aluminium head

[grim jeeper]

Hi everyone, heres a question or two for ya, i have an ali head off a stroked supercharged tj 4.8, it has engraved on it 58 cc, can you guys tell me how much to skim off it to make it run on a stock four liter and what size push rods to use i will be using ali roller rockers on it . if i can make it useable that is, thanx in advance.

[5-90]

As i recall offhand, 58c/c should be right around the OEM chamber volume - so why shave anything?

The head may be thicker tho - so I'd advise getting a "length checking" pushrod to make sure you can accurately gage the length you'll need. You should only need on checking rod. Rollerised rockers should pose no trouble, as long as it uses something akin to the OEM pivot/bridge rockers - or a mounting similar to something OEM (SBC/BBC would be better - they're more plentiful.)

If you want to abbreviate the names of metals/materials, you may want to use something more readily understandable - for instance, you can use "Al" in place of "aluminum" - as it's the chemical symbol for the element. "Iron" would become "Fe" - while steel is an alloy and can be called steel. "Chrome-Molybdenum" is often shortened to "Chromoly," but would more properly be "Cr-Mo." "Ali roller rockers" looks like it might be a brand name that you've discovered - and that we aren't familiar with (yet...)

[grim jeeper]

sorry for the abbreviations being english different "abs" mean different things, and keyboards ain't my thing so short cuts are appealing lol.
Back to the head, i was led to believe that it was a low compression head, and that the stock head was 47 cc, i cannot see any machining only casting pimples, so i was guessing that the difference could be changed by skimming.

[Muad'Dib]

OEM combustion chamber volume is approx 58cc's.

[grim jeeper]

thanx guys i have had some strange things told to me, to do with this head but you guys seem straight talking and knowledgeable, seems a shame to leave the head sitting in the garage when i can put it on the four liter and gain 30hp for a few bucks, then put it back on the stroker when its rebuilt, i have been porting the head to match the gasket using other tips from this site,and am glad it can go straight on, any thing else you guys can shed light on on this subject will be gladly received.

[Cheromaniac]

seems a shame to leave the head sitting in the garage when i can put it on the four liter and gain 30hp for a few bucks....

This sounds like it's the Hesco aluminium head. While it's a good head, it won't deliver a 30hp gain unless you do other mods to allow the engine to breathe better (CAI, bored TB, header, exhaust, camshaft, bigger injectors, chip tune).

[grim jeeper]

i have an f and b throttle body( i think 68mm from memory )inlet manifold opened out to suit, banks power header, high flow cat, custom stainless pipe work, flow master, back box i am running a k and n filter element with a safari snorkle, i have removed the concertina part of the crossover tube that goes from air box to tb and replaced it with a straight silicone one and replaced the snorkle one as above, i have a daz tec unit but am thinking of getting one of the plug and play ones as it seems to be more cost effective than a hole day on the dyno,i have an accel coil and leads etc,hesco water pump. but !!!!! injectors standard at the mo, but i have a set (new) from a yj beige in colour, would these be what i need as i know there is a difference in flow related to fuel pressure, i dont really understand that too well, please bear in mind that this is going on a NOT stroked 4.0.

[grim jeeper]

forgot to say thanx, what gains should i expect given the info i have given stock cam by the way.thanx again for all your help guys, i allmost gave up on the hole thing at one point.

[tirod]

Never give up.

Assembly guides are available for checking the valve train dimensions and relationships ( and a respondent here offers one with a good reputation.) In a stock motor rebuild, most components come close enough for the public. For a performance rebuild, or any custom component, like the Hesco head, double checking pushrod length and rocker sweep on the valve tip, plus valve action in the chamber for interference caused by exotic timing, is almost mandatory. Those who don't check get to try again in a few thousand miles on the next rebuild.

Basically, the rocker arm action needs to be centered on the valve tip - and the push rod length adusts that. Roller tip rockers have a moving contact point on the end because of the static position of the roller - it can't compensate it's arc to stay still. So it has a slight sweep across the end of the valve.

Hopefully in the future DLC coated rocker arms with an appropriate cam faced contact point will come on the market to reduce the sweep and eliminate the need for any bearings at all. NASCAR is testing them, it's going to make the next ten years in performance parts very interesting.

[grim jeeper]

thanx again four your help, i will watch over the guy putting it together(he is gonna love that)and make sure he double checks that area.

[grim jeeper]

more help required, please, manufacturers recommend that i skim the head to 47cc for the four liter,i dont get why given the that 58cc is standard,(i realise that it would increase compression) can you guys shed some light on this and perhaps some one knows how to work out how much i need to skim off,also will the yj injectors i have give me the flow i need for my set up,

[gradon]

Why would they make a head w/ a 58cc CC and then require the customer to get it machined down until it was 47cc? Maybe they are claiming that you can take that much off and not have issues with the heat/increased compression and still run on pump gas(benefits of aluminum).

[SilverXJ]

Who are the manufactures you speak of? Hesco? After my polishing the combustion chambers on my 0630 head they averaged 58.3cc. The recommendation to shave the head to reduce the chamber to 57cc probably comes from the fact that you can run higher compression on an aluminum head and still not ping vs a cast iron head. So, increase the compression a bit and gain a bit more power. If you plan on running this head on a 4.0L and no intentions of putting it on a stroker I would shave it. However, if you are going to put it on a stroker later I'm not sure I would shave it, depending on what build you go with you may need the extra cc to decrease compression.

What aluminum roller rockers did the head come with? If you don't know the brand what color are they, or do you have any pics?

Basically, the rocker arm action needs to be centered on the valve tip - and the push rod length adusts that.

Pushrod length adjusting rocker to valve tip contact is only true with an adjustable valve train that has the adjustment on the rocker arm hold down bolt. For example, if you threw longer pushrods in an other wise stock 4.0L (stock rockers, hydraulic lifters) all that will do is increase the lifter preload, nothing for the rocker tip to stem contact. Also, with most 4.0L adjustable roller rockers the adjustment point is over the pushrod, again, that will only adjust the preload. In order to adjust the rocker to valve tip pattern you need to do something at the rocker pivot point. Either use shims under the rocker or use an adjustable rocker that has the adjustment point at the pivot.

Hopefully in the future DLC coated rocker arms with an appropriate cam faced contact point will come on the market to reduce the sweep and eliminate the need for any bearings at all. NASCAR is testing them, it's going to make the next ten years in performance parts very interesting.

Can you explain that a bit more?

[SilverXJ]

Why would they make a head w/ a 58cc CC and then require the customer to get it machined down until it was 47cc? Maybe they are claiming that you can take that much off and not have issues with the heat/increased compression and still run on pump gas(benefits of aluminum).

Probably because they don't know what the end user intends to do with the head. There are some cases where someone can benefit from the extra CCs to keep the compression down. Its better to be able to remove material than have too small a combustion chamber. Just like the Hesco head has the spacers cast in, so an adjustable valve train can be used with the stock valve cover.

[grim jeeper]

Hesco head and red colour roller rockers from hesco, and have been taken off a 4.8 stroker that was to run an avenger sc.