another j head question

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63dartman

63dartman

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I was going to put some time and effort into a set of 302 castings I have laying around for my 360. I soon realized that The money it would take to make them flow on my 360 is out of my budget for now. I think I will save them for a nice 318 build later.
I currently have stock rebuilt j-heads with stainless valves(1.88-1.6)comp 901 springs. rebuilt less than a year ago. I have no issues with the heads as they are now except that they sit on top of factory dished pistons. I want to shave 50-60 thousandths off the heads to increase compression.
Will shaving the heads give me a decent performance upgrade? I am running spitfire headers and 2 1/4 duals so I think breathing won't be an issue.
Also will I need to worry about valve to piston clearance with a .480 lift cam? If needed I can check the clearance before assembly. I will probably be using the mopar thin gaskets too. I believe they are .024 compressed.
I will also be swapping to crane gold gold rockers. That is another reason for shaving the heads. My pushrods are 60 thousandths short which causes my adusters to sit too far down and throws off the geometry.
It will cost me $250 to get the heads milled and freshen up the valves.
Seems like a win -win situation to me.
I am also calling mrmopartech this weekend to get the specifics on the shaving. I believe there are concerns about shaving too much off the intake side of the head and causing valve cover sealing issues. I have read some of his previous posts on this and he DOES know what he's talking about.
What do you guys think? Does this sound like a a good thing to do?
 
63dartman,
You can do this and you shouldn't have any issues, but when cutting .060 off the deck surface then .072 will have to be machined off the intake side, or the intake manifold will have to be cut, but then this manifold will only fit the heads that they will be cut for. So your better off cutting the intake side of the heads as then they can be used on any engine and so can the intake maniflod. As for valve to piston clearence with the .480 cam. If the piston is at stock location they will be .080 to .105 in the hole, plus the thickness of the gasket and the recess of the valves in the head, by recess I'm talking about how far they are from the deck surface of the head to where they sit on the seat. So valve to piston clearence should be more than enough. I would be more worried about the retainer to guide clearence than valve to piston clearence. As stock guides wont take much more cam without hitting the top of the valve guide, so this needs to be checked. You need .100 clearence over the valve seal to be safe, or it has to be machined.
Stay with the small valves as they will be better for torque on the street and occasional racing.
 
Excellent point BJ about making the heads fit the intake and not the intake fitting the heads. He might want to use that manifold on another engine or two. Topping the guides is always a good idea when you have the heads off. More freedom later. Another good point there BJ.
 
Thanks BJR, I Believe the guides have already been done. Now what kind of improvement will gaining a point on compression do for me? Will it make the car funner to drive down low? I will let you guys know how it works out. I am planning on pulling the heads on Tues. and dropping them off.
 
Something else to think about...The surace you have to cut to make the intake fit is the valve cover sealing flange. There is a limit where the valve covers will need to be modified, and they wont have much to seal on. I use .050 as a max there...and just accept that the intake is now dedicated to that engine only. Also, any milling beyond .030 you must check lifter preload and rocker geometry. You will need either shorter pushrods or shims under the rocker shafts.
 
yep, moper. that is one of the reasons for me shaving the heads. I kinda eyeballed the length of my custom pushrods and now they are too short for the crane adjustables......about 60 thou to be exact. Sometimes I hate telling on myself. Hopefully it will all come together like a big hot fudge sundae with a cherry on top.
I hope you guys understand how grateful I am to have you guys around to answer my questions. More than A few times I've second guessed advice I've got from alot of you and believe me, I am paying the price!!
I am learning alot and having a good time doing it. I just wish I would have put those damn kb pistons in and balanced everything twice. Then I wouldn't be sitting here asking about shaving the heads!!! I think the majority of the posts told me to build it right the first time. I was trying to save a few bucks. Now I know that those few bucks saved are going right back in with alot more work involved. At least I get to see how my cylinder walls and stuff look, I will take pics and post them as I disassemble and put back together. Thanks again everyone.
 
63dartman,
Glad that we/all could help you out keep us informed, you have my # call if you need anything or have a question, let us know how it turns out.
 
Another question, Do the head bolts need to be shortened if the heads are milled? I wouldn't think so but, It's better to ask before I make a mistake that would cause me to tear everything apart again. Also do I need to take a total of .072 off the intake side, .036 per side? or is that .072 per side?
 
here are what the the heads and cylinder look like. I was running a 750 eddy carb. I knew it was to big. Need to rejet it or get a a 650cfm.
 
Now what kind of improvement will gaining a point on compression do for me?
Click to expand...

I remember reading in one of the engine books that it was around 10 hp per compression point. :thumbup:

Someone who knows more that me will have to explain the other benefits.
 
The increase is a percentage, and it is accross all rpm ranges. But, the greatest gains seem to be going from under 9:1 to over 9.5:1. Beyond that, the higher you start with, the less you gain, with arond 5% being the "norm". The best thing is, it helps low speed performance the greatest. That's where a street car needs it. Head bolts dont usually need any help, but you should be running a bottoming tap down each bolt hole and blowing out the debris. I have seen holes so full of gunk (Mopars the holes all end..not go into water jackets) that the bolts may have a rough time setting deeper in the holes, or the torque requirements will be way off. So clean them out, and chase the threads on the head bolts, and you'll be fine. If it's excessive milling (beyond say .100) then you could carefully grind away the bottom of the bolt for one thread or so...

That looks just like a low compression large chamber setup...lol. Jetting the 750 woint help that. A smaller carb that mixes better will. Think of all that carbon residue like a self sustaining compression increase!
 
