all the time and used Edelbrock and TFS heads for $500-800 quite a bit.

Of course, fancy heads don't really show up much unless you've got a pretty heavy foot. Find some with 58cc chambers and it would help wake things up down low a bit more.

Isky's Mil-a-Mor cams are real nice for daily drivers and they've got a 262 cam that's strong if you like to goose it a bit. Either of the Comp cams Paul mentioned would be good.

 

So I finally got a set of GT40 heads that have been freshened up but I don't have any rockers for theses heads. Should I just use the rockers from my smog heads or invest in a set of 1.7, and if so, should I get roller rockers? I am going to go with Conan's cam recommendation of a comp 35-234-3. Also, should I invest in new pushrods?

 

If your pushords are straight and not clogged, and don't have uneven wear on the ends it's fine to reuse them. The rockers on your '84 heads will bolt on the GT40s, roller rockers will free up some friction in the valvetrain but chose 1.6 ratio with that cam.

 

Ok, thanks! I'm assuming that the stock rockers are stud mounted. Would I use stud-mounted 1.6 rollers or pedestal mount?

 

That would be a bad assumption, all SBF heads from about '78 on use pedestal mounted rockers.

 

Thanks Conan! I learn something new every day on this forum!

 

Conan (and anyone else that has done the GT40 head swap)
I read that drilling out the head bolt holes can be done on a drill press. Should I just buy a new 1/2 inch drill bit? Is there anything special I need to do? I called my local speed shop and they want $100 to drill the holes, and can't do it for another two weeks. I want to do the cam/head swap this week (I start a new job on the 23rd and took a week off in between to work on the truck and my GTO). My buddy owns a speed shop and has a big drill press, so if we can do it ourselves, i figured I'd go that route.

Thanks!!

 

Yes do it yourself on a drill press, cast iron is pretty soft so it won't be difficult just make sure the head is sitting flat on the gasket surface(make clearance for the valves) and that the surface is perpendicular to the drill bit in both axis.

P.S. Some of these heads are already drilled at 1/2" so check them first.

 

GT40 heads by themselves are good for about 20hp on an otherwise stock engine but they pave the way for another 100+hp once the rest of the engine is uncorked and the 351W block is good for about 750hp before you need to worry about upgrading..