Aluminum versus cast heads -does the 45#'s make a diff?

[namz7791]

I have been looking into the various options on crate motors for my engine swap into a 77 280Z 2+2. Currently am considering the GM 330 HP 350 HO that comes with the Vortec heads or the ZZ4 which comes with aluminum heads. I can buy the complete 350 HO deluxe which is basically turnkey for around $300 less than the ZZ4 which still needs carb etc.

 

I tried searching on the differences between the weight of the aluminum versus cast heads and find about a 45# difference. In the grand scheme of the JTR conversion is 45# gonna make or break the way the car handles? Will relocating the battery to the rear and such off set the weight difference? The 350 HO does come with an aluminum intake.

 

Thanks for any insite on the weight issues.

[baddriver]

There is a quarter mile calculator here:

 

http://www.web-cars.com/math/qtr_mile.html

 

that you can use to figure approximate quarter mile times. I checked it for a 2800 lb car, and around 220 hp, and got a 14.747 second quarter at 100.24 mph.

 

Adding 45 pounds with no other changes gets you a 14.845 quarter at 99.7 mph. So the difference in acceleration is pretty small, you can put in your own HP numbers and weights to know what it's really worth. As far as braking and turning go, consider what portion of the total weight you are removing. In other words, a 45 pound difference, is about 45/2800 1.6% of your weight. Of course, it's more complex than that, ideally the grip of the tire is related to the normal force, so an increase in weight causes and increase in grip, but we know from the real world that grip does not increase quite as fast, so you don't quite gain enough grip to accelerate the added mass.

 

The straight-line problem can be solved with horsepower. Adding 5 HP to the numbers above gets you back into the 14.7 range, so if you get 10 hp more from the iron heads, that's actually going to work to your advantage in the strait line.

 

The weight change is tiny, you'll never feel it, or even see it in your times until you are a very experienced driver. Everyone knows cutting weight is a good thing, but it's not worth quite the level of obsession that is devoted to it.

[Drax240z]

I'd say the weight difference is a bit bigger of an issue that what baddriver has outlined. This weight is primarily on the front wheels, which will make turning more difficult, as well as LIKELY front-bias the weight distribution of your car.

 

With that said, 45lbs is relatively little in the grand scheme of things and won't make or break the car. However, most attuned drivers would feel the 45lbs additional weight. (At least in a back to back comparison)

 

However it seems to me that the biggest advantage is that aluminum heads can help you make more power.

[grumpyvette]

GENERALLY THE DIFFERANCES WILL BE MORE THAN WEIGHT

 

IRON HEADS..................................................ALUMINUM HEADS

HEAVIER......................................................LIGHTER WEIGHT

CHEAPER.............................................COST MORE

VERY DIFFICULT TO REPAIR DAMAGE.....VERY EASY TO REPAIR DAMAGE

CAN IN THEORY PRODUCE MORE HP.....................REQUIRE SLIGHT INCREASE IN CPR

MORE PRONE TO DETONATE.............................LESS PRONE TO DETONATE

CRACKS EASIER IF MISTREATED........................................WARPS EASIER IF MISTREATED

MORE COROASION RESISTANT................................REQUIRES GOOD QUALITY COOLENT

HARDER TO PORT....................................EASIER TO PORT

 

EVERY GUY WILL SOONER OR LATER DROP A VALVE OR IN SOME OTHER WAY DAMAGE A CYLINDER HEAD IF YOUR RUNNING AN ENGINE CLOSE TO ITS PERFORMANCE LIMITS SOME OF THE TIME, YOU ONLY NEED TO THROW AWAY ONE SET OF DAMAGED HIGH DOLLAR PORTED IRON HEADS THAT IF THEY WERE ALUMINUM ,THAT COULD HAVE BEEN EASILY SAVED WITH WELDING TO REALIZE THE ALUMINUM HEADS HAVE A HUGE HIDDEN ADVANTAGE! sooner of latter every engine thats raced has problems that result in something coming loose and bounceing around in the cylinder, (VALVE FLOAT,BUSTED SPRING,CRACKED PISTON, DETONATION OR NITROUS DAMAGE CAUSEING A RING LAND TO CRACK,ETC> ) now that ALWAYS damages the cylinder head, in most cases ALUMINUM HEADS ARE EASILY REPAIRED and USUALLY FOR $300 or less IRON HEADS wind up in the dumpster behind the machine shop, now thats ESPECIALLY IMPORTANT if you just dumped big $$$ into port work!

now as far as power goes I think the differance is very minor between aluminum and cast iron, and depends more on the port work and compression than the material used, I know I will only use aluminum heads on my personal engines, because I sure don,t want $1000 plus in heads and a weeks port work being thrown in the trash if I bust a piston or drop a valve someday!!!

 

If you put too much heat on an aluminum cylinder head it will warp. If you put too much heat into an iron head it will crack. It's a lot easier to fix a warped aluminum head. A cracked iron head is usually trash. Just some food for thought

 

The more important question is not iron vs aluminum but the air flow potential. Its really in youre wallet where you will notice the difference aluminum is easier to repair and weighs less, but heavy on the wallet. Iron is less on wallet but you could say disposable. as sooner or later problems occure with any heads

 

personally if moneys tight ID GO GET THE TRICKFLOW 23 deg heads at $995

[danc]

There are several other differences between the HO Deluxe and ZZ4 other than HO iron vortec versus the ZZ4 aluminum non-vortec heads. The difference is 25 H.P more for the ZZ4, as well as the hydraulic roller valve train. The ZZ4 can be upgraded to 375-395 H.P (depending on whom you talk to) with a LT-4 "Hot cam" (about $500 for parts) using the same valve springs installed by G.M.

[Michael]

I can personally attest to the repair drawbacks of cast iron heads. After spending something like a year porting my cast iron heads (OK, I’m slow and lazy), I finally took them to the machine shop for new valve guides and seats. First, the shop pressure-tested the heads to make sure that there were no cracks. And indeed, the heads held the standard 30 psi (or whatever their test pressure was) without any problems. After pressing in new guides, the pressure test was repeated. This time, one of the heads failed – it had hairline cracks across two combustion chambers, emanating from the vicinity of the valve seats. Welding the cracks was not an option. So, in the trash they go. That’s a year of porting, plus the cost of cleaning and pressure testing the heads (the machine shop did absorb the cost of the rest of their labor).

 

If you buy a crate engine, and subject it to sufficiently benign use that it won’t need to come apart for years and years, the cast iron heads should be OK. But the more you tinker with those heads, the more the aluminum heads become the better choice.