Wednesday, May 20, 2015

Memorial Day 2015

 

On Monday this nation will observe Memorial Day for the 147th time. Originally call Decoration Day, it was officially instituted in 1868 as a day to honor those who died serving their country in the Civil War. After World War I, the event was expanded to honor those who have fallen in battle in all the wars in which this country has been involved. Strictly speaking, Memorial Day is set aside to honor only those who died in war defending our freedoms, which is appropriate given their sacrifice.




So, in case you are wondering if or how I am going to tie the observance of Memorial Day to the Bible and Christianity (which of course I am prone to do), let's consider a passage from II Samuel chapter 23.

These words are recorded after David had taken his rightful place as king over a united Israel.

These be the names of the mighty men whom David had: The Tachmonite that sat in the seat, chief among the captains; the same was Adino the Eznite: he lift up his spear against eight hundred, whom he slew at one time. And after him was Eleazar the son of Dodo the Ahohite, one of the three mighty men with David, when they defied the Philistines that were there gathered together to battle, and the men of Israel were gone away: He arose, and smote the Philistines until his hand was weary, and his hand clave unto the sword: and the LORD wrought a great victory that day; and the people returned after him only to spoil. And after him was Shammah the son of Agee the Hararite. And the Philistines were gathered together into a troop, where was a piece of ground full of lentiles: and the people fled from the Philistines. But he stood in the midst of the ground, and defended it, and slew the Philistines: and the LORD wrought a great victory.

And this is but the first three of David's soldiers who are all mentioned by name here. In the rest of the chapter, David goes on to name another 32 of the mighty men of his army. Thus it would seem that when we honor the fallen soldiers of our own nation, we do have some biblical example for doing so.

Consider this from Matthew Henry's commentary on II Samuel 23: 

Note, Those that in public stations venture themselves, and lay out themselves, to serve the interests of their country, are worthy of double honour, both to be respected by those of their own age and to be remembered by posterity. To excite those that come after to a generous emulation.  To show how much religion contributes to the inspiring of men with true courage. David, both by his psalms and by his offerings for the service of the temple, greatly promoted piety among the grandees of the kingdom (1Chronicles 29:6), and, when they became famous for piety, they became famous for bravery.


Now, one might argue that nothing which Matthew Henry said about the piety of Israel's army applies to the soldiers of our United States because we have a separation of church and state, and so we are not a Christian nation. But I would suggest that the idea that we are not a Christian nation would have been totally foreign to the great majority of those who have died in the service of our county for more than two centuries. It is far more likely that most of them embraced the thought that they were fighting for God and Country.

So this weekend, as we honor those who have died for God and Country, let us remember Jesus words as recorded in John 15:13

Greater love hath no man than this, that a man lay down his life for his friends.

Over the course of our nation's history many have shown this type of love through fighting and dying for their fellow countrymen who they counted as friends. We should honor them for the bravery and the love which they displayed.

Even more important though, is how those words of Jesus apply to himself.

"Greater love hath no man than this, that a man lay down his life for his friends." And the next verse continues, "Ye are my friends, if ye do whatsoever I command you." "  Jesus gave us many commands during his earthly ministry, but they could perhaps best be summed up when he said repent, and believe the gospel. (Mark 1:15)

Jesus did lay down his life to pay the just penalty for our sins so that we might be forgiven and spend eternity with him. Won't you repent and believe this good news?

Wednesday, May 6, 2015

Vintage Dual Carbs, Part 4

Okay, its high time I finish up this series on vintage dual carbs, or more accurately stated: dual carbs on vintage Harleys. In a previous post, I promised to offer what I see as possibly the best compromise between authenticity, performance and feasibility.

For a Knuckle or a Pan, there are three basic ways to achieve dual carbs. First is the obvious: major modifications to the heads (welding and machining) for one carb with an individual runner on each head. This method is probably the most difficult and/or the most expensive. If you are a good welder, machinist, and have porting experience, then it may just the ticket. If you lack one or more of these talents, well, ...that's where the expensive part comes in. It also suffers from the drawback that, for street use, leg interference is normally a major issue, especially with Linkerts. If using Linkerts or other small bore carbs, this method will also limit maximum air flow.

