What are the cons of Aluminum heads on a street car?

[TURBOPOWERED68]

Yes i know irons have been 6 seconds or what ever. Yes i know aluminums are not needed and a waste of money. Now that is out of the way.

Lets talk about using aluminum heads on a street car.

Why would you NOT use Aluminum heads on a street/strip car?
Is the price difference that much between balls out irons vs Aluminum?
Do they NOT work well at low RPMs? Cruising, idle, 5600 rpm Shifts?
talk to me people

 

[Lil Truck]

The reading I have found on this subject has lead me to believe that with a street/strip combo (quick spooling smaller turbo and smaller cam 212 or less) the aluminum heads may reduce velocity on the low end RPMs and kill the quick off idle response. The quick spooling will lag, mid range will be strong but the top end potential will not be realized due to the smaller cam & turbo. So if your willing to go bigger on everything you will get the top end performance but the (off idle spool up at a street light may still be weak) Stroker motors may cure this?

I have a similar build to yours and have been researching how far I want to build a new motor for mostly street to high 10s with full weight.

 

[coach]

I'll be honest...I was wanting a killer set of irons, done up as far as they could go. I knew who I wanted to do them, but he was not able to take the job. I knew that a set of regular ported Champions was not going to support my needs. I was going to go TA's but a killer set of race ported GN1's went for sale at a super price. I snatched them up within a few hours. I run iron heads on all my street engines and this will be my first Alum headed street engine. I have no doubt that it will be just fine.


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[DrkBluT-TyPe]

I just dropped off my block at the shop yesterday(stock 3.8). Goal is mid to high ten second street car on e85. Pretty sure using the stock pistons with some really good rings unless one of them wasn't shaped right' cracked, etc. haven't decided on a roller cam or tappet yet up for suggestions. I plan on purchasing champion heads, was honestly leaning towards the irons but I do have the funds for alums. Just want the build to be right, been reading up all morning. My stock irons did work, I can't see really any major gain other then weight and what you all have discussed.

 

[TurboTnZ06]

GN1's on my stroker street car. Non-race ported. I'm running individual stud setup with what Don Cruz calls "big block roller rockers". Intake ports are big enough to match a ported lower intake manifold. The exhaust ports will be bigger than stock headers, so I know my stock headers are a restriction, just not sure by how much. Throttle response is awesome. I have an old 3000 stall 9/11 converter and TE45a.63 and I can go from 0 psi boost to 20+ psi boost between .6 to .8 seconds off the line...

I put studs in all the header holes so I wouldn't be threading into alum everytime they needed to come off.

 

[krom]

The reading I have found on this subject has lead me to believe that with a street/strip combo (quick spooling smaller turbo and smaller cam 212 or less) the aluminum heads may reduce velocity on the low end RPMs and kill the quick off idle response. The quick spooling will lag, mid range will be strong but the top end potential will not be realized due to the smaller cam & turbo. So if your willing to go bigger on everything you will get the top end performance but the (off idle spool up at a street light may still be weak) Stroker motors may cure this?

I have a similar build to yours and have been researching how far I want to build a new motor for mostly street to high 10s with full weight.

My experience was that the off idle performance was better and my ET at the track improved by 4 tenths. This was with blue tops and a 3000 stall. The only negative is the need for rockers, pushrods and bolt kit.

 

[GSX-PKV]

I have had GN1 heads on my 99% street car for over 10 years with no problems whatsoever. I even think their lighter weight makes the car handle a little better. I really don't even notice any "turbo lag" off idle or at any time for that matter. It runs 10's at 126 on 93 octane with Razor's alky kit so we're happy campers with the entire setup.

 

[Nasty Wendy]

I've run aluminum heads GN1 heads on the street with no issues. I put them on the car with the intention of putting in a bigger turbo and cranking up the boost and racing the car a lot. That never happened as I could not bring myself to install a cage in the car. So I ran an aluminum headed 12.0 car. I didn't experience any downsides.

 

[kidglok]

Like anything else the rest of the combo will have to be built around the aluminum heads to really take advantage of them. If you are running a small hyd roller with moderate spring pressures on 231ci IMO there is not much being gained over a set of champion irons.

Now if your going to a jesel style rocker setup with an aggressive cam looking for over 600 lift that will make the decision for aluminum heads an obvious one. Streetability is perception as either one of those setups can be run effectively on the street only difference being a little less maintenance on the iron headed valve train. Solid lifters will also require a closer eye kept on lash which the average person is not going to be willing to do.


