LT1 heads: Aluminum vs Iron

[Tom H]

Hi,
LT1 Aluminum heads are certainly lighter than the Iron. Are there more disadvantages to using LT1 Iron heads? I wonder about valve size, port shape and all that. Can the Iron heads produce the same power as the Aluminum?

I am asking because there is a 5.7 LT1 out of a Buick that can be had inexpensively. I would like to put together a test mule to learn more about tuning. Other disadvantage of this setup is that it is a 2bolt main block.

-Tom

[JD1964]

Aluminum heads dissipate heat faster than iron heads. Because of their ability to shed heat faster, you can run higher compression and also handle higher cylinder pressures in boosted applications. The increased ability to shed heat reduces the risk of detonation. Detonation is deadly to an engine.

[LeMarky Dissod]

'96 specs
Camaro / FireBird LT1s produced 285 horse @ 5000RpM & 325ftlb
91 Octane OE spec
F- & Y-cars used the same cam - 200° /207° duration, 0.447 / 0.459 lift, 117° Lobe Separation
Aluminium heads with 10.4:1 compression
less restrictive mufflers and larger tailpipes

Caprice / RoadMaster / Fleetwood LT1s produced 260 horse & 330ftlb
87 Octane OE spec
both 4.3L L99 & 5.7L LT1 used the same cam - 191° / 196° duration, 0.418 / 0.430 lift, 111° Lobe Separation
Iron heads with 10.5:1 compression (they are said to flow a lil bit better, but are prone to heatsoak)
more restrictive intake, mufflers, and 2.0" tailpipes
*make damn sure it ain't a 4.3L L99 V8, they look eerily similar

Even though the horses are now 26 years old, an IronHead LT1 with
a 91 Octane tune
a less restrictive cold-air intake
well-chosen mufflers
mandrel-curved 2.25" or 2.50" tailpipes
should have no problem making at least 285horse

Camaros SS & FireHAWKs made 305-315 horse with Ram Air Hood & intake, & free-flowing exhaust

LT1 engines, even with iron heads, are more resistant to detonation than earlier small block V8s.
LT1 engines are reverse-cooled - cold coolant is routed through the heads first, then through the block.

[steveo]

LT1 Aluminum heads are certainly lighter than the Iron. Are there more disadvantages to using LT1 Iron heads? I wonder about valve size, port shape and all that. Can the Iron heads produce the same power as the Aluminum?

people get better flow numbers (pre-porting) with the stock ports in the iron heads

they are both good heads. two different strategies.

aluminum: take advantage of consistent combustion chamber temperature. the reverse flow cooling of the LT1 with the aluminum heads does a really good job of that. the heads have higher compression. also take advantage of the optispark having a good amount of precision (for its time), and run timing advance up fairly high without blowing it up even on mediocre fuel.

iron: usually put in the heavier chassis. hotter combustion, a bit less compression too, which can help with the heavier vehicles hauling big loads. definitely more efficient. you have to run quite a bit less timing or she explodes but make good torque and power anyway

if you're porting them, though, the LT1 aluminum heads are great on a budget. look what lloyd elliot used to do to his LE3 series ports. guys were getting 450+hp crank horsepower out of those heads with a good cam. pretty amazing for ground down stock castings.

Other disadvantage of this setup is that it is a 2bolt main block.

in practice, though, your two bolt main block doesn't have any issues until you start generating monstrous torque. i have no idea why they bothered with four bolt mains in the 'vette. very much overkill. some good bearings with some arp bolts so nothing goes stretchy can be reliable well over 500hp

[Fast355]

The aluminum heads are worth a bit of power compared to the iron heads, even with the B/D car cam. They also come factory with screw in studs rather than pressed in. The chambers on a LT1 aluminum head are 58cc and the cast iron about 66cc. The iron heads used a thinner head gasket than the aluminum heads, but the aluminum head guys use the iron head head gaskets for more compression. I would not waste my time with the iron heads. I put a pair of 200cc runner, 64cc aluminum heads on my L31 in my Express van and gained torque everywhere and was able to run 87 octane with a 9.6:1 compression ratio and 34* total timing at 2,400 rpm.