The second method is to mount two carbs on opposite ends of a common manifold, 'a la the Seely manifold of yesteryear. This is perhaps the simplest method and easiest to build. However, it does suffer from the same leg clearance problems of the first method; again, especially with the relatively long Linkerts carbs. One advantage this method does have over the first is the ability to either keep each intake track separate for true independent runner (IR.) operation, or to use the manifold as a common plenum so that each cylinder can draw from both carbs at once for maximum power potential.

A third option, as I see it, is a custom manifold for two carbs mounted side by side on the pushrod side of the engine. On a Knuckle or a Pan, since the intake spigots are at the far left hand (primary drive) side of the engine, this method has the advantage of providing more room to accommodate carburetor length. This allows the dual carbs to be the least intrusive in respect to legroom. The drawback is that this last method leads to a compromise between the tuning advantage of individual runner and the increased flow capabilities or a plenum manifold which allows each cylinder to draw from both carbs. Keep in mind (as pointed out in part one of this series) that a pure individual runner manifold with carbs on the pushrod side of the engine will necessarily suffer from a "pinched" port cross section. Given the limited amount of real estate between the cylinders/port spigots, I just don't see any good way around this.

That leaves us with one option (in my humble opinion) as the best overall compromise for vintage style dual carbs. That would be a manifold with a runner from each carb, which merges into a common runner before splitting off into each port. A variation of this would be for the carbs to mount on a "plenum" which then feeds into two separate runners which attach to the ports on the heads. In practice, the section of either of these manifolds which attaches to the heads will essentially mimic (if not actually begin life as) a stock "T" manifold (or in the case of Shovelheads "Y" manifold. For the sake of easy identification, let's call the one a "plenum manifold, and the other an X manifold (for a Shovel it would be pretty much X shaped, though for a Pan or Knuck it would look like an X with the top legs folded down).

X Manifold for Knuck
 
 
 
 
 
Plenum Manifold for Shovel


The natural question then becomes, which is better, a plenum type or an "X" manifold. Outside of building one of each, followed by real world testing of each (including dyno testing), I really cannot give a firm answer. Now if any reader out there would care to provide me with a generous research grant along with dyno facilities, I would be glad to find an answer. As you may surmise from the increasingly length of time between blog posts, I have no spare time to donate. However, we can come get some idea of how such manifolds may work out by use of computer simulations.

As engine simulation programs go, there seem to be three levels readily available. There is the very basic type which uses a limited number of inputs. While these can be fun and useful, they definitely have their limitations. The mid-level programs use many more inputs, provide for a higher level of accuracy, and of course cost more. Finally, there is the professional level simulation program with even more inputs and even higher purchase prices. The basic simulators generally can be purchased for $100 or less, the mid level in the $200-$300 range, with the professional versions in the $500 range.

The simulator which I own, Engine Analyzer from Performance Trends, falls into the middle category. To give you an idea of the data that is utilized in this program, here is a partial list: Bore, stroke, rod length, windage, friction losses, compression ratio, combustion chamber shape, valve diameters, flow efficiency, port diameter, port volume, port centerline length, manifold diameter, manifold centerline length, manifold flow efficiency, runner length, carb cfm, ...and that only covers the first three of seven screens of data to be entered. Obviously the more accurate the data entered, the more accurate the results. The real strength in a program such as this is not in the hard numbers it produces, but rather is revealed in the company name itself:  Performance Trends. While the actual horsepower and torque numbers produced by the program may not match real world results exactly, by changing input data one step at a time, one will see a "trend" in the results.

