Couple questions about milling heads

[redterror302]

Well I am trying to port my stock heads in whatever time I have, but it may take a little while longer still. I just started thinking about milling the heads down a bit. I didn't take them to a machine shop yet to check for true, but I think they will be ok. I will be staying N/A for quite a while, so I wanted to see about raising the compression a bit.

Now for the questions, how much compression would be added if I were to mill the heads say .030 or whatever it usually is? Stock is what, 9.0:1? Would it be worth the money? I am running 87 octane with 10 degree timing right now problem free. Say I would leave the 10 degree timing, would I need to put in higher octane gas?

Also, how does it affect piston to valve clearance. I know I should have at least .080" for intake, and .100" exhaust. Does it directly affect it? Say I had a clearance of .130" and then I milled them down .030, would that leave my clearance at .100?

Thanks for any help you can give me.

BTW, my combo will be: ported heads(valve job, dual springs), XE270HR cam, 1.7 rockers, explorer intake, blah blah blah

 

[Michael Yount]

You've answered your own p to v question - you reduce it by the amount that's removed from the heads.

There are other things to consider. When you 'lower' the heads, there may be misalignment between intake ports (manifold to head interface), and the lower intake bolt holes may not line up over the holes in the heads. Milling the heads moves them both lower and towards the center of the engine - because they're sitting at a 45 degree angle to the top of the block. Depending on how much the heads are cut, you may also have to cut the bottom of the intake, or port match to correct for port misalignment, and/or 'oval' grind the manifold holes towards the center of the engine so the bolts will line up with the heads. Also, depending on the cut, you may have to shim all your rocker arms or use shorter pushrods to restore the proper valve train geometry. Lastly, if it turns out you don't cut the intake but you do cut the heads, the end seal pieces (usually rubber or cork) may be too thick to allow the intake to seat the way it should - this can cause sealing problems, or in the worst case, actually break the intake as it's tightened. A good machine shop should be able to help you navigate the geometry of the situation.

Each engine is a little different - but to get a significant increase in compression ratio, you usually have to cut enough that the geometry issues come into play. If it were me, I'd keep the cut small (.010-.020") -- minimize related geometry issues, and take whatever small compression increase I happened to get.

 

[redterror302]

Mike, you always have an answer to my questions! Props go out to you.

Anyway, I never really thought about all of that. Now that I think about it, all that trouble doesn't seem to be worth the couple extra hp I might get, and the price as well. I just wanted to check with you guys though as to what your thoughts were on milling the heads.

Thanks

 

[Michael Yount]

Potential issues - I was careful to say what 'may' happen. The challenge of course is that you don't know how your pieces are gonna fit together until you start trying it. But, those are the things to think about before you dedide whether to do it or not.

 

[rd]

If you leave most of the other stuff alone, ie, stock cam, or less than .5 in lift, with stock valve sizes, you should be able to mill the heads .030 or so without having piston to valve clearance problems. If the end seals are a problem, delete them and just use silicone. I have two engines with milled heads, and have not yet had to machine the intake. Still using stock bolt down rockers on one, also.

Mill it, and check it, or check it, calculate the clearance stock and milled, and adjust as needed.

Yes it is worth it.

 

[redterror302]

hmmm, now I am not sure. I will NOT be using a cam with less than .500" lift though, even though that shouldn't really matter too much. I will ask the machine shop about what they think when it comes time for me to bring the heads in for the valve job. What kind of compression would it raise it to anyway, and what kind of gain may I see?

Speaking of pushrods, is there anyway to know whether I could still run the stock sized pushrods if I did not mill the heads? Is there anyway to calculate it, or do I just have to measure it? And, how do I measure for that?

Thanks for the replies.

 

[redterror302]

ttt

 

[redterror302]

ttt?

