# Cylinder Head Milling for a 1cc Reduction

In the course of milling cylinder heads for a specific decrease in combustion chamber volume, it becomes necessary to know exactly how much a cylinder head must be milled for a 1cc (cubic centimeter) reduction.  While this value is useful for milling heads for a specific compression ratio increase, this value becomes increasingly more important when attempting to equalize combustion chamber cc’s over the length of the head due to a particular head having cylinder chambers that get progressively larger (or smaller depending upon your perspective) from one end of the head to the other.  For a number of cylinder heads out there on the market, there are resources that can be accessed to obtain this information but for the non mainstream engines such as the Ford Y-Block, that information is vague if it’s to be found at all.  To add to the confusion are the different combustion chamber shapes that were available on the Ford Y-Blocks over the course of its production run.  With all this in mind, I’ll share the steps I use to determine how many thousandths of an inch a particular head must be cut to reduce its chamber volume by 1cc.

1. Measure the distance or length around the edge of the combustion chamber on the head. (inch format)
2. Take this measurement and divide by pi or 3.1416
3. This result multiplied by itself or squared.
4. This result multiplied by 0.7854 (this is the result of pi divided by 4)
5. This result multiplied by 16.387 (this is the result of 2.54 cubed)
6. Take the value one (1.0) and divide by the previous answer.  This will be the amount to mill the cylinder head in an inch format to reduce the combustion chamber volume by 1 cc.

Or looks like this in a math formula:   1 /  (((measured distance / 3.1416) squared) X 12.87)   =  inches cut for a 1 cc reduction.

The first order of business is to measure the actual length around the edge of the combustion chamber and this can be performed from at least two different approaches, either being equally effective.  One method is to simply take a piece of wire or string and lay around the edge of the combustion chamber along its perimeter which will provide a measurement of the length around the chamber itself.  Another method is to lay a piece of paper or light cardboard over the combustion chamber and rub the pattern of the combustion chambers edge onto the paper or cardboard.  This chamber imprint can then be measured for its length with a number of different measuring devices of which a map route reader is both inexpensive and effective.

For the following example, a Ford truck 292 ‘CITE’ casting head is being used.  On this particular head, the measurement around the length of the combustion chamber is 10.63”.  Going through the aforementioned calculation steps, the final result is 0.00678” (rounded to 0.007”) and this would be the amount to mill the head for a one cc reduction.

But to take some of the work out of calculating the amount to mill for some of the various Ford Y-Block heads, here’s a chart with some known values.

 Cylinder   head casting Combustion chamber perimeter Amount of cut for a 1 cc reduction in combustion   volume 113 11.02” 0.0063” 471 11.38” 0.0059” B9TE-A 11.02” 0.0063” COAE-A 10.31” 0.0072” C1AE-C 10.47” 0.0070” C1TE-D 10.63” 0.0068” EBU-A 10.75” 0.0066” EBV-C 10.83” 0.0065” EBY-B 11.06” 0.0063” ECG-D 10.98” 0.0064” ECG-H 10.79” 0.0066” ECL-A 11.02” 0.0063” ECL-B 11.02” 0.0063” ECR-A 11.02” 0.0063” ECR-C 11.50” 0.0058” ECZ-A 11.50” 0.0058” ECZ-B 11.26” 0.0060” ECZ-C 11.02” 0.0063” ECZ-G 10.94” 0.0064” Mummert aluminum 11.34” 0.0060”

Armed with this information, it’s now possible to mill a pair of heads of different or varying cc’s with a specific amount of cut for each head and ultimately having them equalized or all the combustion chambers at the same cc’s on the first cut.

Special thanks goes out to Tim McMaster and Carl Lynn for providing additional head tracings for some of the various Ford Y-Block head castings that were not on hand.                                Until next time, happy Y motoring.  Ted Eaton

This article was originally published in The Y-Block Magazine, Issue #104, May-Jun 2011, Vol 18, No.3

# Milling Heads for a Horsepower Gain

Over the years I have heard a variety of numbers from 2% to 10% for what a point in compression ratio is worth in regards to horsepower output.  The ten percent value obviously sounded a bit exaggerated while the two percent value sounded a bit on the small side.  While dyno testing a variety of cylinder heads on the 312 dyno mule, the opportunity arose to determine exactly to what extent a compression ratio increase would have on the horsepower output.  The dyno mule is the well used, tried and proven +060 over 312 with a Crower Monarch 238@050 camshaft ground on 110° lobe centers,  a Mummert aluminum intake with a carb spacer, and a 750cfm Holley carb.  The bottom end is still pretty much stock with ECZ rods and cast pistons that are sitting 0.025″ in the holes.