So, ...to the simulator! The logical first step was to enter everything in as accurately as possible to match a stock 74 cubic inch Knucklehead. Well, almost stock. I used the flow figures for an unmodified FHP/S&S Knuckle head along with an Andrews "N" Knucklehead cam. The N cam is what Andrews calls its "stock replacement" and though its specs don't quite match my own measurements for an OEM cam, or the S&S stock replacement Knuck cam, I already had the specs loaded into the program and deemed it suitable for these tests.

As I stated earlier, the actual numbers that the program predicts are of much less consequence than the "trends" that it reveals, though I might mention that the numbers generated looked reasonable, remembering that rear wheel HP recorded on a chassis dyno will be 10-15% lower Here was the first thing of note: changing from the stock Knuckle M35 carb to the slightly larger M74 resulted in a gain in average torque (across the tested band of 1500 to 6000 RPM) of 4-1/2 foot pounds, along with along with gain in average horsepower of 4. Peak torque went up by nearly 7 ft pounds and the horsepower peak went up by 5, but also peaked at 500 RPM higher than with the M35 (5000 RPM vs 4500).

M35 vs M74


Next up was to input the added runner length of the dual carb "X" manifold without the additional flow capability of a second carb. This model shows an increase in both torque and horsepower across the entire RPM range, which suggests that added overall intake tract length for the dual carb manifold is a performance enhancement all by itself.

But we really aren't going to the trouble of building a dual carb "X" manifold just for the length, are we? Inserting the flow from an M74 combined with an M35 results in even more impressive gains. Peak torque is up nearly 9 foot pounds compared to the M74 on a stock manifold, while peak horsepower increases by almost 13. Average torque across the tested RPM range is up by 8 with average horsepower up by 7. Perhaps just as important is that the dual carb model show the torque as higher than the stock carb and manifold at all RPMs, even compared to the single M35. That would suggest that we are not going to give up any lower RPM performance in the search for top end power with the dual carb manifold.

M74 on stock manifold vs dual carbs on X manifold


Perusing all of the data, it appears that the M35 on a stock manifold is limiting the peak torque to 3000 RPM and the peak HP to 4500. The simple change to an M74 raises the torque peak to 3500 and the HP peak to 5000, indicating the restriction of the M35. The addition of the dual carb manifold with two carbs leaves the RPM for peak torque at 3500, but raises peak HP to 5500.

At no point in the torque curve did the M74 produce less than the M35. In fact, subsequent "runs" with even much larger carbs still showed a horsepower peak at 5500 RPM (the peak number increased, but not the RPM at which it was reached). That indicates to me that the M35 was limiting the RPM of peak HP, whereas with an M74 there is some other factor that is limiting it (in fact increasing the cylinder head air flow in the test did result in the RPM for peak HP increasing).

Plenum vs X manifold shows which is clearly the better street choice
 
Of course these tests don't tell us much about throttle response and overall driveability, but that's where a little personal experience weighs in. While I have not had the opportunity to field test an "X" manifold, I do have some personal experience with a "Seely" style manifold with no divider which allows each cylinder to draw from both carbs. When I built such a manifold about 25 years ago, it seemed logical to set it up in much the same way as an automotive 4 barrel carb. If you consider a typical 4 barrel, you will notice a couple things. One is that the "primary" throttle plates are normally smaller than the secondary's. The second is that the linkage provides for the primary throttle plates to open part way before the secondary plates begin to open: this is commonly called progressive linkage.

Now think about what that means for a moment. The smaller primary plates will naturally result in better fuel mileage and throttle response when you don't "have your foot in it." The larger secondary plates will allow maximum air flow for WOT (wide open throttle) situations. That should make for a pretty good all around compromise between driveability, mileage, and power. And such proved to be the case. I fabricated throttle linkage (shown below) which allowed the M35 that I used as the primary carb to reach 1/2 throttle before the M74 secondary carb began to open, but which also caused both carbs to reach wide open at the same time. As an added airflow enhancement, I only ran a choke plate on the primary carb (though the choke shaft remained in place on the M74 to keep the low speed needle adjustment mechanism).

