All posts by Ted Eaton

Rocker Arm Geometry

Rocker arm geometry is an area that’s very often overlooked when modifying an engine for increased power output and/or efficiency. Besides the obvious advantage of reducing valve stem and guide wear by minimizing the “scrubbing” action that can take place when the rocker arm geometry is optimized, the maximum or advertised lift at the valve for a given camshaft profile can also be obtained. The method in which the rocker arm geometry is altered will vary depending upon the valve train design. There are basically two rocker arm support designs where the rocker arms are either a ball (fulcrum) and stud arrangement or are shaft mounted. To adjust the rocker arm geometry on the ball and stud style, the length of the pushrod itself is altered in order to change the pivot point but when dealing with a shaft mounted rocker arm such as on our venerable Y-Block or an Fe Ford, then the height of the pedestal stand holding the rocker shaft must be altered.

In the case of the Y-Block, rocker arm geometry whether it’s good or bad, doesn’t change when the heads and/or deck is machined. The relationship of the rocker shaft to the valve stem tips remains the same and the pushrod length only needs changing when required by lieu of the lash adjuster being outside of its usable range. On an engine using the ball and stud arrangement for its rocker arms, any machining done to the head or deck surfaces can necessitate a change in pushrod length to maintain the existing rocker arm ratio.

Fig A.Rocker arm geometry is generally optimal when the travel or movement of the rocker arm tip on the valve stem is minimized. To understand how to achieve correct geometry, it must be understood that the rocker arm tip itself travels in an arc. At zero lift, the rocker arm tip is expected to be closer (or inboard) to the plane of the pivot point and as the valve starts moving down, the rocker arm tip starts moving outboard. If the geometry is close to ideal, then the rocker tip will be at its most outboard position at half or mid lift at which point the rocker tip starts moving inboard again as the valve reaches full lift. Simply put, ideal rocker arm geometry is achieved when the rocker tip is sitting on the valve stem tip at the same position at both zero lift and full lift. In a perfect world where the rocker shaft pedestal stand locating holes, the valve guide, and the rocker itself are all machined to exact specifications, the rocker tip is expected to be sitting slightly inboard of the valve stem center at both zero and full lift while the rocker tip will be sitting the same distance outboard of the center of the valve stem at exactly mid-lift. But because of variances in manufacture, getting the rocker arm to sit on the valve tip in the desired location while optimizing the rocker arm geometry doesn’t always happen. In these cases, lash caps may be utilized to increase the area on the tip of the valve stem in which to increase the working area but in other cases it may require another style of rocker arm of the same ratio. Depending upon the scenario, compromises may be made in which optimum geometry is not achieved in order to allow the rocker tip to be sufficiently located on the valve stem tip.

Now that it’s clear that the rocker tip must be sitting on the valve tip at the same location at both zero lift and full lift, then it’s easy to assume that the rocker arms pivot point most be raised or lowered if the rocker arm tip contacts the valve stem too far inboard or outboard at zero lift in relation to where the tip resides at full lift. In the case of the Y-Block with its shaft mounted rockers, this involves altering the height of the pedestal stands so that the rocker shaft can be moved in the appropriate direction. If the rocker arm tips are sitting too far inboard or closer to the shaft versus where the tip sits at full lift, then the pedestal stands need to be longer or sitting taller. Conversely, if the rocker arm tips are sitting too far outboard as compared to where they reside at full lift, then the pedestal stands need to be shortened. In extreme cases, altering the height of the shafts can require an appropriate change in pushrod lengths to insure adjustability at the rocker arm for valve lash adjustment.

