Screaming Metal
Active Member
As alot of folks are going to alum. heads these days with the cast iron block still intact, I'd like to share a little info with you.
The difference in the expansion rate between the head and block can cause problems, ones that You guys need to keep a eye on. NO, they aren't all bad, but, A eye still needs to be peeled for things you can possibly prevent.
There are several Manufactures like Dart and others, that offer cast iron performance replacements with screw in studs w/guidplates, angle plugs, good compression ratios.
Alum heads from Edlebrock and alot of other co's come with the big valves, a good CR, and alot of flow. Not to mention the big weight savings these offer, theres a large bolt on power increase with these heads, too! And they usually run cooler also.
Now, the diff. in expansion rate causes a 'scrubbing' of the head gasket. especially that area on steel around the cylinder on the head gasket. After a while, this removal of material or 'scratching, as I call it, makes the gasket loose its seal.
Usually on our T's, theres not alot of problem with this, but with the fellas in the climates where these cars can be run year round, yes, it could pose a problem. Ever had mysterious coolant leakage with your alum. heads???? Yep, this could be the culprit! Or a slight power loss?
(When I'm at the track I follow the car up into the staging area. As the temp rises, I will run my hand around the head gasket sealing area, feeling for blowby.
When your running 1:1 on the blower drive, a Big 5oo ci Hemi taking a hit, idling really rough at about 1500 rpm, the possibilities for a FUBAR happening are way on up there. I've seen some of those motors spit out a head gasket in the staging lanes after a burnout.)
Also, on your cast iron block, you have that same gasket scooting back and forth, and it can actually remove metal from the head itself. Usually the metal band that goes around the combustion chamber is SS......and as soft as the alum. head is.....it doesn't take a rocket scientist to figure out the seeping and scooting around does to that alum.
It might take years to happen, but then again, it might only take 5 or 6 startup cycles, just depends.
Another thing, every-once-in-a-while, you need to retorque your head bolts! This is very important! those heads don't actually grow out, they actually grow in thickness, too! If you have very loose or sloppy threads, I have seen them get pulled out!
With all this moving around, you also have to keep a eye on your intake manifold gaskets, too! I've seen some motors get hurt because of a air leak causing a leanout condition.....also affecting tuning and timing (Vacuum Advance).
Those that have both alum. heads and blocks.....theres not a problem usually. This is the reason why the bikes usually have studs, to keep the thread wear down.
Also, if you run those really hot motors with the alum. rods, its best to have those motors completely warmed up before moving the vehicles or throwing a load to them.
Remember, as the motor comes up in temp., your rods and pistons will expand, raising your compression ratios, and also quientening the motor down.
Forged pistons need more clearance, because they will grow in the bore. When you first start your motor, you can hear the piston slapping, until they heat up and expand.
Happy and safe cruisin' out there!
The difference in the expansion rate between the head and block can cause problems, ones that You guys need to keep a eye on. NO, they aren't all bad, but, A eye still needs to be peeled for things you can possibly prevent.
There are several Manufactures like Dart and others, that offer cast iron performance replacements with screw in studs w/guidplates, angle plugs, good compression ratios.
Alum heads from Edlebrock and alot of other co's come with the big valves, a good CR, and alot of flow. Not to mention the big weight savings these offer, theres a large bolt on power increase with these heads, too! And they usually run cooler also.
Now, the diff. in expansion rate causes a 'scrubbing' of the head gasket. especially that area on steel around the cylinder on the head gasket. After a while, this removal of material or 'scratching, as I call it, makes the gasket loose its seal.
Usually on our T's, theres not alot of problem with this, but with the fellas in the climates where these cars can be run year round, yes, it could pose a problem. Ever had mysterious coolant leakage with your alum. heads???? Yep, this could be the culprit! Or a slight power loss?
(When I'm at the track I follow the car up into the staging area. As the temp rises, I will run my hand around the head gasket sealing area, feeling for blowby.
When your running 1:1 on the blower drive, a Big 5oo ci Hemi taking a hit, idling really rough at about 1500 rpm, the possibilities for a FUBAR happening are way on up there. I've seen some of those motors spit out a head gasket in the staging lanes after a burnout.)
Also, on your cast iron block, you have that same gasket scooting back and forth, and it can actually remove metal from the head itself. Usually the metal band that goes around the combustion chamber is SS......and as soft as the alum. head is.....it doesn't take a rocket scientist to figure out the seeping and scooting around does to that alum.
It might take years to happen, but then again, it might only take 5 or 6 startup cycles, just depends.
Another thing, every-once-in-a-while, you need to retorque your head bolts! This is very important! those heads don't actually grow out, they actually grow in thickness, too! If you have very loose or sloppy threads, I have seen them get pulled out!
With all this moving around, you also have to keep a eye on your intake manifold gaskets, too! I've seen some motors get hurt because of a air leak causing a leanout condition.....also affecting tuning and timing (Vacuum Advance).
Those that have both alum. heads and blocks.....theres not a problem usually. This is the reason why the bikes usually have studs, to keep the thread wear down.
Also, if you run those really hot motors with the alum. rods, its best to have those motors completely warmed up before moving the vehicles or throwing a load to them.
Remember, as the motor comes up in temp., your rods and pistons will expand, raising your compression ratios, and also quientening the motor down.
Forged pistons need more clearance, because they will grow in the bore. When you first start your motor, you can hear the piston slapping, until they heat up and expand.
Happy and safe cruisin' out there!
). HP numbers seem to be just about a wash, between most alum and cast head engine setups, but the higher compression allowed with alum makes a snappier and more efficient street runner IMHO. I used a set of Edelbrock perf RPM heads on one of my ot cars (V-8 Fiero). mostly for weight savings, but it's a go cart on steroids and I've had zero problems with gaskets or anything else in the 6-8 years since I built the car. if absolute HP was my only goal I'd use cast, but otherwise it's all alum for me.