Throttle closed

Right carb at 1/2 throttle, Left about to start opening

Both carbs at full throttle


Starting was as easy as stock, and as I recall required abut the same procedure as with one carb. Throttle response was as good as stock. WOT performance was very good, and in fact when I would "roll on" the throttle, I could feel when the second carb started to open, much like you can feel the secondary's of a 4 barrel carb on your V-8 kick in. (Come on, ...at least some of you had to have ridden in an antiquated car with a 4 barrel carburetor.)

Of course this setup was not on a completely stock Knucklehead, which has the potential for skewing some of the results. The engine remained 74 inches, but it used two right side flywheels allowing quicker revving. It also had ported heads with larger valves, along with a 110 Sifton cam; you know... typical Knuck hop up stuff of days gone by.

Full disclosure; the one glitch that I never did quite work out entirely to my satisfaction (at least from a curiosity standpoint) was the idle speed. With the circuit breaker at full advance the idle speed would remain too high despite my attempts to disable the idle circuit of the secondary carb. I think it was due to my use of typically worn out Linkert carbs (with excess wear to the bodies at the throttle plates) allowing too much air to sneak through. Since I did not have any better carbs to try, I "solved" the problem by installing a late '60s auto advance circuit breaker which I did happen to have in my parts stash.  Problem  not solved, but symptoms masked.  Whether I was correct that the source of the high idle was worn out carbs, or if I simply did not do a good job of disabling the idle circuit remains to be seen, and any input from someone with similar experience is welcomed.



So, there you have it, an "X" shaped dual carb manifold; ...my best compromise solution for dual carbs on a vintage Big Twin. No need to do extensive and expensive modifications to your heads. By avoiding the short runner length of a plenum type manifold, RPMs for toque and horsepower peaks stay at a street friendly level. And perhaps one of the biggest advantages is that it sticks out less than 3 inches further than the stock set up, or about an inch more than an S&S E.

Ignore the linkage shown here - pic was taken early in the mock up process

Wednesday, April 22, 2015

Earth Day 2015

In recognition of  Earth Day and the ongoing global warming crisis, I would like to ask everyone to make a small sacrifice.  Could you please take the time to burn some gasoline?  I would suggest at least 20 gallons.  Now I know that most of us don't have the free time to go out driving around aimlessly today, so I have a couple alternative suggestions. 

The first would be to simply pour the 20 gallons of gasoline into an appropriate open container such as your back yard fire pit.  In the interest of safety, you should probably light it by means of a flaming arrow shot from a safe distance, though most earth day supporters would also cheer a reduction in population, no matter how small.

If you just can't get away from work for the sake of the environment, then please consider getting a jump start on gasoline burning by leaving your car idling in the parking lot during business hours.  Sure, that won't burn as much as one might like, but consider this; you can increase the burn rate significantly by the judicious placement of a brick on the foot feed (yeah, I grew up on a farm; for those who didn't, the foot feed is the gas pedal).

Now, this modest contribution to global warming will cost you about $50 depending on your local gas prices, but if enough of you contribute, the rewards for all of us could be significant.  April 22 and here in southern Minnesota we had snow flurries yesterday.  Global warming - give me some of that!  And remember, its for the children.

(If you have your own suggestions on how we can increase global warming, feel free to add them in the comments section)

Saturday, April 4, 2015

He is Risen!


Luke 24:1-7 Now upon the first day of the week, very early in the morning, they came unto the sepulchre, bringing the spices which they had prepared, and certain others with them. And they found the stone rolled away from the sepulchre. And they entered in, and found not the body of the Lord Jesus. And it came to pass, as they were much perplexed thereabout, behold, two men stood by them in shining garments: And as they were afraid, and bowed down their faces to the earth, they said unto them, Why seek ye the living among the dead? He is not here, but is risen: remember how he spake unto you when he was yet in Galilee, Saying, The Son of man must be delivered into the hands of sinful men, and be crucified, and the third day rise again.