Fig A.There are several different methods in which to measure rocker arm geometry. Without any measuring tools available, a visual observation of the rocker arm movement while the valve is going through its range of motion can prove quite adequate. Using a dye or magic marker on the valve stem tips to indicate the path or length of travel on those tips while varying the height of the rocker shaft can also indicate better or worse rocker arm geometry. Measuring the actual valve lift can also be performed as maximum valve lift occurs at “perfect” geometry and if the rocker is above or below this ideal point, then the valve lift starts decreasing logarithmically by the amount that the geometry is incorrect. There are tools available to facilitate measuring rocker arm geometry and one of these is a dial indicator on a fixture that actually measures the relationship of the rocker tip and with the edge of the valve stem at both zero and full lift. Regardless of the method used, the end result remains the same where the contact point of the rocker tip with the valve stem at both zero lift and full lift are being made the same.

As delivered from Ford, the rocker geometry on the Y engine is reasonably close with the stock lift camshafts. As the stock camshafts are replaced with those with increased lift, then it becomes necessary to machine the rocker shaft pedestal bases so that the shaft itself sits lower to re-achieve a more ideal rocker arm geometry. Because of the variability in the various rockers from the different manufacturers, it would be difficult to have a set amount that would need to be removed from the stands for a given amount of lift. Even using aftermarket or replacement valves with different than stock valve stem lengths will dictate checking the rocker arm geometry and correcting as deemed necessary. Due to all the variables involved, it would be prudent to at least check the rocker arm geometry on an engine as it’s being assembled especially when new valves, rocker arms, and possibly rocker shaft assemblies are being replaced.. T.E.

Originally published in Y-Block Magazine, Sep-Oct 2005, Issue #70.

Building the foundation for an eight second Y-Block.

When Randy Gummelt and I set out to build a Y engine for his rear engine dragster, the plan was to have an engine combination that would run an eight second quarter mile. And Randy also had his sights on the Australian Y record and with a target of an 8.99 or better et, that plan would achieve both goals. By now, it’s pretty well known that Randy ran a best of 8.15 @ 162mph at the Y Shootout during this past Labor Day weekend at Columbus Ohio so the plan was definitely a good one. But to back up a bit, in order to accomplish this it was necessary to figure out a workable combination and then to start gathering up the necessary parts that would make this combination work. Thus the plan starts to take shape as follows.

C2AE-C BlockFor the basic foundation, it was decided to use a C2AE-C block due to these particular castings being known for their consistent thicker cylinder walls as well as the additional main support webbing that is already present in these blocks. For an aspirated version, I normally have no issues in boring these particular blocks out to 3.860” (+0.110” over) but because this was to be a serious blown effort, the finished bore was targeted at a smaller 3.800” bore to maximize cylinder wall integrity and in turn reduce any chance that cylinder wall flex would potentially kill or hurt some of the power. Part of the reason for going with a 3.800” bore versus a 3.810” bore was being able to get in on a special run of Total Seal brand 1/16” wide gapless rings for a 3.800” bore that were being made for one of the Nascar teams. The 3.810” bore 1/16” wide rings were already available as an off the shelf item but being in a position to make the bore and stroke ‘square’ was more conducive to the overall plan. Because of the supercharged nature of this engine, the top ring would be gapless by design as opposed to normal practice of using a gapless style ring in the 2nd groove in a normally aspirated application.

It was determined early on to use a Moldex crank in order to get the desired 3.800” stroke. To facilitate this much stroke and free up some much needed clearance at the camshaft , 2.000” rod journals were specified to bring the rod bolt area of the connecting rod inboard and away from the camshaft. To permit the use of an economically priced SFI approved flywheel, a scrub bolt pattern on the flywheel flange was called for and the face of the flange was spaced ~0.420” further to the rear or away from the engine. This additional spacing was to eliminate any spacers between the flywheel and the torque converter while still maintaining the pre-requisite 0.100” freeplay in the transmissions front pump. The C2 block already incorporated 292 main bearing sizes and so the main journal dimensions were sized as standard 292 size which at least kept main bearing selection both simple and inexpensive. The crankshaft is fully counterweighted which means eight counterweights versus the normal six and even with the additional weight afforded by the extra counterweights, lightening holes were needed in the crankpins to facilitate balancing without an extreme use of heavy metal or tungsten. Both the leading and trailing edges of the counterweights are bullnosed or rounded in shape; no knife edging on this crankshaft.

