Aluminum Heads ?

['64 Cuda]

I have something I want clarified for me concerning aluminum heads. We all know you can get away with a higher compression ratio with the same fuel octane when using aluminum heads. I've been told that if you have approx. 9.5 to 1 with an iron head you can use about 10.5 to 1 with an aluminum head. It's my understanding that this is because of the fact that aluminum is better at transferring heat away from the combustion chamber. I've also been told that horsepower increases proportionally with an increase in compression ratio.

To keep things simple, let's assume that everything else is the same, only the material the heads are made of is changed. Also, there is gas with sufficient octane to meet the needs of the engine.

How much power, if any, does the aluminum headed engine lose due to the transfer of heat from the combustion chamber? Would a 10.5 to 1 iron headed engine make more power than the same engine with aluminum heads? How much more power can you expect to gain on an "average" (whatever that is) aluminum headed small block due to the increase in compression ratio allowed with an aluminum head?

 

[street demon]

Car craft did a dyno test with the exact same combo on a small block chevy. One with aluminium and one with cast cast. They flowed the heads and the flow was very close to the same. Same combustion chambers and everything. The results show 2-4 hp difference and that 2-4 was swapped through the rpm range between the two heads. I don't think the cast iron head will make more power given all things being equal.

 

[street demon]

As for will you get more power with an aluminum head I think yes. Mainly because of the modern port design, smaller chambers and quench if you have the right pistons. Another thing that seem to always happen is when you put the new heads on you put a bigger cam in to take advantage of the high cfm numbers.

 

[388dart]

I changed from home ported 596s with a Cr of 10.4 to Eddy magnums with some porting to remove some of the pinch point and blended the intake and exhaust ports with Cr 0f 11.9 with double quench @.035 and gained a whole 2/10ths. would I do it again - NOT. check out the CI EQ magnums if you are upgrading. M2CsW.

 

['64 Cuda]

Street Demon, am I understanding correctly that in your first post the 2-4 hp difference went back & forth between the 2 types of heads depending on the RPM?

I guess the main thing I'm trying to find out is if an IDENTICAL Iron head would make more power than an aluminum head because of the heat loss from the aluminum head. Same cam, combustion chamber, ports, etc. I'm wondering if the bump in compression ratio will increase the power the same amount between an aluminum head & a cast iron one. If I understand street demon's post, the head material itself will have little effect on the power produced, but the increase in compression ratio allowed by the aluminum head will let you make more power than the iron head would when operating on the edge of the compression that is allowed by the octane of the gas.

 

[street demon]

Here is the link. It's a good read.http://www.carcraft.com/techarticles/ccrp_0602_iron_versus_aluminum_cylinder_heads_test/index.html

 

['64 Cuda]

Interesting read. Thanks for the link.

 

[sweatybetty]

seems both heads being equal, the power gain would be in weight loss.

 

[moper]

I'll add my take.. As far as strictly thermal efficiency "loss"? I'd say less than 1-2%. However, that loss can be offset very easily with design adjustments to the engine during the build. The only down sides really are the thermal loss, the added cooling system load, the corrosion issue, gasket choice, and in some cases lash issues from the expansion rates. Most of those can be countered with basic choices. More static ratio, better cooling system, the right type of gasket, and experience/different procedures. The up sides are wieght, thermal loss, modern port designs, easier (cost wise) porting, modern or at least closed chambers, and the bling factor. Changing heads, without accounting for or exploiting all of the benfits, will lead to disappointment if your package is well scienced out. That's why budget is so crutial ina build. That sets the type of head, and the head sets the stage for the power band.

 

[street demon]

I have also seen on dyno sheets that the oil temp raises on average 10 degrees when aluminium heads are used. That's not much but if your pushing the limits oil breakdown now then going to aluminium will only complicate things.

 

[moper]

That's all part of the thermal issue. They transfer more heat to the oil. Truthfully, if the oil is workign right, it takes as much heat away as the cooling system does, and ten degrees should mean nothing. Typical temps are around 220-240 depending on the system, the engine, and the pan. A good oil will survive to 260 pretty easy. Beyond that, synthetics will live better. But really you got problems..lol. Again, I think they are a better option in every application except where rules mandate iron. So long as the design is taken into consideration in the design phase. But, sometimes the budget cant absorb that.