 
The resurrection of Jesus Christ from the dead was miracle, to be sure, but not the only recorded instance of someone coming to life again after dying. We have the case of Elijah raising a young boy from the dead in the Old Testament. You remember the story. Elijah had been staying with a woman and her son. She had only a handful of meal and little oil, but it miraculously never ran out. Eventually the boy took sick and died, but by the power of God, Elijah raised the boy back to life. Some years later his protégé, Elisha, performed a similar miracle in raising a young boy who had died from a head injury.

Shortly before his own death and resurrection, Jesus himself brought his friend Lazarus back to life. Lazarus had been ill, and Jesus seemingly "dragged his feet" in going to him on his sickbed, where his disciples apparently expected a healing to occur. Instead they arrived after Lazarus had been dead for long enough that as it is described in the KJV "he stinketh."

If, then, the resurrection of Jesus Christ was not a unique event in history, why do so many claim that it was the most significant? For that answer we have to understand the significance of his death. The death of Jesus Christ was not significant because of his death on a cross, for many men were crucified in Jesus' day. No, Jesus death on the cross was significant because of who he was and why he was being killed.

Christ Jesus is the spotless lamb of God, pictured in the Passover, who was slaughtered as a payment for our sins. During the crucifixion, God the father poured out his wrath on his beloved Son just as though it was he that had committed all of our sins. That's what makes the resurrection of Christ so important. It is the proof , given to all of us who believe, that his suffering and death was an acceptable payment for our sins.

But let's not just gloss over that word sin too quickly! Sin is the reason that the suffering, death, burial and resurrection of Jesus Christ had to take place. That reason is often passed over lightly, or even ignored. The term "sin" will likely evoke one of several responses when it is brought up. Some will be indifferent to the term "sin", seeing it as an archaic concept, with no relationship to modern life. Others will find the mention of sin to be uncomfortable or even offensive. Immediately they will feel that they are being judged. And for a few, the revealing of sin will bring conviction. There is a fine line between the latter two. Offense has its beginnings in conscience but it is filtered through pride.  Conviction of sin, on the other hand, is a work of the Spirit of God.   

Few, it seems, have much idea what the origins of this word "sin" is. The words that are translated as "sin" in the Bible mean to "miss" or "to fall short."  That doesn't sound so serious now, does it? And it wouldn't be, if it were man's standards that we were falling short of.  But that is not the case. Taking sin "lightly" is a result of taking God lightly. It is a result of a lack of understanding the holiness of God. Until you start to get a glimpse of God's holiness, none of this "suffering, death, burial, and resurrection" of Jesus Christ can be of much meaning to you. because "sin " will not have much meaning to you.

Every place in the Bible that we see a man get a glimpse of God's holiness, we see them taking it very seriously. Isaiah fell to his face and despaired that he was a man of unclean lips. Upon seeing "the appearance of the likeness of the glory of the Lord," Ezekiel fell on his face. John says in the book of Revelation, that when he saw Christ in his glory, he fell at his feet as dead. If you do not take sin seriously, then it is because you have no grasp of the holiness and the glory of God.

Do you want to know what you are falling short of? God has spelled it out very clearly. The ten commandments are a good place to start. Go to Exodus 20 and see for yourself. Thou shalt have no other God's, thou shalt not take the Lord's name in vain, thou shalt not steal, thou shalt not commit adultery, thou shalt not covet; those are just few of them.

The Bible teaches us that we are all sinners, and for some, that fact is a comfort of sorts. "We're all in this boat together, so its no big deal if I am a sinner."  But the truth is, in the end God does not deal with us as a group with respect to sin. He deals with us as individuals. Did you notice how those commandments began with the pronoun "thou." Thou is singular. It means you as an individual.

I believe that standing before God on judgment day will be a very lonely place. Just you and your sin in front of a God that is Holy. Consider what that might be like....

LONELY!