Going to the front end of the crankshaft, the snout was mandated as 1.600” diameter as opposed to the stock 1.250” diameter normally seen on a Y. This allowed the use of the more readily available BBC blower hubs and drive hardware while also reducing significantly any deflection that occurs due to the blower belt pulling heavily on the crankshaft snout. Through the use of a Y marine cover, the crankshaft snout was shortened even more which reduced any potential deflection even further. Although 3/16” woodruff keys (#9 if you’re ordering them) were employed for the timing gear and basic drive hub allignment, an additional groove was machined into the crankshaft at 180° from the other keys so that ¼” keystock could be employed to insure no key failure at the drive hub for the blower.

The 2.000” rod journals made it possible to use the considerably less expensive Eagle 6.125” long H-beam connecting rods that were available as an off the shelf item. Even though the connecting rod cross-section was dimensionally smaller by using the 2.000” journal, there was still less than the required minimum of 0.050” clearance to the camshaft. Although only a pair of connecting rods actually had interference issues with the camshaft, all the connecting rods were subsequently modified to insure that they would clear the camshaft in the event of a catastrophic camshaft timing failure.

Pistons were a custom order item from Wiseco. These pistons maintain a minimum of 0.260” thickness in their decks for the blower application and incorporate an inverted dome (dish) that adds 27cc’s to the total cylinder volume. Because of the unavailability of a pair of usable 471 heads while gathering up parts, it was decided to use the 113 castings which were attained through and already ported by John Mummert. Because the pistons were going to be custom built regardless of the head being used, the particular head in regards to the chamber size being used was not a major player as the piston dish size could be altered in which to compensate and still maintain the targetted 7.5:1 compression ratio. But had 471 heads been available, then a more desirable ‘D’ shaped dish in the piston would have been used. The particular piston blank that was being used to make the pistons only had a given amount of deck thickness which limited dish design when using the smaller chambered 113 heads. The compression height (pin location) for the pistons is 1.715” which places the top of the piston at a calculated 0.010” in the hole for deck clearance.

This basically takes care of the parts required to put a rotating assembly together for the bottom end other than the main support girdle and that’s already been covered in a previous article. Future articles will go deeper into blueprinting and camshaft specifications as well as some of the other modifications that were required to put a final assembly to the engine.


Originally published in the Y-Block Magazine, Mar-Apr 2006, Issue #73

Blueprinting for an eight second Y-Block

Like any engine that’s in its planning stages, particular care must be paid to that engines intended use in  order to select the correct parts and maintain those clearances that would be considered optimal for that combination.  In the case of the blown engine for Randy Gummelt’s rear engine dragster, I’ve already covered some of the parts selection as well as the main support girdle construction in previous articles.  At this point, I’ll cover in more detail some of the specific clearances and specialized machine work that was required to make Randy’s engine a reality.


The C2AE-C block was rough bored to 3.797” and the main journals align honed so that the engine could be initially dry assembled.  The rotating assembly was installed within the block without piston rings which allowed for some preliminary measurements to be made and in particular, connecting rod to camshaft clearance and determine how much would be required to remove from the deck surfaces to obtain the desired piston to deck clearance.  Used bearings were installed on the crankshaft at this stage to prevent any potential damage to the new bearings.  There are no deep pockets in this operation so saving a buck where possible is always a consideration.  Upon removing the rotating assembly from the block, the head bolt holes in the block are drilled and retapped to ½” X 13 and the cylinder bores are notched at the intake valve locations to both aid flow and increase valve to cylinder wall clearance in this area.  Care is taken to insure that the cylinder wall reliefs do not protrude into the top ring area when the piston is at top dead center.  The block is now ready to go back to the machine shop for final cylinder wall honing and block decking. All the hardcore machine work on the block including align honing the mains was performed by Lonnie Putnam in Gatesville, Texas.


