Tag Archives: 312

Intake Manifold Plenum Slots

In dyno testing the different intake manifolds on various engines, it’s found that the intake runner and plenum designs are main players in determining what the power curve for a particular engine combination will look like. One intake manifold feature that comes to the forefront on the aftermarket four barrel dual plane intakes is a slot in the divider located directly under the secondary side of the carburetor. These slots came into prominence in the late Sixties with the popularity and use of the Holley three barrel carburetors and that slot was simply required to allow the secondary throttle blade on those carbs to open without interference at the intake manifold. Although the three barrel carbs have been pretty much extinct for several decades, the practice of the intake manifolds being slotted by the manufacturers has remained. When the Blue Thunder intake for the Y engines was introduced, it too had that slot located at the rear of the divider under the secondary portion of the carb. I’ll hence forth refer to that slot as the ‘three barrel’ slot simply due to it working for that purpose.

For the Ford Y-Block engines, the two aftermarket intakes currently available are the Blue Thunder (BT) and the Mummert. In breaking with conventional practice, the Mummert aluminum intake manifold was introduced without that ‘three barrel’ slot in place. The BT intake being introduced a few years earlier has the slot. So that begs the question, exactly what effect does that slot have on the engines power curve if any?

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To test the effect of the ‘three barrel’ slot on overall engine performance, four 1” tall four hole carb spacers are obtained and appropriately modified so they can be dyno tested. While one 4 hole spacer is left stock, another is modified with a slot across the secondary throttle bores. The other two spacers are machined so that they are dual ovals closely matching the dual oval configuration used in the plenums of both the Blue Thunder and Mummert intakes. Again, one of the dual oval spacers has the slot added so it’s across the secondary throttle bores while the other does not. To add another nuance to the tests, the slotted spacers are tested both right side up and upside down just to see if this provides an additional difference to the power curve. This makes for six different test variants which includes the four different spacers and then the two slotted spacers being run with slots down as well as slots up.

 

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The dyno mule is the well tested +060 over 312 with a set of mildly ported G heads. The intake manifold being used for this test is the Mummert aluminum intake which is being used in lieu of the Blue Thunder intake simply due to the lack of a slot in the plenum divider. The carb is the 750 vacuum secondary Holley which has proven to be a solid performer on this engine in past tests. The camshaft is a Seventies era Crower Monarch grind with 238° duration at 0.050” on both the intakes and exhausts and ground on 110° lobe centers. The cam is installed with 2° of advance (108° intake lobe centerline). The net valve lift is 0.459” lift using the Harland Sharp 1.6:1 roller tipped rockers with the valve lash set at 0.019”.

The following chart shows the various dyno results. The *Score is calculated by adding the average torque and horsepower values together, multiplying by 1000 and dividing by the cubic inch (322).

Spacer > 4 holeNo slot 4 holeSlot up 4 holeSlot down Dual OvalNo slot Dual OvalSlot up Dual OvalSlot down
TQ –Peak 340 341 342 338 338 338
HP – Peak 298 303 302 302 302 302
TQ – Avg2500-5500 rpms 324 324 322 323 320 320
HP – Avg2500-5500 rpms 245 246 245 245 244 243
*Score2500-5500 rpms 1769 1772 1763 1766 1752 1751
TQ – Avg2500-3500 rpms 329 324 319 326 316 315
HP – Avg2500-3500 rpms 189 186 183 187 181 181
*Score2500-3500 rpms 1608 1582 1559 1593 1544 1538

In this case, the charts don’t tell the whole story so this is where a series of graphs come into play. The following two graphs show the HP and TQ results for the four hole spacers. There is a pronounced dip in the torque curve when the slots are incorporated into the spacers versus the dyno runs that are made without the 3 barrel slot in place.

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The next pair of graphs shows the results of testing with the dual oval spacers with and without the three barrel slots. Again, that mid-range dip in the torque curve becomes more pronounced with the slots in place versus without.

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This next pair of graphs simply compares the four hole carb spacer without a slot to the dual oval carb spacer also without a slot. Low end torque is enhanced with the four hole spacer while the top end horsepower is better with the dual oval spacer. No surprise there. This reaffirms the practice of putting the oval slots in the ECZ-B iron intakes for an increase in top end power.