Lonely, that is, unless you have an advocate. One to stand up for you and say "he is guilty, but I have paid the price for his falling short. I have lived a life in which I never fell short of my Father's expectations even once, and I did it in this sinners place. I have purchased him with the price of my blood. He is mine." Yes, the judgment will be a very lonely place for many, but not so if you belong to Jesus!

If you belong to Jesus, then his resurrection is the most significant event in history! It is your proof that his suffering and death on the cross as a payment for your sins is acceptable to God. Doubtless some of you have that assurance. But if you are wondering how you can have Christ as your advocate; how you can belong to Jesus - it is as simple as turning away from your sin and trusting that he paid the penalty for them.  Bend the knee to your risen King!

Wednesday, March 11, 2015

Rumors of my Demise...

Well, I am not aware that there are actually any such rumors circulating yet, though it has been so long since I have posted you may have wondered.  The truth is I have just been so busy trying to keep my head above water in the shop that I have, to my shame, not been able to finish the final installment of Vintage Dual Carbs

One small part of the hold up is that I would like to make part 4 a little more than just a commentary on my past experience, however given the difficulty finding time to write, its unlikely I will find time to do actual real world testing any time soon.  That's where computer simulations come into play.  I would like to take the time to run some simulations on my Engine Analyzer software to re-enforce my thoughts for a good compromise for dual carbs on a vintage Harley.  Nothing takes the place of actual testing, but I fully expect that with some careful measurements and time with the program some valuable information will be revealed.

So stay tuned...

Tuesday, December 23, 2014

One King, One Kingdom

In one of my recent posts, I ventured to state that I had found the answer to a minor point of curiosity on my part dealing with the presence of two similar terms used in the Bible, those terms being "kingdom of heaven" and "kingdom of God". My answer, based on two verses in the Gospel of Matthew was that they are the same.  A reader was quick to point out to me that there is indeed a distinct difference between them in that the kingdom of heaven is a literal physical kingdom that the Jews will inherit while the kingdom of God is a spiritual kingdom that the Church will inherit. In this post I would like to attempt to imitate those of Berea and search the scripture to see if this is so.

As we look at the occurrences of the two terms, it becomes evident that if they are not two names describing the same kingdom, then at the very least both kingdoms share a number of striking similarities.

For instance, from Matthew 13:10-11 and Mark 4:10-11, we can see that truths about both the kingdom of heaven and the kingdom of God were revealed by Jesus in parables so that only those who were chosen to understand, would understand. In fact from these verses we also must conclude that the same parable of the soils can be used to reveal the same mystery regarding each kingdom.

Matthew 13:31-32 coupled with Mark 4:30-32 inform us that both the kingdom of heaven and the kingdom of God are like a grain of mustard seed.

Mark 10:14 and Matthew 19:14 together inform us that both kingdoms are made of those who share the characteristics of little children.

From Matthew 11:11 and Luke 7:28 we may glean that he who is least in the kingdom of heaven is greater than John the baptist, ...and that so is he that is least in the kingdom of God.

Now, the fact that the kingdom of heaven and the kingdom of God share these four characteristics does not by itself prove that they are one in the same, but it should at the very least make one take it into consideration.

If one were to take the position that the kingdom of heaven is to be the inheritance of the Old testament Jews and the kingdom of God will be made up of New Testament saints, then one must consider that Jesus, as recorded in Mark 1:14-15, preached repentance and that the kingdom of God was "at hand." But John the baptist, in Matthew 3:2 preached "repent" for the kingdom of heaven is "at hand." This poses a bit more of a problem for the two kingdom view. It is easy to see a spiritual kingdom as being at hand (or "drawn near", as some translations put it), but how would one apply being "at hand" to a literal physical kingdom for the Jews. If anything concerning such a kingdom was at hand, it was its destruction by Titus in 70 A.D. The absence of anything resembling a Jewish kingdom for nearly 1900 years can hardly be something easily reconciled with "at hand." Was John mistaken or could both he and Jesus have been describing the same kingdom with different words?