The Moldex steel crankshaft is fully counterweighted which alleviates some of the balancing issues that comes from using heavier connecting rods and piston combinations as well as potentially reducing some of the crankshaft flex that can be associated with high horsepower and/or high rpm applications.  The crankshaft was balanced using a 2015 gram bobweight value which includes a calculated amount of ‘over balance’ to compensate for the blower application on this engine.  As a point of reference, a typical bobweight value for a normally aspirated stock Y-Block rebuild will fall in the 1960-2050 gram range.


The Eagle H-Beam connecting rods are an off the shelf item that are 6.125” long and specific for a 2.000” journal and work with the 0.927″ pins being used in the pistons.  These were surprisingly quite economical and should be considered viable options in even a moderate performance build up as opposed to just reworking stock rods.  The rods did however require some modification at the top of the rod bolt area in order to clear the camshaft adequately and this is a result of just pushing the stroke out to 3.800”.  Although only a pair of the connecting rods would have required specific modification for adequate camshaft lobe clearance under a normal camshaft timing event scenario, all eight rods were clearanced in the event of a catastrophic failure in the cam drive.  Minimum connecting rod clearance to the camshaft was targeted for 0.050”.


The Wiseco pistons are machined for 1/16” rings in both the first and second grooves while the oil groove is the common 3/16” size.  The top ring is also spaced 0.330” down from the piston top instead of the more typical 0.250” spacing.  The rings are provided by Total Seal and have a gapless style top ring which was deemed a necessity considering the supercharged nature of the engine.  The main thought process here is to minimize the amount of alcohol that’s ‘blown’ past the pistons and into the crankcase.  Of lesser consequence but still worth considering is that gapless rings also minimize the amount of leakage that’s created by cylinder wall wear which equates to 0.00314” of additional ring gap for each 0.001” of cylinder wall wear in a standard production ring set.  Unlikely that this engine will ever see enough service to make cylinder wall wear and the effect on ring end gap significant, but is a factor regardless.

The Iskenderian camshaft is a custom grind and is designed specifically for this combination.  The lobes are placed on 114° centers while the intake/exhaust durations at 0.050” are 254° and 260° respectively.  Intake and exhaust lobe lifts are 0.350”/0.346” which provides 0.560”/0.554” intake/exhaust lifts at the valve before taking valve lash into account.  Dove Manufacturing 1.6:1 aluminum roller rockers are utilized with the rocker stands being altered in height in order to optimize the valve train geometry.  Isky 3/8” tubular pushrods connect the lifters to the rockers.  A Rollmaster timing set spins the camshaft and is 0.008” shorter than standard in order to bring the slack in the chain to the preferred deflection value of 0.180” or less.  Because the crankshaft snout diameter was increased to 1.600”, the crank timing gear was bored and honed for the proper fit and a new keyway slot for cam timing purposes was broached back into the gear.  The camshaft was installed at 112½° intake lobe centerline or 1½° advanced.


The ‘113’ heads were obtained from John Mummert who also took care of the required porting work.  Valve to piston clearances were checked during dry assembly and these measured out at 0.155” on the intakes and 0.210” on the exhaust before taking into account the head gasket thickness and valve lash values.  This was more than enough clearance and most of the excess in clearance could be attributed to the deep dish in the pistons.  While the heads were apart, the head bolt holes are redrilled with a 17/32” drill bit in which to accommodate the larger than stock ½” head bolts.  The ‘113’ heads require two different length head bolts on the top rows with the end bolts being longer than the center three.  To equalize combustion chamber volumes on both heads at 67cc’s, one head was milled 0.050” while the other was milled 0.055”.  Prior to final assembly on the heads, the gasket surface around each of the combustion chambers was machined by Don Chandler (Gatesville, Tx) for a groove that would hold a stainless steel sealing ring.  These wire rings work in tandem with the copper head gaskets being supplied by SCE that were 0.043” thick.  After setting the valve spring seat pressures to 135 lbs. (337 lbs ‘over the nose’ pressure), the cylinder heads are ready to be bolted in place using a custom set of ARP ½” head bolts and torqued to 110 ft/lbs.