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[Lil Truck]

My experience was that the off idle performance was better and my ET at the track improved by 4 tenths. This was with blue tops and a 3000 stall. The only negative is the need for rockers, pushrods and bolt kit.

Was this improvement over Stock or ported heads? The 3000 stall will help lag at lower rpm. My stall is 2800 running stock intercooler, stock MAF and inlet bell, stock exhaust elbow.

The combo is the key, if your willing to spend the money to match the heads it will payoff well.

 

[Nick Micale]

Like anything else the rest of the combo will have to be built around the aluminum heads to really take advantage of them. If you are running a small hyd roller with moderate spring pressures on 231ci IMO there is not much being gained over a set of champion irons.......................

I fully agree with the first part of this statement as combo is a very important factor especially in a turbo build.

However, you WILL have HP and drivability improvement as performance is all about air flow. With alum heads there is much improved air flow which means you can develop the same HP at less boost.

Since alum transfers heat better than iron, it will allow more boost before knock will happen.

My opinion, the only downside is the cost, and that is your choice!

 

[Pronto]

Can you use a set of T&D roller rockers designed for iron heads on any aluminum heads to save some money on that aspect?

 

[TurboTGuy]

Champion aluminums, a bigger cam and T/C to match will be my next big upgrade.

 

[bison]

Can you use a set of T&D roller rockers designed for iron heads on any aluminum heads to save some money on that aspect?

You could use stock rockers to save money. If you get the correct spacing in between the rockers you can use the roller rockers off of iron heads but there is little to be gained just slamming on a set of untouched aluminum heads with typical cams/converters over a decent set of iron heads. A lot mentioned about airflow but the engine needs to have a have the ability to rev to achieve all that extra potential. From my experience there is a huge increase with good aluminum heads and some decent supporting parts. For a somewhat back to back comparison with the same turbo and converter I made about 500-510whp@ 27-28psi with a cleaned up set of iron heads with stock valves. Just bowl work and not much of the short turn. The car trapped in the high 120's @30psi. With well ported aluminum gn1 heads the same combo made nearly 550+whp@21psi. Both 93/alky. This was the same cast 60-1 turbo. Both engines had small hyd roller cams with the same duration @.050 and lift was only .040" more with the better heads. Duration @.200 was about 3 degrees more with the aluminum heads so the cam was a little more aggressive but not much. Huge increases in mass flow potential are possible even with some pretty standard parts. Those gains I exhibited are mostly from increases in mass efficiency and not air flow though.Both even peaked around the same rpm and the displacement was 3ci less on the higher hp example so the higher hp engine had less air flow. To get the air flow potential possible the engines operating range needs to be increased. The rest needs a lot of attention to do so. It's not going to happen with typical "budget" parts.


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[earlbrown]

The general rule when going from iron to alum is to run about 1 full point higher in compression to maintain volumetric efficiency. The aluminum is going to conduct more heat out of the power stroke and put it in the cooling system.

The only advantage to just sticking a set on for funsies is pretty much just the weight savings.

 

[ttaowner]

From what I understand if you melt a iron head it goes in the scrap pile.melt a aluminum head it goes to the welder and gets fixed

 

[Pronto]

Bison, can you explain the difference between mass efficiency and air flow? If the shortblock is built strong with forged pistons, forged crank, billet center caps and stronger aftermarket rods then the rpm potential should be high enough to benefit, correct?

 

[bison]

Bison, can you explain the difference between mass efficiency and air flow? If the shortblock is built strong with forged pistons, forged crank, billet center caps and stronger aftermarket rods then the rpm potential should be high enough to benefit, correct?

Mass efficiency is how well the cylinder is filled relative to its displacement. 20psi in the intake and 20psi in the cylinder at bdc would be 100% mass efficiency. Of course it would have to be fresh air charge and not diluted with inert gas that is left over. This isn't a realistic situation if back pressure is higher than intake pressure but just a quick explanation. Air flow is solely determined by engine displacement and speed and nothing else. Mass flow is result of both.


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[earlbrown]

I've never used that phrase before. So 'mass efficiency' = VE, or is there a subtle difference between the two?

 

[bison]

I've never used that phrase before. So 'mass efficiency' = VE, or is there a subtle difference between the two?

Whenever you refer to gases in a space the correct word would me "mass" referring to the density of the gas(es) within. The word volume is often misused and should only be used with liquids. Fwiw gases take up the entire container of whatever they are in unlike liquid and liquid isnt very easily compressed so the mass efficiency with a gas literally is always 100%.