As a gear and gearbox designer by profession (and degreed mechanical engineer, licensed and recognized by IL, P.E. #062.068693), this topic of a gear drive for a SOHC motor is of particular interest to me.  If I could help in any way with a potential design I would be more than willing to.  If that were to only check someone else's design over or to assist in coming up with a design I would relish at the opportunity.  I have been limited in my ability so far to accurately conceptualize the layout in my cad program, however, as I do not have an accurate model of a SOHC engine, and do not have a SOHC engine to create a model from! 

As for my qualifications to help, I am a contributor to the AGMA (American Gear Manufacturer's Association) and know some of the highest quality gear manufacturing facilities in the business (Chicago is a large hub for the Gear Industry).  I can help optimize gear geometry, can run gear design calculations per AGMA standards, and can create actual blueprints with appropriate GD&T (geometric dimensioning and tolerancing) per the latest ASME Y14.5M-2009 standard (as opposed to simple drawings with plus/minus tolerancing, which routinely induce unacceptable tolerance stack ups, or simply do not convey the true intent of the part as it would need to function in application).

I freely admit that I am a completely biased party to the discussion of whether a gear drive makes sense for use in this application, and if the standard method of a stretching chain is already good enough (or perhaps even desirable), predictably repeatable in how much it stretches, able to be accurately compensated for, cheaper, easier to maintain, etc. then there's no question that as an engineer I would absolutely advise my management to stick with the simple solution that already works.  I question however how predictably repeatable the amount of stretch is, and whether there would be more precise alternatives to vary the advance if done so intentionally, as opposed to reacting and correcting for whatever the given advance or retard is provided by the system, without really having control over it. 

Additionally I question the power consumption of running the chain as opposed to a gear drive.  I'm not a chain and sprocket designer so I can't really comment with confidence on the losses, but I would imagine a chain that long and heavy would require more power to throw around than the gear sets would be. 

Also one thing that I do know for sure is that in power transmission a chain is about the worst case you can get with respect to overhung load on the shaft.  The chain tension itself (without any load along the chain at all) will already cause a (potentially significant, depending on the amount of tension) radial force on the shaft at the sprocket, and then the shaft will have to then also transmit torque when the system is rotating.  This is a classic case of combined loading in torsion and bending.  Don't get me wrong, the separating forces of a gear set will cause overhung load as well, but only as the torque increases on the system, and the gear set will have significantly lower radial forces than a chain, and can even be designed to limit the separating forces as well.  Now this could all be minutia, and have no real world effect if fatigue failure of the sprocket shafts never occurs in the current design, but then again who's to say it wont happen at the most inopportune moment, like right when its reached its fatigue life and is at its highest stress during a pass at Drag Week and decides to relieve itself from the engine to catch some sun ('cause if it were to happen at all, that's the most likely candidate of when).  As an engineer I would call that a failure, David Freiburger would call that Un-Good.

Some quick comments on the proposed gear design:
Be careful with double helical.  There are a few design considerations that should be investigated before choosing that geometry that I can get into longer detail on that not everyone will probably care about, as I've already gotten way too in depth and long winded as it is.

Some questions about the design:
How much face width can you get away with? This will be key in determining whether a double helical is really the best option.

Last thing:
Don't believe in the limitations of any given rule of thumb for any type of engineering problem.  There's always exceptions to the rule, and if you know the design criteria, the optimal engineering solution (for the given criteria, which may only apply to this one thing) rarely falls in line with rules of thumb.  Most of the time however the truly optimal engineering solution is not chosen due to compromises that make life easier for other considerations, like cost, manufacturing, and assembly which of course are valid and usually more important criteria in industry.  For this case the double helical system could very well be the optimal design, but I also know that if you show me that system I could probably design the "worse" spur system to be quieter, stronger, and cheaper.  There's a lot of questions to be answered before being able to make those kinds of determinations though.

Sorry for the long reply, I'm just a gearhead.
Calvin

P.S.
I think the links to the scans of the Car Craft article may be broken.  I only see X's.