A standard set of Clevite 77 main bearings (MS178P-STD) for a 272/292 engine are used with clearances being maintained at 0.0027”-0.0030”.  Clevite 77 rod bearings (CB663H-STD) keeps the connecting rods in their place with 0.0020”-0.0022” clearances.  Connecting rod side clearances were set at 0.022-0.024”.  Piston wall clearance is 0.0055” while ring end gaps for the Total Seal rings are maintained at 0.032” for the gapless top ring and 0.027” for the second ring.  The pistons themselves sit 0.010” in the hole when they are at top dead center.  Connecting rod bolts are torqued to 63 ft/lbs while the main caps are torqued to 75 ft/lbs.  The outer main girdle bolts at the pan rails are torqued to 18 ft/lbs.

Because the Enderle fuel pump for the injectors is mounted facing forward on the front of the marine timing cover, it required a special drive fixture to be located on the front of the camshaft and camshaft sprocket.  This involved more fabrication and ended up being a two piece affair which allows a hex drive to connect the camshaft to the pump.  The original tach drive location on the marine cover not only provides a location for bolting up the Enderle fuel pump directly in front of the camshaft, the marine cover also permits the blower drive at the crankshaft to be placed closer to the engine which in turn further reduces any flex or deflection on the crankshaft snout caused by the blower belt.


The one component on this engine that remains relatively stock is the oil pump.  The oil pump is a Dynagear P/N DM-42 which is a gerotor (gerorotor) style pump but utilizes a cast iron body instead of the aluminum body normally found on that same style of pump when offered by FoMoCo.  The pump was simply disassembled, checked for any flaws and clearances checked, and reassembled with the only modification being the addition of a 0.150” shim on the bypass spring in order to boost the cold start oil pressure.


Engine break-in was performed on an engine dyno so the engine could be appropriately loaded but was done so before actually installing the 6-71 roots style blower on the engine.  The break-in process was performed using standard carburetion rather than the blower setup; a Blue Thunder intake and a List #1850 600cfm Holley took care of this chore.  After break-in, a single dyno pull was made with the carb in place which peaked 321 HP @ the 5750 rpm cut off point.  Not too shabby for a 7½:1 compression ratio, being over cammed, and no carburetor or ignition timing adjustments.

The blower was then installed and subsequent dyno pulls were made.  Due to ignition constraints, the engine was cutting out (ignition breaking up) after 5500 rpms but still managed to make 642 HP (6000rpm) and 644 lbs torque (4750rpm) before the ignition problems would ultimately terminate the dyno session.  The ignition problems were eliminated when the engine was installed in the chassis by utilizing an MSD crank trigger ignition.

Although the engine is allowed to shift at 6500 rpms in the course of running it down the track, it has bumped the rpm limiter at 7800 rpms during the burnouts.  Teardown of the bottom end to check bearings after a number of quarter mile passes still had everything looking fresh and new even with the given amount of alcohol that was making its way into the pan.  So far, so good, and continues to make quarter mile passes with minimal problems.

 Originally published in Y-Block Magazine, Issue #76, SEPT-OCT 2006

Addendum:  As of this writing, the best et has been an 8.15 second pass at National Trails Dragway.  There have been a multitude of low eight second passes at Texas Motorplex in Ennis but all these have been with the tires breaking loose at mid track and the car just coasting thru the traps.  Even the addition of a wing did not help.  Final conclusion is that the chassis is simply too stiff along with the wheel base being too short for this combination.                           T.E.