Perhaps just as puzzling would be the conversation between Jesus and Niccodemus as recorded in John chapter 3. In verse 3 Jesus says "Except a man be born again, he cannot see the kingdom of God." Okay, if there are two kingdoms, that tells us that the spiritual kingdom occupied by the New Testament believers can only be seen by those who are born again. That is all well and good, but a few verses later Jesus expresses surprise saying "Art thou a master (teacher) of Israel, and knowest not these things?" Well, ...at least I guess you could read that as surprise. I personally don’t believe that Jesus was ever surprised; I see that statement as more of a chastisement. But either way, why should a teacher in Israel be expected to know about a new kingdom that was just coming into existence? Odd.

Another piece of scripture that does not quite seem to fit in with a two kingdom view can be found in Matthew 16:19 where Jesus announces that he will give the keys to the kingdom of heaven to the disciples. Now this verse has often been used (and too often abused) to assert power given to the church. But was Jesus real purpose to teach that the church will have power over the physical kingdom occupied by Old Testament saints?

In my original post on this subject, the scripture that I presented in support of my understanding of the kingdom of heaven and the kingdom of God being one in the same was Matthew 19:23-24. Here is what my argument consisted of: In verse 23 Jesus exclaims how hard it is for a rich man to enter the kingdom of heaven, and then in verse 24 he goes on to say "And again I say unto you, It is easier for a camel to go through the eye of a needle, than for a rich man to enter into the kingdom of God." (Emphasis mine). I postulated that by using the term "again" Jesus made the terms interchangeable, else he would have used the world "also." Of course this argument rests on the reliability of the translation of the Greek word "palin" which it appears could in some cases be translated as "furthermore" instead of "again." However, I am not aware of any translation which uses any word except "again" in this verse. I am pretty sure the translators are smarter than I am and very likely got it right.

The objection I received to my use of this verse to support my case was that one should not build a doctrine on a single verse. I agree completely; thus the study that went into this post. I do have one more argument to offer though, and I believe it to be the strongest one, when taken in conjunction with what I have already presented here. That argument comes from Matthew 8:11 "And I say unto you, That many shall come from the east and west, and shall sit down with Abraham, and Isaac, and Jacob, in the kingdom of heaven." Now consider Luke 13:28 which says: " There shall be weeping and gnashing of teeth, when ye shall see Abraham, and Isaac, and Jacob, and all the prophets, in the kingdom of God, and you yourselves thrust out."

The fact that Abraham, Isaac, and Jacob are said to be in the kingdom of heaven and in the kingdom of God, taken alongside everything else I have presented here, leads me to the inevitable conclusion that those kingdoms are one in the same. One King, One Kingdom.

I am thankful for the "nudging" which I received to search the scriptures for a proper understanding, but I must add that much more than that, I rejoice that I will someday be able to sit down with Abraham, Isaac, and Jacob in the kingdom of heaven.

Thursday, December 18, 2014

Vintage Dual Carbs, Part 3

In part three of this treatise on dual carb Harleys, I would like to put the venerable Linkert under the proverbial microscope. First stop will be an unlikely source for an avowed Knucklehead fanatic such as myself, that being the ’48 to ’57 Panhead Service Manual. The last page of the carburetor section has a handy-dandy chart listing most (all?) of the carbs used from 1936 to 1957. Along with applications, throttle disc angles and even transfer port dimensions, we find venturi sizes listed. Hats off to those technical writers of yesteryear; if only their modern day counterpart would follow their lead.

