Question about heads and valves.

the valves of the 1970 & 1971 closed chamber heads and the 1972 open chamber heads are interchangable. The 1973 & 1974 Cobra Jet heads have the smaller 2V size valves, even though they have the 4V size ports.

cowboy from hell

Thanks George. That is kind of bad news though. Means I am gonna have to wait until I save up another couple of grand.

Measure the head of the valves with a caliper. IF the are close then they will work. Someone might of cut the CJ heads to uses the larger valves. By the way, the size aint too much different. Like 2.05 vs 2.19. Most of the newer valves are only available in the larger size anyway.

But if the valves are too small, that would be bad right??

Yes, small valves are bad. One thing you can do is to mark the face of the valve with layout blue and then rotate the valve against the seat. You can see where the valve is contacting the seat. If it is in the middle, you are good. If it is at the edge, then it is bad and the valves are too small.

I'm not a motor gearhead, but won't such a head swap really change the compression ratio?

As in increase it?

Larry

Thanks Dave. I will do that. I can always buy valves if they don't fit.

Larry, you are right but I already asked George about that and he said that the engine I got now is running about 8 to 1 ratio because it has dished pistons and open chamber heads with lots of room. By putting on the quench heads, they won't quench because I would have to shave off some of the block if I wanted it do that, but it would raise the compresion ratio to about 9 to 1. That would mean I could no longer run regular gas and would have to start using premium, but I drive the car so little the cost factor is not a real show stopper. George say it will only add maybe a few horsepower and probably wouldn't notice the difference, but it is going back to the original heads that came on the car so at least there is that. I am not going for gobs more horsepower, just a little bit extra is all.

When I purchased #7024 I had no idea what, if anything had been done to the engine, but the car always felt strong. It had a stock style cast iron manifold and holley carb, but the decklid was notched, presumably for Webers. I swapped out the intake for an Edelbrock and dynoed it at the first opportunity I got, it put out ~400HP at the flywheel.

After spinning a rod bearing at the track I pulled the motor for rebuild and found it has the dished pistons and closed chamber heads (std ports) and possibly a hotter cam (I haven't got that far to tell), but it goes to show that it doesn't take much other than some simple swaps to add quite a few HP.

In the rebuild I'm changing to flat top pistons, C302B heads and solid roller cam for a few more HP still .

DeTom,

My advice, for any application using a flat tappet hydraulic camshaft, the best budget heads are the iron Australian small port, closed chamber 302C heads. You can buy them ready to install from Power Heads for $1000/pair ($1500 with porting). Combine them with the Edelbrock Performer 2V or the Edelbrock RPM Air Gap intake manifolds, a 750 Holley, the Comp Cams 274XE camshaft and the GTS exhaust system. That's an approximately 400 bhp motor that idles smooth, powerband of 2000 to 6000 rpm, good throttle response, rev to the mid 6000 rpm range. Nothing temperamental, unreliable, exotic about this motor at all. Reliable, drivable, sound in every way. Paint the Edelbrock Performer manifold blue and the motor still looks stock. But the throttle response will put a smile on your face, much stronger than the big port heads.

With flat top pistons the compression ratio will be about 10.6:1 with those heads. That's assuming the block has not been zero decked. With dished pistons the compression ratio will be about 9.7:1.

cowboy from hell

Thanks again George. But the reason I asked was I already have both sets of heads and wouldn't have to buy nothing. Heck if I had the money I would buy the biggest badasseset engine that Mr. McGowen could build for me. But I have lots of things to spend money on my car for now that are of a higher priority. I just asked cause that would be something I could do and would only cost a gasket set.

Just a note Tom. If you swap the valves it might be a good idea to just drop them off to the machine shop to have the seats ground and the valves lapped in. This would be cheap insurance to make sure the valves seal.
Jeff

Lapping valves is actualy a fun job. You got this little hand drill thingie witha rubber valve holder on it and you have a tube of toothpaste and you just keep turning the handle until the whole surface is shiney. Why would I farm out about the only job I can do??????

I lap my valves myself to Tom. My motto is if I can do it myself I do.
Jeff

Well this is a minor setback, but it has caused me to revise my 13 year plan, although ever so slightly.