 

[Michael Yount]

As long as you use a cam that's ground on the same base circle as the stock cam (most aftermarket cams meet this requirement) the stock pushrod length ought to be fine. But it's always wise to check valvetrain geometry with cam/rocker/head/valve changes. Nothing to calculate - it varies combo to combo and use of an adjustable pushrod will allow you measure the pushrod length that'll give you the appropriate geometry. Peak lift doesn't really enter the equation given what we've been talking about. It has some implications with regard to how your ports flow, and you need to know that your springs can handle the lift (bind and pressures), but it's a non-issue with regard to p to v clearance.

 

[redterror302]

Oh I know peak lift has really has nothing to do with this. We have been over this many times No need to worry about the bind, I have double valve springs coming from thumper soon that are good for .590" lift.

I still question about the milling of the heads though. What kind of compression gain and power gain would I see? Noticeable? There is always the possiblity that I will run into no problems at all. Maybe I should just talk to the machine shop about it

Any input you guys can give about that would be helpful.

Just out of curiosity, what kind of compression ratio do you need, where it is mandatory to run higher octane gas? Like say I have 9.0:1 compression running 87 octane, what kind of compression would be needed to make it mandatory to run something like 93?

 

[Michael Yount]

As you're probably aware, knowing how much the compression is gonna change is complex to calculate. Theoretically you'd need to have the head cc'd before the cut and after the cut so you know how much the combustion chamber volume was reduced with the cut. That reduction is a function of the shape of the chamber - which as you know varies with different type heads, and varies somewhat from head to head and chamber to chamber even with the same heads. So for all of this you're talking 'rule of thumb' estimates. The same is gonna be true for the gain you get from a particular bump -- you'll have folks give you an estimate -- maybe 10HP per point of compression. The problem is that each of those estimates 1) rarely come from actual carefully controlled data where careful calculations/measurements nail down the ratio change and carefully controlled dyno testing verifies the results, and 2) the changes vary depending on the combo. As for octane/timing questions - you have the same issues at work. Each combo is different - and where the car is located (ambient temps, seasonal changes) and how it's used (daily driver slugging it out in traffic in a big city or weekend racer only) also impact what can and can't be done with regard to fuel selection and timing.

So if folks come in and say 'here's what happened to mine', take it with a grain of salt. Their results may not be applicable to your situation. My 'guesses' -- I doubt you'll pick up more than a point of static compression ratio with a safe cut. By safe I mean one that leaves plenty of 'meat' in the head, and allows you to work out any resulting geometry issues without major hassels. I doubt you'll pick up more than 10HP/ft-lbs with the change - but the good news is that CR gains help everywhere - from idle right on up. And they make the engine more efficient. If you have emissions laws to pass, the change may hurt you - more compression means more temp. in the chamber which usually means more NOx. As for timing - most folks say that you can get away with something around 10:1 with iron heads, 10.5 or 10.75:1 with aluminum heads and still run decent timing without running into detonation problems - but, again, it varies a lot depending on the cam that's being run, and what kind of shape the engine is in. Fuel selection is a real crap shoot too - all things equal aluminum heads will usually resist detonation with lower octane fuel/more timing than cast iron heads will. But I've read posts from guys who have to run 93 octane in their stock engines to get rid of pinging in the heat of the summer; and I've read posts from guys with modded motors that can run lower octane fuel without problems. It's my opinion that it's pretty unpredictable as to the specifics of what's gonna happen with yours. You pretty much have to decide if you want to try it, and then be prepared to deal with the results in terms of geometry changes, fuel selection and timing.

If it were me and I decided I wanted more ratio - I wouldn't try to get there by cutting the heads. I'd pull the motor and change the pistons -- I'm not suggesting that's what you should do necessarily; many folks have cut their heads with satisfying results. But I'd make a different choice.

 

[redterror302]

Wow, I appreciate the help. I know that I really can't get a an exact answer, I was just looking for a ballpark figure. One last question though. When you said about raising it 1 point in compression, do you mean one tenth, or .1? Like if I have 9.0:1 compression, did you mean it as it would raise it to 9.1:1?

Thanks again.

 

[Michael Yount]

By 'point' I meant from 9:1 to 10:1.

 

[thumper460]

Gota CC the chambers for the total answer... BUT, rule of thumb, .005 off is 1 cc less!