Click on pictures for larger images.

What is obvious on the graphs comparing ‘slot’ versus ‘no slot’ performance is how the addition of a slot does make for a more pronounced dip in the mid range torque values. Based on past experience, that dip or mid-range drop in the torque numbers does look like it can be reduced by simply making the carb spacer taller. For this particular test, the carb spacer height was simply kept at one inch but past testing has shown that the two inch high carburetor spacers are a better choice for optimum horsepower and torque numbers on most Y engine combinations when using either the Blue Thunder or Mummert intake manifolds. There are instances where even more than two inches of spacer works so keep an open mind.

The addition of plenum slots do tend to help the overall performance scores and top end horsepower numbers when used on a 4 hole spacer design. When using ovals under the carbs rather than four individual holes, the same slots prove to be a detriment to the overall score values while top end horsepower values do continue to be higher. The low end performance is reduced with both spacer designs with the slots when compared to the same ‘no slot’ spacers. In summary, not having a slot in the plenum divider does enhance the low end torque values so it simply ends up being a case of exactly what kind of driving is being performed as to whether the intake plenum having a three barrel slot or not is going to be the best for a particular engine combination.

585 HP with 3″ of dual slotted carb spacers on Blue Thunder intake manifold.  Click on picture for larger image.

Until next time, happy Y motoring. Ted Eaton.

This article was previously published in The Y-Block Magazine, Jan-Feb 2014, Issue #120, Vol. 20, No. 6

Hi-Volume Oil Pump For the Y

Although I normally wouldn’t advocate a high volume oil pump for a run of the mill Y block (1954-1964 Ford 239, 256. 272, 292, 312), I did run into a situation where the use of one would at least be a temporary fix until a new engine could be built to replace the current one. Because a high volume oil pump for the Y hasn’t been available for awhile, the basic plan called for building one using currently available parts.  Before I actually get into the modifications required to make a high volume pump for the Y, I’ll give some background relating to the engine for which this particular pump was being built and why a high volume oil pump was deemed necessary.

This story starts with a bored to the hilt 312Y (3.925” bore) with old school popup pistons that was assembled by a Dallas area ‘speed’ shop and then this particular engine laying in wait for a number of years before the car was actually ready for it. When the engine was ultimately fired off, the cold oil pressure seemed satisfactory but there was a serious rear main leak so the engine wasn’t allowed to get sufficiently warmed up. This is where I come into the picture as I was approached to help fix the rear main leak. While the pan was off, I casually checked the rod side clearances by merely doing a hand feel of them. And of course I find something to raise some concern; the rod side play on the number one rod journal seemed excessive and upon measuring it, there was 0.081” clearance. The other three journals were acceptable in that they each had 0.025” or less. After some discussion, it was decided to go forward, fix the rear main seal, and get the car on the road with plans to eventually replace this engine at the earliest opportunity. The rear main oil leak was officially fixed at this point but upon driving the car enough to get the oil hot, the oil pressure was dismally low even at highway speeds. Although it’s determined that the excess rod side clearance is not the reason for the low oil pressure, it’s now questionable exactly what other clearances were not maintained within acceptable tolerances in this engine during its initial buildup or if the block itself has some internal problems. If it wasn’t for the low oil pressure, there would not have been any indication that anything was wrong as the engine runs very well with no unusual noises and has plenty of power evidenced by it being able to light up the rear tires at will. All the right parts are obviously there for performance in the form of increased compression, lots of cam, MSD ignition, Blue Thunder intake, Demon carb, and ported heads. But the low oil pressure is bothersome and having a new engine ready to drop back down into the engine bay was still a good ways off. After ruling out the oil pump, the rubber seal at the inlet of the oil pump, oil viscosity, gauges and the oil filter, I suggested just increasing the volume of oil to get the pressure up into a safer zone as an interim measure.

