I'm sorry bogie, I will give you a break. Thanks for the links and explanation though, it is just what I was looking for.

You’re one of a very few who's asking the right questions about the physics and engineering under pinning all this stuff. It's different from those who just want go fast part numbers.

The problem with, “just give me the part numbers” is that the state-of-art keeps changing, so if you're just chasing part numbers at best you're a race behind and usually at least a season.

The guys that figure out the hidden "rocket science" end up being the guys that design the stuff that becomes everybody else’s part numbers.

The amazing thing about the internal combustion reciprocating engine is 1) that is works as well as it does, what a serendipitous discovery. 2) All that power comes from about 110 degrees of a 720 degree cycle. That's 15 percent of the cycle produces work the rest is overhead. 3) Along with only producing power 15 percent of the time, it's only about 20% thermally efficient. 4) All that's enough to transform the world from horse and buggy to the automobile and put us into the sky.

After a 100 plus years the IC reciprocating engine is still the cause of many PhD papers, so there's a lot about it still to be discovered.

Bogie

Straying farther away from flowbenches, another topic brought up a question that I wante to ask you bogie. Can you inform me about av-gas? What grade, octane, leaded or not, how will it effect the tune of a carbed hot rod? Is it good to use in a hot rod engine (specificially mudder engine). I have seen it ran through two mudders ( a 454 BBC and 514 BBF) and for some reasons both engines had poor ring seal and very worn cylinders after a very short period of time, I realize there is a ton of other variables involved, but both engines were assembled by different machinists so bore preperation may be less of a factor, could've both engines just've been too rich? Or is av-gas commonly hard on rings?

When you talk about engines used in competition, especially late model thin wall castings, even those that haven't been bored, you always are at risk of the cylinder walls changing dimension as the dynamic loads on them change through the cycles. These movements can only be in the ten thousands of an inch, but it gets to be enough to break the oil film and also allow the rings to make unusual movements that dig into the cylinder wall and or twist in their lands. Also, keep in mind that around TDC the ring package is essentially running with no lube what-so-ever. These events conspire to increase wear at the worst and simply dump compression around the ring pack at best.

A rich mixture has a large effect as under the above described circumstances you also have to add the effect of what lube there is being washed off the piston and cylinder walls.

Lastly, for all the noise that's been generated in the automotive press about valves and valve seats pounding in without lead in the fuel. This problem was easily solved with induction hardening of cast iron seats and or the installation of hard alloy seats. But one big thing stands out with the elimination of leaded fuel and that's an overall increase in engine longevity. Ring and valve jobs used to be a common event well into the 1970's and 80s. With leaded fuel you cleaned spark plugs every 3 to 5 thousand miles and replaced them around 8-10 thousand miles. Valves would burn by 30 to 50 thousand miles and rings in a well maintained engine were gone from 70 to 100 thousand miles. Oil had to be rigorously changed every 2 to 3 thousand miles. And all this was mostly due to lead contamination of everything. It would cake valves, especially exhaust valves and port walls, piston crowns. The stuff showed up as a grayish silver sludge in the oil and every pocket inside the engine.

So while modern machining, materials and lubricants have improved, the suddeness of this improvement started with the elimination of leaded fuels, which certainly points a finger at lead as having been a contributor to reduced engine life for a number levels and causes.

Bogie

Ah, I see. I guess I didn't fully realize the durability problems associated with any kind of lead fuel, not only av-gas. But just to throw it out there, the av-gas that is used here is considered "low-lead" and I've heard 2 grams per gallon as a spec. Would this help the durability, or is that still too much. Also, what kind of effects can aromatics have in the fuel, as I've heard that the 100 octane av-gas that is used here does contain them.

Certainly low lead is better than high lead where durability and contamination are concered. However, keep in mind that av gas is formulated for altitude changes. For the most part its vapor pressure point is increased with the introduction of more aromatics so the stuff doesn't just evaporate from the tank at high altitudes. To some extent at lower elevations it then behaves somewhat like it has a higher octane than where it's rated. The effect of vapor pressure increases makes it a little harder to light off and a bit slower to burn.