By lieu of the number of heads being tested, two different test scenarios presented themselves.  One set of tests involved several pairs of heads with the same casting numbers that were simply milled different amounts.  The other test was taking two sets of heads and dyno testing them in a before and after milling scenario to determine exactly how much compression ratio increases were worth on these particular pairs of heads.  This later opportunity was obviously a more controlled test in that variations within the head castings themselves would be eliminated.

In collaboration with Tim McMaster who had already shipped several sets of heads as part of an extensive cylinder head test, it was decided to take two sets of those heads and dyno test these in a before and after milling test.  The heads selected for this test are a pair of ECZ-C’s and a pair of C1TE-D’s.  Both sets of heads were initially run on the test engine in their ‘as delivered’ state of mill.  The heads were then milled and re-ran with everything else on the engine remaining the same.  The headers being used are the Engine Masters Challenge headers with 1.75” tubes stepping up to 1.875” before going into a 3” merge collector.  Mufflers are being used.

The C1TE-D heads have no port work on the intake sides but the exhaust sides have been ground on and opened up.  The valves have been upgraded to 1.805” for the intakes and 1.600” for the exhausts.  Initial combustion chamber volumes averaged 74.2cc providing an 8.41:1 static compression ratio.  Peak horsepower in this format was 294.5 at 5400 rpm while peak torque was 334.6 lbs/ft at 3800 rpm.  The heads are then cut ~0.045” which nets an average of 68.2cc for an 8.95:1 compression ratio.  The peak horsepower jumps to 297.1 at 5100 rpm and the torque increases to 337.4 lbs/ft at 4400 rpm.  That’s a 2.6 HP increase for a 0.54:1 increase in compression ratio or a 1.63% increase per compression point.  The calculated horsepower increase for a full point of compression in this case would be 4.8HP.

The ECZ-C heads have had 1.900” intake and 1.600” exhaust valves installed.  The intake and exhaust ports are still stock and have not been ground on.  The combustion chamber volumes in the ‘before’ test are 74.0cc producing an 8.43:1 SCR (static compression ratio).  The peak dyno numbers for these heads before milling are 289.5HP at 5400 rpm and the torque is 333.8 lbs/ft at 3900 rpm.  The heads are then milled ~0.050” which gets the combustion chambers down to 67.3cc for a 9.04:1 SCR.  The horsepower in this format jumps up to 295.4 at 5300 rpm while the torque increases to 338.5 lbs/ft at 3900 rpm.  That’s a 5.9 HP increase for a compression ratio increase of 0.61:1 or 3.34% increase per point of compression.  The calculated HP increase for a full compression point in this case would have been 9.7HP.

But now we get to discuss the other testing scenario.  There are three sets of stock ECZ-C heads being run on the dyno mule and while the ports and valve sizes were stock, the pairs of heads had been milled differently.  The compression ratios were 8.12, 8.6, & 9.0:1 with the HP values being 273, 280, & 288 respectively.  As expected, there was a HP increase with each increase in compression ratio.   In calculating the increase from 8.12:1 to 8.6:1, there is a 5.34% increase in HP per compression point.  It’s found that the increase in CR from 8.6:1 to 9.0:1 produced a 7.14% HP increase per compression point.  And in examining the overall increase from 8.12:1 to 9.0:1, there is a 6.24% HP increase per compression point.  As mentioned earlier and because this was three different sets of heads being tested, there are still some other variables being introduced but the fact still remains that each compression ratio increase did net an increase in the horsepower output.

In the definitive milling test, there is an average of 2.6% HP increase per point of compression.  In the less definitive test where three sets of heads with different combustion chamber volumes were tested, there is a 6.24% HP increase per point of compression.  Regardless of which value you’d like to use, compression ratio increase is still the easiest and least expensive method in which to up the power output of your engine.

As always, this is food for thought.  Until next time, happy Y motoring.  Ted Eaton.

Click on pictures for a larger image

Originally published in Y-Block Magazine, Issue #106, Sep-Oct 2011, Vol. 18, No. 5

# Camshaft Balancing

I’ve always said, “If it spins, then it likely needs balancing”.  When going for that last bit of detail in blueprinting an engine, then camshaft balancing comes into play.  How much is it worth you ask?  That’s difficult to say as I’ve simply not tested this scenario by itself but suffice to say, it sure can’t hurt.  The camshaft itself runs at half the speed of the crankshaft so any amount of centrifugal imbalance is already reduced to one fourth of the significance of any crankshaft imbalance.   And because the camshaft is somewhat isolated from the crankshaft by lieu of the timing chain, then transmitted harmonics will be minimal to or from the crankshaft.  But any imbalance at this point can still be an issue in regards to camshaft bearing wear and/or valve train related breakage.  And any harmonics transmitted to the distributor as a result of these imbalances can also produce havoc within the ignition and can go so far as reaching the oil pump.

