The Stovebolt Site Forums The Shop Area The HiPo Shop 6 cyl. head milling

I have a 261 in my truck, 270 cam grind, solid lifters, headers, 500 cfm holley, and flat top 60 over pistons. I have a extra 848 head that I would like to some porting on, and then have it angle milled around 160 thou., to 0, to help build comp. Does any one have any experience in doing this. I have heard it before some where, don't remember where though.

I have angle-milled small block V-8 heads, taking off .100" at the spark plug side of the head to zero at the intake manifold, but I've never tried it on a stovebolt engine. I can't think of a reason it shouldn't work, as long as it doesn't change the valve geometry in some oddball manner. I assume you'd angle the head in such a way that the valve-to-piston clerarance wouldn't be compromised?
Jerry

I don't think I will have a valve to piston problem, as I already had to fly cut my pistons for the proper clearance.How much do you think could be removed on the angle mill until I have to address head bolts lining up correctly? I also thought I would have the intake and exhaust angle milled to straighten them up. I believe if I take off around 140 thou., or so, it should make a noticeable compression change. The entire goal is try and gain compression.

.160 to .000...what is that going to do to the head bolt alignment? Just curious.

On the small block heads, I spot-face the area where head bolts pull down on the head square with the block after the angle mill is done. Unless you create a big change in the carburetor base angle, it shouldn't be necessary to modify the carb mounting flange or the exhaust pipe flange. You might want to test-fit the manifolds and use an angle finder to see how far out of level the carb base will be.
Jerry

Well thanks for the reply's, this is the best info on this I have got yet. I had figured that re-aliening for the head bolts to pull down even would be necessary. Next step is to go see the machine shop, they love my 6, said that was the funnest machine work they had done in a while, so I would think they would be happy to do this angle mill for me to. It is my under standing, from experience and reading, that, a large part of the flow problem for this head is in the exhaust, so I plan on porting it as much as I can. The real problem with that is that I don't really have any experience in porting. The good news is I will when this done. I am just trying to get all that I can from my motor, and not buy real expensive pistons, or a head. The motor is in the truck and runs pretty good, trying to get a little more mid range, I think a little more compression and exhaust flo will help a lot.

Care full on the "get as much as I can" exhaust flow. You can get to much. Ideally you want 75% of the intake flow on the exhaust side, so work on both ports if you do anything. As for porting, remove all sharp edges and rough casting and try to maintain a even port size from the valve to the end of the port. A long, cool torch flame pointed down the port will show you where the air flow likes to go. If it jumps off the wall trying to make a corner, work on the corner. Same idea as water flowing off a car, it likes to follow a certain curve, any more and it splashes off.

On the Inliners.org site, they cut one of those heads apart and showed the internals and how to port one, do a search and read up on it.

Joe

If the bolt were the same length as the head is wide, the bolt's new angle would be as far away from original as the distance milled: The bolt head would be moved over .160", etc. How "loose" a fit the bolt is in the head now will determine whether the hole must be enlarged; if it's 9/16" now (bolt is 1/2"), that's only 1/32" radial clearance and the bolt will bend in the head.

I'm not sure .160" is safe, even if only taken from the plug side (which I assume was the idea?).

Let me suggest that you consider another option, since you're getting pretty sophisticated with this sort of modification. Install studs, not head bolts into at least a few places in the block to check for bolt hole clearance. Using studs in all the holes is best. You might have to enlarge the bolt holes to avoid interference problems. This should probably be done on a Bridgeport mill, with the head gasket surface clamped to the mill table, on parallell blocks to allow a drill bit to extend through the head without contacting the table. There should be enough thickness in the casting to enlarge the holes 1/32" or so. Follow up by spot-facing a 1" diameter area at each bolt hole, and use a hardend steel washer between the nut and the head surface. This is pretty much standard procedure on the blower-equipped hemis we run on the tractor pull circuit. For some reason, head gaskets don't blow as often on engines with studs instead of head bolts.