63dartman,
As for the bolts just use the mopar performance head bolt washers as they come 10 to a pack or at least they use to.Then as for milling you have to remove that much from each head if the amount is to be taken off each head. Mopar says to remove .012 for every .010 off the deck. The head bolt washers are about 1/8 to 3/16 thick and are beveled so use the concaved side down, and you wont have any problems with the bolts. You can take .020 less on the intake side if your worried as most heads can be cut .020 without being machined on the intake said. But when taking this much watch out for the end rails of the intake manifold as this will close the gap in a hurry so machining of the end rails may be necessary, as the end rails will drop twice as fast as the sides will, so if your taking .072 per side then the end rails will drop .144. Then the use of silicone will do the job in place of the end gaskets. Some manifolds will be somewhat flat and if this is the case then have your machinist use a end mill and mill just the rail and if theres a lip left on the manifold where the end rail doesn't touch leave it as this will sit down into the lifter valley and help to keep the oil leaks down as the oil will have to get by the lip and block and then the sealant or the gasket. Neat little trick that helps to keep the intakes from leaking. Don't have him take anymore than need be to make the manifold fit, and you may not have to take anything off.
 
Thanks moper and BJR. I dropped off my heads yesterday. Talked to the machinist and he has done j-heads before. He wants to split the amount of material taken off the intake side between the head and the intake. After disagreeing for awhile I told him O.k. I know that makes my combination a custom fit. He told me he will give me all the dimensions so I will know how much to remove from a new intake if I want to change it out. He also wants to do a test fit on the manifold before removing any material.......That I agree with, better to check and recheck before taking too much and scrapping my manifold. Of course he is doing a pre and post cc of the chamber too.
I will let you guys know how everything works out. I will also be swapping to a 650 eddy from the 750.
 
Just got off the phone from the engine shop. Heads were inspected and came out good. Vacuum checked for valve sealing, also told me hardened exhaust seats are already installed. (knew that but, just wanted to make sure) Valve guides and valves good, no other work needed except the milling, that's good news.......Told me they are ready for cc'ing and cutting. Should be back in a couple of days or less.
 
I was quoted at $244.00. I called a couple of shops and all of them were close in price except for one, They were way high! I went with the one I did based on recomendations from a few friends.
 
Thats cheap, around here in the south east (Atlanta) they would get around $500.00 or a little more for everything, and thats the ones that would want to mess with it. Most don't care to do things like this as they want the fast money and the stuff that takes time they dont mess with. This is why I opened my own performance shop 20 + years ago and I'm still here, because I'll do the things that it takes to get the job done and there isn't any rush, the time it takes it the time it takes. You cant rush and do things right. IMO
 
That's a little cheap around me. Not sure what "vaccum tested" was tho. A head inspection for me means pulling all the valves, so you can see the seats and how they are working, measure runout and the guide clearances, and inspect all the parts well. That's $150 without magnafluxing. It's the "extra" milling that drives the costs way high...lol. A skim pass is one thing. More than .020 and they make multiple passes, then have extra setup time for intake flange milling...etc etc etc.
 
Moper,
Vacuum testing is to check the valves seating, if they hold vacuum then they are sealed tight, if not there leaking. I've seen ones that wouldn't leak fluid and would leak vacuum. Vacuum will find very very minor leaks and fluid will not.
 
BJR Racing said:
Moper,
Vacuum testing is to check the valves seating, if they hold vacuum then they are sealed tight, if not there leaking. I've seen ones that wouldn't leak fluid and would leak vacuum. Vacuum will find very very minor leaks and fluid will not.
Click to expand...
Just curious - what vacuum do you pull during testing?
The shop I go to test to 28 inches.

I'm sure I stand to be corrected , but I thought BBs were .012 and Sbs were .0095 off the intake face?
 
63dartman said:
I was quoted at $244.00. I called a couple of shops and all of them were close in price except for one, They were way high! I went with the one I did based on recomendations from a few friends.
Click to expand...

FWIW, you can get a set of high compression pistons and new rings for that price and get more of a bang for you buck in a compression increase than shaving the heads and you wont have to deal with shorter pushrods.
 
Let the fun begin.........I just talked to the engine shop. Heads are milled and cc'ed. just need assembled and I can pick them up tomorrow. Now for the kicker!!
Pre cc was 61, after milling.........48cc holy crap. Did I just make a scrap pair of heads? Is this too much milling? It was all my fault, I didn't tell them to call with the pre cc numbers before starting the milling. I just assumed the heads were close to stock because it didn't seem like my 360 had any compression. I don't think I will be using thin head gaskets anymore:)
Also, when checking piston depth in the cylinder on stock pistons do I check the height at the edge on the higher section or the center dished section? I want to try and get a good estimate on my compression.
 
63dartman,
You check at the high point of the piston which in this case is the outer edge. As for the heads being this small use a .055 gasket and hopefully the piston is .090 or more in the hole, and if it is then this engine will fly as I did one a few years back and was one of the faster engines on pump gas. Mine was .105 in the hole and dished pistons and a .055 gasket I think that I came in around 9.8:1 or so, but I know I ran it on pump premium gas. My heads were 47 cc's.
With these heads and a zero deck piston and alcohol and a .040 gasket and look out, fun is just around the corner.
 
Thanks BJR...I've been around all kinds of shops for about 20+ years..I've never seen a head "vaccum tested". It makes good sense, just never saw it...lol.


63, if your heads started at 61cc, they had already been milled a bit. I'd guess around .050" to go from 72-71cc to 61 ccs. Do I understand right you took off and additional .060? I havent cut small block heads that far ever. I cut big blocks to .100, and that's thin, but you have 5 bolts around the holes. Small blocks dont. If BJR had no issues, maybe you're fine. I'd bolt them on at this point anyway (you spent the $$ on them), but that's too thin on the decks to me. Be careful about the head bolt length too. They may now be too long like you worried about. And your valve train geometry will be WAYY off. Make sure you correct it.
 
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