The different burn characteristics tended to cause the reputation that av gas burns valves in auto engines because the delayed burn rate caused the exhaust valve to run hotter and the older very highly leaded fuels coated the exhast valve and reduced heat transfer again resulting in the valve running hotter than designed.

For competition where detonation with automotive pump gas is a problem, I can't see any problem with using av gas. But running the stuff on the street just doesn't make a lot of sense as in the end it causes more problems than it solves, some being techncial and some being legal. On the techncial side you get lead contamination in the engine and all the problems that brings. The slower burn rate reduces available power unless it's really supressing detonation, which is the worst of the evils. On the legal side it's not taxed as a motor fuel and the government will be nasty to you if they find out your a regular user of av or boat fuels on the street. Of course lead is illegal in an auto fuel for pollution reasons.

Bogie

Great information on the fuel Bogie, thanks a lot

Now I have some more questions regarding porting. Do you have any general rules of thumb for the port throat diameter? Does the 85% 'rule' hold up well for a basic SBC head, and how and when should this number change? Also should you use the throat diameter of the port or the valve diameter when figuring discharge coefficients? Wouldn't the throat diameter be a better judge of the smallest area the air has to pass through?

Hey Bogie, I have some more questions, this time regarding reading of burn-patterns on cylinder heads. Here are all of my pictures from the heads I recently took off a 468 BBC mudder.
http://photobucket.com/albums/a313/GibTG/Teardown%20of%20Nates%20Engine/

I realize it's hard for you to see anything with just the heads and without seeing the whole picture. But I'm just looking for some general guidelines and some insight from your experience. I realize that some cylinders were pumping plenty of oil, and I think that is especially visible in at least one of the pictures; these cylinders had large quantities of oil on the backsides of the valves and seats. Otherwise the ports stayed pretty clean. I also wondered about the "line" in several of the exhaust ports where the carbon is more clean than the areas around it, it is on the left side of the guide boss and goes up the long side of the port to the exit near the middle of the port at the roof. It especially interested me since it is very visible in 4 or 5 ports, even on ports that were moving plenty of oil. Also I was wondering about the carbon dusting on the quench area, but in one of the pictures you see the quench is only half covered with carbon. Can anything be seen from the exhaust port & valve coloration? Thanks again Bogie

Jeeze Gib, thanks for the eye test. That last picture in the set sure looks like someting got loose in the chamber and beat the quench step up a bit.

You speak of oil getting into some of the chambers and evidence of oil on the back side of the valves, I assume this to be the back side of the intakes. This would indicate that oil is either getting into the intake track through a leak to inside the engine; or heavy blow by being vented back to the intake side like into the air cleaner; or excessive valve stem/guide clearance or leaking stem seals. This could also be oil getting around the rings and being carried into the intake tract by reversion effects of a overlap and late intake closing. In any of these cases oil in the combustion chamber is not a good thing as it lowers the octane rating of the fuel and makes the occurance of detonation a bigger risk.

As to how the carbon attaches to the metal surfaces. Carbon usually settles out on cooler surfaces; in areas of less velocity of the gaseous flow; in areas being washed by unburnt fuel or oil at temperatures that carbonize the liquid rather than burn it. However areas of high and repetitive fuel wash tend to be clean. So one has to look carefully at what's going on.

Some of the engines quench areas look quite clean and others rather carbon fouled. I' expect a couple possibilities. The clean quench has either a lot of velocity squeezing the mixture out as the piston comes up on TDC and probably has a faster and hotter burn as well. The carboned up quench would indicate to me a less vigorous ejection of mixture as TDC is passed and or a cooler burn, or more oil or fuel being present. These differences could be caused by the presence of oil; different fuel mixtures reaching different cylinders; a different absolute compression pressure caused by tolerance stack ups resulting in some piston crowns not being as high in the bore at TDC than others, the reasons for this run from different piston dimensions, different center to center lengths of the rods, different stroke lengths and timing orientations of the crank's rod throws; different volumes between combustion chambers; different amounts of cooling at different cylinders. This list goes on and on.