Porting- - - -Usually, "less is more". It's easy to grind through into a water passage and ruin a head after doing lots of expensive work, and the stovebolt head doesn't gain much flow advantage even with radical port modifications due to the cast-in restrictions in the ports. Just clean up any roughness and smooth the passages, and maybe install the oversize exhaust valves that were used on Powerglide cars along with some pocket porting to improve gas flow around the bigger valves. The modifications you're suggesting will only be effective at or near full throttle- - - -big valves and ports have a tendency to reduce, not improve low end and midrange power.
Jerry

If you already have intake valve reliefs in the pistons, the biggest reason for an angle mill is gone (preventing the valve from hitting).
The compression increase from an angle mill is always less than a straight mill to the same distance.
The head's width prevents a high angle cut, because it will take too much off the deep (plug) side before sparking out on the shallow (port) side. This means that the new angle won' improve the ports efficiency (something you might get with a V8 head).

Sorry, guys, but I'm not clear on why the angle milling. Seems like taking .080 off all the way across would be easier and accomplish the same thing as taking .160 on one side.

cm

If the combustion chamber is sit off to one side, then milling most of the material from that side will give the most compression. So angle milling is the easiest way to do it. I would suspect on a V8 you also have a advantage of changing the intake to head angle for a better air flow path to the valve.

Joe

You got the picture, Joe. Looking at a stovebolt head, most of the open area of the combustion chamber is on the spark plug side, so taking more metal off there makes sense. It also minimizes the distance the intake valve is moved toward the piston, so less material needs to be flycut from the piston crown for valve clearance. There doesn't seem to be an advantage from a valve angle difference on the 6-cylinders.
Jerry

Good God, thanks every one for their response, I have posted, and talked to people on this idea, that I know will do some thing, and got either no response, or total negative, so thanks again.
First, I am not angle milling for flow, only to help with compression, as I have flat top pistons. It seems to me to be the time to address the exhaust flow though, as I know it needs to be addressed.. I mostly plan to just open the port mostly around where the valve lets the exhaust go into the port. I am sure it will be confusing, with measuring, and mostly hand tools. Mite ask the machine shop about it, sure proud to do as much as I can my self though, also plan to check the gaskets for matching.
My biggest question is my idea on 160 thou., for my angle mill, is that enough, or to much. I don't want to make a mess, you know, back to less is more.
The motor is in my truck and runs quit well, just the mid to upper RPM range could be better.
If any one else is going to build one of these motors with a big cam, don't go with the 270 cam grind from Clifford. If I could chose again, I go with their circle track cam, gets you a longer exhaust duration, witch would only help in what I am trying to improve on.
thanks again, Oppy

Let me suggest that you start with a good cleanup of the head, and do a CC check of the stock combustion chamber. You'll need to have the valves and spark plug installed on at least one combustion chamber, and a clear plastic cover over the chamber with two holes, one to pour the checking liquid into, and a vent hole to let the air escape. I use Vaseline to seal the plexiglass down to the head surface. Rubbing alcohol with a little food coloring in it makes a good checking medium. Use either a big syringe graduated in CC's, or a Burette cylinder if it's in the budget. The last Burette I bought was a 100 CC capacity, and it cost me about 50 bucks.

On a 76CC small block Chevy head, a .100" angle mill reduces the volume to 60CC, which gives more compression than a very expensive "Camel Hump" head for a 300 HP 327. I also install oversize intake and exhaust valves and do a little pocket porting. The head also has the "low compression" casting number, which makes the claimer engines that I build technically "legal" at the round tracks we run.

Let me reccomend that you start off with about a .100" or maybe .125" angle mill job, followed by a CC check. You can always cut a little more if you need to- - - -it's impossible to put metal back once it's gone!
Jerry

Edit: looks like the price went up since I bought my CC kit!

http://cgi.ebay.com/100mL-Glass-Bur..._DefaultDomain_0&hash=item2c5ddcad77

Jerry

Thanks to every one, Jerry, I have made plans to cc my head with a friend. Figure I can start there, figure, or, as I run, estimate, the milling, in different angle mill cuts, 100thou., 120thou., etc, etc...
So, Starfire4, if you take 80 thou., off all the way across,it will also leave your intake valve sticking a long way into the combustion chamber, on these 6 cyl heads.
I will try to keep you guys posted on the out come of this. The other problem is when I put my cam in, I called Clifford to get cam spec info to degree my cam, and he told me to just put in straight up. I have Cloyes timing gears, so while I'm doing this new head, I am going to check compression, then advance cam timing, check again for compression increase, then retard cam, and check compression again for increase, and set it at the highest compression.
Does this sound rite, or is there a better way?