For our purposes here though, the venturi sizes are indeed what is most useful. The first one we might note is the 3 bolt M-5/ M-55 of early 61" Knucklehead fame. They featured a venturi bore of 1-1/16". OK, so what, you might say. Well, let me put that in terms of modern carbs: 27mm (rounded off). That friends, is not a lot of area to get much air through. But as we go down the list, the venturi sizes do increase, but not much. While we do find the M-25/ M-75 with its whopping 1-5/16 venturi on 1940 Knuckles and as an option on ‘41-’48 models, most Knuckles left the factory with the 1-1/8" M-35. Finally, with the 74" Panheads a 1-5/16" venturi became the standard bearer for brass bodied Linkerts on Harleys, being the largest Linkert offered. Again let’s put those sizes into terminology which will make it easier to compare with modern carbs. The 1-1/8" venturi M-35 series carbs were only 28.6mm (again, rounded off). The big kid on the block M-74 comes in at a whopping 33.3mm (do I really need to point out that this figure too is rounded off?). As a point of reference, when Harley switched to Bendix carbs in the mid 1970s, they put a 36mm version on the XL models, which just happen to come in at very near the same cubic inch displacement as the 61" Knuckle, and a 38mm on 74" Shovelheads.



 
Super E on left, M35 Linkert on right


As a further point of reference, let’s mention a couple modern performance carbs. S and S (why does it bother me so much that blogger’s html will not allow the use of the ampersand?) designates their carbs by the diameter at the manifold surface rather than the venturi size. An S and S Super "E" carb which is called 1-7/8" is actually 40mm at the venturi, while the "G" model’s 2-1/8" bore is 44.7mm at the venturi. Right in between these two carbs is the flat slide Mikuni HSR42. Keep in mind though, none of these three performance carbs relies on a choke plate as a starting aid. All of the Linkert carbs employ such a plate, which further limits their air flow beyond what the already smaller venturi does. And the measured airflow through these carbs bears this out. An S and S "E" carb flows a whopping 73% more than an M74 despite the venturi bore being only 20% larger.

 
Knuckledragger Carbs
 
Right about now you may be thinking, "What about all those old pictures I’ve seen of vintage drag bikes with a pair of Linkerts fitted?" In fact, those paying close attention may even wonder why my own vintage drag bike, "The Knuckledragger" breathes through a pair of them. Speaking for my own situation, I had two reasons to use Linkerts. Nostalgia and pragmatism. The nostalgia portion is self evident. The pragmatic stems from the simple reason that the heads I had in my possession for the project were already set up with Linkert 4 bolt flanges. Had it been a more serious performance effort, I would have reworked the heads.  As it is, I still cut the choke assemblies off, added radius inlets and swapped to the somewhat larger 1-5/16" venturi's on the M35 carbs to maximize air flow.


 
Granddaddy Joe Smith still ran Linkerts on his Knuckle just before switching to a Shovelhead
 
The reason you see Linkert in old pictures of early drag bikes is also pretty straight forward, though maybe not so self evident. Many of the drag bikes you see outfitted with a pair of Linkert carbs were run on nitro methane fuel . "Nitro" as it is commonly called among racers, is quite different than gasoline in that it has oxygen in its chemical makeup. That means that rather than relying on airflow to get enough oxygen into the combustion chamber, with nitro a goodly portion of that oxygen is supplied by way of fuel flow. Remember back in part 3 when I wrote this? "The problem is very seldom getting enough gas into the engine for high performance, the challenge is in getting enough air in." Perhaps I should have more specifically used the word oxygen rather than air and fuel rather than gas, but I think you get the picture.

 That is not to say that the addition of nitro turns the Linkert into killer performance carb with no other changes. Nitro requires a much, much, much richer fuel to air ratio. For a given amount of airflow, nitro will need about 7-1/2 times as much fuel as the same engine running gasoline. This requires some substantial modifications to the fuel delivery system all the way from the petcock to the float system to the jets. The potential results however, are nothing short of awe inspiring. A switch from gasoline to nitro methane comes with a potential of just over double the horsepower. Do I need to mention that the bike and the rest of the motor needs to be strong enough to survive double the power?

Now it looks like this series will drag out into yet another post. God willing, I plan to wrap it up in a post encompassing my thoughts on what makes a viable street application for vintage style dual carbs.