On the exhaust ports, when looking into them with the head flipped up so youre looking from the combustion chamber side, I'd expect the pocket backside and port outside and upper walls to be cleaner since this is the area of strongest flow and that should scrub accumulations from those surfaces. Wedge exhaust, even semi hemi wedges, tend to put most flow in those areas because the shrouding on the cylinder wall side causes  and the centrifugal forces of the flow from the quench side, center, and sparkplug side tend to wrap the major flow onto the outside and upper walls of the port.  

Bogie

Yeah, we sold the engine to a local here a couple years ago, and he choose one night to toy with the carburetor after he had a little too much to drink, dropped a carb stud nut into the engine and continued to run it until it went. Quite the carnage, it beat a whole into one of the pistons so it could expand and take out the rest of that cylinder. New block, new crank, one new piston, new valves (bent the intake very severely in that chamber) and I think & hope everything else is okay.

Once again though Bogie great stuff. I believed in my head before hand that different quench clearances could've caused the differing carbon coverings, the block had never been decked, I know this is not smart but the engine was put together 15 years ago, so I was pretty young to try to tell my dad otherwise. And the crank never turned & "trued."

I don't know why but we can't seem to get rings to seal in any of these engines as much as we would like. We're not having any of these engines dyno'ed and it's mostly backyard stuff, but they are competing and as far as I'm concerned there should be less oil in those chambers. There is really only three machine shops here and one just got a computerized hone, otherwise this block and all of our previous blocks have been honed by hand, which as far as I've read from people like Smokey, John Lingenfelter, and Mr. Vizard this isn't a good thing. But we will have to see with this engine, it will be getting new bronze guides and new valves, but by how gummy the chambers are I don't think that that much oil could've entered through the guides, but I guess I could be surprised. The engine never really ran long enough to really check oil consumption, could it be maybe that the rings never did seat?

Thanks again Bogie, but I've gotta run.

Bogie, do you have any experience applying any of the techline coatings? I made my first attempt tonight and it didn't turn out that great, I wondered if you had any tips or tricks, here are the pics of the final product if you would please take a look for me.
http://photobucket.com/albums/a313/GibTG/1st%20Coating%20Attempt/

I guess I'm not really a very happy camper where coatings are concerned unless they are factory applied to new parts. My experience with home cured coatings has been extremely variable. I find that success is better with new parts than old ones. I think that it’s just too difficult to clean and prep parts used parts contaminated with lubricants and mechanically transferred microscopic wear materials at home. This takes industrial processes that are just too intense in terms of chemistry, temperature management, micro abrasion prep techniques, material handling and protection to just be effective for do-it-yourselfer.

The GM factory is moving into coatings, the new Corvette engine has a considerable amount of this and other technology which will eventually find its way into regular production over the next few years.

I’d like to find coatings that are a solution to problems but so far I haven’t tried anything curable in my wife’s oven that hasn’t made her mad at me on one hand and didn’t deliver sustainable performance on the other whether dispersants, thermal barriers or lubes.

Thermal dispersants would be good on valve springs on competition engines where you want to restrict top end oiling. A lube on the spring ends or spring pocket and retainer can be beneficial by reducing rubbing friction at these points hence temperature. A thermal dispersant on the coils lets the spring surrender heat faster. But so far my experience has been that this isn't better than stripping paint from the spring and glass beading or shot peening the surfaces to improve heat transfer and apply a slight compression layer to the metal which really helps reduce fatigue failures and keeping plenty of oil on the top end to cool the springs.