Advancing or retarding the cam has more to do with torque and horsepower readings on the dyno than compression pressure. Basically, advancing the cam increases low-end torque and drops top end horsepower a little. Retarding the cam helps HP at the expense of a little bottom end. On long, fast tracks where the RPM could be kept on the high side, we would retard the cam a few degrees, usually no more than 4 or 5 degrees. Where we needed a good holeshot off the turns on a short track, we would do a 3 or 4 degree cam advance. For overall good street performance, I'd install it straight up.

Retarding the cam eats up piston/valve clearance in a hurry, as the piston tries to catch up to the exhaust valve as it's closing. On a stovebolt with the deep-set exhaust, that won't be a problem. One very radical roller cam we ran on a 350 engine had the closest piston/valve clearance at 15 degrees AFTER top dead center- - - -the intake valve was accelerating faster than the piston for the first few degrees after TDC. I doubt if you'll encounter that problem on anything you can drive on the street!
Jerry

Thanks again Jerry, I just don't think the cam is in time correctly, I would not buy another cam with out making sure it came with a cam card so I could degree it when installing, that's the reason for the Cloyes timing gears. It just doesn't seem to be as strong at any rpm, than I had hoped for, and doesn't seem to have as much compression as I had planned on. I had my block milled to zero deck height,that removes about .060 off the deck, that's why I had to fly cut my pistons to make room for the intake. I can't get it to idle at much less than 1100 rpm, because of the lack of vacuum, I'm sure. It does sound great, no one can believe it's a 6, until I show them.

You don't need a cam card; just degree it and record the lift every 5 degrees of rotation. You should be able to document the location of the clearance ramps and the actual valve travel, and draw a lift curve on graph paper. Find the lobe centerline for both intake and exhaust, and adjust the advance/retard accordingly. It's possible you've got a bad cam grind. I've never heard of a cam grinder who does not supply a specification card with their cam.
Jerry

"I called Clifford to get cam spec info to degree my cam, and he told me to just put in straight up"
That means he doesn't know.

The highest compression means closing the intake valve at BDC, or advancing the cam 40 or 50 degrees.
As you said, you can't install it "straight up" until you know where straight up (usually split overlap) is.

What's your cranking compression now?

When I said straight up, I meant to just use the factory timing marks. I have degree'd cams before, there is always a cam card to to tell you when the intake valve should open in time with the crank. I am not sure if I did get a bad cam or not, the bad thing is that I have had this cam for about 5 years now. I kind of think I might have got a bad cam. It does sound very mean at a idle, then just doesn't ever have a real strong spot in the rpm range. My old motor was a 235 with a 261 cam, 848 head, Fentons, Clifford intake with Edlbrock carb., and this new motor does not seem to run as strong as I think it should for what I have now. Guess I'm just to hard headed to give up. If I had the money, I would order a new cam from some one else. I still might put original 261 cam back in,?????

The 261 cam has only slightly more duration and possibly a little more lift than the stock 235 cam. It would be a major step backward from what you have in there now, but it would definitely make it idle! In general, about 270 degrees of duration is the max I would reccomend for a street-driven cam. I'm not sure where the 261 cam comes in there, but since it was used in the heavy-duty trucks, it's more of a low-end pulling cam with lots of torque than something designed for high-RPM horsepower. Your compression increase with the decked block probably needs a little more radical cam than the 261 would be. Closing the intake valve too soon with high compression will cause some pretty severe detonation at times due to the fuel trying to self-ignite (diesel) due to compression pressure. A friend put some 11:1 pistons in a Triumph TR-4 engine with a stock cam, and promptly detonated holes in a couple of pistons.
Jerry

I only brought up the 261 cam because I have that to compare with, from my old 235. With my 270 cam, and such a rough idle, it is harder to start, and keep in tune, at least with the 261 cam, it would be street drivable. I did some 261 cam research, and most of them had the same cam grind as the Corvette 6 cylinder cam. It made an improvement in my 235, very noticeable. I probably wont change the cam, has crossed my mind though.
Back to my head, I am going to do a compression check, and report back on that. What do you guys think it should be? I think it should be around 170 pounds, maybe more?