Jay,

        I apologize for stepping over my bounds by asking.  I guess I should really state that my interest has less to do with your exact setup and more to do with asking for your sage advice based on your personal experience with your own shop, on how someone like myself might be able to go about accomplishing the same (or some of the same) thing(s) that you have already.  My wife and I are looking to buy a house in the not so distant future and I have a basic requirement to have a shop large enough to conduct a full restoration/hot rodding of my 69 Mustang Sportsroof.  I would love to be able to do the work myself (of course after learning how to do what I don't know how to already), and the biggest part of that would be with respect to paint and body work, so having a paint booth and being able to do sheet metal fabrication and welding would be primary concerns.  I have seriously considered looking for an open lot and building on it as opposed to retrofitting an existing structure given the constraints of space requirement for the shop.  Obviously I would need to determine what the zoning allows for depending on the location, but I was just looking for your best ideas on what size shop would be required, and if there are things that people should be sure to think about ahead of time to make sure that we would actually be able to do the work we dream of doing and make it a reality like you have, (like electrical or plumbing considerations, special permits for paint work, etc.).  Better to have those concerns thought about now rather than after starting the project, or buying a property that won't end up working for the use.

Thank you again,
Calvin

Calvin,

The reason why an engine consumes more fuel when running ethanol is only due to the required AFR for a given lambda. Energy density has nothing to do with it, yet people often say that the reason why the engine requires more fuel is due to a lower energy density. Energy density is how much energy you'll get from a given amount of fuel, the exact amount of fuel present though has to do with the AFR and displacement.

Exactly.  The A/F ratio of ethanol for instance is 8.966 to 1, whereas the A/F ratio of gas is often referenced as 14.7 to 1.  This would mean that for the same volume of air you would have to burn about 64 percent more fuel using pure ethanol (14.7/8.966 = 1.6395 = ~64% increase).  For an engine of the same displacement, converting from gas to ethanol would net you approximately a 2 percent power increase but also the 64% increase in fuel useage.  For an engine of the same power output, you could reduce the overall displacement by that same 2%, but you would still be burning 62% more fuel with ethanol.

With E85, where 15 percent is gas and 85 percent is ethanol, the A/F ratio would become roughly 9.8 to 1 (.15 x 14.7 + .85 x 8966 = 9.826).  For this fuel you could expect to burn roughly 50% more fuel than regular gas with an engine of the same displacement (14.7/9.826 = 1.496 = ~ 50 percent increase).

Now if the energy density of ethanol was much much greater than gasoline (at least 64% greater), then you could design an overall smaller displacement engine that would burn less fuel than gas and still produce the same or greater power, in spite of the 'richer' A/F ratio.  But that isn't the case.

I don't know if edits automatically alert people to changes in the thread on the forum or not, but for those that may have read this topic earlier, I have added more information to try to help folks understand what I was saying a little better.

Does anyone on the forum (like Jay for instance) have dyno comparisons on the same engine using gas vs alcohol to help Autoholic with his research?  To see how much of the theory holds to the reality?  That kind of info would be really interesting to see.

Calvin

Hello Everyone,

        This is my first post and I see that I have already mistakenly found out that by hitting tab you can accidentally post what you're typing too soon, and that apparently you cannot delete a post you just put up by mistake.  I would like to reply to Autoholic's post regarding his question of the difference between using gas vs alcohol in his topic "Fuel Related Performance" http://fepower.net/simplemachinesforum/index.php?topic=3477.0.  I figured that I would make my response its own topic with its own title so that this might be easier to other users in the future to search for this information again.

        In order to obtain my final credit hour during my senior year at University of Illinois in Mechanical Engineering, I did an independent study for one of my professors who taught the engineering of off-road vehicles.  The topic of my study was the forced induction of internal combustion engines.  In that paper I wrote about the chemistry of combustion and use of oxygenated fuels, amongst other topics.  I figured that I would post the relevant pages here for others to read in case people found this useful.

        I have to admit after re-reading it, that I should make the following qualifying statements:

1.    The intended audience for this paper was my college professor, and as such it is somewhat heavy on the technical side, and some elements that are referenced in the paper are expected to have been known ahead of time and are not explained (for example what the 'lower heating value' of a fuel means).  I will try to answer any questions regarding such things if anyone would like.

2.    The analysis I conducted is based purely in the theoretical, mathematical, and scientific realm, and definitely not from a position of experience or measured data on a dyno for instance.  I believe that Autoholic is more interested in that kind of data to support or contradict his own analysis (correct me if I am wrong here with that assumption).

With that here are the images of the pages (I have never imbedded images before so if it didn't work please let me know).