Thermal barriers on piston crowns, combustion chambers, and valve faces run the combustion temps up which can lead to detonation problems, the old excessive temperature of the end burn problem. This can be controlled by lowering the advance, which actually can produce some additional power by reducing pressure spikes occurring before TDC. So there seems to be some benefit here especially with aluminum heads as it reduces their rather fast heat transfer rate to the coolant. For a short period, like a drag race or on a dyno run, you can accept the additional heat and detonation and see some extra power, but this condition is not sustainable for any time beyond a few seconds. Thermal barriers on the exhaust valve seem to help reduce distortion which helps sealing that improves power on the upper end where getting the red hot valve to close tightly on the seat can be a problem. I’ve seen benefit to this on the backside on intake manifolds where it keeps the heat of the valley from getting to the intake charge in the manifold. They also work well on the exhaust system, keeping the heat in the pipes till you can dump it overboard. For the street this can be a benefit when running long tube headers and a catalytic converter as it keeps the exhaust gasses hotter which results in a quicker and more consistent light off of the converter.

Lube coatings appear to be a good addition on the backside of valves and in the exhaust port as they keep deposits from adhering to these surfaces and keep them functioning closer to what you saw on the flow bench when everything was clean. I've had problems keeping this stuff attached to these surfaces on long duration engines, but it works well for drag engines and short track motors.  I'm not convinced that this stuff provides any real benefit when applied to the crankshaft, crankcase, valley, heads, pan, scraper, or windage tray toward improving oil return to the sump. Somewhat the same for piston skirts, I find that in a long duration engine it’s hard to keep this stuff on the thrust surface, after-all that’s where it’s needed. I’ve shied away from coatings on the intake track simply because if your running a carb or TBI ,a slightly rough surface is necessary to aid in keep fuel remixed into the boundary layer. However, this technique may have good results with port or cylinder injection where keeping fuel and air mixed together over a distance is not a concern.

For the most part I’ve discontinued using these coatings as I just don’t see the benefit against the hassle of application. Perhaps factory applied coatings will prove to be better, but do it yourself just doesn’t seem to be good enough for the environment these parts live in.

Yeah, I realize they are not gonna be a miracle cure, but since they are relatively inexpensive I figured trying them wouldn't hurt, but I may be wrong. According to Leonard Warren I should've pre-baked those pistons in the pictures to help remove the micro-welded material and other contaminants, which I didn't, that is probably why one piston was a disaster. I'm thinking my next try will be on a couple of cheap, but new cast pistons. The kitchen oven didn't hold up to well to these coatings either, I'm thinking since the pistons were used is why the odor was so horrible, it took some time to air-out the house afterwards, but I believe & surely hope they aren't harmful.

All in all though they are so many differing opinions about this stuff that I can't come to a decision to actually put them to work in an engine. A friend really wants to use them on the pistons and valve faces in a 438 BBC and this is sparking the questions and attempts, but I still don't know what I will do with them. In such a low-porformance engine it is looking more and more like too much work, but he is worried of detonation on pump-fuel with the true 10:1 static compression and fairly small cam (226/230 @.050) and thinks the coatings may help, so I will continue to think about it. Thanks for your opinion Bogie.

                                                                                     ~Gibs

I think he'll be OK with that cam and compression on 92 and maybe even 89 octane unleaded. Drop the thermostat to 180 and provide cool air to the intake, perhaps cut back on the exhaust heat crossover if he using one. The quick way is a set of hot rod intake gaskets that block off the heat passage. If you're running on the street and need some cold weather heat, put a 1/4 to 3/8s hole in the gasket.

When preping the pistons use a brass wire brush to clean them up rather than a steel brush. This keeps from adding ferrous contamination to the piston. Not a cure but it helps.

Bogie

Thanks for your word Bogie. After seeing how the first couple pistons turned out with the coatings our family friend is really straying away from the idea. He checked with a local company that is a certified applicator of the Techline coatings, but they want $200 to do it, so that also dissapointed him.

The car is a immaculately restored '69 camaro so the car will never be driven in the winter time, so being able to block-off the heat cross-over will be a thing to do to help keep the charge cooler.

Thanks for the tip for cleaning up the pistons, but that sparks my interest for another question, do you leave the piston top rough or polish it smooth before assembling?