first timer, first question about aluminum heads,be gentle

[lens_xj]

I am building a 4.8 but I am poor so I am going start this from top down starting with the heads. then run it until I have the funds to get the next thing. I want to get more compression but I also want to keep using reg gas. I heard you can get more compression when you use Aluminum heads with out pinging and they are lighter. My question is why. I do not understand why you can get more compression from aluminum with the same spec as the cast iron heads. could anyone please set me straight on this.
My goal is to get as much torque as I can off the bottom, say starting at 800 rpm,torque peaking about 2200 rpm and runing flat at that peek to about 4500 rpm. then dies
I know that is a lot to want this jeep to do but if I am going to even come close to this I have to understand why I am putting on a part and will it play nice with the other parts.
Thanks for your help

[nicpaige]

Aluminum heads dissipate heat much better than a cast steel head. Heat up a cast iron pan on the stove and an aluminum pan. The cast iron pan will stay hot much longer than the aluminum pan because it holds onto that heat. Combustion chamber temps are a large contributor to detonation. They are more forgiving than a cast iron head when it comes to pushing the compression on your engine. That doesn't mean they are a miracle cure for a poor combination. Good luck with your build.

[SilverXJ]

I do not understand why you can get more compression from aluminum with the same spec as the cast iron heads.

If the displacement of the combustion chamber is the same on an aluminum head vs a cast iron head you don't 'get' any more compression. The displacement of the combustion chamber would have to be smaller to gain compression. As nic said you can run more compression on an aluminum head vs a cast head and not experience detonation due to the heat wicking properties of aluminum.

[Russ Pottenger]

The general rule of thumb is you want to run at least a full point of compression more with an aluminum cylinder head.

[jsawduste]

I'll take a well designed cast chamber over an aluminum bathtub.

Much more to the equation of cast iron vs. aluminum then the material they are are of.

[johnj92131]

I'll take a well designed cast chamber over an aluminum bathtub.

Much more to the equation of cast iron vs. aluminum then the material they are are of.

Do we have a well designed cast (iron) chamber head for the Jeep?? Don't think so.

For the Jeep 6 we have 3 different choices of heads, the stock cast iron head with a basic bathtub chamber. The Hesco aluminum head which is a copy of the cast iron stock head in the combustion chamber shape. Last we have the Edelbrock aluminum head with a combustion chamber that seems to be a cross between the Jeep bath tub chamber and a late Chevy fast burn head. When properly ported, all 3 heads flow just about the same.

The cooling effects of the Aluminum heads should more timing advance than a similar cast iron head, so some advantage to the aluminum heads

My question is which one of the first two would be best for torque. The stock cast iron with a 9.2 compression or the Hesco aluminum head with 10.2 compression? Assume the same .040/035 piston/head clearance for each head.

Re the Edelbrock aluminum head - have we seen an engine run with a piston that takes full advantage of the non bathtub combustion chamber yet? Or an ecu tune that would take advantage of the non bathtub combustion chamber?

[jsawduste]

The comment was generic in nature.

To the best of my knowledge there is no one head CI or aluminum that really has features that could be called "modern day" technology for the I6 Jeep family. Edlebrock with their latest release was a feeble attempt at best.

The Edlebrock, while an improvement in chamber leaves a lot off the table. Russ Pottenger has worked with porting and Chris Jensen has had a hand in tuning.

Same came be said for Newcomer racing and their efforts in extracting "power" from the Edlebrock or Hesco.

[Retlaw01XJ]

.......My goal is to get as much torque as I can off the bottom, say starting at 800 rpm,torque peaking about 2200 rpm and runing flat at that peek to about 4500 rpm. then dies .......

For low rpm torque, concentrate on choosing the proper cam. More compression will help, but may require higher octane gas.
An aluminum head will allow you to run more compression, which will help in your case, but performance cylinder heads are generally meant to produce power gains by increasing flow at higher rpm's. Your money would be better spent elsewhere.

Adding a supercharger would be your best solution..... it'll cram more air/fuel in there regardless of rpm!

[lens_xj]

I have been reading you guys for a long time (good source of info) and checking any place on the net I could to get the info I need and you all provided me with an important piece of information for me. It seems like the Aluminum head is the way to go if you are going to stroke the 4.0 out to a 4.8 like I am. Mostly because of the heat (more power = more heat= more ping) and as we all know the XJs have a rough time getting read of this heat. The other thing I wanted to do is to get the compression up to about 10.5 without pinging on reg gas. I don’t care about the flow in the upper rpm range over 4,000 RPM but I want to be able to cruse this XJ all day at a smooth 2,200 RPM. It seems to me everyone is talking about flow numbers but what I don’t get is if the flow is not that big of a deal at low RPM why is everyone talking about it so much. Having a jeep to me is all about getting there and then going slow. Anyway I digress; my idea for this I6 is everything has to work together to build good solid power from the head to the crank AND, Stay in one peace. The Edelbrock aluminum head looks like they are a solid Head and able to take the abuse. also it is the best one out there that I know of,, well at least there are not as many complaints about this head like all the others (like we have a lot to pick from?). So I am still looking and still learning. Thanks for all your help and all the times I will asking you all for help in the future.

[Cheromaniac]

To the best of my knowledge there is no one head CI or aluminum that really has features that could be called "modern day" technology for the I6 Jeep family.

The pushrod OHV hydraulic flat tappet I6 Jeep engine design dates back to the 1960s and though the stock 4.0L head was a vast improvement over earlier I6 heads, it still had to work on a 1960's platform and inevitably the Edelbrock head has to make the best it can out of it.
By comparison, though the SOHC 3-valve 4.6L Modular engine in my Mustang is 12 years old in design, you can see in my sig. how much more power you can get from the same displacement with a more modern efficient engine design.

[jsawduste]

Flow numbers are important no matter what RPM your running.

While there are optimum range(s) when everything (hopefully) sync`s together and the engines efficiency rises to it`s peak. To think low flow is a benefit is misleading. You need just as much air setting surfing jeepstrokers as you do banging off the rev limiter. The difference is how fast you need to flow that air not the amount.

Flow is power, no matter what the RPM is x2..

Dino, Edlebrock bought a lot of "features" to the table but missed out on as many as they bought.

[Cheromaniac]

Dino, Edlebrock bought a lot of "features" to the table but missed out on as many as they bought.

They also came into the game 20 years too late.

[jsawduste]

Dino, Edlebrock bought a lot of "features" to the table but missed out on as many as they bought.

They also came into the game 20 years too late. :lol:

Bingo

[lens_xj]

so what I hear you all saying is there is not one head out there build for the stroker that really works the way we would like. so is it a matter of getting a head off the shelf that comes as close as possible then getting someone that knows what they are doing to "tune" the head. if so, who would that be?

[lens_xj]

so what I hear you all saying is there is not one head out there build for the stroker that really works the way we would like. so is it a matter of getting a head off the shelf that comes as close as possible then getting someone that knows what they are doing to "tune" the head. if so, who would that be?