Tag Archives: Blue Thunder

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?

Click on pictures for larger images.

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.

 

Click on pictures for larger images.

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.

Click on pictures for larger images.

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.

Click on pictures for larger images.

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

Engine Masters Challenge Y-Block Entry for 2007

The idea for entering a Y into Popular Hot Rodding’s Engine Masters Challenge competition was prompted by discussions on the Y-Blocks Forever website.  I sent off the application form and was ultimately assigned the alternate #15 position which meant as the participants within the first thirty competitors either dropped out or failed to qualify then the alternates would be moved up the list.  I realized early on that actually making the competition from alternate #15 was a very slim chance based on what I had seen in previous year’s competitions but would give it a go.  There were some heavy hitters actually placed after myself in the alternate list so that did give some consolation.

Upon looking at the rules, the 312 had an inherit advantage in that it was in the lower spectrum of cubic inches required for the competition.  300 was the lowest manufacturer cubic inch allowed so the 312 was allowable whereas the 292 wasn’t.  Where the Y is strong is actually in the stacked intake port design.  These ports, being what they are, allow each runner length to be equalized and therefore the overall torque being much more pronounced or peaked.  Where runner lengths are varied on other engines due to ports being spaced differently across the length of the head, the torque band for the various cylinders is thereby different and the overall torque of all the cylinders when averaged together is thereby softened or the peak torque reduced.

emcy-blockleftview-1.jpgIf there was any one area in which the Y was handicapped for this competition, it was in the head department.  Aftermarket heads were permissible as long as factory intake and exhaust patterns were maintained.  There are no aftermarket heads for the Y, so a pair of ‘113’ heads were picked out for this combination.  They did not have to be made overly big in port volumes to support a larger cubic inch engine and therefore are more efficient for the smaller cubes.  The heads were set up with a custom set of Ferrea valves and topped off with Comp Cams beehive valve springs and Dove 1.6:1 roller rockers.  Considerable work went into the exhaust porting so that the camshaft could be ground the same for both the intake and exhaust durations.  The camshaft selected for this particular engine was a custom Isky grind with 270° advertised duration, 242° duration at 0.050″, 0.547″ net lift at the valve, and ground on 107° lobe centers.  The cam was installed at 105° intake lobe centerline.  A Rollmaster chain assembly spins the camshaft while Smith Brothers pushrods work the Dove Manufacturing 1.6:1 roller rockers.

Frank Rice shipped me a C2AE block that was a 312 marine engine originally.  This block had the better main webbing but upon sonic checking it, core shift was one of the worst ones I’d seen.  Because I was minimizing the amount of overbore, offset boring to re-center the bores within the casting was not an option.  The other option for a block was to take one of the 292 blocks lying loose and boring the main journals to the 312 size and then boring the cylinders to the desired 312 size.  The rules required factory journal sizes so using the 292 mains on a 312 crankshaft was not an option.  I used Frank’s block for this project though as it saved having to bore a set of main journals to the 312 dimensions and was still an excellent block for this particular project.  Thanks Frank.

For this block, I went one step further in that I had it cryogenically treated.  This ‘cold’ treatment was performed by Cen-Tex Cryogenics of Waco, Texas.  The idea behind this was to make the cylinders walls harder and potentially wear better.  Hard to say just how much more benefit this treatment provides but I couldn’t see it being detrimental and at this point, I’m going for any potential benefit that I can for this particular engine.

The pistons themselves are a custom set from Wiseco which have a left and right specific dome tailored specifically for the Y-Block Ford combustion chamber.  Rules limited the compression ratio to no more than 10½:1 but the smaller cubic inch of the Y still required a domed piston in which to achieve this.  The compression ratio would have been too low otherwise without the dome.  The domes on these particular pistons are configured such that turbulence is created in those areas of the combustion chamber where the head overlaps the decks.  The rules also did not allow gas porting for the rings.  I got around this by using a Dykes style top ring which fits the rules but has superior sealing characteristics in lieu of not being gas ported.  The second ring was a 1/16″ plasma moly design while the oil ring was a low tension 3/16″ unit.  The 10½:1 compression ratio was good for the E85 fuel being used but would not have been suitable for 91 octane pump gas.  E85 fuel is not readily available in this part of the country so tuning a carburetor for this would have taken some time but was doable. The bore was finalized at 0.022” over stock which fit within the max 0.035” overbore restriction and gave a final displacement of 316 cubic inches.  Past dyno experience and calculations indicated an attainable 395 peak HP @ 6200 rpm, 375 lbs-ft peak torque @ 4200 rpm and a flat curve for the torque to give a good average number.  Due to the rules requiring factory journal sizes, I was restricted to using the factory Y rods.  No bolt in aftermarket rods are readily available at this point in time.  I used the C2AE rods as they are slightly longer than the C1 rods and simply fully prepped these with new ARP bolts, bushings, and a resize.

