Milling the Stock Head

[bit]

I plan to mill my stock head at the end of the season. I am researching it now so I know how much to take off. I see so many people running aftermarket heads and I have to wonder why. Milling the stock head is such a cheap and easy performance boost. Is there a reason other than interchangeable domes?

Also if anyone knows what squash gives about 180PSI on a stock head that would be great. I have not checked my current squash, but compress is 160psi on both.

 

[Rickster]

which engine?

 

[bit]

701 sorry

 

[Mark44]

You will probably have a squish of .045 after you are done, what is it now?

Most run the head because of the girdle kit and there motors are ported other than that no reason for me, no need to change domes unless you have engine failure and you waist a dome.

Mark44

 

[Matt_E]

Reasons not to run stock head:

Protect the cylinder. They can and will break with an aftermarket pipe and no girdle kit.

 

[bit]

Is there really any need for me to have a girdled head? Only mods being b-pipe and 180PSI? I remember reading about guys cracking cylinders, but that is with much more power.

 

[Matt_E]

Phill cracked a cyl with 170psi and B-Pipe.

You'll get away with it for a while, and maybe a long time.

You just never know. :biggthumpup:

 

[Mark44]

Phill cracked a cyl with 170psi and B-Pipe.

You'll get away with it for a while, and maybe a long time.

You just never know. :biggthumpup:

True.......

Mark44

 

[Rickster]

Milling the head 30 thousanths will give a stock motor 185-190psi and a squish of about 55 thousanths.

BUT, you should measure the squish prior to milling the head, so you do not cut it too close.

IMO, it's a good cheap mod, especially if you a running a pipe that does not rely on the head for support.

 

[Matt_E]

MO, it's a good cheap mod, especially if you a running a pipe that does not rely on the head for support.

That's what I used to think, until I saw one break with a B-Pipe. :dunno:

 

[Rickster]

That's what I used to think, until I saw one break with a B-Pipe. :dunno:

I'm beginning to believe you and phil could break anything, anywhere....:splatt::brap:

 

[Matt_E]

True. :haha:

When he got towed back with that broke cylinder, his carb was also flopping around loosely on the intake. The nuts had come off. :dunno:

Yesterday, my Round started running like crap. Upon close inspection I found that the exhaust manifold bolts had partially backed out of the cylinder, creating one gnarly exhaust & coolant leak.

Yeah, whatever.

 

[bit]

That's what I used to think, until I saw one break with a B-Pipe. :dunno:

One? Or are they breaking all the time? I am not really worried about one, but if it is common I will get the girdled head. A mod that takes a few hours of my time is always better than a $300 mod.

Rickster,
Can I run 93 with 190psi? I am not really looking to push my luck, 180psi would suit me fine.

 

[Matt_E]

Can I run 93 with 190psi? I am not really looking to push my luck, 180psi would suit me fine.

That depends on many factors, not just your cranking compression.

 

[bit]

That depends on many factors, not just your cranking compression.

True, but there should be a pretty good knowledge base on stock SJ with "good" oil.

Any thought on the loose carb and subsequent vacuum leak causing excessive vibration leading to the cylinder break? If he is the only one something else is going on.

 

[Rickster]

Rickster,
Can I run 93 with 190psi? I am not really looking to push my luck, 180psi would suit me fine.

That depends, as Matt said, but generally you should be able to with no WOT runs...

I know someone that was running 5/6mm stroked lamey's with over 200 PSI on pump gas.:barrel:

I personally consider 185 to be the limit on 93 octane.

 

[Matt_E]

Stock ignition with some advance or MSD enhancer without addt'l advance, 45 thou squish, wet pipe, under 7750RPM, 190 psi - you should be fine on pumpgas.

 

[bit]

Thanks for the help guys, I will measure my squash and go from there. I would like to have 180PSI, so I guess I should aim for 0.050" squash?

 

[Rickster]

Thanks for the help guys, I will measure my squash and go from there. I would like to have 180PSI, so I guess I should aim for 0.050" squash?

Squish and compression are independent of each other. On a stock motor, count on an increase of about 12psi per .010" taken of the head.

.050" squish will give you a good kick down low...

 

[bit]

Squish and compression are independent of each other. On a stock motor, count on an increase of about 12psi per .010" taken of the head.

.050" squish will give you a good kick down low...

That good info, thanks. I will be looking to remove about 0.017" in that case. Subject to a squash reading of course.

In the case of out stock head would the squash not directly relate to amount removed from the head? Meaning, as I remove material I am deceasing combustion chamber volume and squash. Short of recutting the dome how could I decrease squash while keeping the same volume?