My opinion is that you have already addressed compression sufficiently(by zero decking)and should concentrate on flow for additional improvement. Installing larger powerglide intake valves (1.94" dia. GM #3835519) will improve inbound flow and for exhaust open a valve halfway and measure the distance from the valve head to the combustion chamber wall. While doing this you should notice a lump on the chamber wall in that corner and by altering it to unshroud the valve exhaust flow will go up. To see pictures of an 848 head cut thru several planes and observe wall thickness click on webshots in my signature and then the 848 head album.

Ok, so I did a compression check, its only 115 lbs. I knew it was low, but that is very low. I think even more strongly now that the cam is a problem in this motor. I did check more than 1 cylinder.
It is pretty disheartening to put this much time, $, and ambition into this motor and get these results. It does run ok, but my old 235 ran darn near as good, and more drivable, and low end.
I am not sure what to do now, pretty confused, mite still build my other head with the angle mill, and put my other cam in. I just don't have the cash flow to buy another cam, if I did, it would have a cam card, and longer duration on the exhaust.
Thanks for all the input, I appear to be in a holding pattern now.

Before you start swapping cams, at least find the opening and closing point of both valves. Don't forget to account for the clearance ramps when figuring the duration. There will be a noticeable change in the rate of lift once the clearance is taken up. There will be a corresponding slowdown of valve speed just before it touches the seat to prevent battering the valve and the seat. If the intake is closing a long way up the compression stroke, you've found your loss of compression pressure, because pressure isn't going to begin building in the cylinder until the intake gets fully closed. By advancing the cam a few degrees in relation to the crankshaft with an offset Woodruff key on the crankshaft gear, you'll help the compression, and also boost low-end torque. There will be a slight drop in top-end horsepower, but there's no free lunch. Combined with the angle-mill on the head, you might get enough of a compression boost to make the engine come alive without a cam swap.

If I still lived in Merced I'd be glad to help you do that cam-degreeing job. Good grief! Did I just think about going back to Commiefornia? I must be losing my mind!
Jerry

Well thanks, I guess I will try a little harder to stay calm, that is not a strong point of mine. I have a friend local that I can get to help me with cam degree-ing, maybe.I knew the motor was way low powered, I do have experiences some of this. I should be able to advance the cam via my Cloyes timing gears, the crank gear is slotted in 3 places for that.
Just a little disappointing.

You won't know if the cam is bad, timed wrong, or just fine and you have no ring seal until you check it.
The problem is that although advancing the cam (as suggested) will bring up the cranking psi, you don't have much room to work with before the intake valve crashes the piston. Advance always reduces intake PV clearance at overlap; retarding reduces exhaust PV but harmless in the stovebolt.

With a dial indicator and zero lash, you should be able to find the duration with in a few degree's. If you start at .050" and end at .050" you can compare that to most any cam on the market. Theres a lot of number crunching in cam selling!

Joe

Just thought I would throw in my thoughts on this topic.
Having had many chevy 6's, Gen II and Gen III, I have tried many ideas to get the most out of them. Some with success some with not so good results.
On the subject of milling the head; Gen II, if you are going to mill the head, angle milling can be of some benefit if you are willing to move the head to the port side of the block. Bolt holes must be enlarged and spot faced back paralell to the deck.
Also make sure you have not covered any water passages. Moving the head in this manor will put more of the chamber over the cylinder and allow more room for a larger dome on the piston.
This has proved to be a benefit in drag and round track racing.

Gen III can also benefit from this practice as it unshrouds the intake valves by moving the intake valve closer to the center line of the cylinder to eliminate the chamber overhange on the deck.

Little changes can have good results.

I always send my head work for inline sixes out to Sissell's Automotive in El Monte. They have website with this name. Google them up. Great, accurate work, excellent parts used and they do stand behind what they do. I have no complaints and I have been dealing with them for over twenty years.
Normbc9