62 CCs and the compression is 9.4 with the 62CCs and .041 gasket and .005 deck...( rule of thumb) .030 off is {5 into 30 = 6 CC's} !! cool?? So, 62 CC's subtract the 6 CCs and the results are...56 CCs !! Now , with 56CCs and the rest all the same... the compression is now: 10.16:1 and that is good HP increase!! P/V issues will also need to be addressed, but with the stock pistons notches ( bigger with aftermarket) and stock valve size ( as my heads) you should be fine to run a healthy cam!! and you can use the RTV front and rear of the intake manifold to seal the whole thing up!! ( we have cut as much as .040 off and had no problems..P/V or intake match) FYI... this is where the "shims" for the rockers might come into play for proper lifter preloads.. Cool??

NOW... you have both sides of the issue... like was said befor.. check, measure and check again... but me?? do it!

Just me........................

Thumper

 

[redterror302]

Thanks thumper. I just got off the phone with a reputable machine shop near my area. He said for a good valve job, cleaning the heads, assembling, decking and I think that its, $400-450! Isn't that a little expensive? I don't think that the milling was even included in that price either. Should I look somewhere else? He said something like 140 or something for the valve job, per head. Man, I didn't think it was going to be that much.......let me know what you think.

 

[cleanLX]

the deck on E7's is not particularlly thick to begin with.
milling them for compression purposes is only going to weaken the deck, and 'possibly' lead to deck shift and head gasket issues...

Here's the "what I did - grain of salt story"
I had mine milled 0.020" and everything was fine... sort of...
The shop did a poor job on the mill, and I used up a head gasket.
Had a different shop remove 0.004" more in order to make the heads flat.
Now my lower intake does not fit! Nice milkshake situation. Who would have ever believed that!?... a mere 0.004 was the difference between yay, and nay.

In hindsight, I'm with Michael Y. on this one. Don't mill them any more than you have to to ensure flatness... lightweight compression altering pistons would be the proper way to go... just the the factory stock guys do.

Best of luck with your project.

 

[thumper460]

5.0GT... Hmmm.... I cant say for Pa.!! Yes it does seem pricey?? but then even you are a little concerned if you understood!! Usually tha standard Valve job with a surface is about 185-190 for both heads here, usually to mill another .030 is up to the shop, maybe 20-30.00 more ( charge by time spent). Performance valve jobs ( street ) is about 195.00 for both heads... but like I said, that is HERE not in Pa.!! cool?? Clean LX.. I never heard anything about the heads NOT holding compression or leaking coolant from a .030 cut, like I said we have cut quite a few at .040 w/o any problems...( so far...LOL) The intake interface is usally well within the correct alignment!! esp with the RTV in the front and rear valley. But hey... everyone should be aware when they start to mod... right??

Just me..................................

Thumper

 

[cleanLX]

Clean LX.. I never heard anything about the heads NOT holding compression or leaking coolant from a .030 cut, like I said we have cut quite a few at .040 w/o any problems...( so far...LOL) The intake interface is usally well within the correct alignment!! esp with the RTV in the front and rear valley. But hey... everyone should be aware when they start to mod... right??

Ya, when I read your post above it made me raise an eyebrow... was told to be careful in the milling department by Ed H. and that at 0.025" I should be fine with regard to deck stuff, so...
As for the alignment deal, it's likely more of my typical crappy luck. My entire Holley lower experience has been one of misery and wasted $$$...
Of note, and this has just reminded me, a stock lower fits fine in the valley, but not the Holley! yep... very !

 

[redterror302]

Yeah, he did mention something about a standard valve job and a performance valve job. What is the standard valve job, 3 angle? I mentioned something about a 5 angle valve job, and I think that is what he said the performance one was. He said something but I wasn't really paying attention(lol), but I remember hearing something about a backcut. So which one do I want to go with? 5 angle right?

I am going to check around at some other machine shops to see what they charge as well. I wasn't planning on spending that much, but we'll see. Without the valve job, it won't help porting it that much would it?

Thanks for the replies.