On a solid lifter engine such as the Ford Y-Block (239,256,272,292,312), there is the remote possibility of lifters being deflected from the lobes as a result of imbalance.  To compound the potential for problems, the mushroom tappet design of the Ford Y-Block lifter makes the lifters more susceptible to damage than the more traditional lifter designs.  Even if lifter issues are not at the forefront with camshaft imbalance, then cam bearing wearing would be.  Summarized, the higher the rpm, then the greater the potential for issues that arise from camshaft imbalance.  For a stock engine, problems that could arise as a result of camshaft imbalance are minimal if not non-existent.  But for an engine running in excess of 6000 rpms, then this becomes an area worth exploring.

Balancing the camshaft is similar to balancing a crankshaft in that dynamic balancing is incorporated which has any imbalance corrections being performed at the ends of the camshaft.  At this point, the balancing operation becomes specialized as it requires a machine capable of dynamic balancing.  But a fair number of shops with dynamic or crankshaft balancing capabilities do not balance camshafts as it’s an area that’s simply just overlooked.  This is just something that a machine shop will need to be approached about and decide if this is an area that they would want to tackle.

Any production camshaft is inherently out of balance due to engine cylinders being directly across from each other that fire or ignite consecutively in the firing order.  This means the camshaft lobes for those cylinders are bundled up on the same side of the camshaft and subsequently makes the camshaft predominantly heavy sided on that side of the camshaft.  For the Ford Y-Block, the camshaft is lopsided on the drive end of the camshaft while on other engine families (ie. the Ford FE & MEL big blocks) the camshaft may present greater levels of imbalance on the back or rear end of the shaft.  Engine design and/or firing orders will dictate where the imbalances will be most heavily concentrated on the camshaft.

The drive end imbalances on most camshafts are more easily compensated for in that they can be corrected at the timing gear itself whereas any correction that must be done at the back end or rear of the camshaft is typically performed in the rear journal.  The larger diameter of the timing gear simply allows for much easier imbalance correction with less material removal.  If offset keys or bushings are being used with the cam gear at the camshaft snout to degree in the camshaft, then these must be also in place at the time of camshaft balancing.  If the cam is being degreed in at the crankshaft gear, then the cam gear position will not be a consideration at this point.

For the Ford Y-Block, there are at least three different balancing scenarios that can take place with the camshaft installation depending upon what parts are available.

These scenarios can be listed as:

(1) the timing gear being installed with only the fuel pump lobe on the front.

(2) the timing gear being installed with both the fuel pump lobe and the early model counterweight.

(3) the timing gear having the fuel pump lobe removed altogether as would be in the instance where an electric fuel pump is being used.

All of these result in a different amount of imbalance at the drive end of the camshaft.  When balancing the camshaft, it will be important to have the hardware on the front of the camshaft that is actually going to be used.

Click image for a larger picture

For a Y camshaft that was custom ground on 107° lobe centers, the amount of imbalance on the drive end with the fuel pump lobe installed and not including the early model fuel pump counterweight was in excess of one oz-inch.  In balancing terminology, this amounts to a large amount of imbalance.  Installing the fuel pump counterweight reduced this imbalance to 0.44 oz-in which is a significant reduction in balancing terms.  In an irrigation pump or industrial engine, this is likely not enough to worry about but in a peformance application, even the smaller amount of imbalance that’s evident with the fuel pump counterweight in place is enough to warrant some additional attention and correction in a serious effort blueprint or performance application.

As already stated, imbalance corrections on the drive end of the camshaft are performed on the timing gear and more specifically on the outer edges of the gear where centrifugal forces work to our advantage.  Rather than adding weight as in the case of a counterweight, the gear is simply lightened on the indicated heavy side.  The imbalances in the rear or distributor drive end of the camshaft are not as easily compensated for due to the small working diameter of the rear journal.  The rear journal is either lightened in the appropriate location with holes or heavy metal being added and in some instances, both heavy metal and lightening holes are employed simultaneously as imbalance correction methods.  On the Y camshaft, the oiling holes present in the outer edge of the rear journal must be also taken into account; any modifications to the rear journal in regards to balance must still maintain the oil path for the oil to travel to the distributor pilot hole.  A vent hole in the rear cam journal must also remain so that oil pressure within the cam plug area does not unseat the plug thus becoming an external oil leak at the rear of the engine.

Don’t take this article as saying your camshaft has to be balanced.  Balancing the camshaft is just that extra level of detail that can be performed when doing a serious blueprint to an engine.  I simply do it just for that extra bit of performance and engine durability it can provide.

Until next time, Ted Eaton

Originally published in Y-Block Magazine, Issue #96, Jan-Feb 2010, Vol. 17, No.1