Making a high volume oil pump for the Y is not difficult once it’s recognized that the majority of Ford oil pumps have the same diameter gerorotor gear set. A particular nuance to watch out for is the size of the hexagon oil drive shaft which for the Y is ¼” but is conveniently the same size as the Fe (360/390/427), SBF (289/302/351C), and OHV (368,302,332) engines. At this point, the basic plan revolves around using a stock Y-Block gerorotor oil pump housing in conjunction with a longer than stock gerorotor gear set and a fabricated cover that will compensate for the longer gears within the stock housing. The whole key here is to keep it simple, keep it repeatable, and keep it inexpensive. As can be surmised, inexpensive is a subjective term especially when dealing with these older engines.

A high volume oil pump for a 289/302 Ford (Melling P/N M-68HV) was purchased which supplied the necessary longer gerorotor set for this project. Upon comparing the new inner and outer rotors with the stock Y components, the SBF rotors are 25% longer which will effectively increase the oil volume by 25%. Upon comparing the various pump parts, it becomes obvious that the pivot shaft protruding from the SBF inner gear is approximately 1.115” shorter than the one in the Y unit. This makes the stock Y oil pump drive shaft that much too short and is corrected by using the oil pump drive shaft for an OHV Ford engine (368 Lincoln, 302/332 OHV truck) rather than try to relocate the longer center pivot shaft from the Y rotor to the SBF rotor. The OHV oil pump shaft (Melling P/N IS-60A, 9.167″ overall length) was merely shortened 0.100” in which to make the total length to the distributor correct. Next on the list is to measure the inside depth dimension of the Y oil pump housing where the rotors reside, measure the SBF rotor thickness, take the difference of these two values, and add 0.003” to the derived value. This is the depth of the hole or recess that must be machined in a new cover to accommodate the longer gear set while providing the prerequisite 0.003” clearance between the gear and the cover (rotor end play). Another option would be to just machine a spacer that would make up this required distance and use the stock oil pump cover but this ultimately creates another place for an oil leak. These engines are already noted for marking their territory so rather than compound the issue, I stayed to the original plan and simply machined a cover with a recess in it to compensate for the longer gear set.

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The new cover was fabricated from a ½” thick piece of 4” diameter cold roll steel and machined with a 2.634” diameter recess that measured 0.226” deep. An appropriately sized piece of flat plate steel could have also been used but a bar of cold roll was just conveniently at hand. After placing the machined cover on the oil pump housing and over the protruding rotors, transfer screws were used to mark the location for the cover’s bolt holes and the cover was then drilled to accommodate the required four ¼” X 20 cover bolts. While the pump was completely disassembled, the oil pump relief valve spring was also shimmed with a 0.110” spacer to raise the cold oil pressure limit. Upon assembling the pump, it’s imperative that the rotors turn freely within the pump after torquing the cover in place; if they don’t, the reason why must be determined and corrected.

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Prior to final assembly, clearances within the pump were checked using the following guidelines.

Rotor End Play: 0.002″ – 0.003″

Rotor To Housing: 0.006″ – 0.012”

Inner Rotor To Outer Rotor: 0.005″ – 0.010″

Torque Specs For The Cover: 95 – 100 INCH LBS

The pump was installed on the engine and did indeed increase the hot oil pressure. The following table compares the engine oil pressure with the stock pump versus the pressures obtained with the hi-volume pump.

Cold Idle Cold & fast idle Hot Idle Hot & fast idle Hot & In 4th gear at 50mph Hot & In 5th gear at 50mph
Stock oil pump 35psi 50-55psi <10psi 23-25psi 27-28psi 20psi
Hi-Vol oil pump 60psi 70psi 35psi 40-45psi 40-45psi 30psi

As mentioned earlier, this oil pump fix was just an interim measure and in no way takes away from the fact that there are issues within this engine that is allowing an excessive amount of oil flow resulting in a loss of pressure. In summary, all this modified pump did was to increase the oil flow to a point that over-rides the amount being lost and in turn gives an increase in oil pressure. But for the time being, the car can at least be driven while parts for the new engine are being gathered up and machined in preparation for a new shortblock assembly.                    Ted Eaton

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This article was originally published in The Y-Block Magazine, Issue #84, Jan-Feb 2008, Vol 15, No. 1