After reading this first page I figure I will add a few statements that may make the information more understandable or perhaps more relatable, that some readers may have questions on.
1.        Gasoline (as well as other fuels like Diesel, kerosene, natural gas and propane) consists entirely of molecules that only contain hydrogen and carbon atoms, hence the term 'hydrocarbon fuel'.  Since the amount of carbon and hydrogen atoms differs based on the fuel, a term is used to encompass all the fuels that fall into this category which is a 'general hydrocarbon' and is shown as a molecule with 'a' number of carbon atoms and 'b' number of hydrogen atoms: C_aH_b

2.        For this analysis 'gasoline' that you would purchase at the pump is considered a 'practical fuel' which has too much variation for these equations to hold valid all the time.  As such the practical fuel is reasonably approximated by a particular 'Pure Hydrocarbon' called Iso-Octane which has the molecular structure of 8 carbon atoms and 18 hydrogen atoms: C₈H₁₈

3.        The stoichiometric (ideal combustion) equation (1.2) for Iso-Octane then becomes the following:



4.        The stoichiometric air to fuel ratio of Iso-Octane then becomes the following:



This shows that 15.0666 moles of air is required to stoichiometrically combust exactly 1 mole of Iso-Octane.  This is slightly leaner than that of actual Gasoline where other sources reference the stoichiometric A/F ratio as around 14.7 to 1.



The important information in page 2 here (numbered three in the actual document) is in the top and lower paragraphs.  Understanding the technical definition of 'lean' vs 'rich' mixture is somewhat useful, but the really important information is in the concluding paragraph.  Here I basically sum up that in a closed volume with a relatively fixed ratio of fuel to air (meaning that you can't stray too far from the calculated stoichiometric ratio and still achieve combustion), that the limiting factor on the amount of fuel that can be burned (and thus work and also power that can be generated) in that closed volume is the total amount of oxygen available.  Once this is established a list is given of the three available ways to increase the amount of oxygen in the closed volume (ie. the cylinder).

The entire preceding two page analysis basically boils down to stating a very simple conclusion really, which is that you can't burn as much fuel as you want in the cylinder to increase power, and that the amount of fuel you can burn is limited entirely by how much oxygen you can get in there.


Now moving onto the comparison to alcohol fuels...



This first page is useful in that it defines what an alcoholic (oxygenated) fuel is, and how to go about calculating the stoichiometric air to fuel ratio depending on the chemical make up of that fuel.  The importance of that information though is in the table on the next page...



In table 3.4 I have simply taken the stoichiometric A/F ratio of Iso-Octane (gasoline) and divided it by the stoichiometric A/F ratio of the listed alcoholic fuels.  In comparing gas to nitro-methane for example I am showing that for the same mass of air being burned (lets say 1 slug **yes I just used the slug mass**....ok fine lets say 1 pound) that you can burn 8.91 times more nitro than gas.  This DOES NOT mean however, that by switching to Nitro that you can expect to produce 8.91 times more horsepower.

Why?

Well if you look back at equation 3.2 you see that the in the combustion of these fuels that you not only get all these different molecular products like carbon dioxide or carbon monoxide etc. but that what makes the power is the ENERGY released from the combustion, and the amount of energy released is not equal between different fuels being burned.

So the actual comparison of the power difference has to incorporate both the energy release as well as the A/F ratio of the fuels being compared...



The conclusion seen here is that between gas, Diesel, Ethanol, and Methanol, that there is actually pretty little difference in how much energy can be released by the same mass of air, with the exception of Nitro.  Again it isn't 8.91 times more powerful than gas, but actually 2.32 times more powerful.

In fact Jay stated in the topic created by Autoholic, that his experience shows that switching to methanol will net you approximately a 5% increase in power over gas (sorry but I haven't figured out how to quote yet), and based on the equations for the energy released by these different fuels the methanol would net a 5.5% increase in power compared to gas:

3.103/2.940 = 1.05544 = 5.544% increase.

This of course is only comparing if you were to take your existing engine and did not change any parameter to it (like compression ratio for instance) other than what fuel you burn in it and this is the approximate power gain you will see.  The potential however is there to gain much more than that simple 5% from methanol for instance due to the fact that it can cool the inlet charge much more than gas can...



This means that by using an alcoholic fuel, I not only can get an immediate power increase from the energy release of the fuel itself, but I could also now allow myself to increase the compression ratio, or increase the boost pressure without pre-igniting the fuel. 

I hope that my edits over the course of the day has helped some readers understand some of this a little better.

Thank you for welcoming me into your forum,
Calvin