Because pan evacuation or vacuum pumps were not allowed, this permitted me to take advantage of the crankcase breather on the block whereas most blocks do not have this option.  I also added two extra breathers to each valve cover to insure that excessive pressure was not a hindrance to piston movement under load.  The Engine looks achaic or old school with the original side breather on it though but it was put back on specifically for a performance advantage in this particular instance.

Rules required no modifications to the oil pan.  Aftermarket pans were accepted but unfortunately there’s not an off the shelf pan for the Y.  Rules also prohibited the use of truck pans or I would have used one of the HD pans I had sitting here.  Because modifications to the pan were not allowed, I did get an okay from the rules committee to use a windage tray that sandwiches between the pan and the block.  I subsequently built a windage tray that used directional screening and this simply fit in place with a pan gasket on each side of it to seal it in place.  One side of the tray acts as a wiper against the crankshaft and rods.  If I pull it out of the engine or build another, I’ll get some pictures of it and submit to the Y-Block Magazine.  Nothing fancy but every little bit has to help.  The oil pump is the gearotor style.  I still think there’s a slight advantage to using this style pump over the gear style in both power and pumping even though both are rated the same as far a volume goes.  An ARP oil drive keeps it turning.

The Ford Y-Block oiling system is already a ‘side-oiler’ design similar to the later produced 427 FE side-oilers.  The main bearings are fed directly from a proprietary oil gallery in the side of the block and then the cam bearings and rocker arms are fed from the mains.  Rocker arm oiling for this family of engines is normally by way of a grooved camshaft on the middle journal or a camshaft that is crossdrilled in the center journal which alternately feeds each bank as required.  I opted to machine a groove in the block in the center cam journal hole which connects the three holes located there and then this modification is sealed in place with the installed center cam bearing.   This provides a solid flow of oil to the heads which I restrict at the rocker arm pedestals with a 0.046″ orifice.  The overflow tubes at the ends of the rocker shafts are left intact so that they can free flow which provides ample lubrication for both the distributor gear and the timing chain.  This also insures that the rocker shafts are purged of air and that the oil remains cool thus warding off any potential sludging or oil degradation that may occur as a result of stagnation.

Ignition is an MSD distributor using the MSD wires and MSD Digital 6-Plus controller.  Sparkplugs are a set of 18mm NOS Autolite BF32’s that I had been saving for a rainy day as these are getting more difficult to find.  These plugs have been side gapped and indexed to the individual cylinders.  There’s a forthcoming article about how to do this in an upcoming issue of the YBM.   Intake manifold is a Blue Thunder unit that’s been simply port matched to the heads.  Otherwise it’s stock other than what’s being called the 2nd design manifold.  Based on what Gary Burnette has passed on to me, the 2nd design intake flows as well as the 1st design intake after being extrude honed.  Carburetion for gasoline is handled by a Holley 750 cfm HP series carb with vacuum secondaries.  Backup carb is the 650 cfm Speed Demon carb which has been a proven carb on my Y powered roadster.  I lean heavily towards the vacuum secondary carbs due to them being very optimal in flow on a day to day basis as the secondaries only open up as required for a given engine demand.   Testing has shown similar results on the Y with both the 650 and 750 cfm carbs and this has to do with the vacuum secondaries simply opening less on the larger carburetor to get the same amount of power output.  For E85 fuel, I would simply get a alcohol specific carb in the 650 to 750 range and have to work with it to get the tuneup right.

The tech at the EMC competition ultimately called and said that the Y would not be allowed into the competition with the mushroom tappets.  Didn’t matter if it was a factory lifter, rules were specific against mushroom tappets.  As a result the engine was not run and instead relegated to the back of the shop.  But because I was entered into the competition as an individual and not as an engine choice, I was free to change engines and remain in the competition.  As a result, I readied a 427 Tunnel Port engine I had for the competition.  Standard bore, factory steel crank, an Isky flat tappet camshaft, a single plane TP intake, MSD ignition, and that engine was ready to be called up.  But I was simply too far down on the alternate list to be a player.  Do all this again?  Not at a number fifteen on the alternate list for sure.  Definitely way too much work with not much to show for it and especially with the engine being disallowed due to the original tappet design.

Note that this article was actually a response from Ted to one of the topics I’ve been working up for the “Top Ten Y-Block Stories” for the March-April issue of Legendary Ford Magazine (condensed from this).  But the volume and the depth of his response was an article in itself and I know you will enjoy it as much as I did.  Shown at the ßbottom-left is the Y-Blocks Forever picture by Jim Culver of Randy Gummelt’s blown 770 HP Y that took the World Y-Block E.T. mark to 8.15 @ 162 mph in Columbus at the 2005 Y-Block Nationals.  The motor was prepared by Ted Eaton and Lonnie Putnam – but that’s another one of the expanded “Top Ten” story’s for Bruce’s Y-Block Magazine this year.        Bob Martin

Originally published in the Y-Block Magazine, Jan-Feb 2008, Issue #84,  A shorter version of the text was published in Legendary Ford Magazine, Mar-Apr 2008 Issue.