Performance head considerations

[SCW]

I'm starting on porting and polishing a spare head for my 4.0 and I want to have the head milled before installing it to reduce the combustion chamber to about 54cc, which should bump the compression ratio in the stock motor from 8.8 to 9.3, or thereabouts. How far to I deck the head to get from 58cc to 54cc? Bore is 3.875 but the combustion chamber is not the entire diameter of the bore, correct?

The catch is I want this head to be usable when I stroke the engine and from the calculator I have that will bump the stroker compression to around 10:1, a little too high for me.

As far as I can tell, I have a few options, I can use a performance headgasket to save (I think) .008 inches, and maybe deck the head another 15 thousandths or so. This way when I go to the stroked engine I can use an oversize head gasket to partially negate the smaller combustion chamber.

another option is to port and polish the head and use only a thin head gasket, not sure what gains to expect from that.

OR- port and polish this head for now, then expect to use a competely different head (also ported and polished) for the stroker down the road.

Any thoughts? I really don't know anything about quench height, but I know I don't want to mess with the block deck height on the 4.0, but anything is possible on the stroker.

Thanks-
Shane

 

[BBeach]

Patriot performance makes a nice kit, just pricey. What would you need to be able to do it properly yourself?

 

[MudDawg]

Invert the head...level the head accurately...pour 54cc of fluid into the chamber...measure the distance between the head surface and the surface of the fluid.....or you could do some really complicated math...do at least both chambers at opposite ends...if they are off...it will indicate if the head has been milled improperly...if so, you can fix it by remilling with the head properly set up.

Quench is measured as the distance between the head and piston at TDC. I shoot for .040 to .050...an easy way to measure quench clearance is to insert a piece of 1/8" O.D. rosin core solder thru the plug hole so the tip of the solder is against the cylinder in the area you want to measure...turn the engine over by hand...remove the solder and measure the new thickness with a dial gauge or micrometer.

 

[Cjmartz2k]

Just get another head when it's time to stroke it. They are pretty cheap (I'm sure you can track one down for well under $100)

 

[SCW]

I got the spare head I'm using for $50 and I could just hang onto the head that is currently being used to be used when I stroke it. That just means porting and polishing two heads, albeit several years apart.

So if I set up my head for optimum 4.0 use, how much should I deck, what compression ratio should I use?

I've a '92 H.O. with 119K miles that is very strong. I'd like to squeeze as much out of it as I can, and I'm not going to sweat having to use higher octane gas, as long as I'm sure it won't ping under loads at altitude on the high octane. I'm a little worried about losing low-end torque by going to larger valves, so I don't think that will be worth the effort, and roller rockers are way to expensive for the minimal (at best) power gains.

This leaves me with a good P&P, deck the head enough to make as high as 9.5-9.8:1 compression with a MOPAR headgasket and Clifford or Borla header.

The only other thing I can think of is the camshaft and valve springs, but I keep hearing (reading) that the stock bumpstick is about as good as I can get for the 4.0. I'm sure this will also require new injectors and a MAP adjuster, I've already done the intake, TB and exhaust.

Thoughts?

 

[Cjmartz2k]

I don't know where you have been getting your performance info when it comes to cams for the I6. Check out Dino's site jeep4.0performance.4mg.com for all the info you will ever need till you get to stroking. He has another site for that. I'd probably go with a Crane 753905 cam with mopar perf. spings, locks, and retainers. That's what I had in my old 4.0 (before the stroker, now I got a monster cam in it) and it's what Dino runs too.

 

[Dr. Dyno]

I'm starting on porting and polishing a spare head for my 4.0 and I want to have the head milled before installing it to reduce the combustion chamber to about 54cc, which should bump the compression ratio in the stock motor from 8.8 to 9.3, or thereabouts. How far to I deck the head to get from 58cc to 54cc? Bore is 3.875 but the combustion chamber is not the entire diameter of the bore, correct?

The catch is I want this head to be usable when I stroke the engine and from the calculator I have that will bump the stroker compression to around 10:1, a little too high for me.

As far as I can tell, I have a few options, I can use a performance headgasket to save (I think) .008 inches, and maybe deck the head another 15 thousandths or so. This way when I go to the stroked engine I can use an oversize head gasket to partially negate the smaller combustion chamber.

another option is to port and polish the head and use only a thin head gasket, not sure what gains to expect from that.

OR- port and polish this head for now, then expect to use a competely different head (also ported and polished) for the stroker down the road.

Any thoughts? I really don't know anything about quench height, but I know I don't want to mess with the block deck height on the 4.0, but anything is possible on the stroker.

Thanks-
Shane

I suggest you P&P the head, have the surface milled the minimum amount needed to get it flat, use Mopar Performance 4529242 head gasket (0.043" compressed thickness), and keep the stock cam for now.
Then later on when you want to build the stroker, you can reuse the same head/block and copy my stroker combination:

http://www.angelfire.com/my/fan/stroker.html